Investigation of the state of helium and radiation defects in He-irradiated nickel and copper by glancing angle X-ray diffraction

Abstract

Damage caused by low energy helium implantation in nickel and copper has been investigated for the first time by glancing angle X-ray diffraction technique. The damage confined only to the near surface region, typically few thousands Å, comprises of displacement type damage and implanted species. As X-ray penetration depth (for 99% absorption) can be continuously varied as a function of angle of incidence and X-ray wavelength, accurate lattice parameter measurements (back-reflection) can be used to obtain cumulative information regarding long- and short-range strain field of defects. High purity nickel and copper foils were irradiated at room temperature with 100 keV helium ions to fluence levels ranging from 10¹⁶ to 10¹⁸ ions/cm². The results show: (a) simultaneous presence of two defect complexes of opposite strain field character in both nickel and copper, (b) mobility of vacancies is an important parameter for determining the nature and the strength of defect complex, and (c) local strains due to helium bubbles are considerably relieved after a certain dose in both nickel and copper.