Zinc Oxide Microstructures Research Articles

Investigation of zinc oxide doped microstructures with cobalt via electrochemical deposition

The present paper reports electrochemical elaboration of zinc oxide microstructure doped with cobalt (CZO) at various [Co2+]/[Zn2+] (Co/Zn) concentration ratios onto ITO substrates at a pH of 6.5. All Mott-Schottky plots of electrochemical analysis showed that all electrodeposited CZO samples exhibited n-type semiconducting behaviours. XRD spectra revealed that all electrodeposited CZO samples crystallized in the typical hexagonal wurtzite structure with a preferential orientation along the (100) plane with descending crystalline size versus increasing cobalt dopants amount. Reviewing SEM images, notable changes were found on granular morphologies of CZO samples because of doping changing. EDX showed proportionality between the increase of final Co/Zn ratio in the CZO samples and the increase of starting Co/Zn concentration ratio within the initial depositing solutions. UV–Vis measurements indicated that transmittances of most CZO samples were above 80 % in the visible range and their optical band gaps were high and limited between 3.60 and 3.64 eV.

Pyramid-like zinc oxide microstructures as humidity sensor

Pyramid-like zinc oxide microstructures as humidity sensor

Anisotropic thermal property characterizations and optical phonon contribution analysis of ZnO under high pressure

Zinc oxide (ZnO) is a wide band-gap semiconductor material with versatile applications in high-tech fields. Under high pressure, ZnO exhibits multiple phase transitions, which are of great significance for the development of photocatalysts, micro-devices with stress-controlled elements, and the investigation of relevant structure-activity relationships. However, previous studies have reported only theoretical calculations of its thermal transport properties under high pressure due to the challenges of experimental methodology. In this work, we employed a combination of the time-domain thermoreflectance technique and diamond anvil cell to characterize the anisotropic thermal properties of ZnO crystal under 0–20 GPa. Simultaneously, we studied the micro-structure of ZnO in the same pressure range by Raman spectra. Our proposed modified Leibfried-Schlomann equation adequately explained the non-monotonic trend of the thermal conductivity within 10 GPa observed in measurement results. Additionally, we report the ZnO thermal conductivity during the decompression process for the first time. Our experimental results and theoretical analysis advance the understanding of the thermal transport mechanism of wide-gap semiconductors under high pressure and pave the way for their high-pressure modification.

High-resolution light field imaging based on liquid crytal microlens arrays with ZnO microstructure orientation

We proposed a liquid crystal (LC) microlens array (MLA) based on zinc oxide (ZnO) microstructure orientation and used it in a light field imaging system. The system uses convex optimization theory to jointly optimize the multi-voltage light field information and obtain a high-resolution imaging method. The core element in this system is an LCMLA, which induces the horizontal orientation of LC molecules by ZnO microstructure to effectively overcome the physical defects caused by orientation, such as mechanical friction. Combined with the proposed joint optimization high-resolution algorithm based on convex optimization theory, high-resolution imaging can be achieved using the redundant characteristics of light field images. The experiments show that the proposed method's PSNR of the reconstructed image is about 32 dB compared with the conventional method. The designed imaging system is flexible, simple, and suitable for high-resolution reconstruction.

Kinetic and isotherms modeling of methyl orange and chromium (VI) onto hexagonal ZnO microstructures as a membrane for environmental remediation of wastewater

Globally, contamination of water by dyes and heavy metals (HMs) is a serious environmental and public health problem due to their carcinogenic and mutagenic nature. It is incumbent to treat innocuously before discharge. It is the first time, hexagonal zinc oxide (ZnO) microstructure are being employeed as a membrane in the simultaneous removal of methyl orange (MO) and chromium (Cr (VI)) from the aqueous solution. The surface chemistry of hexagonal ZnO was characterized for morphology, surface functional groups, crystalline nature, and elemental composition by scanning electron microscope (SEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Adsorption capacity and removal efficiency was determined by the laboratory batch adsorption experiments, while nonlinear, linear kinetics and isotherm models were fitted to experimental data to investigate the adsorption process. The results exhibited that the maximum adsorption capacity (qmax) of hexagonal ZnO from the Langmuir isotherm model was 80.39 mg g−1 and 84.10 mg g−1 for MO and Cr (VI) respectively. According to the modeling findings, linear langmuir fitted to the experimental data with R2 0.967 and 0.971 for both MO and Cr (VI) which indicates monolayer physical adsorption of both pollutants has taken place. Whereas, kinetic study showed nonlinear pseudo-second order with R2 0.989 and 0.986 for MO and Cr (VI) model best fitted with the experimental data. The values of thermodynamics parameters Gibbs free energy change ΔG°, heat of enthalpy ΔH° and, heat of entropy ΔS° indicate that spontaneous, endothermic, and irreversible adsorption reactions occurred. Overall, it is concluded from our observations that hexagonal ZnO has the potential to be used as an eco-friendly, cost-effective adsorbent for simultaneous remaoval of both MO and Cr (VI) from water. Findings of the current investigation provide valuable insights for the development of an inexpensive, effective and sustainable filtration method for the treatment of MO and Cr (VI) synergistically.

Insight into the Growth Mechanism and Photocatalytic Behavior of Tubular Hierarchical ZnO Structures: An Integrated Experimental and Theoretical Approach.

The hydrothermal synthesis of zinc oxide (ZnO) particles from zinc acetylacetonate monohydrate in "pure" aqueous solution and in aqueous NaOH solution at 90 °C is reported. The structural and morphological properties of ZnO particles were investigated by powder X-ray diffraction, X-ray absorption spectroscopy (XAS), field emission scanning electron microscopy, and transmission electron microscopy. The effect of NaOH on the growth mechanism and photocatalytic performance of hierarchical ZnO structures was investigated. The experimental findings, supported by results of quantum chemical calculations at the level of density functional theory, were used to propose the mechanism of nucleation and preferential growth of finely tuned hollow and nonhollow ZnO structures and their effects on the photocatalytic activity. The calculations indicate that the process of ZnO nucleation in "pure" aqueous solution mainly proceeds by the reaction of small monomers, while tetramers play a crucial role in aqueous NaOH solution. Both the preferred ZnO nanostructure and microstructure growth processes are driven by O-H···O hydrogen bonds as controlling elements. The calculated values of the EO···H interaction indicate a stronger interaction via O-H···O hydrogen bonds in "pure" aqueous media (EO···H = -11.73 kcal mol-1) compared to those obtained in aqueous NaOH solution (EO···H = -8.41 kcal mol-1). The specific structural motif of the (ZnO-H2O)12 dodecamers with calculated negative ΔG*INT free release energy indicates that the formation of anisotropic nanocrystalline ZnO with the c-axis as the primary growth direction is spontaneous and accelerated exclusively in "pure" aqueous solution, whereas it is an unfavorable endergonic process in aqueous NaOH solution (ΔG*INT > 0). Efforts have been made to determine the photocatalytic efficiency of the ZnO samples based on the XAS measurements. ZnO particles obtained in "pure" aqueous solution show the highest photocatalytic activity due to the presence of a larger amount of oxygen vacancies.

Biosynthesis of Zinc Oxide Powder Using Sandoricum koetjape Peel Extract at Various Annealing Temperature

Zinc oxide (ZnO) synthesized with natural reductants has attracted the attention of researchers because it is environmentally friendly and non-toxic. In this study, ZnO was prepared using Sandoricum koetjape (S. koetjape) peel extract. An aqueous extract of S. koetjape peel was used as biological reduction agent for the synthesis of ZnO from zinc nitrate hexahydrate. The ZnO powder obtained was annealed at different temperatures i.e, 300°C, 400°C, and 500°C for 1 hour. Structural, morphological, optical properties, and functional groups of samples were analyzed using X-Ray Diffraction, Scanning Electron Microscopy, UV-Vis Spectroscopy, and Fourier Transform Infrared Spectroscopy, respectively. The X-ray diffraction pattern shows that pure hexagonal wurtzite structure of ZnO particles can be achieved after annealing. The crystal size has also increased with increasing annealing temperature. SEM photo demonstrates the transformation of ZnO particle from spherical to microflower due to annealing. The widest absorption peaks in the UV-Vis spectrum was occurred after annealing at 500°C. The bandgap energy of ZnO increases after annealing from 3.08 eV to 3.20 eV. The FT-IR analysis confirms O-H functional group from extract has been decomposed due to the annealing process. Based on this study, biosynthesized ZnO using Sandoricum koetjape peel extract requires annealing process to improve the purity, enhance the light absorbance and change the microstructure of ZnO.

Effect of pH on the Morphology and Microstructure of ZnO synthesized using Ananas comosus Peel Extract

This research investigated the effect of synthesis pH on the microstructure and morphology of the zinc oxide (ZnO) particles prepared using pineapple (Ananas comosus) peel extract. In this study, ZnO powder were synthesized at different pH, i.e. 8, 9, 10, 11, and 12. ZnO samples were characterized using UV-Vis spectroscopy, Fourier Transform InfraRed spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The UV-Vis absorbances spectroscopy shows the optical absorption peak of the ZnO sample occurred in a wavelength range of 300-360 nm, with bandgap energy of ∼3.22 eV. The FT-IR spectrum shows the peak of Zn-O absorption at the wavenumber of 437.55 cm-1 and the reduction of aromatic compounds with increasing of pH. The micrograph of ZnO particles synthesized at different pH shows that the pH affected the size and shape of ZnO. Micro-sized particles with a granular shape have been found at pH 8, and 9, a spherical shape have been found at pH 10, while micro-sized flower-shaped particles have been found at pH 11 and 12. The XRD pattern reveals a wurzite hexagonal ZnO crystal phase with the hkl plane of (101) as the strongest peak, as well as the purity of the sample increasing as the pH value rises. As the conclusion, synthesis pH has a significant impact on the optical, structural, and morphological properties of ZnO biosynthetic powder.

The Influence of Recrystallization on Zinc Oxide Microstructures Synthesized with Sol–Gel Method on Scintillating Properties

Zinc oxide (ZnO) is one of the wide-bandgap semiconductors, which may be useful in a plethora of electronic, optical, piezoelectric, and scintillating applications. The following article consists in a structural and luminescence analysis of ZnO microfilms grown on a sapphire substrate with a sol–gel method. The films were annealed at different temperatures. The structures were investigated with the XRD and Raman methods, by which the influence of the substrate on the structure of the film was determined. The luminescence of films was investigated with room-temperature fluorescence, radioluminescence, and thermoluminescence.

Nanoscaled Zinc Oxide Prepared by Mono-amino Acid Templated Assembly and Their Superior Biological Properties

Nanoscaled zinc oxide (ZnO) was synthesized via a benign mineralization reaction using mono-amino acid as templates. Characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, it was found that the microstructure of as-prepared ZnO can be fine-tuned into olive-like and flake-like structures with leucine and histidine respectively. Otherwise, the photoluminescence (PL) results indicate that biomineralized ZnO nanoparticles show a potential application in the fields of optical devices. To further explore the biological performance of as-prepared ZnO nanoparticles, antibacterial activity tests against Staphylococcus aureus and Escherichia coli, and cytocompatibility on mouse MC3T3 cells were also investigated. The superior biological properties of these biomineralized ZnO together with their intrinsic photoluminescent properties open perspectives for the development of biomedical applications.

Paracetamol-Assisted Self-Assembled ZnO Porous Microstructures for Enhanced CO2 Detection

Paracetamol-assisted zinc oxide (ZnO) highly porous micro-flakes were synthesized by a rapid two-step synthesis: precipitation (with sodium hydroxide) and calcination (at 250°C for 1 h). Addition of paracetamol during the synthesis not only inhibited the growth of ZnO grains but also originated self-assembly of the micro-flakes resulting in highly porous flower like structures. Increase in paracetamol concentration also increased porosity on ZnO microstructures due to the self-assembly of thinner flakes without any structural changes. X-ray diffraction (XRD) shows the preferential orientation of powders in the (101) direction of hexagonal structure. Raman spectra is dominated by E2 (high) optical mode due to vibration of oxygen atoms. Samples were tested for gas detection at 50, 100, 200, 400, 800 and 1000 (parts per million) PPM concentration of carbon dioxide (CO2). ZnO porous microstructures were obtained with a high concentration of paracetamol, enhancing the carbon dioxide sensing response from 20% to 90% with a response time of 60 s. These simple, low-cost and highly porous self-assembled ZnO structures with enhanced CO2 detection will be of interest for several researchers in the chemical sensor fabrication field.

Synthesis of ZnO material: A new approach by hydrothermal method

Zinc oxide (ZnO) material possesses various morphologies which have given ZnO many fascinating applications in practice. Thus, the controlled synthesis of morphology and size of ZnO microstructures has attracted great interest. Many synthetic methods exhibited their effectiveness in producing pure ZnO, and the hydrothermal synthesis expresses its own considerable advantages for controlling the morphology of ZnO with low particle-size distribution. Moreover, the hydrothermal synthesis can be performed under mild condition rather than the conventional harsh ceramic method. In this work, we performed hydrothermal synthesis by altering different initial seeds by pre-treating of Zinc acetate solution prior to hydrothermal action. Characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and Infrared (IR) spectroscopy were used to determine the morphology and surface functional groups of ZnO final products. Firstly, we processed the pretreatment of Zinc acetate solution by annealing it at 90 ◦C for 1h before putting the solution into autoclave together with NH3 solution for hydrothermal synthesis (this process is called as two-step hydrothermal synthesis). Secondly, the reaction temperatures (120 ◦C, 150 ◦C, 180 ◦C) were investigated to provide the role of temperature synthesis in controlling size and shape of ZnO, and at 150 ◦C, ZnO particles were formed with reasonable uniform morphology. Finally, we examined the effects of initial seeds by pre-treating Zinc acetate solution with H2O2, or, the initial seeds change from only Zn(OH)2 (without H2O2) to mutual existence of Zn(OH)2 and ZnO2 (with H2O2). In this case, ZnO Wurtzite phase was obtained with 100% purity at 180 ◦C, or at higher temperature than other samples whose ZnO Wurtzite phase was formed at only 150 ◦C. The results show that the nature of initial seeds greatly impact not only on the shape and size, but also on the surface functional groups of ZnO final product.

Solution processed laterally grown Zinc Oxide microstructures for next generation computing devices

Traditional charge storage-based computer memories suffered from the scaling limits that stimulate the development of next generation memories with improved performances. This also involves the exploration of new materials and the development/exploration of unique device fabrication processes. In this work, a new type of laterally bridged Zinc oxide (ZnO) micro-bushes-based resistive memory is presented by employing simple Cut and Grow strategy. The growth of lateral ZnO micro-bushes, electrochemically grown across a 100 μm cavity (grooved on copper tape) was controlled by tuning deposition time. The memory device demonstrated unique write once read many times (WORM) behavior with exceptional stability and reliability with an on-off ratio higher than 10 6 . Moreover, the lateral memory device exhibited great potential to tackle large variations in stochastic computing applications. This unique strategy underscores a great potential to develop low cost, simple and highly reliable lateral device fabrication with exceptional functionalities, comparable to traditional fabrication methods. • A facile and simple Cut and Grow strategy to fabricate lateral ZnO nano-microstructures is presented. • The lateral architectures are ideal platform to fabricate next generation resistive switching memories. • The laterally bridged RS device demonstrated write once read many times (WORM) behavior. • The WORM capabilities are quite useful to store permanent data for archiving and non-editable storage equipment.

Controllable Heterogeneous Nucleation for Patterning High-Quality Vertical and Horizontal ZnO Microstructures toward Photodetectors.

High-quality crystalline micro- and nanostructures based on inorganic semiconductors including zinc oxide (ZnO) have attracted considerable interest in electronic and optoelectronic applications due to their outstanding properties. ZnO micro- and nanocrystals can be fabricated by the moderate and high throughput hydrothermal synthesis. Yet it is restricted by patterning large-area ZnO crystals with high-quality and programmable geometries through the hydrothermal process for the optoelectronic integration. Here, a capillary-bridge manipulation approach is demonstrated to control the dewetting process of ZnO precursor solution for patterning precursor arrays. Based on precursor arrays, vertically aligned high-quality ZnO microrod arrays with homogeneous morphology and pure crystallographic orientation are fabricated via a hydrothermal epitaxial method. Statistical results and crystallization theories guide the experimental optimization and discussion of the crystallization mechanism, dominated by the competition between homogeneous nucleation and heterogeneous nucleation. High-quality ZnO microbelt arrays are achieved through a surfactant-mediated hydrothermal method after ZnO microrod arrays are transferred to a polydimethylsiloxane substrate. Photodetectors based on ZnO microbelts exhibit a high responsivity of 2.3 × 104 A W-1 , a light on-off ratio exceeding 105 , and stable recyclability. It is anticipated that this work provides new insights into patterning inorganic high-quality micro- and nanostructures for multi-functional integrated devices.

Densification Behavior, Microstructure, and Property of ZnO with Multi-Oxides Glass Addition at Different Sintering Temperatures

Zinc Oxide (ZnO) mixed with various amount of glasses were sintered at different temperatures. The densification behavior of zinc oxide with glass addition and its microstructure and dielectric constant sintered from 900° to 1200°C have been investigated. A unique glass composition contained GeO2, MoO3, and V2O5 (GMV) was designed to act as the sintering aid to enhance the densification and to adjust the dielectric constant of ZnO. The effect of sintering temperature on the densification behavior and dielectrics properties of ZnO was investigated by dilatometer, x-ray diffractometer, scanning electron microscopy and LCR meter. The glass additive formed a thin continuous liquid phase and rearranged ZnO particles into a dense microstructure at relatively low temperature. The dielectric constants of glass added ZnO ceramics were found to vary with the glass concentration and sintering temperature.

X-Ray Luminescence of ZnO Whisker Microstructures

Morphology and the optical and luminescent properties of zinc oxide (ZnO) whisker microcrystal arrays grown on sapphire using gas-transport synthesis from zinc vapors in oxygen by vapor–liquid–solid (VLS) mechanism have been studied. The arrays consisted of uniaxial microcrystals with two morphologies, combining hexagonal prisms and single-crystalline microrods. Short-wavelength boundary of transparency of the whisker microcrystal arrays occurs in a region of 385−395 nm. Total transmission in the visible and near-IR spectral range is on a level of 10–20% for layer thicknesses about 15–18 μm. The X-ray luminescence spectrum displays two bands: (i) an intense narrow excitonic peak at 388.3 nm and (ii) an about 2.5 times less intense broad band in a region of 430−600 nm. The time constant of the decay of excitonic luminescence from undoped ZnO microstructures has been estimated for the first time at about 1.1 ns (with the exciting pulse width not taken into account).

Enhancement in NH3 sensing performance of ZnO thin-film via gamma-irradiation

In this work, chemically synthesized Zinc Oxide (ZnO) thin films were exposed to Cobalt-60 (Co-60), 1.25 MeV average energy of gamma source at different doses for possible augmentation in NH3 sensing. The hexagonal crystalline structure was confirmed by XRD spectra and an enhancement in crystallite size was observed with an increase in radiation followed by decrease at 50 kGy dose. The FTIR spectra showed there were no significant changes in the peak position after gamma-irradiation. The morphological investigation showed the maturation of 1D ZnO hexagonal nanorods over the surface of the film. However, after gamma-irradiation, the ZnO nanorods were found connected, forming bunches. The band-gap increased for 50 kGy doses as compared to pristine ZnO thin film. However, characterization result analysis showed that gamma-irradiation produced conspicuous improvements in chemically prepared ZnO microstructure. It was found that post-irradiated (at 30 kGy) ZnO thin film sensor achieved 7.29 as response factor for 400 ppm NH3 gas sensing compared to 1.01 for the pristine sample. The outcome of this study showed that gamma-irradiation is an effective technique for improvement in the sensing performance of ZnO thin films which has great potential to use gamma irradiated ZnO sensor in chemical industries and laboratories.

Microstructure of Zinc Oxide Irradiated with Swift Heavy Ions Beam

Microstructure of Zinc Oxide Irradiated with Swift Heavy Ions Beam

Flower-shaped ZnO nanomaterials for low-temperature operations in NOX gas sensors

In this study, we synthesized nanostructured zinc oxide (ZnO) by using various concentrations (0–0.05 M) of cetyltrimethylammonium bromide (CTAB) as a surfactant to optimize its morphology for gas sensor applications. The optimization process was used to elucidate the morphology effects (rod-shaped and flower-shaped morphologies). The morphologies were investigated through scanning electron microscopy, in which the assembly of nanorods leading to a spherical microstructure with a CTAB concentration of 0.005 M was observed. Brunauer–Emmett–Teller isotherm measurements revealed a surface area of 7.928 g/m2 for the flower-like morphology, which was relatively higher than those of other CTAB-assisted morphologies. Such morphological features were expected to contribute toward high-performance gas-sensing. The effect of morphology variation on the resistance of ZnO microstructures was used for gas measurements. Among the varied morphologies, a sample with a spherical flower-shaped morphology exhibited a very high response at low temperatures (~29 at 25 °C) toward NOX gas (0.75 ppm) and a high selectivity toward NOx among ammonia (NH3), toluene (C6H5CH3), carbon monoxide (CO), acetone (CH3COCH3), and ethanol (C2H5OH). Raman and photoluminescence spectroscopy analyses unraveled the presence of a high density of oxygen vacancies in the sample, thereby suggesting a close link between the defective nature of the sample and the high response of the flower-like ZnO at low temperatures.

Raman Spectra and Microstructure of Zinc Oxide irradiated with Swift Heavy Ion

Zinc oxide (ZnO) materials irradiated with 350 MeV 56Fe21+ ions were studied by Raman spectroscopy, Photoluminescence spectra (PL) and Transmission electron microscope (TEM). After 56Fe21+ ion irradiation, a strong oxygen vacancy (Vo) related defect absorption peak at 576 cm−1 and an interstitial zinc (Zni) -related defect at 80 cm−1~200 cm−1 formed, and with the increase of dose, the absorption peak was obviously enhanced. Through theoretical calculation, different Raman incident light test methods wereused to determine the oxygen vacancy defect (Vo). There were no significant variation tendencies in the other Raman characteristic lines. Our results demonstrate an energy loss process contributing to the defect structure during irradiation. TEM images showed a lot of fundamental defects. But we see no distinct amorphization in the samples in the electron diffraction images, indicating that the higher energy and irradiation dose hardly affected the structure and performance of zinc oxide.