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ZnO crystals were implanted with N+, O+, and Al+, and co-implanted with O+/N+ and Al+/N+ ions. Positron annihilation measurements indicate introduction of vacancy clusters upon implantation. In the N+-implanted and Al+/N+ co-implanted samples, these vacancy clusters are only partially annealed at 800 °C, as compared with their entire recovery in the O+- and Al+-implanted samples at 800–900 °C, suggesting a strong interaction between nitrogen and vacancy clusters. However, in the O+/N+ co-implanted sample, most vacancy clusters disappear at 800 °C. Probably oxygen scavenges nitrogen to enhance the annealing of the vacancy clusters. Upon further annealing at 1000–1100 °C, nitrogen also forms stable complexes with thermally generated vacancies. These nitrogen-related vacancy complexes need high-temperature annealing at 1200–1250 °C to be fully removed. [ABSTRACT FROM AUTHOR]

Slow positron beams generally employ a radioactive β+ emitter with a crystal moderator in which the positrons thermalize. A small fraction of the thermalized positrons are desorbed at low (1–3 eV) energy, characteristic of the positron work function in the crystal. The energy width of the emitted positrons from W(110) and Ni(111) moderators can be narrowed significantly by cooling to liquid N2 temperatures. A practical configuration for a cooled moderator positron gun is presented which produces a narrow energy positron beam with good efficiency. [ABSTRACT FROM AUTHOR]

Investigates the solid state reaction of cobalt/silicon and cobalt/titanium/silicon by slow positron beam. Implantation of the variable-energy positrons into samples at different depths; Characterization of the positron energies; Sensitivity of S parameter to thin-film reaction and crystalline characteristics.

A narrow energy beam of slow positrons can be generated by moderating the beta-decay spectrum of a radioactive β[sup +] source. We report here the development and use of the first moderator in which the low-energy positrons are not extracted from the surface facing the β[sup +] emitter but from the opposite surface, i.e., the transmission moderator. An advantage is that such a configuration eliminates the problem of moderated positrons passing by the radioactive source. This is an essential problem when the source is physically large such as the present commerically available Na[sup 22] sources. This moderator is a 5000-Å self-supporting W (100) film. The growth and treatment of the film were found to provide a high-quality positron moderator. The slow to fast positron conversion efficiency, using a Na[sup 22] source, was found to be 4 × 10[sup -4]. [ABSTRACT FROM AUTHOR]

A pulsed, slow positron beam, with a diameter of 200 μm, was extracted into air through a thin SiN window of an atmospheric positron probe microanalyzer (PPMA), and used to measure the ortho-positronium lifetimes τ in polyvinyl alcohol and polycaprolactam sub-μm-thick films. By measuring the variation of τ as a function of relative humidity, the effect of water molecules on the hole sizes, deduced from τ, was examined for the films with consideration to the chain mobility. The results demonstrate the usefulness of the atmospheric PPMA to the in-situ characterization of nanoscopic holes in thin films under practical conditions. [ABSTRACT FROM AUTHOR]