The construction and operation of a scanning positron microbeam is reported. The positrons are obtained from a doubly remoderated positron beam with a normalized brightness-per-volt of 1.8×105 e+ s−1 cm−2 rad−2 V−1 Ci−1. The beam of 8000 e+ s−1 is brought to a 10×50 μm2 focus by a sectored lens and is scanned across a test grid. Possible applications to defect spectroscopy and the observation of small samples will be discussed.

Low-energy positron diffraction intensities were measured for 10 beams from CdSe(101̄0) and 14 beams from CdSe(112̄0). These were compared with calculated intensities for bond-length-conserving relaxed surface structures for both surfaces. Using an R-factor methodology the best-fit structures were obtained for these surfaces corresponding to local planar tilt angles of ω=15°±5° for CdSe(101̄0) and ω=27±7° for CdSe(112̄0). Both results are in excellent correspondence with structures predicted by tight-binding total-energy minimization calculations.

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