Hydrothermal growth of ZnO on the annealed titanate nanotube films results in the oriented hexagonal-needlelike structures. The size, shape, density, and alignment of ZnO film are significantly affected by annealing temperature and orientation of the beneath titanate layer. It is believed that oxygen and hydrogen vacancies, generated due to dehydration of interlayered OH groups while annealing of the titanate, are responsible for the changes in the morphology of the ZnO. Microscopic observations clearly resolved nanoneedles with the base diameter of ∼150nm and length of ∼5μm with lattice spacing of 0.52nm, indicating single crystalline ZnO and grown along the (0001) direction. A growth model is presented based on the layer-by-layer growth (three-step growth) as a function of growth time (2–6h). Thicknesses of these three steps were found increasing with growth time. The second step (II) of growth exhibits the same feature as that of the first step (I), i.e., bounded with six crystallographic, lower surface energy facets of {011¯0} surfaces and capped with {011¯1} planes, but with higher step thickness and sharper tip. Finally, the obtained ZnO nanoneedles exhibit {011¯1} facets, the third step (III), with sharp tip in the [0001] direction.
Cu-doped ZnO nanoparticles were used in the form of a screen-printed electrode on a prefabricated gold-plated electrode for electrochemically determining the concentration of nanomolar myoglobin (Mb), a cardiac biomarker. Initially, Cu-doped ZnO nanoparticles were synthesised through the sol gel method by using three Cu-doping concentrations (varying number of Cu atoms). Then, the synthesised material was analysed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and field emission secondary electron microscopy. Analysis revealed a mixed phase of ZnO and CuO, whereas the vibration band in the range of 650-700 cm -1 indicated metal oxide formation. Morphological observation showed uniform-sized spherical particles of approximately 15-20 nm (as nanoparticles) that were evenly distributed, which were also confirmed based on the average particle size estimated using XRD data. The developed electrodes were tested for biomarker concentration from 3 to 15 nM based on cyclic voltammogram and impedance spectroscopic curves, where the redox potential/current/charge transfer resistance changed linearly with Mb and dopant (Cu) concentration. The sensitivity was estimated as 2.13-10.14~μAnM -1 cm -2 with dopant concentration of approximately 0.46 nM as the limit of detection.
Metal oxide based electrodes play a crucial role in various as a transparent conductive oxide (TCO). One of the metal oxides, nickel oxide is a promising electrical conductive material. Here, we display that incorporation of vanadium in NiO lattice significantly improve both electrical conductivity and hole extraction. Also, vanadium doped nickel oxide exhibits a lower crystalline size compared to pristine nickel oxide, which maintains the reduction of surface roughness. These results indicating that the vanadium is an excellent dopant for NiO.
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