First-principles studies of monolayer MoS2-based hybrid systems

自从2004年石墨烯问世以来，它凭借其自身优异的物理化学性能已成为凝聚态物理，半导体材料，生物医学，化学以及能源等领域的研究热点。近几年随着石墨烯材料在锂离子电池，传感器，半导体光电器件上的成功应用，类石墨烯二维纳米材料的研究也逐渐受到了人们的广泛关注。其中二维层状过渡金属硫化物二硫化钼被认为是极具潜力的石墨烯替代物。单层二硫化钼除了与石墨烯一样具备极佳的导电性能和超强的硬度外，该材料还具备发光性。此外，单层二硫化钼本身具有直接带隙，能够克服石墨烯，硅烯，锗烯等二维材料零带隙的缺陷。而且，近期有研究显示，由不同种类的二维材料结合在一起形成的复合体系，其组分在性能上可以相互补充，产生协同效应，因...Since its discovery in 2004, graphene has become a hot research topic in condensed matter physics, semiconducting material, biomedicine, chemistry, energy and other fields, due to its excellent physical and chemical characteristics. In recent years, with the successful application of graphene in Li-ion batteries, temperature sensor and semiconductor optoelectronic devices, the graphene-like two di...学位：理学博士院系专业：物理与机电工程学院_凝聚态物理学号：1982012015389

Structure and Electronic Properties of Single Walled Nanotubes from AlAs(111) Sheets: A DFT Study

通过卷曲立方AlAs(111)单层片(sheets)构造了一系列(n,0)和(n,m)一维单壁纳米管。用周期性密度泛函理论(DFT)计算并比较了; 不同类型AlAs纳米管在几何结构、能量及电子性质等方面的差别。计算结果表明锯齿型和椅型纳米管应变能均为负值,并随着管径变大而逐渐变小。然而,它们; 的带隙相当不同:椅型纳米管为间接带隙,随着管径的增大而带隙减小;锯齿型纳米管为直接带隙,管径为1.87 nm时存在着一个极大带隙值(2.11; eV)。这种不同主要源于锯齿型纳米管铝原子间3p轨道的耦合贡献。A series of AlAs nanotubes (NTs) can be formed by rolling up two dimensional periodic (111) single layer sheets, namely (n,0) and (n,m) nanotubes. Optimized parameters of the atomic arrangement, energy levels and electronic structure of corresponding nanotubes of different types were calculated and compared by the density functional theory (DFT) method. The calculated results showed that strain energies (E-s) are negative over most of the diameter range for the (n,0) and (n,m) series, indicating that these NTs are more stable than a planar AlAs(111) single layer. The strain energy gradually decreases with increasing diameter. The calculated electronic band structures and density of states profiles reveal that the indirect band gaps (E-g) of armchair AlAs nanotubes gradually decreases with increasing diameter, which is distinct behavior from the zigzag nanotubes. The zigzagAlAs nanotubes feature a direct Eg with a peak value (2.11 eV) for a tube of radius 1.87 nm. The origin of the differences in band gaps could be attributed to the p-p coupling interaction between Al 3p orbitals in the conduction band of the AlAs zigzag nanotube.国家自然科学基金（21573182）资助项

Study on Corner-Fed Cavity-Backed Slot Dual-Polarized Antennas

为了在2.4GHz频段WLAN中实现具有方向性辐射的MIMO技术，采用背腔环形缝隙结构辐射元，通过倒置正交微带线激励，设计具有一定方向性的正交双极化天线结构。为提高端口间的隔离度和辐射场的极化纯度，在馈线正对的另一侧共面加载尺寸完全一致的接地或不接地导体带条。在此基础上，采用角馈的方法以期进一步改善天线的性能，并对各种可能天线形态进行对比分析。具体内容如下。 （1）对于边馈情形（即馈线位置垂直平分矩形导体腔表面的直角边），可以发现，没有加载导体条时，较佳隔离度对应的频带要高于阻抗工作频带，且相隔距离较大。加载导体条但导体条没有接地时，可使较佳隔离度频带下移并靠近阻抗工作频带，但其仍略高于工作...To meet the application requirement of MIMO (Multi Input and Multi Output) dual-polarized directional radiation for 2.4-GHz WLAN systems, the cavity-backed annular slot antennas, which have two orthogonal and inverted microstrip feed lines, are adopted. To improve the isolation between ports and the polarization purity, a pair of conductive strips, which have the same shape and size as the feed mi...学位：工程硕士院系专业：信息科学与技术学院_工程硕士(电子与通信工程)学号：X201122201

Study of low-temperature formation of GeSn nanocrystallite thin films by Sn induced Ge crystallization on insulating substrate

由IV族元素Ge、Sn组成的GeSn合金材料近年来受到了广泛关注，理论研究表明，当Sn组分高于6.3%时，GeSn合金可以转变为直接带隙材料，而且随着Sn组分的改变带隙在0.66eV到0eV范围内连续可调，这可以拓宽Si基材料在红外波段的应用范围。同时GeSn合金材料的迁移率远高于传统的Si、Ge材料，可以应用于制备高速TFT。在绝缘衬底或者柔性衬底上磁控溅射法制备多晶GeSn合金，在低价太阳能电池和柔性薄膜晶体管等方面具有潜在的应用价值。但是在绝缘衬底或者柔性衬底上生长高质量的GeSn合金还面临着几个困难。首先，Sn在Ge中低的固溶度较低(Germanium Tin alloys, being comprised of Group-IV elements, have recently received much attention due to the fact that their directband-transition behavior is predicted when Sn content is greater than 6.3%. Moreover, the bandgap of GeSn alloys can also be readily adjusted from 0 to 0.66 eV by controlling the value of x from 0 to 1. This gives rise to the potential to extend the infrared applicatio...学位：工学硕士院系专业：物理科学与技术学院_微电子学与固体电子学学号：1982014115297

Study on GaN-Based Light-Emitting Diodes for Visible Light Communications

得益于GaN基LED的重大突破，可见光通信逐渐发展并拥有广阔的应用前景，成为当下的研究热点。由于GaN是宽禁带的直接带隙半导体材料，GaN基LED具有很高的发光效率，并且已经在照明和显示方面有着广泛的应用基础。另一方面，作为可见光通信系统中的蓝绿光光源，GaN基LED不仅可以极大地降低系统成本，还可以大幅度提高可见光通信系统的实用价值。LED的调制带宽是影响可见光通信系统传输速率的关键因素之一，然而，对于GaN基LED的调制带宽的研究仍然不够完善和深入。本论文旨在探究影响LED调制特性的因素，特别是我们制作了不同尺寸的LED混合阵列，研究了不同尺寸对LED的调制带宽、电学特性等的影响。主要研究...With the breakthrough in GaN-based light-emitting diodes (LEDs), visible light communication (VLC) develops rapidly and shows high potential for applications. In recent years, it has attracted much attention for further research. Because of large and direct band-gap of GaN materials, GaN-based LEDs with high efficiency have been widely used in illumination and display applications. On the other ha...学位：工程硕士院系专业：信息科学与技术学院_工程硕士(电子与通信工程)学号：2312014115313

Dynamic Analysis of the Mechanism with Joint Clearance

随着工业水平的不断发展，含间隙机构的动力学及其控制的研究逐渐成为了一个热门课题。由于间隙的存在对机械机构的动力学特性造成了一定的影响，所以分析运动副间隙的影响对于机械机构设计和优化的意义就显得十分重大。本文中主要是以具有代表性的含间隙曲柄滑块机构和机械手臂机构为例，来分析间隙以及柔性因素给机械机构动力学特性带来的一些影响。 建立了机械系统的动力学方程，为含间隙机构动力学分析研究提供了理论基础；分析了基于弹簧阻尼模型的Impact接触碰撞函数，为研究轴与轴套间的接触碰撞过程提供了理论依据。 本文利用ADAMS软件建立含间隙曲柄滑块机构模型并进行动力学仿真，在仿真的过程中，利用基于弹簧阻尼模型...As the industry develops fast, the study on the dynamics of mechanism with clearance and mechanism control gradually becomes a hot topic. Due to the exist of the joint clearance, the dynamic characteristics of the mechanism are influenced greatly. It is significant to analyze the influence caused by the joint clearance for the design and optimization of mechanism. In this paper, we take slider-cra...学位：工学硕士院系专业：物理与机电工程学院_机械设计及理论学号：1992012115272

The Study of Band Engineering and Polarization-induced Doping in AlGaN-based Deep Ultraviolet Light-Emitting Diode

Ⅲ族氮化物作为新一代半导体材料，具有宽直接带隙、高电子漂移率、高热导率、耐高温、抗腐蚀、抗辐射等优点，适合制作高频、高功率、耐高温和抗辐射的电子器件，比如AlGaN基紫外发光二极管。但是紫外发光二极管依然存在低量子效率、低光输出功率等问题，提高晶体质量和载流子注入效率是解决问题的两个主要思路。影响载流子注入效率的一个重要因素是内部极化场引起的能带弯曲，本文基于APSYS软件，主要围绕紫外LED的能带调控和极化诱导掺杂展开研究。 首先，本文回顾了紫外LED的发展历程，介绍了AlGaN半导体材料的结构和性质，以及紫外LED的结构、发光机理和亟待解决的研究难题。接着，介绍了紫外LED器件的模拟方法...As a new generation of semiconductor materials, III nitride owning advantages like wide direct band gap, high thermal conductivity, high electron mobility, high temperature resistance, corrosion resistant and radiation resistant. Thus it is suitable for fabricating electronic device like AlGaN-based deep UV LEDs. However, there still exist a number of problems like low quantum efficiency and low l...学位：理学硕士院系专业：物理科学与技术学院_凝聚态物理学号：1982013115296

类单晶硅结构Si（C≡C―C6H4―C≡C）4新材料的力学与光学性质:第一性原理研究

基于单晶硅中Si的四面体成键特征及对其结构单元的替换修饰,我们设计了一种类单晶硅结构的新材料-C40H16Si2。通过广泛的第一性原理计算,研究了这类材料的电子性质、力学性质和光学性质。计算结果表明,这种新材料具有好的热力学稳定性和机械稳定性。该材料的禁带宽度为3.32 eV,价带底和导带顶都位于Gamma点,是直接带隙宽禁带半导体材料。该材料的维氏硬度和密度非常小,不到单晶硅的十分之一,是一类低密度的柔性多孔材料。此外,该材料在紫外光区有强的吸收,有望应用于蓝绿光发光二极管。中央高校基本科研业务费专项资金(20720150215);;国家自然科学基金(21373164,21673185)资助项目~

A CAD/CAM method of individualized prosthesis base on CT reconstructing and robot grinding

人体髋关节髓腔具有个性化的S型形状,现有标准型的直柄股骨假体与病人髓腔形成三点接触,降低了股骨假体与病人髓腔的匹配度。利用猪腿骨的CT数据重建其; 髓腔的三维模型,将该三维模型作为假体设计模型导入机器人仿真软件进行编程和磨削仿真,并生成机器人磨削程序,利用机器人磨削程序将该假体模型复制到铜棒; 上。将加工好的假体与猪腿骨髓腔匹配,通过X射线图检测两者匹配情况,利用截取的骨断面测量假体与髓腔断面间的尺寸误差,验证个性化假体设计方法以及机器; 人磨削个性化假体的可行性。实验结果表明,假体与髓腔完成匹配后,90.84%匹配区域的假体与髓腔的间隙小于1mm。Human hip joint has a S-shaped canal , the existing standard straight; hip prosthesis matching with the femur cavity of the patient , will form; a three-point contact and reduce the fit precision between hip; prosthesis and femur cavity. The pig shank CT data is applied to; reconstruct the three-dimensional model of femur cavity to as a design; model of the prothesis, which is imported into robot simulation software; for programming and simulation of grinding , then,the prosthesis model; is copied on the copper bar by using robotic grinding technology. After; the prosthesis matched with femur cavity, the matching case is detected; by X-ray image , and the size error between the prosthesis and femur; cavity on the cross-sectional is measured to verify the method of; individualized prosthesis design and the feasibility of robot grinding; prosthesis. The experimental results show that 90.84% of the matching; area is less than 1mm when the femur cavity is matched with prosthesis

Investigation of inverted metamorphic multi-junction solar cell epitaxy and device

倒装多结太阳能电池相对于传统的Si基多结太阳能电池或传统的化合物三结太阳能电池具有更高的光电转换效率和更广泛的应用方式。本论文对外延关键技术及结构，如宽禁带隧穿结技术，PIN结构，应力缓冲层技术等在聚光倒装多结太阳能电池上的应用进行了研究。进一步对空间三结太阳能电池，空间四结太阳能电池，GaInP/GaInAs//Si键合三结太阳能电池及柔性倒装三结太阳能电池等进行了探索。取得主要成果如下： 1.采用AlGaAs/GaInP宽禁带隧穿结的电池短路电流为14.27A，相对于AlGaAs/GaAs窄禁带隧穿结的短路电流(13.72A)提升近4%，GaInP/GaAs双结倒装电池最终光电转换效率也...Inverted metamorphic multi-junction solar cell is potential for a high convention efficiency and extensive use relative to convensional Si base solar cell and III-V compound solar cell. In this dissertation, the effects of wide band tunnel junction, PIN structure, strain reducing layer on the concentrator solar cell were studied. On the other hand, triple-junction space solar cell, four-junction s...学位：博士后院系专业：物理科学与技术学院_凝聚态物理学号：201517006