Structural properties and water adsorption behaviour of iron films grown on Cu(111)

Abstract

Thin films of iron are deposited at 300 K on Cu(111). Up to four monolayers (ML), a pseudomorphic growth of iron films is observed by reflection high-energy electron diffraction (RHEED) leading to the formation of (111) planes of γ-fcc iron with a lattice parameter of 3.59 Å. Beyond that thickness, a progressive relaxation towards an α-bcc(110) plane is reported. For thicknesses of about 10 ML, the films are still strained as attested by a lattice parameter slightly smaller than that expected for bulk α-iron. By producing γ-(111) and α-(110) iron surfaces at will, water adsorption properties are investigated in the same conditions on both surfaces. After adsorption at 120 K, no dissociation is observed and the temperature-programmed desorption (TPD) spectra present two desorption peaks attributed to a first layer of chemisorbed molecular water and to multilayers of ice, respectively. The adsorption behaviour of water appears to be independent of the structure of the films. The exposure of the iron films to 250 L of oxygen at room temperature does not induce the dissociation of water on the oxidised surfaces as expected.