Developement of In-situ Modulation Spectroscopy for Atomically Localized Electronic States

我们发展了一种利用调制光谱观察外延薄膜中原子局域电子态的新技术。我们将注意力集中在光子和电子调制的反射信号上。本研究的总结如下。(1)为了发展一种分析方法，我们从理论上研究了半导体表面的电调制度介电函数。(2)我们研制了一套新的半导体表面电子态观测系统。探测光照射样品表面，并检测通过第二次光照射的调制信号。研究发现，探测光的入射角对观察表面电子态是重要的。观察到探测光的p波和S波具有各向异性，反映了介电函数的各向异性。这实现了一种新的对表面电子态的灵敏检测。利用这一技术，我们可以观察到原子的突变表面和吸附原子引起的电子态的变化。(3)发展了一种新的电子束调制技术。调制条件，如电子束密度和加速能，是观察局域电子态的重要参数。这项技术为原位调制光谱的实际应用奠定了基础。

We developed a new observation technique of atomically localized electronic states in epitaxial films by using the modulation spectroscopy. We focus our attention on reflectance signal modulated by photon and electron. The summary of this research are follwed. (1) In order to develope an analysis method, we theoretically investigated electro-modulated dielectric functions at semiconductor surfaces. (2) We developed a new system to observe in-situelectronic states at the semiconductor surface. A probe light irradiate the sample surface, and the modulated signal by a second light irradiation was detected. It was found that the incident angle of the probe light is important to observe the surface electronic states. An anisotropic character was observed for the p and s waves of the probe light, which reflect the anisotropy of the dielectric function. This realizes a new sensitive detection of electronic states localized at the surface. By using this technique, we can observe the electronic states changed by the abrupt surface and adsorped atoms. (3) A new electron-beam-modulation technique was developed. The modulation conditions, such as electron-beam density and accelerated energy, are important parameters in order to observe the localized electronic states. This technique promises a practical use of the in-situ modulation spectroscopy.