Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

Abstract

Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

Atomic Layering, Intermixing and Switching Mechanism in Ge-Sb-Te based Chalcogenide Superlattices

“…These bilayers seem to consist of Sb-Te bilayers from the Z contrast. The bilayer connections were seen by other groups1421, suggesting a general low energy defect of the system.…”

Phase change thin films for non-volatile memory applications

“…4(b)-(h)). 54,59,67,68,[77][78][79] The mixed Ge/Sb layers close to the vdW always are rich in Sb (e.g. Sb66Ge33 (ref.…”

Direct atomic identification of cation migration induced gradual cubic-to-hexagonal phase transition in Ge2Sb2Te5

“…In the absorption coefficient experiment, it claims that the Petrov sequence fits better to the measurement 33 . However, the large broadening phenomenon observed in Raman peaks 34 , and the non-uniform contrast of cationic layers 35,36 from high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image are both inclined to Matsunaga sequence.…”