Andriy Lotnyk
Leibniz Institute of Surface Modification (IOM), Germany
Title: Local atomic arrangement in Ge-Sb-Te phase-change thin films
Biography
Biography: Andriy Lotnyk
Abstract
Phase change materials (PCM), such as Te-based Ge2Sb2Te5 (GST), are known from optical memory applications and can be also used in non-volatile next generation random access memory. The relevant phases of GST are an amorphous phase, a metastable cubic rock salt like structure and a stable hexagonal layered structure. However, the atomic arrangements in the GST lattices are not well-understood and still under discussion. Insights into the local atomic arrangement of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view as well as for optical and electronic applications such as data storage, thermoelectric and ferroelectric. In this work, the local atomic arrangement in metastable GST and in Ge-Sb-Te thin films consisting of GST, Ge1Sb2Te4 and Ge3Sb2Te6 layered crystal structures are studied by using a combination of atomic-resolution aberration-corrected (Cs-corrected) high-angle annular dark-filed scanning transmission electron microscopy (HAADF-STEM) and detailed theoretical image simulation approaches. By comprehensive analyses of experimental and simulated HAADF-STEM image intensities, a structural model for metastable Ge2Sb2Te5 is proposed. In addition, the proper stacking sequences in the Ge-Sb-Te phases are determined. The obtained data are discussed with respect to existing experimental and theoretical structure models reported for bulk Ge-Sb-Te materials.