STRUCTURE AND NATURE OF VERY SMALL POINT DEFECT CLUSTERS STUDIES BY POSITRON LIFETIME AND TRANSMISSION ELECTRON MICROSCOPE

结果表明，利用正电子寿命测量和透射电子显微镜技术可以获得关于极小点缺陷团簇的可靠和新的信息。电子显微镜观察分析了缺陷团簇的局域结构，正电子寿命测量发现了尺寸小于透射电子显微镜分辨率的小空位团簇。铜和硅中位移级联产生的三维空位团的尺寸小于双空位，较大的空位团崩塌为层错四面体(SPT)和位错环。利用弱束暗场(WBDF)方法对空位型和间隙型极小的点缺陷团簇进行了电子显微镜图像识别。通过系统地改变一个偏离Bragg条件的参数，研究了尺寸在1 nm到2 nm之间的位错环的像尺寸的系统变化。通过测量20K下600keV自离子辐照的铜中位错环大小的变化和120K退火后位错环的大小变化，确定了位错环的性质。观察到了空位和间隙两种类型，但几乎没有观察到每种类型的环的尺寸的系统变化。SFT位的正电子寿命已经确定，但接近空位的正电子寿命。正电子寿命法已经能够评估位错环密度的降低，但不能分离空位和间隙类型的影响。用透射电子显微镜进行的立体测量首次揭示了空位型缺陷团的空间分布与间隙缺陷团的空间分布的差异。

It has been concluded that we can obtain reliable and new information about very small point defect clusters using both positron lifetime measurement and transmission electron microscopy (TEM) technique. TEM observation has analyzed the local structure of defect clusters, and positron lifetime measurement has detected small vacancy clusters whose size is smaller than the TEM resolution. The size of three dimensional vacancy clusters produced by displacement cascades in Cu and Si is smaller than divacancies, and the larger vacancy clusters collapse to stacking fault tetrahedra (SPT) and dislocation loops.Weak-beam dark-field (WBDF) method has been applied to identify the very small point defect clusters of vacancy-type and interstitial-type by TEM images. Systematic change of image-size has been examined for dislocation loops whose sizes are between 1 nm and 2 nm by systematically changing a deviation parameter from the Bragg condition. Nature of dislocation loops has been determined by measuring the change in size of the dislocation loops in Cu irradiated with 600 keV self-ions at 20 K and that after 120 K anneal at which temperature all the single interstitial atoms have already moved to dislocation loops and their sinks. Both vacancy and interstitial types are observed, but systematic change of sizes for each type of loops has been hardly observed. Further work using computer image-simulation is needed.Positron lifetime at SFT site has been determined, but is close to that at a vacancy site. Positron lifetime method has been able to evaluate the decrease in dislocation loop density, but has not been able to separate the effects of vacancy and interstitial types. Stereo measurement using TEM has disclosed the difference between the spatial distribution of vacancy-type defect clusters and that of interstitial-type defect clusters for the first time.