Regular Article

Soft landing of metal clusters on graphite: a molecular dynamics study^★

¹ MBN Research Center, Altenhöferallee 3, 60438 Frankfurt am Main, Germany
² Department of Physics, Utrecht University, Heidelberglaan 8, 3584 CS Utrecht, The Netherlands
³ On leave from Ioffe Institute, Polytekhnicheskaya 26, 194021 St. Petersburg, Russia

^a e-mail: verkhovtsev@mbnexplorer.com

Received: 7 May 2020
Received in final form: 24 August 2020
Accepted: 1 September 2020
Published online: 6 October 2020

Abstract

Structure and stability of nanometer-sized Ag₈₈₇, Au₈₈₇ and Ti₇₈₇ clusters soft-landed on graphite (at deposition energies E_dep = 0.001 − 5.0 eV per atom) are studied by means of molecular dynamics simulations. Parameters for the cluster–surface interactions are derived from complementary ab initio calculations. The shape and the contact angle of deposited clusters are systematically analyzed for different deposition energies and temperature regimes. The Ag₈₈₇ cluster deposited at E_dep ≲ 0.1 eV/atom undergoes collision-induced plastic deformation, thus acquiring an ellipsoidal shape with the contact angle close to 180°. In contrast, Au₈₈₇ and Ti₇₈₇ clusters undergo a collision-induced melting phase transition followed by their recrystallization; these processes lead to the formation of the droplet-like shapes of the clusters in a form of truncated spheroids. At larger deposition energies all clusters flatten over the surface and eventually disintegrate at E_dep ≈ 0.75 − 1.0 eV/atom (for Ag₈₈₇ and Au₈₈₇) and ≈3 eV/atom (for Ti₇₈₇). It is found also that the shape of deposited clusters is strongly influenced by the strength of cluster–substrate interaction and the corresponding interaction mechanism, namely the weak van der Waals interaction between metal and carbon atoms or the van der Waals interaction with an onset of covalent bonding. Similar phenomena should arise in the deposition of clusters made of other elements, which interact with a substrate by one of the above-described mechanisms.