Influence of cutoff radius and tip atomic structure on energy barriers encountered during AFM tip sliding on 2D monolayers

Abstract

In computational studies using the Lennard-Jones (LJ) potential, the widely adopted 2.5 σ cutoff radius effectively truncates pairwise interactions across diverse systems (Santra et al 2008 J. Chem. Phys. 129 234704, Chen and Gao 2021 Friction 9 502-12, Bolintineanu et al 2014 Part. Mech. 1 321-56, Takahiro and Kazuhiro 2010 J. Phys.: Conf. Ser. 215 012123, Zhou et al 2016 Fuel 180 718-26, Toxvaerd and Dyre 2011 J. Chem. Phys. 134 081102, Toxvaerd and Dyre 2011 J. Chem. Phys. 134 081102). Here, we assess its adequacy in determining energy barriers encountered by a Si monoatomic tip sliding on various two-dimensional (2D) monolayers, which is crucial for understanding nanoscale friction. Our findings emphasize the necessity of a cutoff radius of at least 3.5 σ to achieve energy barrier values exceeding 95% accuracy across all studied 2D monolayers. Specifically, 3.5 σ corresponds to 12.70 Å in graphene, 12.99 Å in MoS2 and 13.25 Å in MoSe2. The barrier values calculated using this cutoff support previous experiments comparing friction between different orientations of graphene and between graphene and MoS2 (Almeida et al 2016 Sci. Rep. 6 31569, Zhang et al 2014 Sci. China 57 663-7). Furthermore, we demonstrate the applicability of the 3.5 σ cutoff for graphene on an Au substrate and bilayer graphene. Additionally, we investigate how the atomic configuration of the tip influences the energy barrier, finding a nearly threefold increase in the barrier along the zigzag direction of graphene when using a Si(001) tip composed of seven Si atoms compared to a monoatomic Si tip. © 2024 IOP Publishing Ltd.