Two-dimensional layers of tellurium on a copper(001) surface

Abstract

In the course of a series of experiments concerning clean Te surfaces and two-dimensional layers of Te, the initial stage of Te growth on a Cu (001) surface kept at room temperature has been studied by LEED and is found to proceed via two ordered quadratic structures, one is a c(2 × 2) structure simply related to the substrate spacing, the other is a coincidence structure, 5 Te unit meshes fit 6 Cu unit meshes in the Cu[100] direction. The latter structure is believed to contain only Te species and the stage resembles the layered structure of Cu 2Te. The structure shows a sharp reversible order-disorder transition at T c ≈450°K involving loss of the coincidence relation. No parallel growth occurred, but increased Te coverage leads to the formation of three-dimensional Te crystallites with surfaces inclined to the substrate plane. Thermal treatment at ≈800°K transformed the Te crystallites to a two-dimensional hexagonal structure usually only stable above sa 500°K. Occasionally two other coincidence structures have been observed after heat treatment. They seem to obey the relations; 6 Te square unit meshes fit 7 Cu unit meshes in the Cu[100] direction, and 4 Te square unit meshes fit 7 Cu unit meshes in the Cu[110] direction. The last coincidence structure shows a sharp reversible order-disorder transition at T c ≈ 375 °C.