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

Abstract

In computational studies using the Lennard-Jones (LJ) potential, the widely adopted 2.5σ cutoff radius effectively truncates pairwise interactions across diverse systems [1-7]. Here, we assess its adequacy in determining energy barriers encountered by atomic force microscopy (AFM) tips interacting with various two-dimensional (2D) monolayers, which is crucial for understanding nanoscale friction. Our findings emphasize the necessity of a cutoff radius of at least 3.5σ to achieve consistent energy barrier values across different 2D monolayers. Specifically, 3.5σ corresponds to 12.70 Å in graphene, 12.99 Å in MoS2, and 13.25 Å in MoSe2. This cutoff effectively predicts direction-dependent friction in graphene and the frictional differences between graphene and MoS2, corroborating previous experimental observations [8, 9]. Furthermore, we demonstrate the applicability of the 3.5σ cutoff for graphene on an Au substrate and bilayer graphene. Additionally, we investigate how the atomic configuration of the tip influences the energy barrier. Comparing a Si(001) tip composed of seven Si atoms to a monoatomic Si tip, we observe a nearly threefold increase in the energy barrier along the zigzag direction of graphene.