Effects of Surface Disorder, Various Surface Structures of Chemisorbed Gases and Carbon on Helium Atomic Beam Scattering from the (100) Surface of Platinum

Abstract

Low-energy electron diffraction and helium atomic beam scattering have been combined to investigate on the (100) face of a platinum single crystal the effects of changing surface structure on the gas–solid interaction. The angular distribution of a helium beam scattered from the ordered and disordered crystal face has been monitored. The intensity of the beam scattered at the specular angle increases by nearly an order of magnitude upon atomic ordering of the metal surface. Ordered domains of graphitic carbon also yielded high intensity peaks in the specular direction. The magnitude of the intensity maxima for helium beams scattered from ordered surface structures of various chemisorbed gases (CO, C2H2) was sensitive to surface order but insensitive to the type of surface structure formed. For all the surface structures studied the scattered helium beam distribution was directed with the intensity maximum at the specular angle. The surface temperature dependence of the beam dispersion and intensity scattered at the specular angle was monitored in the temperature range 450–1300°K. Anomalous changes in the beam intensity could be associated with the adsorption of carbon monoxide on the crystal face.