Dimensional Zinc Oxide Research Articles

Easily prepared one dimensional zinc oxide crystals, characterization and application in UV photodetector

One dimensional (1D) zinc oxide crystals (ZCs) were prepared using a simple wet chemical route. Structural and morphological characterizations were performed through x-ray diffraction, scanning electron microscopy and transmission electron microscopy. Thus, the prepared sample confirmed the hexagonal crystal phase of zinc oxide and displayed a uniform morphology with 1D structure. The average length and diameter of the prepared ZnO based 1D structure were found to be 8 µm and 0.7 µm respectively. Energy dispersive x-ray spectroscopy and Fourier transform infrared spectroscopy were performed to study the chemical purity of the sample. The prepared sample also showed its excellent ability in ultra-violet (UV) absorption with a sharp absorption peak at 369 nm and a photoluminescence (PL) property with a sharp emission peak at 384 nm. Finally, a UV photodetector device was fabricated with the prepared sample and its photoconductivity with a significant change in resistance was observed upon UV exposure.

Influence of oxygen-related surface adsorbates on the growth of low dimensional nanostructures and enhanced luminescence due to superoxide charge-transfer states in ZnO for application in optoelectronic devices

Kinetically controlled growth of low dimensional zinc oxide (ZnO) nanostructures like nanorods, nanoflowers etc. have been demonstrated with enhanced photoluminescent emission by tuning of the hydroxide ion concentration in the precursor irrespective of the synthesis techniques. Change in concentration of the hydroxide ions in the precursor during the synthesis of ZnO nanostructured samples has been found to tune the aspect ratio of the nanostructures, viz. nanorods grown by electrodeposition, and morphology of nanoflowers to nanogranules synthesized by direct precipitation method. The photoluminescent emission from these samples has been found to increase synchronously with the increase in the concentration of hydroxide ions in the precursor. Observed enhancement in photoluminescence has been proposed to be due to the formation of superoxide (O2−) charge transfer (CT) states CTO2− due to the adsorption of molecular oxygen directly at grain boundaries or induced by hydroxide ions adsorbed over the surface of the nanostructures. The results are in contradiction to the established role of defect states behind photoluminescent emission from ZnO nanostructures. In this work, mathematical modelling has been used to establish the dominant role that superoxide CT states can play in enhancing the efficiency of ZnO based optoelectronic devices such as light-emitting diodes and photodiodes.

Structural, morphological and antibacterial properties of ZnO nanofibers fabricated by electrospinning technique

The one dimensional zinc oxide (ZnO) nanofibers have been fabricated through the sol–gel processing and electrospinning technology. This is achieved by applying a high voltage in the range of 15 to 30 kV at 5 to 10 cm needle distance with a flow rate of 0.1 mL/h. Staphylococcus aureus bacteria was then utilized to examine the antibacterial properties of the prepared nanofibers. Antibacterial effect of the nanofibers have been determined by disk diffusion method. The acquired results have revealed that ZnO nanofibers have a tremendous antibacterial activity. Therefore, the prepared nanofibers can easily be used in various fields such as nano medicine, biomedical, tissue engineering and textile industry. In addition, surface morphology, crystal structure, thermal property and anti-bacterial activity of the prepared nanofibers have been investigated through Field Emission Scanning Electron Microscopy, X-Ray Diffraction methods, Thermo Gravimetric Analysis and Agar Disc Diffusion method respectively.

Effect of Deposition Potential and Bath Temperature on One-Step Electrochemical Synthesis of One and Two Dimensional Nanostructured ZnO Thin Films on Fluorine Doped Tin Oxide Substrates

Different zinc oxide (ZnO) morphologies such as platelets, nanowalls and nanorods were electrochemically synthesized on fluorine doped tin oxide (FTO) substrates by varying the deposition potentials and bath temperatures, respectively. Cyclic voltammetry (CV) curves reveal that ZnO deposition potentials are decreased as the bath temperatures are increased. X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images confirm that the synthesized ZnO nanostructures are hexagonal wurtzite structure. The XRD results reveal that the crystallinity of the films is increased when ZnO deposition potentials and temperatures are increased. Field emission scanning electron microscope (FE-SEM) images display platelets, nanowalls and nanorods structures for films synthesized -1.1 V, -1.2 V and -1.3 V respectively. The increase in deposition potential not only increases the growth rate of ZnO with metallic zinc deposition, but also decreases zinc hydroxide chloride hydrate. Fourier transform infrared microscope (FTIR) spectra confirm that the formation of zinc hydroxide (Zn(OH)₂) is decreased as the bath temperatures are increased from 30 to 70 °C. Photoluminescence (PL) spectra depict that the crystal quality of the ZnO films are notably improved as the bath temperatures are increased. The film thickness is increased as the deposition potentials and bath temperatures are increased. The dye absorbance is increased with respect to the film thickness. The efficiencies of dye sensitized solar cells (DSSCs) fabricated with diverse morphologies such as platelets, nanowalls and nanorods are found to be 0.10, 0.49 and 0.47%, respectively. Electrochemical impedance spectroscopy (EIS) spectra reveal that the charge transfer recombination resistance (Rrec) is continuously decreased as metal zinc deposition is increased in ZnO films with increase in deposition potentials.

Synthesis of Porous ZnO Nanosheets and Carbon Nanotube Hybrids as Efficient Photocatalysts via Pulsed Laser Ablation

Zinc oxide (ZnO) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this material often restricts application. Here, we report that hybridization of one dimensional (1D) carbon nanotubes (CNT) on two dimensional (2D) porous ZnO nanosheets (NS) can be a promising strategy to overcome some of the challenges of ZnO. Specifically, a pulsed laser ablation technique was utilized to hybridize 1D CNT with 2D porous ZnO NS in environmentally friendly as well as super-economic (short time, less than 10 min) conditions. The synthesized ZnO NS-CNT hybrids show a significantly enhanced photocatalytic activity for water splitting relative to their counterpart ZnO NS.

Combined effect of in-situ grown p-type CuSbS2 / n-type CdS coupled with hierarchical ZnO nano disks for improved photovoltaic light harvesting efficiency

In this report, we have synthesized porous two dimensional zinc oxide disk structures, using a biomass derived templating agent i.e., Xanthan gum. This templating agent is mainly accountable to control the growth kinetics of high energy facets of wurtzite zinc oxide crystal structure, to obtain these disk structures. A comparative photovoltaic study of as-synthesized two dimensional porous zinc oxide structures with respect to one dimensional zinc oxide structures (in absence of xanthan gum) is carried out by co-sensitizing with in-situ grown one dimensional cadmium sulfide nanowires array and ternary metal chalcogenide viz. copper antimony sulfide. Superior photovoltaic performance (∼45% enhancement in efficiency) is obtained for co-sensitized device with porous two dimensional zinc oxide disk as compared to one dimensional zinc oxide structures, owing to improved current density and fill factors. This enrichment is mainly attributed to large exposed surface active sites for optimum loading of light absorbing materials, better light scattering and improved hole recovery rate of sensitizers with the better penetration of redox shuttle. Moreover, crystal phase purity of copper antimony sulfide and p-n junction formed between copper antimony sulfide and cadmium sulfide also support the enhanced efficiency by facilitating the electron-hole separation and electron transportation.

Decoration of 3D ZnO nanoelectrodes with CuInS2 for solar water splitting

This study reports the decoration of zinc oxide (ZnO) nanosheets with copper indium sulfide (CuInS2) via sequential metal deposition and post sulfurization methods for photoelectrochemical solar cell application. The three dimensional (3D) ZnO nanosheets are hydrothermally grown on conductive glass substrates by chemical bath deposition. Then, copper/indium metallic alloy is deposited via magnetron sputtering and annealed at high temperature in the presence of elemental sulfur to form CuInS2 absorber on the surface of 3D nanosheets. Photoelectrochemical measurements indicate that the decoration of CuInS2 layer over the ZnO nanosheets results in significant increase in the photocurrent density to 28 mA cm−2 (at 0.5 V vs Ag/AgCl) leading a remarkable amount of hydrogen generation during solar water splitting process, 1387 μmol measured at 0 V vs Ag/AgCl under 1 sun-illumination for 4 h.

Self-organized ZnMgO nanocolumns with ZnO/ZnMgO quantum wells on c-plane Al2O3 substrates by MBE: Growth conditions and properties

One dimensional zinc oxide nanostructures have great potential for applications in the fields of optoelectronic and sensor devices. In this paper, we present the synthesis of ZnO/ZnMgO heterostructures on c- plane Al2O3 by plasma-assisted molecular beam epitaxy and investigation of their structural and optical properties. We demonstrate that it is possible to grow a good quality nanocolumns on c- plane Al2O3 substrate without employing a catalyst such as Au or Ag. We have also studied a shift between polar- and nonpolar- ZnO/ZnMgO quantum wells. The non-polar a- plane ZnO/ZnMgO nanocolumns were achieved on r- plane sapphire substrate, while the on polar c-plane substrate was used to obtain a polar c-orientation of the nanostructures.

Variation of index of refraction in cobalt doped ZnO nanostructures

One dimensional zinc oxide (ZnO) nanostructures were fabricated using a low temperature chemical bath deposition technique. The ZnO nanorods were doped with cobalt using cobalt nitrate with cobalt concentration varying from 0% to 9%. The scanning electron microscope images of the nanostructures indicate that the diameter of ZnO nanorods increased with the increase in cobalt doping concentration. The optical characterizations of the doped and undoped samples were performed by investigating the variation in the band gap, the Urbach energy, the index of refraction, and the extinction coefficient with cobalt concentration. The dispersion of index of refraction in cobalt doped ZnO nanostructures was modeled based on the Wemple DiDomenico single oscillator model. The interband oscillator energy and the dispersion energy were estimated for different cobalt doped ZnO nanorod samples based on this model.

Interaction of Pyrene Ligands with Neat and Defective Two Dimensional ZnO: A First Principles Study

ABSTRACTMany heterogeneous and flat two dimensional (2D) materials with finite band gap have been researched for its suitability in exotic applications. For instance, zinc oxide (ZnO) with honey comb structure has optimum band gap that makes it eligible for opto-electronic applications. Recently, our research group have found that pyrene based tetratopic ligands (PTL) are suitable for functionalizing ZnO nanorods. In this study, neat and defective 2D ZnO layer is functionalized with different pyrene based ligands with various functional groups. First principles calculations are done and the degree of affinity of pyrene ligands towards neat and defective ZnO sheets is compared.

Effect of the morphology of solution‐grown ZnO nanostructures on gas‐sensing properties

AbstractDespite the great potential of zinc oxide (ZnO) nanostructures as a sensing material for high‐performance gas sensors, the correlation between the morphology of ZnO nanostructure and its gas‐sensing performance has not been systematically investigated yet. In this work, ZnO nanostructures with controlled morphologies were synthesized by low‐temperature solution route and chemical bath deposition method. Thin film gas sensors were fabricated from the nanostructures and the sensor performance such as the response, recovery time, and stability was examined for several gases. It is demonstrated that the gas‐sensing performance of a ZnO nanostructure sensor is strongly influenced by its morphology. One dimensional ZnO nanocones are highly promising for practical application to gas sensors, due to their large surface area per unit mass and unique conical structure.

The effect of dewetting process on structural and optical properties of one dimensional ZnO nanostructures

One-dimensional zinc oxide (ZnO) nanostructures of different sizes were synthesized on silicon wafer substrates by controlling the substrate condition using chemical etching and a vapor–liquid–solid (VLS) process. In this work, a thin layer of gold was deposited on the silicon substrate and used as catalyst. Gold is one of the most frequently-used catalysts in the chemical vapor-deposition method. By annealing the gold-coated thin films at different temperatures, the layer was transformed into gold islands, due to the dewetting effect. To investigate the effect of the dewetting process on ZnO nanostructures, samples with various thicknesses are annealed at different temperatures. The results are compared with the uncoated and chemically-etched silicon wafers. Structural and morphological properties of the samples were analyzed using X-ray diffraction and scanning-electron microscopy. Formation of nanowires and nanorods was observed, and their sizes were dependent on the sizes of the gold islands. Photoluminescence spectra of the samples at room temperature were measured and visible emissions were observed from the synthesized nanostructures at room temperature.

Electrospun Self-assembled ZnO Nanofibers Structures For Photocatalytic Activity In Natural Solar Radiations To Degrade Acid Fuchsin Dye

Zinc oxide (ZnO) nanoparticles, self-assembled in the form of one dimensional ZnO nanofibers were synthesized using electrospinning technique from solution of polyvinyl alcohol (PVA) and zinc acetate followed by calcination at 600°C in oxidizing environment. Scanning Electron Microscope (SEM) analysis demonstrates that morphology of ZnO nanofibers having rough surface and corresponding Energy Dispersive Spectrometry (EDAX) confirmed the Zn: O atomic ratio approximately in 50:50. Transmission electron microscopy (TEM) images clearly demonstrate the rough morphology is due to the self-assembling of ZnO nanoparticles having diameter approximately 50nm. X-ray Diffraction (XRD) reveals the polycrystalline structure and Raman spectra show some shifts in phonon modes. The PL graph show exceptional emission at 342nm due to band-band transition. Under solar radiations as produced ZnO nanofibers degrades the 99% of 25ppm acid fuchsine which proven through UV spectra when compared to blank dye solution. This shows that natural solar radiations are sufficient to excite theses self-assembled high surface area ZnO nanofibers to show its photocatalytic activity.

Low temperature insertion of energy levels into the ZnO nanorod's bandgap by nanotube conversion

Finding a material for complete absorption and emission of the visible range of the electromagnetic spectrum has been always a challenge for optoelectronic research groups. One dimensional zinc oxide (ZnO) nanostructures with wide bandgaps have been proposed as candidates to solve this problem. We have developed, characterized and optimized an approach to create a very high level of intentional defects or surface states to fill ZnO nanorods bandgap energy diagram. This process was performed systematically at a low temperature with high throughput on the hexagonal ZnO nanorods. These nanorods were 2.5μm in length and grown with chemical bath deposition. The best conversion process occurred in a 2M KCl solution at 90°C for 5h. ZnO nanotubes have presented a reasonably high performance photon collection and emission.

Controlled Synthesis and Gas-Sensing Properties of One Dimensional Zinc Oxide Architectures

One-dimensional (1D) ZnO nanorods with different shapes and high aspect ratio were successfully synthesized using a cetyltrimethylammonium bromide (CTAB)-assisted or sodium dodecyl sulfate (SDS)-assisted hydrothermal process at 90°C for 5h. The surface morphology and structure of nanocrystals were characterized by FE-SEM and XRD. Experimental results showed that the typical morphology of ZnO crystals grown with additive of CTAB was pencil-like rods, while the ZnO crystals grown with SDS showed needle-like rods. The gas sensors had been fabricated using 1D ZnO powders to examine the response towards 40ppm NO2 in the range of operating temperature from 150 oC to 450 oC. Compared with needle-like ZnO crystals, the NO2 gas sensor based on pencil-like ZnO nanostructure had better selectivity at the same gas concentration.

Highly photocatalytic performance of flexible 3 dimensional (3D) ZnO nanocomposite

Zinc oxide (ZnO) is one of the most powerful materials for purifying organic pollutants using photocatalytic activity. In this study, we have introduced a novel method to design highly photoreactive flexible 3 dimensional (3D) ZnO nanocomposite [F-ZnO-m (m: reaction time, min)] by electrospinning and simple-step ZnO growth processing (one-step ZnO seed coating/growth processing). Significantly, the F-ZnO-m could be a new platform (or candidate) as a photocatalytic technology for both morphology control and large-area production. The highest photocatalytic degradation rate ([k]) was observed for F-ZnO-m at 2.552h−1, which was 8.1 times higher than that of ZnO nanoparticles (NPs; [k]=0.316h−1). The enhanced photocatalytic activity of F-ZnO-m may be attributed to factors such as large surface area. The F-ZnO-m is highly recyclable and retained 98.6% of the initial decolorization rate after fifteen cycles. Interestingly, the F-ZnO-m samples show very strong antibacterial properties against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) after exposure to UV-light for 30min. The antibacterial properties of F-ZnO-m samples are more effective than those of ZnO NPs. More than 96.6% of the E. coli is sterilized after ten cycles. These results indicate that F-ZnO-m samples might have utility in several promising applications such as highly efficient water/air treatment and inactivation of pathogenic microorganisms.

Effect of Ag film thickness on the crystallization mechanism and photoluminescence properties of ZnO/Ag nanoflower arrays

Three dimensional (3D) zinc oxide (ZnO) nanoflowers have been successfully synthesized on oxidized silver clusters using a vapor transportation method on a 50nm Ag layer. One dimensional (1D) ZnO nanorods can be fabricated on even the thinner Ag layers (2nm and 10nm). During the heating process, with a trace amount of oxygen present, the Ag layer (50nm) melted and agglomerated forming silver oxide until the temperature reached the melting point of the zinc powder. Initially, the oxygen-rich phase ZnO formed and the zinc atoms diffused from the ZnO shell forming pistils and after an increase in time formed the zinc-rich ZnO nanoflowers. The ultraviolet (UV) emission (3.28eV) from ZnO nanoflowers and nanorods revealed useful properties relating to the recombination of free excitons and the formation of zinc interstitials or zinc antisites as evidenced by the broad visible peak in the 50nm Ag layer spectra.

Three dimensional ZnO nanostructures realized through a polymer mediated aqueous chemical route: candidate for transparent flexible electronics

A brand new three dimensional zinc oxide nanosheet array was developed through manipulating its crystal growth habits with the anionic polymer, polysodium 4-styrene sulfonate (PSS). Along with being low cost, the process separates itself from other nanosheet array production protocols not only in its unique hierarchical assembly but as it is also devoid of any post-growth high temperature pyrolysis thus offering the opportunity to integrate devices over temperature sensitive substrates. Efficient electron emissions with low operating fields (turn-on field 3.5 V μm−1) are registered from the transparent field emitter based on three dimensional nanosheet assemblies on polymeric substrates and it can preserve its high performance even in a bended state. UV photodetectors based on the same material exhibit photocurrent gains as high as 1.95 × 105 which is 42 times higher when compared to nanowires and this is attributable to the much higher surface area; even after 100 consecutive bending cycles the detector performance degradation is negligible. This study will motivate the development of new morphologies in chemical synthesis routes employing polymers as growth modifiers.

Defect annihilation and morphological improvement of hydrothermally grown ZnO nanorods by Ga doping

One dimensional zinc oxide nanostructures were grown by a low temperature hydrothermal process. Effects of Ga doping on the growth, crystallization, and defect distribution in them were studied by x-ray diffraction, scanning electron microscopy, photoluminescence, and Fourier-transform infrared spectroscopy techniques. It has been shown that Ga doping improves the morphological homogeneity and optical properties of ZnO nanostructures. Improved morphology of the doped nanostructures have been associated with the catalytic effect of Ga. Effects of Ga doping on the quenching of defect emission and improvement of excitonic emission in ZnO nanostructures are discussed.