EXAFS study of noble gases implanted in highly stressed amorphous carbon films

Abstract In this work we report on the study of the local environment of Ar and Kr atoms implanted into an amorphous carbon (a-C) matrix. By intentionally changing the a-C deposition conditions we were able to trap noble gas (NG) atoms under different internal pressure (intrinsic stress) ranging from 1 up to 12 GPa. This enables us to investigate the effects of the internal pressure on the implanted NG atoms subjected to the highly strained environment of the carbon matrix. For this purpose, extended X-ray absorption fine spectroscopy (EXAFS) was performed on the K absorption edge of the implanted Ar (3.2 keV) and Kr (14.3 keV) atoms as a function of the intrinsic stress of the carbon matrix. The analysis of X-ray near edge spectroscopy (XANES) shows an evident increase of the white line for both gases as the stress increases. This result is indicative of clustering of the implanted NG atoms. The analysis of the EXAFS results for Ar atom indicates an increase of the first neighbor distance from 2.4 to about 2.8 A with increasing compressive stress. The latter figure is comparable to the Ar–Ar (Kr–Kr) inter-atomic distance of compressed solid Ar (Kr). This finding gives further evidence for the formation of small NG clusters in a highly strained a-C matrix.