He and Ar beam scatterings from bare and defect induced graphite surfaces

The effect of the local electronic modification of the graphite surface on the gas?graphite interaction has been investigated by the molecular beam scattering technique. The angular intensity distributions of He and Ar beams scattered from pristine and defect induced graphite surfaces have been measured at various surface temperatures. From the He scattering results, the cross-section for the He diffuse scattering per defect is estimated as being as much as 113? nm2. The origin of the extremely large cross-section is ascribed to the modulated electronic states of graphite around the defect based on the STM measurements, which is due to the local breaking of the ? conjugated system of graphite. From the Ar scattering results, the effective mass of the graphite surface for the Ar collision has been estimated as M = 114?u, based on the analysis with the hard cube model. The new component appears in the scattering distribution of Ar for the defect induced graphite surface. The component has a larger peak position angle than that for the pristine graphite surface, indicating that the normal component of the translational energy of the Ar atom was greatly lost by the collision at the electronically modified area of graphite.