Void lattice formation in electron irradiated CaF₂: Statistical analysis of experimental data and cellular automata simulations

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• 作者：G. Zvejnieks ; ^{guntars@latnet.lv" class="auth_mail" title="E-mail the corresponding author} ; P. Merzlyakov ; V.N. Kuzovkov ; E.A. Kotomin
• 关键词：CaF2 ; Radiation defects ; Void lattice self-organization ; TEM image processing ; Cellular automata simulations
• 刊名：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
• 出版年：2016
• 出版时间：1 February 2016
• 年：2016
• 卷：368
• 期：Complete
• 页码：138-143
• 全文大小：2919 K

文摘

Calcium fluoride (CaF₂) is an important optical material widely used in both microlithography and deep UV windows. It is known that under certain conditions electron beam irradiation can create therein a superlattice consisting of vacancy clusters (called a void lattice). The goal of this paper is twofold. Firstly, to perform a quantitative analysis of experimental TEM images demonstrating void lattice formation, we developed two distinct image filters. As a result, we can easily calculate vacancy concentration, vacancy cluster distribution function as well as average distances between defect clusters. The results for two suggested filters are similar and demonstrate that experimental void cluster growth is accompanied by a slight increase of the void lattice constant. Secondly, we proposed a microscopic model that allows us to reproduce a macroscopic void ordering, in agreement with experimental data, and to resolve existing theoretical and experimental contradictions. Our computer simulations demonstrate that macroscopic void lattice self-organization can occur only in a narrow parameter range. Moreover, we studied the kinetics of a void lattice ordering, starting from an initial disordered stage, in a good agreement with the TEM experimental data.