Preferred orientation of nanoscale order at the surface of amorphous Ge2Sb2Te5 films

Abstract

We report evidence that as-deposited amorphous Ge2Sb2Te5 thin films contain nanoscale clusters that exhibit a preferred orientation, attributed to the earliest stages of heterogeneous nucleation. Fluctuation transmission electron microscopy reveals structural order in the samples, but (220)-related contributions are suppressed. When homogeneous nucleation is promoted via electron bombardment, the sample remains diffraction amorphous but the (220) contribution appears. We simulated data for randomly oriented nanoscale order using ab initio molecular-dynamics models of Ge2Sb2Te5. The simulated (220) contribution always has larger magnitude than higher-order signals; thus, the lack of the experimental signal indicates a significant preferred orientation.