Development of high resolution TRAXS and its applications to surface science

该项目的目的是改进“RHEED-TRAXS”方法，即我们最初的表面分析技术，并开发“高分辨率TRAXS”。在本项目期间取得的成果如下：1。针对高分辨率的RHEED-TRAXS（反射-高能电子衍射-全反射-角度- x射线光谱学），我们研制了一种由晶体光谱仪和位置敏感x射线探测器组成的x射线光谱仪。结合我们的分子束外延（RHEED-MBE）装置，我们获得了高分辨率的x射线能谱，该能谱的强度足以在短的数据获取时间内观察动力学过程。使用扁平LiF（200）晶体作为光谱仪，我们证实了GaK线（9.2keV）的能量分辨率约为13eV，比之前的TRAXS方法（150eV）高约10倍。然后，我们期望在这种高能量分辨率下进行EXAFS（扩展x射线吸收精细结构）。利用这种新技术很好地表征了原子结构和化学成分的硅表面，我们测量了表面电导，发现它受表面原子尺度结构的敏感影响。表面原子排列的变化导致表面电子态和空间电荷层的变化，从而导致表面电导率等宏观电学性质的变化。这一发现不仅从根本利益，而且从其设计应用方面都是重要的。

The aim of this project is to improve a "RHEED-TRAXS" method, our original technique for surface analysis, and to develop a "high resolution TRAXS". The achievements in this project term are as follows;1. For the high resolution RHEED-TRAXS (reflection-high-energy electron diffraction--total-reflection-angle-X-ray spectroscopy), we developed an X-ray spectrometer which consisted of a crystal spectrometer and a position-sensitive X-ray detector. Combining it with our RHEED-MBE(molecular beam epitaxy) apparatus, we obtained high-resolution X-ray energy spectra which had intensities enough for observations of dynamical processes with short data-aquisition time.2. Using a flat LiF(200) crystals as a spectrometer, we confirmed an energy resolution of about 13eV at GaK lines (9.2keV), which was about ten times higher than that (150eV) of the previous TRAXS method. Then, we expect to carry out EXAFS (extended X-ray absorption fine structures) with this high energy resolution.3. With use of a Si surface, of which atomic structures and chemical compositions were well characterized with this new technique, we measured the surface conductance, and found it to be sensitively influenced by the atomic-scale structures of the surface. The changes in atomic arrangements on the surface lead to changes of surface electronic states and space-charge layer, resulting in changes in the macroscopic electrical properties such as surface conductance. This findings will be important not only from the fundamental interests, but also from their devise applications.