Electrically charged polymeric substrates enhance nerve fibre outgrowth In vitro - Valentini RF, Vargo TG, Gardella JA, Aebischer P. (Biomaterials, 1992)
The physical, chemical and electrical properties of synthetic guidance devices are known to influence nerve regeneration in vivo. In the present study, neurons were cultured directly on electrically charged polymer growth substrates to determine if local electrical charges enhance nerve fibre outgrowth in vitro. Piezoelectric polymers such as polyvinylidene fluoride (PVDF) generate transient surface charges under minute mechanical strain. Mouse neuroblastoma (Nb2a) cells were cultured directly on electrically poled (i.e. piezoelectric) and unpoled (i.e. non-piezoelectric) PVDF substrates in serum-free and serum-containing media. Nerve fibre outgrowth was analysed 24, 48, 72 and 96 h after plating. Piezoelectric PVDF substrates generated 2-3 mV at 1200 Hz when placed on standard incubator shelves and unpoled PVDF substrates showed no output. Nb2a cells grown on piezoelectric substrates exhibited significantly greater levels of process outgrowth and neurite lengths at all time periods fo r both media conditions. Detailed surface characterization of PVDF substrates using electron spectroscopy for chemical analysis (ESCA) and a comprehensive wettability profile revealed that poled and unpoled PVDF was chemically indistinguishable and showed similar surface wettabilities and adhesive properties. Therefore, we conclude that enhanced process outgrowth was induced by the film's piezoelectric output, making poled PVDF a unique biomaterial for which cell/polymer interactions are mediated predominantly through bulk electrical properties rather than surface properties.

Properties of ferroelectric polymers under high pressure and shock loading - Bauer, F (NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 1995)
Ferroelectric polymers are the most recent class piezoelectric and pyroelectric materials developed. The most common piezoelectric polymers are PVDF, based on the monomer CH2-CF2 and copolymers PVDF with C2F3H. The effects of frequency, temperature and hydrostatic pressure on the dielectric properties, molecular relaxations, and phase transitions of PVDF and a copolymer with 30% trifluoroethylene will be discussed. Pressure causes large slowing down of the beta molecular relaxations as well as large increases in the ferroelectric transition temperatures and melting points, but the magnitudes of the effects are different for the different ''transitions''. A unique application of these polymers as time-resolved dynamic stress gauges based on PVDF studies under very high pressure shock compression is discussed. In particular piezoelectric response of shock compressed PVDF film prepared with attention to mechanical and electrical processing exhibits precise, well defined reproducible behav ior to 35 GPa. P(VDF-TrFE) copolymers exhibit unique piezoelectric properties over a wide range of temperature depending on the compositons. Under high shock pressure loading, unique piezoelectric response is also observed. The first record of detonation profile is presented. Results of PVDF shock sensors subjected to X-ray deposition and to neutron fluence above 10(13) n/cm(2) while stressed at a peak level of 2 GPa will be also discussed.

On the use of polarised PVDF in comparison with some other piezoelectric materials for the manufacture of acoustic transducers - Jain, SK; Gupta, R; Bindal, VN (JOURNAL OF SCIENTIFIC & INDUSTRIAL RESEARCH, 1996)
The use of polyvinylidene fluoride (PVDF) piezoelectric films is fast increasing as the transduction material in many of the ultrasonic and acoustic applications. This is due to a combination of properties such as toughness, flexibility, competitive piezoelectric characteristics etc of this material. Moreover PVDF is much easier to produce in large surface area. Still their use is relatively low in our country. In the present paper an attempt has been made to present and to compare the piezoelectric properties of PVDF with some of the other common piezoelectric materials. The methods of measurement of these properties in PVDF are also reported with a view to give information which may encourage work on the PVDF for its applications.

PREPARATION AND CHARACTERIZATION OF POLYMERIC PVDF FILMS BY ULTRASONIC ATOMIZATION (Integrated ferroelectrics, 2007)
ABSTRACT Polymeric poly (vinylidene fluoride) (PVDF) films which could be available for the piezoelectric and pyroelectric applications were prepared by ultrasonic atomization method. During the ultrasonic atomization processing, the mist of the PVDF-DMA solution source was generated with an ultrasonic atomizer at the frequency of 6 MHz and carried onto the substrates using air as carrier gas at the pressure of 1 atm. The PVDF films were characterized by X-ray diffraction (XRD) and atomic force microscope (AFM). Investigations including piezoelectric coefficient measurements showed that poled PVDF films had strong piezoelectric properties. As a result, ultrasonic atomization is very effective for preparation of PVDF films, and the piezoelectric coefficient of the sample is about 28 pC/N. Keywords: Polymeric PVDF filmsultrasonic atomizationpiezoelectriccharacterization ACKNOWLEDGMENTS The authors gratefully acknowledge the financial fund supported by National Science Fund of China Disti nguished Young Scholars, No. 60425101.

A flexible piezoelectric sensor for microfluidic applications using polyvinylidene fluoride - Chang, Wen-Yang; Chu, Chun-Hsun; Lin, Yu Cheng (IEEE SENSORS JOURNAL, 2008)
A flexible technology for microfluidic applications using piezoelectric polyvinylidene fluoride (PVDF) and polydimethylsiloxane (PDMS) was developed. The flexible piezoelectric PVDF detects the flow rates and impulse pressure signal using piezoelectric characteristics. This study uses microelectromechanical systems (MEMS) technology to fabricate the sensing patterns on PVDF sheets, designs a molding transfer to form the microfluidic channels of the PDMS, and integrates them together. Experimental results show that PVDF films has good piezoelectricity at stretching ratio of 4, the flow rates ranged from 100 to 450 mL/min at dynamic controlling sensing, the miniature curvature radius is about 3 cm, and the cross section of the flexible microchannels is about 200 x 200 mu m(2). The feasibility studies show that molding transfer is an appropriate low-cost technology for fabricating the flexible piezoelectric channels. The PVDF can be easily manufactured using MEMS process because it has a good mechanical strength and electrochemical stability in polymers.

Surface Functionalization of a Poly(vinylidene fluoride): Effect on the Adhesive and Piezoelectric Properties - Lee, Ji Seok; Kim, Gwang Ho; Hong, Soon Man; Choi, Hyoung Jin; Seo, Yongsok (ACS APPLIED MATERIALS & INTERFACES, 2009)
We studied the effect of the surface functionalization and crystalline phase change OF poly(vinylidene fluoride) (PVDF) films on their adhesion and piezoelectric properties, The surface modification of PVDF was carried out with ion beam and/or plasma treatment. These surface modifications were found to alter the interfacial strength between PVDF and metal electrodes and the crystal structure of the piezoelectric PVDF film. A remarkable improvement was found in the interfacial adhesion of the films with thermally deposited metal electrodes, but some piezoelectricity of PVDF film was lost due to the changes in the crystal phase. The proper treatment condition for enhancing the adhesion and retaining piezoelectric structure was suggested.

Preparation and characterization of piezoelectric ceramic-polymer composite thick films by aerosol deposition for sensor application - Choi, Jong-Jin; Hahn, Byung-Dong; Ryu, Jungho; Yoon, Woon-Ha; Lee, Byoung-Kuk; Park, Dong-Soo (SENSORS AND ACTUATORS A-PHYSICAL, 2009)
Lead zirconate titanate (PZT)-based piezoelectric ceramic and polyvinylidene fluoride (PVDF) organic composite thick films (similar to 20 mu m in thickness) were deposited on a 4-in, diameter Pt/Ti/SiO2/Si substrate and a 2-in. diameter Ag-Pd/sapphire substrate by aerosol deposition Using a single 4-in. size nozzle for use as a tactile-sensor device. The PVDF content was varied from 3 to 10 vol% and the films deposited on silicon and sapphire were annealed at 700 and 900 degrees C, respectively. The annealed films showed a relatively high density, even at a 10 vol% of PVDF-piezoelectric ceramic composition. as well as good adhesion to the substrate after annealing. The relative dielectric constant of the composite film decreased sharply with increasing PVDF content, while the piezoelectric d(33) coefficient was conserved at a relatively high value. Therefore, the g(33) coefficient increased and showed the highest value at 3 vol% PVDF The g(33) values of the as-deposited, 700 degrees C annealed and 900 degrees C annealed piezoelectric ceramic-PVDF composite films were 7.77, 16.3 and 41.5 (10(-3) m(2)/N), respectively. (C) 2009 Elsevier B.V. All rights reserved.

Effect of heat treatment on the electrical properties of lead zirconate titanate/poly (vinylidene fluoride) composites (Polymer International, 2010)
Abstract Ceramic/polymer composites are attracting increasing interest in materials research and practical applications due to the combination of excellent electric properties of piezoelectric ceramics and good flexibility of polymer matrices. In this case, the crystallization of the polymer has a significant effect on the electric properties of ceramic/polymer composites. Based on different heat treatment methods, the crystallization of poly(vinylidene fluoride) (PVDF) in composites of lead zirconate titanate (PZT) and PVDF can be controlled effectively. PZT/PVDF composites with various PVDF crystallizations exhibit distinctive dielectric and piezoelectric properties. When the crystallization of PVDF is 21%, the PZT/PVDF composites show a high dielectric constant (ε) of 165 and a low dielectric loss (tan δ) of 0.03 at 10 3 Hz, and when the crystallization of PVDF reaches 34%, the piezoelectric coefficient ( d 33 ) of PZT/PVDF composites can be up to ca 100 pC N −1 . By controlling the crystallization of PVDF, PZT/PVDF composites with excellent dielectric and piezoelectric properties were obtained, which can be employed as promising candidates in high‐efficiency capacitors and as novel piezoelectric materials. Copyright © 2010 Society of Chemical Industry

Piezoelectric actuation of direct-write electrospun fibers - Pu, Juan; Yan, Xiaojun; Jiang, Yadong; Chang, Chien; Lin, Liwei (SENSORS AND ACTUATORS A-PHYSICAL, 2010)
Piezoelectric actuation of doubly clamped electrospun poly (vinylidene fluoride)(PVDF) fibers fabricated by a direct-write process has been demonstrated Near-field electrospinning (NFES) has been utilized to fabricate PVDF fibers with good piezoelectric properties by means of the in situ electrical poling and mechanical stretching process Experimentally PVDF fibers have responded to both piezoelectric and electrostatic effects and a double-electrode approach has been used to minimize the electrostatic effect An average piezoelectric ( efficient d(33) of -57 6 pm/V has been characterized from fabricated fibers and this value is about twice larger than the value reported in PVDF thin-films Various complex patterns of PVDF fibers have been deposited using NFES enabling possible array formats for fiber-based actuator with possible application, including artificial muscles and switches (c) 2010 Elsevier B V All rights reserved

Research on dynamic analysis and wireless sensors of pvdf for structural monitoring - Wang, Yang (2010)

Label free detection of white spot syndrome virus using lead magnesium niobate–lead titanate piezoelectric microcantilever sensors - Joseph A. Capobianco, Wei-Heng Shih, Jiann-Horng Leu, Grace Chu-Fang Lo, Wan Y. Shih (Biosensors and Bioelectronics, 2010)

Fatigue failure characteristics of lead zirconate titanate piezoelectric ceramics - Mitsuhiro Okayasu, Go Ozeki, Mamoru Mizuno (Journal of the European Ceramic Society, 2010)

In situ measurement of material properties of lead zirconate titanate piezoelectric ceramics during cyclic mechanical loading - Mitsuhiro Okayasu, Eriko Sugiyama, Mamoru Mizuno (Journal of the European Ceramic Society, 2010)

Characterisation of residual stress and interface degradation in TBCs by photo-luminescence piezo-spectroscopy - X. Wang, R.T. Wu, A. Atkinson (Surface and Coatings Technology, 2010)

Neurite extension of primary neurons on electrospun piezoelectric scaffolds - Lee, Yee-Shuan; Collins, George; Arinzeh, Treena Livingston (ACTA BIOMATERIALIA, 2011)
Neural tissue engineering may be a promising option for neural repair treatment, for which a well-designed scaffold is essential. Smart materials that can stimulate neurite extension and outgrowth have been investigated as potential scaffolding materials. A piezoelectric polymer polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) was used to fabricate electrospun aligned and random scaffolds having nano- or micron-sized fiber dimensions. The advantage of using a piezoelectric polymer is its intrinsic electrical properties. The piezoelectric characteristics of PVDF-TrFE scaffolds were shown to be enhanced by annealing. Dorsal root ganglion (DRG) neurons attached to all fibrous scaffolds. Neurites extended radially on random scaffolds, whereas aligned scaffolds directed neurite outgrowth for all fiber dimensions. Neurite extension was greatest on aligned, annealed PVDF-TrFE having micron-sized fiber dimensions in comparison with annealed and as-spun random PVDF-TrFE scaffolds. DRG on m icron-sized aligned, as-spun and annealed PVDF-TrFE also had the lowest aspect ratio amongst all scaffolds, including non-piezoelectric PVDF and collagen-coated substrates. Findings from this study demonstrate the potential use of a piezoelectric fibrous scaffold for neural repair applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Structural, microstructural and electrical properties evolution of (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoceramics through NiO doping - F. Rubio-Marcos, P. Marchet, J.J. Romero, J.F. Fernández (Journal of the European Ceramic Society, 2011)

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics during mechanical compressive loading - Mitsuhiro Okayasu, Kazuto Sato, Yoko Kusaba (Journal of the European Ceramic Society, 2011)

Influence of domain orientation on the mechanical properties of lead zirconate titanate piezoelectric ceramics - Mitsuhiro Okayasu, Kazuto Sato, Mamoru Mizuno (Journal of the European Ceramic Society, 2011)

Effect of carbon addition on the ferroelectric hysteresis properties of lead zirconate–titanate ceramic–cement composites - A. Chaipanich, N. Jaitanong, R. Yimnirun (Ceramics International, 2011)

Modified phase transition and electrical properties of [Li 0.05 (Na 0.535 K 0.48 ) 0.95 ]‐(Nb 0.94 Sb 0.06 )O 3 lead‐free piezoelectric ceramic by sintering temperature - Xiaokun Zhao, Boping Zhang, Lei Zhao, Lifeng Zhu, Yan Li, Liqian Cheng (Rare Metals, 2012)
Abstract Li/Sb‐doped (Na,K)NbO 3 with a nominal composition of [Li 0.05 (Na 0.535 K 0.48 ) 0.95 ](Nb 0.94 Sb 0.06 )O 3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 °C, whereby the piezoelectric coefficient d 33 and the electromechanical coupling coefficient k p reached the peak values of 245 pC·N −1 and 41.2%, respectively. The PPT induced by vary ing the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d 33 value.

Orthorhombic to tetragonal phase transition due to stress release in (Li,Ta)-doped(K,Na)NbO3 lead-free piezoceramics - Jia-Jun Zhou, Jing-Feng Li, Xiao-Wen Zhang (Journal of the European Ceramic Society, 2012)

A study of the effects of vibration on the electric power generation properties of lead zirconate titanate piezoelectric ceramic - Mitsuhiro Okayasu, Daisuke Sato, Yuki Sato, Masashi Konno, Tetsuro Shiraishi (Ceramics International, 2012)

Power-generation performance of lead-free (K,Na)NbO3 piezoelectric thin-film energy harvesters - Isaku Kanno, Tomoharu Ichida, Kazuhiko Adachi, Hidetoshi Kotera, Kenji Shibata, Tomoyoshi Mishima (Sensors and Actuators A: Physical, 2012)

Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning - Liu, Z. H.; Pan, C. T.; Lin, L. W.; Lai, H. W. (SENSORS AND ACTUATORS A-PHYSICAL, 2013)
This study reports the use of near-field electrospinning to fabricate polyvinylidene fluoride (PVDF) piezoelectric nanofibers mixed with multiwalled-carbon nanotubes (MWCNT). This study also investigates the mechanical strength and piezoelectric characteristics of a single PVDF/MWCNT nanofiber. The morphology and polarization intensity of piezoelectric fiber can be controlled by adjusting the traveling velocity of the X-Y stage, the DC voltage, and the gap between the needle and collection plate. The optimal parameters of the PVDF solution, such as the PVDF powder weight percentage and MWCNT content, were also determined. X-ray diffraction (XRD) analysis shows a high diffraction peak at 2 theta = 20.8 degrees in the piezoelectric crystal beta-phase structure. ANSYS finite element analysis (FEA) software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. A nano-indentation test (Nanolndenter XP System, MTS co.) was used to investigate Yo ung's modulus of the PVDF fiber. Finally, the fixed-fixed beam structures of PVDF composite fibers were tested using a DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized. (C) 2013 Elsevier B.V. All rights reserved.

Structural changes in PVDF fibers due to electrospinning and its effect on biological function - Damaraju, Sita M.; Wu, Siliang; Jaffe, Michael; Arinzeh, Treena Livingston (BIOMEDICAL MATERIALS, 2013)
Polyvinylidine fluoride (PVDF) is being investigated as a potential scaffold for bone tissue engineering because of its proven biocompatibility and piezoelectric property, wherein it can generate electrical activity when mechanically deformed. In this study, PVDF scaffolds were prepared by electrospinning using different voltages (12-30 kV), evaluated for the presence of the piezoelectric beta-crystal phase and its effect on biological function. Electrospun PVDF was compared with unprocessed/raw PVDF, films and melt-spun fibers for the presence of the piezoelectric beta-phase using differential scanning calorimetry, Fourier transform infrared spectroscopy and x-ray diffraction. The osteogenic differentiation of human mesenchymal stem cells (MSCs) was evaluated on scaffolds electrospun at 12 and 25 kV (PVDF-12 kV and PVDF-25 kV, respectively) and compared to tissue culture polystyrene (TCP). Electrospinning PVDF resulted in the formation of the piezoelectric beta-phase with the highest beta-phase fraction of 72% for electrospun PVDF at 25 kV. MSCs cultured on both the scaffolds were well attached as indicated by a spread morphology. Cells on PVDF-25 kV scaffolds had the greatest alkaline phosphatase activity and early mineralization by day 10 as compared to TCP and PVDF-12 kV. The results demonstrate the potential for the use of PVDF scaffolds for bone tissue engineering applications.

Flexible Thin-Film PVDF-TrFE Based Pressure Sensor for Smart Catheter Applications - Tushar Sharma, Kevin Aroom, Sahil Naik, Brijesh Gill, John X. J. Zhang (Annals of Biomedical Engineering, 2013)

Dye‐Sensitized Solar Cell with Energy Storage Function through PVDF/ZnO Nanocomposite Counter Electrode - Xi Zhang, Xuezhen Huang, Chensha Li, Hongrui Jiang (Advanced Materials, 2013)

Consistent ocean wave energy harvesting using electroactive polymer (dielectric elastomer) artificial muscle generators - S. Chiba, M. Waki, T. Wada, Y. Hirakawa, K. Masuda, T. Ikoma (Applied Energy, 2013)

Effects of Al2O3 on the ferroelectric properties of sodium potassium lithium niobate lead-free piezoceramics - I.H. Lee, H.S. Lee, Y.H. Kim, S.K. Gil, D.H. Kang (Ceramics International, 2013)

d33 mode piezoelectric diaphragm based acoustic transducer with high sensitivity - Zhiyuan Shen, Jingyu Lu, Chee Wee Tan, Jianmin Miao, Zhihong Wang (Sensors and Actuators A: Physical, 2013)

A Giant Electrocaloric Effect in Nanoscale Antiferroelectric and Ferroelectric Phases Coexisting in a Relaxor Pb0.8Ba0.2ZrO3 Thin Film at Room Temperature - Biaolin Peng, Huiqing Fan, Qi Zhang (Advanced Functional Materials, 2013)
Abstract Recently, large electrocaloric effects (ECE) in antiferroelectric sol‐gel PbZr 0.95 Ti 0.05 O 3 thin films and in ferroelectric polymer P(VDF‐TrFE)55/45 thin films were observed near the ferroelectric Curie temperatures of these materials (495 K and 353 K, respectively). Here a giant ECE (Δ T = 45.3 K and Δ S = 46.9 J K −1 kg −1 at 598 kV cm −1 ) is obtained in relaxor ferroelectric Pb 0.8 Ba 0.2 ZrO 3 (PBZ) thin films fabricated on Pt(111)/TiO x /SiO 2 /Si substrates using a sol‐gel method. Nanoscale antiferroelectric (AFE) and ferroelectric (FE) phases coexist at room temperature (290 K) rather than at the Curie temperature (408 K) of the material. The giant ECE in such a system is a ttributed to the coexistence of AFE and FE phases and a field‐induced nanoscale AFE to FE phase transition. The giant ECE of the thin film makes this a promising material for applications in cooling systems near room temperature.

Piezoelectric properties of cement based/PVDF/PZT composites (Materials Letters, 2014)
New and novel cement-based piezoelectric composites were fabricated using lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF) and Portland cement (PC). Dielectric constant (epsilon(33)), piezoelectric charge coefficient (d(33)) and piezoelectric voltage coefficient (g(33)) of the PZT-PVDF-PC composites with 50 vol% PZT and 1-20 vol% PVDF content were investigated. The results indicated that PVDF as a third phase was found to enhance piezoelectric properties where piezoelectric charge coefficient (d(33)) and piezoelectric voltage coefficient (g(33)) increased to 24 pC/N and 25.7 x 10(-3) Vm/N respectively when PVDF was added at 5 vol%. Moreover, a significant reduction in the poling time was found when PVDF was incorporated in the 0-3 composites. (C) 2014 Elsevier B.V. All rights reserved.

Nanofibrillar Poly(vinylidene fluoride): Preparation and Functional Properties - Kim, Nam Kyeun; Lin, Richard J. T.; Fakirov, Stoyko; Aw, Kean; Bhattacharyya, Debes (INTERNATIONAL JOURNAL OF POLYMERIC MATERIALS AND POLYMERIC BIOMATERIALS, 2014)
Poly(vinylidene fluoride) (PVDF) forming -phase polymorphic modification shows strong ferro- and piezoelectric property as a crucial electroactive polymer and can be obtained by subjecting the highly oriented PVDF fibers to strong electric fields. Two different nanofibrillar materials: PVDF nanofibrillar single polymer composite (NF-SPC) and electrospun PVDF nanofibers were produced for this research. PVDF NF-SPC was prepared by hot compaction of PVDF nanofibrils separated from a PVDF nanofibrillar composite and a high electric field was used to drive out electrospun PVDF fibrils. Polymorphic change and morphology of constituents of the two samples were investigated and measurement of ferro- and piezoelectric behavior was performed after poling treatment. As a result, highly oriented nanofibrils were observed from the two samples and the formation of the -phase was clearly detected compared to undrawn isotropic PVDF. Higher remnant polarization values and piezoelectric resonance behavi or were detected from the samples, in which the -phase polymorphic modification dominates.

Application of electrospun piezoelectric PVDF-scaffolds for nerve regeneration - Al Halabi, Fedaa; Behrens, Peter; Glasmacher, Birgit (BIOMEDICAL ENGINEERING-BIOMEDIZINISCHE TECHNIK, 2014)
Piezoelectric polymers have often been studied as films and bulk materials in various medical applications, nevertheless publications of investigations of piezoelectric fiber structures are still limited. In neural tissue engineering some piezoelectric polymers are being investigated as potential scaffolds for supporting the nerve regeneration processes. A promising material is polyvinylidine fluoride (PVDF) because of its proven biocompatibility and piezoelectric properties, which can possibly stimulate the cells ingrowth with its electrical activity when it is mechanically deformed. In a study to prove its suitability to regenerative medicine, PVDF was electrospun into fibrous scaffolds by testing different concentrations (2030 wt.%) of PVDF dissolved in N,N-dimethylformamide (DMF) and acetone (6:4 and 8:2). For the electrospinning process different flow rates (0.3-2 ml/h) and voltages (16-28 kV) were used to produce defined fibrous scaffolds. The structures of the electrospun PVDF s caffolds were observed and analysed with a scanning electron microscope (SEM) and then evaluated for its mechanical properties, biocompatibility and piezoelectric effect. Electrospun PVDF was compared to untreated/raw PVDF pellets with respect to the presence of the nonpolar a-phase and piezoelectric beta-phase by using Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The growing of mouse embryonic fibroblasts cells (3T3) was evaluated on electrospun PVDF scaffolds.Electrospun scaffolds with a concentration of 30 wt.% PVDF resulted in the formation of the piezoelectric beta-phase with the highest beta-phase ratio. 3T3 cells cultured on the scaffolds were well attached as indicated by spread morphology. The results demonstrate the potential for the use of PVDF scaffolds for tissue engineering applications.

Publication 9 # 2009 Acta Materilai (Ist) - Yong Zhang (2014)

Stretchable Conductive Polypyrrole/Polyurethane (PPy/PU) Strain Sensor with Netlike Microcracks for Human Breath Detection - Mufang Li, Haiying Li, Weibing Zhong, Qinghua Zhao, Dong Wang (ACS Applied Materials & Interfaces, 2014)

Large d33 in (K,Na)(Nb,Ta,Sb)O3-(Bi,Na,K)ZrO3 lead-free ceramics - Xiaopeng Wang, Jiagang Wu, Dingquan Xiao, Xiaojing Cheng, Ting Zheng, Binyu Zhang, Xiaojie Lou, Jianguo Zhu (Journal of Materials Chemistry A, 2014)

Effect of cobalt doping on the sintering mechanisms of the lead-free piezoceramic (Bi0.5Na0.5)TiO3 - V. Schmitt, F. Raether (Journal of the European Ceramic Society, 2014)

Enhancing piezoelectric coefficient d33 in LiF-doped BaTiO3 ceramics by optimizing excess Ba content - Li-Feng Zhu, Bo-Ping Zhang, Wei-Gang Yang (Materials Research Bulletin, 2014)

Stable lithium electrodeposition in liquid and nanoporous solid electrolytes - Yingying Lü, Zhengyuan Tu, Lynden A. Archer (Nature Materials, 2014)

TiO2 nanotube @ SnO2 nanoflake core–branch arrays for lithium-ion battery anode - Changrong Zhu, Xinhui Xia, Jilei Liu, Zhanxi Fan, Dongliang Chao, Hua Zhang, Hong Jin Fan (Nano Energy, 2014)

High lithium anodic performance of highly nitrogen-doped porous carbon prepared from a metal-organic framework - Fangcai Zheng, Yang Yang, Qianwang Chen (Nature Communications, 2014)

Two-dimensional layered transition metal disulphides for effective encapsulation of high-capacity lithium sulphide cathodes - Zhi Wei Seh, Jung Ho Yu, Weiyang Li, Po‐Chun Hsu, Haotian Wang, Yongming Sun, Hong‐Bin Yao, Qianfan Zhang, Yi Cui (Nature Communications, 2014)

Dry-air-stable lithium silicide–lithium oxide core–shell nanoparticles as high-capacity prelithiation reagents - Jie Zhao, Zhenda Lu, Nian Liu, Hyun‐Wook Lee, Matthew T. McDowell, Yi Cui (Nature Communications, 2014)

Nanoscale visualization of redox activity at lithium-ion battery cathodes - Yasufumi Takahashi, Akichika Kumatani, Hirokazu Munakata, Hirotaka Inomata, K ocirc kichi ITO, Kosuke Ino, Hitoshi Shiku, Patrick R. Unwin, Yuri E. Korchev, Kiyoshi Kanamura, Tomokazu Matsue (Nature Communications, 2014)

Optoelectronic switching of nanowire-based hybrid organic/oxide/semiconductor field-effect transistors - Eunhye Baek, Sebastian Pregl, Mehrdad Shaygan, Lotta Römhildt, W. Weber, Thomas Mikolajick, Dmitry A. Ryndyk, Larysa Baraban, Gianaurelio Cuniberti (Nano Research, 2014)
A novel photosensitive hybrid field-effect transistor (FET) which consists of a multiple-shell of organic porphyrin film/oxide/silicon nanowires is presented. Due to the oxide shell around the nanowires, photoswitching of the current in the hybrid nanodevices is guided by the electric field effect, induced by charge redistribution within the organic film. This principle is an alternative to a photoinduced electron injection, valid for devices relying on direct junctions between organic molecules and metals or semiconductors. The switching dynamics of the hybrid nanodevices upon violet light illumination is investigated and a strong dependence on the thickness of the porphyrin film wrapping the nanowires is found. Furthermore, the thickness of the organic films is found to be a crucial parameter also for the switching efficiency of the nanowire FET, represented by the ratio of currents under light illumination (ON) and in dark conditions (OFF). We suggest a simple model of porphyrin fil m charging to explain the optoelectronic behavior of nanowire FETs mediated by organic film/oxide/semiconductor junctions.

Graphene: A Dynamic Platform for Electrical Control of Plasmonic Resonance - Naresh Kumar Emani, Alexander V. Kildishev, Vladimir M. Shalaev, Alexandra Boltasseva (Nanophotonics, 2014)
Abstract: Graphene has recently emerged as a viable platform for integrated optoelectronic and hybrid photonic devices because of its unique properties. The optical properties of graphene can be dynamically controlled by electrical voltage and have been used to modulate the plasmons in noble metal nanostructures. Graphene has also been shown to support highly confined intrinsic plasmons, with properties that can be tuned in the wavelength range of 2 μm to 100 μm. Here we review the recent development in graphene‐plasmonic devices and identify some of the key challenges for practical applications of such hybrid devices.

High output piezoelectric nanocomposite generators composed of oriented BaTiO3 NPs@PVDF - Zhao, Yingli; Liao, Qingliang; Zhang, Guangjie; Zhang, Zheng; Liang, Qijie; Liao, Xinqin; Zhang, Yue (NANO ENERGY, 2015)
Piezoelectric nanocomposites (p-NC) composed of piezoelectric nanoparticles (NPs) and flexible polymer have emerged as outstanding applications for flexible nanogenerators (NGs). In this article, we proposed a p-NC NG by combining the barium titanate nanoparticles (BaTiO3 NPs) with the poly-vinylidene fluoride (PVDF). By a facile and scalable solvent evaporation process, the BaTiO3 NPs and PVDF composite (BaTiO3 NPs @ PVDF) films were fabricated. BaTiO3 NPs dispersed uniformly in the PVDF matrix and formed an oriented structure without aggregations. By using this special oriented BaTiO3 NPs @ PVDF composite film, the highest open-circuit voltage reaches 150 V, which is one of the most outstanding output performance in the lead-free piezoelectric field to date. The energy generated from the p-NC NG can light three light-emitting diode (LED) bulbs instantaneously without any storage unit. (C) 2014 Elsevier Ltd. All rights reserved.

Microporous polyvinylidene fluoride film with dense surface enables efficient piezoelectric conversion - Chen, Dajing; Zhang, John X. J. (APPLIED PHYSICS LETTERS, 2015)
We demonstrate that asymmetric porous polyvinylidene fluoride (PVDF) film, with pores mostly distributed in the bulk but not at the surfaces, can be used as a highly efficient piezoelectric energy generation device. For such microporous PVDF film with dense or pore-free surface, piezoelectric theory shows the efficiency of energy conversion by piezoelectric device depends upon the structure compressibility. Film mechanical properties can be controlled by dispersing micro-scale pores in a polymer matrix with a dense top layer. Piezoelectric output is enhanced by optimization of PVDF micro-structure and electromechanical coupling efficiency. The power output increased three folds with a designed three-dimensional asymmetric porous structure as compared to solid film. (C) 2015 AIP Publishing LLC.

The effect of Mn/Nb doping on dielectric and ferroelectric properties of PZT thin films prepared by sol–gel process - Xiaorui Xu; Lihong Xie; Xiaofang Liu; three others (RG visible) (Journal of Sol-Gel Science and Technology, 2015)
Mn/Nb-doped lead zirconate titanate thin films were fabricated by sol-gel process.

Preparation and dielectric properties of poly(vinylidene fluoride)/Ba0.6Sr0.4TiO3 composites - ["Yong Zhang", "Wenda Jiang", "Weiping Xu", "three others (RG visible)"] (Journal of Alloys and Compounds, 2015)
PVDF/BST composites were fabricated by solution casting method and dielectric properties investigated.

Flexible and Controllable Piezo‐Phototronic Pressure Mapping Sensor Matrix by ZnO NW/p‐Polymer LED Array - Rongrong Bao, Chunfeng Wang, Lin Dong, Ruomeng Yu, Kun Zhao, Zhong Lin Wang, Caofeng Pan (Advanced Functional Materials, 2015)
A functional tactile sensing device is essential for next‐generation robotics and human–machine interfaces technologies, since the emulation of touching requires large‐scale pressure sensor arrays with distinguishable spatial‐resolution, high sensitivity, and fast response. Here, a flexible LED array composed of PEDOT:PSS and patterned ZnO NWs with a spatial resolution of 7 μm for mapping of spatial pressure distributions is designed and fabricated. The emission intensity of the LED array sensor matrix is dominated by locally applied strains as indicated by the piezo‐phototronic effect. Therefore, spatial pressure distributions are immediately obtained by parallel‐reading the illumination intensities of the LED arrays based on an electroluminescence working mechanism. A wide range of pressure measurements from 40 to 100 MPa are achieved through controlling the growth conditions of the ZnO nanowire array. These devices may find prospective applications as electronic skins by tak ing advantage of their high spatial‐resolution, flexibility, and wide pressure mapping range.

Mimosa‐Inspired Design of a Flexible Pressure Sensor with Touch Sensitivity - Bin Su, Shu Gong, Zheng Ma, Lim Wei Yap, Wenlong Cheng (Small, 2015)

Sensors: Mimosa‐Inspired Design of a Flexible Pressure Sensor with Touch Sensitivity (Small 16/2015) - Bin Su, Shu Gong, Zheng Ma, Lim Wei Yap, Wenlong Cheng (Small, 2015)

Fabrication and investigation of BCZT/epoxy lead-free piezoelectric composites with spiral structure - Nan Chen, Weibing Ma, Mingyang Wang, Yaoxian Guo, Na Li (Journal of Alloys and Compounds, 2015)

Effect of Li2O addition on sintering and piezoelectric properties of (Ba,Ca)(Ti,Sn)O3 lead-free piezoceramics - Lei Zhao, Bo-Ping Zhang, Peng-Fei Zhou, Li-Feng Zhu, Jing-Feng Li (Journal of the European Ceramic Society, 2015)

Structure–microstructure–property relationships in lead-free BCTZ piezoceramics processed by conventional sintering and spark plasma sintering - Feres Benabdallah, Catherine Elissalde, U.-Chan Chung Seu, Dominique Michau, Angeline Poulon-Quintin, Marion Gayot, Pascale Garreta, Hamadi Khemakhem, Mario Maglione (Journal of the European Ceramic Society, 2015)

Dielectric and piezoelectric properties of (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 lead-free ceramics for piezoelectric energy harvesters - Gun-Hyun Lee, Young-Hoon Kwon, Jung-Hyuk Koh (Ceramics International, 2015)

The electric power generation characteristics of a lead zirconate titanate piezoelectric ceramic under various cyclic loading conditions - Mitsuhiro Okayasu, Keisuke Watanabe (Ceramics International, 2015)

Analysis of the degradation of BaTiO3 resistivity due to hydrogen ion incorporation: Impedance spectroscopy and diffusion analysis - Damoon Sohrabi Baba Heidary, Clive A. Randall (Acta Materialia, 2015)

A hybrid solid electrolyte for flexible solid-state sodium batteries - Jae‐Kwang Kim, Young Jun Lim, Hyojin Kim, Gyu-Bong Cho, Youngsik Kim (Energy & Environmental Science, 2015)
Ceramic-based hybrid solid electrolyte (HSE) is designed to build a flexible pouch-type Na-ion battery.

Beyond Yolk–Shell Nanoparticles: Fe3O4@Fe3C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage - Jianan Zhang, Kaixi Wang, Qun Xu, Yunchun Zhou, Fangyi Cheng, Shaojun Guo (ACS Nano, 2015)
To well address the problems of large volume change and dissolution of Fe3O4 nanomaterials during Li(+) intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk-shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe3O4@Fe3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This particular structure can not only introduce VSIVS to accommodate volume change of Fe3O4 but also afford a dual shell of Fe3C and carbon to restrict Fe3O4 dissolution, thus providing dual roles for greatly improving the capacity retention. As a consequence, Fe3O4@Fe3C-C yolk-shell nanospindles deliver a high reversible capacity of 1128.3 mAh g(-1) at even 500 mA g(-1), excellent high rate capacity (604.8 mAh g(-1) at 2000 mA g(-1)), and prolonged cycling life (maintaining 1120.2 mAh g(-1) at 500 mA g(-1) for 100 cycles) for LIBs, which are much better than those of Fe3O4@C core@shell nanospindles and Fe3O4 nanoparticles. The present Fe3O4@Fe3C-C yolk-shell nanospindles are the most efficient Fe3O4-based anode materials ever reported for LIBs.

Guided Growth of Horizontal ZnSe Nanowires and their Integration into High‐Performance Blue–UV Photodetectors - Eitan Oksenberg, Ronit Popovitz‐Biro, Katya Rechav, Ernesto Joselevich (Advanced Materials, 2015)
Perfectly aligned horizontal ZnSe nanowires are obtained by guided growth, and easily integrated into high-performance blue–UV photodetectors. Their crystal phase and crystallographic orientation are controlled by the epitaxial relations with six different sapphire planes. Guided growth paves the way for the large-scale integration of nanowires into optoelectronic devices. Single-crystal semiconducting nanowires (NWs) have been the focal point of extensive and ongoing research, exploring both new physical phenomena and the compatibility of NWs as building blocks for various applications in electronics,1 optoelectronics,2, 3 sensing,4 and energy harvesting.5, 6 Amongst these devices, most of the planar ones were fabricated by a long, multistep and often serial process where each device was custom fabricated on a randomly located NW. In order to take the next step and enable the transition from single devices to large-scale functional systems, a deterministic control over the location a nd orientation of multiple NWs is greatly needed. Several post-growth methods try to address this need with increasing success.7-11 Nonetheless, each method has its drawbacks, which often include length limitations and insufficient control over the exact location of both ends of the NWs. The guided growth approach can offer an advantageous alternative that eliminates the need for post-growth alignment methods.12, 13 It uses epitaxial and graphoepitaxial relations with the substrate to guide horizontal NWs during the synthesis. This brings about well-aligned NWs that grow in specific and reproducible directions and crystallographic orientations as illustrated in Figure 1A. Furthermore, combining top-down lithography processes with the unique features of guided growth, can realize the fabrication of multiple NW-based devices in a parallel manner.14 Growing interest in this approach is evident through increasing reports on successful horizontal growth of aligned NWs.

Hybrid Metal–Semiconductor Nanostructure for Ultrahigh Optical Absorption and Low Electrical Resistance at Optoelectronic Interfaces - Vijay K. Narasimhan, Thomas M. Hymel, Ruby A. Lai, Yi Cui (ACS Nano, 2015)

Formation of β-phase PVDF by Introduction of CNTs in the CNT/PVDF Composite Film and Resulting Improvement of Piezoelectric Performance (Journal of the Korean Institute of Electrical and Electronic Material Engineers, 2016)
In this paper, we fabricated flexible CNT/PVDF piezoelectric composite device by introducing CNTs (carbon nanotubes) into PVDF (poly-vinylidene fluoride) solution using spray coating technique. Flexible PEDOT:PSS conducting polymer was used as electrodes. We tried to improve the piezoelectric performance from the CNT/PVDF composite film by increasing the portion of the β-phase PVDF in the film. We confirmed the structural conformation of the CNT/PVDF composite film as a function of CNT concentration by using FT-IR (fourier transform infra-red). As increasing CNT concentration, portion of the β-phase PVDF and resulting piezoelectric performance increased in the CNT/PVDF composite film. We found that CNTs introduced were played as seeds for formation of the β-phase PVDF in the CNT/PVDF composite film and resulting improvement of the piezoelectric performance.

Outstanding dielectric constant and piezoelectric coefficient in electrospun nanofiber mats of PVDF containing silver decorated multiwall carbon nanotubes: assessing through piezoresponse force microscopy - Sharma, Maya; Srinivas, Vijay; Madras, Giridhar; Bose, Suryasarathi (RSC ADVANCES, 2016)
In order to enhance the piezoelectric b-phase, PVDF was electrospun from DMF solution. The enhanced b-phase was discerned by comparing the electrospun fibers against the melt mixed samples. While both the processes resulted in phase transformation of a-to electroactive b-polymorph in PVDF, the fraction of b-phase was strongly dependent on the adopted process. Two different nanoscopic particles: carboxyl functionalized multiwall carbon nanotubes (CNTs) and silver (Ag) decorated CNTs were used to further enhance the piezoelectric coefficient in the electrospun fibers. Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (XRD) supports the development of piezoelectric b-phase in PVDF. It was concluded that electrospinning was the best technique for inducing the b-polymorph in PVDF. This was attributed to the high voltage electrostatic field that generates extensional forces on the polymer chains that aligns the dipoles in one direction. The ferroelectric and pie zoelectric measurement on electrospun fibers were studied using piezo-response force microscope (PFM). The Ag-CNTs filled PVDF electrospun fibers showed the highest piezoelectric coefficient (d(33) = 54 pm V-1) in contrast to PVDF/CNT fibers (35 pm V-1) and neat PVDF (30 pm V-1). This study demonstrates that the piezoelectric coefficient can be enhanced significantly by electrospinning PVDF containing Ag decorated nanoparticles.

The use of polyvinylidene fluoride (PVDF) films as sensors for vibration measurement: A brief review - Xin, Yi; Sun, Hongshuai; Tian, Hongying; Guo, Chao; Li, Xiang; Wang, Shuhong; Wang, Cheng (FERROELECTRICS, 2016)
Information about vibrating objects can be obtained by vibration measurements. Piezoelectric sensors made by piezoelectric ceramics, quartz, or organic piezoelectric materials, e. g. polyvinylidene fluoride (PVDF) have been adopted by many researchers to measure vibrations. Among these piezoelectric materials, PVDF has attracted much attention for its excellent properties such as outstanding chemical resistance, high thermal stability, low permitivities, low acoustic impedances, flexibility and membrane forming properties. In this paper, PVDF is introduced in brief. In addition, this paper briefly reviews the use of PVDF films as sensors for vibration measurement in the areas of portable medical detections, structural health monitoring, mechanical equipment vibration measurements and other applications. Meanwhile, some cases which have good low-frequency performances or novel features in structures will be especially introduced to provide helpful experiences for future applications. In the end, a spiral-shaped PVDF cantilever and a double-clamped PVDF beam of two piezoelectric energy harvesters are mentioned to provide ideas for reducing the resonant frequencies and enhancing the output signals of PVDF vibration sensors respectively. The idea of how to enhance the output signals of PVDF sensors for low frequency vibration measurements may be helpful to the development of geophone.

Enhanced Performance of PVDF Piezoelectric Speaker Using PVDF/ZnO Nanopillar Composites - Hur, Shin (Journal of Sensor Science and Technology, 2016)
In this study, we fabricated and evaluated the performance of film speaker using PVDF / ZnO NP composite structure. PVDF piezoelectric films were fabricated and characterized by XRD and SEM. ZnO nanopillars were prepared by hydrothermal synthesis on prepared PVDF piezoelectric films. We analyzed and tested the acoustic signal characteristics of the piezoelectric film. In order to fabricate an acoustic structure with a wide frequency range from low to high frequency, we have fabricated various types of film speakers and investigated the frequency characteristics. As a result, the fundamental piezoelectric properties of PVDF show that the piezoelectric constant due to ZnO NP increases. And the overall acoustic signal level is also increased by 10% or more. We investigated frequency generation from 500 Hz to 10 KHz using different sizes with PVDF / ZnO NP composite film speaker

PVDF/ZnO Nanopillar 복합재료를 이용한 압전필름 스피커의 성능향상 - 곽준혁 (센서학회지, 2016)
In this study, we fabricated and evaluated the performance of film speaker using PVDF / ZnO NP composite structure. PVDF piezoelectric films were fabricated and characterized by XRD and SEM. ZnO nanopillars were prepared by hydrothermal synthesis on prepared PVDF piezoelectric films. We analyzed and tested the acoustic signal characteristics of the piezoelectric film. In order to fabricate an acoustic structure with a wide frequency range from low to high frequency, we have fabricated various types of film speakers and investigated the frequency characteristics. As a result, the fundamental piezoelectric properties of PVDF show that the piezoelectric constant due to ZnO NP increases. And the overall acoustic signal level is also increased by 10% or more. We investigated frequency generation from 500 Hz to 10 KHz using different sizes with PVDF / ZnO NP composite film speaker

Flexible Ionic Diodes for Low-Frequency Mechanical Energy Harvesting - ["Yong Zhang", "Manlin Zhu", "Baowen Zhang"] (Advanced Energy Materials, 2016)
The work demonstrates an ionic polymer-based energy harvester designed for converting low-frequency mechanical motions into electricity.

Improved Electrical Properties of Low-Temperature Sintered Cu Doped Ba0.99Ca0.01Zr0.02Ti0.98O3 Ceramics - ["Huajun Sun", "Yong Zhang", "Xiaofang Liu", "five others (RG visible)"] (Journal of Electronic Materials, 2016)
Ba0.99Ca0.01Zr0.02Ti0.98O3-x mol.% Cu ceramics were fabricated and effects of sintering temperature and Cu doping on electrical properties studied.

Enhancing the Sensitivity of Percolative Graphene Films for Flexible and Transparent Pressure Sensor Arrays - Zhuo Chen, Tian Ming, Mahomed Mehdi Goulamaly, Heming Yao, Daniel Nezich, Marek Hempel, Mario Hofmann, Jing Kong (Advanced Functional Materials, 2016)
Flexible and transparent pressure sensor arrays can find applications in many places such as touch panels, artificial skin, or human motion detection. However, conventional strain gauges are rigid and opaque and are not suitable for such applications. Graphene‐based percolative strain gauges can overcome these challenges but currently are still in the infancy of their development. In this work, the performance of graphene‐based percolative strain gauges is investigated and guidelines to improve the durability and sensitivity of graphene films as sensing elements are developed. It is found that the gauge factor depends on the initial resistance of the graphene film. For the same film resistance, it is found that graphene flake size and film morphology also play a role in determining the gauge factor. Increasing the flake–flake resistance through assembly of surfactant molecules between graphene flakes provides an additional route to enhance the gauge factor. Furthermore, encapsu lating the percolative film in micrometer‐thin Poly(methyl methacrylate) does not disrupt the sensing process but significantly improves the sensor's durability. Finally, thus enhanced graphene strain gauges are integrated into flexible and transparent pressure sensor arrays that exhibit high reproducibility and sensitivity.

Wearable Electronics: Polymer‐Enhanced Highly Stretchable Conductive Fiber Strain Sensor Used for Electronic Data Gloves (Adv. Mater. Technol. 7/2016) - Shuai Chen, Zheng Lou, Di Chen, Kai Jiang, Guozhen Shen (Advanced Materials Technologies, 2016)

Integrated hybrid life cycle assessment and supply chain environmental profile evaluations of lead-based (lead zirconate titanate) versus lead-free (potassium sodium niobate) piezoelectric ceramics - T. Ibn-Mohammed, S. C. L. Koh, I. M. Reaney, A. Acquaye, D. Wang, S. Taylor, A. Genovese (Energy & Environmental Science, 2016)
Contrary to conventional knowledge, LCA of PZT vs. KNN indicates the presence of niobium in KNN constitutes far greater impact across all the 16 categories considered in comparison with PZT. The increased environmental impact of KNN occurs in the early stages of the LCA due to raw material extraction and processing.

Precise analysis of compressive strain effects on electric power generation properties of a lead zirconate titanate piezoelectric ceramic - Mitsuhiro Okayasu, Keisuke Watanabe (Journal of Advanced Ceramics, 2016)

Micropatterning: Direct Writing of Patterned, Lead‐Free Nanowire Aligned Flexible Piezoelectric Device (Adv. Sci. 8/2016) - Meng Gao, Lihong Li, Wenbo Li, Haihua Zhou, Yanlin Song (Advanced Science, 2016)

Nanoscale ferroelectric/relaxor composites: Origin of large strain in lead–free Bi–based incipient piezoelectric ceramics - Thi Hinh Dinh, Jin-Kyu Kang, Jae-Shin Lee, Neamul Hayet Khansur, John Daniels, Hyun-Young Lee, Fang-Zhou Yao, Ke Wang, Jing-Feng Li, Hyoung-Su Han, Wook Jo (Journal of the European Ceramic Society, 2016)

Effects of Bi2O3 additive on sintering process and dielectric, ferroelectric, and piezoelectric properties of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free piezoceramics - Raziye Hayati, Mohammad Ali Bahrevar, Touradj Ebadzadeh, Virginia Rojas, Nikola Novak, Jurij Koruza (Journal of the European Ceramic Society, 2016)

Lead-zirconate-titanate-based thick-film structures prepared by piezoelectric inkjet printing of aqueous suspensions - Tina Bakarič, Barbara Malič, Danjela Kuscer (Journal of the European Ceramic Society, 2016)

A study of the electric power generation properties of a lead zirconate titanate piezoelectric ceramic - Mitsuhiro Okayasu, Keisuke Watanabe (Ceramics International, 2016)

Flexible lead-free piezoelectric nanofiber composites based on BNT-ST and PVDF for frequency sensor applications - Sang Hyun Ji, Jeong Ho Cho, Young Hun Jeong, Jong-Hoo Paik, Jon Do Yun, Ji Sun Yun (Sensors and Actuators A: Physical, 2016)

Giant pyroelectric energy harvesting and a negative electrocaloric effect in multilayered nanostructures - Gaurav Vats, Ashok Kumar, Nora Ortega, Chris R. Bowen, Ram S. Katiyar (Energy & Environmental Science, 2016)
This work examines the potential of PbZr0.53Ti0.47O3/CoFe2O4 (PZT/CFO) multi-layered nanostructures (MLNs) to achieve a giant electrocaloric effect (ECE) and enhanced pyroelectric energy harvesting.

A lithium–oxygen battery based on lithium superoxide - Jun Lü, Yun Jung Lee, Xiangyi Luo, Kah Chun Lau, Mohammad Asadi, Hsien-Hau Wang, Scott M. Brombosz, Jianguo Wen, Dengyun Zhai, Zonghai Chen, Dean J. Miller, Yo Sub Jeong, Jin-Bum Park, Zhigang Zak Fang, Bijandra Kumar, Amin Salehi‐Khojin, Yang‐Kook Sun, Larry A. Curtiss, Khalil Amine (Nature, 2016)

A Facile Synthesis of ZnCo2O4 Nanocluster Particles and the Performance as Anode Materials for Lithium Ion Batteries - Yue Pan, Weijia Zeng, Lin Li, Yuzi Zhang, Yingnan Dong, Dianxue Cao, Guiling Wang, Brett L. Lucht, Ke Ye, Kui Cheng (Nano-Micro Letters, 2016)
ZnCo2O4 nanocluster particles (NCPs) were prepared through a designed hydrothermal method, with the assistance of a surfactant, sodium dodecyl benzene sulfonate. The crystalline structure and surface morphology of ZnCo2O4 were investigated by XRD, XPS, SEM, TEM, and BET analyses. The results of SEM and TEM suggest a clear nanocluster particle structure of cubic ZnCo2O4 (~100 nm in diameter), which consists of aggregated primary nanoparticles (~10 nm in diameter), is achieved. The electrochemical behavior of synthesized ZnCo2O4 NCPs was investigated by galvanostatic discharge/charge measurements and cyclic voltammetry. The ZnCo2O4 NCPs exhibit a high reversible capacity of 700 mAh g−1 over 100 cycles under a current density of 100 mA g−1 with an excellent coulombic efficiency of 98.9% and a considerable cycling stability. This work demonstrates a facile technique designed to synthesize ZnCo2O4 NCPs which show great potential as anode materials for lithium ion batteries.

“Wiring” redox-active polyoxometalates to carbon nanotubes using a sonication-driven periodic functionalization strategy - Jun Hu, Yuanchun Ji, Wei Chen, Carsten Streb, Yu‐Fei Song (Energy & Environmental Science, 2016)
A universal one-step strategy for the periodic deposition of redox-active polyoxometalate nanocrystals on single-walled carbon nanotubes is reported, giving access to high-performance electrodes for lithium-ion batteries.

Hierarchical Assemblies of Carbon Nanotubes for Ultraflexible Li‐Ion Batteries - Shahab Ahmad, Davor Copic, Chandramohan George, Michaël De Volder (Advanced Materials, 2016)
The flexible batteries that are needed to power flexible circuits and displays remain challenging, despite considerable progress in the fabrication of such devices. Here, it is shown that flexible batteries can be fabricated using arrays of carbon nanotube microstructures, which decouple stress from the energy-storage material. It is found that this battery architecture imparts exceptional flexibility (radius ≈ 300 μm), high rate (20 A g−1), and excellent cycling stability. One of the most fascinating paradigm shifts in modern electronics is the fabrication of soft and flexible electronic devices. This development is fueled by a continuous search for more compact and intuitive consumer electronics,1 medical implants,2 and the emergence of the “Internet of Things.”3 While considerable progress has been made in the fabrication of flexible and stretchable circuits,4 radio-frequency identification (RFID) tags,5 and displays,6 the flexible batteries needed to power these devices remain chal lenging.7 Existing flexible batteries are often too heavy, bulky, and rigid, and require a radical redesign of the battery architecture to address these issues.8 Here we demonstrate that extremely flexible batteries can be achieved by designing carbon nanotube (CNT) microstructures, which decouple the stress induced during bending in the collector electrode from stress in the energy-storage material (Fe2O3 anodes and LNCO cathodes in this work).

Hierarchical Tubular Structures Composed of Co3O4 Hollow Nanoparticles and Carbon Nanotubes for Lithium Storage - Yu Ming Chen, Le Yu, Xiong Wen Lou (Angewandte Chemie International Edition, 2016)
Hierarchical tubular structures composed of Co3 O4 hollow nanoparticles and carbon nanotubes (CNTs) have been synthesized by an efficient multi-step route. Starting from polymer-cobalt acetate (Co(Ac)2 ) composite nanofibers, uniform polymer-Co(Ac)2 @zeolitic imidazolate framework-67 (ZIF-67) core-shell nanofibers are first synthesized via partial phase transformation with 2-methylimidazole in ethanol. After the selective dissolution of polymer-Co(Ac)2 cores, the resulting ZIF-67 tubular structures can be converted into hierarchical CNTs/Co-carbon hybrids by annealing in Ar/H2 atmosphere. Finally, the hierarchical CNT/Co3 O4 microtubes are obtained by a subsequent thermal treatment in air. Impressively, the as-prepared nanocomposite delivers a high reversible capacity of 1281 mAh g(-1) at 0.1 A g(-1) with exceptional rate capability and long cycle life over 200 cycles as an anode material for lithium-ion batteries.

A Commercial Conducting Polymer as Both Binder and Conductive Additive for Silicon Nanoparticle-Based Lithium-Ion Battery Negative Electrodes - Thomas M. Higgins, Sang‐Hoon Park, Paul J. King, Chuanfang Zhang, Niall McEvoy, Nina C. Berner, Dermot Daly, Aleksey Shmeliov, Umar Khan, Georg S. Duesberg, Valeria Nicolosi, Jonathan N. Coleman (ACS Nano, 2016)
This work describes silicon nanoparticle-based lithium-ion battery negative electrodes where multiple nonactive electrode additives (usually carbon black and an inert polymer binder) are replaced with a single conductive binder, in this case, the conducting polymer PEDOT: PSS. While enabling the production of well-mixed slurry-cast electrodes with high silicon content (up to 95 wt %), this combination eliminates the well-known occurrence of capacity losses due to physical separation of the silicon and traditional inorganic conductive additives during repeated lithiation/delithiation processes. Using an in situ secondary doping treatment of the PEDOT: PSS with small quantities of formic acid, electrodes containing 80 wt % SiNPs can be prepared with electrical conductivity as high as 4.2 S/cm. Even at the relatively high areal loading of 1 mg/cm(2), this system demonstrated a first cycle lithiation capacity of 3685 mA·h/g (based on the SiNP mass) and a first cycle efficiency of ∼78%. Aft er 100 repeated cycles at 1 A/g this electrode was still able to store an impressive 1950 mA·h/g normalized to Si mass (∼75% capacity retention), corresponding to 1542 mA·h/g when the capacity is normalized by the total electrode mass. At the maximum electrode thickness studied (∼1.5 mg/cm(2)), a high areal capacity of 3 mA·h/cm(2) was achieved. Importantly, these electrodes are based on commercially available components and are produced by the standard slurry coating methods required for large-scale electrode production. Hence, the results presented here are highly relevant for the realization of commercial LiB negative electrodes that surpass the performance of current graphite-based negative electrode systems.

Suppressed Polysulfide Crossover in Li–S Batteries through a High-Flux Graphene Oxide Membrane Supported on a Sulfur Cathode - Mahdokht Shaibani, Abozar Akbari, Phillip Sheath, Christopher D. Easton, Parama Chakraborty Banerjee, Kristina Konstas, Armaghan Fakhfouri, Marzieh Barghamadi, Mustafa Musameh, Adam S. Best, Thomas Rüther, Peter J. Mahon, Matthew R. Hill, Anthony F. Hollenkamp, Mainak Majumder (ACS Nano, 2016)
Utilization of permselective membranes holds tremendous promise for retention of the electrode-active material in electrochemical devices that suffer from electrode instability issues. In a rechargeable Li–S battery—a strong contender to outperform the Li-ion technology—migration of lithium polysulfides from the sulfur cathode has been linked to rapid capacity fading and lower Coulombic efficiency. However, the current approaches for configuring Li–S cells with permselective membranes suffer from large ohmic polarization, resulting in low capacity and poor rate capability. To overcome these issues, we report the facile fabrication of a high-flux graphene oxide membrane directly onto the sulfur cathode by shear alignment of discotic nematic liquid crystals of graphene oxide (GO). In conjunction with a carbon-coated separator, the highly ordered structure of the thin (∼0.75 μm) membrane and its inherent surface charge retain a majority of the polysulfides, enabling the cells to deliver v ery high initial discharge capacities of 1063 and 1182 mAh g electrode –1 for electrodes with 70 and 80% sulfur content, respectively, at the practical 0.5 C rate. The very high sulfur utilization and impressive capacity retentions of the high sulfur content electrodes result in some of the highest performance metrics in the literature of Li–S ( e.g., electrode capacity of 835 mAh g electrode –1 after 100 cycles at 0.5 C with a sulfur content of 80%). We show that the structural order of the shear-aligned GO membrane is key in maintaining good kinetics of the charge transfer processes in Li–S batteries.

Quantifying microstructural dynamics and electrochemical activity of graphite and silicon-graphite lithium ion battery anodes - Patrick Pietsch, Daniel Westhoff, Julian Feinauer, Jens Eller, Federica Marone, Marco Stampanoni, Volker Schmidt, Vanessa Wood (Nature Communications, 2016)
Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of ma gnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

Mass production of two-dimensional oxides by rapid heating of hydrous chlorides - Chunsong Zhao, Haitian Zhang, Wenjie Si, Hui Wu (Nature Communications, 2016)
Two-dimensional (2D) nanoscale oxides have attracted research interest owing to their electronic, magnetic optical and catalytic properties. If they could be manufactured on a large scale, 2D oxides would be attractive for applications ranging from electronics to energy conversion and storage. Herein, we report facile fabrication of oxide nanosheets by rapid thermal annealing of corresponding hydrous-chloride compounds. By heating CrCl3·6H2O, ZrOCl2·8H2O, AlCl3·6H2O and YCl3·6H2O crystals as precursors, we immediately collect large quantities of ultrathin Cr2O3, ZrO2, Al2O3 and Y2O3 nanosheets, respectively. The formation of layered nanosheets relies on exfoliation driven by rapid evaporation of water and/or other gas molecules generated under annealing. Our route allows simple, efficient and inexpensive production of 2D oxides. As a demonstration, we evaluate Cr2O3 nanosheets prepared by our method as anodes in lithium-ion batteries and find superior performance in comparison with the ir microcrystalline counterparts.

The Anode Challenge for Lithium‐Ion Batteries: A Mechanochemically Synthesized Sn–Fe–C Composite Anode Surpasses Graphitic Carbon - Zhixin Dong, Ruibo Zhang, Dongsheng Ji, Natasha A. Chernova, Khim Karki, Shawn Sallis, Louis F. J. Piper, M. Stanley Whittingham (Advanced Science, 2016)
Carbon‐based anodes are the key limiting factor in increasing the volumetric capacity of lithium‐ion batteries. Tin‐based composites are one alternative approach. Nanosized Sn–Fe–C anode materials are mechanochemically synthesized by reducing SnO with Ti in the presence of carbon. The optimum synthesis conditions are found to be 1:0.25:10 for initial ratio of SnO, Ti, and graphite with a total grinding time of 8 h. This optimized composite shows excellent extended cycling at the C/10 rate, delivering a first charge capacity as high as 740 mAh g −1 and 60% of which still remained after 170 cycles. The calculated volumetric capacity significantly exceeds that of carbon. It also exhibits excellent rate capability, delivering volumetric capacity higher than 1.6 Ah cc −1 over 140 cycles at the 1 C rate.

Chiral Graphene Quantum Dots - Nozomu Suzuki, Yichun Wang, Paolo Elvati, Zhibei Qu, Kyoungwon Kim, Shuang Jiang, Elizabeth Baumeister, Jae‐Wook Lee, Bongjun Yeom, Joong Hwan Bahng, Jaebeom Lee, Angela Violi, Nicholas A. Kotov (ACS Nano, 2016)
Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functiona l theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films - Elisa M. Miller, Daniel M. Kroupa, Jianbing Zhang, Philip Schulz, Ashley R. Marshall, Antoine Kahn, Stephan Lany, Joseph M. Luther, Matthew C. Beard, Craig L. Perkins, Jao van de Lagemaat (ACS Nano, 2016)
We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determi ned that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum.

Ultrasensitive PbS quantum-dot-sensitized InGaZnO hybrid photoinverter for near-infrared detection and imaging with high photogain - Do Kyung Hwang, Young Tack Lee, Kwang H. Lee, Yun Jae Lee, Seyed Hossein Hosseini Shokouh, Ji-hoon Kyhm, Junyeong Lee, Hong Hee Kim, Tae-Hee Yoo, Seung Hee Nam, Dong Ick Son, Byeong‐Kwon Ju, Min‐Chul Park, Jin Dong Song, Won Kook Choi, Seongil Im (NPG Asia Materials, 2016)
Lead sulfide (PbS) quantum dots (QDs) have great potential in optoelectronic applications because of their desirable characteristics as a light absorber for near-infrared (NIR) photodetection. However, most PbS-based NIR photodetectors are two-terminal devices, which require an integrated pixel circuit to be practical photosensors. Here we report on PbS QD/indium gallium zinc oxide (InGaZnO, IGZO) metal oxide semiconductor hybrid phototransistors with a photodetection capability between 700 and 1400 nm, a range that neither conventional Si nor InGaAs photodetectors can cover. The new hybrid phototransistor exhibits excellent photoresponsivity of over 10 6 A W -1 and a specific detectivity in the order of 10 13 Jones for NIR (1000 nm) light. Furthermore, we demonstrate an NIR (1300 nm) imager using photogating inverter pixels based on PbS/IGZO phototransistors at an imaging frequency of 1 Hz with a high output voltage photogain of ~4.9 V (~99%). To the best of our knowledge, this report demonstrates the first QD/metal oxide hybrid phototransistor-based flat panel NIR imager. Our hybrid approach using QD/metal oxide paves the way for the development of gate-tunable and highly sensitive flat panel NIR sensors/ imagers that can be easily integrated.

Electrospun nanowire arrays for electronics and optoelectronics - Zhi Zheng, Lin Gan, Tianyou Zhai (Science China Materials, 2016)

Growth of III-V semiconductor nanowires and their heterostructures - Ang Li, Jin Zou, Xiaodong Han (Science China Materials, 2016)

Solution-Processed, High-Speed, and High-Quantum-Efficiency Quantum Dot Infrared Photodetectors - Jianbo Gao, Son C. Nguyen, Noah D. Bronstein, A. Paul Alivisatos (ACS Photonics, 2016)
For over a decade, much effort has been focused on passivation of the high density of localized electronic trap states in colloidal semiconductor quantum dots (QDs), which lead to reduced performance in solar cell, light-emitting diode, laser, and photoconductor applications. However, here we take advantage of the naturally occurring high density of trap states to demonstrate solution-processed high-speed PbSe quantum dot near-infrared photodetectors. Carrier transport dynamics studies reveal multiple trapping and release transport dynamics in band tail states. A sandwich microstrip transmission line photodetector utilizing these QD films was fabricated to achieve high performance by allowing carriers to be swept to the electrodes before they fall into the band tail states. This device demonstrates external quantum efficiency, responsivity, and response time (full width at half-maximum) of 54%, 0.36 A/W, and 74 ps, respectively.

Ultrasound-mediated piezoelectric differentiation of neuron-like PC12 cells on PVDF membranes - Hoop M, Chen XZ, Ferrari A, Mushtaq F, Ghazaryan G, Tervoort T, Poulikakos D, Nelson B, Pané S. (Scientific Reports, 2017)
β-PVDF. Besides, PVDF is more accessible due to its low cost and high production volume. By using the PC12 model for neuronal differentiation of mammalian cells32, we examine the capability of the piezoelectric surface characteristic for the initiation and growth of cell neurites (Fig. 1a). Ultrasound (US) is utilized as a power transmission system for wireless dynamic stimulation of β-PVDF. US has been widely employed in biomedical devices due to its superior biocompatibility and deeply focused penetration in biological tissues33. The electrical charge generation by β-PVDF is focused solely around the polymer, allowing for enhanced spatial control of the neuronal stimulation area. In addition, the molecular differentiation pathway induced by the electrostimulation of PC12 cells is investigated through dedicated experiments with biochemical inhibitors specifically targeting alternative differentiation pathways. The capability of US stimulated β-PVDF membranes to induce neuronal differe ntiation is non-invasive and allows for spatially precise, long-term therapy, making it an ideal candidate for the

Solid-state-processing of δ-PVDF (Materials Horizons, 2017)
3 Graduate School Materials Science in Mainz, Staudinger Weg 9, 55128 Mainz, 4 Holst Centre, High Tech Campus 31,5656AE Eindhoven, The Netherlands 6School of Materials Science and Engineering and School of Chemical & Biomolecular

Design, fabrication and characterization of composite piezoelectric ultrafine fibers for cochlear stimulation (Materials & Design, 2017)
Sensorineural hearing loss, primed by dysfunction or death of hair cells in the cochlea, is the main cause of severe or profound deafness. Piezoelectric materials work similarly to hair cells, namely, as mechano-electrical transducers. Polyvinylidene fluoride (PVDF) films have demonstrated potential to replace the hair cell function, but the obtained piezoresponse was insufficient to stimulate effectively the auditory neurons. In this study, we reported on piezoelectric nanocomposites based on ultrafine PVDF fibers and barium titanate nanoparticles (BTNPs), as a strategy to improve the PVDF performance for this application. BTNP/PVDF fiber meshes were produced via rotating-disk electrospinning, up to 20/80 weight composition. The BTNP/PVDF fibers showed diameters ranging in 0.160-1.325 mu m. Increasing collector velocity to 3000 rpm improved fiber alignment. The piezoelectric beta phase of PVDF was well expressed following fabrication and the piezoelectric coefficients increased accord ing to the BTNP weight ratio. The BTNP/PVDF fibers were not cytotoxic towards cochlear epithelial cells. Neural-like cells adhered to the composite fibers and, upon mechanical stimulation, showed enhanced viability. Using BTNP filler for PVDF matrices, in the form of aligned ultrafine fibers, increased the piezoresponse of PVDF transducers and favored neural cell contact. Piezoelectric nanostructured composites might find application in next generation cochlear implants. (C) 2017 Elsevier Ltd. All rights reserved.

Piezoelectric characteristics of electrospun PVDF as a function of phase-separation temperature and metal salt content - Prasad, Gajula; Sathiyanathan, Ponnan; Prabu, Arun Anand; Kim, Kap Jin (MACROMOLECULAR RESEARCH, 2017)
In this paper, the crystallinity changes in polyvinylidene fluoride (PVDF) as function of varying phase-separation temperatures (0 to 90 A degrees C) and chloride salts (BaCl2, CaCl2, CA degrees Cl-2, NaCl, SnCl2, N(2)H6Cl(2)) were investigated. FTIR quantitative analysis showed higher beta-crystalline and lower alpha-crystalline content for 70 A degrees C phase-separated PVDF and 70 A degrees C phase-separated PVDF-CaCl2 (15 wt%) samples. XRD and DSC studies also confirmed the influence of 70 A degrees C phase-separation temperature and CaCl2 salt in improving the beta-crystallinity in PVDF compared to the neat PVDF sample. Since higher beta-crystalline content is favoured for use in piezoelectric applications, these two sample preparation conditions were optimized for use in piezoelectric studies. Electrospun nanowebs of the selected samples were measured for their piezoelectric output signals under applied pressure of 1 kgf and released periodically at 0.5 Hz. From the peak-to-peak output voltage, 70 A degrees C phase-separated PVDF-CaCl2 sample exhibited significantly higher output voltage (+0.89 V) compared to neat PVDF (+0.48 V) and 70 A degrees C phase-separated PVDF (+0.53 V) samples. These results conclude that the combinative effect of phase-separation temperature and metal salt addition plays a vital role in improving the piezoelectric characteristics of PVDF, which signifies the importance of this study.

Molecular modeling of the piezoelectric properties of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene or graphene oxide - Bystrov, Vladimir S.; Bdikin, Igor K.; Silibin, Maksim; Karpinsky, Dmitry; Kopyl, Svitlana; Paramonova, Ekaterina V.; Goncalves, Gil (JOURNAL OF MOLECULAR MODELING, 2017)
Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene (G) or graphene oxide (GO) were performed using the semi-empirical quantum approximation PM3 in HyperChem. The piezo properties of the composites were analyzed and compared with experimental data obtained for P(VDF-TrFE)-GO films. Qualitative agreement was obtained between the results of the modeling and the experimental results in terms of the properties of the measured effective piezoelectric coefficient d(33eff) and its decrease in the presence of G/GO in comparison with the average computed piezoelectric coefficient <d(33)>. When models incorporating one or several G layers with 54 carbon atoms were investigated, the average piezoelectric coefficient <d(33)> was found to decrease to -9.8 pm/V for the one-sided model PVDF/G and to -18.98 pm/V for the sandwich model G/PVDF/G as compared with the calculated piezoelectric coefficient for pure PVDF (<d(33)> = -42.2 pm/V computed in present work, and <d(33)> = -38.5 pm/V, obtained from J Mol Model 35 (2013) 19: 3591-3602). When models incorporating one or several GO layers with 98 carbon atoms were considered, the piezoelectric coefficient was found to decrease to -14.6 pm/V for the one-sided PVDF/GO model and to -29.8 pm/V for the sandwich GO/PVDF/GO model as compared with the same calculated piezoelectric coefficient for pure PVDF.

The piezoelectric response of electrospun PVDF nanofibers with graphene oxide, graphene, and halloysite nanofillers: a comparative study - Abbasipour, Mina; Khajavi, Ramin; Yousefi, Ali Akbar; Yazdanshenas, Mohammad Esmail; Razaghian, Farhad (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 2017)
Although, many efforts were performed to develop piezoelectric systems with high energy conversion rate, but they still show insufficient performance. In this study, the effect of three nanofillers with different morphology and their concentration on macro/micro structure and piezoelectric properties of polyvinylidene fluoride (PVDF) nanofibers were investigated and compared. Graphene oxide (GO) and graphene (Gr) as planner nanofillers, and halloysite (Hal) nanotube were introduced into a PVDF solution in different concentrations (0.05-3.2 wt/wt%). The prepared solutions were fabricated into nanofibers through electrospinning method. The electroactive phase (beta-phase) of nanofibrous PVDF mat increased up to similar to 49% in comparison with PVDF powder. The presence of nanofiller in PVDF matrix also increased it more up to 10%. Gr nanofiller had least effect on piezoelectric properties attributed to its low interaction with PVDF chains. PVDF/Hal nanocomposite with low filler content concentration (< 0.1 wt/wt%) and PVDF/GO with high content of filler concentration (> 0.4 wt/wt%) caused higher polar phase. Hal nanotubes with a rod like morphology caused more oriented and finer nanofibers than PVDF/GO and PVDF/Gr nanofibers. However, PVDF/0.8 Hal showed higher output voltage (0.1 V), despite of its lower beta-phase in compared with PVDF/0.8GO nanocomposites. It was concluded that the piezoelectric response cannot be just evaluated with dielectric constant of nanofiller or beta-phase percentage in an electrospun PVDF nanocomposite, but there are some other important factors like orientation and fineness of electrospun nanofibers.

Integrated 3D printing and corona poling process of PVDF piezoelectric films for pressure sensor application - Kim, Hoejin; Torres, Fernando; Wu, Yanyu; Villagran, Dino; Lin, Yirong; Tseng, Tzu-Liang (Bill) (SMART MATERIALS AND STRUCTURES, 2017)
This paper presents a novel process to fabricate piezoelectric films from polyvinylidene fluoride (PVDF) polymer using integrated fused deposition modeling (FDM) 3D printing and corona poling technique. Corona poling is one of many effective poling processes that has received attention to activate PVDF as a piezoelectric responsive material. The corona poling process occurs when a PVDF polymer is exposed to a high electric field created and controlled through an electrically charged needle and a grid electrode under heating environment. FDM 3D printing has seen extensive progress in fabricating thermoplastic materials and structures, including PVDF. However, post processing techniques such as poling is needed to align the dipoles in order to gain piezoelectric properties. To further simplify the piezoelectric sensors and structures fabrication process, this paper proposes an integrated 3D printing process with corona poling to fabricate piezoelectric PVDF sensors without post poling pr ocess. This proposed process, named 'Integrated 3D Printing and Corona poling process' (IPC), uses the 3D printer's nozzle and heating bed as anode and cathode, respectively, to create poling electric fields in a controlled heating environment. The nozzle travels along the programmed path with fixed distance between nozzle tip and sample's top surface. Simultaneously, the electric field between the nozzle and bottom heating pad promotes the alignment of dipole moment of PVDF molecular chains. The crystalline phase transformation and output current generated by printed samples under different electric fields in this process were characterized by a Fourier transform infrared spectroscopy and through fatigue load frame. It is demonstrated that piezoelectric PVDF films with enhanced beta-phase percentage can be fabricated using the IPC process. In addition, mechanical properties of printed PVDF was investigated by tensile testing. It is expected to expand the use of additive manufacturing to fabricate piezoelectric PVDF-based devices for applications such as sensing and energy harvesting.

Fabrication and Pressure Sensing Analysis of ZnO/PVDF Composite Microfiber Arrays by Low-voltage Near-field Electrospinning - Si Wenyan; Zhang Hongdi; Liu Yanjie; Zhao Aijing; Zhang Zhiguang; Gong Maogang; Zhang Juncheng; Long Yunze (CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 2017)
Parallel arrays of ZnO/polyvinylidene fluoride (PVDF) microfibers were successfully prepared by low-voltage near-field electrospinning. The ZnO/PVDF microfiber arrays were characterized by optical microscope, scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy(EDS). The average diameter of the composite fibers was about 40 mu m. The EDS analysis demonstrated that ZnO nanoparticles have been doped into the parallel microfibers. Some related piezoelectric properties and electrical properties are presented in this paper. The piezoelectric properties of the ZnO/PVDF microfiber arrays are enhanced, and the mechanism is discussed briefly. These results indicate that the low-voltage near-field electrospun ZnO/PVDF composite microfibers have potential application in piezoelectric pressure sensors and nanogenerators.

A brief review of Ba(Ti 0.8 Zr 0.2 )O 3 -(Ba 0.7 Ca 0.3 )TiO 3 based lead-free piezoelectric ceramics: Past, present and future perspectives - ["Huajun Sun", "Jian Wang", "Baolin Han", "six others (RG visible)"] (Journal of Physics and Chemistry of Solids, 2017)
BCZT based lead-free piezoceramics have attracted attention as an emerging lead-free piezoelectric system.

A microcube-based hybrid piezocomposite as a flexible energy generator - ["Yong Zhang", "Furong Wang", "Yuan Tian", "six others (RG visible)"] (RSC Advances, 2017)
A high-performance piezoelectric energy generator based on PZT microcubes and P(VDF-TrFE) was prepared.

Porous Ionic Membrane Based Flexible Humidity Sensor and its Multifunctional Applications - Tie Li, Lianhui Li, Hongwei Sun, Yan Xu, Xuewen Wang, Hui Luo, Zheng Liu, Ting Zhang (Advanced Science, 2017)
A highly flexible porous ionic membrane (PIM) is fabricated from a polyvinyl alcohol/KOH polymer gel electrolyte, showing well‐defined 3D porous structure. The conductance of the PIM changes more than 70 times as the relative humidity (RH) increases from 10.89% to 81.75% with fast and reversible response at room temperature. In addition, the PIM‐based sensor is insensitive to temperature (0–95 °C) and pressure (0–6.8 kPa) change, which indicates that it can be used as highly selective flexible humidity sensor. A noncontact switch system containing PIM‐based sensor is assembled, and results show that the switch responds favorably to RH change caused by an approaching finger. Moreover, an attachable smart label using PIM‐based sensor is explored to measure the water contents of human skin, which shows a great linear relationship between the sensitivity of the sensor and the facial water contents measured by a commercial reference device.

Humidity Sensors: Porous Ionic Membrane Based Flexible Humidity Sensor and its Multifunctional Applications (Adv. Sci. 5/2017) - Tie Li, Lianhui Li, Hongwei Sun, Yan Xu, Xuewen Wang, Hui Luo, Zheng Liu, Ting Zhang (Advanced Science, 2017)

Preparation, microstructure and relaxor ferroelectric characteristics of BLNT–BCT lead-free piezoceramics - Vijayeta Pal, A. Kumar, O.P. Thakur, R.K. Dwivedi, N Eswara Prasad (Journal of Alloys and Compounds, 2017)

Understanding the piezoelectric properties in potassium-sodium niobate-based lead-free piezoceramics: Interrelationship between intrinsic and extrinsic factors - Fernando Rubio-Marcos, José F. Fernandez, Diego A. Ochoa, José E. García, Rocio E. Rojas-Hernandez, Miriam Castro, Leandro Ramajo (Journal of the European Ceramic Society, 2017)

Composition-driven phase boundary and its energy harvesting performance of BCZT lead–free piezoelectric ceramic - Xiaodong Yan, Mupeng Zheng, Yudong Hou, Mankang Zhu (Journal of the European Ceramic Society, 2017)

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics on a nanoscopic scale - Mitsuhiro Okayasu, Kohei Bamba (Journal of the European Ceramic Society, 2017)

In situ TEM observations of microstructural characteristics of lead zirconate titanate piezoelectric ceramic during heating to 1000 °C - Mitsuhiro Okayasu, Tsukasa Ogawa, Yoshikazu Sasaki (Ceramics International, 2017)

Performance and Mechanism of Piezo-Catalytic Degradation of 4-Chlorophenol: Finding of Effective Piezo-Dechlorination - Shenyu Lan, Jinxi Feng, Ya Xiong, Shuanghong Tian, Shengwei Liu, Lingjun Kong (Environmental Science & Technology, 2017)

A Tunable 3D Nanostructured Conductive Gel Framework Electrode for High‐Performance Lithium Ion Batteries - Ye Shi, Jun Zhang, Andrea M. Bruck, Yiman Zhang, Jing Li, Eric A. Stach, Kenneth J. Takeuchi, Amy C. Marschilok, Esther S. Takeuchi, Guihua Yu (Advanced Materials, 2017)
This study develops a tunable 3D nanostructured conductive gel framework as both binder and conductive framework for lithium ion batteries. A 3D nanostructured gel framework with continuous electron pathways can provide hierarchical pores for ion transport and form uniform coatings on each active particle against aggregation. The hybrid gel electrodes based on a polypyrrole gel framework and Fe 3 O 4 nanoparticles as a model system in this study demonstrate the best rate performance, the highest achieved mass ratio of active materials, and the highest achieved specific capacities when considering total electrode mass, compared to current literature. This 3D nanostructured gel‐based framework represents a powerful platform for various electrochemically active materials to enable the next‐generation high‐energy batteries.

Organohalide Perovskites are Fast Ionic Conductors - Nuria Vicente, Germà García-Belmonte (Advanced Energy Materials, 2017)
Abstract Fast ionic conductors constitute a family of materials exhibiting high values of the ionic conductivity while their crystal structure remains rather rigid. Perovskite‐like compounds are known to be good ionic conductors with applications as solid electrolytes. In hybrid halide perovskites both intrinsic (native) and extrinsic defect migration are regarded to occur. Ion diffusivity analysis is inherently ambiguous in all‐solid‐state configurations because of the multicomponent environment. Here, a liquid electrolyte in contact to the perovskite material forms a reservoir of Li + that is forced to intercalate and migrate within the perovskite electrode. This approach decouples different contributions to transport in such a way that ion diffusion kinetics is easily accessible by means of impedance methods. The room‐temperature chemical diffusion coefficient of lithium ion within the perovskite lattice exhibits values as high as D μ ≈ 10 −7 cm 2 s −1 , which implies conductivities within the range of 10 −3 Ω −1 cm −1 for highly lithiated electrodes. This confirms the superionic intrinsic property of organohalide perovskites from a direct and unambiguous measurement that does not rely upon simulation tools.

From zinc-cyanide hybrid coordination polymers to hierarchical yolk-shell structures for high-performance and ultra-stable lithium-ion batteries - Haosen Fan, Hong Yu, Yufei Zhang, Jing Guo, Zhen Ding, Hao Wang, Xi Hao, Ning Zhao, Hongbo Geng, Zhengfei Dai, Qingyu Yan, Jian Xu (Nano Energy, 2017)

Hydrogen substituted graphdiyne as carbon-rich flexible electrode for lithium and sodium ion batteries - Jianjiang He, Ning Wang, Zili Cui, Huiping Du, Lin Fu, Changshui Huang, Ze Yang, Xiangyan Shen, Yuanping Yi, Zeyi Tu, Yuliang Li (Nature Communications, 2017)
Abstract Organic electrodes are potential alternatives to current inorganic electrode materials for lithium ion and sodium ion batteries powering portable and wearable electronics, in terms of their mechanical flexibility, function tunability and low cost. However, the low capacity, poor rate performance and rapid capacity degradation impede their practical application. Here, we concentrate on the molecular design for improved conductivity and capacity, and favorable bulk ion transport. Through an in situ cross-coupling reaction of triethynylbenzene on copper foil, the carbon-rich frame hydrogen substituted graphdiyne film is fabricated. The organic film can act as free-standing flexible electrode for both lithium ion and sodium ion batteries, and large reversible capacities of 1050 mAh g −1 for lithium ion batteries and 650 mAh g −1 for sodium ion batteries are achieved. The electrode also shows a superior rate and cycle performances owing to the extended π-conjugated system, and the hierarchical pore bulk with large surface area.

Molecular understanding of polyelectrolyte binders that actively regulate ion transport in sulfur cathodes - Longjun Li, Tod A. Pascal, Justin G. Connell, Frank Y. Fan, Stephen M. Meckler, Lin Ma, Yet‐Ming Chiang, David Prendergast, Brett A. Helms (Nature Communications, 2017)
Abstract Polymer binders in battery electrodes may be either active or passive. This distinction depends on whether the polymer influences charge or mass transport in the electrode. Although it is desirable to understand how to tailor the macromolecular design of a polymer to play a passive or active role, design rules are still lacking, as is a framework to assess the divergence in such behaviors. Here, we reveal the molecular-level underpinnings that distinguish an active polyelectrolyte binder designed for lithium–sulfur batteries from a passive alternative. The binder, a cationic polyelectrolyte, is shown to both facilitate lithium-ion transport through its reconfigurable network of mobile anions and restrict polysulfide diffusion from mesoporous carbon hosts by anion metathesis, which we show is selective for higher oligomers. These attributes allow cells to be operated for >100 cycles with excellent rate capability using cathodes with areal sulfur loadings up to 8.1 mg cm –2 .

Synergistic Coupling between Li6.75La3Zr1.75Ta0.25O12 and Poly(vinylidene fluoride) Induces High Ionic Conductivity, Mechanical Strength, and Thermal Stability of Solid Composite Electrolytes - Xue Zhang, Ting Liu, Shuofeng Zhang, Xin Huang, Bingqing Xu, Yuanhua Lin, Ben Xu, Liangliang Li, Ce‐Wen Nan, Yang Shen (Journal of the American Chemical Society, 2017)
Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZTO) ceramics to trigger structural modification of poly(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and C═O group of solvent molecules such as N, N -dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane ( e.g., a high ionic conductivity of about 5 × 10 –4 S cm –1 at 25 °C, high mechanical strength, and good thermal stability). For further illustration, a solid-state lithium battery of LiCoO 2 |PVDF-based membrane|Li is fabricated and delivers satisfactory rate capability and cycling stability at room temperature. Our study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries.

2D Film of Carbon Nanofibers Elastically Astricted MnO Microparticles: A Flexible Binder‐Free Anode for Highly Reversible Lithium Ion Storage - Ting Wang, Hangang Li, Shaojun Shi, Ting Liu, Gang Yang, Yimin Chao, Fan Yin (Small, 2017)
MnO as anode materials has received particular interest owing to its high specific capacity, abundant resources, and low cost. However, serious problems related to the large volume change (>170%) during the lithiation/delithiation processes still results in poor rate capability and fast capacity decay. With homogenous crystals of MnO grown in the network of carbon nanofibers (CNF), binding effect of CNF can effectively weaken the volume change of MnO during cycles. In this work, a CNF/MnO flexible electrode for lithium‐ion batteries is designed and synthesized. The CNF play the roles of conductive channel and elastically astricting MnO particles during lithiation/delithiation. CNF/MnO as binder‐free anode delivers specific capacity of 983.8 mAh g −1 after 100th cycle at a current density of 0.2 A g −1 , and 600 mAh g −1 at 1 A g −1 which are much better than those of pure MnO and pure CNF. The ex‐situ morphologies clearly show the relative volume change of MnO/CNF as anode under var ious discharging and charging times. CNF can elastically buffer the volume change of MnO during charging/discharging cycles. A facile and scalable approach for synthesizing a novel flexible binder‐free anode of CNF/MnO for potential application in highly reversible lithium storage devices is presented.

Tubular titanium oxide/reduced graphene oxide-sulfur composite for improved performance of lithium sulfur batteries - Junhua Song, Jianming Zheng, Shuo Feng, Chengzhou Zhu, Shaofang Fu, Wengao Zhao, Dan Du, Yuehe Lin (Carbon, 2017)

Nanostructured anode materials for lithium-ion batteries: principle, recent progress and future perspectives - Wen Qi, Joseph G. Shapter, Qian Wu, Ting Yin, Guo Gao, Daxiang Cui (Journal of Materials Chemistry A, 2017)
Recent progress in nanostructured carbon, alloys, transition metal oxides and silicon as anode materials for LIBs has been reviewed.

Plasmonic doped semiconductor nanocrystals: Properties, fabrication, applications and perspectives - Ilka Kriegel, Francesco Scotognella, Liberato Manna (Physics Reports, 2017)

Polarity‐Controlled Attachment of Cytochrome C for High‐Performance Cytochrome C/Graphene van der Waals Heterojunction Photodetectors - Maogang Gong, Puja Adhikari, Youpin Gong, Ti Wang, Qingfeng Liu, Bhupal Kattel, W. Y. Ching, Wai‐Lun Chan, Judy Wu (Advanced Functional Materials, 2017)
Abstract Biomolecule/graphene van der Waals heterojunction provides a generic platform for designing high‐performance, flexible, and scalable optoelectronics. A key challenge is, in controllable attachment, the biomolecules to form a desired interfacial electronic structure for a high‐efficiency optoelectronic process of photoabsorption, exciton dissociation into photocarriers, carrier transfer, and transport. Here, it is shown that a polarity‐controlled attachment of the Cytochrome c (Cyt c) biomolecules can be achieved on the channel of graphene field effect transistors (GFET). High‐efficiency charge transfer across the formed Cyt c/graphene interface is demonstrated when Cyt c attaches with positively charged side to GFET as predicted by molecular dynamics simulation and confirmed experimentally. This Cyt c/GFET van der Waals heterojunction nanohybrid photodetector exhibits a spectral photoresponsivity resembling the absorption spectrum of the Cyt c, confirming the role of Cty c as the photosensitizer in the device. The high visible photoresponsivity up to 7.57 × 10 4 A W −1 can be attributed to the high photoconductive gain in exceeding 10 5 facilitated by the high carrier mobility in graphene. This result therefore demonstrates a viable approach in synthesis of the biomolecule/graphene van der Waals heterojunction optoelectronics using polarity‐controlled biomolecule attachment, which can be expanded for on‐chip printing of high‐performance molecular optoelectronics.

Photostriction of strontium ruthenate - Tzu-Chiao Wei, Hsin-Ping Wang, Heng‐Jui Liu, Dung-Sheng Tsai, Jr‐Jian Ke, Chung-Lun Wu, Yu-Peng Yin, Qian Zhan, Gong‐Ru Lin, Ying‐Hao Chu, Jr‐Hau He (Nature Communications, 2017)
Abstract Transition metal oxides with a perovskite crystal structure exhibit a variety of physical properties associated with the lattice. Among these materials, strontium ruthenate (SrRuO 3 ) displays unusually strong coupling of charge, spin and lattice degrees of freedom that can give rise to the photostriction, that is, changes in the dimensions of material due to the absorption of light. In this study, we observe a photon-induced strain as high as 1.12% in single domain SrRuO 3 , which we attribute to a nonequilibrium of phonons that are a result of the strong interaction between the crystalline lattice and electrons excited by light. In addition, these light-induced changes in the SrRuO 3 lattice affect its electrical resistance. The observation of both photostriction and photoresistance in SrRuO 3 suggests the possibility of utilizing the mechanical and optical functionalities of the material for next-generation optoelectronics, such as remote switches, light-controlled elastic micromotors, microactuators and other optomechanical systems.

Color-selective photodetection from intermediate colloidal quantum dots buried in amorphous-oxide semiconductors - Kyung‐Sang Cho, Keun Heo, Chan‐Wook Baik, Jun Young Choi, Heejeong Jeong, Sungwoo Hwang, Sang Yeol Lee (Nature Communications, 2017)
Abstract We report color-selective photodetection from intermediate, monolayered, quantum dots buried in between amorphous-oxide semiconductors. The proposed active channel in phototransistors is a hybrid configuration of oxide-quantum dot-oxide layers, where the gate-tunable electrical property of silicon-doped, indium-zinc-oxide layers is incorporated with the color-selective properties of quantum dots. A remarkably high detectivity (8.1 × 10 13 Jones) is obtained, along with three major findings: fast charge separation in monolayered quantum dots; efficient charge transport through high-mobility oxide layers (20 cm 2 V −1 s −1 ); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns −1 measured with time-resolved photoluminescence is attributed to the intermediate quantum dots buried in oxide layers. These results facilitate the realization of efficient color-selective detection exhibiting a photoconductive gain of 10 7 , obtained using a room-temperature deposition of oxide layers and a solution process of quantum dots. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.

Optical determination of crystal phase in semiconductor nanocrystals - Sung Jun Lim, André Schleife, Andrew M. Smith (Nature Communications, 2017)
semiconductor materials such as cadmium selenide, which exist as two stable phases, cubic and hexagonal, each with distinct properties. However, standard crystallographic characterization through diffraction yields ambiguous phase signatures when nanocrystals are small or polytypic. Moreover, diffraction methods are low-throughput, incompatible with solution samples and require large sample quantities. Here we report the identification of unambiguous optical signatures of cubic and hexagonal phases in II-VI nanocrystals using absorption spectroscopy and first-principles electronic-structure theory. High-energy spectral features allow rapid identification of phase, even in small nanocrystals (∼2 nm), and may help predict polytypic nanocrystals from differential phase contributions. These theoretical and experimental insights provide simple and accurate optical crystallographic analysis for liquid-dispersed nanomaterials, to improve the precision of nanocrystal engineering and improve ou r understanding of nanocrystal reactions.

Inorganic semiconducting materials for flexible and stretchable electronics - Ki Jun Yu, Zheng Yan, Mengdi Han, John A. Rogers (npj Flexible Electronics, 2017)
Abstract Recent progress in the synthesis and deterministic assembly of advanced classes of single crystalline inorganic semiconductor nanomaterial establishes a foundation for high-performance electronics on bendable, and even elastomeric, substrates. The results allow for classes of systems with capabilities that cannot be reproduced using conventional wafer-based technologies. Specifically, electronic devices that rely on the unusual shapes/forms/constructs of such semiconductors can offer mechanical properties, such as flexibility and stretchability, traditionally believed to be accessible only via comparatively low-performance organic materials, with superior operational features due to their excellent charge transport characteristics. Specifically, these approaches allow integration of high-performance electronic functionality onto various curvilinear shapes, with linear elastic mechanical responses to large strain deformations, of particular relevance in bio-integrated devices a nd bio-inspired designs. This review summarizes some recent progress in flexible electronics based on inorganic semiconductor nanomaterials, the key associated design strategies and examples of device components and modules with utility in biomedicine.

Single-crystalline germanium nanomembrane photodetectors on foreign nanocavities - Zhenyang Xia, Haomin Song, Munho Kim, Ming Zhou, Tzu‐Hsuan Chang, Dong Liu, Xin Yin, Kanglin Xiong, Hongyi Mi, Xudong Wang, Fengnian Xia, Zongfu Yu, Zhenqiang Ma, Qiaoqiang Gan (Science Advances, 2017)
Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <50 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. We introduce a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. These single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity.

Superior Self‐Powered Room‐Temperature Chemical Sensing with Light‐Activated Inorganic Halides Perovskites - Hongjun Chen, Meng Zhang, Renheng Bo, Chog Barugkin, Jianghui Zheng, Qingshan Ma, Shujuan Huang, Anita Ho‐Baillie, Kylie Catchpole, Antonio Tricoli (Small, 2017)
Abstract Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self‐powered inorganic halides perovskite for chemical gas sensing at room temperature under visible‐light irradiation is presented. These devices consist of porous network of CsPbBr 3 (CPB) and can generate an open‐circuit voltage of 0.87 V under visible‐light irradiation, which can be used to detect various concentrations of O 2 and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O 2 gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB‐based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.

Niobium pentoxide: a promising surface-enhanced Raman scattering active semiconductor substrate - Yufeng Shan, Zhihui Zheng, Jianjun Liu, Yong Yang, Zhiyuan Li, Zhengren Huang, Dongliang Jiang (npj Computational Materials, 2017)
Abstract Surface-enhanced Raman scattering technique, as a powerful tool to identify the molecular species, has been severely restricted to the noble metals. The surface-enhanced Raman scattering substrates based on semiconductors would overcome the shortcomings of metal substrates and promote development of surface-enhanced Raman scattering technique in surface science, spectroscopy, and biomedicine studies. However, the detection sensitivity and enhancement effects of semiconductor substrates are suffering from their weak activities. In this work, a semiconductor based on Nb 2 O 5 is reported as a new candidate for highly sensitive surface-enhanced Raman scattering detection of dye molecules. The largest enhancement factor value greater than 10 7 was observed with the laser excitation at 633 and 780 nm for methylene blue detection. As far as literature review shows, this is in the rank of the highest sensitivity among semiconductor materials; even comparable to the metal nanostructur e substrates with “hot spots”. The impressive surface-enhanced Raman scattering activities can be attributed to the chemical enhancement dominated by the photo-induced charge transfer, as well as the electromagnetic enhancement, which have been supported by the density-functional-theory and finite element method calculation results. The chemisorption of dye on Nb 2 O 5 creates a new highest occupied molecular orbital and lowest unoccupied molecular orbital contributed by both fragments in the molecule-Nb 2 O 5 system, which makes the charge transfer more feasible with longer excitation wavelength. In addition, the electromagnetic enhancement mechanism also accounts for two orders of magnitude enhancement in the overall enhancement factor value. This work has revealed Nb 2 O 5 nanoparticles as a new semiconductor surface-enhanced Raman scattering substrate that is able to replace noble metals and shows great potentials applied in the fields of biology related.

P-type β-gallium oxide: A new perspective for power and optoelectronic devices - E. Chikoidze, Adel Fellous, Amador Pérez‐Tomás, Guillaume Sauthier, Tamar Tchelidze, Cuong Ton‐That, Tung Thanh Huynh, Matthew R. Phillips, Stephen Russell, Mike Jennings, B. Bérini, François Jomard, Yves Dumont (Materials Today Physics, 2017)

Transferable single-crystal GaN thin films grown on chemical vapor-deposited hexagonal BN sheets - Kunook Chung, Hongseok Oh, Janghyun Jo, Keundong Lee, Miyoung Kim, Gyu‐Chul Yi (NPG Asia Materials, 2017)
Single-crystal gallium nitride (GaN) layers were directly grown on centimeter-scale hexagonal boron nitride (h-BN). Using chemical vapor deposition (CVD), centimeter-scale h-BN films were synthesized on a single-crystal Ni(111) and readily transferred onto amorphous fused silica supporting substrates that had no epitaxial relationship with GaN. For growing fully coalescent GaN layers on h-BN, the achievement of high-density crystal growths was a critical growth step because the sp2-bonded h-BN layers are known to be free of dangling bonds. Unlike GaN layers grown on a typical heterogeneous sapphire substrate, the morphological and microstructural results strongly suggest a high-density growth feature that is driven by the atomic cliffs inherent in the CVD-grown h-BN layers. More importantly, the GaN layers grown on CVD-grown h-BN exhibited a flat and continuous surface morphology with well-aligned crystal orientations both along the c-axis and in-plane, indicating the characteristics o f GaN heteroepitaxy on h-BN. A method for depositing high-quality semiconductor thin films on a two-dimensional material has been developed by researchers in Korea. Growing one defect-free material on another is difficult because of their different atomic structures, particularly when very thin samples are required. Now, Gyu-Chul Yi and co-workers from Seoul National University in Korea have grown large areas of single crystals of the semiconductor gallium nitride directly on boron nitride, which is useful for flexible electronics. They used chemical vapor deposition, which works by exposing a hot volatile gas incorporating atoms of the top material to a cooler substrate. The gallium nitride films could be readily transferred to silica substrates. Since the technique can produce large areas of the material it is a promising for making flexible devices on a commercial scale. Here, we utilize large-size scalable single-crystal 2D films to grow single crystalline inorganic semiconductors. Centimeter-scale hexagonal boron nitride (h-BN) films were synthesized on a single-crystal Ni(111) using chemical vapor deposition (CVD). Single-crystal GaN layers were directly grown on h-BN using metal–organic vapor phase epitaxy. The CVD-grown h-BN exhibited many atomic cliffs that enabled us to grow high-density GaN islands to be merged as homogeneous and flat GaN films. We also investigated the crystallinity and growth mechanism of the GaN films grown on CVD-grown h-BN using transmission electron microscopy and X-ray diffraction.

Biomineralization of a titanium-modified hydroxyapatite semiconductor on conductive wool fibers - Alessio Adamiano, Nicola Sangiorgi, Simone Sprio, Andrea Ruffini, Monica Sandri, Alessandra Sanson, Pierre Gras, David Grossin, Christine Francès, Konstantinos Chatzipanagis, Matthew Bilton, Bartosz Marzec, Alessio Varesano, Fiona C. Meldrum, Roland Kröger, Anna Tampieri (Journal of Materials Chemistry B, 2017)
. This is the first time that a thin film of a wide-band gap semiconductor has been deposited on natural fibers to create a fiber-based building block that can be used to manufacture flexible electronic devices.

Stretchable Electrospun PVDF-HFP Co-ZnO Nanofibers as Piezoelectric Nanogenerators - Parangusan H, Ponnamma D, Al-Maadeed MAA, Al-Maadeed MAA. (Scientific Reports, 2018)
known materials for fabricating piezoelectric devices8. These polymers are used in many fields, such as portable electronic devices, flexible pressure sensors, energy harvesting systems, water purifying devices and in gas separation8–10. In the neat form, these polymers have poor electrical and mechanical performance and the enhancement of their piezoelectricity is still a challenge11. Reports suggest the addition of nanofillers in various dimensions to PVDF and its copolymers like polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) to enhance the piezoelectric, pyroelectric and ferroelectric performances. The piezoelectricity of PVDF-HFP is mainly contributed by polar crystalline phases such as β-phase and γ-phase, rather than the α-phase. Among the various crystalline phases, the electrocactive β- phase imparts the highest dipole moment resulting in high piezoelectricity12.

Polarization behavior of polyvinylidene fluoride films with the addition of reduced graphene oxide (Journal of Industrial and Engineering Chemistry, 2018)
The effect of reduced graphene oxide (RGO) addition on the dielectric and piezoelectric behavior of the polyvinylidene fluoride (PVDF) films was studied. Dielectric constant increased by four times and piezoelectric coefficient also increased twice by the addition of RGO in the PVDF films. Based on capacitance-voltage and ellipsometry measurements and the Kramers-Kronig transformation, it is concluded that the enhanced dielectric and piezoelectric properties of the PVDF/RGO films resulted from the increased orientational polarization due to a phase transition from nonpolar crystalline a phase to polar crystalline beta phase in the PVDF structure. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Enhancement of energy harvesting capability using PVDF/GFRP-laminated films (Journal of Sandwich Structures & Materials, 2018)
PVDF (poly(vinylidene fluoride)) is a promising piezoelectric polymer which can be applied in sensor or energy harvesting fields. To improve the energy harvesting capability of the PVDF film, we proposed a laminated piezoelectric element consisting of two PVDF films sandwiching a GFRP (glass fiber-reinforced plastic) laminate, named as PVDF/GF/PVDF. Its energy harvesting capability and open circuit voltage were experimentally investigated. Compared with PVDF monolayer and bilayer piezoelectric elements, this newly designed PVDF/GF/PVDF possesses remarkably increased energy harvesting capabilities in both AC and DC circuits. The mechanisms for this phenomenon were explored experimentally, theoretically and numerically in detail. Compared with the PVDF monolayer element, the increases of harvested power in the PVDF bilayer element and the PVDF/GF/PVDF are mainly due to their larger PVDF net volume. Compared with the PVDF bilayer element, the reason for the increase of the energy harvesti ng capability in the PVDF/GF/PVDF is its higher piezoelectric stress constant caused by the insertion of stiffer GFRP laminate.

Flexible ZnO-PVDF/PTFE based piezo-tribo hybrid nanogenerator - Singh, Huidrom Hemojit; Khare, Neeraj (NANO ENERGY, 2018)
Triboelectric and piezoelectric nanogenerators based on triboelectric and piezoelectric effects are being explored to harvest electrical energy from the mechanical vibrations. These two different effects can be combined when one of the materials in the triboelectric nanogenerator is a piezoelectric material. In the present work, we have prepared ZnO-PVDF film and fabricated piezo-tribo based hybrid nanogenerator by coupling with PTFE. It is found that when ZnO is incorporated into the PVDF matrix, not only the piezoelectric property but also the triboelectric property of PVDF is enhanced. The ZnO-PVDF based piezo-tribo hybrid generator gives an instantaneous maximum output power of similar to 24.5 mu W/cm(2), which is similar to 2.5 times more as compared to bare PVDF based hybrid nanogenerator. The enhancement has been achieved without any surface treatment or electrical poling, just by introducing ZnO nanorods into PVDF matrix. Therefore, this will give a new approach to enhance both the piezoelectric as well as triboelectric effect and exploiting both the effects simultaneously in one device.

Piezoelectric Response of Aligned Electrospun Polyvinylidene Fluoride/Carbon Nanotube Nanofibrous Membranes - Wu, Chang-Mou; Chou, Min-Hui; Zeng, Wun-Yuan (NANOMATERIALS, 2018)
Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its -phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal content and piezoelectric coefficient (d(33)) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the -phase content to 89% and d(33) to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In be nding tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100 degrees. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.

Phase-Separation-Induced PVDF/Graphene Coating on Fabrics toward Flexible Piezoelectric Sensors - Huang, Tao; Yang, Siwei; He, Peng; Sun, Jing; Zhang, Shuai; Li, Dongdong; Meng, Yan; Zhou, Jiushun; Tang, Huixia; Liang, Junrui; Ding, Guqiao; Xie, Xiaoming (ACS APPLIED MATERIALS & INTERFACES, 2018)
Clothing-integrated piezoelectric sensors possess great potential for future wearable electronics. In this paper, we reported a phase-separation approach to fabricate flexible piezoelectric sensors based on poly(vinylidene fluoride) (PVDF)/graphene composite coating on commercially available fabrics (PVDF/graphene@F). The structural units of -CH2- and -CF2- of PVDF chains were arranged directionally due to the structural induction of graphene and water during phase separation, which is the key for electroactive phase enrichment. In optimized case, integrating into fabric substrates endows the phase-out PVDF/graphene composite coating 4 times higher voltage output than its film counterpart. Piezoelectric sensor based on PVDF/graphenep F exhibits a sensitivity of 34 V N-1, which is higher than many reports. It also shows low detecting threshold (0.6 mN), which can be applied to distinguish the voices or monitor the motion of body. This simple and effective approach toward PVDF/graphene@F with excellent flexibility provides a promising route toward the development of wearable piezoelectric sensors.

Breathable and Flexible Piezoelectric ZnO@PVDF Fibrous Nanogenerator for Wearable Applications - Kim, Minji; Wu, Yuen Shing; Kan, Edwin C.; Fan, Jintu (POLYMERS, 2018)
A novel breathable piezoelectric membrane has been developed by growing zinc oxide (ZnO) nanorods on the surface of electrospun poly(vinylidene fluoride) (PVDF) nanofibers using a low-temperature hydrothermal method. Significant improvement in the piezoelectric response of the PVDF membrane was achieved without compromising breathability and flexibility. PVDF is one of the most frequently used piezoelectric polymers due to its high durability and reasonable piezoelectric coefficient values. However, further enhancement of its piezoelectric response is highly desirable for sensor and energy-harvester applications. Previous studies have demonstrated that piezoelectric ceramic and polymer composites can have remarkable piezoelectric properties and flexibility. However, devices made of such composites lack breathability and some present health risks in wearable applications for containing heavy metals. Unlike other piezoelectric ceramics, ZnO is non-toxic material and has been widely used in many applications including cosmetics. The fabrication of ZnO@PVDF porous electrospun membrane involves a simple low-temperature ZnO growth in aqueous solution, which does not weaken the polarization of PVDF created during electrospinning in the high electric field.

Static-Aligned Piezoelectric Poly (Vinylidene Fluoride) Electrospun Nanofibers/MWCNT Composite Membrane: Facile Method - Shehata, Nader; Elnabawy, Eman; Abdelkader, Mohamed; Hassanin, Ahmed H.; Salah, Mohamed; Nair, Remya; Bhat, Sameer Ahmad (POLYMERS, 2018)
Polyvinylidene Fluoride (PVDF) piezoelectric electrospun nanofibers have been intensively used for sensing and actuation applications in the last decade. However, in most cases, random PVDF piezoelectric nanofiber mats have moderate piezoelectric response compared to aligned PVDF nanofibers. In this work, we demonstrate the effect of alignment conducted by a collector setup composed of two-metal bars with gab inside where the aligned fiber can be formed. That is what we called static aligned nanofibers, which is distinct from the dynamic traditional technique using a high speed rotating drum. The two-bar system shows a superior alignment degree for the PVDF nanofibers. Also, the effect of added carbon nanotubes (CNTs) of different concentrations to PVDF nanofibers is studied to observe the enhancement of piezoelectric response of PVDF nanofibers. Improvement of beta-phase content of aligned (PVDF) nanofibers, as compared to randomly orientated fibers, is achieved. Significant change in the piezoelectricity of PVDF fiber is produced with added CNTs with saturation response in the case of 0.3 wt % doping of CNTs, and piezoelectric sensitivity of 73.8 mV/g with applied masses down to 100 g.

Effect of rolling temperature on the microstructure and electric properties of β-polyvinylidene fluoride films - Yang, Lu; Qiu, Jinhao; Zhu, Kongjun; Ji, Hongli; Zhao, Qiuying; Shen, Mingxia; Zeng, Shaohua (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 2018)
Due to its outstanding dielectric, ferroelectric and piezoelectric properties among polymers, beta-poly(vinylidene fluoride) (PVDF) has been widely used in flexible sensors, transducers and energy harvesters. These applications trigged tremendous interest infabrication of beta-PVDF films with high electric performance over decades. Herein, the traditional solution casting method combined with a novel low-temperature double rolling approach was developed to fabricate beta-PVDF films with superior dielectric, ferroelectric and piezoelectric properties. A systematic investigation was performed to study the effect of rolling temperature on the microstructure and electric properties of original beta-PVDF obtained from solution casting. The results showed that rolling at temperatures between 25 and 60 A degrees C could slightly influence the crystal forms of the beta-PVDF films, but induce a well-oriented beta-phase structure. Moreover, rolling at temperatures below 60 A degrees C can signif icantly reduce the crystallite size of PVDF. With declined crystallite size, improved chain orientation and morphological continuity along the rolling direction, the double rolled beta-PVDF exhibited notably enhanced dielectric and ferroelectric properties. Furthermore, due to the higher breakdown field and lower coercive electric field in comparison with the original beta-PVDF films, the rolled beta-PVDF films can be efficiently poled to obtain excellent piezoelectric properties. A maximum piezoelectric coefficient d (33) of 29pC/N was obtained in the rolled beta-PVDF films with a rolling temperature of around 50 A degrees C.

Effect of processing parameters of the continuous wet spinning system on the crystal phase of PVDF fibers - Jeong, Kun; Kim, Da Hye; Chung, Yong Sik; Hwang, Sang Kyun; Hwang, Hui Yun; Kim, Seong Su (JOURNAL OF APPLIED POLYMER SCIENCE, 2018)
Poly(vinylidene difluoride) (PVDF) has been widely used in piezoelectric applications as films and nanofiber mats, but there are limited publications on piezoelectric wet-spun fibers. In this work, PVDF fibers were prepared using the wet spinning method, and the processing parameters, including the drawing ratio and heat setting temperature, were controlled in the continuous wet spinning system to increase the -phase crystallinity of the fibers. In addition, the wet-spun PVDF fibers were compressed by a rolling press to eliminate voids in the fibers. Then, the compressed PVDF fibers were poled to align the molecular dipoles. The crystal structures of the PVDF fibers were investigated using X-ray diffraction and Fourier-transform infrared spectroscopy. Single filament tensile tests were performed to measure the tensile strength of the fibers. The morphologies of the PVDF fibers with respect to the processing parameters were observed by scanning electron microscope (SEM) and polarization optical microscopy. The piezoelectric constant of the prepared PVDF fibers was then measured using a d(33) meter. The wet-spun PVDF fibers showed the highest -phase and piezoelectric constants when the drawing ratio and heat setting temperature were 6 and 150 degrees C, respectively. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45712.

Preparation of PVDF/PAR Composites with Piezoelectric Properties by Post-Treatment - Oh, Woo Jin; Lim, Hyeon Soo; Won, Jong Sung; Lee, Seung Goo (POLYMERS, 2018)
Thermoplastic composites were prepared using poly (vinylidene fluoride) (PVDF) as the matrix with piezoelectric properties and aromatic polyarylate (PAR) as the reinforcing component. The PVDF/PAR conjugate fibers were prepared by melt conjugate spinning. The PVDF/PAR composites were prepared by compression molding of the PVDF/PAR conjugate fiber laminates at various molding temperatures. Drawing and poling post-treatments of the PVDF/PAR composites were performed to increase the crystalline phase content of the PVDF. The morphologies of the PVDF/PAR composites were observed by scanning electron microscopy, and the tensile properties were tested using an universal testing machine. The crystal structure of the PVDF/PAR composites was confirmed by Fourier transform infrared spectroscopy and X-ray diffraction. The piezoelectric properties were tested using voltmeters and multimeters. The post-treatments enhanced the content of the crystalline phase of the PVDF matrix, thereby improving th e piezoelectric properties of the composites. A molding temperature of 180 degrees C, drawing temperature of 90 degrees C, and poling voltage of 12 kV were identified as the optimal conditions for the preparation of the PVDF/PAR composite.

Piezoelectric Response in Electrospun Poly(vinylidene fluoride) Fibers Containing Fluoro-Doped Graphene Derivatives - Gebrekrstos, Amanuel; Madras, Giridhar; Bose, Suryasarathi (ACS OMEGA, 2018)
Herein, graphene oxide (GO) was suitably functionalized to obtain carboxylated and fluorinated GO (GOCOOH and GOF) derivatives, respectively, via the Hunsdiecker reaction. Electrospun mats of poly(vinylidene fluoride) (PVDF)/GO, PVDF/GOCOOH, and PVDF/GOF fibers were then prepared by electrospinning from well-dispersed GO derivatives. The piezoelectric coefficient (d(33)), as measured using piezoelectric force measurement (PFM), enhanced by more than 2 folds with respect to the control PVDF spun mat. The piezoelectric coefficient though enhanced upon the addition of GO and GOCOOH, however, enhanced significantly in the case of GOF. For instance, a drastic increase in piezoelectric response from 30 pm V-1(electrospun neat PVDF) to 63 pm V-1 (for electrospun PVDF/GOF) was observed as revealed from PFM results. The phase transformation in these fibers was systematically investigated by various techniques such as Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction ( XRD), Raman spectroscopy, and PFM. FTIR and XRD results revealed that the electrospun fiber mats showed predominantly beta-PVDF. Interestingly, the highest beta content was obtained in the presence of GOF. The drastic enhancement in beta phase is due to the presence of highly electronegative fluorine. The addition of GOCOOH and GOF in PVDF not only increases the polar beta phase but also changes the piezoelectric response significantly. More interestingly, PVDF/GOF films exhibited higher energy density and dielectric permittivity when compared with the control PVDF samples. These findings will help guide the researchers working in this field from both theoretical understanding and practical view point for energy storing device and charge storage electronics.

Effect of electrospinning parameters on piezoelectric properties of electrospun PVDF nanofibrous mats under cyclic compression - Hu Jiyong; Gu Yuanyuan; Zhang Hele; Zhu Yinda; Yang Xudong (JOURNAL OF THE TEXTILE INSTITUTE, 2018)
The high piezoelectric response capacity of electrospun PVDF nanofibers is currently a challenging area of research, and this study attempts to optimize the piezoelectric properties of electrospun PVDF nanofibrous mat under controlled electrospinning process. Some experiments were designed to study the relationship between electrospinning processing parameters and the piezoelectric properties of PVDF mats under cyclic compression, and this relationship was compared with the change of crystalline structure features with the electrospinning parameters. The excitation method is based on low velocity compression test by cyclically pressing flat contactor on samples. The impact of each of processing parameters has been investigated. It was found that three electrospinning parameters including: applied voltage, feeding volume flow rate and syringe needle tip diameter, are significant influential factors to the piezoelectric properties of the electrospun PVDF nanofibrous mats. However, the fe eding volume flow rate has a greater effect on the piezoelectric responses to cyclic compression than both applied voltage and volume flow rate does, and its effect on the piezoelectric responses is different from that of -phase fraction of crystalline structure within PVDF nanofiber. It was also observed that the relationship between the piezoelectric peak intensity and the applied voltage as well as the feeding volume flow rate is nonlinear.

Tunable piezoelectric performance of flexible PVDF based nanocomposites from MWCNTs/graphene/MnO2 three-dimensional architectures under low poling electric fields - Yang, Lu; Cheng, Meng; Lyu, Wenyan; Shen, Mingxia; Qiu, Jinhao; Ji, Hongli; Zhao, Qiuying (COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, 2018)
Till date, developing flexible poly(vinylidene fluoride) (PVDF) based nanocomposites with high piezoelectric performance is of great interest for constructing sensors, transducers and energy harvesters. Herein, we proposed a simple strategy to build a three-dimensional hybrid nanostructure consisting of manganese dioxide/graphene/Multi-walled carbon nanotubes (MnO2/graphene/MWCNTs) to enhance the piezoelectric performance of PVDF. By tailoring the MnO2 mass loading of hybrids, tunable breakdown strength and piezoelectric performance can be achieved in the nanocomposites. Meanwhile, employing this hybrid can reduce the high poling electric field (> 100 MV/m) required for PVDF to induce good piezoelectric performance. With a relative low poling electric field (50-80 MV/m), high piezoelectric coefficients d(33) of 17-33 pC/N can be obtained in the nanocomposites, which are twice that of PVDF under the same poling conditions. For the first time, the potential of MWCNTs/graphene/MnO2 in fab ricating nanocomposites with superior piezoelectricity and low poling electric field requirement is demonstrated.

Fabrication of a piezoelectric polyvinylidene fluoride/carbonyl iron (PVDF/CI) magnetic composite film towards the magnetic field and deformation bi-sensor - Sang, Min; Wang, Sheng; Liu, Mei; Bai, Linfeng; Jiang, Wanquan; Xuan, Shouhu; Gong, Xinglong (COMPOSITES SCIENCE AND TECHNOLOGY, 2018)
In this paper, a versatile polyvinylidene fluoride/carbonyl iron (PVDF/CI) composite film was prepared by doping magnetic carbonyl iron (CI) particles into piezoelectric polyvinylidene fluoride (PVDF) matrix. Without influencing the piezoelectric structure of PVDF, CI particles enhanced the Young's modulus and maximum tensile strength of composite films. Due to the magnetic driven characteristic, PVDF/CI composite films exhibited distinct magnetic-mechanic-electric coupling properties. The piezoelectric charge signals could be generated by applying the bending deformation or magnetic field. Taking PVDF/CI-10% (CI content was 10 wt%) film as an example, the piezoelectric charges under 2, 4, 6, 8, and 10 mm bending displacement were 3.0, 9.6, 14.9, 18.6, and 24.6 pC respectively. Moreover, when the magnetic field varied from 0 to 600 mT, the generated magneto electric charges of PVDF/CI-10% film increased from 0 to 676 pC. The quantitative relationship between magnetic field and magneto- electric charges was obtained by the polynomial fitting method and the correlation coefficient was up to 0.97. Owing to the ideal piezoelectricity, excellent stability, light weight and desirable flexibility, PVDF/CI composite films showed promising applications in deformation sensor and magnetic field sensor.

Mechanical Fatigue Resistance of Piezoelectric PVDF Polymers - Shin, Youn-Hwan; Jung, Inki; Park, Hyunchul; Pyeon, Jung Joon; Son, Jeong Gon; Koo, Chong Min; Kim, Sangtae; Kang, Chong-Yun (MICROMACHINES, 2018)
The fatigue resistance of piezoelectric PVDF has been under question in recent years. While some report that a significant degradation occurs after 10(6) cycles of repeated voltage input, others report that the reported degradation originates from the degraded metal electrodes instead of the piezoelectric PVDF itself. Here, we report the piezoelectric response and remnant polarization of PVDF during 10(7) cycles of repeated compression and tension, with silver paste-based electrodes to eliminate any electrode effect. After applying repeated tension and compression of 1.8% for 10(7) times, we do not observe any notable decrease in the output voltage generated by PVDF layers. The results from tension experiments show stable remnant polarization of 5.5 C/cm(2), however, the remnant polarization measured after repeated compression exhibits a 7% decrease as opposed to the tensed PVDF. These results suggest a possible anisotropic response to stress direction. The phase analyses by Raman spec troscopy reveals no significant change in the phase content, demonstrating the fatigue resistance of PVDF.

Biomimetic Porifera-Skeletal Structure of Lead-Free Piezocomposite Energy Harvesters - ["Yong Zhang", "Ming Xie", "J. Adam Roscow", "seven others (RG visible)"] (ACS Applied Materials & Interfaces, 2018)
The elastic composite-based piezoelectric energy-harvesting technology is highly desired to enable a wide range of device applications, including self-powered wearable electronics, robotic skins, and biomedical devices. Recently developed piezoelectric composites are based on inorganic piezoelectric fillers and polymeric soft matrix to take advantages of both components. However, there are still limitations such as weak stress transfer to piezoelectric elements and poor dispersion of fillers in matrix. In this report, a highly enhanced piezocomposite energy harvester (PCEH) is developed using a three-dimensional electroceramic skeleton by mimicking and reproducing the sea porifera architecture. This new mechanically reinforced PCEH is demonstrated to resolve the problems of previous reported conventional piezocomposites and in turn induces stronger piezoelectric energy-harvesting responses. The generated voltage, current density, and instantaneous power density of the biomimetic PCEH d evice reach up to ∼16 times higher power output than that of conventional randomly dispersed particle-based PCEH. This work broadens further developments of the high-output elastic piezocomposite energy harvesting and sensor application with biomimetic architecture.

Bioinspired elastic piezoelectric composites for high-performance mechanical energy harvesting - Yong Zhang; Chris R. Bowen; Sanqiang Geng; seven others (RG visible) (Journal of Materials Chemistry A, 2018)
Sea sponge-inspired piezoelectric composite generators are prepared based on a three-dimensional electroceramic skeleton.

Flexible Energy Harvesting Polymer Composites based on Biofibril-Templated 3-Dimensional Interconnected Piezoceramics - ["Yong Zhang; Zongliang Pan; Furong Wang; eight others (RG visible)"] (Nano Energy, 2018)
Abstract Flexible piezoelectric materials have attracted rapidly growing attention because they offer an efficient route to scavenge energies from the living environment to power personal electronics and nanosystems. Current polymer composites with low-dimensional piezoceramic fillers suffer from poor stress transfer from the polymer matrix to the active ceramic fillers, thus significantly limiting the energy harvesting performance. Herein, an interconnected 3D piezoceramic skeleton has been developed by a biofibril template method using the newly developed rare-earth Samarium-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN–PT) for flexible piezoelectric polymer composites. When subjected to external mechanical stimulation, the 3D interconnected structure results in effective stress transfer, and consequently, greatly enhanced energy harvesting output. The 3D piezocomposite shows the open-circuit output voltage and short-circuit current density up to ~ 60 V and ~ 850 nA cm−2, respectively, with the maximum instantaneous power density of ~ 11.5 µW cm−2 which is ~ 16 times higher than that of the conventional nanoparticle-based composite. The remarkable enhancement in the tress transfer ability and piezoelectric response of the biofibril-templated 3D structure have also been verified by phase-field simulations. This work provides a promising paradigm for the development of high-performance flexible energy harvesting materials.

Flexible Three-Dimensional Interconnected Piezoelectric Ceramic Foam based Composites for Highly Efficient Thermo-Mechanical Energy Harvesting - ["Yong Zhang", "Jing Xie", "Sanqiang Geng", "six others (RG visible)"] (Energy & Environmental Science, 2018)
Flexible piezoelectric materials are important for wearable electronics, sensors, and biomedical devices.

Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature - Byeong Wan An, Sanghyun Heo, Sangyoon Ji, Franklin Bien, Jang-Ung Park (Nature Communications, 2018)
Abstract We developed a transparent and flexible, capacitive fingerprint sensor array with multiplexed, simultaneous detection of tactile pressure and finger skin temperature for mobile smart devices. In our approach, networks of hybrid nanostructures using ultra-long metal nanofibers and finer nanowires were formed as transparent, flexible electrodes of a multifunctional sensor array. These sensors exhibited excellent optoelectronic properties and outstanding reliability against mechanical bending. This fingerprint sensor array has a high resolution with good transparency. This sensor offers a capacitance variation ~17 times better than the variation for the same sensor pattern using conventional ITO electrodes. This sensor with the hybrid electrode also operates at high frequencies with negligible degradation in its performance against various noise signals from mobile devices. Furthermore, this fingerprint sensor array can be integrated with all trans parent forms of tactile pressure sensors and skin temperature sensors, to enable the detection of a finger pressing on the display.

A Flexible Wearable Pressure Sensor with Bioinspired Microcrack and Interlocking for Full‐Range Human–Machine Interfacing - Ying Guo, Zhiyuan Guo, Mengjuan Zhong, Pengbo Wan, Weixia Zhang, Liqun Zhang (Small, 2018)
Abstract Flexible wearable pressure sensors have drawn tremendous interest for various applications in wearable healthcare monitoring, disease diagnostics, and human–machine interaction. However, the limited sensing range (<10%), low sensing sensitivity at small strains, limited mechanical stability at high strains, and complicated fabrication process restrict the extensive applications of these sensors for ultrasensitive full‐range healthcare monitoring. Herein, a flexible wearable pressure sensor is presented with a hierarchically microstructured framework combining microcrack and interlocking, bioinspired by the crack‐shaped mechanosensory systems of spiders and the wing‐locking sensing systems of beetles. The sensor exhibits wide full‐range healthcare monitoring under strain deformations of 0.2–80%, fast response/recovery time (22 ms/20 ms), high sensitivity, the ultrasensitive loading sensing of a feather (25 mg), the potential to predict the hea lth of patients with early‐stage Parkinson's disease with the imitated static tremor, and excellent reproducibility over 10 000 cycles. Meanwhile, the sensor can be assembled as smart artificial electronic skins (E‐skins) for simultaneously mapping the pressure distribution and shape of touching sensing. Furthermore, it can be attached onto the legs of a smart robot and coupled to a wireless transmitter for wirelessly monitoring human‐motion interactivities.

Flexible Piezoresistive Pressure Sensor Using Wrinkled Carbon Nanotube Thin Films for Human Physiological Signals - Sun‐Jun Park, Joshua Kim, Michael Chu, Michelle Khine (Advanced Materials Technologies, 2018)
Abstract Highly sensitive and flexible components are essential for applications in wearable electronics. Using low‐cost and rapid prototyping methods, piezoresistive pressure sensors are fabricated using shrink‐film, a shape memory polymer that retracts upon heat, to introduce wrinkling in carbon nanotube thin films, which improves both elasticity and pressure sensitivity. The wrinkles not only provide strain relief, but it also improves pressure sensitivity by 12 800 fold with a response time of less than 20 ms. The improved sensitivity is due to the surface roughness of the wrinkles. When two wrinkled electrodes are coupled together, the number of electrical contact points changes upon actuation thereby changing the electrical resistivity. This study then demonstrates wearable applications, such as pulsatile blood flow monitoring and voice detection using these sensitive pressure sensors.

Montmorillonite/PVDF-HFP-based energy conversion and storage films with enhanced piezoelectric and dielectric properties - Yuan Ma, Wangshu Tong, Wenjiang Wang, Qi An, Yihe Zhang (Composites Science and Technology, 2018)

Giant electrocaloric effect in compositionally graded PZT multilayer thin films - Tiandong Zhang, Weili Li, Yang Yu, Miao Wang, Jun He, Weidong Fei (Journal of Alloys and Compounds, 2018)

Bi Nanoparticles Anchored in N-Doped Porous Carbon as Anode of High Energy Density Lithium Ion Battery - Yaotang Zhong, Bin Li, Shumin Li, Shuyuan Xu, Zhenghui Pan, Qiming Huang, Lidan Xing, Chunsheng Wang, Weishan Li (Nano-Micro Letters, 2018)
A novel bismuth-carbon composite, in which bismuth nanoparticles were anchored in a nitrogen-doped carbon matrix (Bi@NC), is proposed as anode for high volumetric energy density lithium ion batteries (LIBs). Bi@NC composite was synthesized via carbonization of Zn-containing zeolitic imidazolate (ZIF-8) and replacement of Zn with Bi, resulting in the N-doped carbon that was hierarchically porous and anchored with Bi nanoparticles. The matrix provides a highly electronic conductive network that facilitates the lithiation/delithiation of Bi. Additionally, it restrains aggregation of Bi nanoparticles and serves as a buffer layer to alleviate the mechanical strain of Bi nanoparticles upon Li insertion/extraction. With these contributions, Bi@NC exhibits excellent cycling stability and rate capacity compared to bare Bi nanoparticles or their simple composites with carbon. This study provides a new approach for fabricating high volumetric energy density LIBs.

Inhibiting Polysulfide Shuttling with a Graphene Composite Separator for Highly Robust Lithium-Sulfur Batteries - Tianyu Lei, Wei Chen, Weiqiang Lv, Jianwen Huang, Jian Zhu, Junwei Chu, Chaoyi Yan, Chunyang Wu, Yichao Yan, Weidong He, Jie Xiong, Yanrong Li, Chenglin Yan, John B. Goodenough, Xiangfeng Duan (Joule, 2018)

Interactions between Lithium Growths and Nanoporous Ceramic Separators - Peng Bai, Jinzhao Guo, Miao Wang, Akihiro Kushima, Liang Su, Ju Li, Fikile R. Brushett, Martin Z. Bazant (Joule, 2018)

New horizons for inorganic solid state ion conductors - Zhizhen Zhang, Yuanjun Shao, Bettina V. Lotsch, Yong-Sheng Hu, Hong Li, Jürgen Janek, Linda F. Nazar, Ce‐Wen Nan, Joachim Maier, Michel Armand, Liquan Chen (Energy & Environmental Science, 2018)
This critical review presents the state of the art research progress, proposes strategies to improve the conductivity of solid electrolytes, discusses the chemical and electrochemical stabilities, and uncovers future perspectives for solid state batteries.

SiO2‐Enhanced Structural Stability and Strong Adhesion with a New Binder of Konjac Glucomannan Enables Stable Cycling of Silicon Anodes for Lithium‐Ion Batteries - Songtao Guo, Heng Li, Yaqian Li, Yong Han, Kebei Chen, Gengzhao Xu, Ying‐Jie Zhu, Xianluo Hu (Advanced Energy Materials, 2018)
Abstract Silicon‐based anodes with high theoretical capacity have intriguing potential applications for next‐generation high‐energy lithium‐ion batteries, but suffer from huge volumetric change that causes pulverization of electrodes. Rational design and construction of effective electrode structures combined with versatile binders remain a significant challenge. Here, a unique natural binder of konjac glucomannan (KGM) is developed and an amorphous protective layer of SiO 2 is fabricated on the surface of Si nanoparticles (Si@SiO 2 ) to enhance the adhesion. Benefiting from a plethora of hydroxyl groups, the KGM binder with inherently high adhesion and superior mechanical properties provides abundant contact sites to active materials. Molecular mechanics simulations and experimental results demonstrate that the enhanced adhesion between KGM and Si@SiO 2 can bond the particles tightly to form a robust electrode. In addition to bridging KGM molecules, the SiO 2 ‐functionalized surface m ay serve as a buffer layer to alleviate the stresses of Si nanoparticles resulting from the volume change. The as‐fabricated KGM/Si@SiO 2 electrode exhibits outstanding structural stability upon long‐term cycles. A highly reversible capacity of 1278 mAh g −1 can be achieved over 1000 cycles at a current density of 2 A g −1 , and the capacity decay is as small as 0.056% per cycle.

Hybrid Lithium‐Sulfur Batteries with an Advanced Gel Cathode and Stabilized Lithium‐Metal Anode - Henghui Xu, Shaofei Wang, Arumugam Manthiram (Advanced Energy Materials, 2018)
Abstract The insulating nature of sulfur, polysulfide shuttle effect, and lithium‐metal deterioration cause a decrease in practical energy density and fast capacity fade in lithium‐sulfur (Li‐S) batteries. This study presents an integrated strategy for the development of hybrid Li‐S batteries based on a gel sulfur cathode, a solid electrolyte, and a protective anolyte composed of a highly concentrated salt electrolyte containing mixed additives. The dense solid electrolyte completely blocks polysulfide diffusion, and also makes it possible to investigate the cathode and anode independently. This gel cathode effectively traps the polysulfide active material while maintaining a low electrolyte to sulfur ratio of 5.2 mL g −1 . The anolyte effectively protects the Li metal and suppresses the consumption of liquid electrolyte, enabling stable long‐term cycling for over 700 h in Li symmetric cells. This advanced design can simultaneously suppress the polysulfide shuttle, protect Li metal, an d reduce the liquid electrolyte usage. The assembled hybrid batteries exhibit remarkably stable cycling performance over 300 cycles with high capacity. Finally, surface‐sensitive techniques are carried out to directly visualize and probe the interphase formed on the surface of the Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) pellet, which may help stabilize the solid–liquid interface.

Synergistic Effect of Graphene Oxide for Impeding the Dendritic Plating of Li - Tara Foroozan, Fernando A. Soto, Vitaliy Yurkiv, Soroosh Sharifi‐Asl, Ramasubramonian Deivanayagam, Zhennan Huang, Ramin Rojaee, Farzad Mashayek, Perla B. Balbuena, Reza Shahbazian‐Yassar (Advanced Functional Materials, 2018)
Abstract Dendritic growth of lithium (Li) has severely impeded the practical application of Li‐metal batteries. Herein, a 3D conformal graphene oxide nanosheet (GOn) coating, confined into the woven structure of a glass fiber separator, is reported, which permits facile transport of Li‐ions thought its structure, meanwhile regulating the Li deposition. Electrochemical measurements illustrate a remarkably enhanced cycle life and stability of the Li‐metal anode, which is explained by various microscopy and modeling results. Utilizing scanning electron microscopy, focused ion beam, and optical imaging, the formation of an uniform Li film on the electrode surface in the case of GO‐modified samples is revealed. Ab initio molecular dynamics (AIMD) simulations suggest that Li‐ions initially get adsorbed to the lithiophilic GOn and then diffuse through defect sites. This delayed Li transfer eliminates the “tip effect” leading to a more homogeneous Li nucleation. Meanwhile, CC bonds rupture ob served in the GO during AIMD simulations creates more pathways for faster Li‐ions transport. In addition, phase‐field modeling demonstrates that mechanically rigid GOn coating with proper defect size (smaller than 25 nm) can physically block the anisotropic growth of Li. This new understanding is a significant step toward the employment of 2D materials for regulating the Li deposition.

Revealing Hidden Facts of Li Anode in Cycled Lithium–Oxygen Batteries through X-ray and Neutron Tomography - Fu Sun, Rui Gao, Dong Zhou, Markus Osenberg, Kang Dong, Nikolay Kardjilov, André Hilger, Henning Markötter, Peter Bieker, Xiangfeng Liu, Ingo Manke (ACS Energy Letters, 2018)
The gap between the successful application and perspective promise of lithium–oxygen battery (LOB) technology should be filled by an in-depth and comprehensive understanding of the underlying working and degradation mechanisms. Herein, the correlation between the morphological evolution of the Li anode and the overall cell electrochemical performance of cycled LOBs has been revealed for the first time by complementary X-ray and neutron tomography, together with further postmortem scanning electron microscopy, X-ray diffraction, and Fourier transfrom infrared spectroscopy characterizations. It has been disclosed with solid evidence that the irreversible transformation of anode Li associated with chemical/electrochemical side reactions does link intimately to the observed electrochemical performance decay. The current discoveries not only fundamentally enrich our knowledge of the underlying degradation and failure mechanisms of LOBs but also provide direction for future promising researc h activities aimed at further enhancing their performance.

Solid electrolytes and interfaces in all-solid-state sodium batteries: Progress and perspective - Wenru Hou, Xianwei Guo, Xuyang Shen, Khalil Amine, Haijun Yu, Jun Lü (Nano Energy, 2018)

Boosting lithium storage in covalent organic framework via activation of 14-electron redox chemistry - Zhendong Lei, Qinsi Yang, Yi Xu, Siyu Guo, Weiwei Sun, Hao Liu, Li‐Ping Lv, Yong Zhang, Yong Wang (Nature Communications, 2018)
Abstract Conjugated polymeric molecules have been heralded as promising electrode materials for the next-generation energy-storage technologies owing to their chemical flexibility at the molecular level, environmental benefit, and cost advantage. However, before any practical implementation takes place, the low capacity, poor structural stability, and sluggish ion/electron diffusion kinetics remain the obstacles that have to be overcome. Here, we report the synthesis of a few-layered two-dimensional covalent organic framework trapped by carbon nanotubes as the anode of lithium-ion batteries. Remarkably, upon activation, this organic electrode delivers a large reversible capacity of 1536 mAh g −1 and can sustain 500 cycles at 100 mA g −1 . Aided by theoretical calculations and electrochemical probing of the electrochemical behavior at different stages of cycling, the storage mechanism is revealed to be governed by 14-electron redox chemistry for a covalent organic framework monomer with one lithium ion per C=N group and six lithium ions per benzene ring. This work may pave the way to the development of high-capacity electrodes for organic rechargeable batteries.

Quantification and modeling of mechanical degradation in lithium-ion batteries based on nanoscale imaging - Simon Müller, Patrick Pietsch, Ben-Elias Brandt, Paul Baade, Vincent De Andrade, Francesco De Carlo, Vanessa Wood (Nature Communications, 2018)
Capacity fade in lithium-ion battery electrodes can result from a degradation mechanism in which the carbon black-binder network detaches from the active material. Here we present two approaches to visualize and quantify this detachment and use the experimental results to develop and validate a model that considers how the active particle size, the viscoelastic parameters of the composite electrode, the adhesion between the active particle and the carbon black-binder domain, and the solid electrolyte interphase growth rate impact detachment and capacity fade. Using carbon-silicon composite electrodes as a model system, we demonstrate X-ray nano-tomography and backscatter scanning electron microscopy with sufficient resolution and contrast to segment the pore space, active particles, and carbon black-binder domain and quantify delamination as a function of cycle number. The validated model is further used to discuss how detachment and capacity fade in high-capacity materials can be mini mized through materials engineering.

Mechanical mismatch-driven rippling in carbon-coated silicon sheets for stress-resilient battery anodes - Jaegeon Ryu, Tianwu Chen, Taesoo Bok, Gyujin Song, Jiyoung Ma, Chihyun Hwang, Langli Luo, Hyun‐Kon Song, Jaephil Cho, Chongmin Wang, Sulin Zhang, Soojin Park (Nature Communications, 2018)
High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a genera l principle as how to take the advantage of the large deformation materials for designing high capacity electrode.

Fluorine-free water-in-ionomer electrolytes for sustainable lithium-ion batteries - Xin He, Bo Yan, Xin Zhang, Zigeng Liu, Dominic Bresser, Jun Wang, Rui Wang, Xia Cao, Yixi Su, Hao Jia, Clare P. Grey, Henrich Frielinghaus, Donald G. Truhlar, Martin Winter, Jie Li, Elie Paillard (Nature Communications, 2018)
Abstract The continuously increasing number and size of lithium-based batteries developed for large-scale applications raise serious environmental concerns. Herein, we address the issues related to electrolyte toxicity and safety by proposing a “water-in-ionomer” type of electrolyte which replaces organic solvents by water and expensive and toxic fluorinated lithium salts by a non-fluorinated, inexpensive and non-toxic superabsorbing ionomer, lithium polyacrylate. Interestingly, the electrochemical stability window of this electrolyte is extended greatly, even for high water contents. Particularly, the gel with 50 wt% ionomer exhibits an electrochemical stability window of 2.6 V vs. platinum and a conductivity of 6.5 mS cm −1 at 20 °C. Structural investigations suggest that the electrolytes locally self-organize and most likely switch local structures with the change of water content, leading to a 50% gel with good conductivity and elastic properties. A LiTi 2 (PO 4 ) 3 /LiMn 2 O 4 lit hium-ion cell incorporating this electrolyte provided an average discharge voltage > 1.5 V and a specific energy of 77 Wh kg −1 , while for an alternative cell chemistry, i.e., TiO 2 /LiMn 2 O 4 , a further enhanced average output voltage of 2.1 V and an initial specific energy of 124.2 Wh kg −1 are achieved.

Solid electrolyte interphases for high-energy aqueous aluminum electrochemical cells - Qing Zhao, Michael J. Zachman, Wajdi I. Al Sadat, Jingxu Zheng, Lena F. Kourkoutis, Lynden A. Archer (Science Advances, 2018)
An artificial solid electrolyte interphase on aluminum enables aqueous batteries with high specific energy and good reversibility.

Strong-field optoelectronics in solids - Giulio Vampa, T. J. Hammond, Marco Taucer, Xiaoyan Ding, X. Ropagnol, T. Ozaki, S. Delprat, Mohamed Chaker, Nicolas Thiré, Bruno E. Schmidt, François Légaré, D. D. Klug, A. Naumov, D. M. Villeneuve, A. Staudte, P. B. Corkum (Nature Photonics, 2018)

Transparent, Flexible Silicon Nanostructured Wire Networks with Seamless Junctions for High-Performance Photodetector Applications - Mozakkar Hossain, Gundam Sandeep Kumar, S. N. Barimar Prabhava, Emmet D. Sheerin, David McCloskey, Somobrata Acharya, K. D. M. Rao, John J. Boland (ACS Nano, 2018)
Optically transparent photodetectors are crucial in next-generation optoelectronic applications including smart windows and transparent image sensors. Designing photodetectors with high transparency, photoresponsivity, and robust mechanical flexibility remains a significant challenge, as is managing the inevitable trade-off between high transparency and strong photoresponse. Here we report a scalable method to produce flexible crystalline Si nanostructured wire (NW) networks fabricated from silicon-on-insulator (SOI) with seamless junctions and highly responsive porous Si segments that combine to deliver exceptional performance. These networks show high transparency (∼92% at 550 nm), broadband photodetection (350 to 950 nm) with excellent responsivity (25 A/W), optical response time (0.58 ms), and mechanical flexibility (1000 cycles). Temperature-dependent photocurrent measurements indicate the presence of localized electronic states in the porous Si segments, which play a crucial role in light harvesting and photocarrier generation. The scalable low-cost approach based on SOI has the potential to deliver new classes of flexible optoelectronic devices, including next-generation photodetectors and solar cells.

Micromachined Chip Scale Thermal Sensor for Thermal Imaging - Gajendra S. Shekhawat, Srinivasan Ramachandran, Hossein Jiryaei Sharahi, Souravi Sarkar, Karl A. Hujsak, Yuan Li, Karl Hagglund, Seonghwan Kim, Gary Aden, Ami Chand, Vinayak P. Dravid (ACS Nano, 2018)
The lateral resolution of scanning thermal microscopy (SThM) has hitherto never approached that of mainstream atomic force microscopy, mainly due to poor performance of the thermal sensor. Herein, we report a nanomechanical system-based thermal sensor (thermocouple) that enables high lateral resolution that is often required in nanoscale thermal characterization in a wide range of applications. This thermocouple-based probe technology delivers excellent lateral resolution (∼20 nm), extended high-temperature measurements >700 °C without cantilever bending, and thermal sensitivity (∼0.04 °C). The origin of significantly improved figures-of-merit lies in the probe design that consists of a hollow silicon tip integrated with a vertically oriented thermocouple sensor at the apex (low thermal mass) which interacts with the sample through a metallic nanowire (50 nm diameter), thereby achieving high lateral resolution. The efficacy of this approach to SThM is demonstrated by imaging embedded m etallic nanostructures in silica core-shell, metal nanostructures coated with polymer films, and metal-polymer interconnect structures. The nanoscale pitch and extremely small thermal mass of the probe promise significant improvements over existing methods and wide range of applications in several fields including semiconductor industry, biomedical imaging, and data storage.

Photonic-crystal exciton-polaritons in monolayer semiconductors - Long Zhang, Rahul Gogna, Will Burg, Emanuel Tutuc, Hui Deng (Nature Communications, 2018)
Semiconductor microcavity polaritons, formed via strong exciton-photon coupling, provide a quantum many-body system on a chip, featuring rich physics phenomena for better photonic technology. However, conventional polariton cavities are bulky, difficult to integrate, and inflexible for mode control, especially for room-temperature materials. Here we demonstrate sub-wavelength-thick, one-dimensional photonic crystals as a designable, compact, and practical platform for strong coupling with atomically thin van der Waals crystals. Polariton dispersions and mode anti-crossings are measured up to room temperature. Non-radiative decay to dark excitons is suppressed due to polariton enhancement of the radiative decay. Unusual features, including highly anisotropic dispersions and adjustable Fano resonances in reflectance, may facilitate high temperature polariton condensation in variable dimensions. Combining slab photonic crystals and van der Waals crystals in the strong coupling regime allo ws unprecedented engineering flexibility for exploring novel polariton phenomena and device concepts.

Narrow bandgap oxide nanoparticles coupled with graphene for high performance mid-infrared photodetection - Xuechao Yu, Yangyang Li, Xiaonan Hu, Daliang Zhang, Ye Tao, Zhixiong Liu, Yongmin He, Md Azimul Haque, Zheng Liu, Tom Wu, Qi Jie Wang (Nature Communications, 2018)
Abstract The pursuit of optoelectronic devices operating in the mid-infrared regime is driven by both fundamental interests and envisioned applications ranging from imaging, sensing to communications. Despite continued achievements in traditional semiconductors, notorious obstacles such as the complicated growth processes and cryogenic operation preclude the usage of infrared detectors. As an alternative path towards high-performance photodetectors, hybrid semiconductor/graphene structures have been intensively explored. However, the operation bandwidth of such photodetectors has been limited to visible and near-infrared regimes. Here we demonstrate a mid-infrared hybrid photodetector enabled by coupling graphene with a narrow bandgap semiconductor, Ti 2 O 3 ( E g = 0.09 eV), which achieves a high responsivity of 300 A W −1 in a broadband wavelength range up to 10 µm. The obtained responsivity is about two orders of magnitude higher than that of the commercial mid-infrared photodetecto rs. Our work opens a route towards achieving high-performance optoelectronics operating in the mid-infrared regime.

Advances and prospects of lasers developed from colloidal semiconductor nanostructures - Yue Wang, Handong Sun (Progress in Quantum Electronics, 2018)

Two-dimensional materials with piezoelectric and ferroelectric functionalities - Chaojie Cui, Fei Xue, Weijin Hu, Lain‐Jong Li (npj 2D Materials and Applications, 2018)
Abstract Two-dimensional (2D) layered materials with a non-centrosymmetric structure exhibit great potential for nano-scale electromechanical systems and electronic devices. Piezoelectric and ferroelectric 2D materials draw growing interest for applications in energy harvesting, electronics, and optoelectronics. This article first reviews the preparation of these functional 2D layered materials, including exfoliation methods and vapor phase deposition growth, followed by a general introduction to various piezo/ferro-electric characterization methods. Typical 2D piezoelectric and ferroelectric materials and their electronic properties, together with their potential applications, are also introduced. Finally, future research directions for 2D piezoelectric and ferroelectric materials are discussed.

High-Quality AZO/Au/AZO Sandwich Film with Ultralow Optical Loss and Resistivity for Transparent Flexible Electrodes - Hua Zhou, Jing Xie, Manfang Mai, Jing Wang, Xiangqian Shen, Shuying Wang, Lihua Zhang, Kim Kisslinger, Hui‐Qiong Wang, Jinxing Zhang, Yu Li, Junhong Deng, Shanming Ke, Xierong Zeng (ACS Applied Materials & Interfaces, 2018)
Transparent flexible electrodes are in ever-growing demand for modern stretchable optoelectronic devices, such as display technologies, solar cells, and smart windows. Such sandwich-film-electrodes deposited on polymer substrates are unattainable because of the low quality of the films, inducing a relatively large optical loss and resistivity as well as a difficulty in elucidating the interference behavior of light. In this article, we report a high-quality AZO/Au/AZO sandwich film with excellent optoelectronic performance, e.g., an average transmittance of about 81.7% (including the substrate contribution) over the visible range, a sheet resistance of 5 Ω/sq, and a figure-of-merit (FoM) factor of ∼55.1. These values are well ahead of those previously reported for sandwich-film-electrodes. Additionally, the interference behaviors of light modulated by the coat and metal layers have been explored with the employment of transmittance spectra and numerical simulations. In particular, a he ater device based on an AZO/Au/AZO sandwich film exhibits high performance such as short response time (∼5 s) and uniform temperature field. This work provides a deep insight into the improvement of the film quality of the sandwich electrodes and the design of high-performance transparent flexible devices by the application of a flexible substrate with an atomically smooth surface.

Material platforms for optical metasurfaces - Sajid Muhaimin Choudhury, Di Wang, Krishnakali Chaudhuri, Clayton DeVault, Alexander V. Kildishev, Alexandra Boltasseva, Vladimir M. Shalaev (Nanophotonics, 2018)
Abstract Optical metasurfaces are judicously engineered electromagnetic interfaces that can control and manipulate many of light’s quintessential properties, such as amplitude, phase, and polarization. These artificial surfaces are composed of subwavelength arrays of optical antennas that experience resonant light‐matter interaction with incoming electromagnetic radiation. Their ability to arbitrarily engineer optical interactions has generated considerable excitement and interest in recent years and is a promising methodology for miniaturizing optical components for applications in optical communication systems, imaging, sensing, and optical manipulation. However, development of optical metasurfaces requires progress and solutions to inherent challenges, namely large losses often associated with the resonant structures; large‐scale, complementary metal‐oxide‐semiconductor‐compatible nanofabrication techniques; and incorporation of active control elements. Furthermore, practical metasu rface devices require robust operation in high‐temperature environments, caustic chemicals, and intense electromagnetic fields. Although these challenges are substantial, optical metasurfaces remain in their infancy, and novel material platforms that offer resilient, low‐loss, and tunable metasurface designs are driving new and promising routes for overcoming these hurdles. In this review, we discuss the different material platforms in the literature for various applications of metasurfaces, including refractory plasmonic materials, epitaxial noble metal, silicon, graphene, phase change materials, and metal oxides. We identify the key advantages of each material platform and review the breakthrough devices that were made possible with each material. Finally, we provide an outlook for emerging metasurface devices and the new material platforms that are enabling such devices.

Semiconductor infrared plasmonics - T. Taliercio, Paolo Biagioni (Nanophotonics, 2018)
Abstract The coupling between light and collective oscillations of free carriers at metallic surfaces and nanostructures is at the origin of one of the main fields of nanophotonics: plasmonics. The potential applications offered by plasmonics range from biosensing to solar cell technologies and from nonlinear optics at the nanoscale to light harvesting and extraction in nanophotonic devices. Heavily doped semiconductors are particularly appealing for the infrared spectral window due to their compatibility with microelectronic technologies, which paves the way toward their integration in low‐cost, mass‐fabricated devices. In addition, their plasma frequency can be tuned chemically, optically, or electrically over a broad spectral range. This review covers the optical properties of the heavily doped conventional semiconductors such as Ge, Si, or III–V alloys and how they can be successfully employed in plasmonics. The modeling of their specific optical properties and the technological pr ocesses to realize nanoantennas, slits, or metasurfaces are presented. We also provide an overview of the applications of this young field of research, mainly focusing on biosensing and active devices, among the most recent developments in semiconductor plasmonics. Finally, an outlook of further research directions and the potential technological transfer is presented.

Boron nitride for excitonics, nano photonics, and quantum technologies - Bernard Gil, Guillaume Cassabois, R. Cuscó, Giorgia Fugallo, Lluís Artús (Nanophotonics, 2018)
Abstract We review the recent progress regarding the physics and applications of boron nitride bulk crystals and its epitaxial layers in various fields. First, we highlight its importance from optoelectronics side, for simple devices operating in the deep ultraviolet, in view of sanitary applications. Emphasis will be directed towards the unusually strong efficiency of the exciton–phonon coupling in this indirect band gap semiconductor. Second, we shift towards nanophotonics, for the management of hyper‐magnification and of medical imaging. Here, advantage is taken of the efficient coupling of the electromagnetic field with some of its phonons, those interacting with light at 12 and 6 µm in vacuum. Third, we present the different defects that are currently studied for their propensity to behave as single photon emitters, in the perspective to help them becoming challengers of the NV centres in diamond or of the double vacancy in silicon carbide in the field of modern and developing qua ntum technologies.

Switching excitonic recombination and carrier trapping in cesium lead halide perovskites by air - Yue Wang, Yinjuan Ren, Shengli Zhang, Jianfeng Wu, Jizhong Song, Xiaoming Li, Jiayue Xu, Chorng Haur Sow, Haibo Zeng, Handong Sun (Communications Physics, 2018)
Abstract All-inorganic cesium lead halide perovskites have been emerging as the promising semiconductor materials for next-generation optoelectronics. However, the fundamental question of how the environmental atmosphere affects their photophysical properties, which is closely related to the practical applications, remains elusive. Here, we report the dynamic switching between radiative exciton recombination and non-radiative carrier trapping in CsPbBr 3 by controlling the atmospheric conditions. Specifically, we show that the photoluminescence (PL) intensity from the CsPbBr 3 crystals can be boosted by ~ 60 times by changing the surrounding from vacuum to air. Based on the comprehensive optical characterization, near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) as well as density functional theory (DFT) calculations, we unravel that the physisorption of oxygen molecules, which repairs the trap states by passivating the PL-quenching bromine vacancies, is accountable for the enhanced PL in air. These results are helpful for better understanding the optical properties of all-inorganic perovskites.

Highly Sensitive Impact Sensor Based on PVDF-TrFE/Nano-ZnO Composite Thin Film (Sensors, 2019)
A thin film of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) has good flexibility and simple preparation process. More importantly, compared with PVDF, its piezoelectric β-phase can be easily formed without mechanical stretching. However, its piezoelectricity is relatively lower. Therefore, at present, PVDF-TrFE is always compounded with other kinds of piezoelectric materials to solve this problem. The effect of nano-ZnO doping amount on the sensing characteristics of the piezoelectric films was studied. PVDF-TrFE/nano-ZnO films with different nano-ZnO contents were prepared by spin coating process and packaged. The dispersion of nano-ZnO dopants and the crystallinity of β-phase in piezoelectric films with different nano-ZnO contents were observed by scanning electron microscopy and X-ray diffraction, and the piezoelectric strain constants and dielectric constants were measured, respectively. The effect of different nano-ZnO contents on the output performance of the piezoelectr ic sensor was obtained by a series of impact experiments. The results show that the piezoelectric strain constant and dielectric constant can be increased by doping nano-ZnO in PVDF-TrFE. Moreover, the doping amount of nano-ZnO in PVDF-TrFE is of great significance for improving the piezoelectric properties of PVDF-TrFE/nano-ZnO thin films. Among the prepared piezoelectric films, the output voltage of PVDF-TrFE/nano-ZnO piezoelectric sensor with 7.5% nano-ZnO doping amount is about 5.5 times that of pure PVDF-TrFE. Thus, the optimal range of the doping amount for nano-ZnO is about 4⁻10%.

Enhanced piezoelectricity of a PVDF-based nanocomposite utilizing high-yield dispersions of exfoliated few-layer MoS2 (Ceramics International, 2019)
Piezoelectric polymer composite films have attracted extensive attention due to their comprehensive characteristics such as low cost, good flexibility, mechanical property and excellent processability. Among the known polymers, poly (vinylidene fluoride) (PVDF) is an ideal piezoelectric polymer because the beta-crystalline form of PVDF has the highest polarization per unit cell. However, initial PVDF mostly suffers from the lack of a beta phase, restricting its potential applications. Few-layer MoS2 is predicted to be strongly piezoelectric owing to the opposite orientations of adjacent atomic layers. In this work, we report an efficient approach to enhance the piezoelectric property of PVDF-based nanocomposites by combining few-layer MoS2 with PVDF. The product yield for few-layer MoS2 reached a value as high as 83.3% via a unique liquid-exfoliation technique. For a few-layer MoS2/PVDF composite film with 1 wt.% few-layer MoS2, a high piezoelectric performance enhancement of 360% was achieved compared with the initial PVDF film. In addition, due to the intrinsic lubrication of MoS2, the highest elongation of the piezoelectric composite film was found to be four times higher than that of the pure PVDF film.

Mechanically stretchable piezoelectric polyvinylidene fluoride (PVDF)/Boron nitride nanosheets (BNNSs) polymer nanocomposites - Zhang, Jin; Liu, Dan; Han, Qi; Jiang, Lu; Shao, Hao; Tang, Bin; Lei, Weiwei; Lin, Tong; Wang, Chun H. (COMPOSITES PART B-ENGINEERING, 2019)
Mechanically stretchable piezoelectric materials are required by wearable devices, such as self-powering sensors and energy harvesters that can monitor human movement and vital biosignals. Polyvinylidene fluoride (PVDF) is a common choice for making flexible piezoelectric sensors but has limited stretchability (strain to failure). Herein we present a new method of significantly increasing the strain-to-failure of PVDF nanofibre membranes by incorporating amino-functionalised boron nitride nanosheets (BNNSs). The PVDF-BNNS nanocomposites were prepared by firstly dispersing a small amount of BNNSs, less than 1.5 wt%, into a PVDF solution and electro-spinning. Compared to the un-modified PVDF, the addition of BNNSs yielded increases of eleven times, twice, and forty times in strength, stretchability, and in-plane thermal conductivity, while piezoelectric performance remains unaffected. The higher thermal conductivity offers significantly better heat dissipation ability of piezoelectric se nsors than the un-modified PVDF material.

Dehydrofluorination Induced High Piezoelectric Poly(Vinylidene Fluoride) and Applications - Lin, Jiajun (2019)

Enhanced Piezoelectric Response of Electrospun PVDF with ZnO Nanorods: The Comparison of Three ZnO Addition Methods - Kim, Minji (2019)

Piezoelectric Response in Hybrid Micropillar Arrays of Poly(Vinylidene Fluoride) and Reduced Graphene Oxide - Pariy IO, Ivanova AA, Shvartsman VV, Lupascu DC, Sukhorukov GB, Ludwig T, Bartasyte A, Mathur S, Surmeneva MA, Surmenev RA. (Array, 2019)
This study was dedicated to the investigation of poly(vinylidene ﬂuoride) (PVDF) micropillar arrays obtained by soft lithography followed by phase inversion at a low temperature. Reduced graphene oxide (rGO) was incorporated into the PVDF as a nucleating ﬁller. The piezoelectric properties of the PVDF-rGO composite micropillars were explored via piezo-response force microscopy (PFM). Fourier transform infrared spectroscopy (FTIR) and X-ray diﬀraction (XRD) showed that α, β, and γ phases co-existed in all studied samples, with a predominance of the γ phase. The piezoresponse force microscopy (PFM) data provided the local piezoelectric response of the PVDF micropillars, which exhibited a temperature-induced downward dipole orientation in the pristine PVDF micropillars. The addition of rGO into the PVDF matrix resulted in a change in the preferred polarization direction, and the piezo-response phase angle changed from −120◦to 20◦–40◦. The pristine PVDF and PVDF loaded with 0.1 wt % of rGO after low-temperature quenching were found to possess a piezoelectric response of 86 and 87 pm/V respectively, which are signiﬁcantly higher than the |d33eﬀ| in the case of imprinted PVDF 64 pm/V. Thus, the addition of rGO signiﬁcantly aﬀected the domain orientation (polarization) while quenching increased the piezoelectric response.

Wearable piezoelectric nanogenerators based on reduced graphene oxide and in situ polarization-enhanced PVDF-TrFE films - Hu, Xiaoran; Ding, Zhitian; Fei, Lixun; Xiang, Yong; Lin, Yuan (JOURNAL OF MATERIALS SCIENCE, 2019)
PVDF-TrFE-based wearable nanogenerators were designed and fabricated with enhanced performances via reduced graphene oxides (rGO) and in situ electric polarization. Our laboratory-made polarization system may complete the in situ poling of PVDF-TrFE films in 5min without heating, which has the advantages of high production efficiency, excellent piezoelectric performances, and favorable uniformity, compared to traditional poling approaches. The addition of rGO into PVDF-TrFE significantly improved the crystallinity of the -phase PVDF-TrFE and enhanced the formation of hydrogen bonds via interaction of dipoles between rGO and PVDF-TrFE. This further improved the energy-harvesting performances of these piezoelectric nanogenerators with 1.6 times of the open-circuit voltage and 2 times of the power density than that of pure PVDF-TrFE-based devices. The high production efficiency and excellent piezoelectric performances of in situ polarized rGO/PVDF-TrFE make them of great potential for sel f-powered, wearable/portable devices.

Flexible Energy Harvester Based on Poly(vinylidene fluoride) Composite Films - Yoon, Sanghyun; Shin, Dong-Jin; Ko, Young-Ho; Cho, Kyung-Ho; Koh, Jung-Hyuk (JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 2019)
In these days, we are facing emerging energy crisis due to depletion of fossil fuels. Therefore, renewable energy which is based on wind energy, mechanical force energy, microwave energy and vibrations energy have attracted a lot of attentions. Piezoelectric energy harvesting is one of the promising renewable energy sources. As the use portable electronic devices increases, the need for portable renewable energy sources further increases. Especially, piezoelectric materials can be the best selection due to their robust properties. In this research, piezoelectric composites were prepared and investigated for piezoelectric energy harvesting applications. In this study, two types of flexible energy harvesters, 0.36BS-0.64PT-PVDF composite and PVDF film, were prepared and analyzed. Due to its high Curie temperature and low lead content, BS-PT is expected to be a substitute for PZT in the near future. The composite materials based on the PVDF and 0.36BS0.64PT film showed higher open circuit voltage (0.73 V) than PVDF film (0.49 V). Also, the stored voltage of 0.36BS-0.64PT-PVDF composite film was 330 nJ which is 5.68 times higher than 58 nJ for PVDF films. By introducing the piezoelectric BS-PT ceramics, 0.36BS-0.64PT-PVDF composite film shows the enhanced performance such as open circuit voltage, energy and dielectric constant compared with those of PVDF materials. It seems that 0.36BS-0.64PT-PVDF composite film is more suitable for flexible energy device.

Research and validation of design principles for PVDF wideband ultrasonic transducers based on an equivalent circuit model - Zheng, Dan-Dan; Mao, Yang; Lv, Sheng-Hong (MEASUREMENT, 2019)
With the increasing use of ultrasonic measurement technology in many fields, the demand for the wideband ultrasonic transducers is also growing. In order to design a wideband piezoelectric ultrasonic transducer, the design principles of wideband PVDF piezoelectric ultrasonic transducers are studied in this paper. A new equivalent circuit model of piezoelectric ultrasonic transducer is used here to simulate the piezoelectric ultrasonic transducer, which combines with the controlled source model and the lossy transmission line model. Based on this model, the relationships between physical structures and properties of PVDF transducers are studied both in simulation and experiment. It shows that the center frequency and many other property parameters of PVDF ultrasonic transducers are strongly related to the physical structures of it. Finally, a wideband PVDF piezoelectric ultrasonic transducer is produced with the center frequency of about 5.3 MHz +/- 0.1 MHz and the bandwidth of more tha n 90%. (C) 2019 Elsevier Ltd. All rights reserved.

Effect of HfO2 on the dielectric, optoelectronic and energy harvesting properties of PVDF - Veved, Albert; Ejuh, Geh Wilson; Djongyang, Noel (OPTICAL AND QUANTUM ELECTRONICS, 2019)
In this article, energy recovery based on PVDF doped with HfO2 is proposed. The free energy of CH2=CF2 is determined in different base with the B3LPY functional. The basis set LanL2DZ was chosen because it takes into account the atom of hafnium of atomic number Z = 72 which exceeds the extension of some basis sets. In addition, LanL2DZ gives an accurate result and a reasonable computing time. The geometries of the molecules were optimized with B3LPY/LanL2DZ. The motivation of this study is the improvement of the optoelectronic, dielectric and piezoelectric properties of PVDF by introducing HfO2 into its matrix. We determined the parameters of (-CH2-CF2-)(3) center dot xHfO(2) and identified the effect of HfO2 on the PVDF. It appears that the permittivity of the modified PVDF increases. When the PVDF is doped once or twice, a fluorine atom is captured by the hafnium. The migration of fluorine towards HfO2 considerably favors the electric polarization of the molecule. It then results in an important dipole moment with a polar phase undoubtedly favored. Our results show that the molecule (-CH2-CF2-)(3) center dot HfO2 is a good dielectric material (E g = 5.90 eV) and can be a good piezoelectric material. The electronic affinity of the modified PVDF is significantly higher than that of virgin PVDF. This demonstrates that HfO2-doped PVDF is more stable than virgin PVDF. The piezoelectric properties are significantly improved. The piezoelectric coefficient varies between 13.111 and 25.635 pC N-1 for the modified PVDF compared to 11.979 pC N-1 for the virgin PVDF. In conclusion, HfO2 improves the dielectric, optoelectronic and piezoelectric properties of PVDF.

3D printing of polyvinylidene fluoride/photopolymer resin blends for piezoelectric pressure sensing application using the stereolithography technique - Kim, Hoejin; Manriquez, Luis Carlos Delfin; Islam, Md Tariqul; Chavez, Luis A.; Regis, Jaime E.; Ahsan, Md Ariful; Noveron, Juan C.; Tseng, Tzu-Liang B.; Lin, Yirong (MRS COMMUNICATIONS, 2019)
A simple and facile stereolithography 3D printing technique was utilized to fabricate piezoelectric photopolymer-based polyvinylidene fluoride (PVDF) blends. Different process variables, such as solvent (N,N-dimethylformamide, DMF) to PVDF ratio and PVDF solution to photopolymer resin (PR) ratio, were engineered to enhance the dispersion of the PVDF into the PR so as to achieve the maximum piezoelectric coupling coefficient. Our results demonstrate that a ratio of 1: 10 (PVDF: DMF) and 2 wt%-PVDF/PR was optimal for the best dissolution of the PVDF, 3D printability, and piezoelectric properties. Under these conditions, the blend generated +/- 0.121 nA under 80 N dynamic loading excitation. We believe that the findings of this work would promote many further studies on the mass production of flexible piezoelectric polymer blends with higher quality finished surface and design flexibility.

Space debris positioning based on two-dimensional PVDF piezoelectric film sensor - Tang, E. L.; Wang, L.; Han, Y. F. (ADVANCES IN SPACE RESEARCH, 2019)
In order to determine the positions of debris collision spacecraft accurately, the experiments have been performed to impact orthogonal stacking two-dimensional Polyvinylidene fluoride (PVDF) piezoelectric film at different collision speeds based on the piezoelectric effects of the PVDF film by using two-stage light gas gun loading system and the self-constructed positioning system. The debris source was positioned accurately by PVDF strips sensor and testing system, which has been established to extract piezoelectric signals of the PVDF film during the process of impacting. The visualization of the position for debris impacting spacecraft was achieved through the LABview language programme and signal processing acquired by the signal acquisition system in the experiments. The experimental results show that the positions of the debris impacting source can be realized accurately by the piezoelectric effects of the orthogonal stacking two-dimensional PVDF film, the flight velocity and th e incidence angle of the debris can be determined by installing the double-set PVDF film as the targets with a certain spacing. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.