Papers by Keyword: ZnO Thin Films

Abstract: In this study, eco-friendly and low-cost highly porous ceramic substrates were fabricated to enhance the performance of photocatalysts. ZnO as a model photocatalyst deposited as thin films by dip-coating sol-gel method on naturally extracted kaolin clay (90%) and Corn starch (10%)-made highly porous ceramic substrates prepared as pellet form and sintered at different temperatures: 1150, 1200, 1250, and 1300 °C. The effect of temperature on the prepared substrates modified their porosity and the best value obtained was 56% with a specific surface area of 38.80 m²/g for 1150 °C. Structural analysis of the X-ray diffraction spectra revealed a hexagonal wurtzite structure for ZnO and mullite/cristoballite structures for substrates. Scanning electron microscopy images confirmed the porosity and uniform formation of ZnO on the substrates. The high porosity samples resulted in a high reflectance of over 90%, and band gap energies values around 3.11 eV were verified by UV–VIS spectroscopy. The photocatalytic properties of ZnO thin films on ceramic substrates were studied by testing the degradation of Orange II dye in an aqueous medium under UV light irradiation. The highest degradation rate of 92% was obtained for ZnO thin films deposited on porous substrates treated at 1150 °C. The kinetic study indicated that the photocatalytic degradation of Orange II correlated with the pseudo-first-order kinetic model.

Abstract: Zinc Oxide (ZnO) thin films were deposited on glass substrate by radio frequency (RF)reactive magnetron sputtering technique at variable Oxygen flow rates while Argon flow rates waskept constant. The effect of oxygen flow rate on structural, electrical, optical properties of nanostructured ZnO thin films were investigated by X-ray diffractometer, scanning eletron microscopy(SEM), Hall effect measurements and UV-Visible spectrophotometer. X-ray diffraction (XRD) datareveals films are polycrystalline hexagonal structure with (002) peak as a preferred orientation andcrystallite size was found to be in range12 nm-16 nm.The electrical resistivity of films decreasesfrom 10^-1 Ω-cm to 10^-2 Ω-cm. All deposited ZnO thin films shows high transmittance above 95% inthe visible range 360 nm-800 nm. The optical band gap and refractive indices have been calculatedusing UV-Vis transmission spectra. Oxygen gas flow rates found to have large impact onoptoelectronic properties of ZnO films.

Abstract: In this work, ZnO thin films grown on heated glass substrates in a temperature range of 300 to 500 °C with a 50°C step. The prepared solution is composed of methanol and zinc acetate Zn(CH₃COO)₂.2H₂O. ZnO thin films are deposited by pyrolysis spray technique, our work focuses on the study of the substrate temperature influence on the structural and optical properties of these layers. Therefore, The X-ray diffraction, showed a Wurtzit hexagonal structure of elaborated films, with (002) as a preferred orientation, and a grain size of 64 to 74 nm. The optical transmission spectroscopy UV-Visible, illustrated an increase of optical band gap from 3.19 to 3.25 eV, proportionally with the substrate temperature.

Abstract: In this work, the ZnO films are deposited on conducting silicon chips by radio frequency magnetron sputtering. The as-deposited thin films are annealed at 800 °C in a N₂, O₂ and CO+N₂ atmosphere for 1h, respectively. The microstructure and electrical properties of the films are comprehensively investigated. XRD studies reveal that the ZnO films have a hexagonal wurtzite structure and they are highly oriented along (002) direction. The surface roughness of ZnO films decreased after annealing, which indicates better film quality. Room temperature PL spectrum is used to investigate the band gap and native defects existing in the films. Defects of thin films for different annealing conditions are analyzed in detail and the possible mechanism of the defects emission is discussed. We suggest that annealing atmosphere of CO+N₂ is the most suitable annealing conditions for obtaining ZnO thin films with better crystal quality and good luminescence performance.

Abstract: ZnO thin films on glass substrates have been successfully fabricated by sol-gel method for various aging time and annealing temperature. X-ray diffraction (XRD) patterns showed the crystallites at (100), (002) and (101) plane of hexagonal wurtzite structure. Atomic force microscope (AFM) images were used to investigate the surface morphology. The transmittance, energy gap, Urbach energy and photoluminescence (PL) of samples were investigated to explore the effects of annealing temperature on optical properties of ZnO thin films under different sol aging time. The transmittance spectra of thin films aged for 24 hours and 48 hours revealed the enhanced transmittance in visible region as rising annealing temperature, also, the optical band gap of the samples increased and Urbach energy decreased. The photoluminescence (PL) spectra of samples aged for 24 hours and 48 hours were studied and found the increased ultraviolet emission at ~387 nm, and various decreased visible emissions with rising annealing temperature. Nevertheless, the excessive sol aging time for 72 hours deteriorated the optical characteristics of thin films, resulting in that transmittance, energy gap and ultraviolet emission declined, and visible emissions increased with rising annealing temperature. The optical performances of the ZnO films aged for different time have no the same dependence of annealing temperature.

Abstract: In this work, Zinc oxide (ZnO) thin films were deposited on silicon and glass substrates using spin-coating method with different concentrations of precursor (zinc acetate dihydrate) and stabilizer (monoethanolamine). The concentrations of zinc acetate dihydrate and monoethanolamine in isopropanol were varied from 6 mM to 500 mM. Subsequently, the substrate with ZnO thin film as a seed layer was used to grow ZnO nanostructures by hydrothermal process with the same concentration of precursor (zinc nitrate hexahydrate), temperature, and time for each growth. The samples were characterized by field-emission scanning electron microscopy (FESEM), X-rays diffractometer (XRD), and UV-visible spectrophotometer (UV-vis) to study morphology, crystallographic structure, and optical property, respectively. The results showed that particle size, crystallinity, and transmittance of seed layers were changed with increasing concentrations of spin-coated precursor. Furthermore, the nanostructures were found that higher precursor concentration of seed layers affected the formation of ZnO nanorods to be nanosheets.

Abstract: Transparent semiconductor ZnO thin films deposited on interdigitated electrode (IDE) substrate substrates were obtained by low-cost sol-gel method. The coated ZnO films were annealed in furnace at 500°C for 2 hours. The influence of surface morphologies, crystallization and optical properties was investigated. The structural properties of the annealed ZnO thin films were examined with FESEM and AFM. XRD result shows that all polycrystalline ZnO thin film after annealing have the orientation along the (002) plane. Both FESEM and XRD results revealed that ZnO thin films were composed of hexagonal ZnO crystals in nanoscale dimensions. Moreover, UV-Vis was employed to study the optical properties of the ZnO films. Besides that, the deposited ZnO thin film will further use for pH by I-V curve tracer.

Abstract: Pure ZnO thin films and Ag doped ZnO thin films were prepared on quartz substrates by sol-gel process. Structural features and UV absorption spectrum have been studied by XRD and UV-Vis-Nir scanning spectrophotometer. Taking phenol as pollutants, further study of the effect of different annealing temperature and Ag dopant amount of ZnO films on photocatalytic properties was carried out. The results showed that, the optimal annealing temperature on photocatalytic degradation of phenol in this experiment was 300 °C, the best molar ratio of ZnO and Ag was 30:1, which was better than pure ZnO film greatly. Excellent adhesion, recyclable and efficient degradation Ag doped ZnO thin films were found in this experiment.

Abstract: Zinc oxide (ZnO) films are prepared on n-Si substrates by means of radio frequency (RF) magnetron sputtering method. The influences of substrate temperature on the crystal orientation and crystalline structure of ZnO films are investigated by X-ray diffraction (XRD) and Raman spectroscopy. The surface morphologies are studied by scanning electron microscope (SEM). It is indicated that ZnO films with wurtzite structure were successfully prepared. When the substrate temperature reduced to 100°C, the wurtzite structure with highly preferred orientation along the (002) plane of the ZnO film is prepared and the elliptical shape particles distributed uniformly on the ZnO film surface. The higher substrate temperature can offer more kinetic energy for mobility of particle on the surface to achieve other crystalline growth, resulting in the highly c-axis-oriented crystalline structure is destroyed.

Abstract: Zinc oxide (ZnO) thin films were prepared by sol-gel spin coating technique, which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), NKD thin film analysis system and fluorescence spectrophotometer. The results show that ZnO thin films with the each layer thickness of 80 nm present obvious c-axis orientation. With the increase of coating layers, the c-axis orientation characteristic weakens. The reason is considered that the growth mode of ZnO thin films transforms from layer growth to island growth. For the ZnO thin film with 4 layers, it has a compact surface and a uniform particle size of approximately 50 nm, and the photoluminescence (PL) spectrum primarily consists of two PL emission bands, one is a strong and narrow ultraviolet (UV) emission band, another is a weak and broad luminescence emission band from 400 nm to 650 nm. The average transmittance in the visible range is beyond 90%. A optical band gap of 3.26 eV, slightly less than the intrinsic band gap width of 3.37 eV, is obtained by Tauc plotting method. The defects, such as Zn or O vacancies, grain boundaries, are considered to be the main factors causing this situation.