β-碳化硅/碳纳米管核壳结构的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了β-碳化硅/(15, 0) 碳纳米管和β-碳化硅/(16, 0)碳纳米管核壳结构的电子结构特性. 结果表明, 两种核壳异质结构都呈现出金属性, 它们的金属性主要是由碳纳米管和碳化硅纳米线表面的原子所贡献的. 碳化硅纳米线表面呈现的金属性由其结构本身决定, 而对于金属性的 (15, 0) 和半导体性的 (16, 0) 碳纳米管在填充碳化硅纳米线之后都表现出金属性, 主要是由于碳纳米管和碳化硅纳米线之间的电荷转移导致的, 而并不是由于碳纳米管形变造成的. 关键词： 核壳结构 电子结构 第一性原理     

(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.     

第一原理研究界面弛豫对InAs/GaSb超晶格界面结构、能带结构和光学性质的影响

通过广义梯度近似的第一原理全电子相对论计算, 研究了不同界面类型InAs/GaSb超晶格的界面结构、电子和光吸收特性. 由于四原子界面的复杂性和低对称性, 通过对InAs/GaSb超晶格进行电子总能量和应力最小化来确定弛豫界面的结构参数. 计算了InSb, GaAs型界面和非特殊界面(二者交替)超晶格的能带结构和光吸收谱, 考察了超晶格界面层原子发生弛豫的影响.为了证实能带结构的计算结果, 用局域密度近似和Hartree-Fock泛函的平面波方法进行了计算. 对不同界面类型InAs/GaSb超晶格的能带结构计算结果进行了比较, 发现界面Sb原子的化学键和离子性对InAs/GaSb超晶格的界面结构、 能带结构和光学特性起着至关重要的作用.     

六角蜂窝结构光子晶体异质结带隙特性研究

利用蜂窝结构光子晶体具有两个范围较大绝对带隙的特性，设计新型六角蜂窝结构光子晶体异质结，采用平面波展开和超晶胞相结合的方法来研究异质结的能带结构特性.给出异质结的结构和相应的能带图，分析异质结界面传导模，研究两侧结构作横向拉开和侧向滑移时对传导模的影响，讨论这些结构的实际可行性.计算结果表明，没有任何晶格移动，此种结构异质结在绝对带隙中就有导模存在，两边晶格横向拉开对导模影响较大，而侧向滑移的影响则较小. 关键词： 光子晶体 异质结 光子带隙 超晶胞     

(InAs)1/(GaSb)1超晶格原子链的第一原理研究

利用第一原理平面波赝势法, 对(InAs)₁/(GaSb)₁超晶格原子链的原子结构、力学特性、电子能带结构、 声子结构和光学特性进行研究, 并结合密度泛函理论数值原子轨道赝势法和非平衡格林函数法计算量子输运特性. 与二维层结构的(InAs)₁/(GaSb)₁超晶格相比, (InAs)₁/(GaSb)₁超晶格原子链的能带结构有明显不同, 在某些情况下表现为金属能带特性. 对理想条件下(InAs)₁/(GaSb)₁ 超晶格原子链的力学强度计算表明, 该结构可承受的应变高达 ε=0.19. 通过对声子结构的完整布里渊区分析, 研究了(InAs)₁/(GaSb)₁超晶格原子链的结构稳定性. 对两端接触电极为Al纳米线的InAs/GaSb超晶格原子链的电子输运特性计算表明, 电导随链长和应变的改变而发生非单调变化.光吸收谱的计算结果表现出在红外波段具有陡峭吸收边, 截止波长随超晶格原子链的结构而变化.预计InAs/GaSb超晶格原子链可应用于红外光电子纳米器件, 通过改变超晶格原子链的结构来调节光电响应波段.     

六角氮化硼(h-BN)对单层硒化铟(InSe)的调制效应及这一新结构的电子性质

采用基于密度泛函理论的第一性原理计算和分析了三种InSe/h-BN异质结的结构和电子性质.研究发现InSe/h-BN异质结具有间接带隙特点,并且价带顶和导带底的贡献均来自于InSe,差分电荷密度表明体系中没有明显的电荷交换.通过体系能带结构,我们发现h-BN层对单层InSe有着明显的调控效应.对比纯粹应变调控下单层的InSe的能带结构,发现h-BN对InSe能带结构的调控效应实际上是由InSe和h-BN之间的相互作用而诱导的晶格应变引起的.我们的研究结果表明,单层InSe沉积或生长在不同h-BN片上可以获得不同的晶格应变,实现对单层InSe能带结构的有效调控.     

生长在Si(OO1)衬底上的超晶格(Si_2)_4/(GaAs)_4的电子能带结构及光学性质

按照Peressi等的第一性原理赝势计算得到的原子几何构形及能带边不连续值,采用紧束缚方法计算了生长在Si(001)衬底上的超晶格(Si_2)_4/(GaAs)_4的电子能带结构及光跃迁振子强度.相应于两种不同的原子几何构形:X端界面及Y端界面情况,超晶格具有不同的基本带隙.但是不管哪种情况,它们都存在能量近乎简并的两类导带底能谷——Γ能谷及△能谷,它们的价带顶都处在Γ点.X端界面超晶格的价带顶附近的状态主要由GaAs层的价态波函数组成.对于Y端界面超晶格的价带顶附近的状态,Si层和GaAs层的价态波函数     

多壳层铜纳米线结构和电子特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,系统地研究了多壳层Cu纳米线的稳定结构和电子特性.得到不同线径多壳层Cu纳米线的平衡态晶格常数相差不大,都表现出金属特性,且其单原子平均结合能和量子电导随着纳米线直径的增加而增加.纳米线中内壳层Cu原子表现出体相结构Cu原子相似的电子特性,而表面壳层由于配位数的减少,其3d态能量范围变窄且整体向费米能级发生移动.电荷密度分析表明,相对于体相Cu晶体中原子间的相互作用,纳米线表面壳层Cu原子与其最近邻原子间的相互作用明显增强.     

AlN/InN和AlN/GaN超晶格能带结构研究

利用Krönig-Penney 模型和形变势理论,从理论上探讨了纤锌矿型AlN/InN和AlN/GaN超晶格系统的能带结构及不同应变模式对能带结构的影响,计算得到了能带结构随各亚层参量变化的一般性规律、超晶格的能量色散关系、应变造成的影响以及不同亚层厚度的系统禁带宽度和导带第一子禁带宽度.研究发现,通过改变亚层厚度可以从不同形式设计能带结构,应变会改变系统禁带宽度,使带阶和子能带明显窄化,价带结构趋于复杂甚至生成准能带结构.与实验结果对比后发现,该模型适于模拟窄势阱结构超晶格,而对于宽势阱则必须 关键词： AlN/InN和AlN/GaN超晶格 Krönig-Penney模型 应变 子能带     

石墨烯莫尔超晶格的晶格弛豫与衬底效应

当两个晶格常数不同或具有相对转角的二维材料叠加在一起时,可形成莫尔超晶格结构,其电学性质对层间堆垛方式、旋转角度和衬底具有很强的依赖性.例如,双层石墨烯的旋转角度减小到一系列特定的值(魔角)时,体系的费米面附近出现平带,电子-电子相互作用显著增强,出现莫特绝缘体和非常规超导量子物态.对于具有长周期性的莫尔超晶格体系,层间相互作用所引起的晶格弛豫会使原子偏离其平衡位置而发生重构.本文主要围绕晶格自发弛豫和衬底对石墨烯莫尔超晶格物性的影响展开综述.从理论和实验的角度出发,阐述旋转双层石墨烯、旋转三层石墨烯、以及石墨烯与六方氮化硼堆垛异质结等体系中自发弛豫对其能带结构和物理性质的影响.最后,对二维莫尔超晶格体系的研究现状进行总结和展望.     

真空热蒸发制备CdS/ZnS核/壳异质结纳米线

将传统的真空热蒸发镀膜实验加以改进,先以催化剂辅助蒸发制备出CdS纳米线,再将其作为模板,以ZnS为蒸发源物质,二次蒸发包覆ZnS层,成功制备出大量的CdS/ZnS核/壳异质结纳米线.经X射线衍射、X射线能量色散谱、透射电镜分析表明,所得CdS/ZnS异质结纳米线的核心部分为CdS单晶纳米线,外层为ZnS多晶层.本文的实验方法简便易行,所得纳米结构在光电纳米器件领域有一定应用前景.     

The stability and electronic properties of wurtzite and zinc-blende ZnS nanowires

The stability and electronic properties of the pristine wurtzite (WZ) and zinc-blende (ZB) structural ZnS nanowires are investigated and compared by using first-principles approaches. It shows that the WZ-ZnS nanowire is more stable energetically than the ZB-ZnS nanowire. The two kinds of ZnS nanowires have different electronic properties due to both the quantum confinement effect and the surface effect. The band gaps of pristine WZ nanowires become larger than that of the corresponding bulk ZnS, while those of ZB nanowires are smaller. The electronic properties of the hydrogen-passivated WZ-ZnS and ZB-ZnS nanowires are further calculated. The underlying physical reason for their energetic and electronic structures is elucidated.     

镓掺杂氧化锌和硫化锌电子结构差异的第一性原理

运用第一性原理进行了相关计算研究Ga掺杂的ZnO和ZnS的电子结构的差异. 结果表明,LDA和LDA+U计算的结果在定性上是一致的. 掺杂Ga以后,ZnO和ZnS的费米能级处均出现杂质态. 掺杂中的ZnO,杂质态在导带是离域的. 掺杂后的ZnS,虽然p态比较离域,但其s态在费米能级处却是局域的. 前线轨道的电荷密度分布也给出了相同的信息. 交换ZnO和ZnS的晶格结构,结果不变. 局域化的Ga-s态是导致掺杂ZnS电学性能差的原因.     

Electronic structure of twinned ZnS nanowires

The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs.     

First-principles study of the electronic and optical properties of ZnO nanowires

The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.     

Electrical characteristics and optoelectronic properties of metal--semiconductor--metal structure with zinc oxide nanowires across Au electrodes

This paper reports on a method of assembling semiconducting ZnO nanowires onto a pair of Au electrodes to construct a metal--semiconductor metal （MSM） structure by dieleetrophoresis and studying on its electrical characteristics by using current-voltage （Ⅰ - Ⅴ） measurements. An electronic model with two back to back Sehottky diodes in series with a semiconductor of nanowires was established to study the electrical transport of the MSM structures. By fitting the measured Ⅰ - Ⅴ characteristics using the proposed model, the parameters of the Schottky contacts and the resistance of nanowires could be acquired. The photoelectric properties of the MSM structures were also investigated by analysing the measurements of the electrical transports under various light intensities. The deduced results demonstrate that ZnO nanowires and their Schottky contacts with Au electrodes both contribute to photosensitivity and the MSM structures with ZnO nanowires are potentially applicable for photonic devices.     

ZnO and ZnS Nanostructures: Ultraviolet-Light Emitters,Lasers, and Sensors

ZnO and ZnS, well-known direct bandgap II–VI semiconductors, are promising materials for photonic, optical, and electronic devices. Nanostructured materials have lent a leading edge to the next generation technology due to their distinguished performance and efficiency for device fabrication. As two of the most suitable materials with size- and dimensionality-dependent functional properties, wide bandgap semiconducting ZnO and ZnS nanostructures have attracted particular attention in recent years. For example, both materials have been assembled into nanometer-scale visible-light-blind ultraviolet (UV) light sensors with high sensitivity and selectivity, in addition to other applications such as field emitters and lasers. Their high-performance characteristics are particularly due to the high surface-to-volume ratios (SVR) and rationally designed surfaces. This article provides a comprehensive review of the state-of-the-art research activities in ZnO and ZnS nanostructures, including their syntheses and potential applications, with an emphasis on one-dimensional (1D) ZnO and ZnS nanostructure-based UV light emissions, lasers, and sensors. We begin with a survey of nanostructures, fundamental properties of ZnO and ZnS, and UV radiation–based applications. This is followed by detailed discussions on the recent progress of their synthesis, UV light emissions, lasers, and sensors. Additionally, developments of ZnS/ZnO composite nanostructures, including core/shell and heterostructures, are discussed and their novel optical properties are reviewed. Finally, we conclude this review with the perspectives and outlook on the future developments in this area. This review explores the possible influences of research breakthroughs of ZnO and ZnS nanostructures on the current and future applications for UV light–based lasers and sensors.     

Control of the shell structure of ZnO–ZnS core-shell structure

Nanostructured ZnO–ZnS core-shell powders were synthesized through a solution method using a thioacetamide (TAA) solution in deionized water. ZnO powder and TAA solution were employed to supply zinc and sulfur ions to form the ZnO–ZnS core-shell structures. The structure of the ZnS shell was strongly affected by the mole concentration of the TAA, and the structural properties were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The optical properties of the nanostructured powders were also compared with those of pure ZnO powder. The ultraviolet (UV) emission was greatly enhanced compared to when pure ZnO powder was used in the nanostructured powder synthesized using the 0.5 M TAA solution, while the UV emission of that with the 0.05 M TAA solution was reduced. The green emission of the nanostructured powders was reduced compared to when the pure ZnO powder was used. The mechanism of the structural changes in the core-shell structures is proposed here and its effect on the luminescent properties is discussed.     

Novel photoluminescence properties of InAlO3（ZnO）m superlattice nanowires

One-dimension InAlO 3 (ZnO) m superlattice nanowires were successfully synthesized via chemical vapor deposition.Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the 0001 direction.The photoluminescence properties of InAlO 3 (ZnO) m superlattice nanowires are studied for the first time.The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states.The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region.A new luminescence mechanism is proposed,combined with the special energy band structure of InAlO 3 (ZnO) m.