Study of excited-state dynamics on the quasi-two dimensional system of reconstrucetd semiconductor surfaces

重构半导体表面准二维系统的激发态动力学研究

基本信息

批准号：
17204025
负责人：
TANIMURA Katsumi
金额：
$ 30.04万
依托单位：
OSAKA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

The purpose of this project is to elucidate the dynamical properties of excited states on semiconductor surfaces, a typical quasi-two dimensional system, from a unified view point. For this purpose, we tried to apply experimental methods that probe directly the relaxation dynamics of electronically excited states with fs-temporal resolution and structural changes at the atomic level. The former has been achieved by two-photon photoemission (2PPE) spectroscopy, while the latter by the scanning tunneling microscopy (STM). The knowledge of the dynamics provides fundamental basis on which mechanisms of structural response of the surfaces can be understood from microscopic point of view. Main results obtained are summarized below.1) By using tunable fs-laser pulses as pump pulses, hot-carrier dynamics in Si, including the inter-valley scattering, intra-valley scattering, energy relaxation have been probed directly to obtain quantitative values of relaxation rates. Also, ultrafast carrier sc … More attering into surface states have been demonstrated for Si (001)-(2x1).2) The photoinduced structural changes on covalent semiconductor surfaces with different symmetries and structural properties have been studied systematically for Si (111)-(7x7), Si (001)-(2x1), Si (111)-(2x1), and InP (110)-(1x1). The mechanism of the instability has been identified to be the two-hole localization, which describes quantitatively and systematically the observed features of sensitive structural responses of the surfaces. Thus, we could solve almost completely one of the most important problems of surface science.3) The fundamental mechanism of low-energy electrons less than 15 eV with surfaces have been elucidated by our extensive studies by means of direct observation of surface structural changes at the atomic level.Non-elastic excitation of both the surface localized states, like Si-H bond, and Plasmon generation leads to the local structural changes on Si surfaces.4) The mechanism of tunneling-current induced local bond rupture of surface atoms has been identified to be the two-hole localization mechanism, similar to the case of laser excitation. The hole injection from STM tips to a surface region of atomic level is thus modified with a controlled fashion.5) A new type of surface structural changes of photoinduced structural phase transition fromGraphite-to-Diamond has been discovered for the first time under ultrafast laser excitation at visible region. These results have provided us crucial knowledge for establishing thorough understanding of the dynamical properties of semiconductor surfaces, viewed as a new class of condensed matters with two-dimensionality. Less

该项目的目的是从统一的观点点阐明激发态在半导体表面（典型的准二维系统）上的动态特性。为此，我们尝试采用实验方法，以直接探测具有FS时空分辨率和原子水平上的结构变化的电子激发态的弛豫动力学。前者是通过两光子光发射（2PPE）光谱来实现的，而后者则通过扫描隧道显微镜（STM）实现。动力学的知识提供了基本的基础，从微观的角度可以理解表面结构响应的机制。通过使用可调的FS激光脉冲作为泵脉冲，SI中的热载体动力学，包括谷化散射，谷体内散射，能量弛豫，可以直接证明获得的主要结果。另外，已经证明了SI（001） - （2x1）.2）超快载体SC…更多地进入表面状态。 INP（110） - （1x1）。不稳定性的机制已被确定为两孔定位，它在定量和系统上描述了表面敏感结构响应的观察到的特征。 3）3）通过我们的广泛研究，通过直接观察表面结构性变化在原子水平上的表面结构变化。隧道电流诱导的表面原子的局部粘结破裂的机理已被确定为两孔定位机制，类似于激光兴奋的情况。因此，从可见的区域，在超快的激光兴奋下，首次发现了一种新型的光诱导的结构相变向二凸状的孔从STM尖端到原子水平的表面区域的孔注射。这些结果为我们提供了至关重要的知识，以彻底了解半导体表面的动态特性，该特性被视为具有二维性的新类凝性问题。较少的