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Local structures around Mn in In 1Ϫx Mn x As films grown by molecular-beam epitaxy have been studied by using Mn K-edge extended x-ray-absorption fine-structure ͑EXAFS͒ technique. Substitution of Mn atoms for the In sites is found in samples either grown at low substrate temperatures ͑near 200°C͒ or with a low Mn concentration ͑about 1 at. %͒. This result represents a significant extension of an earlier EXAFS study and serves as direct experimental evidence for III-V diluted magnetic semiconductors obtained by substitutional doping of Mn impurities in InAs.

Pronounced structure in x-ray excited luminescence (XEL) has been observed in dilute Tb-doped Y2O3 (Y2O3:Tb) nanocrystals. This effect affords a means to assess different energy transfer mechanisms in the nanocrystals and also an opportunity for novel device applications. Sharp jumps and oscillations are found in the XEL output with the incident x-ray energy around the absorption edges of Y and Tb. When compared with a bulk Y2O3:Tb sample, these effects are attributed to some unique electronic and optical properties of doped nanocrystals related to quantum confinement of charge carriers, and the main features can be explained by a proposed model of multichannel energy transfer. Extended x-ray absorption fine structure techniques have also been employed to study the effect of size variation and chemical doping on the local structures in Y2O3 and Y2O3:Tb nanocrystals. The local environment surrounding Y and Tb in the nanocrystals is compared with that in the respective bulk material. The results indicate that Tb impurity atoms substitute for Y sites in bulk Y2O3, while doping in the nanocrystals is complicated by the large fraction of surface atoms and local disorder.

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Influence of lattice strain on charge/orbital ordering and phase separation in Pr0.7(Ca0.6Sr0.4)0.3MnO3 thin films

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