用扫描隧道显微镜测量局域功函数

用扫描隧道显微镜在Cu（111）-Au和Pt（111）-Ag表面上对局域功函数进行了测量．在扫描的同时通过测量隧道电流对针尖样品间距离变化的响应，可以在得到扫描隧道显微镜（STM）图的同时得到功函数图．用这种方法，成功地观察到Au，Ag覆盖层与Cu，Pt衬底间的功函数的差别．结果表明：Au覆盖层的功函数介于Cu（111）和Au（111）的功函数之间，这与其它方法的结果一致．在Pt（111）-Ag表面观察到了局域功函数随覆盖层厚度的变化．本工作表明：扫描隧道显微镜在研究功函数与表面结构的关系方面是十分有用的；用测量局域功函数的方法还可以区分表面不同种的物质 关键词：     

Surface reactivity of oxygen on cleaved and sputtered graphite

The characterization of reactions which occur during the oxidation of highly oriented pyrolytic graphite (HOPG) was performed using high-resolution electron energy loss spectroscopy (HREELS) temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). The results of this investigation provide spectroscopic evidence for the presence of semi-quinone functionalities on sputtered and oxidized HOPG STM images are presented to quantify the increase in defect sites after oxygen ion sputtering, and to correlate defect site density with reactivity.     

双成象单元扫描隧道显微镜与原子尺纳米计量技术

研制了双成象单元扫描隧道显微镜(STM),可同时对参考样品的原子晶格和被测样品扫描成象.计数原子晶格的数目,即可精确测定被测样品图象的尺度,以原子尺方式实现严格的纳米计量.本文介绍双成象单元的STM的原理和仪器系统,讨论原子尺纳米计量的可行性,给出被测样品图象的纳米计量结果.     

Scanned-probe topological and spectroscopic study of surface states on clean and Si-deposited GaAs (0 0 1)-c(4×4) surfaces

Microscopic topological and spectroscopic properties of MBE-grown GaAs c(4×4) surfaces without and with monolayer Si deposition were investigated by the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Empty state STM images on as-grown surface showed bright and dark cells, and they exhibited strong correlation with the spatial distribution of normal and anomalous conductance gaps of the STS spectra. Bias dependent STM images indicated presence of pinning areas with continuous space and energy distribution of surface gap states. By deposition of monolayer Si, dark areas reduced a great deal and the rate of finding normal STS spectra increased, indicating large reduction of surface states.     

Ge在Si(111)7×7表面的选择性吸附

利用超高真空扫描隧道显微镜研究了室温条件下Ge在Si(111)7×7表面上初期吸附过程.在Ge所形成团簇中存在一个临界核.这些Ge团簇的吸附中心总是在三个增原子所围成的区域中.它们的电子结构具有类似半导体的性质,即其局域态密度在远离费米面的能级处很大,而在费米面附近的能级处非常小. 关键词： 扫描隧道显微镜 Si(111)7×7表面 Ge团簇     

Bias-dependent STM images of oxygen-induced structures on Ti(0001) facets

Titanium films grown on Si(111) surfaces in ultrahigh vacuum were investigated using scanning tunneling microscopy (STM). STM images of adsorbate structures induced by oxygen adsorption on Ti(0001) facets are observed to change from protrusions to depressions depending on the applied bias voltage. Using electron spectroscopic data we interpret our results in terms of local, oxygen-induced modifications of the density of states.     

甘氨酸在Cu(111)表面吸附的扫描隧道显微镜研究

用超高真空扫描隧道显微镜(UHV-STM)研究了室温下甘氨酸在Cu(111)表面的吸附行为.实验发现,在低覆盖度下甘氨酸分子在表面表现为二维气体.当覆盖度足够高时,甘氨酸分子最终会形成二维固相结构,为(4×8)超结构.针对这种结构提出了两种可能的结构模型,模型能够很好地解释STM图.当覆盖度介于气相和固相之间时,根据蒸镀条件和退火条件的不同,表面可能出现两种不同的中间相,一种为条纹结构,另一种为六角结构,对于中间相有待于进一步的研究 关键词： 表面吸附 甘氨酸 铜 扫描隧道显微术     

Continuous-time observation of pseudo-vacancy diffusion at Si(111)-7 × 7 surfaces

Scanning tunneling microscopy (STM) is used to study surface diffusion of a special type of point defects at Si(111)-7 × 7 surfaces. These defects survive even after annealing up to 1250°C. They appear darker than Si adatoms at the tunneling biases ranging from −3 to +3 V, but they are not true vacancies. We found that these vacancy-like defects (hereafter, we refer to them as pseudo-vacancies) are not caused by adsorption of major contaminants in the vacuum chamber, nor by dopants. We also observed migration of pseudo-vacancies between nearest neighboring Si adatom sites at temperatures above 500°C. Most of the jumps are within a half of the 7 × 7 unit cell. Thousands of STM images were recorded from 520 to 610°C and the activation energies and frequency factors were determined. Varying the tunneling current produces almost no effect on the diffusion, but varying the scanning speed produces a small effect.     

Scanning tunneling microscopy observation of copper-phthalocyanine molecules on Si(100) and Si(111) surfaces

Molecules of Cu-phthalocyanine (CuPc) deposited on Si(100) and Si(111) surfaces have been observed by an ultra high vacuum field ion scanning tunneling microscope (FI-STM). On a Si(100) surface, STM images with four-fold symmetry are observed, which reflect the shape of the CuPc molecule. The STM pictures show that CuPc molecules are deposited with the molecular plane parallel to the substrate surface and have three kinds of adsorption configurations on the dimer-row of Si(100). The images of the CuPc are modified by the electronic state of the Si(100) surface. This behavior suggests strong interaction between the molecule and the substrate. The molecular images on the Si(111) surface have a unique bias-voltage dependence. At a sample bias of 1.6 V, the molecule looks transparent by STM, and becomes dark like a vacancy at 1.2 V. From the bias dependence, the electronic interaction between the CuPc molecule and the Si surface is discussed.     

石墨上纳米尺度金岛的形成

用扫描隧道显微镜研究了真空蒸镀在高定向热解石墨上金岛的形成和形状．随着蒸镀量的增加及时间的推移，金原子在表面通过扩散而逐渐合并成越来越大的原子团，以至岛，甚至岛群．虽然几个纳米大小的原子团仍十分可动，但在蒸镀量大于20单层时的岛或岛群已十分稳定．研究发现，同一蒸镀量下，各个金岛具有非常接近的宽度和高度，用薄膜成核的圆柱状模型计算岛的宽度与高度之比表明，金岛非常接近热力学平衡状态．这些形状各异的通过生长而自组装形成的纳米尺度金岛可用来进行介观物理的研究 关键词：     

自旋极化扫描隧道显微术

自旋极化扫描隧道显微术是一种新兴的表面自旋分辨技术，文章主要介绍了自旋极化的扫描隧道显微镜和扫描隧道谱实现表面自旋分辨的原理以及在各种磁性表面研究中的应用，采用自旋极化技术的扫描隧道显微镜可以测量表面磁结构，其空间分辨可以达到原子尺度，分辨率超过其他磁显微技术，而自旋极化扫描隧道谱不但可以分辨空间精细磁畴结构，而且能研究表面态的交换劈裂，文章作者还进一步提出了利用自旋极化扫描隧道显微镜实现自旋注入的设想。     

Growth of germanium nanoislands and nanowires on singular and vicinal Si(111) surfaces prior to the formation of a wetting layer

Physics of the Solid State - The growth of germanium nanoislands and nanowires on singular and vicinal Si(111) surfaces is investigated by scanning tunneling microscopy (STM). It is shown that the...     

INVESTIGATION ON THE STRUCTURE AND ELECTRIC PROPERTIES OF BUCKY ONIONS

Bucky onions were fabricated by the DC discharge method and their behaviors and electric properties on Highly Oriented Pyrolytic Graphite (HOPG) were studied by using an atomic force microscope (AFM), a scanning tunneling microscope (STM) and a transmission electron microscope (TEM). Small-sized Bucky onions demonstrated the properties of semiconductors and as the size increased their metallicity became stronger. AFM and STM images revealed the tendency of Bucky onions to form dimers.     

Folding and cracking of graphene oxide sheets upon deposition

Graphene Oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) and studied using Raman spectroscopy, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM phase imaging shows a distinct contrast between GO and the underlying HOPG substrate. Raman spectroscopy clearly showed the presence of GO sheets on the top of HOPG substrate. The AFM and STM images also reveal wrinkling, folding, and tearing of individual GO sheets after depositing onto an HOPG substrate. We have also observed a distinct cracking of a GO sheet after folding. We attribute this new cracking phenomenon to a weakening of C–C bonds during the oxidation of a graphene sheet.     

An artefact in scanning tunneling microscopy images of highly oriented pyrolytic graphite

An artefact with a structure that appears as an ordered array of chains, several 1000 Å long and with distances of between 10 Å and 30 Å in STM images of HOPG is reported. The artefact, which emerges from a too low point density in the scanning grid during data aquisition in the scanning tunneling microscope, is explained using the atomically resolved image, the orientation of the substrate in the STM, the sequential character of data acquisition in scanning tunneling microscopy together with the limited number of data points for the reconstruction of STM images and related image-processing problems, and the specific noise spectrum of the tunneling current. The identification of the artefact is verified by a computer simulation of the STM images, which reproduces the experimental data in detail.     

Barrier height imaging of Si(1 1 1)3 × 1-Ag reconstructed surfaces

We investigated the bias voltage polarity dependence of atomically resolved barrier height (BH) images on Si(1 1 1)3 × 1-Ag surfaces. The BH images were very similar to scanning tunneling microscopy (STM) images in both the empty and filled states. This similarity strongly supports the interpretation that the BH image reflects the vertical decay rate of the surface local density of states (LDOS). Differences in contrast and protrusion shapes between BH and STM images were observed. We attributed these differences to the geometric contribution to the STM image and to the improved spatial resolution of the BH image due to the lock-in technique.     

Theoretical consideration on dimer vacancy images in the STM observations of Si(001) surfaces in terms of the adsorption of O2 molecules

Geometric and electronic structures of dimers on the Si(001)-2 × 1 reconstructed surfaces before and after O₂ adsorption have been investigated with an ab initio molecular orbital (MO) calculation at the Hartree-Fock level. The theoretically predicted electron tunneling current in the dimer before and after O₂ adsorption has strongly suggested that the O₂-adsorbed dimer on clean Si(001) surfaces is observed as dark in the scanning tunneling microscope (STM) images. The dark spot images which have so far been recognized to be a dimer vacancy type defect could be due to the O₂ adsorption in parallel to a Si dimer.     

Scanning tunneling microscopy and molecular orbital calculation of pentacene molecules adsorbed on the Si(100)2×1 surface

Adsorption of the organic molecule pentacene on Si(100)2×1 surfaces was imaged using scanning tunneling microscopy (STM). The molecular images exhibit distinct shapes corresponding to the expected shapes for adsorption configurations. Semi-empirical molecular orbital (MO) calculations reveal a local surface density of states for the adsorbed pentacene on the Si surface. In the cases where the pentacene molecule is adsorbed on an Si dimer row, the calculated MOs are in good agreement with the molecular images observed in STM. In the case of pentacene adsorbed on two or three Si-dimer rows, however, the MOs of the pentacene do not correlate directly with the observed STM images. It is thus considered that the STM images are produced by a combination of Si dimer states and MO.     

扫描隧道显微镜图象的重构

扫描隧道显微镜(STM)图象的解析，是STM应用的关键问题之一，STM的原始图象不能适应各种需要，而采用各种方法重构后，可以适应不同的应用。本文介绍了6种不同的重构方法。     

Palladium nano-clusters grown on prestructured HOPG substrates

The growth of Palladium nano-clusters prepared by atomic beam deposition on prestructured highly oriented pyrolytic graphite (HOPG) surfaces has been investigated by means of scanning tunnelling microscopy (STM). Preformed nanosized pits created on the HOPG surfaces are used as localized pinning sites for Pd cluster nucleation and growth at room temperature. We succeeded in obtaining Pd clusters of nanometric size and with rather sharp size distributions. A systematic morphological study conducted by STM reveals a linear dependence between the height and the diameter of the Pd nanostructures. Finally, Pd nano-clusters stabilized on prestructured HOPG surfaces were found to be active catalysts in the Heck cross-coupling reaction.