Phase-dependent Friction on Exfoliated Transition Metal Dichalcogenides Atomic Layers

The fundamental aspects of energy dissipation on 2-dimensional (2D) atomic layers are extensively studied. Among various atomic layers, transition metal dichalcogenides (TMDs) exists in several phases based on their lattice structure, which give rise to the different phononic and electronic contributions in energy dissipation. 2H and 1T' (distorted 1T) phase MoS₂ and MoTe₂ atomic layers exfoliated on mica substrate are obtained and investigated their nanotribological properties with atomic force microscopy (AFM)/ friction force microscopy (FFM). Surprisingly, 1T' phase of both MoS₂ and MoTe₂ exhibits ≈10 times higher friction compared to 2H phase. With density functional theory analyses, the friction increase is attributed to enhanced electronic excitation, efficient phonon dissipation, and increased potential energy surface barrier at the tip-sample interface. This study suggests the intriguing possibility of tuning the friction of TMDs through phase transition, which can lead to potential application in tunable tribological devices.