Ultrathin films of Pd on Nb(111): Intermixing and effect of formation of a surface alloy

Abstract

Pd/Nb(111) adsorption system was investigated by the LEED, AES, and CPD methods. Pd was deposited at room temperature, and annealed from 400 to 2150 K. The growth of Pd deposit follows the monolayer plus simultaneous multilayer growth mode. Up to 24 ML the deposit grows without a long-range order. For coverage higher than 24 ML, Pd(111) domains with the $\mathrm{Pd}〈110〉||\mathrm{Nb}〈211〉$ epitaxial relation appear. Similar domains are seen for coverage higher than 12 ML in the temperature range 400--900 K. Starting from 600 K the process of intermixing of Pd and Nb occurs for each annealed film thicker than 1 ML. It causes formation of the surface alloy with the $(1\ifmmode\times\else\texttimes\fi{}1)$ lateral periodicity with reference to Nb(111). The surface alloy exists from 800 K to 1400 K.