Spectroscopic Studies of Surface Layers of Semiconductor Microcrystals

点击翻译按钮获取中文摘要

In general, optical studies of solid surfaces are extremely difficult, because the number of atoms interacting with incident light is extremely small and the optical signals containing the information about the surfaces are extremely weak. However, for the study of surface layers of microcrystals, which are essentially the systems having large surface-tovolume ratios, the optical spectroscopies are expected to be effective. In this research project, we used mainly the infrared and Raman spectroscopy in an attempt to prove the effectiveness of the optical studies of the micocrystalline surfaces.It turned out that infrared absorption by surface oxide layers of gas-evaporated Si and Ge microcrystals can easily be observed. Furthermore, processes of the formation of the natural and thermal oxides could be investigated in detail. Under the conditions of surface plasmon excitation, the surface-enhanced Raman scattering from the surface layers of Ag small particles could be clearly observed. The Raman signals from surface layers of extremely small Ge microcrystals (less than 50A in diameter) could also be observed. All these experimental results demonstrate the effectiveness of the optical spectroscopy for the studies of the microcrystalline surfaces.we also studied the phase transition behavior of gas-evaporated W03 microcrystals using the Raman spectroscopy. We found a new phase which is not reported so far for the bulk crystals. The appearance of the new phase seems to be caused by the existence of the surfaces. For various kinds of microcrystals, we have demonstrated the quantumsize effects from the measurements of resonance-Raman scattering, optical absorption and photoluminescence. In some cases, we suggested the importance of the surface effects, which are superposed on the quantum size effects.