Optical second harmonic spectroscopy of the surface and interface electronic states

这个研究项目的目的是探索几个电子伏费米能级范围内的表面和界面电子能级，并将它们与典型的表面和界面现象的驱动力联系起来。靶材系统为(1)催化剂，(2)纳米金属，(3)半导体结构。(1)阐明了光催化剂(110)面的表面带隙比体带隙具有更大的带隙能。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，带隙向更高能端移动。我发现了Ziegler-Natta催化剂的催化活性与α-TiCl3颗粒在224 cm~(-1)&gt~(-1)处出现边缘振动模之间的关系。(2)我从玻璃或氯化钠表面的金膜中发现了SH强度的共振。除了等离子体激元共振，我还发现了Au(111)和(100)表面电子能级之间跃迁的共振。我成功地跟踪了这种金属随着薄膜生长而电子态的变化。(3)我发现了Ge(111)/热氧化物界面在[普朗克常数]ω=1.17 eV附近的新的电子共振。对于自然氧化物界面，没有发现这种共振。热氧化物界面和自然氧化物界面的SH强度随方位角的变化规律有很大不同。这一结果表明，Ge界面的电子态对氧化条件很敏感，为使用Ge和Si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.