Microstructure Of ZnO Thin Films Research Articles

Structural and Optical Properties of Graphene-ZnO Nanohybrid Thin Films Synthesized by Spray Pyrolysis

Graphene-ZnO nanohybrid thin films were prepared by spray pyrolysis technique at 350 °C. Different graphene nanoplate concentrations of 0.1, 0.2, 0.3, 0.4, and 0.5 wt.% were used to deposit films on quartz substrates. The Structural and optical properties of the nanohybrid films have been investigated. X-ray diffraction XRD results show that the films have a hexagonal wurtzite polycrystalline structure and no secondary phases were observed. The structural parameters of crystallite size, dislocation density, and microstrain have indicated that the addition of graphene has a strong effect on the microstructure of zinc oxide films. Surface morphological analysis of the ZnO-graphene films reveals that the graphene content effectively modifies the morphologies and grain growth of the ZnO microstructure. It was also found from the optical properties that the maximum energy gap for pure ZnO films was 3.4 eV which decreases to 2.7 eV as the concentration of graphene increases to 0.5 wt.%. Results confirmed that graphene can be used as an efficient modifier for band gap engineering and the microstructure of ZnO thin films for enhanced photovoltaic applications.

Effect of the Microstructure of ZnO Thin Films Prepared by PLD on Their Performance as Toxic Gas Sensors

In 2008, the modified European Restriction of Hazardous Substances (RoHS) directive prohibited the use of hazardous substances such as lead, cadmium, and mercury. As such, an urgent need for lead-free components emerged in Europe. In this frame, we have decided to study the microstructure influence of zinc oxide thin films on the detection of hydrogen sulfide (H2S). Zinc oxide thin films were deposited by PLD on silicon substrates under different conditions to modify the microstructure. In order to compare our demonstrators to current commercial semiconductor gas sensors, measurements under H2S were also performed with sensors from Figaro and Winsen corporations. Gas sensors were therefore implemented by using commercial cases in view to test them with Simtronics gas detector DG477. The good sensitivity values measured at T = 400 °C under 100 ppm H2S, and response times as low as 30 s, definitely confirm that ZnO thin films could be developed for commercial sensors.

Effect of precursor concentration on corrosion resistance and microstructure of ZnO thin films using spray pyrolysis method

This paper presents the preparation and characterization of ZnO at various molarities deposited on glass and 316L stainless steel (316L SS) substrates via spray pyrolysis technique (SPT) for multifunctional applications such as anti-corrosion of various types of steel in oil and gas companies , marine industry, and optoelectronic applications. Zinc acetate solution was employed as precursor. The X-ray diffractometry (XRD) result showed no significant effect on crystal size and microstrain when the molarity of ZnO increased from 0.1 M to 0.2 M, but with 0.3 M, the crystal size increased from 17.33 nm to 23.10 nm, while the microstrain of the film varied from 0.13 nm to 0.10 nm. The coated films’ particles were observed to adhere suitably to the 316L SS substrate and were evenly distributed across the substrate surface. The results of the energy dispersive X-ray spectroscopy (EDX) and XRD affirm the presence of Zn and O in the deposited samples. The percentage of elements in the 316L SS are Fe = 70.10%, Ni = 10.10%, and Cr = 16.20% but on deposition of thin films. The signals of the Fe, Cr and Ni contents of the 316L SS were suppressed with increased ZnO concentration. The transmittance at the ultraviolet visible (UV-visible) region of (300 – 900 nm) showed that ZnO is highly transparent to visible light. The coated ZnO thin films improved the corrosion resistance of the 316L SS as seen from the electrochemical test result. Molarities were observed to increase with corrosion potential, which is related to corrosion resistance.The results show that the deposited ZnO coatings has a viable transparent oxide thin layer suitable for metal corrosion resistance.

Microstructural evolution and optical dispersion of sputtered ZnO thin films at low annealing temperature

In an attempt to understand microstructural evolution and its effect on optical properties, nanocrystalline ZnO thin films are deposited by pulsed DC magnetron sputtering and then heat treated at a low temperature for several hours. X-ray diffraction experiments confirm that texture and residual stress are sensitive to morphological changes from globular to plate-like grains. Nanocrystalline ZnO thin films are highly transparent to visible light but opaque to UV light below 350 nm. The transparency in the UV region is limited by its fundamental absorption below 400 nm. The spectral dependence of optical constants demonstrates normal dispersion and the films deposited at 70 W of sputtering power and then heat treated have higher values of refractive indices and significantly high extinction. The dispersion parameters evaluated under the purview of a single oscillator model propose vital linkages of optical properties with the microstructure of ZnO thin films. Dispersion parameters viz. plasma frequency can be attuned by controlling the microstructure of ZnO thin films via simply varying process parameters and post-deposition heat treatment at low temperature. This study confirms that high tensile residual stress and texture are favorable for the development of novel nanocrystalline ZnO thin films.

Influence of Preparation Conditions on the Microstructure of ZnO Thin Films Prepared by Electrodeposition

Influence of Preparation Conditions on the Microstructure of ZnO Thin Films Prepared by Electrodeposition

Microstructure of ZnO thin films produced by magnetron sputter oblique deposition

ZnO films deposited at different oblique angles of 40, 60 and 80°, under different Ar pressures 0.27, 0.67, 1.33 and 2.67Pa, DC currents of 0.15 and 0.25A, and distances of 10–15cm from the target were studied. It was found that the film grains grow at an angle to the substrate when deposition angle is above 40°. It was shown that the grains consisted of a number of small crystals growing one on top of the other and shifted towards the target with the crystal orientation not along the grain growth but perpendicular to the substrate. Crystal size decreased with the deposition angle and internal stress disappeared when α=80°. It was found that 1.33Pa pressure provided the best balance between the deposition parameters. Growth rate reached maximum, samples had the biggest crystal size and high crystal density. However, crystal spatial alignment changed gradually with pressure and distance.

Study of nanocluster‐assembled ZnO thin films by nanocluster‐beam deposition

AbstractNanocluster‐assembled ZnO thin films were obtained by nanocluster‐beam deposition, in which nanoclusters were produced by a magnetron sputtering gas aggregation source. Two kinds of ZnO thin films were obtained using this method with the one grown under the on‐line heating temperature of 700 °C, and the other grown without on‐line heating. Film microstructure and optical properties are investigated by various diagnostic techniques. It was found that both of film microstructure of ZnO thin films keep wurtzite structure as that of ZnO bulk materials. The averaged particle size for the film grown without on‐line heating is around 6 nm, which is a little lower than that grown with the on‐line heating. It was also found that as increasing the wavelength, both of the absorbance spectra for the films decrease sharply near ultra‐visible to extend slowly to the visible and infrared wavelength range. For the film grown without on‐line heating, the bandgap energy was estimated to 3.77 eV, while for the film grown with on‐line heating, the bandgap energy was redshift to 3.71 eV. Similar behavior was also found for PL spectra analysis, where PL spectrum exhibited a peak centered at 3.31 eV without on‐line heating, while it redshift to 3.20 eV with on‐line heating. The mechanisms behind these behaviors were presented in this article. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Different Thermal Treatment on Optical Properties and Microstructure of ZnO Thin Films

ZnO thin films were prepared by DC reactive magnetron sputtering at room temperature. Two of them were annealed with different modes under vacuum condition. One was annealed with constant temperature of 300°C ; the other was annealed with temperature rising step by step from room temperature to 300°C . By comparing the microstructure and optical properties of the as-grown and annealed samples, the effects of different annealing modes on ZnO films performances were revealed. The experiment results investigated that the sample annealed with constant temperature of 300°C has the high grain size and surface roughness. Both of the two annealing modes could release the intrinsic stresses to some degree. The optical band gap of the samples narrowed after annealing, and the two annealed samples have almost the same band gap. Strong green emissions are observed for all the samples, but the emission intensity decreased of the sample annealed with the temperature rising step by step compared with that of other samples.

Influence of glucose on the structural and optical properties of ZnO thin films prepared by sol–gel method

In this work, ZnO thin films were prepared by sol–gel method on glass substrates followed by calcinations at 500 °C for an hour. The effect of glucose on the structure and optical properties of the films was studied. The structural characteristics of the samples were analyzed by X-ray diffractometer (XRD) and atomic force microscope (AFM). The optical properties were studied by a UV–visible spectrophotometer. The results show that some of the prepared ZnO thin films have a high preferential oriented c-axis orientation with compact hexagonal wurtzite structure due to a proper amount of glucose introducing. After introducing the glucose additive in ZnO colloids, the intensity of (002) peak, the transmittance, and the optical band gap of the ZnO thin films increases because of the enhanced ZnO crystallization. On the contrary, the absorbance, the film thickness, and the surface root-mean-square (RMS) roughness of the ZnO thin films decreases. The glucose additive could not only improve the surface RMS roughness and microstructure of ZnO thin films, but also enhance the transmittance and the energy band gap more easily.

Improvement of the performance of ZnO TFTs by low-temperature supercritical fluid technology treatment

In this paper, the supercritical CO 2 (SCCO 2) fluid technology is successfully applied to improve the electrical characteristics of sputtered ZnO TFTs at low temperature (150 °C). After the treatment of SCCO 2 fluids mixed with water, the ZnO TFT exhibited superior transfer characteristics and lower threshold voltage. According to X-ray photoelectron spectroscopy (XPS) analyses, the improvements were attributed to the increase of binding energies of Zn–O bonds, hydrogen-related donors and the reduction of traps at the grain boundaries in ZnO thin films. In addition, the crystalline quality and microstructure of ZnO thin films were also investigated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The transmittance of the ZnO film was measured by an N&K analyzer 1280 (N&K Technology, Inc.), which is a new type of thin-film measurement system.

Microstructural aspects for defect emission and E2high phonon mode of ZnO thin films

The ZnO thin films were prepared using a cost-effective vacuum-carbon-arc technique combined with thermal oxidation under ambient conditions from zinc nanoparticles in carbon matrix. The microstructural analysis of grazing incidence x-ray diffraction pattern using Rietveld method was investigated systematically under the influence of different annealing temperature. Photoluminescence spectroscopic properties of the samples studied at room temperature exhibits the dependence of violet emission accompanying with blue and green emission on oxidation temperature. The origin of defect emission mechanism through the microstructure of ZnO thin films was analyzed. The anharmonic properties of the upper E2 phonon mode were investigated using Raman scattering spectroscopy at room temperature. The downshift of phonon frequency and linewidth broadening of high frequency E2 phonon mode were analyzed through defect state according to annealed conditions.

Influence of sputtering parameters on crystalline structure of ZnO thin films

The relations between the sputtering parameters and the crystalline microstructure of ZnO thin films are presented. The energetic bombardment of substrate by neutral atoms, ions and electrons during sputtering is characterized by total energy flux density which affects the film. This parameter can be estimated by RF power, substrate bias voltage and concentration of reactive gases. Substrate temperature and total energy flux density are the major parameters which have a significant influence on ZnO thin film crystalline structure.

Influence of PMAA‐graft‐PEO copolymers on the formation of thin ZnO films from aqueous solutions

AbstractThe microstructure of ZnO thin films was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The ZnO films were deposited on bare silicon as well as on Si wafers modified with self‐assembled monolayers (SAMs) by the thermohydrolysis of zinc salts from aqueous solution with the addition of water‐soluble copolymers. The influence of polymethacrylic acid partially grafted with polyethylenoxide side‐chains on the morphology of the thin films was investigated.X‐ray photoelectron spectroscopy (XPS) was carried out to determine the composition of the thin films. A comparison of the position of the O 1s peak in as‐deposited and annealed films suggests that the copolymer remains attached to the precipitated ZnO particles. After calcination at 723 K the copolymer is completely removed, yielding ZnO films with a thickness of ∼70 nm. Copyright © 2002 John Wiley & Sons, Ltd.

Preparation and microstructure of ZnO thin films by SOL-GEL process

Abstract Zinc oxide thin films were prepared from metallo-organic compounds through the sol-gel process. The crystal structure of ZnO films was investigated by XRD and SEM. Optical properties of the thin films were analyzed by using UV/visible spectroscopy. Strongly c-axis oriented ZnO thin films were obtained on fused quartz substrates; the surface of the thin films was smooth, homogeneous, crack-free, and dense. The growth of the thin films depends strongly on the heat-treatment conditions. The Crystal lattice constant of the thin films is a little larger than that of the ZnO crystal, the band gap is 3. 444 eV, and the absorption limit shifts to shorter wavelengths.