Pressure-induced physical changes of noble gases implanted in highly stressed amorphous carbon films

Noble gases (Ar, Kr, and Xe) were trapped in an amorphous carbon matrix in the 1--11-GPa pressure range. Extended and near-edge x-ray-absorption spectroscopies indicate clustering of noble gases induced by the host matrix internal pressure. Simultaneously, the matrix pressure promotes a shift of the noble-gas core-level binding energy of ~1eV. The Auger parameter reveals that both the initial state and the host relaxation terms contribute to the binding-energy shift. Ab initio calculations performed on an Ar₇ cluster and on Ar atoms clustered in aromatic molecules support the experimental findings.