Characterization of Frictional Properties of Single-Layer Molybdenum-Disulfide Film Based on a Coupling of Tip Radius and Tip–Sample Distance by Molecular-Dynamics Simulations

Abstract

Lateral-force microscopy is a powerful tool to study the frictional properties of two-dimensional materials. However, few works distinctly reveal the correlation between the tip radius with the tip–sample distance and the frictional properties of the two-dimensional (2D) materials. We performed molecular-dynamics simulations to study the atomic-scale friction of a typical two-dimensional single-layer molybdenum disulfide (SLMoS2). The effects of tip radius and tip–sample distance on the frictional properties were analyzed and discussed. The frictional force–sliding-distance curves show typical stick–slip behaviors, and the periodicity can be used to characterize the lattice constants of SLMoS2. Sub-nanoscale stick-slip movements occur in one-lattice sliding periods along with only the armchair (AC) direction and only when the tip radius is smaller than 3 Å with 1.47 Å tip-sample distance. At the same tip–sample distance, a smaller tip can provide a more detailed characterization and higher-precision frictional properties of SLMoS2. A larger tip is capable of providing comparative frictional properties of SLMoS2 at a proper vertical tip–sample distance, compared with the small tip.

Smoothed particle hydrodynamics study of friction of the coarse-grained α-Al2O3/α-Al2O3 and α-Fe2O3/α-Fe2O3 contacts in behavior of the spring interfacial potential

“…However, it should be noticed that because of lattice structure the lower peaks additionally appear to interleave the higher peaks in the friction force curves as seen in this work (Fig. 4) and the work of Pang et al [24] that simulated the atomic-scale friction of a typical two-dimensional singlelayer molybdenum disulfide. This work also states that at micron-scale there is a little difference of the average friction and normal forces between the CG Al2O3 and Fe2O3 oxides.…”

Atomic-Scale Friction on Monovacancy-Defective Graphene and Single-Layer Molybdenum-Disulfide by Numerical Analysis

“…However, the vacancy defects, known as the most commonly reported defects in graphene [20,21] and SLMoS 2 [22,23], are inevitable during the production process and can result in considerable changes in surface morphology. So far, most experimental, theoretical, and simulation studies on the atomic-scale friction of graphene and SLMoS 2 have focused on atomically flat surfaces [24][25][26][27][28]; nevertheless, these simplified idealizations cannot reflect the topography and frictional properties of many practical surfaces such as vacancy-defective surfaces. Molecular dynamics (MD) simulations have indicated that the frictional forces of defective graphene were significantly increased in the vicinity of vacancy point defects compared to that of the perfect graphene [29,30].…”

Improving the atomic-resolution AFM imaging of monolayer MoS2for worn tips: a molecular dynamics study

“…In general, sample topography recorded by an AFM is considered to be more exquisite with a sharper tip. [11][12][13] However, the tip-sample interaction for silicon tips 14) during AFM scanning and indentation experiments inevitably causes tip wear, though carbon nanotube tips and diamond-coated tips are quite resistant to wear. 15,16) The tip wear may enlarge the tip radius gradually, and the AFM imaging resolution and quality become degraded.…”

“…17) Besides, it is difficult when only using the AFM force curves to measure or control the tip-sample distance in an actual experiment for the reasons that various component forces, such as Coulomb (electrostatic), 18) van der Waals (dispersion), 19) atomic 20) and dipole forces, 21) are exerted by sample atoms on the tip, and these force curves remarkably differ from each other. 11) Many endeavours have been devoted to testing the ultrahigh resolution of AFM through modifying the tip apex or state. [22][23][24][25] However, they emphasized their works on the effects of tip apex on imaging a single atom or cluster on the substrate and did not move the tip parallel to the sample surface with different vertical distance between the surface and the tip.…”

“…Ignoring the same other conditions for new or sharp tips, for blunt tips in this work, we only consider two factors, the tip radius and the tip-sample distance, to investigate their feasibility of achieving sub-atomic resolution AFM imaging. We are pleasantly surprised that the atomic-scale AFM imaging quality, following the LFM imaging, 11) can be obtained by a coupling effect of the tip-sample distance and the tip radius, and such investigation may shed light on the AFM operation when one expects to achieve highresolution AFM imaging of 2D materials.…”