Monte-Carlo simulations of the epitaxy of Ge on Ag(111)

Monte-Carlo simulations of the epitaxy of Ge on Ag(111)

Supervisor : Jean-Noël Aqua
Contact :
Funding : Sorbonne Université
keywords : Growth - Organization - Interfaces, Internship M2, and Theorical
Gratification : Oui
Team(s) internship page(s) : Chemical Physics and Dynamics of Surfaces
Internship description
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The recent discovery of two-dimensional materials (2DMs) has revolutionized solid-state physics thanks to their ability to confine carriers. Since the discovery in 2004 of graphene, these materials have aroused an ever-growing interest since different materials form 2D layers: carbon, silicon, transition metal dichalcogenides… Graphene has shown remarkable properties, such as the Dirac-cone-shaped energy band and high carrier mobility. However, despite significant efforts, there has been no reproducible method to open up its bandgap while preserving high carrier mobility. 2DMs based on group IV elements such as Si (silicene) and Ge (germanene) are promising alternatives. Manufacturing good quality, quality-controlled such 2D crystals is thence of major importance from both fundamental and applied perspectives. Their growth by epitaxy that is both the fundamental cleanest way and a technological lock is thence the focus of different experimental studies. The growth on some metallic substrates revealed possible alloying effects that need to be understood and controlled. The goal of this internship is to advance in the theoretical understanding of these systems by using kinetic Monte-Carlo (KMC) simulations that is the most suitable tool to describe these systems over the relevant space and time scales, yet including atomistic time scales.

We will investigate the growth of germanene on top of Ag(111) substrates. A significant experimental work was performed in the hosting team on this system. It revealed new growth modes, and different deposited layer structures as a function of the effective coverage and temperature. Our goal is to rationalize these growth modes thanks to the description of the dynamics and self-organization at work in these systems. We will consider a modelization that will incorporate alloying effects and the possibility of intermixing so as to describe surface alloys revealed by experiments. We will also include surface effects in the dynamics that were shown to be at work in a previous experimental/theoretical study done at INSP concerning the growth of silicene on Ag(111). The numerical part will include the derivation of rejection-free KMC simulations following the Bortz-Kalos-Lebowitz algorithm. The algorithm will include different atomic events starting with the fundamental deposition, diffusion and attachment/detachment processes. These processes will be made dependent on different configurations (local height, local configuration …) to account for different effects (segregation, alloying, wetting etc). Energy barriers will be derived both thanks to experimental and ab-initio results, but also thanks to the analysis of the simulation and experimental morphologies. The aim of this coupling between theory and experiment is to gain control on the growth procedure in order to obtain two-dimensional epitaxial deposits of large size and good crystalline quality. The internship will be done in close collaboration with the experimental group at INSP.

Techniques/methods in use:   kinetic Monte-Carlo simulations

Applicant skills:   numerical abilities, solid state physics