It is found that both of the band-edge and defect emission from aligned ZnO nanorods are strongly polarized, and the intensities vary with the polarization angle by the relation of a square cosine function. The intensity of the UV emission has its maximum along the c axis of a ZnO crystal. However, the intensity of the green emission is minimum in this direction. Namely, the two intensity curves are 90° out of phase. This unique characteristic of the polarization provides useful information to identify the fact that the green emission mostly occurs on the surface defects of the nanorods. This result is consistent with the currently accepted model that the green emission arises from the recombination between holes trapped at the surface defects and electrons trapped at the oxygen vacancy.

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Abstract:The electrochemical oxidation of nitric oxide (NO) gas at the Pt/Nafion ® electrode has been studied at a concentration of 500 ppm. The electrooxidation of NO taking place over a wide potential range can be described by a transcendental equation, from which the half-wave potential of the reaction can be determined. For NO oxidation with appreciable overpotentials but negligible mass-transfer effects, the Tafel kinetics applies. The obtained charge transfer coefficient (α) and the exchange current density (i o ) are 0.77 and 14 µA/cm 2 , respectively. An amperometric NO gas sensor based on the Pt/Nafion ® electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm. The Pt/Nafion ® electrode was used as an anode at a fixed potential, preferably 1.15 V (vs.Ag/AgCl/sat. KCl), which assures current limitation by diffusion only. The sensitivity of the electrochemical sensor was found to be 1.86 µA/ppm/cm 2 . The potential interference by other gases, such as nitrogen dioxide (NO 2 ) and carbon monoxide (CO), was also studied in the range 0-500 ppm. Both sensitivity for NO and selectivity of NO over NO 2 /CO show significant enhancement upon using a cyclic voltammetric (CV) activation, or cleaning procedure.

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Photoluminescence ͑PL͒ has been observed in an In y As 1Ϫy N/In x Ga 1Ϫx As single quantum well on InP grown by gas source molecular beam epitaxy at room temperature. The PL spectroscopies show redshift as the nitrogen content increases. Through a detailed study of the dependence of PL spectra on temperature, pumping intensity, and nitrogen content, we point out that the occurrence of PL arises from the localized states due to potential fluctuations induced by the incorporation of nitrogen in InAs. Further evidence is supported by the comparison between the photoconductivity and photoluminescence spectra, which show that the Stokes shift increases with nitrogen content.