On the stability of vapor grown palladium particles supported on amorphous alumina

Abstract

Transmission electron microscopy studies of small supported metal particles grown by vapor deposition under ultrahigh vacuum (UHV) conditions often require stabilizing overcoats (also called "fixing layers") in order to preserve the initial structure of the deposit. Whether such stabilizing overcoats must be used depends on the specific combination of support and deposit materials and on the stage of deposition to be studied. In this study, the influence of a SiOx overlayer on nanometer-size palladium particles deposited on an in situ cleaned amorphous alumina support film is investigated. For supported palladium particles at the very early stages of metal film growth, deposits coated in situ with SiOx show higher number densities and smaller mean sizes than uncoated ones. The comparison between uncoated and coated palladium deposits shows that the SiOx substantially retards sintering of palladium cluster deposits which had to be exposed to laboratory air during transfer from the UHV deposition environment to a standard transmission electron microscope for size and number density analysis. SiOx also retards but does not prevent electron beam effects during high-resolution transmission electron microscopy. © 1992.