新型功能化合物的晶体结构和电子能量损失谱研究

本文深入研究了六方层状结构钴氧化物中的层间阳离子排列,电荷/轨道序和金属超导体NbB2中的电子能量损失谱,阐述了现代透射电子显微镜(TEM)技术和电子能量损失谱在功能化合物研究领域的应用.基于MxCoO2(M=Na,Sr或Ca)化合物的TEM结构分析,总结给出了反映这种层状结构化合物中阳离子含量和结构特性关联的相图.以Na0.5CoO2材料作为研究主体,系统分析了材料结构随温度的变化,并对Na离子有序和结构相变进行了深入探讨.在100 K到20 K温度区间观测到了两个超结构相,其基本特性可以用电荷/轨道有序模型很好地解释.NbB2是典型的层状超导体,电子能量损失谱表现出很强的各向异性.结合第一性原理计算对其电子结构和电子能量损失谱的特性进行了仔细分析,获得了费米能级附近B的2p轨道未占据态信息.在这些实验和理论结果的基础上,系统分析了六方层状钴氧化物中结构相变和物理性能的关联,并对NbB2和MgB2超导材料电子结构区别进行了讨论.     

介电函数及其在电子能量损失谱低能区分析的应用

一、前言:电子能量损失谱学(EELS或ELS)是研究电子激发的一次过程。一幅电子能量损失谱大致可分为三个区域:零损失区、低能损失区(5～50eV)和高能损失区(>50eV)。对各谱区进行细致的分析研究、可获得与样品化学成分或电子结构有关的信息。利用电子能量损失谱低能区研究固体的电子结构、引起物理和电子显微学界的关注。因为它不仅能提供固体的电子结构信息、还能在同一台仪器上研究固体的微区晶体结构、成分和形貌。但在电子能量损失谱5～50eV的低能区很难直接确定有关电子结构方面的信息。这是由于在该区等离子激发占主导地位、而外     

NaxCoO2·yH2O体系的高分辨电子能量损失谱和电子结构研究

本文通过高分辨电子能量损失谱(EELS)的实验分析与密度泛函计算相结合的方法,研究了NaxCoO2·yH2O系统的电子结构特性和电子关联效应.实验结果表明,金属性Na0.3CoO2材料和电荷有序绝缘体Na0.5CoO2的O-K吸收边存在明显的结构差别,在Na0.5CoO2的EELS中第一个峰发生明显分裂,密度泛函计算证实这种分裂现象和电子关联效应直接相关.通过理论模拟谱线与实验谱线的比较确定了其电子关联强度为U=3.0 eV.在Na0.3CoO2·yH2O(y=0,0.6,1.3)超导体系中,实验发现其能损谱的低能部分随着水含量的增加发生系统的变化,损失峰向低能量方向逐步移动.电子结构计算表明水分子的插入可以引起费米面附近能态原子轨道杂化情况的改变,从而导致EELS的变化.     

幻角和线性二向色性电子能量损失谱技术

很多重要的材料具有各向异性的电子结构。由于低对称性的空态电子结构的存在，它们的电子能量损失谱对样品的取向敏感，其敏感程度受到其他实验条件(如电子束的会聚角和散射电子的接收角)的调控。通过研究电子能量损失谱对方向的依赖性以及受实验条件影响的机制，可以通过合理的     

电子能量损失谱在类金刚石碳膜结构表征中的应用

本文先介绍了类金刚石碳膜的结构特点及电子能量损失谱的原理和分类;然后着重评述了近年来电子能量损失谱在类金刚石碳膜(及有些金刚石膜)结构表征中的应用;同时也讨论了类金刚石碳膜经某些后处理后其能量损失谱的变化特征。     

电子能量损失谱低能谱区的分析和应用

本文讨论电子能量损失谱低能谱区的分析及其在研究固体材料电子结构方面的应用。作为实例,给出了Bi_2Sr_2CaCu_2O_8高温超导体的体等离子色散试验结果和YBa_2Cu_3O_(7-x)高温超导体的电子能量损失谱低能谱区的计算机拟合分析试验结果。     

基于自适应陷波器的电子能量损失谱能量漂移的消除方法

电子能量损失谱是透射电子显微术中一种重要的分析手段,它可以帮助人们从纳米尺度上认识材料的电子结构等信息。但电子能量损失谱仪特别容易受到周围环境因素的影响,比如说固定工频干扰,而产生电子能量损失谱能量的漂移。本文结合串行快响应能谱探测器和自适应陷波器手段,提出了一种消除电子能量损失谱中能量漂移的方法,实验结果表明这种方法能够有效消除电子能量损失谱中由于固定工频干扰所造成的能量漂移。     

高温超导体Bi2Sr2CaCu2O8电子能量损失谱研究

自从发现高温超导体以来,对它的导电机理及电子结构研究引起了人们广泛的兴趣。本文用电子能量损失谱(EELS)研究了Bi_2Sr_2CaCu_2O_8超导体的价电子结构,能量损失函数及介电函数,计算了其它各种光学常数。实验过程为将烧结超导样品在盛有CCl_4的玛璃研钵中研碎,然后将其滴于由铜网支持的微孔碳膜上。实验在装备有GATAN-666同时检测电子能量损失谱仪     

用高分辨电子能量损失谱和紫外光电子谱研究多孔硅的电子结构

本文首次使用分辨电子能量损失谱（ＨＲＥＥＬＳ）和紫外光电子能谱（ＵＰＳ）研究新腐蚀的多孔硅样品（ＰＳ）的电子结构．实验结果发现，从ＨＲＥＥＬＳ谱中能量损失阈值测得的多孔硅的能隙最可几值移到２．９ｅＶ左右，与文献报道的光激发谱（ＰＬＥ）的结果相近．ＵＰＳ结果发现多孔硅费米能级到价带顶的距离不同于单晶硅，结合ＨＲＥＥＬＳ和ＵＰＳ结果可以初步得出多孔硅与硅界面的能带排列．     

用HREELS和UPS研究多孔硅的电子结构

使用高分辨电子能量损失谱(HREELS)和紫外光电子能谱(UPS)研究了新腐蚀的多孔硅(PS)样品的电子结构。实验结果表明,从HREELS谱中能量损失阚值测得的PS的能隙移到2．9eV,与文献报道的光激发谱(PLE)结果相近。UPS结果表明PS的费米能级到价带顶的距离不同于单晶Si。结合HREELS和UPS结果可以初步得出PS与Si界面的能带排列。     

Structural,electronic,magnetic and optical properties of neodymium chalcogenides using LSDA+U method

正We have studied the electronic,magnetic and optical properties of neodymium chalcogenides by performing LSDA+U and full potential linearized augmented plane wave(FP-LAPW) method.The electronic structure calculation shows that the electronic states in Nd-chalcogenides were mainly contributed by Nd-4f electrons near Fermi energy and 3p,4p and 5p state electrons of X(S,Se and Te),respectively.We have also studied the absorption of light via the imaginary parts of the dielectric function of Nd-chalcogenides.     

Electronic transfer from aluminum into the core of gold nanoparticles capped with conjugated 2-naphthalenethiol

The electronic contact between a bulk metal and metal nanoparticles can be significantly different from that between two bulk metals due to the unique electronic structure in the nanometer size. In this work, the electronic contact between Au nanoparticles and Al is studied by X-ray photoelectron spectroscopy. Al is deposited on a layer of Au nanoparticles capped with conjugated 2-naphthalenethiol (Au-2NT NPs) in high vacuum by e-beam deposition at room temperature. The Au 4f X-ray photoelectron spectrum (XPS) significantly changes after the Al deposition. New XPS bands with higher binding energy appear. The angle dependence of the Au 4f XPS bands indicates that the electron transfer takes place at the contact between Al and Au-2NT NPs. In contrast, the Al deposition hardly changes the Au 4f XPS spectrum for Au nanoparticles capped with saturated 1-dodecanethiol. The effect of the Al deposition on the Au 4f XPS spectrum of Au nanoparticles capped with 2-naphthalenethiol is attributed to the electron transfer from Al through the conjugated 2-naphthalenehiol into the core of Au nanoparticles, as the Fermi energy of Al is higher than Au. This understanding on the contact between metal and metal nanoparticles provides guidance for the development of novel electronic devices.     

Structural, electronic, magnetic and optical properties of neodymium chalcogenides using LSDA+U method

We have studied the electronic,magnetic and optical properties of neodymium chalcogenides by performing LSDA+U and full potential linearized augmented plane wave (FP-LAPW) method.The electronic structu...     

垂直电场作用下的钎锌矿相GaN电子输运特性的Monte Carlo研究

在GaN NMOSFET中,沟道电子由于受垂直于其运动方向电场的作用而产生界面散射,从而影响MOSFET特性.研究采用Monte Carlo体模拟方法计算钎锌矿相GaN材料在界面散射下的电子输运特性.模拟中在电子漂移方向加一个水平电场,同时在与其垂直的方向加另外一个电场,在垂直电场作用下,电子发生界面散射.采用基于指数...     

The electron transport properties in a three-barrier structure based on monolayer graphene

Using the transfer matrix method, we theoretically investigate the electron transport properties in a three-barrier structure based on monolayer graphene. The numerical results show that the transmission probability and the conductance strongly depend on the barrier height, the barrier width and the incident energy as well as the incident angle of carriers. Therefore, by changing the configuration of the structure, the electron transport properties can be adjusted to be suitable for the practical application in various graphene-based electronic devices such as the graphene-based transistor with the high on/off ratio and the direction-dependent wave vector filter.     

Effect of warpage on the electronic structure and optical properties of bilayer germanene

The electronic structure and optical properties of bilayer germanene under different warpages are studied by the first-principles method of density functional theory. The effects of warpages on the electronic structure and optical properties of bilayer germanene are analyzed. The results of the electronic structure study show that the bottom of the conduction band of bilayer germanene moves to the lower energy direction with the increase of warpages at the K point, and the top of the valence band stays constant at the K point, and so the band gap decreases with the increase of warpage. When the warpage is 0.075 nm, the top of the valence band of bilayer germanene changes from K point to G point, and the bilayer germanene becomes an indirect band gap semiconductor. This is an effective means to modulate the conversion of bilayer germanene between direct band gap semiconductor and indirect band gap semiconductor by adjusting the band structure of bilayer germanene effectively. The study of optical properties shows that the effect of warpage on the optical properties of bilayer germanene is mainly distributed in the ultraviolet and visible regions, and the warpage can effectively regulate the electronic structure and optical properties of bilayer germanene. When the warpage is 0.069 nm, the first peak of dielectric function and extinction coefficient is the largest, and the energy corresponding to the absorption band edge is the smallest. Therefore, the electron utilization rate is the best when the warpage is 0.069 nm.     

Realization of Wurtzite GaSb Using InAs Nanowire Templates

The crystal structure of a material has a large impact on the electronic and material properties such as band alignment, bandgap energy, and surface energies. Au‐seeded III–V nanowires are promising structures for exploring these effects, since for most III–V materials they readily grow in either wurtzite or zinc blende crystal structure. In III–Sb nanowires however, wurtzite crystal structure growth has proven difficult. Therefore, other methods must be developed to achieve wurtzite antimonides. For GaSb, theoretical predictions of the band structure diverge significantly, but the absence of wurtzite GaSb material has prevented any experimental verification of the properties. Having access to this material is a critical step toward clearing the uncertainty in the electronic properties, improving the theoretical band structure models and potentially opening doors toward application of this material. This work demonstrates the use of InAs wurtzite nanowires as templates for realizing GaSb wurtzite shell layers with varying thicknesses. The properties of the axial and radial heterointerfaces are studied at the atomic scale by means of aberration‐corrected scanning transmission electron microscopy, revealing their sharpness and structural quality. The transport characterizations point toward a positive offset in the valence bandedge of wurtzite compared to zinc blende.     

Consequences of structural disorder on laser properties in quantumwire lasers

The effect of interface-roughness-related disorder on the electronic and optoelectronic properties of a quantum wire structure are studied. It is seen that the disorder causes strong localization in the quasi-one-dimensional system. While the electronic states are seriously perturbed, the density of states is not affected drastically. Optoelectronic properties as reflected in the interband transition related phenomenon are not found to suffer significant deterioration as a result of the disorder. However, the results suggest that intraband relaxation processes may be seriously affected because of electron (hole) states being localized in different regions of the wire     

A DFT study on ternary compounds of GaAlAs and InAlAs nanoclusters

The realistic structures such as hexagonal ring, hexagonal sheet, ladder and cube isomers of GaAlAs and InAlAs are designed and optimized using density functional theory. The hexagonal ring structure is found to be more stable from the calculated energy. The dipole moments of GaAlAs and InAlAs nanoclusters are reported and hexagonal ring of GaAlAs and ladder structure of InAlAs nanoclusters are found to have a high dipole moment. The point symmetry of GaAlAs and InAlAs nanoclusters has either C₁ or C_s symmetry. The HOMO–LUMO gap provides an insight into the transition of the electron for different isomers of GaAlAs and InAlAs clusters. The electron density depends on the geometry of the cluster. The electronic properties are discussed in terms of ionization potential and electron affinity. The hexagonal sheet isomer has the high value of IP and EA due to its geometry. The cube structured GaAlAs and InAlAs nanoclusters have the highest binding energy. The embedding energy is found to be low for GaAlAs and InAlAs hexagonal sheet isomers. The vibrational studies identify the stable clusters of GaAlAs and InAlAs nanoclusters. The result of the present work will give insight into tailoring and improving the electronic properties of GaAlAs and InAlAs nanoclusters which find their importance in optoelectronic devices.     

Electronic Interpretation of Interlayer Energy Landscape in Layered Materials

The interlayer energy landscape of layered materials is essential to disassemble their structure–property relationships. However, a clear definition of interlayer electronic coupling that generally rules the interlayer energy landscape for their outstanding electronic and tribological properties, remains a matter of debate. Herein, diverse methods for electron coupling are evaluated to discriminate their feasibility to interpret interlayer sliding energy landscape for frictional sliding or stacking faults, by using density functional theory calculation of the layered models in the case of transition metal dichalcogenides (TMDs). It is discovered that the charge density evolution in dynamic stacking configurations dictates the interlayer energy landscape along the sliding pathway, challenging the prevailing belief that the energy corrugation arises from the nonuniform distribution of charge density or the charge density in the interface region. The present studies may open the way to disassemble the electron coupling principle underlying interlayer energy landscape for structure–property relationships as stacking faults, registry effects, even superlubric behavior in layered structures.