Effect of ZnS/C Mass Ratio on the Morphologies and Luminescence Properties of ZnO Nano/Microstructures Synthesized via Thermal Evaporation of ZnS and C Powder Mixtures

ZnO nano/microstructures were grown via a simple thermal evaporation process in air at atmospheric pressure. Mixtures of ZnS and carbon powders were used as the sources. The effects of growth temperature and mass ratio of carbon powder to ZnS on the morphologies and luminescence properties of the ZnO nano/microstructures were investigated in this study. When the growth temperature was 1000 ^oC, ZnO nanowires with a hexagonal wurtzite crystal structure started to be formed and were preferentially grown along the [0001] direction. As the temperature increased to 1200 ^oC, the crystal growth in the lateral direction perpendicular to the [0001] direction was enhanced, which resulted in a decreasing aspect ratio of the onedimensional ZnO nanowires. When source powders with different mass ratios of ZnS:C=2:1, 1:1 and 1:2 were used to grow ZnO nano/microstructures at 1200 ^oC, ZnO microrods with wurtzite crystal structure were formed in all the samples. As the mass ratio of carbon powder to ZnS increased, the aspect ratio of ZnO microrods was reduced, which suggests that the carbon powder enhanced the growth of ZnO microrods in the lateral directions. A strong ultraviolet emission band centered at 380 nm was observed in the ZnO nano/microstructures synthesized using the source powders with the mass ratios of ZnS:C=1:1 and 1:2, indicating that the ZnO nano/microstructures had a high crystalline quality.

Fabrication of Pyramid Structure Substrate Utilized for Epitaxial Growth Free-Standing GaN

Metal–organic chemical vapor deposition (MOCVD)-grown GaN on sapphire substrate was etched by hot phosphoric acids. Pyramid structures were obtained in the N-polar face of the MOCVD–GaN. Details of the formation process and morphology of the structures were discussed. The crystallographic plane index of the pyramid facet was calculated dependent on the symmetry of the wurtzite crystal structure and the tilt angle. The substrates with pyramid structures were utilized in subsequent hydride vapor phase epitaxy (HVPE) growth of GaN. Free-standing crystals were obtained, while HVPE-grown GaN achieved a certain thickness. Raman spectroscopy was employed to obtain the stress conditions of the HVPE–GaN without and with sapphire substrate. The mechanism of the self-separation process was discussed. This facile wet etching method may provide a simple way to acquire free-standing GaN by HVPE growth.

Formation Mechanism and Properties of Foam-Structured ZnO Films Prepared Using Catalyst-Free Carbothermal Method

Foam-structured ZnO films were formed on c-axis Al2O3 substrates by using a catalyst-free carbothermal method. The morphological properties of the films strongly depended on their substrate position in the reactor, implying that the quantity of Zn vapor transported played a crucial role in determining the film structure. The formation mechanism of the films is proposed to be as follows: with increased transport of Zn vapor, vaporized Zn elements transformed into liquid Zn nanoparticles, and the liquid Zn elements on the rods promoted the new nucleation of ZnO nanorods. The repeated growth of ZnO rods at the nucleation sites led to the foam-like structure. The as-formed foam-structured ZnO films exhibited the wurtzite crystal structure, and the atomic composition ratio of Zn to O was 1 : 0.85. The main photoluminescence emissions were centered at 3.3 and 2.5 eV, and they were attributed to band-to-band and defect-related transitions, respectively.

Structural and Optical Studies on Nanosized Thermoelectric Oxide-Zn1−xAlxO

Aluminum doped ZnO ([Formula: see text]AlxO, [Formula: see text], 0.02, 0.03 and 0.04) (AZO) nanoparticles were synthesized using citrate-gel method. We report the effect of aluminum doping along with variation of metal to citrate ratio on structural and optical properties of AZO nanoparticles with crystallite size optimization. The X-ray diffraction analysis confirmed Wurtzite crystal structure wherein the crystallite size was within the range of 15–40[Formula: see text]nm. Optical properties were studied with the help of UV-Visible spectroscopy. Bandgap calculated using Tauc plot is found to be between the range of 2.39–2.75[Formula: see text]eV and morphological analysis using Scanning Electron Microscopy (SEM) showed the distribution of synthesized material.

Microstructure and optical properties of ZnO nanorods prepared by anodic arc plasma method

Introduction: A one-dimensional ZnO nanostructure is a versatile and multifunctional n-type semiconductor. In this paper, ZnO nanorods were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere. Methods: The composition, morphology, crystal microstructure, and optical properties of ZnO nanorods were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and the corresponding selected-area electron diffraction (SAED), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible (UV-VIS) spectroscopy, Raman scattering spectrum (Raman), and photoluminescence spectrum (PL). Results: The experiment results show that ZnO nanorods synthesized by this method possess hexagonal wurtzite crystal structure with good crystallization, no other impurity phases are observed, the crystalline size is about 18 nm, and the lattice constant distortion occurs compared to that of bulk ZnO. The morphology of the sample is a rod-like shape, the length ranges from 100 nm to 300 nm, the average diameter is approximately 20 nm, and the aspect ratio is relatively high. The UV-VIS absorption spectrum occurs red shift, The Raman spectrum further demonstrates that the major peaks are assigned to ZnO optical vibrational modes, and the PL spectrum exhibits coexistence properties of ultraviolet (UV) and green emission. Conclusions: The results prove that ZnO nanorods with hexagonal wurtzite crystal structure were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere.

GaAs wurtzite nanowires for hybrid piezoelectric solar cells

The properties of the hybrid energy sources “piezoelectric nanogenerator-solar cell” based on GaAs nanowires with the wurtzite crystal structure were investigated. Measurements were performed by the bending of the nanowire by the probe of the atomic force microscope with simultaneous recording of short circuit current in dark and illuminated conditions. We show that a piezoelectric current pulse of ~10 pA arises in the “nanowire-probe” circuit during the deformation of nanowire by the AFM probe. Under laser illumination, the value of the pulse increases by two orders of magnitude as a result of the piezophototronic effect. Deformation of the nanowire boosts the photocurrent by 40% up to 0.5 nA.

Synthesis of Hydroxyapatite and ZnO Nanoparticles via Different Routes and its Comparative Analysis

Hydroxyapatite (HAp) was prepared from egg shells by various routes using hexane and acetic acid followed by heat treatment. HAp has a wide application in water treatment by removal of metal ions. XRD of the samples showed use of acetic acid followed by high temperature sintering leads to formation crystalline phases of HAp. Strong evidence of CaCO3 in calcite phase was obtained in other samples. Zinc oxide nanoparticles have also been synthesized by different methods such as sol-gel, co- precipitate and green synthesis. The effect of different synthesis methods were investigated using X-Ray Diffraction (XRD). The structural properties of nanoparticles including particle size were calculated from XRD data. The XRD reveals that the prepared ZnO samples were highly crystalline, having wurtzite crystal structure. The comparative analysis shows variations in particle size with different synthesis methods.