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Undoped a-axis oriented single crystalline zinc oxide (ZnO) films were deposited by sol-gel dip-coating method. The films were characterized by X-ray diffraction (XRD) and ultraviolet visible (UV-VIS) absorbance spectra. The films of ZnO were deposited on amorphous microscopic glass substrate at various temperatures. The XRD showed that the ZnO film was crystallized with a hexagonal structure with a strong orientation in the (100) plane, which is exactly along the a-axis and beneficial for the development of optoelectronic devices. The optical band gap energy found for this a-axis oriented ZnO film was 3.30 eV through UV-VIS absorbance spectra. The Fourier Transform Infrared Spectroscopy (FTIR) analysis was carried out by taking the IR absorbance spectra for ZnO film deposited on the silicon substrate at 450°C. It showed that the strong Zn–O stretching bond is present in the deposited film.

The surface O or Zn vacancy of ZnO is extremely important, so in this paper we have studied the structural and electronic properties of the ZnOO-polar surface with O vacancy and Zn-polar surface with Zn vacancy comparatively using the first-principles calculations. For the former case, the topmost oxygen atoms relax outward and the angle between Zn–O–Zn bonds in the topmost double-layer decreases to 105.01° with respect to the unrelaxed surface. However, for the latter case, the topmost zinc atoms relax inward and the angle between O–Zn–O bonds in the topmost double-layer increases to 117.61° with respect to the unrelaxed surface. Both the two reconstructed surfaces become semiconducting property in contrast to the metallic property of the unreconstructed surface. The calculated surface vacancy formation energy indicates that the surface with O vacancy is slightly more easier to be formed compared to the surface with Zn vacancy. By employing the technique of ab initio atomistic thermodynamics, we calculated the surface Gibbs free energy to determine the lowest-energy structure, indicating that the surface with O vacancy is more stable than the surface with Zn vacancy under the oxygen poor condition.

In the present study, we demonstrate the performance of Zinc oxide thin film transistors (ZnO TFTs) array subjected to the strain under high bending test and the reliability of TFTs was confirmed for the bending fatigue test of 2000 cycles. Initially, ZnO TFTs were fabricated on Si substrate and subsequently transferred on flexible PET substrate using transfer printing process. It was observed that when the bending radius reached ≥ 11 mm then cracks start to initiate first at SiO₂ bridges, acting as interconnecting layers among individual TFT. Whatever the strain is applied to the devices, it is almost equivalently adopted by the SiO₂ bridges, as they are relatively weak compared to rest of the part. The initial cracking of destructed SiO₂ bridge leads to the secondary cracks to the ITO electrodes upon further increment of bending radius. Numerical simulation suggested that the strain of SiO₂ layer reached to fracture level of 0.55% which was concentrated at the edge of SiO₂ bridge layer. It also suggests that the round shape of SiO₂ bridge can be more fruitful to compensate the stress concentration and to prevent failure of device.

In this paper, ZnO thin film has been synthesized on fluorine doped tin oxide (FTO) glass substrate by annealing the Zn film in air flow. The SEM image shows that the high density and thread-like ZnO nanowires could grow on the thin film. XRD pattern shows that ZnO was the only compound. The high-resolution transmission electron microscopy (HRTEM) results of individual ZnO nanowires show that the nanowires grown on the ZnO thin film are single-crystalline, and the selected area electron diffraction pattern (SAED) shows that the nanowires grow along the (001) direction.

Pure and silver added zinc oxide nanoparticles (ZnO-NPs and ZnO:Ag-NPs) were synthesized through a modified sol–gel method. The prepared samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. In the XRD patterns, silver diffracted peaks were also observed for the samples synthesized at different calcination temperatures of 500°C, 700°C, 900°C except 1100°C, in addition to ZnO. TEM images indicated that the average size of ZnO:Ag-NPs increases with the amount of Ag concentration. The PL spectra of the samples revealed that the increase of Ag concentration results in the increase of the visible emission intensity, whereas by increasing the calcination temperature the intensity of visible emission of the samples decreases.

In this paper, we have investigated the effect of Mn doping on the electrical properties of ZnO thin films. ZnO thin films with different amounts of Mn concentrations (0, 5, 10 and 15 mol.%) were prepared by spray pyrolysis technique. The crystal structure was examined by X-ray diffraction (XRD) analysis. XRD patterns showed that all the samples were crystallized in wurtzite structure while a decrease in crystallinity and switch in preferential orientations were observed in Mn-doped thin films comparing to undoped ZnO. The element composition of all thin films was detected by energy dispersive X-ray (EDX). The surface morphology of the films was investigated using field emission scanning electron microscope (FESEM) and optical properties were studied using UV-vis spectroscopy. UV-vis study revealed that the band gap blueshifts with the increase in Mn content and $E_g$ increases with the increase in Mn concentration. The resistivity and activation energy were measured at room temperature and ranging from 373 K to 573 K. Comparing to undoped ZnO thin film, the resistivity of Mn-doped ZnO films increased because of different parameters such as increasing barrier height energy and reducing the oxygen deficiency.

In the current work, we have demonstrated the phase of ZnO by reference to block theory, in which the phase may be considered to show a paramagnetic ordering between block spins, which in turn comprise random spins that have a majority of individual spins in a given direction. By making use of the Curie–Weiss law of block spins for zinc oxide, we obtained the susceptibility for the lower approximation of the Brillouin function and calculated the resistivity. The resistivity of ZnO mainly stems from spin glass-like disorders according to our analysis.

Hydrophones with three different resonant cavities (microscope slide, cavity with 9.8 mm diameter and 5.7 mm${}^{-1}$ curve surface, and cavity with 14 mm diameter and 6.5 mm${}^{-1}$ curve surface) and with two different electrode structures (interdigital electrode, without the interdigital electrode but with top–bottom structure) were designed and fabricated. Zinc oxide (ZnO) film was deposited on indium–tin oxide/glass as seed layer and ZnO nanocolumns were grown as the piezoelectric material. Grown ZnO nanocolumns were used in all samples as the sound receiver of all designed hydrophones to enhance the sensing effect and efficiency of fabricated hydrophones. The electrode mask was then adhered on the surfaces of ZnO nanocolumns to complete the electrodes of designed resonant cavity. While measuring the hydrophones without interdigitated electrode, the measurement probes were contacted directly on the substrate and on the top layer of the material. Finally, the resonant cavities in all designed hydrophones were encapsulated using epoxy resin to finish the package of the fabricated hydrophones, and then the sound receiving performance of the hydrophones was evaluated in the water and the results were well compared in this study.

The double-stacked gate dielectrics (DSGD), which consisted of either NbLaO/Al₂O₃ or NbLaO/SiO₂, were used to improve the electrical performance of zinc oxide thin-film transistor (ZnO-TFT) with single-layer NbLaO gate dielectric (SLGD). Compared to ZnO-TFT with SLGD, the ZnO-TFTs with DSGD exhibit better electrical performance, specifically for the device with the NbLaO/SiO₂ DSGD, with an increase of the field-effect mobility from 5.77 cm²V${}^{-1}$s${}^{-1}$ to 39.64 cm²V${}^{-1}$s${}^{-1}$, an enhancement of the on/off current ratio by two orders of magnitude, a reduction of the subthreshold slope from 110 mV/decade to 70 mV/decade. The performance enhancements are attributed to a low root-mean-square surface roughness of less than 0.3 nm and a low trap-state density of less than $6\times 10^{11}$ cm${}^{-2}$ (even $2.4\times 10^{11}$ cm${}^{-2}$ for the NbLaO/SiO₂ DSGD) in the bulk of the channel and at the ZnO/NbLaO interface. The results imply that ZnO-TFTs with DSGD have the potential for the application of high-resolution flat panel display.

Zinc oxide (ZnO) and yttrium-doped ZnO nanoparticles with particle size in the nanometer range have been successfully synthesized by the alkali precipitation method. The nanoparticle size and morphology have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The average particle size of Y-doped ZnO nanoparticles is about 17–29 nm. The absorption and photoluminescence (PL) spectra of the undoped and doped ZnO nanoparticles were also investigated. The optical band gap of ZnO nanoparticles can be tuned from 3.27 to 3.40 eV with increasing yittrium doping levels from 0 to 5%. The nanoparticles gave two emission peaks, one at around 376 nm and the other at 500 nm.

A new method for preparation of a carbon nanotube (CNT)–zinc oxide hybrid on a glass substrate at low temperature is introduced and the stability improvement of field emission of CNTs is reported. The emission current stability and substrate material are the two main commercial parameters for field emission applications of CNTs. The two alternative current (AC) and direct current (DC) plasma enhancement chemical vapor deposition (PECVD) is used to achieve low-temperature growth of vertically aligned CNTs and the hydrothermal processing is used for production of zinc oxide nanowires to improve the emission current stability and properties. The nanoscale junction between a semiconductor and conductive material are critical for electronic applications. The present study examined the field emission properties of CNTs near the crystalline structure of the zinc oxide hybrids and showed the improvement in the field enhancement factor and emission current stability of CNT–ZnO hybrid than the CNT emitters.

In this paper, we prepared the rattle type nanoparticles ZnO@void@SiO₂ by two successive coating processes, followed by heat treatment. The carbon layer was formed over ZnO surface with the aid of the hydrothermal treatment of glucose. Then the resulting composite was used to fabricate a silica shell on the surface by sol–gel method. Finally, ZnO particles were released but still trapped inside the silica hollow after calcination, that is, ZnO@void@SiO₂. The composites were characterized by scanning and transmission electron microscope, N₂ adsorption experiment, X-ray diffraction, Fourier transform infrared spectroscopy and UV-Vis absorption spectra. The rattle type structure was conformed and the sphere-like structure with the average size of 70 nm and hexagonal wurtzite crystal structure were also observed. The measurement results of optical properties showed even though ZnO@C@SiO₂ presented no photocatalysis, ZnO@void@SiO₂ showed high activity even the ZnO core was encapsulated with the SiO₂ hollow.

In this work, we report theoretical and experimental study of Pd/ZnO nanorod (NR) Schottky diodes-based ultraviolet photodetector (UV-PD). The ZnO-NRs are deposited on indium tin oxide (ITO) coated glass substrates by using a low-temperature hydrothermal method. The surface morphology of the ZnO-NRs film is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM image shows vertically grown NRs with uniformity, and XRD shows the preferred (002) orientation of ZnO-NR films. The current–voltage characteristics of Pd/ZnO-NR Schottky diodes are studied under dark and UV light. A voltage bias from $-$1V to $+$1V is applied and the ratio of photocurrent to dark current was ($\sim 0.17\times 10^2$ at $V=0.5$V) calculated from the $I$–$V$ curve. The value of responsivity was found to be 0.111A/W at $\lambda =365$nm and at $\mathrm{\text{bias}}=0.50$V. An approximated UV-PD structure has also been numerically simulated using three-dimensional (3D) device simulator from Visual TCAD of Cogenda International. The simulated $I$–$V$ characteristics have also been plotted under both dark and light conditions. The simulated results are found to be following the nature of experimental results.

Photoelectrochemical (PEC) sensor is an important type of biosensor widely used in glutathione (GSH) sensing. The PEC properties of the photoanode present in the sensor are critical to its sensing performance. Zinc oxide (ZnO) is an excellent semiconductor with a suitable band gap and light absorption ability for photoanode applications. Meanwhile, the interfacial layer is also important in the separation and transportation process of the excitons. In this work, high-quality ZnO nanorods were grown on the indium tin oxide (ITO) substrates. An interfacial layer consisting of reduced graphene oxide (RGO) or MXene (a two-dimensional transition metal carbide)-derived TiO₂ was introduced. Our results show that the introduction of the RGO/TiO₂ hybrid interfacial layer can promote both the high-quality growth of ZnO nanorods and also provides suitable band gap grading for efficient excitons separation and transportation. The GSH sensing performance of the PEC sensor based on the ZnO nanorods grown on the RGO/TiO₂ hybrid layer-coated ITO photoanode can dramatically improve the photocurrent strength and linearity.

Novel Cu-based binary composite phases were synthesized with an octadecylamine (ODA) synthetic system. HR-TEM was used to characterize the binary composite phase indicating that the Cu-based binary composite phase was a mixed phase of two oxides. ZnO gas sensing films decorated with Cu-based binary composite phase were parallel fabricated. The gas sensing performance to nitric oxides (NO, N₂O, NO${}_2)$ was studied. Cu–Mo–O binary composite phase-modified ZnO was screened out with high sensitivity and selectivity to NO. The gas sensing response to 0.5 ppm NO was 128.1. The detection limit of Cu–Mo–O binary composite phase-modified ZnO to NO was less than 10 ppb. Cu–Mo–O binary composite phase-modified ZnO also shows good selectivity to NO even using NO₂ as interference gas. It is of great importance for the detection of NO.

Selaginella willdenowii, a commonly used greenhouse fern, was often used as a biowaste to synthesize zinc oxide nanoparticles (ZnO NPs) in an eco-friendly and cost-effective way. UV–Visible spectra studies were carried out to confirm the synthesis of S. willdenowii-mediated ZnO NPs (SW-ZnO NPs), and a peak at 367nm with a sharp band gap of 3.415eV was observed. The X-ray diffraction analysis indicated that the crystalline size of the synthesized SW-ZnO NPs was 11.971nm. The phytochemicals present in the extracts and the compounds involved in the reduction of metal to nanoparticles were determined by Fourier Transform Infrared analysis. Scanning electron microscopy was utilized to analyze the surface morphology and size of the obtained SW-ZnO NPs. The examination revealed that they exhibited a hexagonal shape, with an average size falling within the range of 17–23nm. Under ultra-violet light, reactive blue 220 and reactive yellow 145 dyes showed 78.06% and 60.14% degradation, showing potential photocatalytic degradation activity. The synthesized SW-ZnO NPs also exhibited antimicrobial activity against bacterial strains (Escherichia coli and Bacillus subtilis) and fungal cultures (Candida tropicalis and Candida albicans) showed cytotoxic activity against Hep-G2 cell lines. Our results suggest the green synthesized SW-ZnO NPs have potential photocatalytic, antimicrobial and cytotoxic potential.

In present study ZnO nanorods were synthesized in an aqueous solution using a domestic microwave oven for irradiation. The nanorods have been grown on substrates immersed in an aqueous solution which contains zinc nitrate and hexamethylenetetramine as precursors. Eventually, effect of some parameters such as precursor's concentration and heating time on growth mechanism was characterized. The product phase was detected using X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) exhibited the resultant structure is uniform and single crystalline. Finally Uv-Vis spectroscopy was used to measure the nanorod's band gap.

Nanostructured zinc oxide overlayered by nanoporous strontium titanate was synthesized using sol-gel method and tested in a photoelectrochemical (PEC) cell for splitting of water. It was found that compared to the pristine ZnO and SrTiO₃, the resistivity of bilayered thin film was reduced and a negative shift in open circuit potential and flatband potential of bilayered ZnO/SrTiO₃ was observed, thus improving the photocurrent density and photoconversion efficiency. Significantly, bilayered ZnO/SrTiO₃ thin film offered the best photocurrent density i.e. 0.46 mA/cm² at 0 V/SCE. XRD, SEM and UV-Vis spectroscopic studies were carried out to explore the structural, surface morphological and optical properties of various thin films.