An assessment of multiple-scattering effects in Auger-electron diffraction and photoelectron diffraction

Abstract

Multiple-scattering effects in Auger electron diffraction and photoelectron diffraction are assessed using a new spherical-wave multiple scattering formalism which is based on a separable approximation to the scattering Green's function. Results obtained in both single-scattering and fullyconverged multiple-scattering limits are presented for linear chains of Cu atoms. Simulations of some Auger electron diffraction and photoelectron diffraction experimental results with this new theory are also presented for the first time.

The Study of Surface Structures by Photoelectron Diffraction and Auger Electron Diffraction

“…57 ,85 A more reasonable procedure is to include events up to, say, the fifth order if the total path length rj + 'ik + rkl + . .. is less than some cutoff value of 10-20 A,20,25,57,85 although an inproved cutoff criterion has been suggested by Kaduwela et al 84 As noted previously, there is by now a considerable body of data which indicates that useful structural information can be derived at the SSC-SW or even SSC-PW level, and we will show illustrations of this in subsequent sections. Nonetheless, MS effects such as those described above can cause discrepancies between experiment and theory for certain classes of system, and full MS treatments of both photoelectron and Auger electron diffraction are beginning to be more often used.…”

“…24 84 One effect of MS first discussed by Poon and Tong 24 is a defocusing of intensity occurring in multiple forward scattering at higher energies along a dense row of atoms, such that an SSC-PW or SSC-SW calculation along such a row may overestimate the intensity by a factor of two or more. This is illustrated schematically in Fig.…”

“…73 ,82,83 Such defocusing effects have been very nicely illustrated in recent MSC-SW calculations by Barton, Xu, and van Hove 73 ,82,83 and by Kaduwela et at. 84 for emission from chains of Cu atoms of variable length. Some recent results of this type are shown in Figs.…”

X-ray photoelectron diffraction and low-energy electron diffraction study of the interaction of oxygen with the Ni(001) surface: c(2 × 2) to saturated oxide

“…MS effects inXPD are not significant unless there are long rows of atoms present in the cluster which lie within about 10° of the photoemission direction [32,33]. MS also may produce some effects for the thicker annealed oxide, where it would be expected to yield a reduction of the intensity of the forward scattered peaks predicted by sse theory, but it is not expected to significantly influence the conclusions of this analysis.…”

“…A more sophisticated program that takes into account photoelectron multiple scattering (MS) events is also available to us, although computer-time constraints limit the size of the clusters that can be used at present to about 30-40 atoms [32,33]. In general, .…”