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Here, we demonstrate the synthesis of aligned CdS nanowires by a solvothermal process where the alignment of the nanowires was controlled by tuning the reaction conditions. The normal and photoassisted field emission properties of the aligned CdS nanowires were studied. The turn-on field is found to be 0.68 V/μm which is much lower than the reported values. From the I-t plot, it is shown that the emission current remains nearly constant over 4 h at preset current value of 5 μA. Upon illumination, the photofield emission current shows a reproducible switching property with a rise in the current level of almost 50% of the initial value. The field emission properties indicate promising applications in field emission based devices.

Sn-doped ZnO nanowire films have been successfully synthesized by electrodeposition on zinc foil followed by annealing in air at 400°C for 4 h. The XRD patterns of the annealed specimens exhibit a set of welldefined diffraction peaks indexed to the wurtzite phase of ZnO. The surface morphology of the as-synthesized films showed a network of densely packed flakes/sheets on the substrate. However, upon annealing, the formation of ZnO nanowires, processing length in the range of several micrometers and diameter less than 150 nm, on the entire substrate is observed. The relative atomic percentage of Sn, estimated from the energy dispersive spectra, was found to be 0.5 and 2.0 in the ZnO films deposited for 10 and 40 min durations, respectively. From the field emission studies, the values of the turn-on field and threshold field, required to draw emission current density of 10 and 100 µA/cm 2 , are observed to be 0.68 and 1.1 V/µm for 0.5% Sndoped ZnO and 1.72 and 2.25 V/µm for 2.0% Sn-doped ZnO, respectively. The field emission current stability investigated for a duration of 6 h at the preset value of 100 µA is found to be excellent. A prominent photoenhancement in the field emission current upon visible light illumination of the Sn-doped ZnO nanowires films has been observed. This enhancement has been attributed to the photoconductivity of the Sn-doped ZnO.

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A systematic experimental and theoretical study of the origin of the enhanced photocatalytic performance of Mg-doped ZnO nanoparticles (NPs) and Mg-doped ZnO/reduced graphene oxide (rGO) nanocomposites has been performed. In addition to Mg, Cd was chosen as a doping material for the bandgap engineering of ZnO NPs, and its effects were compared with that of Mg in the photocatalytic performance of ZnO nanostructures. The experimental results revealed that Mg, as a doping material, recognizably ameliorates the photocatalytic performance of ZnO NPs and ZnO/graphene nanocomposites. Transmission electron microscopy (TEM) images showed that the Mg-doped and Cd-doped ZnO NPs had the same size. The optical properties of the samples indicated that Cd narrowed the bandgap, whereas Mg widened the bandgap of the ZnO NPs and the oxygen vacancy concentration was similar for both samples. Based on the experimental results, the narrowing of the bandgap, the particle size, and the oxygen vacancy did not enhance the photocatalytic performance. However, Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH) models showed that Mg caused increased textural properties of the samples, whereas rGO played an opposite role. A theoretical study, conducted by using DFT methods, showed that the improvement in the photocatalytic performance of Mg-doped ZnO NPs was due to a higher electron transfer from the Mg-doped ZnO NPs to the dye molecules compared with pristine ZnO and Cd-doped ZnO NPs. Moreover, according to the experimental results, along with Mg, graphene also played an important role in the photocatalytic performance of ZnO.