arXiv subjects

Holger Vach

Publications and source records attributed to Holger Vach.

3 recordsLinked to original sources

arXiv2025

The unexpected dewetting during growth of silicene flakes with dendritic pyramids

Silicene growth on graphene has emerged as a novel method for fabricating silicon-based van der Waals heterostructures. However, the silicene flakes produced in this manner are the result of an exotic growth mode characterized by metastable nanostructures with varying degrees of deviation from equilibrium, with large two-dimensional flakes surrounded by a rim that coexist with small 3D islands, and, at large deposits, thick dendritic pyramids separated by a denuded zone. In order to rationalize and control this growth, a model is derived that revisits the dewetting thermodynamics and considers generally ignored adsorption and step-edge energies. The model is investigated using kinetic Monte-Carlo simulations and mean-field rate equations, and implemented by close inspection of microscopy images. This model perfectly reproduces the experimental outcomes, unveiling an anomalous growth mode, and provides guidelines on experimental conditions for high-quality silicene growth.

cond-mat.mtrl-sci↗

arXiv2022

Van der Waals heteroepitaxy of air stable quasi-free standing silicene layers on CVD epitaxial graphene/6H-SiC

Graphene, consisting of an inert, thermally stable material with an atomically flat, dangling bond-free surface is by essence an ideal template layer for van der Waals heteroepitaxy of two-dimensional materials such as silicene. However, depending on the synthesis method and growth parameters, graphene (Gr) substrates could exhibit, on a single sample, various surface structures, thicknesses, defects, and step heights. These structures noticeably affect the growth mode of epitaxial layers, e.g. turning the layer-by-layer growth into the Volmer-Weber growth promoted by defect-assisted nucleation. In this work, the growth of silicon on chemical vapor deposited epitaxial Gr (1 ML Gr/1ML Gr buffer) on 6H-SiC(0001) substrate is investigated by a combination of atomic force microscopy (AFM), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy measurements. It is shown that the perfect control of full-scale almost defect-free 1 ML Gr with a single surface structure and the ultra-clean conditions for molecular beam epitaxy (MBE) deposition of silicon represent key prerequisites for ensuring the growth of extended silicene sheets on epitaxial graphene.

cond-mat.mtrl-sci↗

arXiv2021

Hydrogen-mediated CVD epitaxy of Graphene on SiC: growth mechanism and atomic configuration

Despite the large literature focused on the growth of graphene (Gr) on 6H-SiC(0001) by chemical vapour deposition (CVD), some important issues have not been solved and full wafer scale epitaxy of Gr remains challenging, hampering applications in microelectronics. With this study we shed light on the generic mechanism which produces the coexistence of two different types of Gr domains, whose proportion can be carefully controlled by tuning the H2 flow rate. For the first time, we show that the growth of Gr using CVD under H2/Ar flow rate proceeds in two stages. Firstly, the nucleation of free-standing epitaxial graphene on hydrogen (H-Gr) occurs, then H-atoms eventually desorb from either step edges or defects. This gives rise, for H2 flow rate below a critical value, to the formation of (6x6)Gr domains on 6H-SiC(0001). The front of H-desorption progresses proportionally to the reduction of H2. Using a robust and generic X-ray photoelectron spectroscopy (XPS) analysis, we realistically quantify the proportions of H-Gr and (6x6)Gr domains of a Gr film synthetized in any experimental conditions. Scanning tunnelling microscopy supports the XPS measurements. From these results we can deduce that the H- assisted CVD growth of Gr developed here is a unique method to grow fully free-standing H-Gr on the contrary to the method consisting of H-intercalation below epitaxial Gr on buffer layer. These results are of crucial importance for future applications of Gr/SiC(0001) in nanoelectronics, providing the groundwork for the use of Gr as an optimal template layer for Van der Waals homo- and hetero-epitaxy.

cond-mat.mtrl-sci↗