Daniel Forster, département de physique, UdeMchercheur postdoctoral dans le groupe de Laurent Lewis

Abstract:

Graphene, graphite or epitaxial graphene on metal as a substrate for nanoparticle deposition have recently become an active field of experimental and theoretical research [1, 2]. In particular, epitaxial graphene on metal forms moiré structures due to incommensurate lattice constants favoring self-assembly of adsorbates. In this work, we consider weakly interacting platinum nanoclusters [3] on these substrates and compare them to more strongly bound ruthenium adsorbates [4].

In order to study the dynamical properties of such systems of reasonable size (up to thousands of atoms), we employed a semi-empirical bond-order potential [5]. However this type of potential lacks the contribution of long-range London dispersion forces which affect the behavior of the adsorbates significantly due to the semi-infinite nature of the substrate. We address this issue by extending the covalent force field by the empirical Grimme D2 dispersion correction commonly used in combination with electronic structure calculations [6]. In a coarse-grained approach we have integrated the contribution of entire substrate layers to the dispersion forces. Non-additivity of dispersion forces involving the metal part of the substrate is taken into account via an empirical screening factor.

Through local optimizations, we studied the influence of the dispersion description on the structure and stability of defective graphene on metal as well as nanoclusters deposited on the different substrates. At finite temperature molecular dynamics simulations shed light on the surface diffusion mechanism of the adsorbates. Further the analysis of viational properties of the different subsystems gives insight into anharmonicities. Throughout these computations the effect of the explicit and implicit dispersion description is always evaluated. Validation against available experimental [7] and ab-initio [8] results is attempted.

[1] J. Wintterlin. and M.-L. Bocquet, Surf. Sci. 603, 1841 (2009).[2] H. Tetlow, J. Posthuma de Boer, I. J. Ford, D. D. Vvedensky, J. Coraux, and L. Kantorovich, Phys. Rep. 542, 195 (2014).[3] G. D. Förster, F. Rabilloud, and F. Calvo, Phys. Rev. B 91, 245433 (2015).[4] G. D. Förster, F. Rabilloud, and F. Calvo. Phys. Rev. B 92, 165425 (2015).[5] D. W. Brenner, Phys. Rev. B 42, 9458 (1990).[6] S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010).[7] M. Gao, Y. Pan, L. Huang, H. Hu, L. Z. Zhang, H. M. Guo, S. X. Du, and H.-J. Gao, Appl. Phys. Lett. 98, 033101 (2011).[8] G. Ramos-Sanchez and P. B. Balbuena, Phys. Chem. Chem. Phys. 15, 11950 (2013).

Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et le Département de génie physique de Polytechnique Montréal.