Abstract
We report high-resolution angular diffraction measurements of CH(4) and Ne from Ni(111) and from a graphene (Gr) layer grown on Ni(111), whose effective atomic mass is enhanced by the strong Gr-Ni interaction. The incident energies are between 43 and 68 meV for Ne, and between 62 and 108 meV for CH(4) beams. Sharp diffraction features are observed with Ne beams from both Ni(111) and Gr/Ni(111) surfaces. However, using methane beams, clear diffraction peaks are observed only from Ni(111), with broad angular distributions measured from Gr/Ni(111), as expected for classical particles, with no quantum features. This is surprising, since Ne and methane have similar masses and therefore a comparable quantum behavior is expected for the same incident energy. This effect is mainly due to the larger physisorption well of CH(4) on Gr/Ni(111), as shown by DFT calculations, in addition to the larger corrugation of the potential energy surface and the excitation of phonon modes of the graphene overlayer.