LEED Observations of Epitaxially Grown Thorium on (100) Tantalum

Abstract

The growth of thorium overlayers on (100) tantalum at 950°C has been studied to an equivalent depth of 20 monolayers by LEED. The thorium intinally forms an incomplete c (2×2) structure, in `island,' up to a density of 3×1014 atoms/sq cm. Thereafter the 2D LEED pattern shows that the thorium has apparent (1×1) registry with the tantalum substrate up to a density of 1.8×1015 atoms/sq cm. The possibility of pseudomorphism is discussed. Recent electron micrographs of the surface show that thorium agglomerates in random islands after completion of the first 2D psendomorphic monolayer.