Hexagonal Phase Of Wurtzite Structure Research Articles

Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) hexagonal tube and microrods structures: Optical, refractive index, electrical and solar photocatalytic properties

The optical, refractive index, electrical, dielectric and solar photocatalytic properties of pure and Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) compositions synthesized by coprecipitation method have been studied. Pure single phase of hexagonal wurtzite structure of ZnO was confirmed by XRD and Rietveld refinement analysis. The SEM obviously illustrated that Cu doping and Cu/V codoping have great impacts on morphology of ZnO particles. Remarkably, incorporation of Cu ions converts the spherical shape of the pure ZnO particles to open hexagonal tube and microrods structures while Cu/V ions lead to formation of mixed particles possess microrods and very fine spherical shapes. Optically, lowering in the optical band gap energy of ZnO with formation of long tails extend to visible light wavelengths (460 nm) were detected due to insertion of Cu and Cu/V ions. Based on Ravindra, Moss, Hervé, Reddy, and Kumar models, hexagonal Zn0.97Cu0.03O exhibits the highest refractive index values of 2.1558, 2.3509, 2.2961, 2.7368 and 2.3355, respectively. At different frequencies, 3 wt% Cu doping enhanced the room temperature electrical conductivity values of ZnO and further improvements were seen due to insertion of V3+/4+ ions plus Cu2+ dopant. Zn0.95Cu0.03V0.02O composition revealed a colossal dielectric constant of 1947 at 50 Hz and at nearly all frequency it possesses the highest values. The low cost solar photocatalytic test showed that both Zn0.97Cu·03O and Zn0.93Cu0.03V0.04O catalysts have high efficiencies of 81% and 82% to degrade the organic Congo red pollutant in 90 min.

Enhanced Photocatalytic Activity of ZnO–CdS Composite Nanostructures towards the Degradation of Rhodamine B under Solar Light

A simple chemical precipitation route was utilized for the synthesis of ZnO nanoparticles (NPs), CdS NPs and ZnO–CdS nanocomposites (NCs). The synthesized nanostructures were examined for the crystal structure, morphology, optical properties and photodegradation activity of rhodamine B (RhB) dye. The ZnO–CdS NCs showed a mixed phase of hexagonal wurtzite structure for both ZnO NPs and CdS NPs. Pure ZnO NPs and CdS NPs possessed bandgaps of 3.2617 and 2.5261 eV, respectively. On the other hand, the composite nanostructures displayed a more narrow bandgap of 2.9796 eV than pure ZnO NPs. When compared to bare ZnO NPs, the PL intensity of near-band-edge emission at 381 nm was practically suppressed, suggesting a lower rate of photogenerated electron–hole (e−/h+) pairs recombination, resulting in enhanced photocatalytic activity. Under solar light, the composite nanostructures displayed a photodegradation efficiency of 98.16% towards of RhB dye. After four trials, the structural stability of ZnO–CdS NCs was verified.

Enhanced Electrical Properties of Alkali-Doped ZnO Thin Films with Chemical Process

Doped ZnO are among the most attractive transparent conductive oxides for solar cells because they are relatively cheap, can be textured for light trapping, and readily produced for large-scale coatings. Here, we focus on the development of alternative Na and K-doped ZnO prepared by an easy low-cost spray pyrolysis method for conducting oxide application. To enhance the electrical properties of zinc oxide, alkali-doped Zn1−x MxO (x = 0.03) solid solutions were investigated. The resulting layers crystallize in a single hexagonal phase of wurtzite structure with preferred c-axis orientation along a (002) crystal plane. Dense, well attached to the substrate, homogeneous and highly transparent layers were obtained with great optical transmittance higher than 80%. The optical energy band gap of doped ZnO films increase from 3.27 to 3.29 eV by doping with Na and K, respectively. The electrical resistivity of the undoped ZnO could be decreased from 1.03 × 10−1 Ω.cm to 5.64 × 10−2 Ω.cm (K-doped) and 3.18 × 10−2 (Na-doped), respectively. Lastly, the carrier concentrations increased from 5.17 × 1017 (undoped ZnO) to 1 × 1018 (doped ZnO).

Photoluminescence and Magnetic Properties of Undoped and (Mn, Co) co-doped ZnO Nanoparticles

Objective: The influence of Manganese (Mn2+) and Cobalt (Co2+) ions doping on the optical and magnetic properties of ZnO nanoparticles was studied. Methods: Nanoparticle samples of type ZnO, Zn0.97Mn0.03O, Zn0.96Mn0.03Co0.01O, Zn0.95Mn0.03 Co0.02O, Zn0.93Mn0.03Co0.04O, and Zn0.91Mn0.03Co0.06O were synthesized using the wet chemical coprecipitation method. Results: X-ray powder diffraction (XRD) patterns revealed that the prepared samples exhibited a single phase of hexagonal wurtzite structure without any existence of secondary phases. Transmission electron microscope (TEM) images clarified that Co doping at high concentrations has the ability to alter the morphologies of the samples from spherical shaped nanoparticles (NPS) to nanorods (NRs) shaped particles. The different vibrational modes of the prepared samples were analyzed through Fourier transform infrared (FTIR) measurements. The optical characteristics and structural defects of the samples were studied through Photoluminescence (PL) spectroscopy. PL results clarified that Mn2+ and Co2+ doping quenched the recombination of electron-hole pairs and enhanced the number of point defects relative to the undoped ZnO sample. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer (VSM). (Mn, Co) co-doped ZnO samples exhibited a ferromagnetic behavior coupled with paramagnetic and weak diamagnetic contributions. Conclusion: Mn2+ and Co2+ doping enhanced the room temperature Ferromagnetic (RTFM) behavior of ZnO. In addition, the signature for antiferromagnetic ordering between the Co ions was revealed. Moreover, a strong correlation between the magnetic and optical behavior of the (Mn, Co) co-doped ZnO was analyzed.

Influence of Fe concentration on the physicochemical properties and inactivation of Pseudomonas aeruginosa of ZnO nanoparticles

Undoped and Fe-doped ZnO nanoparticles were synthesized by the sol–gel method, and the related physicochemical properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy (SEM). Annealing of the nanoparticles at 400 and 500 °C was studied. The prepared nanoparticles showed the hexagonal phase of wurtzite structure, and the grain size was in the range of 30–47 nm. Fe ions were in oxidation state of + 3 as was revealed by XPS analysis of the 0.7 at% Fe-doped powder. The photocatalytic properties of ZnO:Fe nanoparticles were investigated by inactivation of Pseudomonas aeruginosa under UV–B lamp irradiation. Optical density, colony counting method and SEM were used to survey the antibacterial activity of the nanoparticles. After analyzing the results, it was found that the prepared nanoparticles have a very effective antimicrobial activity against P. aeruginosa. This activity increases by increasing/decreasing the amount of Fe in the compound/annealing temperature. Heavily doped ZnO nanoparticles showed a considerable antibacterial effect against P. aeruginosa.

Green synthesis of ZnO nanoparticles using Tecoma castanifolia leaf extract: Characterization and evaluation of its antioxidant, bactericidal and anticancer activities

An efficient, facile and green synthesis of zinc oxide nanoparticles (ZnO NPs) using Tecoma castanifolia leaf extract was reported. ZnO NPs was characterized by UV–Vis spectroscopy, TEM, EDX, XRD and FTIR. Phytochemical constituents of T. castanifolia leaf extract were analyzed by GC–MS. UV–Vis absorption showed SPR band at 370–400 nm which confirms the formation of ZnO NPs. TEM analysis exhibits spherical shape with size 70–75 nm and XRD results revealed the hexagonal phase of wurtzite structure. FTIR spectra confirmed the presence of OH, CH, amide-I, II groups, CO bond and metal‑oxygen groups. The presence of bioactive phytochemical constituents in the methanolic extracts of T. castanifolia was identified by GC–MS. An excellent antibacterial activity was observed for both Gram positive and Gram negative bacteria. Results of antioxidant activity showed that increase in concentration of ZnO nanoparticles increases the radical scavenging activity. Anticancer activity with IC50 value as 65 μg/mL which conferred better cytotoxic effects of ZnO NPs on proliferation of A549 cell line. The present study revealed that the pharmacologically active compounds present in the green synthesized ZnO nanoparticles pave the way to lead its effective application in biomedical and nano-drug delivery systems.

Study of structural and electrical properties of ZnO thin film for Thin Film Transistor (TFT) applications

This work reports the room temperature deposition of undoped ZnO thin film using RF magnetron sputtering technique for thin film transistor (TFT) applications. RF sputtered ZnO thin film of thicknesses 100 and 200 nm were deposited over n-type silicon (Si) substrate using 99.9% pure ZnO target. For the deposition of ZnO thin films, a deposition pressure of 28 mTorr and RF power of 50 W was maintained. The gas flow rate was 5 and 20 sccm for oxygen and argon respectively. Structural and surface morphological characterization was done using X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) techniques. XRD analysis of the thin film gives a dominant X-ray diffraction peak corresponding to strong c-axis oriented phase of hexagonal wurtzite structure of ZnO. The XRD results confirm the polycrystalline nature of the thin film and shows crystallinity improvement with increase in film thickness. Further, FESEM results confirm that the grain size increases with the film thickness. The surface roughness is studied through AFM while surface elemental survey is done using XPS. To measure the resistivity of deposited films, four point probe method was used. The resistivity of undoped 100 nm thick ZnO film is found to be 4.47 kΩ cm, while the resistivity of undoped 200 nm thick ZnO film reduces to 724.13 Ω cm because of improved crystallinity.

Thermal decomposition synthesis of single-crystalline porous ZnO nanoplates self-assembled by tiny nanocrystals and their pore-dependent magnetic properties

High quality porous ZnO nanoplates with a pure crystal phase of hexagonal wurtzite structure were fabricated by thermal decomposition route for the first time. Electron microscopy investigations show that each porous ZnO nanoplates has a single-crystalline nature, which is self-assembled by tiny nanocrystals. The size and pore density of the ZnO nanoplates can be tuned by only changing the amount of zinc source. Magnetic investigations show that the magnetic phase can be converted from paramagnetism to ferromagnetism at room temperature, by increasing the pore density of ZnO nanoplates. The ZnO nanoplates with highest pore density show a d° room-temperature ferromagnetic characteristic, and the saturation magnetization reaches 26 memu/g. Several experimental evidences, including XPS, PL and ESR spectra, demonstrate that the defects of singly charged oxygen vacancies related to the pore density contribute to the long-range ferromagnetic ordering in the dopant-free porous ZnO nanoplates. This finding suggests that the pore-dependent ferromagnetism can be manipulated by tuning the surface-volume ratio, which is significant for the understanding and exploration of diluted magnetic semiconductors.

Structural and optical characterization of ZnO thin films for optoelectronic device applications by RF sputtering technique

This work reports structural and optical study of ZnO thin films grown over p-type silicon (Si) and glass substrates by RF magnetron sputtering technique. Surface morphological and optical properties of thin film have been studied using X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX), ellipsometry and photoluminescence (PL) spectroscopy. Strong diffraction peak (002) obtained from XRD spectra of ZnO thin film indicates a preferential growth of single crystalline thin film along the c-axis oriented phase of hexagonal wurtzite structure. Surface morphological feature reveals uniform growth of undoped ZnO thin film over the substrate. Different important microstructural parameters for the film such as grain size, lattice parameters, defect density, stress and strain have been obtained. Optical properties such as transmittance, reflectance, absorption coefficient, refractive index and dielectric constant for a spectral range of 300–800nm have been evaluated. A good optical transmittance of 83–92% has been observed for visible region, and the optical bandgap of ZnO films was found to be 3.23eV. Energy Loss Function (ELF) and photoluminescence (PL) spectra for ZnO thin film has also been analyzed and reported.

Effects of Reaction Temperature on Structural Properties of ZnO Nanocrystals Prepared via Solochemical Technique

In this research, ZnO nanocrystals were prepared in a few hours by solochemical processing using sodium hydroxide and zinc nitrate hexahydrate as raw materials. Different reaction temperatures have been investigated and revealed their effects on the crystallite size, morphology and crystalline phase of ZnO nanocrystals. Materials synthesized by this technique were investigated employing X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-Visible spectroscopy and Rietveld method. XRD and TEM showed that the ZnO samples are formed by a single hexagonal phase of wurtzite structure containing predominantly rod-like particles, except for the sample obtained at 90 degrees C that is basically formed by rounded nanometric particles. The sample obtained at 90 degrees C presented the smallest average crystallite size (approximately 20 nm) and the highest blue shift between the UV-Vis absorption spectra of the samples when compared to that of ZnO bulk. These size/disorder effects can also explain the attenuation of the ZnO Raman spectrum with increase of reaction temperature.

Large-Scale Synthesis of ZnO Nanorods by a Surfactant-Free and Low-Temperature Process

ZnO nanorods have been successfully synthesized by employing ZnCl2, NaOH as the starting materials without surfactants, template supporting and structure-directing solvent at a low temperature (room temperature – 90 °C ). X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure with no impurity of others. Also, TEM images revealed that the size of a single ZnO nanorod is between 32 – 60 nm in diameter and 470 – 740 nm in length. Furthermore, the ZnO nanorods exhibit significant optical properties in Raman spectrum, suggesting that they could be found promising potential for opto-electronic application.

Large-Scale Synthesis of ZnO Nanorods by Different Surfactant-Assisted and Low-Temperature Process

In this work, ZnO nanorods have been successfully synthesized by employing ZnCl2, NaOH as the starting materials by using different surfactants (including CTAB, SDS and SDBS), without using template supporting and structure-directing solvent at a low temperature ( 60 up to 90 °C ). X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure with no impurity of others. Also, TEM images revealed that the size of a single ZnO nanorod is between 20 nm and 40 nm in diameter and between 200 nm and 2 μm in length. The structures, growth mechanism and the PL spectra properties of ZnO microcrystals are investigated.

Ion sensitivity of the flowerlike ZnO nanorods synthesized by the hydrothermal process

Flowerlike ZnO nanorods were synthesized by the hydrothermal process. A simple two-step process was developed for growing ZnO nanorods on the silicon substrates at about 85°C. The concentration of zinc acetate dehydrate pretreatment is 0.01M. The x-ray diffractometer pattern of ZnO nanorods at 2θ=31.77°, 34.42°, and 36.25° indicates three reflection peaks of hexagonal wurtzite structure, (100), (002), and (101), respectively. It has been shown that the ZnO nanorods are of single hexagonal phase of wurtzite structure. The scanning electron microscopy image revealed that the average diameter of ZnO nanorods was about 360nm. In addition, the ZnO nanorods/Si structure was utilized as a pH sensor head and connected with the metal-oxide-semiconductor field-effect transistor when the extended-gate field-effect transistor was finished. Afterward, the semiconductor parameter analysis instrument (Keithley 4200) was used to measure the current-voltage characteristic curves in the different pH buffer solutions. The experimental result found that the pH sensing response is obtained and the output voltage shifted right with increasing pH values.

Hydrothermal synthesis of hexagonal ZnO clusters

Hydrothermal process was applied to synthesize zinc oxide nanocrystals. X-ray powder diffraction and scanning electron microscopy were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure (space group P63 mc) with no impurity of Zn and Zn(OH) 2. Also, SEM images revealed that the size of a single ZnO crystal is between 200–500 nm in diameter and 2–5 μm in length. The influence of potassium iodide (KI) as a surfactant on the crystallinity of ZnO has been investigated.