Abstract
Al2O3 samples grown with natural well-ordered channels (having sizes of 30–90 nm indiameter) perpendicular to the surface, one side closed, were measured by means ofDoppler broadening (DB) by variable energy positron (VEP) beam and positronannihilation lifetime (PAL) spectroscopy. The samples annealed at 300 and560 °C showed amorphous structure and no positronium (Ps) formation. The sample annealed at850 °C showedγ-phase polycrystalline structure and Ps formation. We were not able to prove from the PALspectroscopy results themselves whether Ps is confined to the channels. We discussthe results of decomposition of the DB annihilation peak into four Gaussians.We conclude that the greater Ps fraction is confined to the channels. From theCompton-to-peak ratio analysis, the fraction of all the injected positrons which formo-Ps and in this form escape from the sample (for a VEP experiment, we havee+ injected from the open side of the channels) has been estimated as being∼20%.
Published Version
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