载流子穿越具有双Mot势垒的半导体晶界的输运行为

讨论了穿越具有双Mot势垒的n型半导体晶界的载流子输运行为，重点分析了受主缺陷扩散层对偏压下晶界势垒、直流电流、非线性特性和电容等的作用．晶界势垒在偏压下的变化决定了载流子穿越晶界的输运行为分为预击穿、击穿和回复三个区域．受主缺陷扩散层的存在改变了势垒及其偏压关系，使电流的变化和非线性特性大幅度加强，很大程度上决定了预击穿区的漏电流；同时也使势垒加宽而减小高频电容，但使直流偏压下因晶界电荷的共振响应而产生的电容峰值增大 关键词：     

双晶衬底晶界的显微研究

在空气中加压烧制了钇稳定氧化锆（ＹＳＺ）双晶衬底，利用光学显微镜和透射电镜对其晶界进行了观察，以了解其与衬底上ＹＢＣＯ晶界结超导弱连接性能的关系。我们发现晶界在光学显微镜下清楚笔直，在透射电镜高分辨像下原子排列很规则，晶界宽度约一个纳米。同时，在晶界结性能差的双晶衬底上，发现了十分之一微米量级的被非晶态物质填充的孔洞。     

纳晶铜晶粒尺寸对热导率的影响

用热压烧结法制备得到纳晶铜块体. 用激光法测定了不同温度下制备得到的纳晶铜块体的热导率, 并建立卡皮查热阻模型对样品热导率进行模拟. 通过对比, 模拟结果与实验数据基本一致. 随着热压烧结温度的升高, 纳晶铜晶粒尺寸也随之增大. 在900和700 ℃其热导率分别达到了最大和最小值且所对应的热导率分别为200.63和233.37 W·m^-1·K^-1, 各占粗晶铜块体热导率的53.4%和60.6%. 验证了纳晶铜热导率在一定的晶粒尺寸范围内具有尺寸效应, 随着晶粒尺寸的减小, 热导率逐渐减小.     

金刚石衬底原位生长石墨烯的复合结构热输运

石墨烯作为一种具有超高导热性能的二维纳米材料,不断引起人们的关注。实际应用中,石墨烯需附着在一定的衬底材料上,从而导致界面处强烈的声子散射和热导率的显著降低。为解决此类问题,本文采用一种原位催化生长技术制备出了金刚石/石墨烯复合材料。与转移到SiO_2/Si衬底的结构相比,在金刚石上生长得到的复合结构热导率被明显提高(约793 W·m~(-1)·K~(-1)),且石墨烯与金刚石衬底的界面热阻小于4.85×10~(-5)m~2·K·W~(-1)。这源于金刚石衬底为石墨烯提供了可观的热学贡献,而原位键合的生长让界面中产生有别于非键相互作用的杂化结构,使得界面热阻被降低。该结构优异的传热性能为石墨烯复合材料提供了一种新的方案。     

含有倾斜界面硅/锗超晶格的导热性能

采用非平衡分子动力学(NEMD)方法模拟含有倾斜界面的硅/锗(Si/Ge)超晶格在不同倾斜角、不同周期长度、不同样本长度和不同温度下的导热性能.模拟结果表明,Si/Ge超晶格的热导率随着界面倾斜角的增加而非单调变化.当周期长度为4—8原子层时,界面倾斜角为45°的热导率比其他界面倾斜角时热导率增大了一个数量级,且热导率...     

基于深度卷积神经网络的α-Fe晶界能预测

本文提出了一种预测晶界能以研究α-Fe晶界性质的深度学习方法.在分子动力学生成的α-Fe对称倾斜晶界的基础上,通过中心对称参数和原子密度信息构造出晶界特征—积累中心对称参数,提出了数据增强和按倾斜角分层抽样的方法,建立了预测晶界能的卷积神经网络模型.测试集结果表明,预测晶界能的平均相对误差小于1.75%,平均每个晶界的预测用时在0.002 s以内.该方法在一定范围内具有较高的准确性和鲁棒性,提供了研究晶界的微观结构特征与宏观性能之间关联的途径.     

扫描热显微镜测量机理的研究

从理论上分析了扫描热显微镜的传热过程和测量原理,建立了两种工作模式下的热阻网络模型,并对热阻网络中各热阻进行了具体分析,得出了样品本身热阻的表达式;用多种参考材料样品进行了系列实验,结果表明仪器的输出信号与热导率的倒数成线性关系,对理论分析作出了部分验证,为亚微米尺度的热导率测试打下了基础。     

铜（001）扭转晶界能的原子级计算

采用改进分析型嵌入原子法（MAEAM）计算了铜（001）未松弛扭转晶界的晶界能。结果表明，除扭转角为（完整晶体）时的能量为零外，对应和扭转角为36.87°时的晶界能为最小，和实验结果一致；对于其它扭转角，包括很小的扭转角1.94°，晶界能几乎为一常数；均匀膨胀和垂直于晶界面的膨胀都会使晶界能明显降低，尤其是后者。     

碳纤维与热沉间接触热阻随温度变化的实验研究

由于微纳米材料特征尺寸小,难以测量其与热沉间的接触热阻。本文利用拉曼光谱测量不同温度下单根PAN基碳纤维的热导率及其与导电银胶、焊锡和硅油间的接触热阻。结果表明,在实验温度范围内其热导率随温度的降低而增大;接触热阻随温度的变化规律与接触物质有关。     

Significant decrease in interfacial energy of grain boundary through serrated grain boundary transition

The mechanism of serrated grain boundary formation and its effect on liquation behaviour have been studied in a wrought nickel-based superalloy – Alloy 263. It was newly discovered that grain boundaries are considerably serrated in the absence of γ?′-phase or M₂₃C₆ at the grain boundaries. An electron energy-loss spectroscopy study suggests that serration is triggered by the discontinuous segregation of C and Cr atoms at grain boundaries for the purpose of relieving the excessive elastic strain energy. The grain boundaries serrate to have specific segments approaching one {111} low-index plane at a boundary so that the interfacial free energy of the grain boundary can be decreased, which may be responsible for the driving force of the serration. The serrated grain boundaries effectively suppress grain coarsening and are highly resistant to liquation due to their lower wettability resulting from a lower interfacial energy of the grain boundary.     

A two-channel model for transport across high T c bicrystal grain boundary junctions

This paper describes an investigation of the microscopic configuration of the barrier which exists at the boundary in high T _c grain boundary junctions. A model for describing the properties of bicrystal and biepitaxial grain boundary junctions is proposed. Two channels for transport currents are assumed, the supercurrent being carrier by one channel only. The measurable macroscopic parameters of a junction, (critical current density and normal state resistance) are computed in terms of the microscopic parameters that appear in this model. The model well describes major features of the characteristics observed for high T _c bicrystal junctions.     

考虑界面散射的金属纳米线热导率修正

理论分析了声子和电子输运对Cu, Ag金属纳米线热导率的贡献. 采用镶嵌原子作用势模型描述纳米尺寸下金属原子间的相互作用, 应用平衡分子动力学方法和Green-Kubo函数模拟了金属纳米线的声子热导率; 采用玻尔兹曼输运理论和Wiedemann-Franz定律计算电子热导率; 并通过散射失配模型和Mayadas-Shatzkes模型引入晶界散射的影响. 在此基础上, 考察分析了纳米线尺度和温度的影响. 研究结果表明: Cu, Ag纳米线热导率的变化规律相似; 电子输运对金属纳米线的导热占主导地位, 而声子热导率的贡献也不容忽视; 晶界散射导致热导率减小, 尤其对电子热导率作用显著; 纳米线总热导率随着温度的升高而降低; 随着截面尺寸减小而减小, 但声子热导率所占份额有所增加. 关键词： 纳米线 热导率 表面散射 晶界散射     

The effect of surface contact conditions on grain boundary interdiffusion in a semi-infinite bicrystal

The Kirkendall effect is conditioned by active diffusion as well as by active sources and sinks for vacancies. In the case of grain boundaries under the condition of negligible bulk diffusion, the Kirkendall effect is highly localized and responsible for the formation of an extra material wedge in the grain boundary, which may lead to high stress concentrations. The Kirkendall effect in grain boundaries of a binary system is described by a set of partial differential equations for the mole fraction of one of the diffusing components and for the stress component normal to the grain boundary completed with the respective initial and boundary conditions. The contact conditions of the grain boundary with the surface layer acting as source of one of the diffusing components can be considered as equilibrium ones ensuring the continuity of generalized chemical potentials of both diffusing components. Thus, the boundary conditions are determined by the difference in chemistry (i.e. how the thermodynamic parameters depend on chemical composition) of the grain boundaries and of the surface layer. The simulations based on the present model indicate a drastic influence of the chemistry on the grain boundary interdiffusion and Kirkendall effect.     

Critical current density behaviors across a grain boundary inclined to current with different angles in YBa_2Cu_3O_(7-δ) bicrystal junctions

The critical current density behaviors across a bicrystal grain boundary(GB) inclined to the current direction with different angles in YBa_2Cu_3O_(7-δ) bicrystal junctions in magnetic fields are investigated.There are two main reasons for the difference in critical current density in junctions at different GB inclined angles in the same magnetic field:(i) the GB plane area determines the current carrying cross section;(ii) the vortex motion dynamics at the GB affects the critical current value when the vortex starts to move along the GB by Lorentz force.Furthermore,the vortex motion in a bicrystal GB is studied by investigating transverse(Hall) and longitudinal current–voltage characteristics(I–V_(xx) and I–V_(xy)).It is found that the I–V_(xx) curve diverges from linearity at a high driving current,while the I–V_(xy) curve keeps nearly linear,which indicates the vortices inside the GB break out of the GB by Lorentz force.     

Simulation of grain boundary effect on characteristics of ZnO thin film transistor by considering the location and orientation of grain boundary

The grain boundaries (GBs) have a strong effect on the electric properties of ZnO thin film transistors (TFTs). A novel grain boundary model was developed to analyse the effect. The model was characterized with different angles between the orientation of the grain boundary and the channel direction. The potential barriers formed by the grain boundaries increase with the increase of the grain boundary angle, so the degradation of the transistor characteristics increases. When a grain boundary is close to the drain edge, the potential barrier height reduces, so the electric properties were improved.     

Different effects of grain boundary scattering on chargeand heat transport in polycrystalline platinum and goldnanofilms

The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen (77K) and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann--Franz law. We build an electron relaxation model based on Matthiessen's rule to analyse the thermal conductivity and employ the Mayadas & Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann--Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.     

Grain boundary interdiffusion in the case of concentration-dependent grain boundary diffusion coefficient

The grain boundary diffusion in a binary system which exhibits a grain boundary phase transition is considered in the framework of Fisher's model. The kinetic law of the growth of the grain boundary phase and the distribution of the diffusant near the grain boundary are calculated. The method of determining of the concentration dependence of the grain boundary diffusion coefficient from the experimentally measured penetration profiles of the diffusant along the grain boundaries is suggested. The experimental results on Zn diffusion in Fe(Si) bicrystals, Ni diffusion in Cu bicrystals and grain boundary grooving in Al in the presence of liquid In are discussed in light of the suggested model.