扫描隧道显微镜对不同样品测试条件的分析

概述了扫描隧道显微镜（STM）的应用,讨论了扫描隧道显微镜（STM）对不同样品测试的条件,这对STM图象的分析有着重要的作用。     

STM的同胞兄弟--原子力显微镜(AFM)

介绍了在扫描隧道显微镜（ＳＴＭ）基础上发展起来的原子力显微镜（ＡＦＭ）的工作原理、关键部分、工作模式及其应用。     

STM灵敏度系数的校正

讨论了隧道扫描显微镜（ＳＴＭ）中压电陶瓷压电系数的测量计算及高定向裂解石墨（ＨＯＰＧ）的ＳＴＭ相象。这对ＳＴＭ图象的分析有着重要的作用。     

用扫描隧道显微镜(STM)观察纳米粉体的形貌

将不导电的纳米粉体压成薄片,在薄片的表面溅射上金膜,再经过适当的处理,将薄片固定在样品台上,这样制得样品可用于纳米粉体形貌,由于用于ＳＴＭ观察的样品必须导电这一限制,使得样品表面溅射的金膜厚度对成像有很大影响,此类工作可安排在学生物理实验的小型科研实验课程中。     

利用STM和CV方法测定有机发光材料的能带参数

利用扫描隧道显微镜/扫描隧道谱(STM/STS)的技术,研究了有机发光材料Alq₃、DPN-2CN和DNP-2CN的表面电子结构。将材料DPN-2CN和DNP-2CN的表面电子结构与Alq₃的表面电子结构进行对比,判定了DPN-2CN和DNP-2CN的最低空轨道(LUMO)能级。通过电化学循环伏安(CV)法,对DPN-2CN和DNP-2CN的LUMO能级和最高占有轨道(HOMO)能级进行了表征。两种测试方法所得到的LUMO能级参数基本一致。     

外电场下STM钨针尖电子结构的理论研究

采用离散变分局域密度泛函方法，研究了外电场对钨(111)面针尖电子结构的影响.详细计算和分析了在不同偏压和距离条件下，钨针尖的隧道激活轨道和电荷分布.研究结果表明：隧道激活轨道中针尖原子的成分对外偏压的极性、大小以及针尖与样品之间的距离都较敏感.与过去理论计算结果不同，钨针尖原子的5d_z²轨道对隧道激活轨道有一定贡献，但并不是最主要的.在加正偏压时对隧道激活轨道贡献最大的为5d_xz和5d_yz轨道，而在加负偏压时则为包括 关键词：     

基于脉冲电压STM的单原子识别预研究装置

建立起一套工作于真空环境下的基于脉冲电压扫描隧道显微镜(STM)的单原子识别预研究装置.该装王主要由脉冲发生器、真空系统和STM系统三部分组成,能够在5×10-5Pa的真空环境下进行快脉冲STM实验.利用此装置,进行了单个快脉冲诱导的石墨表面超大周期结构的脉冲实验以及脉冲偏压不破坏STM针尖和样品表面的阈值实验.     

STM钨针尖的制备

设计了STM钨针尖制备电路,可实现纳秒级快速断电.采用粗、细腐蚀流程,可以保证针尖低纵横比,同时减少其表面附着的氧化膜杂质.对针尖进行稀盐酸超声清洗,可以彻底去除针尖的氧化层.该针尖经盐酸超声后再进行STM扫描得到了清晰的高序热解石墨图像.     

高定向热解石墨表面局域导电增强现象的扫描探针显微学研究

基于导电型原子力显微镜和扫描隧道显微镜的对比观察,研究高定向热解石墨表面上残留石墨片的导电增强现象.根据样品电阻的测量数据,将这种现象归结为导电针尖与石墨表面的点接触问题,并且发现接触电导和接触点处局域的电子密度成正比,从而确定石墨表面的局域导电增强现象的原因在于残留在石墨表面的石墨片具有较高的电子密度. 关键词： 扫描隧道显微镜 导电原子力显微镜 高定向热解石墨 导电性     

扫描隧道显微镜研究石墨表面的莫尔图

利用扫描隧道显微镜研究石墨表面的大尺度周期性图样．研究结果表明,莫尔图起源于石墨深层的缺陷,实验结果与理论完全吻合,并且第一次在实验上证明了纳米波可以穿透多层石墨而没有明显衰减．     

STM中量子点接触的电导计算

采用模式匹配和散射矩阵方法，对扫描隧道显微镜(STM)中量子点接触过程中的电导进行了计算.结果表明由量子点接触形成的纳米结构的电导呈现量子化特征，这种量子化现象随所形成的纳米结构的横向尺寸和锥角的减小而增强.而且在半导体材料中比金属中更易观察到电导量子化现象. 关键词： STM 量子点接触 量子化电导     

基于不完整描述样本的制冷系统故障诊断研究

制冷系统故障信息样本中的部分特征缺失时,已有的故障诊断模型无法使用这些样本。为解决该问题,提出了一种新颖的故障诊断策略。该诊断策略可通过以下步骤实现:(1)在部分问题描述与历史数据库的相互作用及领域知识的基础上,产生了用于特征转换的相似转换矩阵;(2)将不完整描述样本中的未知特征转变为与其相关的已知特征,形成检索目标;(3)通过计算和比较检索目标与数据库中样本间的相似度,得到最佳案例,将该案例中的相应值赋予未知特征;(4)运用已有的故障诊断模型及再生的完整描述样本,对制冷系统进行故障诊断。利用实验数据对该诊断策略进行验证,取得了满意的结果。     

光子扫描隧道显微镜和扫描隧道显微镜联用系统的研制

报导我们研制的一套光子扫描隧道显微镜（ＰＳＴＭ）和扫描隧道显微镜（ＳＴＭ）联用系统的初步实验结果。联用系统采用的基本结构为早先研制的一台ＰＳＴＭ，另外增加了一个ＳＴＭ通道，通过真空蒸镀金膜制作了既导电又导光的光纤探针，联用系统用ＳＴＭ通道隧道电流反馈控制探针高度。初步实验结果表明，ＰＳＴＭ和ＳＴＭ通道既能分别单独成像，亦能用导电导光探针实现ＰＳＴＭ和ＳＴＭ同时成像。     

Collective and plastic vortex motion probed by STM

The motion of flux line lattices (VL) in various single crystals of NbSe₂ has been observed using fast scanning tunneling microscopy. In crystals with intrinsic weak point disorder the VL creeps coherently as a large bundle along one of the principal axes of the VL. However, we observe striking and for the creep regime unanticipated velocity modulations in the direction of motion, related to the VL periodicity, i.e. with the “washboard” frequency. In the transverse direction the fluctuations of the center-of-mass displacement are random. In crystals with strong line disorder (correlated pinning) caused by columnar defects due to swift ion irradiation collective pinning is observed in fields up to almost double the dose-equivalent field Bφ while interesting plastic flow patterns are detected at 2Bφ.     

A theoretical STM study of Co n /Pt(111)

It is shown that by ‘stacking’ together a semi-infinite sample subsystem with a semi-infinite tip subsystem, difficulties with respect to a common Fermi level for the whole system can approximately be overcome in all those cases when the substrate (serving as lead) and the second lead are different materials. Based on this procedure by means of the spin-polarized (fully) relativistic screened Korringa–Kohn–Rostocker method and an equivalent Kubo equation, theoretical spin-polarized STM spectra for Pt(111)/Co _n /Cr₁₅ W₂₂/Cu(111) with respect to an applied external magnetic field are evaluated in terms of difference conductivities as a function of the corresponding free energy. These spectra are interpreted using layer-resolved contributions to the difference conductivities in order to indicate which parts of the sample dominate changes in the tunneling current caused by changing the orientation of the magnetization. Also shown are estimates of the time-scales to switch from perpendicular to in-plane and vice versa. All investigated properties suggest that different situations apply when the number of Co layers on top of Pt(111) is increased from one to three.     

Defects of SiC nanowires studied by STM and STS

For the first time the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are employed to investigate the morphology and the surface electronic structure of the defective silicon carbide nanowires (SiCNWs). The SiCNWs produced via combustion synthesis route are studied. The STS measurements are performed in the current imaging tunneling spectroscopy mode (CITS) that allows us to determine the correlation between STM topography and the local density of electronic states (LDOS) around the bend of an isolated SiCNW. The measurements reveal fluctuations of LDOS in the vicinity of the defect. The local graphitisation and the inhomogeneous concentration of doping impurities (e.g. nitrogen, oxygen) are considered to explain these fluctuations of metallic-like LDOS in the vicinity of the SiCNW's deformation.     

Photon mapping of MgO thin films with an STM

The light emission from an STM junction consisting of an MgO thin film on Mo(0 0 1) and an Au tip is analyzed with respect to its spatial distribution for various excitation conditions. The spectral characteristic of the light is compatible with an emission mechanism mediated by tip-induced plasmons that are excited by inelastic electron tunneling involving field-emission resonances in the tip-sample gap. The dependence of field-emission resonances on the MgO work function allows the controlled stimulation of differently thick oxide islands in the photon maps by changing the sample bias.     

Real-time STM observation of molecular dynamics on a metal surface

Dynamic processes of molecular assembly on a metal surface were examined using scanning tunneling microscopy (STM). Molecules of a porphyrin derivative were deposited on a Cu(1 1 1) surface and were found to be highly mobile at room temperature. The real-time STM observation enabled visualization of molecular activity such as surface diffusion, domain formation and phase transition. The high mobility of the molecules caused build-up and break-down of molecular domains. Metastability of the molecular assembly caused various domain formations with different molecular alignments, including square and hexagonal motifs. A phase transition from a hexagonal to a square domain structure was successfully observed by sequential STM imaging.     

STM studies of PTCDA supramolecular self-assembling on anisotropic surfaces of reconstructed InSb

Self-assembly of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules on a c(8 × 2) reconstructed InSb(0 0 1) surface as well as on an asymmetrical (1 × 3) InSb(0 0 1) is investigated by means of high resolution scanning tunneling microscopy. The formation of well-ordered one-dimensional molecular lines is observed at low coverage on a former face, whereas on the latter molecules are found as isolated entities. At room temperature spontaneous hopping between energetically similar sites is observed within the lines. At a monolayer coverage flat molecular surface is obtained for both reconstructions, on the c(8 × 2) the layer is composed of neighboring one-dimensional lines, on the (1 × 3) molecular structure does not reveal any long range order. Application of the special experimental procedure provides direct comparison of molecule behavior on both reconstructions of the same sample.