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.
Highlights
Ge-Sb-Te (GST) compounds are of high interest due to their technologically outstanding optical and electronic properties
The formation of building blocks with different local composition can be expected in the produced thin films which is in agreement with the equilibrium phase diagram Ge-Sb-Te21
The formation of GST124 and GST225 building blocks was observed in the film heated at 493 K (Fig. 1a) whereas the formation of GST124, GST225 and GST326 building blocks was found in the GST films heated at 523 K and 563 K (Fig. 1b)
Summary
Ge-Sb-Te (GST) compounds are of high interest due to their technologically outstanding optical and electronic properties. The knowledge of the proper local atomic arrangement in layered GST alloys is of paramount importance in order to understand the switching mechanism of iPCMs and their material properties. The overall structure of layered GST compounds consists of rocksalt-type building blocks with alternating cation (GeSb) and anion (Te) layers These blocks are stacked along the c-axis and periodically separated from each other by intrinsic vacancy layers (van der Waals gaps, vdWg’s) between adjacent Te layers[19]. The aim of this work is to study the local atomic arrangement and lattice distortions in Ge-Sb-Te thin films consisting of layered Ge2Sb2Te5 (GST225), Ge1Sb2Te4 (GST124) and Ge3Sb2Te6 (GST326) crystal structures by using a combination of atomic-resolution aberration-corrected (Cs-corrected) high-angle annular dark-filed scanning transmission electron microscopy (HAADF-STEM) imaging and theoretical image simulation. The approach used here can be applied to the fast evaluation of stacking sequences in layered GST crystal structures grown by different methods
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.