Overcoming nanoscale friction barriers in transition metal dichalcogenides

Abstract

We study the atomic contributions to the nanoscale friction in layered MX2 (M = Mo, W; X = S, Se, Te) transition metal dichalcogenides by combining ab initio techniques with group theoretical analysis. Starting from stable atomic configurations, we propose a computational method, named Normal-Modes Transition Approximation (NMTA), to individuate possible sliding paths from only the analysis of the phonon modes of the stable geometry. The method provides a way to decompose the atomic displacements realizing the layer sliding in terms of phonon modes of the stable structure, so as to guide the selection and tuning of specific atomic motions promoting MX2 sheets gliding, and to adjust the corresponding energy barrier. The present results show that main contributions to the nanoscale friction are due to few low frequency phonon modes, corresponding to rigid shifts of MX2 layers. We also provide further evidences that a previously reported Ti-doped MoS2 phase is a promising candidate as new material with enhanced tribologic properties. The NMTA approach can be exploited to tune the energetic and the structural features of specific phonon modes, and, thanks to its general formulation, can also be applied to any solid state system, irrespective of the chemical composition and structural topology.

Phonon–phonon scattering selection rules and control: an application to nanofriction and thermal transport

“…Nanoscale intrinsic friction in lamellar van der Waals MX 2 transition metal dichalcogenides occurs during relative sliding of adjacent layers. We have already shown [26][27][28][29] that all possible sliding directions can be represented by suitable combinations of few vibrational modes, namely sliding modes; moreover, the layer sliding occurs until such modes own enough energy, and therefore, the frictional forces are all those forces which activate dissipative processes producing a depopulation of the sliding modes. 30 Such depopulation occurs via phonon-phonon scattering involving sliding and non-sliding, hence dissipative, modes; if such scattering is forbidden, then dissipation does not occur and sliding is longer active.…”

Friction Anisotropy of MoS2: Effect of Tip–Sample Contact Quality

“…Another factor that can contribute to friction anisotropy is the energy landscape at the contact established between the tip and sample. In the classical Prandtl-Tomlinson (PT) model 43,44 , friction at the atomic scale depends on the height of the surface energy barrier (affected by several parameters such as surface roughness 45 and composition 46 ) that the tip has to overcome to slide.…”

Resonant and anti‐resonant modes of the dilute, spin‐inbalanced, two‐dimensional electron liquid including correlations

“…However, accounting for correlation effects lowers the spin‐plasmon dispersion, implying that it enters the strong damping continuum at much lower wave vectors . Similar situations are known for the acoustic modes in other binary Coulomb systems, such as ionic mixtures, electron bilayers, semiconductor double wells, or the interface 2DEL of perovskites coupled to graphene (the list being far from complete; note also recent work on static many‐body correlations in graphene and the linear mode in the graphene‐related MoS 2 ). The transverse counterpart of the spin‐plasmon, i.e.…”