Growth mechanism and epitaxy of ultra-thin cobalt films on Pd(001)

Evidence for a strain-stabilized bct phase of cobalt deposited on Pd{100}: An x-ray photoelectron diffraction study

“…This is evidence that islands at least three layers in height already exist on the surface, a result that confirms those reported in Ref. 13. By a coverage of five LE's, all XPD features are fully formed along both azimuths.…”

“…13, XPD azimuthal curves show that the structure of the cobalt film is related to the fcc bulk structure of pure cobalt. However, compared with the positions of the forward-focusing peaks from clean palladium, the peak positions for the cobalt overlayer are substantially shifted to higher polar angles.…”

“…6 We can rule out the formation of different cobalt phases; for instance, a hcp phase could not give rise to the observed fourfold symmetry in the azimuthal curves. 13 We can also consider it highly unlikely that alloying takes place during deposition. Cobalt and palladium form bulk alloys over the whole range of compositions; 16 however, surface alloying at bimetallic interfaces at room temperature has normally been observed to be very slow, or not detectable at all.…”

“…In a previous paper, 13 we used low-energy ion scattering and x-ray photoelectron spectroscopy to determine that cobalt grows initially on Pd͕100͖ in three-dimensional islands. We also reported that a good agreement could be found in the azimuthal XPD data by means of a simple model that assumed a fcc structure for the cobalt layer with the ͕100͖ plane parallel to the substrate surface.…”

“…12 In the present work the estimated coverages are quoted in layer equivalents ͑LE's͒, corresponding to the amount of Co required to form a perfect monolayer. Since the growth of cobalt on Pd͕100͖ is known to be in three-dimensional islands, 13 the quoted values are expected to underestimate the actual Co coverage. All XPD measurements were made at room temperature using nonmonochromatized Al K␣ radiation ͑hϭ1486.6 eV͒.…”