Molecular Beam Scattering from Single Crystal Surfaces under Ultrahigh Vacuum Conditions

Abstract

Studies of the angular distribution of scattered atomic and molecular beams from single crystal surfaces give detailed information about the gas-solid interaction. An ultrahigh vacuum system combining molecular beam scattering with in situ observation of the same crystal surface by low-energy electron diffraction is described. A rotating quadrupole mass spectrometer and lock-in detection of the modulated (150 Hz) incident beam provide density profiles of the scattered gases. The scattering of thermal energy helium and oxygen beams from the (100) face of a platinum single crystal is given to demonstrate the types of surface studies that may be carried out in such an apparatus. Data are presented showing the effects of CO adsorption and surface roughness on the scattered beam intensity, and the scattering of various molecular beams from clean and contaminated surfaces.