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A 10 keV positron beam has been developed using coaxially symmetric electromagnetic lenses for reflection high-energy positron diffraction (RHEPD) experiments. The beam brightness is 10 $^{7}$ e $^{+}$ /sec/cm $^{2}$ /rad $^{2}$ /V which is comparable to that obtained using brightness enhancement technique. The beam parallel and normal coherence lengths are over 100 and 40 , respectively, which are long enough to observe diffraction patterns associated with large surface super-structures. RHEPD patterns from a Si(111)-(77) reconstructed surface have been successfully observed with a much better quality than previously reported.

Journal Articles

Kinematical and dynamical analyses of reflection high-energy positron diffraction (RHEPD) patterns from Si(111)77 surfaces

Hayashi, Kazuhiko; Fukaya, Yuki; Kawasuso, Atsuo; Ichimiya, Ayahiko

Applied Surface Science, 237(1-4), p.34 - 39, 2004/10

https://doi.org/10.1016/S0169-4332(04)00994-8

no abstracts in English

Journal Articles

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*

Materials Science Forum, 445-446, p.385 - 389, 2004/02

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.

JAEA Reports

Development of reflection high-energy positron diffraction (RHEPD) based on an electrostatic positron beam

Ishimoto, Takayuki*; Kawasuso, Atsuo; Ito, Hisayoshi; Okada, Sohei

JAERI-Tech 2003-091, 32 Pages, 2003/12

JAERI-Tech-2003-091.pdf:3.96MB

no abstracts in English

Journal Articles

Si(111)-77 surface probed by reflection high-energy positron diffraction

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

Physical Review B, 68(24), p.241313_1 - 241313_4, 2003/12

https://doi.org/10.1103/PhysRevB.68.241313

Times Cited Count：25 Percentile：72.06(Materials Science, Multidisciplinary)

We report the first observation of reflection high-energy positron diffraction from a reconstructed Si(111) surface with an well-collimated 20 kV positron beam. The diffraction pattern clearly exhibited the 1/7-th to 3/7-th order Laue zones in addition to the zero-th and first Laue zones. From the dynamical calculation of the rocking curve in the total reflection region, the vertical position of adatom layer was determined to be 1.52 relative to the stacking fault layer. This value is greater than that predicted in the first principles study suggesting a significant outward relaxation of adatoms.