Hexagonal Wurtzite Type 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.

Predicting the formation enthalpy and phase stability of (Ti,Al,TM)N (TM = III-VIB group transition metals) by high-throughput ab initio calculations and machine learning

The development of transition-metal-alloyed (Ti,Al)N thin films has become a common strategy to achieve optimized mechanical and thermal properties. Selection of a suitable alloying element, however, should consider the effect on Al solubility, directly influencing phase stability during the deposition. Here we use high-throughput ab initio formation enthalpy calculations to assess stability of the cubic (c) vs. hexagonal wurtzite-type (w-) phase of TM-alloyed (Ti,Al,TM)N. This compositionally-limited ab initio dataset serves to fit several machine-learning (ML) models enabling phase stability predictions over the entire compositional range. Of all the models, the linear regression using Magpie feature descriptor pre-processed by a genetic algorithm has the highest accuracy. For Ta, Nb, Mo, and W addition below ∼10 at.%, our ML model predicts enhanced stability of c-(Ti,Al,TM)N due to increased solubility of Al. Other alloying elements, especially Sc and Y from IIIB group and Hf and Zr from IVB group, decrease the cubic metastable solubility limit. In agreement with available experimental data, all transition metals except for Cr and V increase the volume of c-(Ti,Al,TM)N and w-(Ti,Al,TM)N.

Long Electrical Stability on Dual Acceptor p-Type ZnO:Ag,N Thin Films.

p-type Ag-N dual acceptor doped ZnO thin films with long electrical stability were deposited by DC magnetron reactive co-sputtering technique. After deposition, the films were annealed at 400 °C for one hour in a nitrogen-controlled atmosphere. The deposited films were amorphous. However, after annealing, they crystallize in the typical hexagonal wurtzite structure of ZnO. The Ag-N dual acceptors were incorporated substitutionally in the structure of zinc oxide, and achieving that; the three samples presented the p-type conductivity in the ZnO. Initial electrical properties showed a low resistivity of from 1 to 10-3 Ω·cm, Hall mobility of tens cm2/V·s, and a hole concentration from 1017 to 1019 cm-3. The electrical stability analysis reveals that the p-type conductivity of the ZnO:Ag,N films is very stable and does not revert to n-type, even after 36 months of aging. These results reveal the feasibility of using these films for applications in short-wavelength or transparent optoelectronic devices.

Synthesis and Characterization of ZnO-CuO Nanocomposites Thin Film for Optoelectronics Applications

In this work, the spray pyrolysis technique on glass substrates at 480°C was effectively used to generate ZnO, CuO, and n-ZnO/p-CuO nanocomposite thin films. The structure of the ZnO thin films exhibited a hexagonal wurtzite type. In the visible region of the spectrum (400–700 nm), the resulting films had optical transmission ranging from 73% to 83% and optical band gap fluctuations of 3.23 to 3.25 eV. Analysis of the m-lines spectroscopy revealed that the obtained thin layers (ZnO, ZC3, and ZC7) exhibited two modes for both TE and TM polarizations across different molar percentages. This observation confirms the efficacy of the spray pyrolysis deposition technique in producing high-quality waveguides based on ZnO.

The influence of temperature and pressure technological parameters on the characteristics of ZnO nanostructures synthesized by sol-gel process in isopropanol

The sol-gel process was employed to successfully synthesize ZnO nanostructures in isopropanol, employing various subcritical temperature and pressure conditions: (90°C, 2 bar), (120°C, 6 bar), (160°C, 14 bar), and (200°C, 30 bar). The resulting products were subsequently annealed at 500°C for 2 hours and subjected to characterization using different analytical techniques, including X-ray diffraction (DRX), infrared (ATR), UV-Visible, and photoluminescence (PL) spectroscopies. The DRX measurements confirmed that the ZnO nanostructures exhibited a polycrystalline structure of the hexagonal wurtzite type. The cell parameters and stresses within the crystallites were found to be influenced by the synthesis conditions (temperature and pressure), in contrast to the particle size. ATR spectra indicated high purity of the produced nanostructures, and it was observed that the position of the absorption band associated with the Zn-O vibrational bond of ZnO shifted towards lower wavenumbers as the temperature increased. UV-Visible spectra demonstrated that the absorption band shifted towards shorter wavelengths with increasing temperature and pressure. The optical gap displayed a similar trend to the lattice parameters and strain within the nanoparticles. PL measurements revealed that the processing temperature and pressure resulted in increased UV emission and decreased visible emission. However, the positions of the UV emission bands were independent of the synthesis parameters.

An approach to investigate the structural, morphological, and optical properties of spray pyrolyzed B and Mg co-doped ZnO thin films

Thin films of Boron (B) and Magnesium (Mg) co-doped Zinc Oxide (BMZO) were produced by spray pyrolysis on a glass substrate at a temperature of 350 °C. This study considers BZO as the base material and then varies the Mg (as dopant) percentage to produce BMZO thin films. The surface morphology and structural aspects of the films are affected by different doping concentrations. By altering the Mg (dopant) content between 1%, 3%, and 5%, the influence of varied doping concentrations on the surface morphology and structural properties of the BMZO thin films was examined and discussed. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the surface morphology and structural characteristics of the synthesized films. All ZnO films, according to X-ray diffraction, are polycrystalline and preferred orientations along the (100), (002), (101), (102), and (110). The prominent peak orientation of the crystal was in the (002) direction. A typical hexagonal wurtzite structure was identified in the films, with crystallite sizes ranging from 6.12 to 13.5 nm. The Crystallite size increased with Mg doping up to a certain threshold (3% Mg doping), and then decreased with more doping. According to SEM results, nano-fiber diameter and area grew when Mg concentration in MgxB.03Zn.97-xO (BMZO) increased and subsequently decreased at 5% Mg-doped BZO. The optical characterization was done using a UV–Visible spectrophotometer. Transparency of the films was very high (above 90%) in the ultraviolet range of spectral for 3% Mg-doped BZO with a corresponding band-gap was 3.28 eV. Transparency reduced slightly for 1% Mg-doped and undoped BZO with increasing deposition concentration, while it decreased significantly for 5% Mg-doped BZO.

Effect of Substrate Temperature on Photoelectric Properties of AZO Thin Films

Herein, Al‐doped ZnO (AZO) thin films are prepared on quartz glass substrates by RF magnetron sputtering. The effects of substrate temperature (T s) on the structure, morphology, electrical, and optical properties of AZO films are investigated by X‐ray diffraction, field emission electron microscopy, Hall effect testing instrument, and ultraviolet spectrophotometer, respectively. The results show that the doping of Al element does not change the structure of ZnO films, and all films have typical hexagonal wurtzite structure with preferred c‐axis orientation. The film sample has the strongest (002) diffraction peak and the smallest value of full‐width at half‐maximum at the T s value of 150 °C. With the increase of T s value, the grain size of the film increases first and then decreases. At 150 °C, the film exhibits good electrical conductivity, and its resistivity is 0.6210−2 Ω cm, the carrier concentration is 9.841019 cm−3, and the Hall mobility is 13.66 cm2 V−1 s−1. All samples show high transmittance, and the average transmittance in the stable visible light region is as high as 95% at the T s value of room temperature and 250 °C, and the average transmittance of all samples is above 80%. This provides a method for the application of ZnO transparent conductive films.

Manipulating the optoelectronic characteristic of AZO films by magnetron sputtering power

We investigated the effects of sputtering power on the structure, morphology, electrical and optical properties of AZO films. The results show that all the films show typical hexagonal wurtzite structure with preferred c-axis orientation. When the sputtering power is 120 W, the film has the smallest FHWH value and the largest grain size (24.33 nm), and the AZO thin films obtained the best conductivity, the electrical characteristic parameters are ρ = 3.25 × 10−3 Ω cm， N = 3.512 × 1019 cm−3, μH = 8.642 cm2V−1s−1, respectively. With the increase of sputtering power, the carrier concentration and hall mobility are increasing, which are directly related to the improvement of crystal quality, that is, the higher the crystal quality of the film, the better the conductivity. The average transmittance of all samples is above 80%, and the band gaps increase first and then decreased. This work implies that the application of controllable growth AZO transparent conductive film in photovoltaic devices.

Green hydrothermal synthesis of Ga doping derived 3D ZnO nanosatellites for high sensitive gas sensors

A green hydrothermal synthesis methodology is employed for the synthesis of Ga3+ doped ZnO 3D nanosatellite structures. XRD technique exposed the hexagonal wurtzite type crystal structure of the 3D Ga3+ doped ZnO nanostructures. Ga3+ induced 3D morphology evolution in accordance to Ga doping concentration is realized via. the FESEM images. The FESEM images indicated one sided capped rod like structures (50–250 nm) in pristine ZnO, whereas 3D satellite kind of morphology (>500 nm) was observed in 5% Ga3+ doped ZnO structures. TEM images revealed physical specifications of 3D nanosatellite structures exposing the central rod of 500 nm length & 250 nm in width and the branch rods grown vertical to the central rod of length 300 nm and width of 50 nm. Further, optical absorbance and photoluminescence spectra confirmed the electron rich state of ZnO with Ga3+ doping. The gas sensing performance has shown selectivity toward CO gas at a working temperature of 250 ⁰C. High CO sensing was recorded for 5% Ga3+ doped ZnO 3D nanosatellites with attractive sensing characteristics such as good response, fast response time & fast recovery time.

Nanoscale AgI-WO3 binary photocatalyst: Synthesis, brief characterization, and investigation of its photocatalytic activity

A novel AgI/WO3 binary system with good visible-light photocatalytic performance was fabricated and characterized by XRD, FTIR, SEM-EDX, X-ray map, photoluminescence (PL), and UV–Vis DRS techniques. A hexagonal wurtzite type β-AgI and monoclinic WO3 crystallites were detected. The average crystallite size of about 37.7 nm (by Scherrer formula) and 34.7 nm (by Williamson-Hall formula) was obtained for the binary catalyst. W–O–W and O–W-O vibrational modes showed intense absorption bands at 591, 761, and 828 cm−1 (or at 816 cm−1), and Ag-I around 595 and 640 cm−1 (that were broadened due to ionic future of AgI) in FTIR spectra. Absorption edge wavelengths of 506, 464, and 465 nm correspond to Eg-values of 2.45, 2.67, and 2.66 eV were estimated for AgI, WO3, and AgI/WO3 samples, respectively. PL spectra showed the most negligible intensity for the binary catalyst regarding the individual AgI and WO3 systems. PL intensity as a function of AgI: WO3 mole ratio of binary catalyst in two acetone and ethanol solvents was followed and good illustrated. The system with a mole ratio of 1:2 showed the lowest PL intensity and the highest photocatalytic activity. The peak intensity in ethanol as a higher polar solvent than acetone was increased. Synergistic photocatalytic activity of the proposed binary catalyst was observed toward methylene blue (MB) that depended on the AgI: WO3 mole ratio. The kinetics of the process obeyed the pseudo-first-order Hinshelwood model with k-values of 0.0123, 0.0216, and 0.0395 min−1 for WO3, AgI, and AgI/WO3 catalysts, respectively. The rate constant for the binary catalyst is 1.83 and 3.21 times greater than the values obtained for WO3 and AgI NPs, respectively. The Hinshelwood plot constructed based on COD data for the binary catalyst showed a rate constant of 0.0365 min−1, comparable with that obtained based on the photodegradation data.

Analysis and characterization of tin-doped ZnO nanostructures

In this paper, undoped and tin-doped ZnO nanostructures were grown onto non-conductive substrates by a simple solution method. Structural, morphological, optical and electrical properties of the structures were investigated with respect to tin concentration. From XRD studies, all the ZnO nanostructures were found as hexagonal wurtzite type structures growing preponderantly oriented with c-axis nor- mal to the substrate. An increase in tin content resulted in a decrease in grain size, whereas the dislocation density in- creases. SEM observations indicated that all the structures were textured throughout the substrates without any cracks or pores. The influence of incorporation of tin on surface morphology of the samples was clearly seen. Average diameter of the nanostructures decreased with increasing tin content. Absorption spectra of the structures revealed that the band gap of the films increases with increasing tin concentration. It is found that the tin-doped samples have higher average transmittance than the undoped one. The 1 % tin-doped sample exhibited ∼80 % average transparency, which was the best transparency among the doped samples. Electrical measurements showed that resistivity of the structures increased with increasing dopant concentration. This increasing was attributed due to a decrease in carrier con- centration caused by carrier traps at the grain boundaries.

Preparation and photoelectric properties of Bi doped ZnO nanoarrays

ZnO has a large band gap, which affects its photoelectric catalytic performance to a certain extent. In this paper, Bi-doped ZnO nanoarray was successfully prepared by electrochemical deposition to improve the photoelectrochemical performance of ZnO as a photoanode. XRD results show the prepared Bi-doped ZnO is a typical hexagonal wurtzite crystal, and the SEM results also proved this point. The prepared Bi-doped ZnO presents a neat nano-array, and the doping of Bi also reduces the diameter of the nanorods from the original 500–350 nm. The results of XPS show that Bi is successfully doped into the ZnO nanoarrays, and it exists in the form of Bi2O3. Subsequently, the prepared Bi-doped ZnO was analyzed by fluorescence spectroscopy and photoelectrochemical properties, and it was found that when the doping concentration was 5%, the fluorescence intensity was the lowest, and at this time the carrier recombination rate corresponding was the lowest, the photoelectric catalytic effect was the best.

Facile Controlling of the Physical Properties of Zinc Oxide and Its Application to Enhanced Photocatalysis.

In this study, the physical properties of ZnO were facile controlled by the synthesis method with the addition of capping and precipitation agents. As-prepared ZnO samples had different morphologies such as carnation flower-like ZnO (CF-ZnO), rose-flower-like ZnO (RF-ZnO), rod-like ZnO (R-ZnO), and nanoparticle ZnO (N-ZnO) and were characterized by SEM, XRD, N2 adsorption/desorption isotherms, FT-IR, and DR/UV-vis. All samples had a crystallite structure of hexagonal wurtzite type. The CF-ZnO and RF-ZnO samples had the hierarchical structure like a carnation flower and a beautiful rose, respectively. R-ZnO was composed of many hexagonal rods and few spherical particles, while N-ZnO microstructures were made up of nanoparticles with approximately 20–30 nm, exhibiting the largest surface area, pore volume, and pore width among as-prepared samples, and their crystal size and bandgap energy were 17.8 nm and 3.207 eV, respectively. The catalytic performances of ZnO samples were evaluated by degradation of Tartrazine (TA) and Caffeine (CAF) under low UV irradiation (15 W). N-ZnO showed a high photocatalytic activity compared to other samples. Besides, the reaction kinetics was investigated by the first-order kinetic model, and the catalytic performance of ZnO was evaluated through several organic pollutants.

The growth mechanism of zinc oxide micro-rods via vapor-phase method

Two different ZnO micro-structures were deposited by a Chemical Vapour Deposited method in a small quartz tube. The micro-rods and micro-wires were found on the edge of the tube respectivly. The morphology and structural properties were texted by scanning electronic microscopy technique and X-ray diffraction. The results shows that the micro-rods have typical hexagonal wurtzite structure without any defect and the micro-wires have two types, the single ZnO crystal and the double-like one. The X-ray diffraction gives some information through the intense 002 peak which means the samples have a great wurtzite structure and grown up along the c-axis. The mechanism of the two samples also discussed, it is in relation to the substrate temperature and the concentration of the mixed gas.

Mg and Ni incorporated ZnO diluted magnetic semiconductor for magnetic and photo-catalytic applications

Zinc oxide is recently being used as a magnetic semiconductor with the introduction of mag- netic elements. In this work, we report phase pure synthesis of Mg and Ni co-substituted ZnO to explore its structure, optical, magnetic and photo-catalytic properties. X-ray diffraction analysis reveals the hexagonal wurtzite type structure having P63mc space group without any impurity phase. UV-Vis spectrophotometry demonstrates the variation in bandgap with the addition of Mg and Ni content in ZnO matrix. Magnetic measurements exhibit a clear boosted magnetization in Ni and Mg co-doped compositions with its stable value of bandgap corroborating the structural stability and magnetic tuning for its advanced applications in modern-day spintronic devices. Photo-catalytic measurements performed using methyl green degradation demonstrate an enhanced trend of activity in Mg and Ni co-doped compositions.

Dual-ultraviolet wavelength photodetector based on facile method fabrication of ZnO/ZnMgO core/shell nanorod arrays

ZnO/ZnMgO core/shell nanorod arrays with a large surface-to-volume ratio and negligible lattice mismatch are considered as a promising candidate applied in ultraviolet photodetection. Herein, ZnO/ZnMgO core/shell nanorod arrays were fabricated by using simple and facile hydrothermal and radio frequency magnetron sputtering methods and applied in the dual-ultraviolet wavelength photodetector successfully. The morphology and crystallization show the formation of core/shell nanorod arrays and typical hexagonal wurtzite structure. The fabricated device demonstrates significant ohmic contact and has a high photo-to-dark current ratio and a fast rise/decay time under the 254 nm and 365 nm illumination at 5 V bias. ZnO/ZnMgO core/shell nanostructure could bring about the speedy separation of photogenerated electron-hole pairs and suppress the recombination of photogenerated carriers because of the formation of built-in electric field in the interfacial region of core/shell structure and the passivated surface states of bare ZnO nanorods. Therefore, our work offers a method to fabricate high performance dual-ultraviolet wavelength photodetector for the potential application in future ultraviolet detection.

Synthesis, Characterization, and Anti-Algal Activity of Molybdenum-Doped Metal Oxides

In this study, we attempted to synthesize visible light active nano-sized photocatalysts using metal oxides such as zinc oxide, zirconium oxide, tungsten oxide, and strontium titanium oxide with (MoCl5)2 as a dopant by the simple ball-milling method. Fourier-transform infrared spectroscopy data confirmed the presence of M-O-Mo linkage (M = Zn, Zr, W, and SrTi) in all the molybdenum-doped metal oxides (MoMOs), but only MoZnO inhibited the growth of the bloom-forming Microcystis aeruginosa under visible light in a concentration-dependent manner up to 10 mg/L. Further, structural characterization of MoZnO using FESEM and XRD exhibited the formation of typical hexagonal wurtzite nanocrystals of approximately 4 nm. Hydroxyl radical (·OH), reactive oxygen species (ROS), and lipid peroxidation assays revealed ·OH generated by MoZnO under the visible light seemed to cause peroxidation of the lipid membrane of M. aeruginosa, which led to an upsurge of intracellular ROS and consequently introduced the agglomeration of cyanobacteria. These results demonstrated that nano-sized MoZnO photocatalyst can be easily synthesized in a cost-effective ball-mill method and utilized for biological applications such as the reduction of harmful algal blooms. Further, our study implies that a simple ball-milling method can provide an easy, green, and scalable route for the synthesis of visible light active doped metal oxides.

Structural Investigations on Hydrothermally Grown ZnO Nanostructures

This study investigates the influence of aqueous solution molarity on the structural characteristics of zinc oxide (ZnO) grown by hydrothermal method. From the X-ray diffraction (XRD) patterns of the ZnO nanostructures, the diffraction peaks confirm the ZnO hexagonal wurtzite type crystalline structure. To investigate the structural properties of ZnO structures in more detail, we analyze the XRD line profiles of the samples by Warren-Averbach model. Based on the model, the diffraction intensity of the XRD is calculated in Fourier space and the information on the size distribution can be derived. Observing the calculated nanostructure size distribution of the samples, we can see that the breadth of the size distribution function decreases then increases with increasing molarities. Furthermore, the theoretical analyzed results are verified by photoluminescence (PL) measurements and the scanning electron microscope (SEM) images.

Visible-Light Driven Photocatalytic and Antibacterial Assessment of Ag/ZnO/Cellulose Nanocomposite

Ag/ZnO/cellulose nanocomposites were synthesised through in-situ solution casting method, which offers a good adhesion and dispersity of nanostructured materials. SEM analysis revealed formation of nanodiscs-like structures for ZnO while nanospheres and hierarchical nanosheets were observed for Ag and cellulose, respectively. XRD analysis pointed to the monoclinic type-1 phase of cellulose. Peaks corresponding to typical hexagonal wurtzite structure of ZnO and face-centredcubic Ag structure were also identified. Photodecomposition of aqueous methylene blue (MB) under direct sunlight irradiation was monitored to study the photocatalytic activity of the nanocomposite. About 92% of MB dye was photodegraded in the presence of Ag/ZnO/cellulose nanocomposite. The influence of Ag+ ions on the photocatalytic efficiency of ZnO is discussed. The antibacterial efficiency of the synthesised samples was investigated against two Gram positive pathogenic bacteria species: Staphylococcus aureus and a spore forming Bacillus subtilis as well as a Gram-negative Escherichia coli. The prepared nanocomposite exhibited strong activity against the growth of all the bacterial species though in different quantified measures.

Graphene oxide coated flower-shaped ZnO nanorods: Optoelectronic properties

Abstract In this paper, the influence of graphene oxide coating on optical and photoluminescence properties of zinc oxide nanorods (ZnO NRs) has been investigated. ZnO NRs were prepared using a hydrothermal route (from zinc nitrate hexahydrate and hexamethylenetetramine), graphene oxide (GO) was fabricated by Hummer’s method, while for synthesis of ZnO nanorods:graphene oxide nanocomposite (ZnO NRs:GO) on Si (100) substrate, a facile technique (drop coating) was proposed. The structural, morphological, optical and luminescence properties of the films were investigated using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), together with Fourier transform infrared (FT-IR), Raman, ultraviolet–visible–near-infrared (UV/VIS/NIR) and photoluminescence (PL) spectroscopies. As revealed by XRD analysis, composites display a hexagonal wurtzite type structure with a (101) preferred grain orientation. The average crystallite sizes decrease from 45 to 40 nm after GO coating. The SEM study confirms successful coating of GO layers on flower-like ZnO nanostructures. The FTIR and Raman analyses validated the hybridization of nanocomposite and the strong interaction between ZnO NRs and GO. The band gap of the ZnO NRs:GO nanocomposite is lower (2.95eV) compared to that of ZnO NRs (3.11 eV), as determined from the analysis of UV absorbance spectra. The ZnO NRs:GO nanocomposite exhibits a broad PL band, from ∼450 nm to ∼750 nm, with a nearly white-light integrated emission and a chromaticity coordinate of (0.25, 0.34). Gaussian deconvoluted broad PL band exhibits three distinct sub-bands, associated with radiative recombinations in ZnO and GO.