AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA5
Normal Incidence X-ray Standing Wave and Medium-energy Ion Scattering Investigation of the Structure of Ultra-thin Films on Cu(111)

Wednesday, October 4, 2000, 3:20 pm, Room 210

Session: Surface and Interface Structure I
Presenter: M.D. Crapper, Loughborough University, U.K.
Authors: M.D. Crapper, Loughborough University, U.K.
M.T. Butterfield, Loughborough University, U.K.
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Many of the techniques available for surface structural determination fall into two broad categories. The first of these is the family of diffraction techniques, where long-range order is required to allow investigation of a structure. In samples that are not completely ordered, a diffraction based technique will often preferentially reveal information about the regions of the sample that are ordered. The second category is the so-called local probes, which sample the environment around a particular species but do not reveal information about the long-range order. Two techniques that do not clearly fall into either category, but have aspects of each are medium energy ion scattering (MEIS) and the normal incidence X-ray standing wave method (NIXSW). Both of these methods can yield valuable information where imperfect order is present, but on a scale larger than merely local. We report the novel application of a combination of these methods to investigate the structure of ultra-thin overlayers of Co, Fe and Mn on Cu(111). In the case of Co on Cu(111), pure fcc growth does not continue after the first two layers, but there is no one single growth mode. Instead there is a gradual inclusion of stacking faults with evidence of both hcp and fcc twinning. The initial growth of Fe on Cu(111) is also fcc but with a transition of the entire film to bcc at around 5-8 ML rather than a gradual transition. Overlayers of Mn show no site coherence, even below one monolayer. Upon annealing, however, an alloy is formed to a depth of around five layers that has an effective fcc structure but with increased d-spacing over that found in Cu(111) and with Mn substituting some Cu sites.