摘要
正电子湮没技术是研究材料微观结构的一种原子尺度表征方法,通过分析正电子湮没行为可以得到湮没位点处局域电子密度和原子结构信息.近年来,正电子湮没谱学技术已经发展成为优于常规手段的特色表征技术,其中符合多普勒展宽技术在研究缺陷附近的电子和原子结构方面具有独特优势,商谱曲线中高动量区域形状的变化反映了正电子湮没位点周围的元素信息.在常规符合多普勒展宽技术发展基础上,能量可调的慢正电子束流符合多普勒展宽技术在获取表面微观结构的深度分布信息上展示出独特的作用,同时也弥补了常规符合多普勒展宽技术只能表征体材料中缺陷环境的不足.本文结合国内外相关进展,综述了符合多普勒展宽技术在各类材料中的研究进展:1)合金中空位型缺陷和纳米沉淀的演化行为;2)半导体中晶格空位与杂质原子的相互作用;3)氧化物中氧空位和金属阳离子浓度的变化.除此之外,在聚合物中自由体积孔洞的大小、数量及分布的估算表征领域中,符合多普勒展宽技术也逐步得到应用.
Abstract
Positron annihilation technique is an atomic-scale characterization method used to analyze the defects and microstructure of materials,which is extremely sensitive to open volume defects.By examining the annihilation behaviour of positrons and electrons in open volume defects,local electron density and atomic structure information around the annihilation site can be obtained,such as the size and concentration of vacancies,and vacancy clusters.In recent years,positron annihilation spectroscopy has evolved into a superior tool for characterizing features of material compared with conventional methods.The coincident Doppler broadening technique provides unique advantages for examining the local electronic structure and chemical environment(elemental composition)information about defects due to its effectiveness describing high momentum electronic information.The low momentum portion of the quotient spectrum indicates the Doppler shift generated by the annihilation of valence electrons near the vacancy defect.Changes in the peak amplitudes and positions of the characteristic peaks in the high momentum region can reveal elemental information about the positron annihilation point.The physical mechanism of element segregation,the structural features of open volume defects and the interaction between interstitial atoms and vacancy defects are well investigated by using the coincidence Doppler broadening technology.In recent years,based on the development of Doppler broadening technology,the sensitivity of slow positron beam coincidence Doppler broadening technology with adjustable energy has been significantly enhanced at a certain depth.It is notable that slow positron beam techniques can offer surface,defect,and interface microstructural information as a function of material depth.It compensates for the fact that the traditional coincidence Doppler broadening technique can only determine the overall defect information.Positron annihilation technology has been applied to the fields of second phase evolution in irradiated materials,hydrogen/helium effect,and free volume in thin films,as a result of the continuous development of slow positron beam and the improvement of various experimental test methods based on slow positron beam.In this paper,the basic principles of the coincidence Doppler broadening technique are briefly discussed,and the application research progress of the coincidence Doppler broadening technique in various materials is reviewed by combining the reported developments:1)the evolution behaviour of nanoscale precipitation in alloys;2)the interaction between lattice vacancies and impurity atoms in semiconductors;3)the changes of oxygen vacancy and metal cation concentration in oxide material.In addition,coincident Doppler broadening technology has been steadily used to estimate and quantify the sizes,quantities,and distributions of free volume holes in polymers.
维普
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