AUGER EMISSION ANGULAR-DISTRIBUTIONS FROM A SILVER MONOLAYER IN THE PRESENCE AND ABSENCE OF AN IODINE OVERLAYER - EVIDENCE FOR THE PREDOMINANCE OF INHOMOGENEOUS INELASTIC-SCATTERING OF AUGER ELECTRONS BY ATOMS

Complete Auger electron angular distributions have been measured from a monolayer of Ag atoms (355 eV) in the presence and absence of an ordered monoatomic overlayer of iodine atoms. In the presence of the iodine overlayer, the Auger emission from the Ag monolayer is anisotropically attenuated to form a distinct hexagonal intensity distribution, and the Auger intensity does not increase relative to that observed for the bare Ag monolayer along any direction of emission. The extent of attenuation is in good agreement with gas-phase cross section measurements for Xe, which also indicate that inelastic scattering predominates over elastic scattering in this energy range. These results are consistent with previous studies in which Auger emission from an ordered monolayer of adsorbed iodine atoms was found to be attenuated along the interatomic directions. Analysis of the Ag/I bilayer data by use of a model in which atoms behave as isotropic point emitters and spherical scatterers of Auger electron leads to a structure which agrees with the results of LEED, STM, AES, and electrochemical measurements. Data for the bare Ag monolayer reveal that the silver layer is nearly hexagonal and is rotated 27.2 degrees with respect to the hexagonal Pt(111) substrate surface.