In the present investigation we show the effect of Al doping on the length, size, shape, morphology, and sensing property of ZnO nanorods. Effect of Al doping ultimately leads to tuning of electrical and optical properties of ZnO nanorods. Undoped and Al-doped well aligned ZnO nanorods are grown on sputtered ZnO/SiO2/Si (100) pre-grown seed layer substrates by hydrothermal method. The molar ratio of dopant (aluminium nitrate) in the solution, [Al/Zn], is varied from 0.1 % to 3 %. To extract structural and microstructural information we employ field emission scanning electron microscopy and X-ray diffraction techniques. The prepared ZnO nanorods show preferred orientation of ZnO <0001> and are well aligned vertically. The effects of Al doping on the electrical and optical properties are observed by Hall measurement and photoluminescence spectroscopy, respectively, at room temperature. We observe that the diameter and resistivity of the nanorods reach their lowest levels, the carrier concentration becomes high, and emission peak tends to approach the band edge emission of ZnO around 0.5% of Al doping. Sensing behavior of the grown ZnO nanorod samples is tested for H2 gas. The 0.5 mol% Al-doped sample shows highest sensitivity values of ~ 60 % at 250 ˚C and ~ 50 % at 220 ˚C.

We report on an all-solution-processed hydrothermal method to control the morphology of ZnO nanostructures on Si substrates from three-dimensional hemispherical structures to two-dimensional thin film layers, by controlling the seed layer and the molar contents of surfactants during their primary growth. The size and the density of the seed layer, which is composed of ZnO nanodots, change with variation in the solute concentration. The ZnO nanodots act as heterogeneous nucleation sites for the main ZnO nanostructures. When the seed layer concentration is increased, the ZnO nanostructures change from a hemispherical shape to a thin film structure, formed by densely packed ZnO hemispheres. In addition, the morphology of the ZnO layer is systematically controlled by using trisodium citrate, which acts as a surfactant to enhance the lateral growth of ZnO crystals rather than a preferential one-dimensional growth along the c-direction. X-ray diffraction and energy dispersive X-ray spectroscopy results reveal that the ZnO structure is wurtzite and did not incorporate any impurities from the surfactants used in this study.

1-D ZnO nanowires have been attractive for their peculiar properties and easy growth at relatively low temperature. The length, diameter, and density of ZnO nanowires were determined by the several synthetic parameters, such as PEI concentration, growth time, temperature, and zinc salt concentration. The ZnO nanowires were grown on the<001> oriented seed layer using the hydrothermal process with zinc nitrate and HMTA (hexamethylenetetramine) and their structure and optical properties were characterized. The morphology, length and diameter of the nanowires were strongly affected by the relative and/or absolute concentration of Zn2+ and OH-1 and the hydrothermal temperature. When the concentrations of the zinc nitrate HMTA were the same as 0.015 M, the length and diameter of the nanowires were 1.97μm and 0.07μm, respectively, and the aspect ratio was 28.1 with the preferred orientation along the<001> direction. XRD and TEM results showed a high crystallinity of the ZnO nanowires. Optical measurement revealed that ZnO nanowires emitted intensive stimulated UV at 376 nm without showing visible emission related to oxygen defects.

ZnO nanostructures were grown on an Au seed layer by a hydrothermal method. The Au seed layer was deposited by ion sputter on a Si (100) substrate, and then the ZnO nanostructures were grown with different precursor concentrations ranging from 0.01 M to 0.3M at 150˚C and different growth temperatures ranging from 100˚C to 250˚C with 0.3 M of precursor concentration. FE-SEM (field-emission scanning electron microscopy), XRD (X-ray diffraction), and PL (photoluminescence) were carried out to investigate the structural and optical properties of the ZnO nanostructures. The different morphologies are shown with different growth conditions by FE-SEM images. The density of the ZnO nanostructures changed significantly as the growth conditions changed. The density increased as the precursor concentration increased. The ZnO nanostructures are barely grown at 100˚C and the ZnO nanostructure grown at 150˚C has the highest density. The XRD pattern shows the ZnO (100), ZnO (002), ZnO (101) peaks, which indicated the ZnO structure has a wurtzite structure. The higher intensity and lower FWHM (full width at half maximum) of the ZnO peaks were observed at a growth temperature of 150˚C, which indicated higher crystal quality. A near band edge emission (NBE) and a deep level emission (DLE) were observed at the PL spectra and the intensity of the DLE increased as the density of the ZnO nanostructures increased.