Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Sol–gel derived nickel-doped TiO2 films as wear protection coatings

Thin films of pure and Ni-doped TiO₂ were prepared on a glass substrate by sol–gel and spin-coating process from specially formulated ethanol sols. The morphologies of the films surface were observed with atomic force microscope (AFM). The tribological properties of the obtained thin films sliding against steel ball were evaluated on a one-way reciprocating friction tester. AFM results show that by the addition of the Ni in TiO₂, smooth surfaces were obtained. As a result, the Ni-doped TiO₂ films exhibit better wear protection properties than pure TiO₂. The best protection was observed for 5% Ni-doped TiO₂ films in this study.     

PMMA–SiO2 hybrid films as gate dielectric for ZnO based thin-film transistors

In this paper we report a low temperature sol–gel deposition process of PMMA–SiO₂ hybrid films, with variable dielectric properties depending on the composition of the precursor solution, for applications to gate dielectric layers in field-effect thin film transistors (FE-TFT). The hybrid layers were processed by a modified sol–gel route using as precursors Tetraethyl orthosilicate (TEOS) and Methyl methacrylate (MMA), and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. Three types of hybrid films were processed with molar ratios of the precursors in the initial solution 1.0: 0.25, 0.50, 0.75: 1.0 for TEOS: TMSPM: MMA, respectively. The hybrid films were deposited by spin coating of the hybrid precursor solutions onto p-type Si (100) substrates and heat-treated at 90 °C for 24 h. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared Spectroscopy to confirm their hybrid nature. The refractive index of the hybrid films as a function of the TMSPM coupling agent concentration, were determined from a simultaneous analysis of optical reflectance and spectroscopic ellipsometry experimental data. The PMMA–SiO₂ hybrid films were studied as dielectric films using metal-insulator-metal structures. Capacitance–Voltage (C–V) and current–voltage (I–V) electrical methods were used to extract the dielectric properties of the different hybrid layers. The three types of hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA–SiO₂/p-Si with a common bottom gate and patterned Al source/drain contacts, with different channel lengths. We analyzed the output electrical responses of the ZnO-based TFTs to determine their performance parameters as a function of channel length and hybrid gate dielectric layer.     

Sol–gel derived Ag-doped ZnO thin film for UV photodetector with enhanced response

Ultraviolet (UV) photodetectors based on pure zinc oxide (ZnO) and Ag-doped ZnO (Ag:ZnO) thin films with different Ag doping contents (0.05, 0.15, 0.65, 1.30 and 2.20 %) have been prepared by sol–gel technique. Photoresponse characteristics of the prepared detectors have been studied for UV radiation of λ = 365 nm and intensity = 24 μW/cm². The Ag:ZnO thin film-based photodetector having an optimum amount of 0.15 at. wt% Ag dopant exhibits a high photoconductive gain (K = 1.32 × 10³) with relatively fast recovery (T _37 % = 600 ms) and minimal persistence in comparison to other prepared photodetectors. The incorporation of Ag dopant (≤0.15 %) at Zn lattice sites (Ag_zn) in ZnO creates acceptor levels in the forbidden gap, thereby reducing the value of dark current. Upon illumination with UV radiation, the photogenerated holes recombine with the captured electrons at the Ag_zn sites. The photogenerated electrons increase the concentration of conduction electrons, thereby giving an enhanced photoresponse for Ag:ZnO photodetector (0.15 % Ag). At higher dopant concentration (≥0.65 %), Ag incorporated at the interstitial sites of ZnO leads to the formation of deep energy levels below the conduction band along with increase in oxygen-related defects, thereby giving higher values of dark current. The incorporation of Ag at interstitial sites results in degradation of photoresponse along with the appearance of persistence in recovery of the photodetector in the absence of UV radiation.     

Sol–gel and rf sputtered AZO thin films: analysis of oxidation kinetics in harsh environment

Al-doped ZnO (AZO) thin film, which possess the advantages of low cost, low sheet resistance and high transmittance, are one of the most promising candidates to replace indium tin oxide films as the transparent electrode. However, oxidation causes a substantial increase in the sheet resistance of AZO film after exposing in ambient and especially, damp heat environment. In this work, we compare structural, optical, electrical properties and environmental stability between films prepared by two different methods: sol–gel and rf sputtering. Experimental results indicate that the properties of film can be affected by different deposition method. From the X-ray diffraction analysis, all films have hexagonal wurtzite crystal structure with different preferable orientation in two different methods. Optical transmittance spectra of the AZO films exhibited transparency higher than about 80 % within the visible wavelength region and the optical band gap (E_g) of these films was increased in sputtered film, probably due to the increase of carrier concentration. The better environmental stability was found in AZO film prepared by sputtering method. Improved surface morphology and enhancement of crystal orientation (110) was considered for this improvement.     

Orientation-dependent microwave dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel method

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thin films have been prepared on the (100) LaAlO₃ single-crystal substrates by sol–gel technique. The X-ray diffraction study indicated that the thin films exhibited (100) preferred orientation and random orientation depending upon the concentration of precursor solution. The nonlinear dielectric properties of the BST films were measured using an interdigital capacitor. The temperature dependence of dielectric constant of the BST thin films was measured at 1 MHz in the temperature range from ?100 to 80 °C. The Curie temperature T _c of the films derived from 0.1, 0.2 and 0.3 M was found to be ?18.5, ?32.5 and ?39.9 °C, respectively. The tunability of BST films with the (100) preferred orientation was 30.74 %, which was much higher than that of thin films with random orientation at the frequency of 10 kHz with an applied electric field of 80 kV/cm. The microwave dielectric properties of the BST thin films were measured by a vector network analyser from 1 to 10 GHz.     

Preparation of nanocrystalline nickel oxide thin films by sol–gel process for hydrogen sensor applications

Preparation of nanocrystalline NiO thin films by sol–gel method and their hydrogen (H₂) sensing properties were investigated. The thin films of NiO were successfully deposited on the glass and SiO₂/Si substrate by a sol–gel coating method. The films were characterized for crystallinity, electrical properties, surface topography and optical properties as a function of calcination temperature and substrate material. It was found that the films produced by this method were polycrystalline and phase pure NiO. The H₂ gas sensitivity of these films was studied as a function of H₂ concentration and calcination temperature. The results indicated that the sol–gel derived NiO films could be used for the fabrication of H₂ gas sensors to monitor low concentration of H₂ in air quantitatively at low temperature range (< 200 °C).     

Single and multiple doping effects of silicon–boron and fluorine on ZnO thin films deposited with sol–gel spin coating technique

Undoped, Si and B single doped, Si–B co-doped and Si–B–F triple doped ZnO thin films were grown by sol–gel spin coating method. Effects of these doping elements on microstructural, morphological and optical properties were investigated. X-ray diffraction studies showed that all films had hexagonal wurtzite structure. Although Si doping increased crystallinity of ZnO, single boron doping, Si–B co-doping and Si–B–F triple doping gave rise to a decreasing in crystallinity. Scanning electron microscope micrographs indicated that the grain size and morphological characters of ZnO depended on doping element type and their concentrations. The micrographs also demonstrated that Si doping deteriorated grain size and their distribution on film surface of ZnO structure. Although single B, doubly Si–B and triple Si–B–F doping at low contents improved grain distribution and film morphology, when their content increased, film morphology started to deteriorate. Optical band gap value of undoped film increased with Si doping irrespective of Si doping content. Although single B, doubly Si–B and triple Si–B–F doping at low contents caused an increase in optical band gap of undoped ZnO, more doping content brought about a decrease in optical band gap. From the optical parameters such as absorption coefficient, the Urbach energy values of the films were calculated by using ln α vs. photon energy graphs. In generally, Urbach energies of the films changed reversely with the band gap energies of the films.     

Effects of Bi doping on dielectric and ferroelectric properties of PLBZT ferroelectric thin films synthesized by sol–gel processing

[Pb _0·95(La_1???y Bi _y ) _0·05][Zr_0·53Ti_0·47]O₃ (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content ${\mathit{y}}$ is not more than 0·4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0·6, the pyrochlore phase appears and the remnant polarization P _r of PLBZT thin films is smaller than that of $\left({Pb}_{{1-x}} {\bf La}_{x}\right)\!\!\left({Zr}_{{1-y}} {Ti}_{y}\right){O}_{3}$ (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.     

Effects of Mg doping on sol–gel derived nanocrystalline hydroxyapatite thin films

Abstract

Both pure and Mg doped thin films were fabricated by sol–gel dip coating. The films were sintered either at 800 or 1000°C. The average grain size of the films was significantly affected by Mg substitution in the hydroxyapatite (HA) structure and change in the sintering temperature. The grains were considerably larger in the films sintered at higher temperatures. In addition, Mg doped films contained significantly larger grains compared to undoped HA films. Mg doping also caused rodlike grains at 800°C, and led to whitlockite (β-TCP) formation at 1000°C. The ratio of the existing phases was estimated as β-TCP/HA=27 : 73. All the films had rough surfaces with high porosity. It was also observed that undoped films had higher surface roughness than Mg doped ones.     

Magnesium metallic interlayer as an oxygen-diffusion-barrier between high-κ dielectric thin films and silicon substrate

The deposition of a thin magnesium metallic interlayer on an Si substrate prior to the deposition of an oxide thin film using rf-sputtering was investigated. The deposition of high-κ HfO₂ thin film was more particularly studied and it was demonstrated that the metallic interlayer acts as an oxygen barrier, preventing the formation of a low-κ layer at the high-κ/Si interface during the deposition. A post-deposition annealing treatment performed on the films induced the diffusion of the metal barrier into the HfO₂ film and allowed obtaining a sharp interface. However, the degree of diffusion depends not only on the interlayer thickness, but also on the thickness of the high-κ film. X-ray photoelectron spectroscopy was used to study the degree of oxidation of the Mg interlayer. High resolution transmission electron microscopy and energy filtered transmission electron microscopy were used to characterize the films and the diffusion of the Mg interlayer into the high-κ film after annealing. In this work we will stress on the engineering of the interface via the diffusion of the Mg interlayer during the growth process and on annealing.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Enhanced breakdown strength of ferroelectric–dielectric multilayered thin films by blocking oxygen vacancies through linear dielectric layer

Journal of Materials Science: Materials in Electronics - In this work, to study the influence of heterogeneous interface on electrical performance and energy storage performance, the A-doped...