Glancing-incidence x-ray-absorption fine-structure measurements have been performed for an eight-monolayer-thick Cu film epitaxially grown on a Ag(001) surface and covered by an epitaxial ten-monolayer Au film. It is demonstrated that when the top passive layer is a heavier element, but thin, the glancing-incidence technique is still applicable. The x-ray-absorption near-edge structure for this Cu structure is obtained almost free from the distortion due to anomalous dispersion effects and it is different from that of normal fcc Cu. From the extended x-ray-absorption fine-structure analysis, the structure of the Cu film has been determined to be body-centered tetragonal with lattice constants a=2.88 Å and c=3.10 Å, which is 7.6% expanded vertically from a perfect bcc structure.

• Received 26 March 1991

DOI:https://doi.org/10.1103/PhysRevB.44.6401