Optical second harmonic spectroscopy of the surface and interface electronic states

本研究项目的目的是探索费米能级几个电子伏特内的表面和界面电子能级，并将它们与典型表面和界面现象的驱动力联系起来。目标材料系统是(1)催化剂，(2)纳米结构金属和(3)半导体结构。(1)澄清了TiO_2光催化剂的表面带隙比（110）面具有更大的隙能。我还发现，这个表面的电子态的波函数，作为能量的函数，变化很大。我还发现，当材料被紫外光催化激活时，带隙转移到更高的能量侧。我发现Ziegler-Natta催化剂的催化活性与α-TiCl_3颗粒在224cm^<-1>处出现边缘振动模式之间存在相关性。(2)我发现在玻璃或NaCl（100）上的Au膜在SH强度上存在共振。除了等离子体共振外，我还发现了Au（111）和Au（100）表面电子能级之间的跃迁共振。我成功地跟踪了这种金属随着薄膜的生长而发生的电子态变化。(3)在【普朗克常数】ω=1.17eV附近发现了Ge(111)/热氧化物界面新的电子共振。这种共振在原生氧化物界面中没有发现。热氧化界面和天然氧化界面的SH强度随方位角的变化规律有很大不同。这一结果表明锗界面的电子态对氧化条件很敏感，为使用锗和硅的半导体材料物理提供了基础信息。

The objective of this research project is to explore the surface and interface electronic levels within several electron volts of Fermi level and relate them to the driving forces of typical surface and interface phenomena. The target material systems are (1) catalyst, (2) nanostructured metals, and (3) semiconductor structures.(1) I have clarified that the surface band gap of photocatalyst TiO_2 has a larger gap energy than that of the bulk for (110) face. I have also found that the wavefunction of the electronic states of this surface varies drastically as a function of the energy. I have also found that the band gap shifts to the higher energy side when the material is catalytically activated by UV light. I have found a correlation between the catalytic activity of the Ziegler-Natta catalyst and the emergence of an edge vibrational mode of α-TiCl_3 granules at 224cm^<-1>.(2) I have found a resonance in SH intensity from Au films on glass or NaCl(100). Besides plasmon resonance, I have found resonances of the transitions between electronic levels of Au(111) and (100) surfaces. I succeeded in following the variation of the electronic states of this metal as its film grows.(3) I have found a new electronic resonance of Ge(111)/thermal oxide interface near 【planck's constant】ω=1.17eV. This resonance was not found for a native oxide interface. The SH intensity patterns as a function of the azimuthal angle are quite different between the thermal oxide and native oxide interface. This result suggests that the electronic states of the Ge interface is sensitive to the oxidation condition and offers a basic information for the semiconductor material physics using Ge and Si.