X-RAY PHOTOELECTRON DIFFRACTION FROM ULTRA-THIN CR LAYERS ON AU(100) AND AG(100) - A COMPARISON

Ultra-thin Cr films deposited at room temperature on Au(100) and Ag(100) single crystals have been studied by X-ray photoelectron diffraction (XPD). For Cr coverages higher than 7 layer equivalents (LE), the modulations of the Cr 2p level intensities versus the polar angle theta present maxima indicating for both substrates the growth of epitaxial body centered cubic (bcc) Cr. However, at low coverages (1-3 LE), the curves show Cr 2p core line enhancement at angles different from those expected for a bcc layer. We show that, for Cr/Au(100), the Cr atoms are in a face centered cubic (fcc) environment and are incorporated in the Au(100) matrix. In contrast, for Cr/Ag(100), the shift of the forward scattering angular positions can be mainly related to Ag segregation on top of the bcc Cr layers and, possibly, to some distortion from a bcc environment in these ultra-thin layers.