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) at room temperature using angle-resolved photoelectron spectroscopy (ARXPS, AlK alpha) and polar-scan photoelectron diffraction (XPD, AlK alpha), exploiting the forward scattering (FS) enhancement of photoelectrons along atomic chains. The structure of the Fe 3p and 2p XPD polar diagrams and the development of the FS features with film growth evidence 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 segregated Au monolayer (surfactant layer) exists on top of the Fe film This follows from the comparison of a simple model for the development of the substrate and film FS enhancements with the experimental data. By using angular shifts of the Fe 3p and Fe 2p bcc-C-[111] and bcc-[101] FS peaks we could determine the Au(on top)-Fe and Fe-Fe interlayer distances for 1 and 2 ML thick films to be 1.71(0.04)Angstrom and 1.48(0.08)Angstrom, respectively, showing that very thin films have a slightly expanded bcc structure (bet). The regular bce angle positions are observed above 4-6 ML.