HIGH-ANGULAR RESOLUTION X-RAY PHOTOELECTRON DIFFRACTION MEASUREMENTS OF SI(111)

The surface crystallography of a single Si(111) 7x7 crystal has been i nvestigated, for the first time, using high-angular resolution (+/-1 d egrees) X-ray photoemission diffraction measurements. Polar scans of t he Si2p core-level intensity have been measured along the principal az imuthal directions of the Si(lll) substrate. Observation of prominent forward scattering features along with fine structure characteristic o f a given azimuth, allow us to identify unambiguously the orientation of the substrate and more specially to distinguish the opposite [1 $($ ) over bar$$ 21] and [($) over bar 12 $$($) over bar 1] directions. Th e forward scattering peaks correspond to the [111], [011] and [11 $$($ ) over bar 1] ([111] and [100]) low-index directions along the [1 $($) over bar$$ 21] ([($) over bar 12 $$($) over bar 1]) azimuth and to th e [111] and [($) over bar 131] crystallographic axis along the [TIG] a zimuth. The maximum polar intensity anisotropy, measured as (Imax-Imin )/Imax, is similar to 51% for the peak located at normal emission. Imp rovement of angular resolution results in a strong enhancement of the profile contrast, and much fine structure which cannot be explained in the simple forward focusing picture. Such data can be used to test th e capabilities of single and multiple scattering simulations.