RESUMEN
We have synthesized inverse-perovskite-type oxysilicides and oxygermanides represented by R3SiO and R3GeO (R = Ca and Sr) and studied their characteristics in the search for nontoxic narrow band gap semiconductors. These compounds exhibit a sharp absorption edge around 0.9 eV and a luminescence peak in the same energy range. These results indicate that the obtained materials have a direct-band electronic structure, which was confirmed by hybrid DFT calculations. These materials, made from earth abundant and nontoxic elements and with a relatively light electron/hole effective mass, represent strong candidates for nontoxic optoelectronic devices in the infrared range.
RESUMEN
Metal oxide semiconductor gas sensors have been widely studied for the selective detection of various gases with trace concentrations. The identification of the reaction scheme governing the gas sensing response is crucial for further development; however, the mechanism of ethanol (EtOH) gas sensing by ZnO is still controversial despite being one of the most intensively studied target gas and sensing material combinations. In this work, for the first time, the detailed mechanism of EtOH sensing by ZnO is studied by using a bulk single-crystalline substrate, which has a well-defined stoichiometry and atomic arrangement, as the sensing material. The sensing response is substantial on the ZnO substrate even with a millimeter-size thickness, and it becomes larger with resistance of the substrate. The large sensing response is described in terms of the adsorption/desorption of the oxygen species on the substrate surface, namely, oxygen ionosorption. The valence state of the ionosorbed oxygen involved in EtOH sensing is identified to be O2- regardless of the temperature. The increase in the sensing response with the temperature is attributed to the enhanced oxidation rate of the EtOH molecule on the surface as analyzed by pulsed-jet temperature-programmed desorption mass spectrometry, which has been newly developed for analyzing surface reactions in simulated working conditions.
RESUMEN
Scandium nitride (ScN) films were grown on α-Al2O3( 1 1 ¯ 02 ) substrates using the molecular beam epitaxy method, and the heteroepitaxial growth of ScN on α-Al2O3( 1 1 ¯ 02 ) and their electric properties were studied. Epitaxial ScN films with an orientation relationship (100)ScN || ( 1 1 ¯ 02 )α-Al2O3 and [001]ScN || [ 11 2 ¯ 0 ]α-Al2O3 were grown on α-Al2O3( 1 1 ¯ 02 ) substrates. Their crystalline orientation anisotropy was found to be small. In addition, [100] of the ScN films were tilted along [ 1 ¯ 101 ] of α-Al2O3( 1 1 ¯ 02 ) in the initial stage of growth. The tilt angle between the film growth direction and [100] of ScN was 1.4â»2.0° and increased with growth temperature. The crystallinity of the ScN films also improved with the increasing growth temperature. The film with the highest Hall mobility was obtained at the boundary growth conditions determined by the relationship between the crystallinity and the nonstoichiometric composition because the film with the highest crystallinity was obtained under the Sc-rich growth condition. The decreased Hall mobility with a simultaneous improvement in film crystallinity was caused by the increased carrier scattering by the ionized donors originating from the nonstoichiometric composition.
