Electron–Phonon Coupling Constant of 2H-MoS2(0001) from Helium-Atom Scattering

We have studied the (0001) surface of 2H-MoS2 by means of helium-atom scattering (HAS). The electron-phonon coupling constant, A, 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 X 10(12) cm(-2), we find lambda similar to 0.40. We discuss the derivation of A from HAS reflectivity data in this class of two-dimensional materials with regard to its dependence on the carrier density and effective mass.