Development of a Local-Surface-Analysis Apparatus with Micro-Electron Beam and Retarding Two-Dimensional Display Type Electron Analyzer

我们研制了一种适合分析局部表面结构和化学成分的仪器。该仪器由微电子束流和减速场二维显示式电子能量分析仪（RDA）组成，称为mu-GBMEED；掠入射后向散射中能电子衍射的缩写。该方法将能量为1 ~ 3kev的单色电子束以掠射角入射到试样表面，利用RDA分析仪对反向弹性散射电子进行分析。这给了我们一个所谓的mu-GBMEED模式。通过分析该模式，可以得到-0.1 μ m数量级局部表面的结构和成分信息。该装置是在专门设计的超高真空室中，将商用微电子束枪与国产RDA分析仪相结合而实现的。来自RDA分析仪的信号由ccd摄像系统记录，该系统具有宽立体角的mu-GBMEED模式可以有效地存储在计算机存储器中。该仪器还与UHV-STM系统相结合，可以在同一试样表面测量原子尺度的STM图像，并作为mu-GBMEED分析的指导。作为设备的测试，我们研究了Si（001）表面，以确定已知存在的屈曲Si二聚体的背倾角。据报道，屈曲角约为19^ <s:1>，但不确定。用μ电子束在1 ~ 2 KeV下对单畴Si (001) 2x1表面进行了研究，记录了mu-GBMEED模式。借助目前发展的单散射方法，发现了GBMEED的正向散射衍射特征。然而，该模式的质量不够好，无法最终确定屈曲角。我们正处于通过多种手段提高GBMEED模式质量的阶段。

We have developed an apparatus suitable for analyzing structures and chemical compositions of local surfaces. This apparatus is composed of a micro-electron beam and a retarding-field two-dimensional display-type electron energy analyzer (RDA analyzer) and called mu-GBMEED ; abbreviation for Grazing-incidence Backscattering Medium Energy Electron Diffraction. The method of GBMEED has been invented by the head investigator in which a monochromatic electron beam of an energy of 1 to 3 keV is incident on a specimen surface at a grazing angle and elastically scattered electrons along backward direction are analyzed by the RDA analyzer. This dives us a so-called mu-GBMEED pattern. By analyzing this pattern, structural and compositional information about local surface of an order of -0.1 mum can be obtained. The apparatus has been realized by combining a commercial mu-electron beam gun and a home-made RDA analyzer on a specially designed ultrahigh vacuum chamber. Signals from the RDA analyzer are recorded with a CCD-camera system which mu-GBMEED patterns with a wide-solid angle can be efficiently stored in a computer memory. The apparatus is also combined with a UHV-STM system, so that atomic-scale STM images on the same specimen surface can be measured and used as a guide for thr analysis by mu-GBMEED.As a test of the apparatus, we have investigated a Si (001) surface in order to determine the backling angle of the buckled Si-dimers wich are known to be present. The buckling angle is reported to be about 19^ﾟ but is not so certain. A single domain Si (001) 2x1 surface was investigated with mu-electron beam at 1 to 2 KeV and mu-GBMEED patterns were recorded. With the aid of presently developed single-scattering method for GBMEED,a forward-scattering diffraction feature was found. However, the quality of the pattern was not good enough to finally determine the buckling angle. We are in the stage of improving the quality of GBMEED patterns by several means.