The Development of a Reflection High Energy Positron Diffraction (RHEPD) Spectrometer

作为一种表面分析技术，反射高能电子衍射(RHEED)技术已被成功地应用。在本项目中，研究人员首次致力于发展反射高能正电子衍射(RHEPD)技术。与RHEED相比，RHEPD具有低多次散射、无交换作用、内电势几乎为零等优点。在本项目中，研究人员在世界上首次试制了反射式高能正电子衍射仪。在1991财政年度，已经完成了衍射仪真空系统的安装、单能正电子束的亮度增强、正电子加速到50keV等工作。1992财年，我们成功地进行了超高真空系统的运行，并研制出了一种由钨薄膜和硅片组成的新型高效正电子慢化器。开发了RHEPD图形二维图像数据采集的计算机程序。结果，实时积累二维数据成为可能。作为RHEPD实验的第一个靶材，我们选择了镀Se的GaAs(100)表面。目前，在5 5 0ﾟC加热后观察到了2×1结构，目前正在积累高统计量的RHEPD数据。经过两年的研究，初步搭建了REPD光谱仪的基础。

As a surface analysis technique, a Reflection High Energy Electron Diffraction (RHEED) technique has been successfully used. In the present project, the investigator aimed to develop a Reflection High Energy Positron Diffraction (RHEPD) technique for the first time. As compared with RHEED, RHEPD is superior in the following points; low multiple scattering, no exchange interaction, nearly zero inner potential and so on.In this project, the investigator manufactured trially a Reflection High Energy Positron Diffractometer for the first time in the world. In FY1991, the installation of vacuum systems for the diffractometer, the brightness enhancement of the monoenergetic positron beam, the acceleration of positrons up to 50 keV and so on have been completed. In FYI1992, the operation of ultra high vacuum systems was successfully conducted and a new and high efficient positron moderator composed of a W film and A Si wafer has been developed. The computer program for the data aquisition of two dimensional images of RHEPD patterns has been developed. As a result, the accumulation of two dimensional data in real time has been possible. As the first target of the RHEPD experiment, we selected the Se-coated GaAs(100) surface. At present, the 2 X 1 structure was observed after heating at 550ﾟC. The high statistic RHEPD data are now being accumulated. During the two years research , the basis for the REPD spectrometer has been constructed.