Publication by Hervé Roussel & Françoise Hippert

Here you will find the article by Hervé Roussel & Françoise Hippert:
"Scanning transmission electron microscopy (STEM) techniques are used to improve the understanding of out-of-plane oriented Sb₂Te₃ thin films deposited by sputtering on SiO₂ and Si substrates. Nanobeam precession electron diffraction, energy-dispersive X-ray spectroscopy, and high-angle-annular dark-field imaging show that the presence of 1–2 atomic planes of Te on top of the substrate is a crucial factor for successful growth of such films, which can be achieved by optimizing cosputtering of Te and Sb₂Te₃ targets. The formation of an actual van der Waals (vdW) gap between the substrate and the first Sb₂Te₃ quintuple layer allows for vdW epitaxy. This gap is larger than those separating Te planes in the pseudo-2D Sb₂Te₃ structure. HAADF image analysis provides detailed information on the atomic arrangement such as interplanar distances, vdW gaps, and Debye–Waller coefficients, all these with a few pm precision. For the anisotropic atomic displacements, a new methodology is introduced based on the statistical analysis of atomic column positions that provides information on the low-frequency phonon modes. Ab initio calculations are used to support our results. Overall, this study provides quantitative STEM tools particularly well suited for nonperiodic pseudo-2D materials, such as Sb₂Te₃/GeTe superlattices."