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

Positron annihilation induced Auger electron spectroscopy (PAES), elec tron induced Auger electron spectroscopy (EAES), and low-energy electr on diffraction have been used to study the temperature dependent compo sition of vapor-deposited of Rh on Ag(100). Earlier work using AES, io n 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 sa ndwiched between a Ag cap layer and the Ag substrate. In this work, th e 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 la yer during the approximately 3 h required to take PAES data when the s ample is maintained at the 173 K temperature of deposition. There is a clear indication that significant migration of Ag to the surface take s place by 373 K. The Ag content of the top layer increases to approxi mately 100% above 473 K.