Studies on the Structure of Gel during Preparing ZnO Thin Films by Sol-gel Method

<正>Transparent thin films of ZnO have been prepared on ordinary glass substrates by the inorganic sol-gel method using citric acid as chelating agent and zinc nitrate as the starting material.A novel structure on zinc citrate complex was put forward by using DTA-TG and FT-IR absorbance spectrum of citrate gels.Phase formation,morphology and optical properties of ZnO films are investigated by XRD,AFM and UV-vis transmittance spectra.The experimental results show that ZnO thin films derived from zinc citrate sol-gel method showed a(002)oriented hexagonal wurtzite structure,good crystalline property,a uniform range of grain size(40 nm), smooth surface of films,band gap of 3.28 eV and optical transmittances ratio over 90%in the visible range.     

Influence of Substrate-Target Distance on Structural and Optical Properties of Ga and (Al + Ga)-doped ZnO Thin Films Deposited by Radio Frequency Sputtering

Ga-doped ZnO and (Ga?+?Al) co-doped ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering for three distances d between a substrate–target. The influence of the distance between substrate–target upon structure, microstructure, vibrational properties, and optical band gap of the thin films was analyzed by X-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy, and optical transmission measurements. The diffraction patterns revealed that the ZnO film crystallites are preferentially oriented with the (002) planes parallel to the substrate surface. AFM images show a smooth and uniform surface as well as a high compact structure. The Raman results reveal that the co-doping with Al?+?Ga introduces 2B₁(low) band and leads to the increase of intensity for longitudinal-optic’s band. In the visible region, the average value of the transmittance was above 80%.     

RF magnetron sputtering of ZnO and Al-doped ZnO films from ceramic and nanopowder targets: a comparative study

Undoped zinc oxide (ZnO) and aluminium-doped zinc oxide (ZAO) thin films have been prepared on glass substrates by RF magnetron sputtering from ceramic and nanopowder targets at room temperature (RT). The effects of target nature on the properties of the films have been studied. The X-ray diffraction (XRD) patterns show that ZnO and Al-doped ZnO thin films are highly textured along the c-axis perpendicular to the surface of the substrate from either nanopowder or ceramic targets. From the SEM images, it appears that the surface morphologies of ZAO films exhibit difference from that of undoped ZnO films. All films exhibit a transmittance higher than 80% in the visible region. The optical band gap (E_g) of ZnO and ZAO films obtained from nanopowder target is higher than those prepared using ceramic target. In two cases, Al-doping leads to a larger optical band gap (E_g) of the films.     

Nanocrystalline Zn1−x−yBexMgyO thin films synthesized by the sol–gel method: structural and near infrared photoluminescence properties

In this paper, we reports on the structural and optical properties of Zn_1?x?yBe_xMg_yO thin films prepared by sol–gel method, which are new materials for optoelectronic and ultraviolet-light-emitting devices. The crystal structure and core level spectra of these films are studied by X-ray diffraction and X-ray photoelectron spectroscopy. Surface morphology of the films is analyzed by scanning electron microscope images and the surface is composed of spherical shaped grains. Micro-photoluminescence shows a near edge band emission and the peak values tuned from 3.26 eV for the undoped to 3.4 eV for the doped ZnO film. Near infrared emission is observed in the region 1.64–1.67 eV for pure and co-doped ZnO films. In micro-Raman spectra, multiple-order Raman bands originating from ZnO-like longitudinal optical (LO) phonons are observed. A Raman shift of about 5–18 cm^?1 is observed for the first-order LO phonon. A comparative study was made on Raman band for BeZnO, MgZnO and BeMgZnO nanocrystals with the LO phonon band of bulk ZnO. The ultraviolet resonant Raman excitation at room temperature shows multi-phonon LO modes up to the fourth order. Deformation energy of all the films is calculated and BeMgZnO film has the minimum deformation energy.     

Preparation and characterization of nanocomposite ZnO–Ag thin film containing nano-sized Ag particles: influence of preheating,annealing temperature and silver content on characteristics

Nanocomposite ZnO–Ag thin film containing nano-sized Ag particles have been grown on glass substrate by spin-coating technique using zinc acetate dihydrate as starting precursor in 2-propanol as solvent and monoethanolamine as stabilizer. Silver nanoparticles were added in the ZnO sol using silver nitrate dissolved in ethanol-acetonitrile. Their structural, electrical, crystalline size and optical properties were investigated as a function of preheating, annealing temperature and silver content. The results indicated that the crystalline phase was increased with increase of annealing temperature up to 550 °C at optimum preheating temperature of 275 °C. Thermal gravimetric differential thermal analysis results indicated that the decomposition of pure ZnO and nanocomposite ZnO–Ag precursors occurred at 225 and 234 °C, respectively with formation of ZnO wurtzite crystals. The scanning electron microscopy and atomic force microscopy revealed that the surface structure (the porosity and grain size) of the ZnO–Ag thin film (the film thickness is about 379 nm) was changed compared to pure ZnO thin film. The result of transmission electron microscopy showed that Ag particles were about 5 nm and ZnO particles 58 nm with uniform silver nanoclusters. Optical absorption results indicated that optical absorption of ZnO–Ag thin films decreased with increase of annealing temperature. Nanocomposite ZnO–Ag thin films with [Ag] = 0.068 M and [Ag] = 0.110 M showed an intense absorption band, whose maximum signals appear at 430 nm which is not present in pure ZnO thin films. The result of X-ray photoelectron spectroscopy revealed that the binding energy of Ag 3d_5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.     

Structure and morphology of nanostructured zinc oxide thin films Prepared by dip-vs. spin-coating methods

In this study, we use dipping and spinning methods to coat glass slides with sol-gel ZnO thin films, composed of zinc acetate dihydrate, monoethanolamine (MEA), de-ionized water and isopropanol. The effect of the annealing temperature on the structural morphology and optical properties of these films is investigated. These ZnO films were preheated at 275 °C for 10 min and annealed either at 350, 450 or 550 °C for 60 min. As-deposited films, formed by amorphous zinc oxide-acetate submicron particles, are transformed into a highly-oriented ZnO after thermal treatment. The surface morphology, phase structure and optical properties of the thin films were investigated by scanning electron microscopy, X-ray diffraction (XRD) and optical transmittance. Both techniques produced nanostructured ZnO thin films with well-defined orientation. The annealed films were transparent in the visible range with an absorption edge at about 375 nm and a transmittance of ca 85–90% with an average diameter of 40 nm. XRD results show the film was composed of polycrystalline wurtzite, with a preferential c-axis orientation of (002) and a single sharp XRD peak at 34.40, corresponding to the hexagonal ZnO. The grain size is increased by the annealing temperature. Both coating techniques create sol-gel ZnO films with the potential for application as transparent electrodes in optic and electronic devices.     

Synthesis and characterization of semiconductor tin oxide thin films on glass substrate by sol–gel technique

In this study, synthesis and characterization of semiconductor tin oxide (SnO₂) thin films on glass substrate were systematically investigated by using sol–gel technique for gas sensing applications. Turbidity, pH values, wettability and rheological properties of solution were measured by turbidimeter, pH meter, contact angle goniometer and rheometer machines before coating process. The thermal, structural, microstructural and optical properties of the coatings and powders made from the sols were extensively characterized by using DTA-TG, FT-IR, XRD, SEM-EDS, refractometer and spectrophotometer. Four different solutions, including 6, 8, 10 and 14 mL methanol content, were prepared by sol–gel technique to determine solvent influence on microstructure and semiconducting properties of the thin films. Refractive indiceses, band gaps, absorbance and transmittance values of SnO₂ thin films, containing different methanol quantity, were determined and their variations depending on solvent content were obtained. It is concluded that solvent content influences microstructural and semiconducting properties of Sn based oxide thin films notably.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Process optimization and characterization of thin films of SrFeO3-x by the pechini method

Nanostructured coatings have recently attracted increasing interest because of the possibilities of synthesizing materials with unique physical-chemical properties. Highly sophisticated surface related properties, such as optical, magnetic, electronic, catalytic, mechanical, chemical and tribological properties can be obtained by advanced nanostructured coatings, making them attractive for various industrial applications. In this report we describe our efforts at developing methodology for the fabrication of SrFeO_3-x based thin films using a modified Pechini method. Thin films of SrFeO_3-x were fabricated using spin coating and a drop coating method developed in-house on Al₂O₃ and Si- substrates. The films annealed at 600°C for one hour show a perovskite phase. The grain size increases with increase in annealing temperature. The influence of various variables such as metal to chelant ratio, drying control reagents, calcination conditions, substrate type and mode of film formation were studied using XRD, optical microscopy, SEM and AFM.     

Photocatalytic activities of multilayered ZnO-based thin films prepared by sol–gel route: effect of SnO2 heterojunction layer

In present study, ZnO/SnO₂/ZnO/SnO₂/ZnO multi–layer, ZnO/SnO₂/ZnO triple layer and ZnO single layer films have been deposited on glass substrate by sol–gel dip–coating technique. The structural and optical properties of thin films have been investigated by X-ray diffractometer, UV–visible, photoluminescence spectroscopies and scanning electron microscopy. The structural analysis reveals structural inhomogeneities and different crystallite growth processes as function of number of deposited layers. A comparison between photocatalytic activity of zinc oxide samples toward photodegradation of phenol, 4-aminophenol and 4-nitrophenol has been performed under UV light irradiation. Experiments were conducted to study the effects of operational parameters on the degradation rate. Pseudo-first-order photodegradation kinetics was observed on all films and the reaction constants were determined. The results showed that the photocatalytic activity of ZnO multi–layer film was superior to that of the ZnO single- and triple-layer films. Differences in film efficiencies can be attributed to differences in crystallinity, surface morphology, defect concentration of oxygen vacancy and to presence of SnO₂ sublayer that may act as trap for electrons generated in the ZnO layer thus preventing electron–hole recombination. The results reveal that SnO₂ hetrojunction layers improve crystalline quality, optical and photocatalytic properties of ZnO multilayered films.     

CdO as the archetypical transparent conducting oxide. Systematics of dopant ionic radius and electronic structure effects on charge transport and band structure

A series of yttrium-doped CdO (CYO) thin films have been grown on both amorphous glass and single-crystal MgO(100) substrates at 410 degrees C by metal-organic chemical vapor deposition (MOCVD), and their phase structure, microstructure, electrical, and optical properties have been investigated. XRD data reveal that all as-deposited CYO thin films are phase-pure and polycrystalline, with features assignable to a cubic CdO-type crystal structure. Epitaxial films grown on single-crystal MgO(100) exhibit biaxial, highly textured microstructures. These as-deposited CYO thin films exhibit excellent optical transparency, with an average transmittance of >80% in the visible range. Y doping widens the optical band gap from 2.86 to 3.27 eV via a Burstein-Moss shift. Room temperature thin film conductivities of 8,540 and 17,800 S/cm on glass and MgO(100), respectively, are obtained at an optimum Y doping level of 1.2-1.3%. Finally, electronic band structure calculations are carried out to systematically compare the structural, electronic, and optical properties of the In-, Sc-, and Y-doped CdO systems. Both experimental and theoretical results reveal that dopant ionic radius and electronic structure have a significant influence on the CdO-based TCO crystal and band structure: (1) lattice parameters contract as a function of dopant ionic radii in the order Y (1.09 A) < In (0.94 A) < Sc (0.89 A); (2) the carrier mobilities and doping efficiencies decrease in the order In > Y > Sc; (3) the dopant d state has substantial influence on the position and width of the s-based conduction band, which ultimately determines the intrinsic charge transport characteristics.     

Photoelectrochemical performance of dye and semiconductor sensitization on 1-D hollow hexagonal ZnO rods: A comparative study

One-dimensional hollow hexagonal ZnO rods (1-D HHZRs) were grown onto the SnO₂: F (FTO) coated glass substrates by using two-step deposition techniques. Initially, the ZnO seed layer was coated onto the FTO which was followed by hydrothermal route in order to grow 1-D HHZRs. These 1-D HHZRs were decorated with Eosin-Y dye and CdS semiconductor nanoparticles (NPs) by using a chemical routes like dip coating and successive ionic layer absorption reaction (SILAR) technique, respectively to improve its photoelectrochemical (PEC) performance. The structural, morphological, optical and electrochemical characterizations of the thin films were analyzed by various sophisticated instruments. X-ray diffraction (XRD) pattern corroborated the phase formation of ZnO and CdS with the hexagonal and cubic crystal structure, respectively. 1-D HHZRs films were obtained by scanning electron microscopy (SEM) with rod diameter of about 1.47 μm. Furthermore, SEM image clearly showed the CdS NPs covered 1-D HHZRs. The direct optical bandgap energy of the samples were estimated to be 3.28, 3.24 and 3.03 eV. CdS NPs-sensitized 1-D HHZRs samples showed hydrophilic nature for water contact angle, which is advantageous for the better improvement in the PEC performance as compared with pristine and dye-sensitized 1-D HHZRs.     

Synthesis and characterization of chemically grown electrochromic tungsten oxide

Tungsten oxide thin films, which are cathodic coloration materials that are used in electrochromic devices, were prepared by a chemical growth method and their electrochromic properties were investigated. The thin films of WO₃ were deposited onto electrically conducting substrates: fluorine doped tin oxide coated glass (FTO) with sheet resistance of about 10 Ω/cm. Transparent, uniform and strongly adherent thin film samples of WO₃ were studied for their structural, morphological, optical and electrochromic properties. The XRD data confirmed the monoclinic crystal structure of WO₃ thin films. The direct band gap Eg for the films was found to be 2.95 eV which is good for electrochromic device application. The electrochromism of WO₃ thin film was evaluated in 0.5 M LiClO₄/propylene carbonate for Li⁺ intercalation. Electrochromic properties of WO₃ thin films were studied with the help of Cyclic Voltammetry (CV), Chronoamperometry (CA) and Chronocoulometry (CC) techniques.     

The influence of various deposition techniques on the photoelectrochemical properties of the titanium dioxide thin film

Thin sol–gel TiO₂ layers deposited on the conductive ITO glass by means of three various deposition techniques (dip-coating, inkjet printing and spray-coating) were used as photoanode in the three-compartment electrochemical cell. The thin TiO₂ films were treated at 450 °C and after calcination all samples possessed the crystallographic form of anatase. The relationship between surface structure and photo-induced conductivity of the nanostructured layers was investigated. It was found that the used deposition method significantly influenced the structural properties of prepared layers; mainly, the formation of defects and their quantity in the prepared films. The surface properties of the calcined layers were determined by XRD, Raman spectroscopy, SEM, AFM, UV–Vis analyses and by the optical microscopy. The photo-induced properties of nanoparticulate TiO₂/ITO photoanode were studied by electrochemical measurements combined with UV irradiation.     

Effects of ZnO Buffer Layer Thickness on Properties of MgxZn1-xO Thin Films Deposited by MOCVD

High-quality MgxZn1-xO thin films were grown on sapphire（0001 ） substrates with a ZnO buffer layer of different thicknesses by means of metal-organic chemical vapor deposition. Diethyl zinc, bis-cyclopentadienyl-Mg and oxygen were used as the precursor materials. The crystalline quality, surface morphologies and optical properties of the Mg, Zn1-xO films were investigated by X-ray diffraction, atomic force microscopy and photoluminescence spectrometry. It was shown that the quality of the MgxZn1-xO thin films depends on the thickness of the ZnO buffer layer and an Mg, Zn1-xO thin film with a ZnO buffer layer whose thickness was 20 nm exhibited the best crystal-quality, optical properties and a flat and dense surface.     

Facile synthesis of spray pyrolyzed ZnO/NiO nanocomposites thin films

Abstract

This study reviews ZnO, NiO, and ZnO/NiO nanocomposites thin films deposition using the Spray Pyrolysis Technique (S.P.T). The thin films were deposited onto ordinary glass substrates heated at 500?°C from aqueous solutions of zinc chloride and nickel chloride precursors dissolved in distilled water. The structural, morphological, and optical properties of the ZnO, NiO, and ZnO/NiO thin films have been studied by X-ray diffraction, scanning electron microscopy, Raman spectroscopies, and so on. The optical band gaps are 3.3 and 3.5?eV for ZnO and NiO thin films, respectively obtained by UV–Vis spectroscopy. However, the optical band gaps of ZnO/NiO nanocomposites thin films, are noticeable out of the range (3.4–3.64?eV).     

Characterization of CuInS2 Thin Films with Different Cu/In Ratio

Thin films of CuInS₂ were grown on glass substrate by successive ionic layer adsorption and reaction method with different [Cu]/[In] ratios and annealed at 400 °C for 30 min. The crystal structure and grain sizes of the thin films were characterized by X-ray diffraction method. Atomic force microscopy was used to determine surface morphology of the films. Optical and electrical properties of these films were investigated as a function of [Cu]/[In]ratios. The electrical resistivity of CuInS₂ of thin films was determined using a direct current-two probe method in the temperature range of 300—470 K. It is observed that, the electrical resistivity values show a big decreasing with increasing [Cu]/[In] ratio. Hence, the [Cu]/[In] ratio in the solution can drastically affect the structural, electrical, and optical properties of thin films of CuInS₂.     

Formation,densification and properties of sol–gel TiO<Subscript>2</Subscript> films prepared from triethanolamine-chelated soluble precursor powders

Amorphous, soluble powders were synthesized with triethanolamine (TEA) as chelating agent as precursors for TiO₂ sol–gel solutions. Dip coating on glass substrates and subsequent annealing yielded thin films with excellent optical properties. Furthermore as-dried films were scraped of substrates, annealed at different temperatures and characterized in order to investigate the structural changes during processing. The observations were systematically compared with previous studies on precursor powders based on acetylacetone. Results indicate that triethanolamine provides both a sufficient hydrolytical stability of the Ti-precursor during coating and an adequate plasticity of the film material throughout thermal densification. These characteristics significantly improve the practical workability of the respective process. Additionally former assumptions regarding the relationship between film properties and intermediate structural features were verified and refined.     

Scalable Production of Ambient Stable Hybrid Bismuth-Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films**

Large homogeneous and adherent coatings of phenethylammonium bismuth iodide were produced using the cost-effective and scalable aerosol-assisted chemical vapor deposition (AACVD) methodology. The film morphology was found to depend on the deposition conditions and substrates, resulting in different optical properties to those reported from their spin-coated counterparts. Optoelectronic characterization revealed band bending effects occurring between the hybrid material and semiconducting substrates (TiO₂ and FTO) due to heterojunction formation, and the optical bandgap of the hybrid material was calculated from UV-visible and PL spectrometry to be 2.05 eV. Maximum values for hydrophobicity and crystallographic preferential orientation were observed for films deposited on FTO/glass substrates, closely followed by values from films deposited on TiO₂/glass substrates.     

Indium selenide thin film preparation by sol–gel technique

Preparation and characterization of In–Se compound thin films prepared by sol–gel methods on glass substrate have been studied. X-ray diffraction analyses and optical transmission spectrum of In–Se compound thin film samples show that the fabricated sol–gel In–Se thin films features formed mainly as an In₂Se₃ crystal structure. From transmission spectra of In–Se thin films band gap energy were estimated approximately as ∼1.24 eV.