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Atomic Processes Induced by Electronic Excitation in Solids

固体中电子激发引起的原子过程

基本信息

批准号：
62065003
负责人：
ITOH Noriaki
金额：
$ 176.64万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Specially Promoted Research
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62065003/
关键词：
transient Raman spectrscopy cascade excitation spectroscopy Laser-induced particle emmision adiabatic potential energy suraface atomic processes induced by electronic excitation high-density excitation effect defect formation surface defect

项目摘要

The purpose of this research project is to understand basic atomic processes induced by electronic excitation in several types of non-metallic solids. Two major directions of research are taken : one to reach complete understanding of the processes of the self-trapping of excitons and of defect formation arising from exciton relaxation and to apply the concept obtained in alkali halides to other materials including amorphous silica and to the processes in the bulk and on surfaces induced by dense electronic excitation. Several new experimental apparatus are developed : femtosecond cascade excitation spectroscopy, Raman spectroscopy for excited states and resonance ionization spectroscopy of neutral particles emitted by laser irradiation.Major results of the studies are summarized as follows.1) The dynamical de-excitation processes on the adiabatic potential energy surfaces of the lowest excited state of NaCl, KI and KBr were examined using femtosecond time-resolved spectroscopy. For Na … More Cl, femtosecond laser pulses were used to excite the lowest state of the self-trapped excited to next higher excited states. This cascade excitation technique turns out to be useful to examine the de-excitation processes at the lowest adiabatic potential energy surface of the self-trapped excitons in alkali halides. Specific coherent oscillation in a double-well potential energy surface is newly found. It is found also that the lowest adiabatic potential energy surface has a multi-well structure with small phonon frequencies.2) The experimental results of resonant Raman spectra revealed that the self-trapped excitons is a composite comprising an F center and an H center. Using the results of current observation by Kan'no et al. that the excitons in alkali halides can relax into several structures, we suggested a new model of several types of relaxed configurations of excitons in alkali halides.3) It has been examined whether the concept obtained for alkali halides can be used in other solids, such as fluorides and silicon dioxide and these materials are found to behave similarly not only for relaxation of exciton but also for evolution of defects in the process of exciton relaxation. In particular the results for amorphous silicon dioxide indicate clearly that the model for the luminescence suggested by Mott and Street does not hold in this material.4) Creation of another exciton in the proximity of a self-trapped exciton was shown to result in formation of defects in a condition where single excitation does not lead to defect formation. This high density effects are found to occur in NaCl, MgF_2, CaF_2 and are interpreted in terms of formation of deformable lattice by localization of two holes.5) Using high-sensitivity measurements of Ga atoms emitted from GaP and GaAs (110) surfaces by laser irradiation, defectinitiated emission of Ga atoms is found. The emission from some types of defects is found to be most efficient for excitation at the surface states and that the yield vs. fluence relations can be fitted to power functions with powers ranging from 1 to 6, depending, on the type of defects. The higher power is attributed to the necessity of multi-hole localization for emission to be induced.In conclusion the results of the present investigation have revealed details of static and dynamic properties of exciton relaxation in alkali halides and similarity of the processes in several solids including amorphous SiO_2. Furthermore localization of multi-holes can cause drastic structural changes in the system where localization of a hole cannot cause any effects. Less

本研究项目的目的是了解在几种类型的非金属固体中由电子激发引起的基本原子过程。研究的两个主要方向是：一个是完全理解激子的自陷过程和激子弛豫引起的缺陷形成过程，并将碱金属卤化物中得到的概念应用于其他材料，包括无定形二氧化硅和致密电子激发引起的体相和表面过程。建立了飞秒级联激发光谱、激光激发态拉曼光谱和中性粒子共振电离光谱等实验装置，主要研究结果如下：1）利用飞秒时间分辨光谱研究了NaCl、KI和KBr最低激发态绝热势能面上的动力学退激发过程。对Na ...更多信息 C1，使用飞秒激光脉冲将自陷激发的最低态激发到下一个更高的激发态。这种级联激发技术被证明是有用的检查在最低绝热势能面的碱金属卤化物的自陷激子的去激发过程。首次发现了双阱势能面中的相干振荡现象，并发现最低绝热势能面具有声子频率较小的多阱结构。2）共振拉曼谱实验结果表明，自陷激子是由F心和H心组成的复合体。利用Kan'no等人目前观察到的碱金属卤化物中激子可以弛豫成几种结构的结果，我们提出了碱金属卤化物中激子几种弛豫构型的新模型。3）研究了碱金属卤化物中激子弛豫构型的概念是否可以用于其它固体，例如氟化物和二氧化硅，并且发现这些材料不仅对于激子的弛豫而且对于激子弛豫过程中缺陷的演化表现类似。特别是无定形二氧化硅的结果清楚地表明，Mott和Street提出的发光模型在这种材料中不成立。4）在自陷激子附近产生另一个激子被证明会导致在单一激发不会导致缺陷形成的条件下形成缺陷。在NaCl、MgF_2、CaF_2中发现了这种高密度效应，并从两个空穴局域化形成可变形晶格的角度进行了解释。5）利用激光辐照GaP和GaAs（110）表面发射Ga原子的高灵敏度测量，发现Ga原子的缺陷引发发射，发现某些类型的缺陷的发射对于表面态的激发最有效，根据缺陷的类型，产率与注量的关系可以拟合为幂函数，幂的范围从1到6。本文的结果揭示了碱金属卤化物中激子弛豫的静态和动态特性，以及包括非晶SiO_2在内的几种固体中激子弛豫过程的相似性。此外，多孔的局部化可以引起系统中的剧烈结构变化，而孔的局部化不能引起任何影响。少