金属铝在半导体表面的吸附

本文采用集团模型,用自洽的EHT方法计算金属Al在Si(111)和GaAs(110)面上吸附的稳定的几何构型和电子态,结果表明,Al在Si(111)面的三度开位上的离子吸附比顶位的共价吸附更稳定,态密度与实验符合也更好,Al吸附在GaAs(110)面上,将取代表面Ga原子,形成AlAs,此时GaAs(110)面将恢复到不弛豫的理想位置。 关键词：     

Xe原子吸附对GaAs(110)表面重构的影响

基于第一性原理的自洽场密度泛函理论(DFT)和广义梯度近似(GGA),利用缀加平面波加局域轨道(APW+lo)近似方法，建立了五层层晶超原胞模型，模拟了GaAs(110)表面结构和单个Xe原子在其表面的吸附.利用牛顿动力学方法，对GaAs(110)表面原子构形的弛豫和Xe原子在GaAs(110)表面的吸附进行了计算.从三种不同的初始构形出发，即Xe原子分别在Ga原子的顶位，As原子的顶位以及桥位，都发现Xe原子位于桥位时体系能量最低.由此，认为Xe原子在GaAs(110)表面的吸附位置在桥位，并且发现吸附Xe原子后GaAs(110)表面有趋向于理想表面的趋势，表面重构现象趋于消失，表面原子间键长有一定的恢复,这与理论预言相符合. 关键词： 密度泛函理论 表面结构 APW 表面原子吸附     

碱金属在GaAs(110)表面上的吸附

本文讨论Li,Na,K,Cs在GaAs(110)表面上的吸附,考虑理想表面和弛豫表面两种情况。计算采用集团模型,用电荷自洽的ExtendedHucheltheory(缩写为EHT)方法进行。结果表明,吸附后表面原子趋向于理想位置,碱金属原子位于垂直于表面沿[001]方向横跨表面Ga原子的对称平面上。碱金属吸附后的费密能级在价带顶以上约0.7eV处,是由表面Ga原子与碱金属原子间的相互作用决定的。而在价带中碱金属原子主要与表面As原子成键。 关键词：     

AI在GaAs(110)面上的吸附

用电荷自洽的EHMO方法研究了Al在GaAs(110)面上的吸附问题。比较了两种吸附构型,从能量极小的观点定出了稳定的吸附应为Al取代表面Ga原子,使Ga落在表面As的悬挂键上。还计算了电荷转移、成键情况和状态密度。 关键词：     

GaAs(110)面的电子结构

本文研究GaAs(110)面旋转弛豫的电子结构,采用一个原子集团来模拟GaAs(110)面,在其内边界上用一些“类Ga”和“类As”原子来钝化伸向体内的悬挂键,以消除由于有限模型而引起的多余边界效应。用EHT方法计算集团的总能量,由能量极小定出GaAs(110)面最稳定的弛豫位置为表面旋转角ω=18°,表面Ga原子向体内下降0.33?,As原子上升0.13?,这与Pandey等人从光电子部分产额谱所得的结果基本一致。本文还计算了理想和弛豫的GaAs(110)面的态密度,发现对于理想的(110)面禁带中确实存在一个空的表面峰。弛豫后,该峰向上移动进入导带,禁带中不再出现表面峰,与实验结果相符。 关键词：     

CHx(x=2~4)在Fe(110)表面吸附的DFT研究

采用密度泛函理论与周期平板模型相结合的方法,对物种CHx(x=2~4)在Fe(110)表面的top,hcp,SB和LB位的吸附模型进行了结构优化、能量计算,得到了各物种较有利的吸附位;并对最佳吸附位进行密立根电荷和总态密度分析。结果表明：CH4在Fe(110)表面的最稳定吸附位都是SB位,吸附能别是-38.14 kJ•mol-1,CH3在Fe(110)表面的最稳定吸附位都是top位,吸附能别是-171.78 kJ•mol-1,而CH2在Fe(110)表面的最稳定吸附位hcp的吸附能是-342.43 kJ•mol-1;CH3 和CH2两物种与金属表面成键,属于化学吸附。     

CHx(x=2~4)在Fe(110)表面吸附的DFT研究

采用密度泛函理论与周期平板模型相结合的方法,对物种CHx(x=2~4)在Fe(110)表面的top,hcp,SB和LB位的吸附模型进行了结构优化、能量计算,得到了各物种较有利的吸附位;并对最佳吸附位进行密立根电荷和总态密度分析。结果表明：CH4在Fe(110)表面的最稳定吸附位都是SB位,吸附能别是-38.14 kJ•mol-1,CH3在Fe(110)表面的最稳定吸附位都是top位,吸附能别是-171.78 kJ•mol-1,而CH2在Fe(110)表面的最稳定吸附位hcp的吸附能是-342.43 kJ•mol-1;CH3 和CH2两物种与金属表面成键,属于化学吸附。     

Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋     

S钝化GaAs(100)表面的电子特性

用TB-LMTO方法研究单层的S原子在理想的GaAs (100) 表面的化学吸附, 对GaAs(100)表面是Ga-和As-中断两种情况分别进行考虑. 计算了S原子在不同位置的吸附能、吸附体系与清洁的GaAs(100)表面的层投影态密度, 以及电子转移情况. 结果表明, 两种情况下S原子都是桥位吸附最稳定, S-Ga相互作用比S-As稍强, S钝化GaAs(100)表面可以取得明显的钝化效果.     

ZrMn2（110）表面结构及吸氢机理的第一性原理研究

采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法,研究了ZrMn2（110）清洁表面结构和氢原子在表面的吸附。弛豫表面结构的计算结果表明表面结构的最表层为曲面,且表面结构的原子间隙变小。由1Zr2Mn原子组成的空位是氢原子吸附在ZrMn2（110）表面的最佳吸附位,吸附能为3.352 eV,氢原子吸附后离表面的距离为1.140 Å。Mulliken电荷布居分析表明吸附的氢原子与表面原子的相互作用主要是接近氢原子的第一层原子与氢原子的相互作用。过渡态计算表明被吸附的氢原子进入表面内部需克服的最大势垒为1.033 eV。     

Cluster model approach for electronic structure of Si and Ge(111) and GaAs(110) surfaces

For the purpose of exploring how realistic a cluster model can be for semiconductor surfaces, extended Huckel theory calculations are performed on clusters modeling Si and Ge(111) and GaAs(110) surfaces as prototypes. Boundary conditions of the clusters are devised to be reduced. The ideal, relaxed, and reconstructed Si and Ge(111) surfaces are dealt with. Hydrogen chemisorbed (111) clusters of Si and Ge are also investigated as prototypes of chemisorption systems. Some comparison of the results with finite slab calculations and experiments is presented. The cluster-size dependence of the calculated energy levels, local densities of states, and charge distributions is examined for Si and Ge(111) clusters. It is found that a 45-atom cluster which has seven layers along the [111] direction is large enough to identify basic surface states and study the hydrogen chemisorption on Si and Ge(111) surfaces. Also, it is presented that surface states on the clean Si and Ge(111) clusters exist independent of relaxation. Further, the calculation for the relaxed GaAs(110) cluster gives the empty and filled dangling-orbital surface states comparable to experimental data and results of finite slab calculations. The cluster approach is concluded to be a highly useful and economical one for semiconductor surface problems.     

Photoemission studies of the electronic structure of III–V semiconductor surfaces

The photoemission technique using synchroton radiation in the photon energy range 5–450 eV has been applied to the study of the electronic structure of some III–V semiconductor surfaces, prepared by cleavage in situ under ultrahigh vacuum conditions, ? 10^?11 Torr. For p-type GaAs(110), the Fermi level is pinned at the top of the valence band and thus no filled surface states extend into the band-gap. The situation is more complicated for n-type GaAs(110), where band bending easily can be introduced by extrinsic effects (impurities, cleavage quality, etc.) and push the Fermi level down to about midgap. Chemical shifts of inner core levels (3d for Ga and As) are used to obtain information on the bonding site of oxygen on the (110) surface. GaAs(110) can be exposed to atmospheric pressure of molecular oxygen without breaking the bonds between the surface atoms and the bulk. Oxygen is predominantly bonded to the As atoms on the surface. The oxidation behavior is strikingly different for GaSb(110) with formation of gallium and antimony oxides on the surface directly upon oxygen exposure. Heavier oxidation of GaAs(110) and breaking of the surface bonds will also be reported.     

GaAs(110)面的紧束缚计算

本文研究了GaAs(110)弛豫表面的紧束缚计算,采用了有饱和的slab(薄片)模型,来模拟半无限大的晶体。通常的slab模型有两个表面,本模型与其不同之处在于用类As和类Ga原子来饱和伸向体内的悬挂键,使之只保留一个表面,从而大大降低久期矩阵的阶数。从计算的表面定域态密度表明,采用五层的有饱和的Slab模型,就可以得到较好的结果。 关键词：     

Photothermal desorption spectroscopy with IR lasers

Medium-energy ion scattering on the relaxed GaAs(110) surface measures a value of 29° ± 3° for the rotation of the top Ga-As atomic chains. Measurements in a scattering geometry especially sensitive to the surface-parallel displacements concomitant with such a bond rotation, show that bond-lengths in the relaxed surface remain unchanged.     

AB initio calculation of the atomic and electronic structure for Sb adsorbed on GaAs(110)

We report results obtained by a systematic study of Sb adsorption on the relaxed GaAs(110) surface, using density-functional theory within the local-density approximation (LDA) and norm-conserving, fully separable, ab-initio pseudopotentials. The GaAs(110) surface is simulated by a slab geometry wherein the atomic structure of the Sb atoms at the preferred adsorption positions and the uppermost substrate layer is optimized by minimizing the total energy, in contrast to previously reported theoretical approaches obtaining the surface bandstructure for given geometrical equilibrium structures. Sb coverages of Q=1/2 and Θ=1 are considered. We give a detailed analysis of the total-energy surface of the Sb/GaAs(110) system and identify stable and metastable adsorption sites. The resulting equilibrium geometries are discussed: We interpret these results in terms of the Sb-Sb interaction within the chains parallel to the [1¯11] direction and of possible structural instabilities in such chains. The atomic positions are compared with results of LEED analysis, stating an overall agreement except the buckling of the chain atoms. The resulting electronic properties (surface bandstructure, photothreshold, Schottky barrier) are discussed within the context of experimental data available from STM, photoemission spectroscopy, etc.     

CI在Si和Ge(111)面上的化学吸附

考虑了Si(111)和Ge(111)面吸附Cl的几何构形,本文采用集团模型,用电荷自洽的EHMO方法,对Si(111)和Ge(111)面,分别用能量极小的原则,确定了Cl的化学吸附位置。计算结果表明,对于Si(111)面,Cl是在顶位被吸附,形成共价结合,与实验结果一致。对于Ge(111)面,计算表明在顶位和三度开位上都能吸附Cl,与以前结论有一些不同,但本文认为偏振光电子谱的实验结果并不能完全排除Cl在Ge(111)面上顶位吸附的可能性。希望有其他实验能对Cl在Ge(111)面上的吸附作进一步的观察。此外,还计算了Cl在Si(111)面顶位上的吸附和它在Ge(111)面三度开位上的吸附时的状态密度,和实验结果进行了比较,相符甚好。 关键词：     

Isobar,low energy electron diffraction and loss spectroscopy measurements of cesium covered (110) gallium arsenide

Two thermodynamic “surface phases” are observed in the first Cs monolayer on (110) GaAs. These phases are characterized by different physical properties. We have also shown that in the first step of cesiation, the Cs atom is chemically bonded to the Ga atoms.