Wurzite Structure Research Articles

Oxygen vacancy induced ferromagnetism in ball milled Zn0.97Ni0.03O: Confirmation through electron spin resonance

Among the semiconducting materials, ZnO is a versatile multifunctional candidate with a direct band gap of 3.37 eV at 300 K and large excitonic binding energy of 60 meV which can be useful for spintronics device applications. ZnO has high solubility for transition metals. The transition metals which have been used for DMS, Ni is the most efficient doping element to improve the electrical, magnetic properties of ZnO. Ni doped ZnO would be a good candidate to achieve ferromagnetic property with a high curie temperature i.e. above the room temperature. In this study, Zn1−xNixO (x = 0.03) powder sample was successfully synthesized by a ball milling technique. The X-ray diffraction analysis confirms the polycrystalline, hexagonal wurzite structure for 3% Ni doped ZnO nanoparticles. The substitution of Ni in the ZnO matrix has been confirmed by micro-Raman analysis with the observation of E2 (High) vibrational mode at 437 cm−1 which refers to the strongest mode of vibration in wurtzite crystal structure. A broadened peak observed at 570 cm−1 informs about the presence of clusters of oxygen vacancies. VSM measurement of the sample shows the ferromagnetic hysteresis loop at room temperature with saturation moment of 9 × 10−5 emu/g. The calculated ‘g’ value of 1.95 from electron spin resonance spectrum suggests that the observed ferromagnetism is due to the oxygen vacancy.

Effect of Sintering Temperature on the Characteristics of Zn0.99Li0.01O Thin Film on Si Substrate

Lithium-doped zinc oxide (Zn0.99Li0.01O) film was manufactured by the sol-gel method using uniform and stable solution of zinc acetate dehydrate and lithium acetate dehydrate in methanol. Films were deposited by spin-coating using spinner between 4500 and 5000 rpm on silicon substrates. The prepared samples were sintered at various temperatures (600 oC ~ 1000 oC) in the air. The structural, morphological, and optical properties of the prepared lithium-doped ZnO films were investigated. The XRD pattern of Zn0.99Li0.01O film demonstrated the hexagonal wurzite structure. However, new crystal phase was discovered at a sintering temperature of 800 oC. New peak was found near 2θ = 22.6o in XRD patterns. The peak is thought to be the (101) plan in SiO2 cristobalite structure. Moreover, another new crystal phase related to Li2SiO5 was occurred at a sintering temperature of 900 oC. From XRD analysis, it was confirmed that C axis was decreased and the stress was increased, as sintering temperatures was increased from 600 oC to 900 oC. In cathodo luminescence (CL) data, zinc oxide usually appears ultra violet and green emission. However, the green emission did not appear in all these samples used in this study. The ultra violet emission showed red shift from 600 oC to 800 oC in the CL spectrum as the sintering temperature was increased. The phenomenon of the red shift can be explained in Burstein-Moss effect. At sintering temperature of 700 oC, the intensity of ultra-violet emission was the largest and full width at half maximum (FWHM) was the smallest.

Synthesis and Characterization of Co-Doped ZnO Diluted Magnetic Semiconductor for Spintronics Application

The diluted magnetic semiconductor (DMS), are promising materials in the ferromagnetic exchange coupling between localized spins. ZnO nanoparticles in pure and cobalt doped with 2%, 4%, 6% and 8% were prepared through co-precipitation method at room temperature. XRD analysis showed the Co doped ZnO crystalizes in a wurzite structure. The particle size decreases with increase in concentration of cobalt. The SEM micrographs shows similar and regular equal in size depends with the increase of Co concentration and formation of spherical super structure and confirmed the Co2+ is completely replaced into the Zn2+ site of ZnO host structure. The size depends with the concentration are evident from EDAX analysis. The remarkable spin performances with increase of Co are confirming the above results.

Pseudomonas aeruginosa antibacterial textile cotton fiber construction based on ZnO–TiO2 nanorods template

An alternative method of synthesizing ZnO–TiO2 nanorods is through route precipitation and sintering at 600 °C. In this study, the introduction of Ti into Zn in the molar ratio Ti:Zn (1:3) produced a composite ZnO-Low TiO2 (ZnO-LTiO2) while 1:1 produced ZnO-High TiO2 (ZnO–HTiO2). The effect of the Ti introduced on the anti-bacterial properties of ZnO–TiO2 nanorods was investigated with the product structure characterized by XRD and the optimal intensity at 2θ: 31.72°, 34.37°, 36.19° showed a Wurzite structure and a crystal size of 35.8–41.5 nm. The average pore diameters for ZnO-LTiO2 and ZnO–HTiO2 were around 5.159 nm and 6.828 nm while the surface areas were 15.692 m2/g and 15.421 m2/g respectively. The anti-bacterial textile fiber construction was prepared using dip-spin coating with the application of an adipic acid crosslinker for 6 h and stable coating up to 10 times washing. The improvement of Pseudomonasaeruginosa (Pa) antibacterial properties in the textiles with coating had an inhibition zone of 20.5–25.0 mm and 16.2 mm without the coating. The elements of the cotton fiber construction include C at 54.60%, O at 40.89%, Ti at 0.81% and Zn at 2.60% while the TG-DTA analysis conducted showed an increase in the heat stability of the textile fibers to a temperature of 400°C, after which the textiles were modified by coating ZnO–TiO2 nanorods. The findings of this research could be successfully applied to improve the antibacterial properties of textiles.

Synthesis of Zinc Oxide/Reduced Graphene Oxide Composites for Fabrication of Anodes in Dye-Sensitized Solar Cells

In this study, graphene oxide (GO) was synthesized using the improved Hummers’ method, and reduce graphene oxide (rGO) was synthesized from GO with hydrazine hydrate as reducing agent. Zinc oxide (ZnO) was synthesized from zinc acetate using the precipitation method. Zinc oxide/reduced graphene oxide (ZnO/rGO) composites were synthesized using the ex-situ method. The ZnO/rGO composites with different rGO weight percents (0.05, 0.1, 0.5, 1, and 5 wt%) were used for fabrication of ZnO/rGO anodes. A control anode was fabricated from ZnO (ZnO anode). The band gaps of fabricated anodes were measured using the ultraviolet-visible spectroscopy (UV-vis). The dye-sensitized solar cells (DSSCs) were assembled and investigated by current density-voltage (J-V) curves and electrochemical impedance spectroscopy (EIS). The ZnO/rGO composite with appropriate rGO content was determined to be 1 wt%, with the efficiency of 1.55 %. The Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) results confirmed wurzite structure of ZnO and the reduction of functional groups of GO to create rGO and ZnO/rGO. The transmission electron microscopy (TEM) showed that the ZnO nanoparticles with size of 10 - 20 nm were evenly distributed on rGO sheets. These results indicated that ZnO/rGO could be the potential material to improve the efficiency of DSSCs.

Investigation of structural, morphological and optical characteristics of Mn substituted Al-doped ZnO NPs: A Urbach energy and Kramers-Kronig study

Present work deals with the investigation of structural, morphological, elemental, chemical bonding and optical properties of simple sol-gel synthesized Al-doped ZnO and Mn-substituted Al-doped ZnO nanoparticles (NPs) using XRD, FE-SEM, EDAX, FT-IR and DRS techniques, respectively. A comprehensive evaluation of optical properties has also been done by Kramers-Kronig (KK) relations. The structural studies have revealed that the obtained patterns are mainly assigned to the hexagonal wurzite structure of the reference. The morphological investigations confirm the constitution of homogenous nanoscale particles with average grain sizes less than 40 nm for both samples. The optical band gap of the prepared samples is calculated using DRS data in two ways, Kubelka-Munk relation, and KK method. The band gap results show a red-shift with Mn-substitution in Al-doped ZnO. The disorderness (Urbach energy) of the samples is observed to be decreased with an increase in both band gap energy and crystallite size. Moreover, the optical parameters of the prepared samples such as refractive index, extinction coefficient and also dielectric constants are evaluated by applying KK relations on reflectivity curves.

Electrical conductivity study of poly(p-anisidine) doped and undoped ZnO nanocomposite

Polymeric blends of Poly (p-anisidine) with ZnO nanoparticles was prepared by chemical oxidative polymerization. Zinc oxide doped PPA polymer nanocomposite (ZPPA) and Magnesium doped Zinc oxide PPA polymer nanocomposite (MZPPA) were synthesized with the addition of semiconductor metal oxide to the polymeric solution. The X-ray diffraction studies of ZnO nanoparticles showed hexagonal wurzite structure. The surface morphological study also confirms the formation of hexagonal structured nanoparticles. The peak for Magnesium and Zinc in EDS spectra confirms the formation of Magnesium doped polymer nanocomposite. The addition of ZnO/MgZnO onto PPA conducting polymer showed agglomeration of semiconductor material results in spherical shaped polymer nanocomposite and irregular overlapping over the PPA polymeric surface. The electrochemical conductivity studies suggested that the doped PPA conducting polymeric blends showed enhanced conductivity nature.

Structure, morphology and luminescence properties of sol-gel method synthesized pure and Ag-doped ZnO nanoparticles

Highly Crystalline pure and Ag-doped ZnO nanoparticles were prepared using the inexpensive sol-gel synthesis method with the stimulation of transition metal ion surfactant. The prepared pure and Ag-doped (Silver doped) ZnO nanoparticles were characterised by various sophisticated techniques like x-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Dynamic Light scattering (DLS), Fourier Transform Infrared Spectroscopy (FTIR), UV–visible absorption, Photoluminescence (PL) and Zeta potential. The result indicates that the average grain size of the prepared nanoparticles was found to be a minuscule 24 nm with a commendable bandgap of 3.21 eV and 1.73 eV respectively. The hexagonal wurzite structures of pure and Ag-doped ZnO at room temperature confirmed the luminescence characteristics of the nanoparticles.

Effect of hydrazine hydrate as complexing agent in the synthesis of zinc selenide thin films by chemical bath deposition

ZnSe thin films were deposited using hydrazine hydrate (HH) as the only complexing agent. The deposition was carried out on glass substrates in an alkaline medium at low temperature using the chemical bath deposition method. The films were annealed at 300 °C for 2 h. The effects of varying the HH volumes on the structural and optical properties of the films were investigated. The investigations were based on glancing incidence X-ray diffraction, Raman spectroscopy, Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), UV-Visible spectrophotometry, and photoluminescence (PL) spectroscopy. The results revealed that the ZnSe films were of the wurzite structure. Raman spectra showed longitudinal optical vibrational peaks with intense peak at around 251 cm−1. There were fluctuations in the Raman peaks intensities. However, the intensity of the 20 mL HH sample emerged the highest. The morphology of the thin films changed from spherical grains to nanoflakes as the HH volume was increased from 5 to 35 mL, respectively. EDS of the films confirmed the presence of Zn and Se. The bandgaps of the films decreased with an increase in the HH volume. PL measurements indicated two emission peaks at 530 and 678 nm when excited at 325 nm. These emission peaks are attributed to the intrinsic intra-bandgap defects. The intensities of the peaks increased with an increase in the HH volume. The commission Internationale de l'Elcairage color coordinates confirmed that the deposited ZnSe films exhibited green-red emission and the emission color was influenced by varying the HH volumes.

ZNO Nanostructures & Microstructures: Synthesis using Different Materials

Thermal decomposition and heat treatment method is used for the preparation of ZnO and the precursor are used for this is zinc oxalate, zinc nitrate and zinc sulfate after preparation of ZnO study on its optical and electrical properties has also been performed then its photoconductivity in air and two minutes rise and fall curve also measured. Which is very useful in study of switching characteristic of materials. XRD clearly shows that prepared material has good quality of ZnO, SEM indicates that synthesized materials of wurzite structure. Two minutes rise and fall curve shows that zinc oxalate has the best switching time among all three materials.

Morphological and structural control of pulse electrodeposited ZnO thin films and its influence on the photoelectrocatalytic degradation of methyl orange

ZnO thin films were obtained by pulsed electrodeposition (PE). A potential of − 1.1 V is applied during the time-On (ton) period, while open-circuit potential is applied during the time-off (toff) period. The effect of the toff duration on the properties of ZnO films and their photoelectrocatalytic activity was studied in detail. Decreasing toff from 7 s to 1 s tailors the structural, morphological and optical properties of ZnO films and improves their photoelectrocatalytic activity. XRD analysis confirms a wurzite hexagonal structure along the (002) direction for all samples. The SEM images show an amelioration of ZnO morphology from nanosheets to nanorods films. The photocurrent response indicates a high value of 480 µA/cm2 for ZnO film deposited at toff = 1 s. All the electrodeposited films were tested for the photoelectrocatalytic degradation of methyl orange (MO). The ZnO film deposited at low toff (1 s) reveals a faster degradation of MO, reaching 67% after 360 min UV-irradiation. This is attributed to the nano-rod morphology that provides greater surface area and to the lower energy band-gap of the sample.

Electronic structure of (ZnO)1−x(InN)x alloys calculated by interacting quasi-band theory

We calculated the electronic structure of (ZnO)1−x(InN)x, (=ZION), which belongs to a novel category of hybrid (II–VI)1−x(III–V)x alloys, by the interacting quasi-band theory aided by the sp3 tight-binding model of the wurzite structure. The tight-binding parameters of the irregular bonds (Zn–N and In–O) were estimated by iterating the relevant normal bonds and the absolute atomic levels were corrected by the electron affinities of ZnO and InN. We thus obtained the quasi-band structure of ZION at various concentrations. Across the entire range of concentrations, ZION exhibited a direct energy gap at Γ, and the band-gap energy continuously changes from 0.7 to 3.3 eV with a large band-gap bowing. A particularly, large shift was observed around x = 0.5. The obtained theoretical results imply that ZION (x = 0.1–0.3) is a suitable material for visible-light devices.

Thermal decomposition synthesis and magnetic properties of crystalline zinc oxide powders

Crystalline zinc oxide powders are prepared by a direct thermal decomposition of zinc nitrate hexahydrate in air at 500 °C for 2 h. The thermal behavior of zinc precursor compound was studied using TG-DTA analysis in order to define the ZnO formation temperature. The structure of the calcined sample was characterized by X-ray diffraction (XRD). The XRD result indicates that the sample has a pure phase with ZnO wurzite structure. The morphology and elemental composition have been identified through SEM and EDX analyses. The oxidation state of ZnO sample was investigated using X-ray absorption near-edge spectroscopy (XANES). The ZnO sample reveals ferromagnetic behavior with the magnetization of ∼0.50 emu/g at 15 kOe. Our results indicate that room-temperature ferromagnetism of ZnO is intrinsic.

Metastability effects on the photoluminescence of ZnO nano-micro structures grown at low temperature and influence of the precursors on their morphology and structure

Nanocrystalline ZnO films were grown on silicon substrate by hydrothermal synthesis at 125 °C, using diethanolamine as additive. A powder containing ZnO spheres, with diameters between 100 to 200 nm and formed by aggregation of ZnO nanoparticles, was also obtained as a secondary reaction product. The samples were studied by scanning electron microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. The effects of the [diethanolamine]/[Zn2+] molar ratio on morphological, structural and optical properties were studied, as well as the effect of laser illumination (λ = 325 nm) and annealing treatment on photoluminescence properties. The film samples exhibited a compact columnar structure, with thickness between 180 to 210 nm, which were not strongly affected by the diethanolamine concentration. The X-ray diffraction patterns from the films evidenced preferred orientation along the c-axis of the ZnO wurzite structure; while the nanospheres did not show any preferential crystalline direction. The PL spectra from the films showed large initial UV emission and a weak defect band centered in the yellow. A PL evolution while the samples were UV illuminated was observed. The relaxation of metastable phases (formed during the low temperature growth) involving the creation of point defects, is suggested. The predominance of the yellow defect band before and after treatment points at oxygen vacancies as the possible point-defect candidate.

Fabrication of cost effective g-C3N4+Ag activated ZnO photocatalyst in thin film form for enhanced visible light responsive dye degradation

The aim of this study is to analyze the photocatalytic dye degradation efficacy of ZnO/g-C3N4/Ag composite thin films prepared using a simple jet nebulizer spray pyrolysis technique. The XRD results confirm the presence of phases related to silver and graphitic carbon nitride in addition to the host ZnO wurzite structure. The photocatalytic studies show that the addition of Ag and g- C3N4 remarkably improves the photocatalytic efficiency of ZnO. The ZnO/g-C3N4/Ag thin film causes 96 and 99% decomposition of Methylene Blue (MB) and Malachite Green (MG) dye molecules, respectively. The mineralization of the dyes is confirmed by COD measurements. To find the optimum operating pH of the dye, the point of zero charge and the pH corresponding to the maximum surface negative charge of ZnO/g-C3N4/Ag film are found out experimentally. The possible mechanism and reasons for the enhanced photocatalytic activity of the ZnO/g-C3N4/Ag thin films are discussed with appropriate evidences and related literature.

Synthesis, characterization and application of Cu doped ZnO nanocatalyst for photocatalytic ozonation of textile dye and study of its reusability

Highly coloured wastewater generated from textile industries contain exhausted dyestuffs which are generally refractory in nature and resist the conventional treatment methods. The current research work focuses on the synergistic effect of Cu doped ZnO (Cu–ZnO) nanocatalyst in combination with ozonation for the degradation of dyes in the wastewater. Hydrothermal method was used for preparing the nanocatalyst. X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) with Energy dispersive x-ray spectroscopy (EDAX) were used to assess structure and morphological properties of Cu–ZnO. Hexgonal Wurzite structure was confirmed by XRD and the formation of 1D nanorod from FESEM studies. Prepared nanocatalyst in combination with ozone was used for the photocatalytic ozonation (PCO) of Amaranth dye which is taken for the present study. The experiments were conducted by varying ozone dosages (0.12–0.57 g h−1), pH (3–9), catalyst load (0–2 g L−1) and dye concentration (5–50 mg L−1) to optimize nano PCO for degradation of Amaranth. Under optimized conditions, 98% decolourisation in 30 min and 72.4% mineralization in 180 min were achieved. The efficiency and reusability of the catalyst was assessed which showed 24% reduction in the performance after six successive PCO cycles. Based on the above results, the current route is promising alternate for the application of Cu–ZnO based nanocatalyst in combination with ozonation for degradation of recalcitrant dyes in wastewater.

Influence of Molar Concentration on the Structure and Optical Properties of ZnO Films Grown by Spray Pyrolysis Method

ZnO films were deposited on glass substrates using precursor solution of 0.05M and 0.025M at 623K through spray pyrolysis technique. The comprehensive work has been carried out to analyze the change in the structure and optical properties of deposited films with respect to various precursor solutions concentrations. The XRD pattern shows that, deposited thin films are hexagonal wurzite structure. The deposited film transmittance and optical energy band gap increased with decrease in molar concentration of precursor solution.

Synthesis of self-bridged ZnO nanowires and their humidity sensing properties

In this study, self-bridged ZnO nanowires were grown by a simple annealing process and their humidity sensing properties were investigated. The wurzite structure and high crystallinity of the ZnO nanowires were confirmed by XRD and PL analyses. The humidity sensing characteristics varied exponentially with increasing humidity. A conventional sensor device should have good repeatability and superior humidity sensing response. The experimentally obtained response and recovery times of the ZnO nanowires were 35.3 and 32.6 s, respectively. A possible humidity sensing mechanism is also proposed.

Structural, optical and photocatalytic properties of zinc oxides obtained from spent alkaline batteries

The structural, optical and photocatalytic properties of two zinc oxides prepared from spent alkaline batteries were analysed. After leaching the anode of alkaline batteries, zinc was precipitated from the leachate liquor by introducing oxalic acid (O-ZnO) or sodium carbonate (C-ZnO). The structure of ZnO samples were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), SBET, DRS-UV-vis spectroscopy and positron annihilation lifetime spectroscopy (PALS). Both oxides present the ZnO wurzite structure and similar morphology. C-ZnO presents a cell lower lattice parameters and bang gap energy (2.99 eV) than O-ZnO (3.05 eV), possibly due to higher concentration of oxygen vacancies. The photocatalytic activity in the degradation of methylene blue (MB) of O-ZnO (achieving 70% MB degradation at 90 min) was superior to C-ZnO, due to its higher surface area and degree of crystallinity and lower bulk/surface defects ratio.

Enhancing the photocatalytic degradation of selected chlorophenols using Ag/zno nanocomposites

Chlorophenols are among the priority listed water contaminants due to their estrogenic, mutagenic or carcinogenic health effects. The Ag/ZnO nanocomposites (NCs) were synthesized, characterized and tested for photacatalytic degradation of chlorophenols in water. The synthesis was done using zinc nitrate hexahydrate (ZnNO3. 6H2O) precursor and sodium hydroxide (NaOH). Silver nitrate (AgNO3) was added to ZnO and reduced with sodium brohydride to produce the silver nanoparticles (NPs) within the ZnO structure. The silver content was varied from 1, 3 and 5wt% for optimisation. The nanocomposites were characterised using ultraviolet - visible spectroscopy (UV-Vis), photolumniscence (PL), x-ray diffraction (XRD), and scanning transmission electron microscopy (STEM). The nanocomposites were tested for their photocatalytic properties on 2- chlorophenol (CP), 2- chlorophenol (CP) and 2,4- dichlorophenol (DCP) in water. The UV-Vis results showed that, as the amount of silver was increased a gradual slight red shift was observed. The XRD patterns for Ag/ZnO exhibited peaks that were characteristic of the hexagonal wurzite structure and peaks characteristic for Ag appeared at 38.24o, 44.37o, 64.67o and 77.58o corresponding to (111), (200), (220) and (311) reflection planes. STEM results showed the presence of Ag in ZnO with ZnO appearing as rods shapes. The EDX elemental analysis confirmed the presence of Ag in the Ag/ZnO nanocomposites with no contaminants peaks. On testing the nanocomposites for phohotocatalytic degradation of chlorophenols, addition of Ag to ZnO improved degradation of the chlorophenols compared to the pristine ZnO.