9502459 Weiss Positron annihilation induced Auger Electron Spectroscopy (PAES) utilizes a fundamentally new process in which the excitations necessary for Auger spectroscopy are created by positrons annihilating core electrons and not, as in conventional Auger methods, by collisional ionization. PAES is uniquely sensitive to the critical topmost atomic layer of solids due to the trapping of positrons in an image potential well just outside the surface before annihilation. Experiments are proposed which will capitalize on this ability of PAES to determine the elemental content of the topmost atomic layer in achieving an understanding of catalytically important ultrathin metal fillm systems, including neodynium on copper, and copper on palladium, as well as to study surface segregation in alloys such as platinum- nickle and platinum-gold. The fact that PAES measurements can be made using energy doses many orders of magnitude less than those needed with conventional Auger techniques will be utilized to study fragile adsorbed layers and chemically unstable systems including hydrogen and organic molecules on metal surfaces. %%% Positron annihilation induced Auger Electron Spectroscopy (PAES) utilizes a fundamentally new process in which the input energy required for the emission of so-called Auger electrons from a solid results from the annihilation of positive electrons (antimatter) with negative electrols in atomic cores rather than from collisions of energetic incident electrons with the core electrons, as in conventional Auger methods. PAES is uniquely sensitive to the composition of the critical topmost atomic layer of solids due to the trapping of positrons just outside the surface before annihilation. The proposed experiments will capitalize on this sensitivity of PAES to determine the elemental content of the topmost atomic layer to advance undertanding of catalytically important ultrathin film materials, such as copper on palladium, and to study the surface segregation of constituent elements in alloys such as platinum-nickel. In addition, the fact that PAES measurements can be made using energy doses hundereds of times weaker than those needed with conventional Auger methods will be utilized to study fragile adsorbed layers and chemically unstable coverings such as hydrogen and organic molecules on metal surfaces. ***
