Observation of fast positron diffraction from a Si(111)77 surface

Kawasuso, Atsuo; Fukaya, Yuki   ; Hayashi, Kazuhiko; Maekawa, Masaki; Ishimoto, Takayuki*; Okada, Sohei; Ichimiya, Ayahiko*

We so far discovered the total reflection and the first Bragg peak in reflection high-energy positron diffraction (RHEPD). However, the fractional order diffractions from reconstructed surfaces have been eluded from the observation. We therefore attempted to get RHEPD patterns from a Si-77 surface. Consequently, the 1/7, 2/7 and 3/7 diffraction rings due to Si(111)-77 reconstruction were clearly found in addition to the zeroth and the first Laue zones. The specular intensity was measured as a function of glancing angle. A small structure was found in the total reflection region. The small structure was attributed to the interference of positron wavefunction because of adatoms. However, the overall intensity profile was not well reproduced using a model already determined in the electron diffraction studies. To reproduce the obtained intensity profile, we may need to modify the vertical positions of the topmost surface and/or the absorption potential due to inelastic scattering processes.