The geometrical interelectrode capacitances of superconducting microbridges are too small to account for the observed hysteresis in their I-V characteristics. We propose a new model of microbridges in finite voltages, in which the relevant time constant is the supercurrent relaxation time τR. From an analysis of the experimental I-V curves it follows that τR can be identified with the pair relaxation time within a numerical factor. By equating τR/2π to the time constant C/G of the shunted Josephson junction model, we obtain values of C in reasonable agreement with those typically obtained from I-V characteristics.
CdS/Si multi-interface nanoheterojunctions (CdS/Si-NPA) were fabricated by depositing CdS nanocrystallites (nc-CdS) on silicon nanoporous pillar arrays (Si-NPA) by chemical bath deposition. White electroluminescence (EL) with a high colour rendering index from a prototypical light emitting diode based on CdS/Si-NPA has been reported, which does not need complex colour mixing or conversion techniques. The white EL can be composed into three primary colours, which include blue emissions from the Si-NPA, the green emissions from the bandgap emission of nc-CdS and red emissions from the defects in the nc-CdS. Through the annealing treatment, the chromaticity coordinate and correlated colour temperature can be tuned. This indicates that CdS/Si-NPA is a potential candidate in the one-chip white LEDs.
CdS nanocrystals are synthesized through a chemical bath deposition method. After annealing, these nanocrystals are enlarged according to Scherrer’s formula. Small nanocrystals display wide band gaps as a result of the quantum effect experienced by nanocrystals of a certain size. However, the absorption edge and green and red emissions of annealed CdS nanocrystals show obvious blueshift compared with the as-grown ones. After annealing, the intensity ratio of these green and red emissions increases, which indicated that the defect states are reduced. Therefore, the improvement in crystalline quality and the reduced strain contribute to the unusual blueshifting of the optical band gap and of the green and red emissions.
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