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SSRN 2023年

作者： Madoune, Yassine Ahmed Ismail, Ayman Abdallah School of Physics and Electronics Central South University Hunan Province Changsha410083 China Hunan Key Laboratory of Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University No.932 South Lushan Road Hunan Province Changsha410083 China School of Metallurgy and Environmen engineering Central South University Changsha410083 China

Two-dimensional layered transition-metal dichalcogenides (2D-TMDs) have garnered significant attention due to their layer number-dependent electronic properties, making them promising candidates for atomically thin electronics and optoelectronics. However, current research has primarily focused on exfoliated TMD materials, which have limitations in size, layer number control, and yield. Therefore, a crucial challenge remains in producing large-sized TMD single crystals with precise control over the layer number. A comprehensive understanding and precise control of the growth conditions are imperative to address this challenge. This study systematically investigated key growth conditions, including temperature, precursor flow, growth duration, material quantity, gas flow, and slide position. By optimizing these parameters, we successfully synthesized TMD materials with an impressive size of 850 µm. Notably, we achieved the preparation of monolayer WS2 single crystals on a large scale within a remarkably short duration of 10 minutes, exhibiting a lateral growth rate of up to 1.4 μm/s, which is comparable to the best-exfoliated monolayers. The findings from our study provide a robust pathway for the rapid growth of high-quality TMD single crystals, facilitating further advancements in this field. © 2023, The Authors. All rights reserved.

关键词： Monolayers

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Nitrogen and Sulfur Co-Doped Carbon Dots with Excellent Fluorescent Thermal Stability for Anti-Counterfeiting and Information Encryption

SSRN

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SSRN 2024年

作者： Ahmed, Nouman Abbas, Aumber Hussain, Manzoor Qamar, Tauqeer Haidar ul Hassan, Sibt Xia, Pengkun Ma, Lei Ouyang, Fangping Deng, Lianwen Gao, Xiaohui Central South University China Hunan Provincial Key Laboratory for Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha410083 China School of Electronic Information Central South University Changsha410083 China Department of Chemistry Karakorum International University Gilgit Pakistan Songshan Lake Materials Laboratory University Innovation Park Dongguan523808 China

In this work, a series of nitrogen and sulfur co-doped carbon dots (CDs) were synthesized with high photoluminescence quantum yields (PLQYs) and outstanding thermal stability. With the reaction solvent changing from water, ethanol, methanol, and dimethylformamide (DMF), a significant fluorescence emission with PLQY improvement from 42%, 33%, 25%, and 18%, respectively, accompanied by a red shift from 430 to 590 nm, (the color changes from blue, green, yellow, and red respectively). Simultaneously, excellent fluorescence stability can also be obtained across temperatures ranging from 15 to 95 °C. Combined with the density functional calculations (DFT) results, the underlying mechanism investigation reveals that the color change of fluorescence emission was probably induced by the increased particle size of CDs and increased graphitic N content. The enhanced thermal stability is induced by the presence of stable surface functional groups, including C=O, C=N, C=S, and -NH, among others, contributing to improved hydrophilicity, regulated particle aggregation, and mitigated thermal oxidation by limiting oxygen diffusion to fluorescent hubs. Notably, the obtained outstanding optical properties finally render these multicolor CDs suitable for information encryption and anti-counterfeiting applications. © 2024, The Authors. All rights reserved.

关键词： Fluorescence

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Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition

Effect of nitrogen pressure on the fabrication of AlCrFeCoNi...

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作者： Jiang, Tenghao Zhao, Hong Tsoutas, Kostadinos Sun, Lixian Liu, Hongwei Liu, Yanping Xu, Fanjun Zheng, Zhong Bilek, Marcela M. Liu, Zongwen School of Chemical and Biomolecular Engineering The University of Sydney SydneyNSW2006 Australia School of Physics The University of Sydney SydneyNSW2006 Australia School of Biomedical Engineering The University of Sydney SydneyNSW2006 Australia Guangxi Key Laboratory of Information Materials Guangxi Collaborative Innovation Center of Structure and Property for New Energy and Materials School of Material Science & Engineering Guilin University of Electronic Technology Guilin541004 China The University of Sydney SydneyNSW2006 Australia Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Hunan410083 China The University of Sydney Nano Institute The University of Sydney SydneyNSW2006 Australia

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01-0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film. © 2023 Author(s).

关键词： Entropy

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2D transition metal dichalcogenides for neuromorphic vision system

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Journal of Semiconductors 2021年第9期42卷 7-9页

作者： Kaoqi Zhou Jie Jiang Liming Ding Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China Center for Excellence in Nanoscience(CAS) Key Laboratory of Nanosystem and Hierarchical Fabrication(CAS)National Center for Nanoscience and TechnologyBeijing 100190China

It has been a long-sought dream for human beings to realize a powerful and reliable artificial vision system that can liberate human beings from tedious brain *** the past few years,computer vision based on brain-inspired algorithm has made great achievements in several commercial applications such as the face recognition,medical image diagnosis and driverless vehicles.

关键词： computer artificial system

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Generation of maximal three-state field-free molecular orientation with terahertz pulses

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Physical Review A 2021年第1期104卷 013108-013108页

作者： Qian-Qian Hong Li-Bao Fan Chuan-Cun Shu Niels E. Henriksen Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha 410083 China Department of Chemistry Technical University of Denmark Building 207 DK-2800 Kongens Lyngby Denmark

We present a combined analytical and numerical investigation to show how an optimal control field can be designed to generate maximum field-free orientation of molecules for three populated rotational states. Based on a model involving pure rotational ladder-climbing excitation between rotational states, a set of optimal amplitude and phase conditions are analytically derived for the applied control fields. The maximum degree of orientation can be achieved when the field satisfies amplitude and phase conditions at the two transition frequencies. Multiple optimal solutions exist, and to examine these conditions, we devise a quantum coherent control scheme using two terahertz pulses and successfully apply it to the linear polar molecule HCN at ultracold temperature. The sensitivity of both populations and phases of rotational states to control field parameters, i.e., the detuning, bandwidth, and time delay, is analyzed so as to understand the optimal orientation mechanism. This work thus examines the frequency-domain landscape belonging to optimal pulses.

关键词： Coherent control Quantum description of light-matter interaction Single- and few-photon ionization & excitation

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Thinning Effect of Few-Layer Black Phosphorus Exposed in Dry Oxidation

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SSRN 2024年

作者： Zheng, Xiaoming Zheng, Xiaofang Chen, Siyang Guo, Xiao Liu, Bowen Wang, Chuanxin Han, Yujie Guo, Yujing Nie, Guozheng Huang, Han Wei, Yuehua Yang, Hang Hunan Province Key Laboratory of Intelligent Sensors and Advanced Sensor Materials School of Physics and Electronic Science Hunan University of Science and Technology Xiangtan411201 China Institute of Environmental Science Shanxi University Taiyuan030006 China Hunan Key Laboratory of Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha410083 China University of Defense Technology Changsha410073 China Xiangtan University School of Physics and Optoelectronics Xiangtan411105 China Beijing Blue Sky Innovation for Frontier Science Beijing100085 China

Few-layer black phosphorus (BP) exhibits great potential for next-generation electronics because of the tunable band gap and high carrier mobility. The layer modulation of BP is essential in the applications of electronic device ascribed to its thickness-dependent electronic properties. However, precisely controlling its thickness still exists challenge for the preferable performance. Here, we find that BP will be thinned controllably when exposed to dry oxygen (40% humidity, low oxygen concentration) in dark environment, which is different from that exposed to humid oxygen (100% humidity, low oxygen concentration) without light illumination. The thinning BP not only exhibits better stability, but its electrical properties can be apparently improved. The ION/IOFF ratio increased from 103 to 106, resulting in the variation of band gap from 0.3 to 2 eV, and the hole mobility improved from 235 cm2V-1s-1 to 851 cm2V-1s-1, ascribed to the layer by layer thinning and p-type doping effects induced by the formed PxOy. Our finding shows significant potential of BP in future nanoelectronic and optoelectronic applications. © 2024, The Authors. All rights reserved.

关键词： Electronic properties

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Interfaces between MoO x and Mo X2(X=S,Se,and Te)

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Chinese Physics B 2020年第11期29卷 106-116页

作者： Fengming Chen Jinxin Liu Xiaoming Zheng Longhui Liu Haipeng Xie Fei Song Yongli Gao Han Huang Hunan Key Laboratory of Super-microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China Shanghai Synchrotron Radiation Facility Shanghai Institute of Applied PhysicsChinese Academy of SciencesShanghai 201204China Department of Physics and Astronomy University of RochesterRochesterNY 14627USA

In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like *** structural analogues of graphene but with a sizeable band gap,monolayers of atomically thin transition metal dichalcogenides(with formula of MX2,M=Mo,W;X=S,Se,Te,etc.)have emerged as the ideal 2D prototypes for exploring fundamentals in physics such as valleytronics due to the quantum confinement effects,and for engineering a wide range of nanoelectronic,optoelectronic,and photocatalytic *** metal trioxides as promising materials with low evaporation temperature,high work function,and inertness to air have been widely used in the fabrication and modification of *** this review,we reported the fabrications of one-dimensional MoS2 wrapped MoO2 single crystals with varied crystal direction via atmospheric pressure chemical vapor deposition method and of 2D MoOx covered MoX2 by means of exposing MoX2 to ultraviolet *** prototype devices show good *** approaches are common to other transition metal dichalcogenides and transition metal oxides.

关键词： MoOx epitaxial relationships MoX2 layer-by-layer oxidation

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Quantized perfect transmission in graphene nanoribbons with random hollow adsorbates

arXiv

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arXiv 2024年

作者： Yu, Jia-Le Hou, Zhe Bhat, Irfan Hussain Hu, Pei-Jia Sun, Jia-Wen Chen, Xiao-Feng Guo, Ai-Min Sun, Qing-Feng Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics Central South University Changsha410083 China School of Physics and Technology Nanjing Normal University Nanjing210023 China School of Physical Science and Technology Lanzhou University Lanzhou730000 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China Hefei National Laboratory Hefei230088 China

Impurities exist inevitably in two-dimensional materials as they spontaneously adsorb onto the surface during fabrication, usually exerting detrimental effects on electronic transport. Here, we focus on a special type of impurities that preferentially adsorb onto the hollow regions of graphene nanoribbons (GNRs), and study how they affect the quantum transport in GNRs. Contrary to previous knowledge that random adatoms should localize electrons, the so-called Anderson localization, noteworthy quantized conductance peaks (QCPs) are observed at specific electron energies. These QCPs are remarkably robust against variations in system size, GNR edge, and adatom properties, and they can reappear at identical energies following an arithmetic sequence of device width. Further investigation of wavefunction reveals a unique transport mode at each QCP energy which transmits through disordered GNRs reflectionlessly, while all the others become fully Anderson localized, indicating the survival of quantum ballistic transport in the localized regime. Our findings highlight the potential utility of hollow adatoms as a powerful tool to manipulate the conductivity of GNRs, and deepen the understanding of the interplay between impurities and graphene. Copyright © 2024, The Authors. All rights reserved.

关键词： Impurities

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Precise Quantum Control of Molecular Rotation Toward a Desired Orientation

arXiv

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arXiv 2025年

作者： Hong, Qian-Qian Dong, Daoyi Henriksen, Niels E. Nori, Franco He, Jun Shu, Chuan-Cun Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha410083 China Australian Artificial Intelligence Institute Faculty of Engineering and Information Technology University of Technology SydneyNSW2007 Australia Department of Chemistry Technical University of Denmark Building 207 Kongens LyngbyDK-2800 Denmark Quantum Computing Center Theoretical Quantum Physics Laboratory RIKEN Saitama351-0198 Japan Physics Department University of Michigan Ann ArborMI48109 United States

The lack of a direct map between control fields and desired control objectives poses a significant challenge in applying quantum control theory to quantum technologies. Here, we propose an analytical framework to precisely control a limited set of quantum states and construct desired coherent superpositions using a well-designed laser pulse sequence with optimal amplitudes, phases, and delays. This theoretical framework that corresponds to a multi-level pulse-area theorem establishes a straightforward mapping between the control parameters of the pulse sequence and the amplitudes and phases of rotational states within a specific subspace. As an example, we utilize this approach to generate 15 distinct and desired rotational superpositions of ultracold polar molecules, leading to 15 desired field-free molecular orientations. By optimizing the superposition of the lowest 16 rotational states, we demonstrate that this approach can achieve a maximum orientation value of |〈cos θ〉|max above 0.99, which is very close to the global optimal value of 1 that could be achieved in an infinite-dimensional state space. This work marks a significant advancement in achieving precise control over multi-level subsystems within molecules. It holds potential applications in molecular alignment and orientation, as well as in various interdisciplinary fields related to the precise quantum control of ultracold polar molecules, opening up considerable opportunities in molecular-based quantum techniques. © 2025, CC BY.

关键词： Molecular orientation

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First-Principles investigation of the First-order Phase Transition in Kagome Na2Ti3Cl8

arXiv

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arXiv 2022年

作者： Liu, Shuang Yin, Zhi-Bo Long, Meng-Qiu Wang, Yun-Peng School of Physics and Electronics Hunan Key Laboratory for Super-micro structure and Ultrafast Process Central South University 932 South Lushan Road Changsha China

The antiferromagnetic kagome material Na2Ti3Cl8 exhibits a first-order phase transition;the low-temperature phase is characterized by the trimerizations of Ti ions. In this work, we carry out first-principles calculations on the crystal and electronic structure of Na2Ti3Cl8 at the high- and low-temperature phases. The crystal structures, including the lattice constant and the trimerization of Ti ions, are well reproduced by taking account a small Hubbard correction of 1 eV. The calculated total energy landscape reveals a first-order phase transition with the total energy barrier of 80 meV per formula unit. Analysis of the electronic structure indicates a direct metal bonding among Ti in the trimierized low-temperature phase. © 2022, CC0.

关键词： Sodium compounds

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