Effect of substrate atomic structure on intersolubility and alloying in Pd/Nb adsorption system

Abstract

In order to investigate to what extent the crystallographic structure of the substrate affects the process of interdiffusion and surface alloy formation in the case of the same components, adsorption systems of Pd on Nb(0 1 1), Nb(0 0 1) and Nb(1 1 1) have been studied by means of low-energy electron diffraction, Auger electron spectroscopy, and contact potential measurement. For all the systems, Pd dissolves in the substrate, when its population on the surface exceeds 1 ML. Kinetics of the mutual solution depends on the amount of deposited Pd, and increases with increasing amount of the adsorbate. Independent of the substrate structure, there was no evidence for a mixing of Pd and Nb in the top-most layer. For the Pd/Nb(0 1 1) system, the lateral interactions inside the Pd adlayer surpass the adsorbate–substrate interaction. The adsorbate–substrate interaction is dominant for the Pd/Nb(0 0 1) and Pd/Nb(1 1 1) systems, and results in the formation of a sandwich-like laminar surface alloy with a Pd layer on top.