Photo-induced Defect Formation and Structural change of Amorphous Silicon Dioxide

本研究的目的是阐明电子激发下非晶态材料(1)发光、(2)缺陷形成和(3)结构变化的模型。对已有文献进行了计算机模拟和复核。结果表明，上述现象都是由激子的弛豫引起的：(1)发光是由自俘获激子的辐射重组引起的；(2)缺陷是在高度扭曲的非晶态位置产生的激子的亚稳态；(3)结构变化是由激子的辐射和非辐射重组引起的。二氧化硅在重离子路径上的密电子激发非晶化也进行了研究。研究的进一步细节如下。a .电子激发下非晶材料缺陷形成的机理。重新研究了晶体二氧化硅中自困激子的结构。结果表明，在非晶二氧化硅高畸变处形成的自困激子比在晶体二氧化硅中形成的自困激子转化为具有更低势垒的亚稳态。b .电子激发下非晶材料结构变化的机理指出伴随结构变化的光吸收变化比缺陷形成的光吸收变化要大得多，认为结构变化是由激子的形成引起基态势能面的变化引起的。c .密集电子激发下非晶化的机理高能重离子辐照下记录径迹的材料和非晶材料比较了激子自捕获的情况。指出轨迹配准的原因是自困激子的密集产生。结果已发表在几篇关于电子激发效应的评论和一篇原创论文中。

The purpose of this investigation is to clarify the models of (1) luminescence, (2) defect formation and (3) structural change, of amorphous materials induced by electronic excitation. Computer simulation and re-examination of existing literatures have been carried out. It is concluded that all phenomena stated above are due to the relaxation of excitons : (1) the luminescence arises from the radiative recombination of self-trapped excitons, (2) defects are metastable states of excitons created at highly distorted amorphous sites and (3) the structural change is induced as a result of radiative and non-radiative recombinations of excitons. Amorphisation of silicon dioxide by dense electronic excitation along heavy ion paths is also investigated. Further details of the study follow. A.The mechanism of defect formation in amorphous materials by electronic excitationThe structure of self-trapped exitons in crystalline silicon dioxide is reinvestigated. It is concluded that self-trapped excitons formed at highly distorted part of amorphous silicon dioxides are converted to metastable states with lower potential barriers than those in crystalline silicon dioxides. B.The mechanism of structural change of amorphous materials by electronic excitationIt is pointed out that the optical absorption change accompanied with structural changes is much larger than that of defect formation and suggested that the structural change is due to alternation of the ground state potential energy surface by formation of excitons.C.The mechanism of amorphisation by dense electronic excitationThe materials in which irradiation with energetic heavy ions register tracks and those in which excitons are self-trapped have been compared. lt is pointed out that the cause of track registrarion is the dense generation of self-trapped excitons. Results have been published in a few reviews on the effects of electronic excitation and in an original paper.