Electron-Phonon Coupling Constant of 2H-MoS 2 (0001) from Helium-Atom Scattering

We have studied the (0001) surface of 2H-MoS 2 by means of helium-atom scattering (HAS). The electron-phonon coupling constant, λ λ, of this system has been determined by measuring the thermal attenuation of the specular peak at surface temperatures between 100 and 500 K. HAS diffraction also reveals a 3% planar dilation of the surface layer, whereas step interference measured at low incidence energy indicates a slight contraction of the surface layer thickness. By employing a recently developed quantum-theoretical approach applied to the case of layered degenerate semiconductors for a carrier concentration of 5 × 10 12 cm -2 , we find λ ∼ 0.40. We discuss the derivation of λ from HAS reflectivity data in this class of two-dimensional materials with regard to its dependence on the carrier density and effective mass.