Partially Disordered Crystalline State in a Thin Ge2Sb2Te5 Film: Manifestation of the Thermally Induced Nanoscale Effect

A phase transition in a ~10-nm-thick Ge2Sb2Te5 (GST) film upon heating it from room temperature to ~400°C has been studied using a pulsed electron diffractometer. During crystallization of a freely suspended amorphous sample, the formation of a hexagonal GST phase has been detected, in which mixing of Sb and Ge leads to a formal violation of the translational and unit-cell symmetries. However, upon heating an identical amorphous GST film on a carbon membrane, the crystalline state is represented only by a cubic phase. A qualitative explanation within the Phillips theory for such a nanoscale effect in GST has been proposed, which opens up new possibilities for controlling structural ordering in phase-change memory materials.