Narrow Results

We demonstrate the synthesis of zinc oxide microshells by thermal evaporation of ZnO and Zn powders. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) observations reveal that the products are ZnO microshells with hollow cores, of which the wall thickness is about several hundred nanometers. The possible growth process is discussed.

ZnO nano wire synthesized by microemulsion mediated hydrothermal process is characterized by X-ray diffraction, scanning electron microscope, UV–VIS and photoluminescence. The optical and thermal properties are then studied by photoacoustics. These studies reveal that the ZnO nano wires exhibit a strong ultra violet absorption and a relatively weak defect emission.

ZnO thin films were prepared by an unbalanced magnetron sputter on silicon substrates and glass slides. An ITO layer was applied on Si substrate as a buffer layer. Microstructure and mechanical deformation behaviors of the ZnO films were investigated by XRD, SEM and nanoindentation methods. Results showed that ITO buffer layer plays an important role for ZnO heteroepitaxy growth on Si substrates. The strains at the interface induced by the lattice mismatch of Si and ZnO are repressed. As a result, ZnO films with the buffer layers showed larger grain size and better crystallinity. The hardness and modulus of ZnO films with buffer layer decreased. Continuous stiffness measurement (CSM) technique was also used to investigate the effects of buffer layer and substrate materials on the mechanical performance of the prepared ZnO films. The relationship between microstructure and mechanical properties of ZnO films are discussed based on the experimental results.

Zinc oxide (ZnO) thin films were deposited onto glass substrates by d.c. magnetron sputtering. The structural analysis, by X-ray diffraction and atomic force microscopy, indicate that the studied films are polycrystalline and have a wurtzite (hexagonal) structure. The film crystallites are preferentially oriented with (002) planes parallel to the substrates.

The mechanism of electronic transport is explained in terms of Seto's model elaborated for polycrystalline semiconducting films (crystallite boundary trapping theory). Some parameters of used model (impurity concentration, density and energy of the trapping states, etc.) have been calculated. The optical bandgap (E_g0 = 3.28–3.37 eV) was determined from absorption spectra.

The ternary system Zn_1-xCd_xO (x = 0.00, 0.01, 0.05, 0.10 and 0.15) samples have been synthesized by the solid solution route. The synthesized samples were characterized by their electrical, magnetic and dielectric properties. The resistivity of the samples decreases with increase of Cd concentration and temperature, respectively. The activation energy at 339 K varies from 0.426 to 0.146 eV. The ternary system possesses a negative mass susceptibility having pair of electrons confirmed by the magnetic mass susceptibility measurement. The dielectric constant of the samples increases with increase of Cd and decreases with frequency initially and then remains constant.

This review is in general about group 12 elements and their small microclusters. In this part, after presenting an extensive literature survey of the electric dipole polarizability studies of the Zn, Cd and Hg atoms, we specifically target zinc-containing small clusters, beginning with the Zn₂ dimer, the Zn₃ trimer, higher Zn_n clusters and the neutral, cationic and anionic zinc oxide clusters: ZnO, ZnO⁺ and ZnO^-. We tabulated experimental and theoretical results for the spectroscopic constants (dissociation energy D_e or D₀, bond length r_e, fundamental frequency w_e, anharmonicity constant w_ex_e and dipole moment μ_e) of the diatomic clusters and the first and second ionization potentials IP₁ and IP₂ and electron affinity EA of the species reviewed.

Separation and recovery of valuable metals including silver (Ag) and copper (Cu) from electronic waste mixtures are of great economic and environmental importance. Recent years, semiconductor photocatalysts have been investigated intensively for the removal of Ag from wastewater. Few studies have been carried out on the effect of pH and co-exist metal ions such as Cu on Ag. In this study, ZnO and TiO₂ were applied as photocatalysts to target on the selective recovery Ag and Cu from its mixtures under UV light. The effects of pH, catalyst, ethylene-diamine tetraacetic acid (EDTA) on the Ag and Cu photo-reduction were studied. Modeling of Ag${}^{+}$ and Cu${}^{2+}$ with and without EDTA distribution together with metal precipitations was plotted against pH to understand the chemistry involved in photocatalysis. Experimental results showed that Ag${}^{+}$ photo-reduction was nearly completed by ZnO and TiO₂ to Ag metal, while Cu${}^{2+}$ photo-reduction to Cu₂O only occurs by ZnO in the presence of EDTA. This work illustrates that semiconductor photocatalysts are suitable for selective recovery of Ag and Cu from wastewaters.

Density functional theory (DFT) and generalized gradient approximation (GGA) have been employed to study origins of the intrinsic $n$-type electrical conductivity in the zinc oxide. Hubbard-like term has been introduced to provide a better description for the Zn 3$d$ electrons. Two intrinsic point defects, namely oxygen vacancy and hydrogen impurity, were taken into consideration. Results on conductivity are analyzed using density of states patterns for different configurations of defects. Microstructure and local magnetic moments are studied as well. The obtained results clearly indicate that oxygen vacancy does not and cannot be responsible for the intrinsic $n$-type electrical conductivity whereas inserted hydrogen atoms tend to lose its only valence electron, which in turn becomes a free electron contributing towards the $n$-type conductivity.

In this study, we show that by applying appropriate deposition conditions, Zn nanostructured templates for the growth of zinc oxide (ZnO) nanowires can be fabricated, from which ultrafine high optical quality nanowires can be grown by means of post-deposition low-temperature oxidation. By identifying and optimizing the appropriate parameters, we successfully fabricated long ultrafine ZnO nanowires up to 30 microns in length and 50 nm in diameter. Our report contradicts the commonly held paradigm that sputter deposition can only be used to fabricate thin films with no significant nanostructure morphology and provides a low cost, high throughput method of fabricating different ZnO nanostructures. The studies of photoluminescence (PL) of the nanowires showed their high optical quality with band edge dominated emission with small defect-related input.

${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x$O asymmetric quantum barriers on JGS1 quartz glass and ${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ substrates were prepared by a pulsed laser deposition (PLD) technique. Microstructure characterization confirmed the designed structure. Because of the design of ${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x\mathrm{\text{O}}$ asymmetric quantum barrier, representative exciton peaks were observed in the optical absorption spectrum at room-temperature. This confirmed that the designed ${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x\mathrm{\text{O}}$ asymmetric quantum barrier structure realized the quantum-binding effect at room-temperature. Moreover, when $x=0.15$, the asymmetric quantum barrier structure had optimum performance compared with other $x$ values.

A zinc oxide–silver doped with graphite and nitrogen (ZnO/Ag doped with C/N) heterostructure was prepared by a simple method with a study of the photodegradation of methylene blue (MB) dye under sunlight irradiation. Results from X-ray diffraction (XRD) experiments show the presence of sharp peaks for ZnO, Ag, and C, with the wurtzite phase of ZnO. Energy-dispersive X-ray spectroscopy (EDX) results match the results of XRD and confirm the presence of Ag, Zn, C, O, and N. Field emission scanning electron microscope (FESEM) images confirm the presence of clusters of spherical nanoparticles (NPs). The optical properties results confirm the high-absorption ability in the visible area with an energy gap of 2.95eV. After 140min of exposure to sunlight radiation, the photocatalysis results show that the MB dye can be broken down very well by light.

In this work, an innovative seedless and surfactant-free chemical bath deposition (CBD) method at low temperature was applied to obtain flower-shaped ZnO nanostructures (FZONSs) on glass and p-type silicon substrates for the first time. Structural properties of these FZONSs were examined. The NSs were produced from zinc nitrate hexahydrate and hexamethylenetetramine, HMTA solution without any catalyst, template, or seed layer. An electric soldering iron pen was used to simultaneously heat the substrate and aqueous mixture of the constituents to grow the FZONSs. Field emission scanning electron microscopy images of the samples showed the presence of three-dimensional (3D) flower-shaped nanomorphology. Energy-dispersive X-ray spectroscopy detected the right trace elements in the FZONSs. X-ray diffraction analysis of the as-grown samples confirmed the existence of high purity nanocrystalline hexagonal phase of ZnO with preferred growth along (002) lattice planer orientation. The growth of ZnO nanorods into unified flower-like morphology was interpreted using a nucleation dissolution-mediated recrystallization mechanism. The fabricated FZONSs may provide potential in various applications including advanced catalysts, sensing devices, and solar cells.

Electronic and magnetic properties of transition metal (TM) ion-doped monolayer zinc oxide (ML-ZnO) have been analyzed using ab-initio calculations in the frame work of density functional theory. Spin–spin interaction study reveals that Cr, Mn, Fe and Cu doped at Zn site of ML-ZnO show stable ferromagnetic ordering along with the half-metallic behavior for most of the cases. The electronic and magnetic properties of the pristine system can also be modified by using co-doping. 3d orbital electrons of the dopants are primarily responsible for the origin of magnetic moment and the remaining part comes from the 3d and 2p orbital electrons of Zn and O atoms, respectively. Moreover, the magnetic ordering in Fe-doped ML-ZnO can change with the doping distance between the dopants.

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.