Hexagonal Wurtzite Structure Of ZnO Research Articles

Structural, optical and Urbach energy properties of ITO/CdS and ITO/ZnO/CdS bi-layer thin films

The thin films of ITO/CdS and ITO/ZnO/CdS bi-layer have been fabricated and studied for structural, morphological, optical, and Urbach energy properties. ZnO thin films were coated onto ITO plated glass slides by a spin-coating method and CdS thin films by electron beam evaporation method. X-Ray Diffraction patterns of both ITO/CdS and ITO/ZnO/CdS thin films confirmed the hexagonal wurtzite structure of ZnO and hexagonal structure of CdS, respectively. AFM images show better uniformity and bigger grain size in the case of OTO/ZnO/CdS samples. Optical transmittance spectra show a slight redshift (~ 493 nm to ~ 505 nm) for the film ITO/ZnO/CdS compared to ITO/CdS. Urbach energy was calculated for all the samples to study the structural imperfections leading to the band tails. A decrease in Urbach energy is observed for ITO/ZnO/CdS compared to ITO/CdS. The obtained results indicate that the ITO/ZnO/CdS thin films are more suitable for optoelectronic devices compared to ITO/CdS films. The results obtained are discussed in detail and presented in this paper.

Synthesis of Al-Doped ZnO Films Assisted with Hollow-Cathode Glow Discharge and Their Characterization

Transparent conductive oxides, such as aluminum-doped zinc oxide (AZO), are of substantial importance for use in a broad range of applications because of their excellent optical and electrical properties. AZO film can be deposited by using several conventional techniques, although they suffer from limitations such as long deposition time, high cost, and the requirement for complex deposition equipment. Here, we used hollow-cathode glow discharge, which produces a high-density plasma and achieves high deposition efficiency. Remarkably, instead of metallic target materials, we used Al2O3 and ZnO powders filled in the hollow cathode as a target, thus avoiding the need for specifically designed targets in this technique. The films were deposited using mixtures of argon and oxygen at various ratios (0% to 50% oxygen), to improve the film characteristics. The films deposited under all conditions exhibited hexagonal wurtzite ZnO structure, while the grain size increased with increasing oxygen content. The film was thick and porous when using low oxygen content, but became thin and dense with increasing oxygen content. The optical transmittance was found to be strongly dependent on the processing gases used, with the highest transmittance of 84% being attained when using 25% oxygen gas. The bandgap of the films lay between 3.27 eV and 3.33 eV. The highest carrier concentration and mobility were attained when using 25% oxygen, and the Hall resistivity decreased with increasing oxygen content. Besides the excellent transmittance and electrical properties of the deposited films, it is expected that the results of this study will be useful for solar cells and optoelectronic applications due to the relatively low cost of this technique and the lack of specific target requirements.

Structural and optical study of high concentrate Co-doped ZnO nanostructures

High concentrate Co doped ZnO nanostructures, were prepared using solution method. Prepared samples were characterized by different characterization techniques. Structural analysis was done by X ray-diffraction (XRD) and found the formation of the wurtzite hexagonal structure of ZnO without any essence presence of the Co related clusters. Field emission scanning electron microscope (FESEM) images indicated change in surface morphology of ZnO due to introducing of Co ions into ZnO lattice. UV visible spectroscopy showed red shift in the optical band gap of ZnO because of Co doping. Fourier transform infrared spectroscopy (FTIR) showed stretching vibration mode of Zn-O at 527 cm-1which indicated the formation of the wurtzite hexagonal structure of ZnO.

Critical positive temperature coefficient of resistivity of Li/Y co-doped ZnO ceramics modified by Cr-ions

ZnO-based ceramics doped with Li/Y and modified by various contents of Cr-ions, (Zn0.9475Y0.0025Li0.05)1-xCrxO (0 ≤ x ≤ 0.025), were prepared by a wet chemical route followed by a traditional ceramic sintering technology. The effect of Cr-ion content on the electronic conductivity and resistance–temperature characteristics of the prepared ceramics was investigated. All the ceramics have hexagonal wurtzite ZnO structure, and exhibit critical positive temperature coefficient of resistivity (C-PTCR) effect. With various contents of Cr-ions, the maximum temperature coefficient of resistivity (TCR) reaches 61.1%·°C−1 or the resistivity jump log(ρmax/ρmin) is up to 4.74. The critical transition temperature of resistivity can be adjusted in the temperature range of 76–147 °C for different various contents of Cr-ions. The complex impedance analysis shows that the C-PTCR effect of the ZnO ceramics resulted from both grain effect and grain boundary effect. According to the analysis of the dielectric temperature spectra, the ZnO-based ceramics have ferroelectricity at room temperature, and the ferroelectric–paraelectric transition around the critical transition temperature of resistivity during the temperature increases.

Structure, physical, dielectric and magnetic properties of Zn1– x Co x O nanoparticles prepared via coprecipitation method

Zn1– x Co x O nanoparticles have been prepared by coprecipitation method. X-ray diffraction study confirms the polycrstalline nature with hexagonal wurtzite ZnO structure of the Zn1– x Co x O nanoparticles. The W–H analysis results confirms the mean crystallite size of the Co-doped samples was increased from 62 to 72 nm. All samples have nanocrystalline particles were investigated by field emission scanning electron microscopy. Optical absorption studies showed a red shift absorption spectra due to the incorporation of Co atoms in ZnO lattice. Dielectric constant and dielectric loss were decreasing with increasing Co content. Magnetic hysteresis loops of prepared nanoparticles exhibit paramagnetic behavior at room temperature.

Enhanced photocatalytic activity of supported Cu-doped ZnO nanostructures prepared by SILAR method

Abstract Cu-doped ZnO (CZO) nanostructures were prepared on a glass substrate using the successive ionic layer adsorption and reaction (SILAR) method. Copper (Cu) doping has been used as a key to enhance the photocatalytic activity of ZnO. X-ray diffraction (XRD) results revealed the polycrystalline nature of the nanostructures prepared with a hexagonal wurtzite structure of ZnO. The field emission scanning electron microscopy (FE-SEM) analysis showed a change of the morphology from a granular structure to a hexagonal structure and the particle size decreased with increasing copper concentration. The transmittance showed a decrease in the visible range with the increase of copper concentration and a decrease of the optical band gap values was observed. The X-ray photoemission spectroscopy (XPS) analysis indicated that copper was in a divalent state (Cu2+) which confirms the successful incorporation of copper ions into ZnO lattices. The photocatalytic activity of CZO nanostructures prepared by the SILAR method was studied for the first time. The photocatalytic study showed that an increase in copper concentration leads to an increase in degradation efficiency. CZO nanostructures showed an enhancement in degradation efficiency of about 52% compared to undoped ZnO.

Photocatalytic and fluorescent chemical sensing applications of La-doped ZnO nanoparticles

Herein, we report the facile solution phase precipitation synthesis of ZnO nanoparticles doped with various concentrations, i.e. 1, 5 and 10 mol% of lanthanum (La). The synthesized nanoparticles were characterized in detail by several techniques which confirmed the high-density growth and well-crystalline nature of La-doped ZnO nanoparticles. The XRD results revealed the successful incorporation of 1 mol% La ions in the hexagonal wurtzite structure of ZnO; however, small XRD peaks of La2O3 were detected in 5 and 10 mol% La-doped samples. All the La-doped nanoparticles were found to be UV responsive. For the application prospective, all the synthesized nanoparticles were used as photocatalyst for the photocatalytic degradation of three toxic dyes, i.e. methyl orange (MO), Rhodamine B (Rh B) dyes and picric acid (PA). By detailed photocatalytic investigations, interestingly, 1 mol% La-doped ZnO was found to be most efficient photocatalyst towards the degradation of all three organic dyes. Further, the synthesized nanoparticles were also used as fluorescent probe for the fluorescence sensing of picric acid (PA). Remarkably, the 1 mol% nanoparticles exhibited highest sensitivity, i.e. lowest limit of detection (LOD) value (1.05 µM L−1) towards PA compared to 5 and 10 mol% (1.38 µM L−1) La-doped ZnO nanoparticles.

Hydrothermally derived co, Ni co-doped ZnO nanorods; structural, optical, and morphological study

Thin films of ZnO and Co, Ni co-doped ZnO nanorods were successfully synthesized on the silicon substrate (100) by the hydrothermal method. The grown thin films were annealed at 105 °C for 4.5 h and characterized by employing different analytical techniques to investigate the effects of co-doping on structural, morphological, and optical properties of ZnO nanorods. X-ray diffraction (XRD) analysis confirmed the successful substitution of dopants (Co and Ni) without altering the hexagonal wurtzite structure of ZnO. The crystallite size and micro-strain of grown films were calculated by employing Scherer, W–H, and SSP methods. The unit cell volume and lattice parameters were increased for Co doping, moreover by increasing Ni concentration as a co-dopant these parameters were decreased. Crystallite size of ZnO, ZnCo, ZnCoNi3, ZnCoNi6 and ZnCoNi9 grown thin films were 73 nm, 42 nm, 71 nm, 60 nm, and 52 nm respectively. The Fourier transform infrared spectroscopy (FTIR) has shown the existence of characteristic vibrational bonds of Zn–O in all co-doped samples at 499.35 cm −1 , 561.25 cm −1 , 570.89 cm −1 , 565.10 cm −1 , and 553.53 cm −1 , respectively. SEM images show the surface morphology of grown thin films, which indicates that the diameter of nanorods is increased by increasing Ni contents. The UV–visible spectroscopy was employed to measure the energy bandgap ( E g ) using Tauc's plot. The optical energy band gap was decreased (3.37–3.16) eV for all co-doped samples. The redshift in energy bandgap by Co and Ni co-doping is mainly due to the strong orbital coupling and generation of new energy states between the VB and CB . The other optical parameters including optical absorption coefficient ( α ) , transmittance (T) , skin depth, optical density (OD) , extinction coefficient ( k ), refractive index ( n ), optical conductivity ( σ opt ), and dielectric constants ( ε r , ε i ) of the grown thin films were also discussed. • Hydrothermally derived Co, Ni co-doped ZnO nanorods; Structural, optical, and morphological study. • Variation in microstructural parameters calculated by Scherrer, W–H, and SSP methods. • Nanorods are successfully grown on thin film of Si (100) substrate. • The optical parameters i.e. energy band gap, optical absorption coefficient, transmittance, skin depth, etc. were studied.

Hydrothermal synthesis of hexagonal ZnO nanoplates used for photodegradation of methylene blue

Abstract ZnO nanoplates were successfully synthesized by hydrothermal method in the solutions containing CTAB. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). In this research, the as-synthesized samples were hexagonal wurtzite ZnO structure without any impurities and were composed of hexagonal ZnO nanoplates with the vibration mode of Zn–O bonds. The photocatalytic activity of hexagonal ZnO nanoplates showed superior photodegradation of methylene blue (MB) of 94.15 % under UV light irradiation within 80 min. The degradation efficiency of reused hexagonal ZnO nanoplates as photocatalyst indicated that ZnO nanoplates are very stable and reusable under UV light illumination.

Effect of Mn Content on Structural Evolution and Magnetic Properties of ZnO Particles

ZnO dilute magnetic semiconductor (DMS) is one of the most promising materials for room temperature ferromagnetic applications. In this paper, Zn1-xMnxO (x = 0.00, 0.03, 0.06, and 0.09) samples were prepared through Mn-doped ZnO by using sol-gel method. And the intrinsic relationship between the point defects and magnetic properties were investigated. The hexagonal wurtzite structure of ZnO was confirmed by X-ray diffraction (XRD) measurement in all prepared samples. The morphological features of prepared samples were studied by scanning electron microscopy (SEM). The distribution of Mn element was analyzed by energy dispersive X-ray analysis (EDAX). The number of oxygen vacancies (Vo) is varied with increasing Mn content by X-ray photoelectron spectroscopy (XPS). A suitable Vo density in Zn1-xMnxO (x = 0.03) samples is considered to be important and has positive effect on the ferromagnetism. Magnetic properties were tested by vibrating sample magnetometer (VSM). The anti-ferromagnetism exchange interaction between Mn ions is the main reason to cause the diamagnetic properties.

Effective strategy to coupling Zr-MOF/ZnO: Synthesis, morphology and photoelectrochemical properties evaluation

Zr-MOF was coupled with ZnO particles by mechanical mixture followed by heat treatment at 400 ​°C. The Zr-MOF influence on the ZnO structure was investigated by means of X-ray diffraction (XRD), surface area analysis (BET), electron microscopy (SEM and TEM), spectroscopy (XPS) and photoelectrochemical experiment. The main phase of the synthesized samples well matched the hexagonal wurtzite structure of ZnO. The XPS analysis confirm the heterostructure formation between ZnO and Zr-MOF materials and shows that the sample with 25 ​wt% Zr-MOF (ZnO/MOF25) has the higher proportion of lattice oxygen compared to the pristine ZnO and the sample with 50 ​wt% Zr-MOF (ZnO/MOF50). The reduction in the oxygen vacancies in the ZnO/MOF25 sample supports the greater effectiveness of heterostructure formation in this sample. The results also indicated that the ZnO/MOF25 sample is a promising photoelectrode for solar cells.

Enhanced magnetic, antibacterial and optical properties of Sm doped ZnO thin films: Role of Sm doping

Abstract Thin films of Sm3+ ions doped ZnO were prepared by dip coating method. To enhance the oxygen vacancy in the host ZnO lattice and obtain crystallinity, the thin films were annealed at 400 °C for 2 h in air. X-ray diffractions (XRD) study displays the hexagonal wurtzite structure of ZnO with crystallite size in the range of 27.37–24.21 nm. The induced carrier concentration, intrinsic defects and oxygen vacancies produced a blue shift in the band gap (Eg) with an increase in Sm doping percentage. The surface morphology is granular with slight agglomeration. Thin films have shown violet photoluminescence. The emissions intensity can be tailored by increasing the Sm percentage which is due to the increase in defect concentration as well as find application in optoelectronic devices. Room temperature ferromagnetism is recorded in the thin films. Hysteresis show that 1 at. wt. % Sm doped ZnO has larger saturation magnetization than 5 at. wt. % Sm doped thin films. The work has established that rare earth element doping in ZnO produces diluted magnetic semiconductors which can be part of absorber layer of solar cell, to store data in memory devices and optoelectronics applications. Antibacterial studies were conducted for Staphylococcus aureus (S. Aureus), klebsiella pneumonia (K. B), Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) bacterial strains by applying the agar well diffusion method to suspension containing undoped ZnO and Sm doped ZnO nanoparticles. The enhancement in the zone of inhibition with an increase in samarium exhibits high antibacterial activity. The results predict that Sm doped ZnO is a good possibility of food packing, removal of the tumor, treatment of pneumonia and a diagnosis of malign diseases.

Hibiscus subdariffa leaf extract mediated 2-D fern-like ZnO/TiO2 hierarchical nanoleaf for photocatalytic degradation

Green synthesized nanoparticles are utilized as a photocatalyst for the degradation of an organic dye such as methylene blue. In this study, Hibiscus subdariffa leaf extract act as a capping agent. 2-D fern ZnO/TiO2 hierarchical Nanoleaf was prepared by a self-assembled route. The XRD studies have revealed the hexagonal wurtzite structure of ZnO and a single phase of anatase crystalline form of TiO2. The 2-D fern hierarchical patterns showed needle-like morphologies having a large surface area to volume ratio with a wide absorption band. Compared with the cauliflower structure of ZnO nanoparticles, it’s charge carrier recombination and transfer resistance are low. A high-performance of photocatalytic degradation and photomineralization were observed on the 2-D fern ZnO/TiO2 nanoleaf, under UV–visible irradiation compared to HS-ZnO.

Effect of Hf doping content on the structure, optical and electrical properties of flexible HfxZn1-xO thin films by sol-gel method

Transparent and conducting HfxZn1-xO thin films with nominal Hf doping concentration (x = 0–7%) were successfully synthesized on flexible polyimide (PI) substrates by the sol-gel spin coating method. All films showed hexagonal wurtzite structure of ZnO with preferred orientation of c-axis after air and vacuum annealing. The minimum resistivity reached to as low as 6.3 × 10-2 Ω cm after annealed in vacuum atmosphere with 3% Hf content. The carrier concentration increased from 1018 cm-3 to 1019 cm-3, while Hall mobility decreased from 23 cm2v-1s-1 to 3 cm2v-1s-1 with increasing Hf concentration. According to the SEM and XPS analysis, for x = 0–3%, grain boundary scattering was the major factor of mobility, while for x = 5–7%, besides the grain boundary scattering, ionized impurity and natural scattering also play a crucial role in the variation of mobility. The minimum resistivity was due to the competition of increasing carrier concentration and decreasing mobility.

Structural, electrical and optical properties of copper-doped zinc oxide films deposited by spray pyrolysis

Abstract The effect of copper doping on structural, electrical, and optical properties of zinc oxide films was evaluated. Copper-doped films (ZnO:Cu) were successfully deposited on a glass substrate by spray pyrolysis at doping levels of 0, 2.5, and 7.5 at% (ZnO, ZC2.5, ZC7.5). All films were polycrystalline, single-phase with ZnO hexagonal wurtzite structure. The films presented nanostructured crystallites, from 36.7 to 38.2 nm. Cu doping increased the electrical conductivity of the ZnO films; this change was proportional to the Cu concentration. The films presented high optical transmittance of 70-80% in the visible wavelength. The energy gap decreased upon Cu doping. The photoluminescence spectrum of all films displayed an intense ultraviolet emission and a weaker blue emission. The emissions shifted to lower wavelengths with increasing dopant concentrations. ZC7.5 presented the most promising properties for an application as transparent conducting oxide: intense optical transmittance and UV photoluminescence, also the lowest electrical resistivity.

Effect of Morphology on Near-Infrared Shielding Properties of Aluminum-Doped ZnO by Solvothermal Synthesis

In this work, aluminum-doped ZnO (AZO) is synthesized for heat-shielding applications. A family of ethanolamine (EA: monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine TEA)) is used to control the morphology of aluminum-doped ZnO (AZO) synthesized via a simple solvothermal method at the temperature of 120°C for 6 h. The samples were characterized by field-emission scanning electron microscopy (FE-SEM). The formation of primary ZnO nanoparticles (NPs) showed that TEA yielded highly packed-spherical aggregates not found when DEA and MEA were used. X-ray diffraction (XRD) found that all AZO samples have peaks of the ZnO hexagonal wurtzite structure. XRD patterns of aluminum were found for >10 mol%. UV-Vis-NIR spectrophotometer was used to study the optical property and heat-shielding of the near-infrared region (NIR, the wavelength from 700 - 2500 nm). All AZO NPs of 0, 2, 4, and 10 mol% exhibited strong NIR shielding ability up to 80% insulation. From these results, the AZO NPs have potential use as NIR shielding materials of low-cost and simple processes to be coated on an energy-efficient window as smart window coating in buildings and automotive thus reducing energy consumption, especially in air conditioning usage.

Fabrication and characterization of B/Sn-doped ZnO nanoparticles via mechanochemical method for photocatalytic degradation of rhodamine B

Undoped and B/Sn-doped ZnO nanoparticles are successfully produced by a simple mechanochemical method, and are characterized by XRD, FTIR, EDX, SEM, XPS and BET techniques. The XRD studies reveal that the prepared nanoparticles possess the hexagonal wurtzite structure of ZnO. The presence of various functional groups (–OH, –CH, Zn–O) are observed by FTIR. It is clear from EDX analysis that B, Sn, Zn and O elements are present in the nanoparticles. SEM images confirm the relatively smooth surface of B/Sn-doped ZnO nanoparticles. XPS results indicate that B and Sn are successfully doped into ZnO matrix. The photocatalytic performances of undoped and B/Sn-doped ZnO nanoparticles are investigated for the degradation of aqueous solution of Rhodamine B (RhB) dye in natural sunlight irradiation. The photocatalytic degradation of RhB dye in 1 h with B/Sn-doped ZnO nanoparticle is about 70.2%, which is significantly enhanced compared with the undoped ZnO (51.8%).

Highly conducting and transparent low-E window films with high figure of merit values based on RF sputtered Al and In co-doped ZnO

In this work, we have studied the correlation between the electrical, optical and plasma properties of RF sputtered 1 at.% Al and In co-doped ZnO (AIZO) thin films with thickness 210–1590 nm in a comprehensive manner. The lattice strain of the hexagonal wurtzite ZnO structure decreases as the film thickness increases. The lowest resistivity of 8.9 × 10−4 Ω-cm is obtained for the 930 nm thick film with an electron concentration and mobility values of 3.96 × 1020 cm−3 and 17.7 cm2/Vs respectively. Optical transmission value is ~85%–90% in the range 400–700 nm for all the films. Most notably the figure of merit value of 2.65 × 10−2 Ω−1 for the 930 nm thick film is the highest among all the reports on AIZO films till date. High transparency in the visible region as well as higher reflectivity in the NIR region (with a plasma frequency of 8.2 × 1014 Hz) indicates its promising application in the low-E window.

ZnO as photocatalyst: An approach to waste water treatment

ZnO nanorods having uniform size have been synthesized using hydrothermal method. Different standard analytical techniques were employed to investigate the microscopic structure and optical properties of the prepared sample. The formation of the hexagonal wurtzite structure of ZnO was established by XRD and SEM analyses. UV-visible spectra of the as-synthesized ZnO show absorption band edge in UV region at 373 nm, corresponding to which the calculated band gap of ZnO nanorods is found to be 3.4 eV. Photodegradation of methylene blue (MB) using ZnO as photocatalyst have also been studied. Experiments revealed that ZnO nanorods with high aspect ratio can degrade 65% of initial concentration of MB in only 50 min.

Tuning of CO gas sensing performance of spray pyrolyzed ZnO thin films by electron beam irradiation

Electron beam induced effects on the sensing performance of spray-coated ZnO thin films for carbon monoxide (CO) detection are reported. The optical transmittance of pristine film was around 80% and decreased upon e-beam treatment. XRD studies confirmed the hexagonal wurtzite structure of ZnO. Carbon monoxide (CO) sensing measurements performed at 300 °C revealed that irradiated ZnO films exhibited enhanced response and recovery time compared to pristine film. The 5 kGy irradiated film displayed improved sensing performance with respect to response and recovery time towards the CO concentrations tested. It showed a quick response time of 43 s and a recovery time of 77 s towards the lowest detected CO gas limit of 2 ppm. The response time of 10 kGy irradiated film was 5 s towards 2 ppm. The 5 kGy irradiated ZnO sensor exhibited an excellent response of 1.39 and 2.63 towards 2 ppm and 5 ppm of CO gas respectively. The observed enhancement in both response and recovery times as well as response of the sensor is ascribed to the oxygen vacancies present in the film which is evident from the photoluminescence studies and also due to large number of grain boundaries.