Si(001)表面In量子线的第一原理研究

利用第一原理理论研究了金属In在Si(001)表面吸附的原子结构.结果表明,In原子的吸附不破坏衬底Si的二聚体化学键.在低覆盖率时,In原子在Si(001)衬底上形成有序量子线,取向沿衬底Si的二聚体化学键方向.计算结果显示相邻In线之间不存在排斥作用.     

Ge(112)-(4×1)-In表面重构的原子结构

用扫描隧道显微镜(STM)研究了亚单层In原子引起的Ge(112)-(4×1)-In表面重构.结合随偏压极性不同而显著不同的STM图象和相应的“原子图象”,为这个重构提出了一个原子结构模型,供进一步研究参考.其中,In原子的吸附位置与它在Si(112)表面的吸附位置一致,但与Al原子和Ga原子在Si(112)表面的吸附位置不同.这个吸附位置的不同主要是由In原子较长的共价键键长引起的 关键词： 表面结构 In Ge 扫描隧道显微镜(STM)     

高能电子衍射研究H钝化偏角Si衬底上Si,GexSi1-x的分子束外延生长模式

用高能电子衍射(RHEED)研究H钝化偏角Si衬底上Si,Ge_xSi_1-x材料的分子束外延(MBE)生长模式,发现经低温处理的H钝化Si衬底上要经过10nm左右的Si生长才能获得比较平整的表面.Si,Ge_xSi_1-x外延时的稳定表面均以双原子台阶为主,双原子台阶与单原子台阶并存的结构.Si双原子台阶上的Si二聚体列(dimerrow)取向垂直于台阶边缘,而Ge_xSi_1-x双原 关键词：     

用扫描隧道显微镜操纵Cu亚表面自间隙原子

在超高真空环境下使用扫描隧道显微镜研究了吸附有双甘氨肽分子的Cu(001)表面.在一定的 偏压条件下，针尖在该表面扫描后会形成纳米尺度的Cu团簇，这些团簇可以根据意愿排列成 字母或图形.团簇的高度同偏压、隧道电流以及时间等条件有密切关系.在室温下可以稳定存 在的团簇为制造纳米器件提供了技术上的可能性.实验结果表明，形成团簇的Cu原子不是来 自Cu衬底表面或是针尖.化学吸附在Cu表面的双甘氨肽分子，受到隧道电场的作用会在Cu表 面形成张应变场，Cu亚表面自间隙原子在张应变场作用下迁移到表面是形成团簇的原因. 关键词： 扫描隧道显微镜 纳米尺度Cu团簇 自间隙原子     

局域功函数图像及其在Cu(111)-Au/Pd表面的应用

用扫描隧道显微镜（STM）对Cu(111)-Au和Cu(111)-Pd表面的局域功函数进行了研究.通过 测量隧道电流对针尖样品间距的响应，得到了与STM形貌图一一对应的表面局域功函数图像. 实验发现，Au/Pd覆盖层和Cu衬底间的功函数有明显的不同.Pd薄膜的功函数甚至超过了其体 本征值，且功函数在台阶处变小.用偶极子的形成解释了台阶处功函数的降低.这一工作表明 ，用测量局域功函数的方法容易区分表面上不同的元素，并具有纳米尺度的空间分辨率. 关键词： 扫描隧道显微镜 局域功函数 台阶     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜     

铜箔上生长的六角氮化硼薄膜的扫描隧道显微镜研究

利用扫描隧道显微镜研究了采用化学气相沉积法在铜箔表面生长出的高质量的六角氮化硼薄膜. 大范围的扫描隧道显微镜图像显示出该薄膜具有原子级平整的表面, 而扫描隧道谱则显示, 扫描隧道显微镜图像反映出的是该薄膜样品的隧穿势垒空间分布. 极低偏压的扫描隧道显微镜图像呈现了氮化硼薄膜表面的六角蜂窝周期性原子排列, 而高偏压的扫描隧道显微镜图像则呈现出无序和有序排列区域共存的电子调制图案. 该调制图案并非源于氮化硼薄膜和铜箔衬底的面内晶格失配, 而极有可能来源于两者界面处的氢、硼和/或氮原子在铜箔表面的吸附所导致的隧穿势垒的局域空间分布.     

Sr/Si界面沉积SrTiO3初始生长阶段的扫描遂道显微术研究

本文工作利用脉冲激光沉积术(PLD)和超高真空扫描隧道显微术(UHV-STM),研究了在Sr/Si(001)-(2×1)衬底表面上真空室温沉积几个单层SrTiO₃薄膜的初始生长过程.经660 ℃退火处理后,Sr/Si衬底表面上形成了纳米岛状结构.经分析,这些纳米小岛为C49-TiSi₂和 C54-TiSi₂.实验结果表明,在没有氧气的情况下退火,Sr/Si界面无法有效阻止SrTiO₃薄膜与Si衬底之间的相互作用. 关键词： 脉冲激光沉积术(PLD) 扫描隧道显微镜(STM) 3')" href="#">SrTiO₃ 2')" href="#">C54-TiSi₂     

Si(111)-(7×7)表面上Ge量子点的自组织生长

用扫描隧道显微镜研究了Si(111)(7×7)表面上Ge量子点的自组织生长.室温下用固相外延法在硅基底上沉积亚单层的Ge,然后在适当的温度下退火可以聚集形成有序的Ge量子点.由于Ge在Si(111)(7×7)表面选择性的吸附而形成有序的Ge量子点. 关键词： 锗 硅 扫描隧道显微镜 自组织生长     

稳定In/Si表面的LEED研究

利用LEED图形拟合的方法对大量不同取向In/Si表面的稳定性和小面化进行了研究，新发现了In覆盖度在1/2单层原子以下的三个稳定表面：Si(214)-In，Si(317)-In和Si(436)-In，以及In覆盖度在1单层原子左右的两个稳定表面Si(101)-In和Si(313)-In.此外还确定了In覆盖度在1单层原子左右的6个稳定In/Si表面的家族领地以及In覆盖度在1/2单层原子以下的4个稳定In/Si表面的家族领地.特别值得注意的是 Si(103)-In的家族领地相当大，甚至比最稳定的Si(1 关键词： 硅表面 铟 稳定表面 家族领地     

Growth of single-domain monatomic In chain arrays on the vicinal Si(0 0 1) surface

Using the annealed vicinal Si(0 0 1) surface with 4° miscut toward the [1 1 0] direction as a substrate, single-domain monatomic In chain arrays have been fabricated. High-resolution STM images reveal that deposited In atoms preferentially form In dimers between two neighboring Si dimer rows along the step edges on the lower terrace. Formation of In dimers removes the surface dangling bonds and saturates the In valency. With increasing coverage, the In dimers develop into straight monatomic In chains along the step running direction. It is found that the ordered narrow terrace and rebonded double-layer (D_B) step edge are the keys for the formation of monatomic In chains.     

Step instability of the In0.2Ga0.8As （001） surface during annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8 As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton–Cabrera–Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.     

One-dimensional diffusion of Pb atoms on the Si(553)-Au surface

One-dimensional diffusion along long atomic chains of the Si(553)-Au surface is studied with scanning tunneling microscopy. Ab initio calculations reveal aligned preferential adsorption sites between Si step edge atomic chain and double Au atomic chain on each terrace. At 220 K the Pb atoms hop between shallow potential basins forming a potential groove and move parallel to the atomic chains. By combining the results of measurements with the model calculations of the Pb atoms static energy on the Si(553)-Au surface the attempt frequency ν? is determined.     

Step instability of the In_0.2Ga_0.8As （001） surface during annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8 As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton–Cabrera–Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.     

New tetramer structures in the initial process of Si homoepitaxial growth on Si (0 0 1)

We have studied the interaction between Si ad-dimers in the initial process of Si homoepitaxial growth on Si (0 0 1) surface by molecular dynamics simulations using the Stillinger-Weber potential. The interactions determine the formation of larger clusters from diffusing dimers. We show different pathways for the formation of multiple-dimer clusters and propose two new tetramer structures (T_BB and T_CC) formation by two diffusing dimers interacting. These tetramer structures have been found to be energetically stable with respect to isolated ad-dimers. Moreover, their local bonding configuration is very similar to the B-type step edge which is known to be the favored adsorption site for epitaxial growth. The proposed tetramers may play a crucial role as the nucleus of the new epitaxial layer on Si (0 0 1).     

Surface mass transport of Ag and In on vicinal Si(111)

Mass transport of Ag and In on vicinal Si(111) has been investigated by scanning Auger microscopy (SAM). Highly anisotropic surface diffusion and surface electromigration due to direct current were observed for Ag and In adatoms on 0°−, 0.5°−, 3°− and 6°−off vicinal Si(111) surfaces. The diffusion on the intermediate layer is strongly enhanced in the direction parallel to the step edge for Ag adatoms, while it is remarkably suppressed in the direction perpendicular to the step edge for In adatoms. The activation energy of the diffusion for the Ag adatoms ranged between 0.81 and 1.3 eV, while that for In adatoms increased from 0.31 to 0.66 eV with increasing the vicinal angle. The anisotropic diffusion transport is explained in terms of the step structure and the difference in the binding energy at the step site and the terrace site.     

Quintuple-period Si atomic wires with alternative double and triple modulations by metal: Mg/Si(557)

The formation of Mg-induced quasi-one-dimensional atomic wires on a Si(557) surface was studied by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and first-principles calculations. The atomic wires were produced on the Si(557) surface without faceting when heated to 330 ?C. The atomic wires had a × 5 period along the wires, as observed by LEED. STM images showed the existence of three kinds of atomic wires in a unit cell: an atomic wire located at the step edge and the others on the terrace. Interestingly, alternative double and triple modulations resulting in the × 5 period was observed at the atomic wire located at the step edge. Among the variety of atomic structure models available, the one based on a honeycomb-chain-channel model, which is that of a metal/Si(111)-(3 × 1) surface, reproduced the STM images well and was relatively stable energetically.     

Identification of Ge/Si intermixing processes at the Bi/Ge/Si(111) surface

The chemical contrast between Si and Ge obtained by scanning tunneling microscopy on Bi-covered Si(111) surfaces is used as a tool to identify two vertical Ge/Si intermixing processes. During annealing of an initially pure Ge monolayer on Si, the intermixing is confined to the first two layers approaching a 50% Ge concentration in each layer. During epitaxial growth, a growth front induced intermixing process acting at step edges is observed. Because of the open atomic structure at the step edges, relative to the terraces, a lower activation barrier for intermixing at the step edge, compared to the terrace, is observed.     

First principles study of Si(3 3 5)-Au surface

The structural and electronic properties of gold decorated Si(335) surface are studied by means of density-functional calculations. The resulting structural model indicates that the Au atoms substitute some of the Si atoms in the middle of the terrace in the surface layer. Calculated electronic band structure near the Fermi energy features two metallic bands, one coming from the step edge Si atoms and the other one having its origin in hybridization between the Au and neighboring Si atoms in the middle of the terrace. The obtained electronic bands remain in good agreement with photoemission data.