Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO₃)₃.9H₂O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al₂O₃). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.     

Characterization of low-temperature solution-processed indium–zinc oxide semiconductor thin films by KrF excimer laser annealing

We have employed KrF excimer laser annealing (ELA) treatment on sol–gel derived indium–zinc oxide (IZO) precursor films to develop a method of low thermal-budget processing. As-coated IZO sol–gel film was dried at 150 °C and then annealed using KrF excimer laser irradiation under ambient air. The laser irradiation energy density was adjusted to 150, 250, 350, and 450 mJ/cm² to investigate the effects of laser irradiation energy density on the microstructure, surface morphology, optical transmittance, and electrical properties of laser annealed IZO thin films. Results of GIXRD and TEM-SAED indicated that the ELA IZO thin films had an amorphous phase structure. The surface characteristics and electrical properties of laser annealed IZO thin films were significantly affected by the laser irradiation energy density. It was found that the dried IZO sol–gel films irradiated with a laser energy density of 350 mJ/cm² exhibited the flattest surface, the highest average optical transmittance in the visible region, and the best electrical properties among all ELA samples.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Synthesis and dielectric properties of polyaniline/titanium dioxide nanocomposites

Two series of polyaniline–TiO₂ nanocomposite materials were prepared in base form by in situ polymerization of aniline with inorganic fillers using TiO₂ nanoparticles (P25) and TiO₂ colloids (Hombikat), respectively. The effect of particle sizes and contents of TiO₂ materials on their dielectric properties was evaluated. The as-synthesized polyaniline–TiO₂ nanocomposite materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermal analysis (DTA/TGA), and X-ray diffraction (XRD). Dielectric properties of polyaniline–TiO₂ nanocomposites in the form of films were measured at 1 KHz–1 MHz and a temperature range of 35–150 °C. Higher dielectric constants and dielectric losses of polyaniline–TiO₂ nanocomposites than those of neat PANI were found. PANI–TiO₂ nanocomposites derived from P25 exhibited higher dielectric constants and losses than those from Hombikat TiO₂ colloids. Electrical conductivity measurements indicate that the conductivity of nanocomposites is increased with TiO₂ content. The dielectric properties and conductivities are considered to be enhanced due to the addition of TiO₂, which might induce the formation of a more efficient network for charge transport in the base polyaniline matrix.     

p-Type and n-type Cu2O semiconductor thin films: Controllable preparation by simple solvothermal method and photoelectrochemical properties

p-Type and n-type Cu₂O thin films were controllably prepared using a simple solvothermal method by adjusting pH value of the copper (II) acetate aqueous solution. Photoelectrochemical experiments show that the Cu₂O thin films synthesized in acid and alkaline (or neutral) media present n-type and p-type semiconductor character, respectively. Moreover, the films prepared at pH 5 have the best photoelectrochemical properties. The mechanism for the formation of these p-type and n-type Cu₂O films is discussed. The Cu₂O p–n homojunction fabricated in this study shows typical p–n junction character. This facile preparation method may be a promising way to prepare p–n homojunctions for semiconductor devices.     

Giant dielectric permittivity and non-linear electrical behavior in CaCu3Ti4O12 varistors from the molten-salt synthesized powder

CaCu₃Ti₄O₁₂ (CCTO) powder has been prepared by a molten salt method using the NaCl–KCl mixture. Crystal structure and microstructure of the powder and the resulting ceramics have been characterized by using X-ray diffraction (XRD) and scanning electron microcopy (SEM). Impedance analyzer and current–voltage meter were employed to analyze dielectric and nonlinear (I–V) properties of the CCTO ceramics with different sintering durations and subsequent cooling rates. The values of dielectric permittivity and nonlinear coefficient of the quenched sample were found to be higher than those of the slowly cooled sample. More specifically, the cooling methods (quenching and furnace-cooling) have allowed to adjust; (?) the breakdown voltage within a rather low range of 0.3–4.4 kV cm⁻¹; (??) the nonlinear coefficient between 2 and 6 and (???) the giant dielectric permittivity for the ceramics within a range from 5000 to 20000. A double Schottky barrier can be evidenced from the linear behavior between the ln J and E^1/2 in grain boundary regions. The relationship between the electrical current density and the applied electrical field indicates that the potential barrier height Φ_B is holding time dependent.     

Spark plasma sintering technique for reaction sintering of Al2O3/Ni nanocomposite and its mechanical properties

Al₂O₃/Ni nanocomposites were prepared by spark plasma sintering (SPS) using reaction sintering method and the mechanical properties of the obtained nanocomposites are reported. The starting materials of Al₂O₃–NiO solid solution were synthesized from aluminum sulfate and nickel sulfate. These Al₂O₃–NiO powders were changed into Al₂O₃ and Ni phases during sintering process. The obtained nanocomposites showed high relative densities (>98%). SEM micrographs showed homogeneously dispersed Ni grains in the matrix. The 3-point strength and the fracture toughness of the composites significantly improved from 450 MPa in the monolithic α-Al₂O₃ to 766 MPa in the 10 mol% (2.8 vol.%) Ni nanocomposite and from 3.7 to 5.6 MPa m^1/2 in 13 mol% (3.7 vol.%) Ni nanocomposite. On the other hand, Young's modulus and Vickers hardness of the nanocomposites were mostly same as those of the monolithic α-Al₂O₃.     

The investigation on electrochemical reaction mechanism of CuF2 thin film with lithium

Crystalline CuF₂ thin films were prepared by pulsed laser deposition under room temperature. The physical and electrochemical properties of the as-deposited thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic cycling and cyclic voltammetry (CV). Reversible capacity of 544 mAh g⁻¹ was achieved in the potential range of 1.0–4.0 V. A reversible couple of redox peaks at 3.0 V and 3.7 V was firstly observed. By using ex situ XRD and TEM techniques, an insertion process followed by a fully conversion reaction to Cu and LiF was revealed in the lithium electrochemical reaction of CuF₂ thin film electrode. The reversible insertion reaction above 2.8 V could provide a capacity of about 125 mAh g⁻¹, which makes CuF₂ a potential cathode material for rechargeable lithium batteries.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

Colour performance investigation of a Cr2O3 green pigment prepared via the thermal decomposition of CrOOH

In this study, Cr₂O₃ green pigments were prepared using two types of CrOOH, α-CrOOH and γ-CrOOH, and the resulting pigments were characterised. The thermal decomposition behaviours of the two types of synthesised CrOOH were discussed. The resulting Cr₂O₃ pigments were characterised using X-ray diffraction (XRD), scanning electron microscope (SEM), International Commission on Illumination (CIE-L^?a^?b^?) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The key factors and mechanism that influenced the preparation of the Cr₂O₃ green pigments were studied. The results revealed that γ-CrOOH produces Cr₂O₃ that is more homogeneous, has a uniform size of 200–400 nm and a yellowish-green colour compared to α-CrOOH, which produces Cr₂O₃ with non-uniform sizes and a brownish-green colour. In addition to the different particle morphologies and sizes, the change in the crystal field, which leads to a shift in the ⁴A_2g→⁴T_1g and ⁴A_2g→²T_2g transition, also affects the colour of the pigment. Lastly, a series of Cr₂O₃ green pigments displaying a wide range of colours were prepared by calcining mixtures of α-CrOOH and γ-CrOOH with different compositions.     

Rapid deposition of YBCO films by laser CVD and effect of lattice mismatch on their epitaxial growth and critical temperature

a-Axis- and c-axis-oriented YBa₂Cu₃O_7–δ (YBCO) films were grown on (100) SrTiO₃ substrate by laser chemical vapour deposition (laser CVD). The effect of lattice mismatch between films and substrates on in-plane and out-of-plane crystallinity and critical temperature (T_C) was investigated. The preferred orientation changed from a-axis to c-axis as the deposition temperature increased from 928 to 1049 K. The c-axis-oriented YBCO showed a minimum of full width at half maximum of 0.5° for the ω-scan and 1.0° for the φ-scan. A smaller mismatch between YBCO films and substrates led a higher crystallinity for in-plane and out-of-plane epitaxial growths. A high T_C of 90 K was obtained for the c-axis-oriented YBCO films. The deposition rate of the YBCO films was 58–101 μm h⁻¹, approximately 60–1000 times higher than that of conventional CVD.     

Lightwave irradiation-assisted low-temperature solution synthesis of indium-tin-oxide transparent conductive films

Transparent conductive oxide (TCO) films have important applications in many areas. Unfortunately, TCOs are usually fabricated using vacuum and high-temperature methods, preventing them from applications in low-cost flexible devices. In this paper, facile low-temperature sol-gel method is described that can be used to fabricate high-quality TCO films. This study uses lightwave (LW) irradiation (at ～280 °C) with indium-tin-oxide (ITO) as a typical example. Both structure and key properties of ITO films are investigated for different LW irradiation conditions. ITO can be formed via LW irradiation after a period as short as 5 min. Furthermore, it is found that LW irradiation can promote the formation of M ? O framework, effectively remove Cl impurities, and facilitate the elimination of hydroxyl oxygen defects - even at temperatures as low as ～280 °C. The optimal ITO films show excellent electronic properties, including low sheet-resistance (14.5 Ω·sq^?1) and high conductivity (1.7 × 10³ S cm^?1). Moreover, ITO films also show high transmittance (above 87%). Overall, our ITO films have a figure of merit (FOM) of 1.72 × 10^?2 Ω^?1, which is comparable to (or higher than) those of previous ITO films that were produced using conventional vacuum and high-temperature methods. Our LW irradiation method provides facile and effective approach to produce high-performance TCO films at remarkably low cost. This means these films could be used in affordable flexible large-area devices.     

Electropolymerization of a poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes counter electrode for dye-sensitized solar cells and characterization of its performance

Composite films of poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes (PEDOT–MWCNT) were fabricated by a simple oxidative electropolymerization method. These films were formed on fluorine-doped, tin oxide, glass substrates as counter electrodes (CEs) of platinum-free, dye-sensitized solar cells (DSSCs). The surface morphology, formation mechanism and electrochemical nature of PEDOT–MWCNT films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The SEM and AFM images showed that PEDOT–MWCNT films were more porous than PEDOT films. CV and AC impedance spectroscopy revealed that the PEDOT–MWCNT electrode had higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction and a smaller charge transfer resistance than the PEDOT electrodes. The energy conversion efficiency of the DSSC with a PEDOT–MWCNT CE was 13.0% higher than with a PEDOT CE using the same conditions with a ruthenium sensitizer.     

Micro-EIS of anodic thin oxide films on titanium for capacitor applications

The present work focuses on the investigation of the effect of the different crystallographic orientation of titanium grains on the formation of anodic oxide films and consequently their dielectric and semiconductive properties. By using a microcapillary cell the formation process and the electrochemical impedance spectroscopy (EIS) can be performed at high lateral resolution on variously orientated single grains of polycrystalline titanium. The oxide films were potentiodynamically formed by cyclovoltammetry. EIS measurements immediately followed by the oxide formation were used for a detailed investigation of the film properties, in particular, the relative permittivity ?_r and the donor concentration N_D. In contrast to the most publications it was found that under the chosen conditions the crystallographic orientation of titanium substrate has no significant influence on the oxide thickness d, the relative permittivity ?_r or on the donor concentration N_D of the oxide films. The relative permittivity ?_r is approximately 50. The donor concentration depends on the film thickness and amounts to approximately 3 × 10¹⁸ cm⁻³ in minimum.     

Performance enhancement of dye-sensitized solar cells using nanostructural TiO2 films prepared by a graft polymerization and sol–gel process

Nanostructural TiO₂ films with large surface areas were prepared by the combined process of graft polymerization and sol–gel for use in dye-sensitized solar cells (DSSCs). The surface of the TiO₂ nanoparticles was first graft polymerized with photodegradable poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP), after which the particles were deposited onto a conducting glass. The PMMA chains were removed from the TiO₂ films by UV irradiation to generate secondary pores, into which titanium isopropoxide (TTIP) was infiltrated. The TTIP was then converted into small TiO₂ particles by calcination at 450 °C, as characterized by energy-filtering transmission electron microscopy (EF-TEM) and field emission scanning electron microscopy (FE-SEM). The nanostructural TiO₂ films were used as a photoelectrode in solid-state DSSCs; the energy conversion efficiency was 5.1% at 100 mW/cm², which was higher than the values achieved by the pristine TiO₂ (3.8%) and nongrafted TiO₂/TTIP photoelectrodes (3.3%). This performance enhancement is primarily due to the increased surface area and pore volume of TiO₂ films, as revealed by the N₂ adsorption–desorption isotherm.     

Structural,electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess

Pure polycrystalline Bi_1−xSm_xFeO₃ (BSFO) (x=0–0.12) thin films were successfully prepared on FTO/glass substrates by the sol–gel method. The influence of Sm doping on the structure, dielectric, leakage current, ferroelectric and ferromagnetic properties of the BSFO films was investigated. X-ray diffraction analysis and FE-SEM images both reveal a gradual rhombohedra to pseudo-tetragonal phase transition with the increase of Sm dopant content. On one hand, a proper amount of Sm doping can decrease the leakage current densities of the BSFO thin films. On the other hand, excess Sm substitution for Bi will lead to multiphase coexistence in the film, the lattice inhomogeneity results in more defects in the film, which can increase the leakage current density. The result shows that defects in the complexes lead to electric domain back-switching in the BSFO_x=0.06 thin film, resulting in a decreased dielectric constant, leakage current and remanent polarization. The BSFO_x=0.09 thin film is promising in practical application because of its highest dielectric constant, remanent polarization and remanent magnetization of 203–185, 70 μC/cm² and 1.31 emu/cm³, respectively.     

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

In this paper the dielectric properties of crack‐free, Bi₁₂SiO₂₀ thin films were investigated. The films were prepared on Pt/TiO₂/SiO₂/Si and corundum substrates using the sol–gel method. The formation of a pure Bi₁₂SiO₂₀ phase was observed at a temperature of 700°C. The Bi₁₂SiO₂₀ thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness (R_a) of 50 nm. The dielectric properties of the film were characterized by using both low‐ and microwave‐frequency measurement techniques. The low‐frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10^?3, respectively. The thin‐film dielectric properties at the microwave frequency were measured using the split‐post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10^?3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10^?3, respectively.     

Effects of electron-beam irradiation,a thin-Ti layer,and a BeO additive on the diffusion of titanium in synthetic sapphire

Titanium was allowed to diffuse into synthetic sapphire (α-Al₂O₃) at 1773–1923 K for 200 h in air. Specimens were prepared by four different methods. Samples were irradiated with a 10 MeV electron beam to fluencies of 2×10¹⁷ cm⁻² for 1 h to induce vacancy formation. A 1-μm layer of titanium was sputtered onto sapphire samples to provide intimate contact with the diffusing elements. Ti diffusion was performed using TiO₂ powder or a mixture of TiO₂ and BeO powders in a ratio of 95:5 to take advantage of the beryllium activity. Ti diffusion was profiled using scanning electron microscope-energy dispersive X-ray spectrometry (SEM–EDX). The diffusion coefficients of Ti were as follows:     

Aloe vera gel: a new thickening agent for pigment printing

An attempt was made to print cotton fabric with pigments using a new thickening agent based on Aloe vera gel in combination with sodium alginate. The results were compared with the standard conventional printing recipe containing synthetic thickener, and a favourable effect of Aloe vera introduction was achieved. The results show that the properties of the printed fabric (sharpness, colour yield, overall fastness properties, softness, and water vapour transmission) are dependent on the percentage of Aloe vera gel in the thickener combination, the concentration of printing auxiliaries, and the curing conditions. Optimal printing properties were achieved by using a printing paste containing 80% Aloe vera/20% sodium alginate (700 g kg^?1), pigment (50 g kg^?1), binder (145 g kg^?1), fixer (10 g kg^?1), and ammonium sulfate (5 g kg^?1), followed by drying at 85 °C for 5 min and curing at 150 °C for 3 min. The sample printed with the new recipe showed superior rubbing fastness and handle properties, with a slightly lower colour yield, when compared with the sample printed with synthetic thickener. Finally, economic issues arising from synthetic thickener substitution are highlighted.     

Mass transfer kinetics and diffusion coefficient estimation of bioinsecticide terpene ketones in LDPE films obtained by supercritical CO2‐assisted impregnation

Release kinetics of thymoquinone and R ‐(+)‐pulegone impregnated in low‐density polyethylene (LDPE) films into air and the effect of supercritical CO₂‐assisted impregnation process on the diffusional properties of these films were investigated. The incorporation of both ketones into LDPE films was performed under different conditions (pressure, depressurization rate, time, and initial ketone mole fraction). Release experiments were performed under controlled laboratory conditions (24 °C, 60% relative humidity), and the total release profile was determined gravimetrically, while the individual release of each ketone was quantified by Fourier transformed infrared. The experimental data were used to fit a mass transfer model based on the second Fick's law for unsteady‐state diffusion, and the diffusion coefficients of both ketones in LDPE were estimated, ranging from 2.35 × 10^?13 to 5.53 × 10^?13 m² s^?1 (thymoquinone) and from 1.24 × 10^?13 to 4.52 × 10^?13 m² s^?1 (pulegone). Finally, analysis of variance testing indicated that impregnation pressure and depressurization rate (and their combination) have significant effects on the diffusion coefficient values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45558.