Positron annihilation spectroscopy in behavior of defects by chemical analysis of nano-space in solids

点击翻译按钮获取中文摘要

The aim of this research project is to clarify the chemical state of vacancy-impurity complex defects, or nano-space, in solids. We have developed a coincidence Doppler broadening(CDB)method in positron annihilation spectroscopy. The positrons trapped at V-I complexes annihilate electrons due to impurity. Annihilation with core electrons gives larger Doppler shifts compared with valence electrons, so that it is possible to identify the impurity by analyzing the high electron momentum region. The CDB method improves the peak to background ratio in the annihilation spectrum to around 10^5 and fine structures due to core electrons from impurity atom can be discussed. In this project, the defects in Si implanted with various kinds of ions have been investigated.Firstly, it is found that the CDB spectrum for Si ion implanted Si is appropriate as the reference for the defect study in Si. Some characteristic structures due to V-O, V-F and V-H complexes appear in high momentum region in the CDB spectra. From the CDB spectra and positron lifetime, the defect behavior has been considered. For example, the defect induced by O implantation to Si is identified as V_3O, which is transformed into V_6O_2 in annealing at 600°C.An anneal at 800°C results in formation of V_<10>O_6.Further, we have studied the defects in Fe implanted with Cu ions. Simple vacancy-type defects are observed in the surface layer of the sample implanted with less than 5x10^<14>/cm^2, while it has been found that in 5x10^<15>/cm^2, the inner wall of voids is covered with Cu atoms. Combined with the positron lifetime measurement, CDB technique becomes a powerful tool for investigating the defect structure, especially vacancy-impurity complexes.