As吸附在InP(110)表面电子性质的理论研究

利用形式散射的格林函数方法，研究了As在InP(110)表面不同吸附结构的电子性质.体材料采用实用的经验紧束缚近似方法的哈密顿，分别计算了As-P交换作用和形成外延连续层结构表面态的性质，指出了表面态和表面共振态产生的原因.在计算中，一些表面紧束缚相互作用参数进行了调整，所得结果好于其他理论方法. 关键词：     

室温下InP(100)表面K诱发催化氮化反应的同步辐射光电子能谱研究

利用同步辐射光电子能谱研究了室温下p型InP(100)表面,由于K吸附诱发的催化氮化反应过程。对于N_2/K/InP(100)体系的P2p;In4d芯能级和价带谱的研究表明:碱金属吸附于InP(100)表面可以强烈地影响其在室温下的氮化反应,K的存在极大地提高了N_2在InP(100)表面的粘附系数。由我们的实验结果和碱金属吸附于GaAs(110),InP(110),GaP(110)表面的研究结果可知,碱金属吸附于Ⅲ-V族半导体表面后,可以极大地提高N_2在Ⅲ-V族半导体表面的粘附系数,从而促进Ⅲ-V族半 关键词：     

InGaAs(110)解理面的扫描隧道谱的理论诠释

本工作应用截面扫描隧道显微镜(XSTM)研究了 In_(0.53)Ga_(0.47)As/InP异质结构的(110)解理面.扫描隧道谱(STS)测量结果显示,InGaAs的电流-电压(I-V)隧道谱呈现与衬底InP(110)面完全不同特点.InP的I-V谱呈现的零电流平台宽度(隧道谱表观带隙)接近材料带隙,可基于平带模型解释.In_(0.53)Ga_(0.47)As的表观带隙却比其带隙(室温0.74 eV)高出约50%.这反映了针尖与InGaAs发生隧穿时的不同物理图像,需应用针尖诱导能带弯曲(TIBB)模型来解释.基于三维TIBB模型的计算,我们发现表面态密度是对隧道谱线特征具有敏感影响的参数.适当选取参数不仅能定量解释InGaAs的I-V谱的零电流平台宽度,而且能较准确预言零电流平台的起、止能量位置,并能计算给出与实验高度重合的I-V理论谱线.     

水汽在淀积金属钠的InP()表面的吸附

用UPS和HREELS研究室温下水汽在清洁的和淀积了金属钠的InP(Ⅲ)表面的吸附。表面淀积了0.3单层金属钠之后,水汽在InP(Ⅲ)表面的粘附系数显著增加,推测其原因可能与钠原子和表面的磷原子间的电荷转移有关。水汽主要以不分解的分子态形式吸附在表面。在HREELS谱中观察到与P—H键有关的282meV能量损失峰,表明部分水汽可能与淀积在表面的钠原子发生反应或者在表面发生分解。     

水汽在淀积金属钠的InP(111)表面的吸附

用UPS和HREELS研究室温下水汽在清洁的和淀积了金属钠的InP(111)表面的吸附。表面淀积了0.3单层金属钠之后,水汽在InP(111)表面的粘附系数显著增加,推测其原因可能与钠原子和表面的磷原子间的电荷转移有关。水汽主要以不分解的分子态形式吸附在表面。在HREELS谱中观察到与P—H键有关的282meV能量损失峰,表明部分水汽可能与淀积在表面的钠原子发生反应或者在表面发生分解。 关键词：     

MgO、SnO_2、TiO_2表面氧空位性质对气体光学传感特性的影响

光学气敏传感器是当今研究领域的一个热门方向.文章采用密度泛函理论(DFT)体系下广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析和计算了光学气敏材料岩盐型MgO、金红石型SnO_2和锐钛矿型TiO_2表面氧空位的特性.以CO作为吸附分子进行微观机理研究,研究不同氧化物表面吸附气体分子的机理.对氧化物表面的几何结构、吸附能、态密度、差分电荷密度、电荷布居、电荷转移、光学性质等进行分析.研究发现:含有氧空位缺陷的MgO(001)、SnO_2(110)和TiO_2(101)能稳定的吸附CO分子,吸附后造成了材料光学性质的变化,可作为光学气敏传感材料.分析发现:氧空位氧化能力的大小是光学性质改变的核心原因.表面吸附CO分子后,发现SnO_2(110)表面对分子的吸附能最大,分子与表面的吸附距离最短.通过差分电荷密度和电荷布居数发现,表面与CO分子间存在电荷转移,其转移电子数目大小为:SnO_2(110)TiO_2(101)MgO(001),由此得出不同氧化物表面氧化性的大小为:SnO_2(110)TiO_2(101)MgO(001);通过对比吸收谱和反射谱发现:吸附气体分子后SnO_2(110)表面的光学性质变化最为明显,是一种较好的光学气敏传感材料.     

O在预覆盖K的Ag(110)表面的共吸附及其性质

本文用X射线光电子能谱(XPS),紫外光电子能谱(UPS),电子能量损失谱(EELS)和低能电子衍射(LEED)研究了O与预覆盖K的Ag(110)表面相互作用及其性质。在低覆盖度K下,发现有两种O的吸附态,经鉴别为溶解到表面下的O^2-和表面上吸附的O^x-增加K的覆盖度,出现分子状态的吸附物O₂^δ-,它与表面下存在的K相联系。XPS和UPS均清楚地显示出对应于三种不同吸附态的光电子发射峰。Ag(110)表面预覆盖K后的粘滞系数大大增加。K和O的共吸附引起它们彼此向Ag(110)表面下的溶解。LEED实验结果表明,清洁Ag(110)表面覆盖单层K原子后衍射图形从(1×1)变到(1×2),再吸附O后表面吸附层结构变为(2×1)。另外,结合UPS和EELS测量初步考察了O/K/Ag(110)共吸附系统的电子结构。本文还提出了一个共吸附模型来解释这些现象。 关键词：     

氧在Nb(110)表面吸附的第一性原理研究

通过第一性原理赝势平面波方法研究了氧在Nb(110)表面的吸附性质随覆盖度变化规律. O在Nb(110)表面最稳定吸附位是洞位,次稳定吸附位是长桥位. 在长桥位吸附时, O诱导Nb(110)表面功函数随覆盖度的增加而几乎线性增加;但当O在洞位吸附时, 与干净Nb表面相比, 覆盖度为0.75 ML和1.0 ML时功函数增加, 而覆盖度为0.25 ML和0.5 ML时功函数减小.通过对面平均电荷密度分布和偶极矩变化的讨论, 解释了由吸附导致功函数复杂变化的原因.通过对表面原子结构和态密度分析, 讨论了O在Nb表面吸附时引起表面原子结构变化以及O和Nb(110)表面原子的相互作用.     

软X射线辐照引起的InP表面电子态变化

采用X光电子能谱(XPS)和紫外光电子能谱(UPS)研究了软X射线辐照InP所产生的表面电子态的变化．实验结果表明,软X射线的照射,对In原子影响不大,而对P原子影响很大．分析了InP的辐照效应机理,解释了产生上述影响的原因. 关键词：     

碱金属促进CO在Ag(110)上分解的实验证据

本文用X射线光电子能谱(XPS)和紫外光电子能谱(UPS)研究了CO与预覆盖Ne的Ag(110)表面的相互作用。低温下CO饱和吸附在Na/Ag(110)上存在两种吸附态,随衬底温度升高仅留下一种吸附态。实验结果表明,该吸附态与Ag(110)上存在的Na有关它是CO解离的前驱态。 关键词：     

On different mechanisms of electron-phonon scattering of electron and hole excitations on an Ag(110) surface

We present the results of a detailed theoretical study of the electron-phonon scattering of electron and hole excitations in the unoccupied and occupied surface states on an Ag(110) surface. We show that the electron-phonon coupling parameter λ in the unoccupied surface state is approximately three times smaller than that in the occupied one, because the scattering of these states is determined by different phonon modes. The difference in the phonon-induced decay mechanisms of electron and hole excitations is determined by different spatial localizations of the unoccupied and occupied surface states at the $ \overline Y $ \overline Y point of the two-dimensional Brillouin zone.     

ZnTe(110)表面电子态及其弛豫对表面电子态的影响

给出了Ⅱ-Ⅵ族半导体化合物ZnTe(110)表面电子特性的理论研究.考虑最近邻的sp³s模型描述体态电子结构，使用散射理论方法，给出了理想和弛豫ZnTe(110)表面的波矢分辨的电子态密度和表面投影带结构.结果表明：弛豫的ZnTe(110)表面在带隙中没有表面态存在.在价带中的表面态及表面共振态和其他弛豫的Ⅲ-Ⅴ族及Ⅱ-Ⅵ族半导体的(110)表面具有相似的特征.与实验结果及第一性原理的自洽赝势计算结果相比，计算的结果符合得很好. 关键词：     

Calculation of the optical absorption between surface states of silicon

A detailed calculation of the optical absorption between surface states on silicon is reported and the results compared with the observed absorption. Actually the observations relate to the (111) surface whereas the calculations involved the better understood (110) surface, but arguments are advanced to suggest that similar results should be obtained for both and a simulated (111) calculation presented. A model, which accurately reproduces the results of complete theoretical calculations, is used to obtain the surface state energies throughout the two-dimensional Brillouin zone, and to obtain the momentum matrix elements at each k point by utilising the effective mass sum rule. The formation of a band gap between the surface state bands, arising from surface rearrangement, is incorporated into the model in a physically sensible manner. There is very good agreement in both shape and absolute magnitude between the calculated and observed absorption clearly indicating that the measured absorption does arise from surface states. The (1, 1, 0) calculations show large polarisation effects which should be observable on reconstructed (1, 1, 0) silicon surfaces or on the III–V compounds.     

Density of states of the clean Mo (110) surface

The electronic structure of the (110) surface of Mo is calculated using transfer matrix method. The Hamiltonian is of tight-binding type with a basis of nine orbitals per atom. Spectral densities of states for special points of the 2-D Brillouin zone are presented on the surface and in the three consecutive layers. The band structure in the σ direction and the local density of states are also calculated. The results are compared with the few experimental data available in the literature.     

Large wave vector spin waves and dispersion in two monolayer fe on w(110)

We present the first surface spin-wave (SW) dispersion measurements up to the surface Brillouin zone boundary of a two monolayer Fe film on W(110) by using spin-polarized electron energy loss spectroscopy. Pronounced features of SW peaks are observed in the spectra at room temperature. We found that the SW energies in the Fe film are strongly reduced compared to spin waves in bulk Fe and to theoretical predictions. Our results suggest that this reduction is caused by the reduction of exchange interaction within the 2 ML Fe on W(110) as compared to bulk Fe.     

Relaxation and electronic states of Au(100), (110) and (111) surfaces

Using a first-principles method based on density functional theory, we investigate the surface relaxation and electronic states of Au(100), (110) and (111) surfaces. The calculated results show that the relaxations of the (100) and (110) surfaces of the metal are inward relaxations. However, the Au(111) surface shows an ‘anomalous’ outward relaxation, although several previous theoretical studies have predicted inward relaxations that are contrary to the experimental measurements. Electronic densities of states and the respective charge density distribution along the Z-axis of the relaxed surfaces are analyzed, and the origin of inward and outward relaxation is discussed in detail.     

Local density of states of GaAs and InAs surfaces: Ideal (111), (001) and (110) surfaces and monoatomic steps on the (111) and the (001) surface

The ideal (111), (001) and (110) surfaces of GaAs and InAs are investigated by means of the LCAO Green function recursion method to obtain local density of states. Main emphasis is laid on the analysis of the nature and character of the inherent surface states. For this purpose, several imperfections on the (111) and the (001) surface (i.e. vacancies and steps with varying topology) are treated to demonstrate the local character of Shockley surface states and to confirm their chemical nature. The applicability of the results obtained to other A³B⁵ compounds is discussed. Comparison with experiment and other theoretical investigations is also made.     

Surface electronic structure of SnO2(110)

We report theoretical investigations on the surface electronic structure of the (110)-face of SnO₂, a semiconductor of rutile bulk structure. Starting with a tight binding Hamiltonian for the bulk, we determine the surface electronic structure using the scattering theoretic method. As results we obtain the surface bound states, the surface resonances and the wave-vector resolved surface layer densities of states. The dominant features are two backbond states in the stomach gap of the main valence band and two Sn-s derived states in the lower conduction band region. In the upper valence band region, only weak resonances occur, like in other materials with relatively strong ionicity.