电化学沉积Fe单晶纳米线生长中的取向控制

利用电化学沉积方法，发现了一种能够动态地控制铁纳米线生长方向的沉积方法，利用该方法沉积了包括［110］取向，［200］取向及非晶态三种结构和取向的一维Fe纳米线阵列.对于三种纳米线阵列，测量了它们的磁特性，分析发现具有[200]择优取向纳米线阵列的方形度，各向异性特性和矫顽力都比[110]取向阵列有很大的改善. 关键词： 磁性纳米线 电化学沉积 取向控制     

The elastic properties and energy characteristics of Au nanowires: an atomistic simulation study

This paper have performed molecular static calculations with the quantum corrected Sutten Chen type many body potential to study size effects on the elastic modulus of Au nanowires with [100], [110] and [111] crystallographic directions, and to explore the preferential growth orientation of Au nanowires. The main focus of this work is the size effects on their surface characteristics. Using the common neighbour analysis, this paper deduces that surface region approximately consists of two layer atoms. Further, it extracts the elastic modulus of surface, and calculate surface energy of nanowire. The results show that for all three directions the Young＇s modulus of nanowire increases as the diameter increases. Similar trend has been observed for the Young＇s modulus of surface. However, the atomic average potential energy of nanowire shows an opposite change. Both the potential and surface energy of [110] nanowire are the lowest among all three orlentational nanowires, which helps to explain why Au nanowires possess a [110] preferred orientation during the experimental growth proceeds.     

Anisotropy and temperature dependences of thermal conductivity for silicon nanowires

The anisotropy and temperature dependences of thermal conductivity for silicon nanowires with diameters higher than 50 nm is investigated using the Callaway three-mode model. Contributions to the thermal conductivity from the boundary and bulk mechanisms of phonon scattering are calculated at room temperature. The relationship between the thermal conductivity and nanowire diameter is analyzed in symmetrical directions and at room temperature.     

(InAs)1/(GaSb)1超晶格纳米线第一原理研究

半导体纳米线作为纳米器件的作用区和连接部分具有理想的形状, 把电子运动和原子周期性限制在一维结构当中.通过体材料的已知特性, 有效地选择材料组分使纳米线的低维结构优点更加突出.此外, 还可以通过其他方式来调整纳米线特性, 如控制纳米线直径、晶体学生长方向、结构相、表面晶体学晶面和饱和 度等内部或固有的特性;施加电场、磁场、热场和力场等外部影响. 体材料InAs和GaSb的晶格常数非常相近, 因此InAs/GaSb异质结构晶格失配很小, 可生长成为优良的红外光电子材料.另外, 体材料InAs在二元III---V化合物半导体中具有最低的有效质量, 这使得电子限制在InAs层的InAs/GaSb超晶格具有良好的输运特性. 本文通过第一原理计算研究轴线沿[001]和[111]闪锌矿晶体学方向的 (InAs)₁/(GaSb)₁超晶格纳米线(下标表示分子或双原子单层的数量) 的结构、电子和力学特性, 以及它们随纳米线直径(线径约为0.5---2.0 nm)的变化规律.另外, 分析了外部施加的应力对电子特性的影响, 考察了不同线径(InAs)₁/(GaSb)₁超晶格纳米线的电子带边能级随轴向应变的变化, 从而确定超晶格电子能带的带边变形势.     

Al纳米线不同晶向力学行为和变形机制的模拟

采用分子动力学模拟计算方法,考察具有较高层错能的Al纳米线沿不同晶向的力学行为和变形机制。在相同计算条件下与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线进行比较。结果表明：在力学行为方面,Al纳米线的弹性模量呈现明显的结构各向异性,满足E_[111] > E_[110] > E_[100]的关系,这一关系在FCC金属纳米线中普遍成立;Al纳米线的屈服应力随晶向呈现σ_y[100] > σ_y[111] > σ_y[110]的关系,这一关系在具有较低层错能的FCC金属纳米线中不具有普遍性,这与体系中位错形成机制密切相关。根据拉伸变形过程微观结构的演变规律,阐明Al纳米线不同晶向的变形机制,并与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线的变形机制进行比较。结果表明,对于尺度较小的高层错能Al纳米线,Schmid因子和广义层错能均难以准确预测其变形机制。     

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     

碳纳米管电缆式复合材料的热导率

通过非平衡分子动力学方法, 对单壁碳管填充金纳米线的碳纳米管电缆式复合材料开展热导率的模拟分析. 采用Tersoff势函数描述碳-碳原子间的相互作用, Lennard-Jones长程作用势描述碳-金原子间的相互作用, 嵌入原子势函数描述金-金原子间相互作用. 研究结果表明: 相同尺寸下, 金纳米线的电子热导率相较于空碳管以及电缆式复合材料的声子热导率小很多, 对复合材料总热导率的贡献可以忽略; 由于管内金纳米线的存在, 其与碳管的相互作用使得碳管碳原子倾向于沿着轴向振动, 声子间U散射随之减少, 声子平均自由程增加, 导致复合材料热导率明显大于空碳管, 在100–500 K温度范围内高出约20%–45%, 但增大幅度随温升呈降低趋势; 复合材料热导率随着管长增加而增大, 变化趋势和空碳管相似, 但其增长幅度更大; 复合材料和空碳管的热导率随管径增大而减小, 且变化幅度基本一致. 关键词： 碳纳米管 纳米线 电缆式复合材料 导热     

In-plane anisotropy in two-dimensional electron gas at LaAlO_3/SrTiO_3(110) interface

A systematic study of the two-dimensional electron gas at La AlO_3/SrTiO_3(110) interface reveals an anisotropy along two specific directions, [001] and 1ī0. The anisotropy becomes distinct for the interface prepared under high oxygen pressure with low carrier density. Angular dependence of magnetoresistance shows that the electron confinement is stronger along the 1ī0 direction. Gate-tunable magnetoresistance reveals a clear in-plane anisotropy of the spin–orbit coupling,and the spin relaxation mechanism along both directions belongs to D'yakonov–Perel'(DP) scenario. Moreover, in-plane anisotropic superconductivity is observed for the sample with high carrier density, the superconducting transition temperature is lower but the upper critical field is higher along the 1ī0 direction. This in-plane anisotropy could be ascribed to the anisotropic band structure along the two crystallographic directions.     

(In, Mn)As nanowires with ultrahigh Mn concentration: Growth, morphology and magnetic anisotropy

(In,Mn)As nanowires with ultrahigh Mn concentration have been successfully grown on GaAs(001) substrates by molecular beam epitaxy. The morphology dependences on Mn concentration and growth temperature are investigated. High Mn concentration and high growth temperature are both necessary for the growth of nanowires. All the (In,Mn)As nanowires are self-aligned along [−110]GaAs, and therefore have the shape magnetic anisotropy with the easy axis along the alignment orientation of the nanowires.     

(100)Si基应变p型金属氧化物半导体[110]晶向电导率有效质量双椭球模型

利用应变技术和沟道晶向工程技术,均可有效增强Si基金属氧化物半导体器件的性能.本文提出了(100)Si p型金属氧化物半导体(PMOS)[110]晶向电导率有效质量双椭球模型,从理论上解释了Si PMOS[100]晶向沟道空穴迁移率为[110]晶向沟道空穴迁移率1.15倍的原因.基于(100)Si基应变PMOS反型层E-k关系,拓展应用该模型,首先获得了(100)Si基应变PMOS反型层价带第一子带等能图,然后给出了(100)Si基应变PMOS器件反型层[110]晶向空穴电导率有效质量模型.本文的模型方案合理可行,可为Si基应变PMOS器件的研究与设计提供有价值的参考.     

Formation and growth mechanism of ripple-like AlN nanowires

Single-crystal ripple-like AlN nanowire with tuned diameter was fabricated through direct reaction aluminum with nitrogen by arc discharge method. The nanowires grow along the [0001] direction and have a radial expansion along the [10[`1]0][10\bar{1}0] direction. The periodic variation of the radial expansion toward [10[`1]0][10\bar{1}0] direction produces the ripple-like AlN nanowires. The growth mechanism of the AlN nanowires is discussed by considering the Al adlayer diffusion on the polar (0001) surface.     

磁场对模板法制备的Co纳米线结构和磁性的影响

在用二次氧化法制备的高度有序的氧化铝模板上通过交流电化学方法制备了Co纳米线阵列．研究了外加磁场及电解液pH值对纳米线生长的影响．在pH值为6.0和6.5的电解液中分别在不加磁场和沿纳米线轴向施加0.3 T磁场情况下制备了hcp结构的Co纳米线阵列．实验数据表明,沉积时外加磁场和调节pH值能有效影响纳米线中hcp结构的Co晶粒的易磁化轴沿纳米线长轴方向生长．由于晶粒的磁晶各向异性和纳米线沿长度方向的宏观形状各向异性叠加,制备的Co纳米线阵列具有高垂直各向异性,高矫顽力和较高矩形比． 关键词： Co纳米线阵列 织构 磁性     

Temperature effect on the elastic properties of yttrium garnet ferrite Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript>

The Young’s moduli along the [100] and [110] crystallographic directions and the shear modulus along the [100] direction in a high-purity yttrium garnet ferrite single crystal are measured in the temperature range from 20 to 600°C. All the independent elastic constants are calculated for this temperature range. The behavior of the elastic moduli and elastic anisotropy factor is analyzed in the vicinity of the critical temperature of the magnetic phase transition.     

Nontrivial tensile behavior of rutile TiO<Subscript>2</Subscript> nanowires: a molecular dynamics study

In this paper, we study the tensile behavior of cylindrical rutile TiO₂ nanowires, employing molecular dynamics (MD) simulation technique. The third-generation charge optimized many-body (COMB3) has been used for interatomic potential modeling. The influence of temperature and nanowire diameter on Young’s modulus is investigated. Our simulations exhibit the anisotropic behavior of Young’s modulus as a function of diameter for different crystallographic orientations. Although our results are in good accord with the existing results in [1 0 0] direction, Young’s modulus adds up monotonically with increasing the cross-sectional diameter of nanowire in [0 0 1] direction. It is found that Young’s modulus of the nanowires are lower (higher) than the bulk value for [0 0 1] ([1 0 0]) direction. Furthermore, simulation results also indicate that Young’s modulus of rutile TiO₂ nanowire increases as a function of temperature for a given diameter, unexpectedly. The obtained results may be useful in the field of nanotechnology for optimizing mechanical performance to gain specific applications.     

金属纳米线应力分布特征的原子级模拟研究

运用分子静力学方法结合量子修正Sutten-Chen多体力场研究了Ni纳米线在平衡状态下的应力分布特征,考虑了三种不同取向的纳米线,即轴线方向分别沿［100］,［110］和［111］方向的纳米线.计算的结果表明：由于表面张应力的作用,纳米线在弛豫过程中沿轴线方向长度发生收缩;纳米线从表面向中心区域呈现出由张应力向压应力连续分布的特征.随着纳米线直径的增加,纳米线的表面区域的张应力先上升,然后略有下降,并趋向一个非零的常值;而中心区域的应力则属于压应力,其值随着直径的增加显著地减小,并趋向于零值.无论是轴向 关键词： 纳米线 应力分布 分子静力学     

InAs/GaAs和InAs/InxGa1-xAs/GaAs纳米线异质结构的生长研究

利用金辅助金属有机化学气相沉淀法(MOCVD)在GaAs(111)B衬底上分别制备了InAs/GaAs和InAs/In _{x Ga1-xAs/GaAs(0≤x≤1)纳米线异质结构.实验结果显示,直接生长在GaAs纳米线上的InAs纳米线生长方向杂乱或者沿着GaAs纳米线侧壁向衬底方向生长,生长的含有In x Ga1-xAs组分渐变缓冲段的InAs/In x Ga1-x关键词： 纳米线异质结构 xGa1-xAs')" href="#">InxGa1-xAs 组分渐变缓冲层 金属有机化学气相沉淀法}     

Raman mapping of laser-induced changes and ablation of InAs nanowires

Indium arsenic (InAs) nanowires were irradiated with a focused laser beam, followed by in situ Raman spectroscopy mapping and scanning electron microscopy imaging to investigate the changes of the nanowires due to laser irradiation. It was found that laser irradiation with the power intensity above a certain threshold causes arsenic (As) atoms to disintegrate from InAs and accumulate on the surface of the nanowire; the accumulated As atoms evaporate under the continued laser irradiation. This process reduces the As content in the nanowire. The reduction of As content, in turn, lowers the melting temperature of the nanowire locally and facilitates laser ablation, which eventually fractures the nanowire. The laser irradiation induced changes of the InAs nanowires are attributed to the local temperature rises due to the irradiation, as confirmed by the Raman peak shifts. The results from this work show that in situ Raman spectroscopy mapping can provide detailed information about the entire process of laser-induced change and ablation of InAs nanowires and has the potential to become a powerful tool for the characterization of laser modification of nanowires and other nanometer-sized objects.     

量子局域效应和应力对GaSb纳米线电子结构影响的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法, 研究了不同晶体结构和尺寸的GaSb纳米线能带结构特性和载流子的有效质量, 以及单轴应力对GaSb纳米线能带结构的调控. 研究结果表明: 闪锌矿结构[111]方向和纤锌矿结构[0001]方向的小尺寸GaSb纳米线均出现间接带隙的能带结构, 并可通过单轴应力来实现纳米线能带结构由间接带隙到直接带隙的转变, 其中, 闪锌矿结构[111]方向GaSb纳米线仅在受到单轴拉伸应力时才发生能带由间接带隙到直接带隙的转变, 而纤锌矿结构[0001]方向GaSb纳米线无论受单轴拉伸还是压缩应力的作用均可实现能带由间接带隙到直接带隙的转变; [111]和[0001]方向GaSb纳米线的带隙和载流子有效质量与纳米线直径呈非线性关系, 并随纳米线直径的减小而增大; 同一方向和尺寸的GaSb纳米线, 其空穴有效质量要小于电子有效质量, 这表明小尺寸GaSb纳米线有利于空穴载流子输运.     

Synthesis and characterization of crystalline carbon nitride nanowires

Carbon nitride nanowires were synthesized by thermal nitridation of multiwalled carbon nanotubes in a horizontal tube furnace. Scanning electron microscopy and transmission electron microscopy images revealed the large-scale formation of nanowires. Selected-area electron diffraction images and high-resolution transmission electron microscopy images show that the as-synthesized nanowires grow preferentially along the [110] direction, with diameters of 15 to 100 nm and lengths from several tens of micrometers to several millimeters. Here, the growth mechanism of these nanowires is proposed.     

Unidirectional hexagonal rare-earth disilicide nanowires on vicinal Si(100)-2×1

Rare-earth disilicide nanowires grown on vicinal Si(100) with a miscut of 2–2.5° toward the [110] azimuth at 600 °C were studied by scanning tunneling microscopy and compared with those grown on flat Si(001). In contrast to rare-earth disilicide nanowires grown on flat Si(100) surfaces, the nanowires grow unidirectionally along the [01̄1] direction of the vicinal Si(100) surface. Rare-earth disilicide nanowires form bundles composed of single nanowire units on both flat and vicinal surfaces. Yet, on the vicinal surface, the bundle width is comparable to the width of the terrace. The average nanowire length on the vicinal substrate is longer than that on the flat substrate. Scanning tunneling spectroscopy shows that the rare-earth disilicide nanowires have metallic properties. PACS 81.07.Vb; 81.16.Dn; 68.65.La; 68.37.Ef