Evidence for crystalline overpressurized Ar clusters in Al and Si

In the present paper we report an extended x-ray-absorption fine-structure study of Ar ion implanted in Al and Si matrices. The as-implanted samples show the presence of crystalline overpressurized Ar clusters at room temperature. The Ar-Ar nearest-neighbor distance allows us to estimate the presence of an overpressure of 25 and 44 kbar exerted on Ar bubbles by the Al and Si matrices, respectively. The presence of second- and third-coordination-shell signals confirms that the precipitates are in a crystalline phase. The Debye temperatures, calculated from the Debye-Waller factors, are found to be in excellent agreement with the values obtained with use of a thermodynamic equation of state.