AN ANGLE-SCANNED PHOTOELECTRON DIFFRACTION (XPD) STUDY OF THE GROWTH AND STRUCTURE OF ULTRATHIN FE FILMS ON AU(001)

We report a study of the growth and structure of Fe films on Au(001) a t room temperature using angle-resolved photoelectron spectroscopy (AR XPS, AlK alpha) and polar-scan photoelectron diffraction (XPD, AlK alp ha), exploiting the forward scattering (FS) enhancement of photoelectr ons along atomic chains. The structure of the Fe 3p and 2p XPD polar d iagrams and the development of the FS features with film growth eviden ce that Fe grows pseudomorphically in a nearly perfect layer-by-layer mode with bcc (001) structure rotated by 45 degrees about the surface normal. At least up to 4 and probably up to 6 monolayers Fe, a segrega ted Au monolayer (surfactant layer) exists on top of the Fe film This follows from the comparison of a simple model for the development of t he substrate and film FS enhancements with the experimental data. By u sing angular shifts of the Fe 3p and Fe 2p bcc-C-[111] and bcc-[101] F S peaks we could determine the Au(on top)-Fe and Fe-Fe interlayer dist ances for 1 and 2 ML thick films to be 1.71(0.04)Angstrom and 1.48(0.0 8)Angstrom, respectively, showing that very thin films have a slightly expanded bcc structure (bet). The regular bce angle positions are obs erved above 4-6 ML.