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Facile intercalation of alkali ions in WO_(3)for modulated electronic and optical properties:Implications for artificial synapses and chromogenic application

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Science China(Physics,Mechanics & Astronomy) 2024年第2期67卷 149-160页

作者： Changmeng Huan Zihan Lu Silin Tang yongqing cai Qingqing Ke School of Microelectronics Science and Technology Sun Yat-sen UniversityZhuhai 519082China Guangdong Provincial Key Laboratory of Optoelectronic Information Processing Chips and Systems Sun Yat-sen UniversityZhuhai 519082China Institute of Applied Physics and Materials Engineering University of MacaoTaipaMacao 999078China

Tungsten oxides(WO_(3))are widely recognized as multifunctional systems owing to the existence of rich *** diverse phases exhibit distinct octahedra-tilting patterns,generating substantial tunnels that are ideally suited for ***,a quantitative comprehension regarding the impact of distinct phases on the kinetics of intercalated conducting ions remains ***,we employ first-principles calculations to explore the spatial and orientational correlations of ion transport inγ-and h-WO_(3),shedding light on the relationship between diffusion barriers and the size of the conducting *** findings reveal that different types and concentrations of alkali-metals induce distinct and continuous lattice distortions in WO_(3)***,γ-WO_(3)is more appropriate to accommodate Li+ions,exhibiting a diffusion barrier and coefficient of 0.25 eV and 9.31×10^(-8)cm^(2)s^(-1),***,h-WO_(3)features unidirectional and sizeable tunnels that facilitate the transport of K+ions with an even lower barrier and a high coefficient of 0.11 e V and 2.12×10^(-5)cm^(2)s^(-1),***,the introduction of alkali-metal into WO_(3)tunnels tends to introduce n-type conductivity by contributing s-electrons to the unoccupied W 5d states,resulting in enhanced conductivity and tunable electronic *** alkali metals in WO_(3)tunnels are prone to charge transfer,forming small polaronic states and modulating the light absorption in the visible and nearinfrared *** tunable electronic and optical properties,combined with the high diffusion coefficient,underscore the potential of WO_(3)in applications such as artificial synapses and chromogenic devices.

关键词： WO_(3)polymorphs ion insertion kinetic activity tunable electronic and optical properties iontronics

Mechanical behavior of Cu-Zr bulk metallic glasses (BMGs): A molecular dynamics approach

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Chinese Physics B 2013年第9期22卷 490-495页

作者： Muhammad Imran Fayyaz Hussain Muhammad Rashid yongqing cai S.A.Ahmad Department of Physics Simulation Lab The Islamia University of Bahawalpur Department of Physics National University of Singapore2 Science Drive 3117542Singapore

In the present work, three-dimensional molecular dynamics simulation is carried out to elucidate the nanoinden- tation behaviors of CuZr Bulk metallic glasses （BMGs）. The substrate indenter system is modeled using hybrid interatomic potentials including both many-body Finnis Sinclair （FS） and two-body Morse potentials. A spherical rigid indenter （diameter= 60 A（1 A = 10 ^-10 m）） is employed to simulate the indentation process. Three samples of BMGs including Cu25Zr75, CusoZr50, and Cu75Zr25 are designed and the metallic glasses are formed by rapid cooling from the melt state at about 2000 K. The radial distribution functions are analyzed to reveal the dynamical evolution of the structure of the atoms with different compositions and different cooling rates. The mechanical behavior can be well understood in terms of load-depth curves and Hardness-depth curves during the nanoindentation process. Our results indicate a positive linear relationship between the hardness and the Cu concentration of the BMG sample. To reveal the importance of cooling rate provided during the processing of BMGs, we investigate the indentation behaviors of CusoZr50 at three different quenching rates. Nanoindentation results and radial distribution function （RDF） curves at room temperature indicate that a sample can be made harder and more stable by slowing down the quenching rate.

关键词： Bulk metallic glasses (BMGs) nanoindentation deformation quenching rate

Phonon anharmonicity and thermal conductivity of two-dimensional van der Waals materials: A review

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Science China(Physics,Mechanics & Astronomy) 2022年第11期65卷 36-45页

作者： Xuefei Yan Bowen Wang Yulong Hai Devesh RKripalani Qingqing Ke yongqing cai Joint Key Laboratory of the Ministry of Education Institute of Applied Physics and Materials EngineeringUniversity of MacaoMacao 999078China School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore School of Microelectronics Science and Technology Sun Yat-sen UniversityZhuhai 519082China Guangdong Provincial Key Laboratory of Optoelectronic Information Processing Chips and Systems Sun Yat-sen UniversityZhuhai 519082China

Two-dimensional(2D) van der Waals(vdW) materials have extraordinary thermal properties due to the effect of quantum confinement, making them promising for thermoelectric energy conversion and thermal management in microelectronic *** this review, the mechanism of phonon anharmonicity originating from three-and four-phonon interactions is derived. The phonon anharmonicity of 2D vdW materials, involving the Grüneisen parameter, phonon lifetime, and thermal conductivity, is summarized and derived in detail. The size-dependent thermal conductivity of representative 2D vdW materials is discussed experimentally and theoretically. This review will present fundamental and advanced knowledge on how to evaluate the phonon anharmonicity in 2D vdW materials, which will aid the design of new structures and materials for applications related to energy transfer and conversion.

关键词： van der Waals materials two-dimensional phonon anharmonicity thermal conductivity

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Study on denoising of continuous spectrum on-line monitoring signal of water quality with micro-reagents based on HHT

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Optoelectronics Letters 2022年第2期18卷 115-121页

作者： LI Wen LÜ Binbin FU Hao cai yongqing Institute of Mechanical and Electrical Engineering North China University of TechnologyBeijing 100144China

A continuous spectrum water quality on-line monitoring signal processing method based on Hilbert-Huang transform(HHT) is proposed in this paper, which combines the micro-reagent water quality on-line monitoring technology of sequential injection. The modulation signal and spectrum curve of each intrinsic mode function(IMF) component of the original spectrum signal were obtained by empirical mode decomposition(EMD). The water sample data of different concentrations in the continuous spectrum on-line monitoring system was analyzed by the HHT model. The noise signal was excavated to realize the noise reduction processing, and the reconstruction of the continuous spectrum signal was realized after the noise reduction processing was completed. The research results show that this method can effectively reduce the noise of continuous spectrum signals according to different signal-to-noise characteristics of continuous spectrum, and has convenient use, fast processing speed, and high resolution in the time-frequency domain, which effectively improves the stability and accuracy of the micro-reagent continuous spectrum water quality on-line monitoring system.

关键词： signal spectrum continuous

Aqueous and mechanical exfoliation, unique properties, and theoretical understanding of MoO3 nanosheets made from free-standing a-MoO3 crystals： Raman mode softening and absorption edge blue shift

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Nano Research 2018年第3期11卷 1193-1203页

作者： Hongfei Liu yongqing cai Mingyong Han Shifeng Guo Ming Lin Meng Zhao Yongwei Zhang Dongzhi Chi Institute of Materials Research and Engineering (IMRE) A＊STAR (Agency for Science Technology and Research) 2 Eusionopolis Way Singapore 138634 Singapore Institute of High Performance Computing (IHPC) A ＊STAR (Agency for Science Technology and Research) 1 Fusionopolis Way Singapore 138632 Singapore

Crystalline α-MoO3 belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO3 powders at elevated temperatures. The MoO3 belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional （2D） nanosheets were processed via the scotch-tape and bovine serum albumin （BSA） assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO3 exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo-O-Mo stretching mode （Ag） at - 818 cm^-1, which was accompanied by mode-softening of up to 5 cm^-1 This mode softening, hitherto not reported for 2D α-MoO3 nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO3 nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO3 crystals, illuminate the possibility of further 2D α-MoO3 nanosheet production and lattice dynamic studies.

关键词： α-MoO3 two-dimensionalmaterials exfoliations lattice vibrationaldynamics micro-Raman scattering

Optical cavity structure design and optical path simulation for rapid nitric oxide detection

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Optoelectronics Letters 2021年第12期17卷 757-762页

作者： LI Wen cai yongqing CHEN Mengfan LIU Peng Institute of Mechanical and Electrical Engineering North China University of TechnologyBeijing 100144China

According to the chemiluminescence reaction mechanism of nitric oxide(NO)and ozone(O_(3)),a new cylindrical total reflection S-type optical cavity design for rapid detection of NO gas is *** optical cavity model is based on the total reflection S-type structure on the inner wall of the *** software ZEMAX was used to simulate the optical path of the model,and software FLUENT was used to simulate and verify the *** comparative analysis showed that the chemiluminescence collection efficiency of the S-type optical cavity collection path was 36.6%,and the gas reaction and mixing in the S-type optical cavity model was more sufficient,and the reaction mixing stability error was 0.049,which was 2 times higher than the traditional stability *** model is simple in structure and meets the new national *** provides a practical idea of design for the real-time exhaust gas detection.

关键词： structure. structure mixing

Ultra-low thermal conductivity of two-dimensional phononic crystals in the incoherent regime

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npj Computational Materials 2018年第1期4卷 478-484页

作者： Guofeng Xie Zhifang Ju Kuikui Zhou Xiaolin Wei Zhixin Guo yongqing cai Gang Zhang School of Materials Science and Engineering Hunan University of Science and Technology411201 XiangtanChina Hunan Key Laboratory of Micro-Nano Energy Materials and Devices School of Physics and OptoelectronicsXiangtan University411105 HunanChina Institute of High Performance Computing Singapore 138632Singapore

Two-dimensional silicon phononic crystals have attracted extensive research interest for thermoelectric applications due to their reproducible low thermal conductivity and sufficiently good electrical *** thermoelectric devices in high-temperature environment,the coherent phonon interference is strongly suppressed;therefore phonon transport in the incoherent regime is critically important for manipulating their thermal *** the basis of perturbation theory,we present herein a novel phonon scattering process from the perspective of bond order imperfections in the surface skin of *** incorporate this strongly frequency-dependent scattering rate into the phonon Boltzmann transport equation and reproduce the ultra low thermal conductivity of holey silicon *** reveal that the remarkable reduction of thermal conductivity originates not only from the impediment of low-frequency phonons by normal boundary scattering,but also from the severe suppression of high-frequency phonons by surface bond order imperfections *** theory not only reveals the role of the holey surface on the phonon transport,but also provide a computation tool for thermal conductivity modification in nanostructures through surface engineering.

关键词： conductivity thermal regime

Surface Passivation Toward Efficient and Stable Perovskite Solar Cells

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Energy & Environmental Materials 2023年第1期6卷 1-24页

作者： Junmin Xia Chao Liang Hao Gu Shiliang Mei Shengwen Li Nan Zhang Shi Chen yongqing cai Guichuan Xing Joint Key Laboratory of the Ministry of Education Institute of Applied Physics and Materials EngineeringUniversity of MacaoAvenida da UniversidadeTaipa China

Although metal halide perovskites are increasingly popular for the next generation of efficient photovoltaic devices,the inevitable defects from the preparation process have become the notorious barrier to further improvement of performance,which increases non-radiative recombination and lowers the power conversion efficiency of solar *** passivation strategies have been affirmed as one of the most practical approaches to suppress these ***,it is necessary to have a detailed review on the surface passivation to reveal the improvements of the ***,the mechanism and recent advances of surface passivation have been systematically summarized with respect to various passivation approaches,including the Lewis acid–base,the low-dimensional perovskite,inorganic molecules,and ***,the review also offers the research trend and prospects of surface passivation.

关键词： defects efficiency perovskite solar cells stability surface passivation

Molecular dynamics simulation of nanoscale surface diffusion of heterogeneous adatoms clusters

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Chinese Physics B 2016年第7期25卷 341-348页

作者： Muhammad Imran Fayyaz Hussain Muhammad Rashid Muhammad Ismail Hafeez Ullah yongqing cai M Arshad Javid Ejaz Ahmad S A Ahmad Material Simulation Research Laboratory(MSRL) Department of PhysicsBahauddin Zakariya UniversityMultan 60800Pakistan Department of Physics COMSATS Institute of Information Technology44000 IslamabadPakistan Department of Physics Govt.College University FaisalabadLayyah CampusLayyah 31200Pakistan Institute of High Performance Computing A*STARSingapore 138632Singapore Department of Basic Sciences(Physics) UETTaxila Department of Physics Simulation Laboratorythe Islamia University of Bahawalpur63100Pakistan

Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface diffusion of heterogeneous adatoms clusters can be vital for the binary island growth on the surface and can be useful for the formation of alloy-based thin film surface through atomic exchange process. The results of the diffusion process show that at 300 K, the diffusion of small adatoms clusters shows hopping, sliding, and shear motion; whereas for large adatoms clusters（hexamer and above）, the diffusion is negligible. At 500 K, small adatoms clusters, i.e., dimer, show almost all possible diffusion mechanisms including the atomic exchange process; however no such exchange is observed for adatoms clusters greater than dimer. At 700 K, the exchange mechanism dominates for all types of clusters, where Zr adatoms show maximum tendency and Ag adatoms show minimum or no tendency toward the exchange process. Separation and recombination of one or more adatoms are also observed at 500 K and 700 K. The Ag adatoms also occupy pop-up positions over the adatoms clusters for short intervals. At 700 K, the vacancies are also generated in the vicinity of the adatoms cluster,vacancy formation, filling, and shifting can be observed from the results.

关键词： molecular dynamics surface diffusion adatoms atomic exchange