Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5
| Autor: | Richard Dronskowski, R. Calarco, Christian Pauly, Volker L. Deringer, Gustav Bihlmayer, Marcus Liebmann, Jens Kellner, Jos E. Boschker, Alessandro Giussani, Markus Morgenstern |
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| Rok vydání: | 2017 |
| Předmět: |
010302 applied physics
Materials science Local density of states 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Molecular physics law.invention law Metastability Phase (matter) Vacancy defect 0103 physical sciences Density functional theory Scanning tunneling microscope 0210 nano-technology Spectroscopy Molecular beam epitaxy |
| Zdroj: | Physical Review B. 96 |
| ISSN: | 2469-9969 2469-9950 |
| DOI: | 10.1103/physrevb.96.245408 |
| Popis: | Scanning tunneling microscopy (STM) and spectroscopy (STS) in combination with density functional theory (DFT) calculations are employed to study the surface and subsurface properties of the metastable phase of the phase-change material Ge2Sb2Te5 as grown by molecular beam epitaxy. The (111) surface is covered by an intact Te layer, which nevertheless permits the detection of the more disordered subsurface layer made of Ge and Sb atoms. Centrally, we find that the subsurface layer is significantly more ordered than expected for metastable Ge2Sb2Te5. First, we show that vacancies are nearly absent within the subsurface layer. Secondly, the potential fluctuation, tracked by the spatial variation of the valence band onset, is significantly less than expected for a random distribution of atoms and vacancies in the subsurface layer. The strength of the fluctuation is compatible with the potential distribution of charged acceptors without being influenced by other types of defects. Thirdly, DFT calculations predict a partially tetrahedral Ge bonding within a disordered subsurface layer, exhibiting a clear fingerprint in the local density of states as a peak close to the conduction band onset. This peak is absent in the STS data implying the absence of tetrahedral Ge, which is likely due to the missing vacancies required for structural relaxation around the shorter tetrahedral Ge bonds. Finally, isolated defect configurations with a low density of 10-4nm-2 are identified by comparison of STM and DFT data, which corroborates the significantly improved order in the epitaxial films driven by the buildup of vacancy layers. |
| Databáze: | OpenAIRE |
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