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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

本项目的目的是从统一的角度阐明半导体表面这一典型的准二维系统的激发态的动力学性质。为此，我们尝试用实验方法直接探测电子激发态的弛豫动力学，具有fs-temporal分辨率和原子水平上的结构变化。前者是通过双光子光发射光谱（2PPE）实现的，后者是通过扫描隧道显微镜（STM）实现的。动力学知识为从微观角度理解表面结构响应机制提供了基础。获得的主要结果总结如下。1)利用可调谐fs激光脉冲作为泵浦脉冲，直接探测了Si中的热载流子动力学，包括谷间散射、谷内散射和能量弛豫，得到了弛豫速率的定量值。此外，Si (001)-(2x1)的超快载流子sc…2)系统地研究了Si (111)-(7x7)、Si (001)-(2x1)、Si (111)-(2x1)和InP (110)-(1x1)在不同对称和结构性质的共价半导体表面上的光致结构变化。双孔局域化可以定量、系统地描述表面敏感结构响应的观测特征。这样，我们几乎可以完全解决表面科学中最重要的问题之一。3)我们通过在原子水平上直接观察表面结构变化的广泛研究，阐明了小于15 eV的低能电子与表面的基本机理。表面局域态（如Si- h键）的非弹性激发和等离子体激元的产生都会导致Si表面的局部结构变化。4)隧道电流诱导表面原子局部键断裂的机制与激光激发类似，为双空穴局域化机制。因此，从STM尖端到原子水平表面区域的空穴注入以一种可控的方式进行了修改。5)在可见光区超快激光激发下，首次发现了石墨到金刚石的光致结构相变的一种新型表面结构变化。这些结果为我们建立对半导体表面动力学性质的透彻理解提供了重要的知识，半导体表面被视为一类新的二维凝聚态物质。少