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.