PhD Thesis at INSP in Sorbonne Université, Paris
Supervisor : Jean-Noël Aqua
aqua@insp.jussieu.fr
co-supervisor : Goeffroy Prevot
prevot@insp.jussieu.fr
2D-materials are under active scrutiny as promising candidates for both fundamental science and electronic and photonic applications. A significant interest is devoted to silicene layers due to their exotic properties and easy integration in devices. Among other techniques, the production by molecular beam epitaxy of these 2D-layers is under extensive investigation in order to improve their quality. The need for a control of the growth procedure is clear and requires understanding of the growth mechanisms. Extensive experiments have been performed in the hosting group on the growth of Si on Ag (111), revealing especially the importance of alloying effects. However, the precise scenario leading to experimental morphologies remains unknown [1,2].
The best numerical tool to investigate the growth dynamics is kinetic Monte-Carlo simulations (KMC). Thanks to a number of controlled approximations, they can efficiently describe the dynamics of realistic atomistic models on large-scale systems (from hundreds of nanometers up to micrometers) and on experimental growth time-scale (from minutes up to hours). By assuming a lattice-dynamics, these simulations have been first developed to accurately describe the growth of submonolayer deposition and have been extended to describe epitaxial growth more generally [3]. These models can be implemented to account for the relevant microscopic effects (covalent binding, wetting effects, alloying, elasticity, etc).
The goal of this thesis is twofold. First, the PhD-student will develop a KMC framework for the simulation of the growth of silicene and germanene layers on different substrates, Ag(111), Al(110) etc. The student will implement a KMC code that will include the mechanisms relevant in experiments : interaction with the substrate, geometry, alloying, exchange etc. This work will take benefit from the results of experimental investigations, that will feed the modelization with microscopic parameters, but also of first-principles calculations. Of special interest will be the account of alloying that was precisely revealed on Ag in the hosting group. A systematic analysis of the resulting model will be done in order to shed new light on the experimental growth modes. Second, the student will also participate to dedicated experimental runs for the growth and characterization of silicene and germanene layers.
Overall, this work is expected to reveal the mechanisms that trigger the growth of 2D silicene and germanene, and to guide experimental procedures to produce new materials.
References :
[1] A. Curcella, R. Bernard, Y. Borensztein, M. Lazzeri, A. Resta, Y. Garreau, Prévot G., 2D Materials 4 (2017) 025067
[2] W. Peng W., T. Xu, P. Diener, L. Biadala, M. Berthe,X. Pi, Y. Borensztein, A. Curcella, R. Bernard, G. Prévot, B. Grandidier, ACS Nano 12 (2018) 4754
[3] P. Gaillard P., J.-N. Aqua, T. Frisch, Physical Review B 87 (2013) 125310