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Local phenomena at grain boundaries:An alternative approach to grasp the role of oxygen vacancies in metallization of VO_(2)

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Journal of Materiomics 2018年第4期4卷 360-367页

作者： Wanheng Lu Lai-Mun Wong Shijie Wang kaiyang zeng Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1117576Singapore Institute of Materials Research and Engineering(IMRE) Agency for ScienceTechnologyand Research(A*STAR)Fusionopolis WayInnovis#08-03138634Singapore

Vanadium dioxide(VO_(2))undergoes an insulator to metal transition(MIT)and an accompanied phase transition from a monoclinic(M)structure to rutile(R)structure near room temperature,forming the basis for many VO_(2)-based functional *** MIT transition of VO_(2)and the functionality of VO_(2)-based devices can be controlled by a variety of chemical and physical *** these external stimuli,defects,such as oxygen vacancies,are often inevitably ***,due to the VeO systeminduced challenge to synthesize stable VO_(2)with different oxygen vacancy concentrations,the impact of oxygen vacancies on the resistance and transition of the VO_(2)is not fully *** vacancy,as one of the typical defects in VO_(2),is expected to concentrate at grain boundaries,and hence a concentration gradient of oxygen vacancies may exist between the grains interior and the boundaries,and this suggests a possibility to study the effects of oxygen vacancies on the transition of VO_(2)by probing local phenomena at the grain *** investigating local phenomena at the grain boundaries,Scanning Probe Microscopy(SPM)techniques are effective,which allows probing the structure and various properties at the *** this work,a series of SPM techniques,including Atomic Force Microscopy(AFM),conductive-AFM(c-AFM),Electrochemical Strain Microscopy(ESM),and Kelvin Probe Force Microscopy(KPFM),are employed to measure variations of the surface structure,the resistance,the oxygen vacancy concentration,and the work function between the grain interior and the grain *** has been demonstrated that,for most cases,both the resistance and the work function are lower at the grain boundaries as a result of the accumulation of oxygen vacancies at those *** addition,the resistance change induced by the electric field has been observed in the deposited VO_(2)thin films,which may be associated with the generation/annihilation of the oxygen vacancies,rather

关键词： Fermi level VO_(2)thin film c-AFM KPFM ESM

Effects of oxygen and moisture on the I-V characteristics of TiO_(2) thin films

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Journal of Materiomics 2018年第3期4卷 228-237页

作者： Wanheng Lu Lai-Mun Wong Shijie Wang kaiyang zeng Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1117576Singapore Institute of Materials Research and Engineering(IMRE) Agency for ScienceTechnology and Research(A*STAR)2 Fusionopolis WayInnovis#08-03138634Singapore

Current-voltage(I-V)characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory(ReRAM).It has been observed that the atmospheric environment can affect the resistive switching performance,but the origin of this effect is still under *** Atomic Force Microscopy(c-AFM)is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory *** study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO_(2)thin film by performing c-AFM measurements in ambient air,synthetic air,and argon *** is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching,and it can also reduce the resistance at the low resistance state(LRS).Where the moisture in the environment can increase the set and reset voltages,and increase the resistance at *** effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes,which have been further confirmed by Kelvin Probe Force Microscopy(KPFM)*** addition,it is found that the local ionic dynamics of TiO_(2)during the resistive switching are strongly dependent of the environments by performing the FORC-IV(First Order Reversal Curve-Current-Voltage)measurements in the three gas *** in this work can provide a new perspective on the effect of environments on the resistive switching of materials,that is,the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip.

关键词： Resistive switching Environmental control c-AFM KPFM FORC-IV

Correlation of resistance switching and polarization rotation in copper doped zinc oxide(ZnO:Cu)thin films studied by Scanning Probe Microscopy

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Journal of Materiomics 2019年第4期5卷 574-582页

作者： Juanxiu Xiao Tun Seng Herng Yang Guo Jun Ding Ning Wang kaiyang zeng State Key Laboratory of Marine Resource Utilization in South China Sea Hainan UniversityNo.58Renmin AvenueHaikouHainan570228China Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1Singapore117576 Department of Materials Science and Engineering National University of Singapore9 Engineering Drive 1Singapore117576

This paper presents multiple-modes Scanning Probe Microscopy(SPM)studies on characterize the correlation of resistance switching(RS)and polarization rotation(PR)in copper doped ZnO(ZnO:Cu)thin ***,the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy(c-AFM).The PR with almost 180phase angle is confirmed by using the Piezoresponse Force Microscopy(PFM)on the same *** addition,it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy(KPFM).Furthermore,it is found that the region with downward polarization has low resistance state(LRS),whereas the region with upward polarization has high resistance state(HRS).Moreover,the Piezoresponse Force Spectroscopy(PFS)and Switching Spectroscopy PFM(SS-PFM)measurements further confirm that the existence of the built-in voltage,V_(built-in) is largest in the ZnO:Cu(8 at.%)film deposited at the oxygen partial pressure of 2×10^(-4) *** schematic diagrams of energy band diagram with varied built-in field,Ebuilt-in,polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior.

关键词： Resistive switching Polarization rotation Built-in voltage ZnO:Cu thin film Next generation memory

Insight into the structure-capacity relationship in biomass derived carbon for high-performance sodium-ion batteries

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Journal of Energy Chemistry 2021年第11期30卷 497-504,I0011页

作者： Jianguo Sun Yao Sun Jin An Sam Oh Qilin Gu Weidong Zheng Minhao Goh kaiyang zeng Yuan Cheng Li Lu Department of Mechanical Engineering National University of SingaporeSingapore 117575Singapore School of Science Harbin Institute of TechnologyShenzhen 518055GuangdongChina National University of Singapore Chongqing Research Institute Chongqing 401123China Graduate School for Integrative Sciences and Engineering National University of SingaporeSingapore 138632Singapore Singapore Institute of Manufacturing Technology A*STAR(Agency for ScienceTechnologyand Research)Singapore 138634Singapore Department of Materials Science and Engineering National University of SingaporeSingapore 117575Singapore Monash Suzhou Research Institute Suzhou 215123JiangsuChina

Carbonaceous materials are the most promising candidates as the anode for sodium-ion batteries (SIBs), however, they still suffer from low electric conductivity and sluggish sodium ion (Na+) reaction kinetics. Appropriate composition modulation using heteroatoms doping and structure optimization is highly desired. A basic empirical understanding of the structure-capacity relationship is also urgent in tackling the above problems. Herein, multi-functional nitrogen (N) doped carbon micro-rods with enlarged interlayer spacing are synthesized and investigated as the anode in SIBs, showing an ultra-stable capacity of 161.5 mAh g^(−1) at 2 A g^(−1) for over 5000 cycles. Experimental investigations and first-principle calculations indicate that the enlarged interlayer spacing can facilitate Na+ intercalation and N doping can guarantee the high electric conductivity and favorable electrochemical active sites. Additionally, pyridinic N is theoretically proved to be more effective to enhance Na+ adsorption than pyrrolic N due to the lower adsorption energy and stronger binding energy with Na+. Full SIBs show a high capacity and cyclability, making the biomass-derived carbon micro-rods to be a promising anode for practical SIBs applications.

关键词： Biomass Nitrogen doping Hard carbon Sodium-ion batteries

Alleviating mechanical degradation of hexacyanoferrate via strain locking during Na^(+) insertion/extraction for full sodium ion battery

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Nano Research 2022年第3期15卷 2123-2129页

作者： Jianguo Sun Hualin Ye Jin An Sam Oh Yao Sun Anna Plewa Yumei Wang Tian Wu kaiyang zeng Li Lu Department of Mechanical Engineering National University of SingaporeSingapore 117575Singapore National University of Singapore Chongqing Research Institute Chongqing 401123China Department of Chemical&Biomolecular Engineering National University of SingaporeSingapore 117585Singapore Integrative Sciences and Engineering Programme NUS Graduate SchoolNational University of SingaporeSingapore 138632Singapore Singapore Institute of Manufacturing Technology A*STAR(Agency for ScienceTechnologyand Research)Singapore 138634Singapore School of Science Harbin Institute of TechnologyShenzhen 518055China Faculty of Energy and Fuels AGH University of Science and Technology al.Mickiewicza 30 30-059 KrakowPoland Institute of Materials Research and Engi

Generation of large strains upon Na^(+) intercalation is one of the prime concerns of the mechanical degradation of Prussian blue(PB)and its *** construction from the atomic level is imperative to maintain structural stability and ameliorate the long-term stability of ***,an inter nickel hexacyanoferrate(NNiFCN)is successfully introduced at the out layer of iron hexacyanoferrate(NFFCN)through ion exchange to improve structural stability through compressive stress locking by forming NNiFCN ***,the kinetics of sodium ion diffusion is enhanced through the built-in electric *** electrochemical performance is therefore significantly improved with a remarkable long-term cycling stability over 3,000 cycles at 500 mA·g^(–1) in the full sodium-ion batteries(SIBs)with a maximum energy density of 91.94 Wh·g^(–1),indicating that the core-shell structured NNiFCN/NFFCN could be the low-cost and high-performance cathode for full SIBs in large-scale EES applications.

关键词： mechanical degradation core-shell structure Prussian blue full sodium-ion battery built-in electric field

Variation of contact resonance frequency during domain switching in PFM measurements for ferroelectric materials

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Journal of Materiomics 2020年第1期6卷 109-118页

作者： Yue Liu Yao Sun Wanheng Lu Hongli Wang Zhongting Wang Bingxue Yu Tao Li kaiyang zeng Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1117576Singapore Center for Spintronics and Quantum System State Key Laboratory for Mechanical Behavior of MaterialsSchool of Materials Science and EngineeringXi’an Jiaotong UniversityShanxi 710049Xi’anChina

Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric ***,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic *** work therefore studies the signal of the contact resonance frequency during the PFS *** comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric *** analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.

关键词： Ferroelectricity Piezoresponse force spectroscopy Contact resonance frequency Dual AC resonance tracking Domain switching Damping harmonic oscillator model

Enhanced energy storage properties and temperature stability of fatigue-free La-modified PbZrO3 films under low electric fields

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Science China Materials 2020年第11期63卷 2325-2334页

作者： Xiaojun Qiao Wenping Geng Xi Chen Le Zhang Dongwan Zheng Liaoyuan Zhang Jian He Xiaojuan Hou Yun Yang Min Cui kaiyang zeng Xiujian Chou Science and Technology on Electronic Test and Measurement Laboratory School of Instrument and ElectronicsNorth University of ChinaTaiyuan 030051China Department of Mechanical Engineering National University of SingaporeSingapore 117576Singapore

Electrostatic energy^-storage capacitors,with their ultrahigh storage density and high temperature stability,have been receiving increasing attention of late for their ability to meet the critical requirements of pulsed power devices in low^-consumption *** such a context,this work reports on the successful production of anti^-ferroelectric(AFE)thin films with excellent energy storage performance under a relatively low electric *** particular,La^-doped Pb Zr O3 thin films were fabricated using a sol^-gel method,yielding a recoverable energy storage density of 34.87 J cm^-3 with an efficiency of 59.23%at room temperature under the electric field of^800 k V cm^-*** temperature dependence of the energy storage property was demonstrated from room temperature to 210°C,indicating a stable density variation between 34.87 and 27.98 J cm^-*** films also exhibited excellent anti^-fatigue property(endurance of up to 3×10^9cycles and the recoverable energy storage density varied from 39.78 to 29.32 J cm^-3 combined with an efficiency of 61.03%–44.95%under the test frequencies from 10 to 5000 Hz).All results were obtained using compact films with a high polarization(Pmax)of approximately 103.7μC cm^-2 and low remnant polarization(Pr^7μC cm^-2),which was owing to the combination of La Ni O3 buffer layers and vacancies at Pb *** results illustrate the great potential of pulsed power devices in low^-consumption systems operating in a wide range of temperatures and long^-term operations.

关键词： antiferroelectric energy storage sol-gel Pb Zr O3thin film stability

NANO-INDENTATION STUDIES OF TRANSPARENT CONDUCTING OXIDE THIN FILMS

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NANO-INDENTATION STUDIES OF TRANSPARENT CONDUCTING OXIDE THI...

第8届国际材联电子材料国际研讨会

作者： kaiyang zeng Furong Zhu Jianqiao Hu Lu Shen Keran Zhang Hao Gong Institute of Materials Research and Engineering 3 Research Link Singapore 117602 Dept. of Mat.Sciences National University of Singapore Lower Kent Ridge Road Singapore 119260

＜正＞ Transparent conductive oxide （TCO） thin films have widespread applications due to their unique properties of low electrical resistivity and high optical transmission in the visible spectrum range. TCO films have been used in photovoltaic devices, liquid crystal displays and organic light emitting diodes. It is well known that the optical, electrical, mechanical and morphological properties of TCO films have direct implications for determining and improving the device performance and reliability. Much effort has been

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胃肠运动调节中药研究进展

现代中西医结合杂志 2019年第2期28卷 225-228页

作者：曾凯洋宋驰曲妍霏张静泽武警后勤学院天津300309

胃肠道平滑肌运动是消化道生理功能的重要组成部分,其功能紊乱是引起消化道疾病的重要因素之一。胃肠动力学异常性疾病在我国发病率较高,加之胃炎、溃疡病等其他常见病引起的动力学异常,则导致发生率更高。胃肠动力疾病是目前消化内科... 详细信息

胃肠道平滑肌运动是消化道生理功能的重要组成部分,其功能紊乱是引起消化道疾病的重要因素之一。胃肠动力学异常性疾病在我国发病率较高,加之胃炎、溃疡病等其他常见病引起的动力学异常,则导致发生率更高。胃肠动力疾病是目前消化内科的研究热点,胃肠动力调节中药在临床运用广泛,疗效确切。中医以辨证论治、整体观念的治病原则,使其在功能性疾病的治疗上具有突出的优势。近年来,随着对胃肠动力调节机制研究的深入,越来越多的学者针对中药的胃肠动力调节作用进行了实验探索,并提出“胃肠动力中药”这一概念。胃肠动力中药是指具有增强蠕动、促进排空、降逆止呕、消痞除满、疏肝利胆、健脾和胃及攻积导滞等作用的一类中药。

关键词：胃肠运动中药神经调节肠平滑肌运动