STUDY OF THE STRUCTURE OF THE RH AG SURFACE USING POSITRON-ANNIHILATION INDUCED AUGER-ELECTRON SPECTROSCOPY

Positron annihilation induced Auger electron spectroscopy (PAES), electron induced Auger electron spectroscopy (EAES), and low-energy electron diffraction have been used to study the temperature dependent composition of vapor-deposited of Rh on Ag(100). Earlier work using AES, ion scattering spectroscopy, and TDS has shown that a Ag layer diffuses to the Rh surface upon annealing to form a structure in which Rh is sandwiched between a Ag cap layer and the Ag substrate. In this work, the top layer selectivity of PAES was utilized to study the diffusion of Ag to the surface as Rh films deposited at 173 K were heated to 573 K. Analysis of the PAES spectra indicates that Rh remains in the top layer during the approximately 3 h required to take PAES data when the sample is maintained at the 173 K temperature of deposition. There is a clear indication that significant migration of Ag to the surface takes place by 373 K. The Ag content of the top layer increases to approximately 100% above 473 K.