硫在Fe(111)面吸附的密度泛函研究

采用基于密度泛函理论的第一性原理方法,系统研究了不同覆盖度下硫在Fe（111）表面的吸附构型和吸附特性,计算并分析了硫在Fe（111）表面的吸附能、电荷密度、分波态密度、电荷布局、电子局域化函数等数据. 研究结果表明：S在Fe（111）面的H位吸附最稳定,并且吸附能随着覆盖度的增加而增加. 另外,电子态密度、电子局域化函数和布局分析表明Fe、S之间呈较弱的共价键,这种作用力主要是Fe的3d轨道和S的2p轨道杂化所贡献,而随着覆盖度的增加,Fe、S之间的作用力逐渐减弱,这可能是由于S原子之间的排斥力减弱了Fe、S之间的作用. S在Fe（111）、Fe（110）和Fe（100）这三个晶面上吸附情况的对比分析发现,S与Fe（111）表面的相互作用最强,Fe（100）面次之,而Fe（110）面最弱.     

Si{111}晶面粒子堵塞坑的新现象

本文报道了从粒子背散射堵塞效应的实验中所发现的单晶Si的{111}晶面粒子堵塞坑的新现象。单晶Si的{111}晶面有两个面间距d_{(111)^(a)和d(111)^(b),而{110}晶面只有一个面间距d(110)。由此导致两者的堵塞坑是不同的,我们已从α粒子和质子的Si单晶堵塞效应的实验得到了证实。并由此估计了d(111)^(a)和d(111)^(b)以及d(110)的2ψ1/2角。据作者了解,到目前为止,国内外还没有人发现此现象。此现象的发现对复杂晶体的堵塞和沟道效应的研究开阔了前景。 关键词：}     

Ge/Si(111)与Si/Ge(111)体系的生长特性与表面再构研究

本文利用RHEED和AES对Ge/Si(111)和Si/Ge(111)体系的生长特性与表面再构进行了研究。由此提出了其生长模式,并讨论了应力对生长特性、界面特性和表面再构的作用。     

Rh在CeO_2(111)表面吸附的第一性原理研究

采用基于广义梯度近似的投影缀加平面波(Projector augmented wave)赝势和具有三维周期性边界条件的超晶胞模型,用第一原理计算方法,计算并分析了Rh在CeO_2(111)表面吸附所形成的Rh/CeO_2(111)界面体系的吸附能,价键结构和局域电子结构.考虑了Rh在不同吸附位置的吸附情况.结果表明:1)Rh在CeO_2(111)面有较大的吸附能,表明Rh与CeO_2(111)面有较强的相互作用,而且Rh在位于表面O的三度位,且位于次层氧的顶位的吸附最强;2)Rh的4d态同衬底O的2p态有明显的杂化作用,这是Rh同CeO_2较强作用的主要原因;3)Rh被CeO_2(主要是Rh的次近邻的Ce)氧化为Rh~(3+),并伴随着Ce~(4+)→Ce~(3+)反应的发生.     

钴原子及其团簇在Rh(111)和Pd(111)表面的扫描隧道显微学研究

利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.     

bcc Fe中刃型位错的结构及能量学研究

基于位错理论，利用分子动力学方法建立了〈100〉{010}，〈100〉{011}，1/2〈111〉{011}和1/2〈111〉{112}刃型位错的芯结构，并计算了这四种刃型位错的形成能、位错芯能量和芯半径.计算结果表明：〈100〉{010}和〈100〉{011}刃型位错的形成能比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的要高，这表明〈100〉刃型位错比1/2〈111〉刃型位错更难形成.而〈100〉{010}和〈100〉{011}刃型位错的芯半径比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的小，这说明在1/2〈111〉刃型位错中位于奇异区的原子数多于〈100〉刃型位错，而这些原子要比完整晶体中的原子具有更大的活性.可见，1/2〈111〉刃型位错比〈100〉刃型位错更易运动，且〈100〉刃型位错在bcc Fe中难以形成. 关键词： bcc Fe 刃型位错 分子动力学模拟     

CO在Pd掺杂Rh(111)表面吸附的理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对CO在Rh(111)表面top、fcc、hcp、bridge四个吸附位和Rh-Pd(111)表面Rh-top、Pd-top、Rh Rh-bridge、Rh Pd-bridge、Pd Pd-bridge、Rh2Pdhcp、Rh Pd2-hcp、Rh2Pd-fcc、Rh Pd2-fcc九个吸附位的13种吸附模型进行了构型优化、能量计算,得到了CO较有利的吸附位;并对最佳吸附位进行总态密度分析.结果表明:CO在Rh(111)和Rh-Pd(111)表面的最稳定吸附位分别为Rh-hcp和Rh-top位,其吸附能的大小顺序为Ph(111)Rh-Pt(111);CO与金属表面成键,属于化学吸附.     

CVD金刚石薄膜孪晶形成的原子机理分析

采用X射线衍射技术、电子背散射衍射技术和扫描电镜分别观察了不同甲烷浓度条件下沉积的CVD自支撑金刚石薄膜的宏观织构、晶界分布和表面形貌. 研究了一阶孪晶在金刚石晶体{111}面生长的原子堆垛过程. 结果表明，由于一阶孪晶〈111〉60°的取向差关系以及{111}面的原子堆垛结构，使{111}面上容易借助碳原子的偏转沉积产生一阶孪晶. 低甲烷浓度时，碳原子倾向于在表面能较低的{111}面沉积，为孪晶的形成提供了便利，且高频率孪晶使薄膜织构强度减弱. 甲烷浓度升高使生长激活能较小的{001}面成为主要前沿生长面，因而只有〈001〉晶向平行薄膜法向的晶粒能够不断长大，因此孪晶形核概率明显减小. 另外，在薄膜中发现二阶孪晶，并对二阶孪晶的形成进行了分析. 关键词： 金刚石薄膜 孪晶 原子机理 取向差     

Si,GaAs和LiNbO3单晶的堵塞效应

我们利用背散射方法得到Si,GaAs和LiNbO₃单晶堵塞图,以及GaAs单晶{110},{100}和{112}面堵塞半角ψ_1/2值.并得到因离子注入受损伤Si片{110}面堵塞坑深度随注入剂量增加而变浅的结果。作为对实验装置和方法的检验,我们也得到了Si单晶堵塞图和测量了Si单晶{110},{111}和{100}晶面堵塞半角ψ_1/2值。 关键词：     

Si,GaAs和LiNbO_3单晶的堵塞效应

我们利用背散射方法得到Si,GaAs和LiNbO_3单晶堵塞图,以及GaAs单晶{110},{100}和{112}面堵塞半角ψ_(1/2)值.并得到因离子注入受损伤Si片{110}面堵塞坑深度随注入剂量增加而变浅的结果。作为对实验装置和方法的检验,我们也得到了Si单晶堵塞图和测量了Si单晶{110},{111}和{100}晶面堵塞半角ψ_(1/2)值。     

On the adsorption of oxygen on the Mo{110} surface and its vicinals

The adsorption of oxygen on a Mo{110} surface and four vicinal planes with steps parallel to 〈100〉, 〈110〉 and 〈111〉 directions, is studied by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The work has the goal to elucidate whether O adsorption on Mo{110} is really as different from O adsorption on W{110} as reported, and what is the cause of the apparent discrepancies between the various reported sticking coefficients on stepped surfaces.     

过渡元素掺杂对Mo力学性能的第一性原理研究

基于密度泛函理论,采用第一性原理方法计算了在Mo中掺杂摩尔百分比分别为2.08%和4.17%的过渡金属元素W,Ti,Cu和Fe后,体系在[111](110)滑移系统上的广义层错能以及解理能,并研究了掺杂元素对Mo的剪切形变以及脆性一韧性的影响,研究发现,掺杂W和Ti原子会使体系剪切形变的发生变得困难,并使Mo材料变脆;而掺杂Cu和Fe原子则会使体系剪切形变的发生变得相对容易,并使Mo材料的韧性增强,此外,随着掺杂浓度的增加,掺杂W会使体系剪切形变的发生变得更为困难,并使Mo材料脆性更强;而掺杂Fe则会使体系剪切形变的发生变得更为容易,并使Mo材料的韧性更强。     

Spectral functions of isolated Ce adatoms on paramagnetic surfaces

We report photoemission experiments revealing the full valence electron spectral function of Ce adatoms on Ag(111), W(110), and Rh(111) surfaces. A transfer of Ce 4f spectral weight from the ionization peak towards the Fermi level is demonstrated upon changing the substrate from Ag(111) to Rh(111). In the intermediate case of Ce on W(110) the ionization peak is found to be split. This evolution of the spectra is explained by means of first-principles theory, which clearly demonstrates that a reliable understanding of magnetic adatoms on metal surfaces requires simultaneous low and high energy spectroscopic information.     

Electron states and atomic positions at the {001}, {110} and {111} faces of W and Mo

The results of ab initio calculations on the {001}, {110} and {111} surfaces of W and Mo and on the (√2 × √2)R45° reconstructed W {001} surface are presented. A distribution of surface states in reasonable agreement with experiment is found. A simple parametrisation of the short range repulsive force between transition metal atoms is used to predict, for all these surfaces, relaxations which are comparable with those observed. This same parametrisation indicates that the W and Mo {001} surfaces are stable to proposed reconstructive displacements.     

晶面结构非均匀性对金刚石晶形的影响

 不仅考虑表面能，同时也引入表面结构非均匀性自由焓G_stⁱ，通过热力学分析，解释了随着晶体的逐渐长大而{110}面常在金刚石的外形中消失的机理，并用逆推法计算了有关数值。     

Temperature-dependent ideal strength and stacking fault energy of fcc Ni: a first-principles study of shear deformation

Variations of energy, stress, and magnetic moment of fcc Ni as a response to shear deformation and the associated ideal shear strength (τ(IS)), intrinsic (γ(SF)) and unstable (γ(US)) stacking fault energies have been studied in terms of first-principles calculations under both the alias and affine shear regimes within the {111} slip plane along the <112> and <110> directions. It is found that (i) the intrinsic stacking fault energy γ(SF) is nearly independent of the shear deformation regimes used, albeit a slightly smaller value is predicted by pure shear (with relaxation) compared to the one from simple shear (without relaxation); (ii) the minimum ideal shear strength τ(IS) is obtained by pure alias shear of {111}<112>; and (iii) the dissociation of the 1/2[110] dislocation into two partial Shockley dislocations (1/6[211] + 1/6[121]) is observed under pure alias shear of {111}<110>. Based on the quasiharmonic approach from first-principles phonon calculations, the predicted γ(SF) has been extended to finite temperatures. In particular, using a proposed quasistatic approach on the basis of the predicted volume versus temperature relation, the temperature dependence of τ(IS) is also obtained. Both the γ(SF) and the τ(IS) of fcc Ni decrease with increasing temperature. The computed ideal shear strengths as well as the intrinsic and unstable stacking fault energies are in favorable accord with experiments and other predictions in the literature.     

Grain-boundary faceting at a = 3, [110]/{112} grain boundary in a cubic zirconia bicrystal

The atomic structure of a = 3, [110]/{112} grain boundary in a yttria-stabilized cubic zirconia bicrystal has been investigated by high-resolution transmission electron microscopy (HRTEM). It was found that the grain boundary migrated to form periodic facets, although the bicrystal was initially joined so as to have the symmetric boundary plane of {112}. The faceted boundary planes were indexed as {111}/{115}. The structure of the {111}/{115} grain boundary was composed of an alternate array of two types of structure unit: {112}- and {111}-type structure units. HRTEM observations combined with lattice statics calculations verified that both crystals were relatively shifted by (α/4)[110] along the rotation axis to form a stable grain-boundary structure. A weak-beam dark-field image revealed that there was a periodic array of dislocations along the grain boundary. The grain-boundary dislocations were considered to be introduced by the slight misorientation from the perfect = 3 orientation. The fact that the periodicity of the facets corresponded to that of the grain-boundary dislocations must indicate that the introduction of the grain-boundary dislocations is closely related to the periodicity of the facets. An atomic flipping model has been proposed for the facet growth from the initial = 3, {112} grain boundary.     

Submonolayer structures of Ce adsorbed on Mo(110) surface

The surface structure of Ce adsorbed on a Mo(110) surface was studied by reflection high energy electron diffraction. Five kinds of surface structures were found with different deposition coverages in the submonolayer region. These structures have a common feature that Ce atoms possess a periodicity with double spacing at the atomic rows in the Mo[ 10] direction. Observed at 1 ML of Ce coverage was a surface structure related to a deformed fcc Ce(111) plane.     

Surface self-diffusion behavior of individual tungsten adatoms on rhombohedral clusters

The diffusion of single tungsten adatoms on the surfaces of rhombohedral clusters is studied by means of molecular dynamics and the embedded atom method. The energy barriers for the adatom diffusing across and along the step edge between a {110} facet and a neighboring {110} facet are calculated using the nudged elastic band method. We notice that the tungsten adatom diffusion across the step edge has a much higher barrier than that for face-centered cubic metal clusters. The result shows that diffusion from the {110} facet to a neighboring {110} facet could not take place at low temperatures. In addition, the calculated energy barrier for an adatom diffusing along the step edge is lower than that for an adatom on the flat (110) surface. The results show that the adatom could diffuse easily along the step edge, and could be trapped by the facet corner. Taking all of this evidence together, we infer that the {110} facet starts to grow from the facet corner, and then along the step edge, and finally toward the {110} facet center. So the tungsten rhombohedron can grow epitaxially along the {110} facet one facet at a time and the rhombohedron should be the stable structure for both large and small tungsten clusters.     

氦泡在bcc钨中晶界处成核长大的分子动力学模拟

钨(W)是潜在的聚变堆面向等离子体材料.聚变反应中产生的氦(He)不溶于金属W,并在其中易聚集形成He泡,使W基体发生脆化,从而导致W基体的性能发生退化.在前人工作的基础上,本文采用分子动力学研究了He泡在单晶bcc-W中以及bcc-W中∑3[211](110)和∑9[110](411)晶界处He泡形核长大初期的演化过程.结果发现,晶界处He泡的长大机制和单晶W中有所不同.单晶W中He泡通过挤出位错环促进长大.而He泡在∑3[211](110)晶界处的长大机制为:首先挤出并发射少量自间隙W原子,而后挤出1/2⟨111⟩位错线,随后,该位错线会沿晶界面上[111]方向迁移出去;在∑9[110](411)晶界处,He泡在我们的模拟时间尺度范围内没有观察到W自间隙子的发射和位错的挤出.