First-principles comparative study on the interlayer adhesion and shear strength of transition-metal dichalcogenides and graphene

Due to their layered structure, graphene and transition-metal dichalcogenides (TMDs) are easily sheared along the basal planes. Despite a growing attention towards their use as solid lubricants, so far no head-to-head comparison has been carried out. By means of ab initio modeling of a bilayer sliding motion, we show that graphene is characterized by a shallower potential energy landscape while more similarities are attained when considering the sliding forces; we propose that the calculated interfacial ideal shear strengths afford the most accurate information on the intrinsic sliding capability of layered materials. We also investigate the effect of an applied uniaxial load: in graphene, this introduces a limited increase in the sliding barrier while in TMDs it has a substantially different impact on the possible polytypes. The polytype presenting a parallel orientation of the layers (R0) bears more similarities to graphene while that with antiparallel orientation (R180) shows deep changes in the potential energy landscape and consequently a sharper increase of its sliding barrier.