Preparation of stable crystalline surfaces for subsequent fundamental reaction studies

Abstract

Distributed nickel crystallites were prepared by the deposition of nickel vapor in a vacuum of 4 × 10 -8 Torr preferentially onto tin oxide island nucleation sites. Previous studies on thin tin films by Caswell and Budo indicated that tin oxide crystallites form stable discontinuous surfaces when they are vapor deposited at very low temperatures and then oxidized during warm-up. Nickel, in the form of the oxide NiO, was identified from selected area diffraction studies performed with a transmission electron microscope, and dark field investigations of the different metal phases (tin, nickel and their oxides) indicated that the nickel had been deposited onto the tin oxide crystallites only. There was a critical thickness of nickel for each tin oxide island distribution beyond which interisland deposits of nickel formed, e.g. the thickness t of nickel was greater than 5.0 nm on a distribution of tin oxide islands nominally 10.0 nm thick. Different distributions of the stable dispersed tin oxide islands were achieved by varying the temperature at which oxidation of the tin film took place as it broke up into islands during warm-up.