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Cu2ZnSn(S,Se)4 (CZTSSe) is an earth-abundant semiconductor with potential for economical photovoltaic power generation at terawatt scales. In this work, we use Raman scattering to investigate phase coexistence in combinatorial CZTS thin films grown at 325 or 470°C. The surface of the samples grown at 325°C is rough except for a prominent specularly reflective band near and along the ZnS-Cu2SnS3 (CTS) tie line in the Cu-Zn-Sn-S quaternary phase diagram. All structurally incoherent secondary phases (SnS2, CuS) exist only as surface phases or are embedded as separate grains, whereas the structurally coherent secondary phase CTS coexists with CZTS in the dense underlying film. In films grown at 325°C, which are kinetically trapped by the low growth temperature, a change is observed in Cu and Sn site occupancy, evidenced by the shift from cubic-CTS in the Cu-rich region (Cu/Sn>2) to more tetragonal-CTS in the Sn-rich region (Cu/Sn<2). For CZTS samples grown at 470° C, CTS is not observed and regions grown under excess Sn flux are more disordered than Cu-rich regions evidenced by broader CZTS A mode peaks. Therefore, increasing Sn chemical potential results in more CZTS lattice disorder, suggesting, with other evidence, the formation of Sn antisite defects. In contrast, the CZTS A mode breadth is insensitive to Zn richness suggesting that excess Zn does not induce significant disorder within the CZTS lattice. We postulate that initially growing CZTS films Cu-rich (Cu/Sn>2) results in higher cation ordering meaning fewer antisite defects. [ABSTRACT FROM AUTHOR]

MgxZn1-xO (x=0.15) and ZnO nanocrystals of about 40 nm in diameter were studied using x-ray diffraction and diamond-anvil cells. The equation of state (EOS) for MgZnO is reported for the first time. Between pressures of 9.45 and 10.7 GPa, MgZnO transforms into the rocksalt (NaCl) structure, which persisted to 1.1 GPa upon decompression. The EOS parameters for ZnO are close to their bulk values and in good agreement with values obtained previously. The bulk modulus for MgZnO was slightly lower than that of ZnO. The pressure-induced decrease in c/a ratio was greater for MgZnO, consistent with the tendency for MgZnO to move toward a cubic structure. From previous photoluminescence measurements [J. Huso et al., Appl. Phys. Lett. 89, 171909 (2006)], the band-gap volume deformation potentials for ZnO and Mg0.15Zn0.85O were determined to be -3.6 and -4.0 eV, respectively. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the conductivity of ZnO nanoparticles has implications for nanoscale optoelectronic devices. In this study, infrared reflectance spectra of as-grown and hydrogen-annealed ZnO nanoparticles were measured at near-normal incidence. The as-grown particles were electrically semi-insulating and show reflectance spectra characteristic of insulating ionic crystals. Samples annealed in hydrogen showed a significant increase in electrical conductivity and free-carrier absorption. A difference was observed in the reststrahlen line shape of the conductive sample compared to that of the as-grown sample. The effective medium approximation was applied to model the reflectance and absorption spectra. The agreement between experimental results and the model suggests that the nanoparticles have inhomogeneous carrier concentrations. Exposure to oxygen for several hours led to a significant decrease in carrier concentration, possibly due to the adsorption of negative oxygen molecules on the nanoparticle surfaces. [ABSTRACT FROM AUTHOR]

Impurities play a major role in determining the optical and electrical properties of semiconductor nanoparticles. In this work, the presence and source of CO2 impurities in ZnO nanoparticles were studied by IR absorption spectroscopy. Isotopic substitution was used to verify the vibrational frequency assignment. Isochronal annealing experiments were performed to study the formation and stability of the molecular impurities. Our results indicate that the molecules are much more stable than CO2 adsorbed on bulk ZnO surfaces. By comparing our observations with similar results from IR spectroscopy of CO2 trapped in carbon nanotubes [C. Matranga, L. Chen, M. Smith, E. Bittner, J. K. Johnson, and B. Bockrath, J. Phys. Chem. B 107, 12930 (2003)], we conclude that the molecules are trapped in the ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

A 10-year Malaysian sunshine data of four stations were fitted to three models, namely the Bendt, Hollands and Huget and Saunier models. Distribution parameters of the models were determined from the valuesof the observed mean of the sunshine data. The Kolmogorov-Smirnov test was applied to determine the goodness of fit. It was found that the Saunier model was suitable for the Petaling Jaya and Subang stations while the Hollands and Huget model well suited the Bayan Lepas and Kota Bharu stations. The Bendt model did not give a good fit for all stations. It was also found that for the months that have the same observed mean but different observed standard deviations the distribution models were able to fit well only if the estimated standard deviations were close in value to the observed standard deviations. [ABSTRACT FROM AUTHOR]