Structural change of crystalline andamorphous-Ge2Sb2Te5 by reverse Monte Carlo analysis of x-ray diffraction data and extended x-ray absorptionfine structure data

Abstract

Reverse Monte Carlo analyses of crystalline and amorphousGe2Sb2Te5 thin films were carried out using x-ray diffraction data and three spectra fromextended x-ray absorption fine structure measurements. To produce a crystal model,we employed a large system with 12 800 Ge, 12 800 Sb and 32 000 Te atoms. Theobtained model for the crystal structure was used for the initial configuration of theamorphous model. As a result of a series of reverse Monte Carlo analyses withvarious constraints, we found that the partial pair distribution function in theamorphous state with the largest deviation from the crystal state is a Ge–Sbpair and the distance is less than 2.7 Å. This suggests that Sb atoms in amorphousGe2Sb2Te5 thin film have a four-coordinate within 3.2 Å.