SEXAFS investigation of bct Mn grown epitaxially on Ag(001) at room temperature

Mn layers deposited at room temperature on AE(001) in the 2-15 monolayers ( ML) range are investigated by polarization-dependent surface-extended X-ray absorption fine structure (SEXAFS) and X-ray photoelectron diffraction (XP D) techniques. Up to about 3 ML, the Mn forms a pseudomorphic interfacial a lloy with a face centered cubic (fcc) structure that continues the Ag latti ce. Yet, above 3 ML, an essentially pure Win phase with a body-centered tet ragonal (bct) structure grows on top of the interfacial alloy. The in-plane kin-Mn distance is found to be 2.86 +/- 0.02 Angstrom, essentially the sam e as in Ag (001) plane, i.e. the film growth is coherent. The shortest out of plane Mn-Mn distance is 2.60 +/- 0.02 Angstrom, but there is evidence th at it must be taken as a mean value, because of an inhomogeneity in the int erlayer spacing along the [001] growth axis. This may be related to the eff ect of marked interfacial relaxations in these ultrathin films and particul arly a strong sensitivity of the Mn atomic volume to its local environment. (C) 1999 Elsevier Science B.V. All rights reserved.