Low-energy positron diffraction from the (110) surfaces of GaAs and InP

Abstract

The intensities of 16 nonequivalent beams of normally incident positrons difFracted from the (110) surfaces of GaAs and InP are reported. The sample temperature was approximately 110 K. The intensities were measured over the energy range 30 eV~E(200 eV. The atomic geometries of GaAs(110) and InP(110) were extracted from these intensities via their comparison with the predictions of a multiplescattering model using the criterion of minimization of the x-ray R factor. The best-fit surface geometries resulting from these analyses are approximately bond-length-conserving top-layer and second-layer rotations characterized by the tilt angles (co&=28. 5'+2. 5' co2= -3.5 +3 ) for GaAs (110) and (co, =24. 5'+1.5', co2= -3. 0'+3') for InP(110). Comparable low-energy electron intensity data were obtained and analyzed for InP(110) leading to (m& = 31 +5 and co2 = -3'+3 ). Small changes 0 (Ad & 0.07 A) in the bond lengths associated with the top-layer species are characteristic of the best-fit structures, but of these, only a small contraction (hd/d~3%) of the bond between the top-layer cation and second-layer anion seems likely to lie outside the uncertainties inherent in the analysis.

The scientific contributions of Karl Frederick Canter (1944–2006)

“…The second triumph of Karl's positron diffraction work was that he was able to make more precise determinations of the surface structure of the compound semiconductors than were possible using electron diffraction [55][56][57][58][59][60][61][62] (see Fig. 15).…”

“…15. Positron diffraction pattern from a GaAs surface (left) [61] and CdTe (right) [62]. one could easily see with the naked eye if you squint.…”

Observation of Low-Energy Positron Diffraction Patterns with a Linac-Based Slow-Positron Beam

“…They developed an electrostatic slow-positron beam with a radioisotope (RI) source emitting positrons through β + -decay. The Brandeis group also demonstrated that in LEPD, experimental intensity profiles were more closely reproduced by the dynamical diffraction theory than in LEED [5][6][7][8][9][10].…”

Analytical Methods Using a Positron Microprobe

“…[39][40][41] Chen et al applied LEPD to GaAs and InP (110) surfaces, and showed that LEPD can more precisely specify the surface structure than LEED alone. 40 More precise studies of other ordered multi-component surfaces are expected.…”