Development of diffracted electron spectroscopy in RHEED and its application to structural and morphological study on crystal surface

采用通道电子探测器、高频缓速电压调制和锁相放大器，构建了新型的滤能反射高能电子衍射仪，并与能量损耗测量系统相结合。将频率为ω的调制幅值叠加在缓速电压上。通过能量滤波器的透射电子束由可动通道电子检测。放大后的电子束电流最后输入到锁相放大器。当锁相放大器输出频率为ω的信号分量时，直接得到能量微分谱，即常规能量损失谱。利用该装置测量了Si(111)7x7表面及其上的In层的镜面反射电子束的能量损失谱。所得结果总结如下：1. 对于Si(111)7x7表面，表面等离子激元激发的平均次数与1/sin θ /成正比，其中θ表示掠射角。实验得到的1/sin θ系数与Lucas计算的理论值基本吻合。特别是首次发现，在[11-2]方位角θ = 4°处，由于衍射条件，表面等离子激元激发数异常增加。3. Si的表面等离子体能量为11.7 eV，即使在1层In的覆盖下也几乎没有变化。在1层以上，能量值逐渐降低，在30A左右沉积厚度时达到10.4 eV的恒定值。该能量值仍大于In表面等离子体能量8.9 eV，接近于Si和In表面等离子体能量的中间位置，被认为受Si和In界面区域的强烈影响。结合能量损耗测量系统的efe -RHEED仪器将成为研究未知非弹性散射场的有力工具。

Newly improved energy-filtered reflection high-energy electron diffraction apparatus has been constructed, which is combined with energy-loss measurement system using channeltron detector, high frequency modulation of retarding voltage and lock-in amplifier. The modulation amplitude with frequency of ω is superimposed on the retarding voltage. Transmitted electron beam passing through the energy filter is detected by the movable channeltron. The amplified electron beam current is finally inputted to lock-in amplifier. When the signal component of frequency ω is outputted from the lock-in amplifier, the energy-differentiated spectra, conventional energy loss spectra, are directly obtained.Using this apparatus, energy loss spectra of specularly reflected electron beam have been measured for Si(111)7x7 surface and In over-layer on it. The obtained results are summarized as follows. 1. For Si(111)7x7 surface, the averaged number of surface plasmon excitations changes in proportion to 1/sin θ /where θ denotes the glancing angle. It has been confirmed that the experimentally obtained coefficient of 1/sin θ nearly agree with the theoretical value calculated by Lucas. 2. Especially, it has been found for the first time that the number of surface plasmon excitations abnormally increases at θ = 4° for [11-2] azimuth due to diffraction condition. 3. Surface plasmon energy of Si, 11.7 eV, hardly changes even for 1 monolayer coverage of In. Over 1 monolayer, the energy value gradually decrease and becomes constant value of 10.4 eV, at about 30A deposition thickness. The energy value is still larger than the surface plasmon energy of In, 8.9 eV, and nearly corresponds to the middle of Si and In surface plasmon energies, which is considered to be strongly influenced by the interface region between Si and In.The EF-RHEED apparatus combined with the energy loss measurement system will become powerful tool for unknown inelastic scattering field in RHEED.