Crystallographic and electronic structure of Cr films on Au(100)

Abstract

We have investigated the crystallographic and electronic structure of thin Cr films deposited at room temperature (RT) on a clean Au(100) single crystal, using X-ray photoelectron forward scattering, as well as angle resolved ultra-violet photoemission (ARUPS). The X-ray photoelectron diffraction curves were obtained by following the Cr2p 3/2 or Au4f 7/2 core line intensity versus polar angle θ. When 7 layer equivalent (LE) of Cr or more are deposited (1 LE Cr corresponds to the Cr(100) surface atomic density), the diffraction curves are structured and exhibit Cr2p 3/2 core line enhancement at θ = 0° and 45° in the Au(011) azimuthal plane, indicating the growth of a body centered cubic (bcc) Cr layer. However, at low coverages (1-3 LE), the curves show maxima at quite different positions, for example at θ = 0°, 35° and 54° in the Au(011) plane, and they are similar to the curves obtained for the face centered cubic (fcc) Au(100) substrate. These data indicate that the Cr atoms are embedded in a fcc environment, most likely the Au matrix. Thus we conclude that low coverages a substitutional Cr—Au alloy is formed at RT. We also show that our ARUPS results are in agreement with this conclusion.