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Supersaturated ZnO–Al2O3 (>20 at. % Al) thin films are grown by pulsed laser deposition technique on silica glass substrates at 600 °C. They are characterized by combining x-ray diffraction, Al-K edge x-ray absorption near edge structures (XANESs), high resolution transmission electron microscope (TEM) imaging, TEM analysis, and a series of first principles calculations. The films are composed of textured wurtzite grains with c planes parallel to the substrate. The distance between c planes expands significantly when the Al concentration is greater than 10 at. %. The expansion disappears after annealing the films at above 800 °C. High density of dislocationlike defects is found in the as deposited film. Any segregation of Al cannot be detected either at the grain boundaries or inside the grains. The lattice expansion toward c axis and the experimental XANES can be satisfactorily explained by taking a hypothetical homologous model with the composition of (ZnO)3(Al2O3) as the local environment of Al in the supersaturated solid solution. Simplified substitutional models with Al at the Zn site in wurtzite ZnO cannot explain these experimental results. First principles calculations show that the homologous phase is energetically more favorable than the simplified substitutional models, although decomposition into ZnO and ZnAl2O4 is more favorable than the homologous phase. The local atomic structures of the supersaturated solid solution are therefore concluded to be analogous to the metastable homologous phase. [ABSTRACT FROM AUTHOR]

Mn-doped Ga2O3 thin film showing room temperature ferromagnetism has been grown on a sapphire (0001) plane by using a pulsed-laser deposition technique. The microstructure of the Mn-doped film is investigated in detail using selected-area electron diffraction, high-resolution transmission electron microscopy (HRTEM), x-ray energy-dispersive spectroscopy, and electron energy-loss spectroscopy, in comparison with an undoped film. Careful diffraction analysis with the [2110]Al2O3 and [1010]Al2O3 zone axes of the substrates reveals that the Mn-doped film shows the γ-Ga2O3 phase with a defective spinel structure, while the undoped film shows the β-Ga2O3 phase. The orientation relationship between the film and substrate is determined by electron diffraction and HRTEM from the interface region to be (201)β-Ga2O3//(0001)Al2O3 and [102]β-Ga2O3//[2110]Al2O3 or 102β-Ga2O3//2110Al2O3 for the undoped film, and (111)γ-Ga2O3//(0001)Al2O3 and [211]γ-Ga2O3//[2110]Al2O3 or [211]γ-Ga2O3//[2110]Al2O3 for the Mn-doped film. Mn ions are uniformly dissolved in the film with 7.8 cation % and no detectable precipitates are found. Mn-L2, 3 energy-loss near-edge structure reveals that Mn ions take the valency of 2+, which is consistent with Mn-L2, 3 near edge x-ray absorption results in our previous report. [ABSTRACT FROM AUTHOR]

The atomic structure and energies of SmBa[sub 2]Cu[sub 3]O[sub 6](Sm123)/BaZrO[sub 3](BZO) and Sm123/MgO interfaces have been investigated using first-principles calculations. The interfacial energies were evaluated for various atomic configurations under relevant conditions of the chemical potentials. For the Sm123/BZO, an interface composed of a BaO layer is found to be energetically favorable, irrespective of the chemical potentials. This is much lower in energy than the Sm123/MgO interfaces where the preferable configuration even varies with the chemical potential conditions. The stability of the Sm123/BZO interface is attributed to the local atomic arrangement and chemical composition common to Sm123 and BZO, and such an atomic structure is confirmed by high-resolution transmission electron microscopy. The results suggest that the insertion of a BZO buffer layer facilitates the epitaxial growth of Sm123 films on MgO substrates because of the energetically favorable film/buffer layer interface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The local structure of Al solute atoms in supersaturated ZnO-[Al.sub.2][O.sub.3] solid solutions is examined. The local atomic structures of the supersaturated solid solution are analogous to the metastable homologous phase.

The microstructure of Mn-doped [gamma]-[Ga.sub.2][O.sub.3] thin epitaxial film, grown on sapphire (0001) plane with room temperature ferromagnetism is studied. The analysis clearly reveals that Mn ions are evenly and uniformly distributed throughout the film with no other detectable precipitates.

Research is done on Pr and Co doped ZnO bicrystals with various types of grain boundaries, which were fabricated to investigate their current-voltage characteristics. In conclusion, the change in the nonlinearity is attributed to the difference of the Pr concentration that is associated with the grain boundary structure.

Zn3N2 thin films have been grown at different substrate temperatures by reactive magnetron sputtering in an ultrahigh vacuum chamber. It is demonstrated that low temperature deposition is beneficial for producing nondegenerate Zn3N2 thin films, in stark contrast to previously reported Zn3N2 with high electron concentrations. Elevating the growth temperature will increase the carrier concentration significantly. Analyses of defect concentrations based on the defect formation energies estimated from first-principles calculations indicate that all the native defects are not responsible for the high carrier concentration, whereas unintentional oxygen-on-nitrogen (ON+) and/or hydrogen interstitial (Hi+) defects act as dominant donors in Zn3N2 thin films. Moreover, the remarkable deposition temperature dependence of the carrier concentration in Zn3N2 thin films would be attributed to the Boltzmann distribution of oxygen and/or hydrogen impurities. These results could pave a general way for controlling the carrier concentration in nominally nondoped nitride semiconductors. [ABSTRACT FROM AUTHOR]