Physical and electrical properties of polyimide/ceramic hybrid films prepared via non-hydrolytic sol–gel process

In this study, TiO₂ and SiO₂ were chosen as ceramic fillers in the 3,3′,4,4′-benzophenone tetracarboxylic dianhydride–4,4′-oxydianiline (BTDA–ODA) polyimide matrix. Physical properties of hybrids with up to 30 wt% SiO₂ and 7 wt% TiO₂ were evaluated and discussed. Nano-size ceramic particles were prepared by non-hydrolytic sol–gel (NHSG) process. SEM micrographs show that both films have nano-sized ceramic particles with a narrow size distribution. Thermal conductivities of the hybrids increase from 0.12 to 0.21 W/m-K, as the SiO₂ and TiO₂ in the hybrid increases from 0 to 30 and 7 wt%, respectively. Electrical surface resistivity slightly decreases with increasing ceramic filler content. Dielectric constant of the hybrid increases from 2.45 to 2.72 with the incorporation of the 7 wt% (5.4 vol%) TiO₂. Water absorption decreases considerably with increasing filler content. With 30 wt% (20.2 vol%) SiO₂ addition, the water absorption of the hybrid film reduces by 85% from that of pure polyimide.     

Effect of stabilizer on optical and structural properties of MgO thin films prepared by sol–gel method

The effects of monoethanolamine (MEA) and acetylacetone (ACAC) addition as stabilizer on the crystallization behaviour, morphology and optical properties of magnesium oxide were investigated using thermogravimetry (TG/DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. Stabilizer addition reduces transparency of the films. MgO films prepared at 500 °C showed weak orientation of (200). However, the films prepared by addition of stabilizer are amorphous. MgO powders were prepared for exhibiting the structural properties. The patterns of MgO powders showed a preferred orientation of (200). The addition of stabilizer causes a reduction in grain size. SEM micrographs show that a homogenous and crack-free film can be prepared at 500 °C and addition of stabilizer causes an increase in packing density.     

Effect of Zn doping on structure and ferroelectric properties of PST thin films prepared by sol–gel method

(Pb _y Sr_1−y )Zn _x Ti_1−x O_3−x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology and ferroelectric property of the thin film were studied. All the thin films show the typical perovskite phase structure. Both the crystallinity and c/a ratio of the perovskite phase increases initially and then decreases gradually with doping Zn in the thin film. Ferroelectric properties of the Zn-doped PST thin films, including ferroelectric hysteresis-loop, remnant polarization and coercive force, decrease gradually with increasing Zn. And the effect of Zn on ferroelectric properties is more obvious in PST thin film with high content of Pb than that with low Pb although the high lead thin film exhibits high intrinsic ferroelectric properties.     

Photoconductive properties of TiO2 films prepared by the sol–gel method and its application

The Photoconductive characteristics of TiO2 films prepared by the sol-gel method, and the photovoltaic characteristics fabricated with the resulting TiO2 film and phthalocyanine nickel (NiPc) are investigated. For a TiO2 film with hydroxypropyl cellulose (Hpc) heat treated at 500°C for 10 min, the relative sensitivity is about ten times higher than that without Hpc. A space-charge-limited current is observed in the dark current–voltage characteristic of the TiO2 film with Hpc. It is found that the TiO2 film with Hpc has a photosensitizing effect. The photovoltaic characteristics of TiO2(Hpc)/NiPc are as follows: the short-circuit current density, Jsc is 5.6×10-7 A cm-2, the open-circuit voltage, Voc is 0.24 V, the fill factor (F.F) is 0.64 and the power conversion efficiency, is 0.73. Furthermore, the carrier transport mechanisms of the TiO2(Hpc)/NiPc photovoltaic cell are discussed.     

Effect of temperature on dielectric and electrical properties of Co–Zr doped barium hexaferrites prepared by sol–gel method

In the present research, temperature dependence of dielectric properties of cobalt–zirconium substituted barium hexaferrites, fabricated using citric acid sol gel method, has been reported. The dielectric constant, loss tangent and A.C. conductivity were investigated on the circular pellets in temperature range 30–350 °C and frequency range 10 kHz–1 MHz using impedance analyzer. This paper also presents impedance (Z*) and electric modulus (M*) analysis of all the samples. The single semi-circular arcs, observed in impedance Nyquist plots, suggest the dominance of grain boundaries in the conduction process. Dielectric constant and dielectric loss tangent show very small variation up to 200–250 °C temperature and abrupt increase afterwards up to 350 °C. Thus, these ferrites can be successfully implemented in the practical applications like capacitors, microwave devices etc. up to 250 °C, without any significant change in properties.     

Enhanced electrical properties of PZT thick films prepared by sol–gel technique through step-by-step crystallization process

[Pb(Zr_xTi_1-x)O₃: PZT] films at morphotropic phase boundary composition (x = 0.52) were deposited on bare Si, ZrO₂/Si and Pt/Ti/SiO₂/Si substrates by sol–gel spin on technique. Films deposited on the bare Si and ZrO₂/Si substrates had low degree of crystallization and micro cracks. Well crystallized films with smooth microstructure were obtained on Pt/Ti/SiO₂/Si substrates. Further, the thickness of the films on Pt/Ti/SiO₂/Si substrate was increased up to ~1 μm by step-by-step crystallization process. The single perovskite phase of the above films was confirmed with X-ray diffraction analysis. Films had enhanced dielectric properties at room temperature and the dielectric constant values were comparable to those of bulk values at Curie temperature (T_c) from the temperature dependent dielectric measurements. Films exhibit higher remnant polarization (P_r) and lower coercive field (E_c) values. Further, capacitance–voltage (C–V), current–voltage (I–V) measurements and rough estimation of piezoelectric coefficient of the films were carried out.     

Influence of pH on ZnO nanocrystalline thin films prepared by sol–gel dip coating method

ZnO nanocrystalline thin films have been prepared on glass substrates by sol?Cgel dip coating method. ZnO thin films have been coated at room temperature and at four different pH values of 4, 6, 8 and 10. The X-ray diffraction pattern showed that ZnO nanocrystalline thin films are of hexagonal structure and the grain size was found to be in the range of 25?C45?nm. Scanning electron microscopic images show that the surface morphology improves with increase of pH values. TEM analysis reveals formation of ZnO nanocrystalline with an average grain size of 44?nm. The compositional analysis results show that Zn and O are present in the sample. Optical band studies show that the films are highly transparent and exhibit a direct bandgap. The bandgap has been found to lie in the range of 3 $\boldsymbol\cdot$ 14?C3 $\boldsymbol\cdot$ 32?eV depending on pH suggesting the formation of ZnO nanocrystalline thin films.     

The effects of solvents on the highly oriented ZnO films prepared using sol–gel method

The effects of solvents in ZnO precursor solutions on highly oriented ZnO films is studied in this work. Three different solvents, including ethanol, isopropanol and 2-methoxyethanol, are used for the preparation of ZnO film on fused quartz wafer substrates in this study. The structural properties of ZnO films are investigated by X-ray diffraction and scanning electron microscopy analysis. It is found that ZnO film formed using 2-methoxyethanol precursor solution shows a strong preferred orientation and has the smoothest surface among the films. The properties of ZnO sol solutions are also studied using the thermal gravimetric-differential thermal analysis and ultraviolet–visible spectroscopy. The absorbance spectrum of the sol using 2-methoxyethanol as solvent shows an apparent ZnO absorbance edge while the others do not, which means ZnO nano-particles are formed in the sol. The mechanism of the formation of highly oriented ZnO films using different solvents is also discussed in this paper.     

Optical properties and electrical resistivity of boron-doped ZnO thin films grown by sol–gel dip-coating method

Sol–gel dip-coating was used to grow ZnO thin films doped with various concentrations of B ranging from 0 to 2.5 at.% on quartz substrates. The effects of B doping on the absorption coefficient (α), optical band gap (E_g), Urbach energy (E_U), refractive index (n), refractive index at infinite wavelength (n_∞), extinction coefficient (k), single-oscillator energy (E_o), dispersion energy (E_d), average oscillator strength (S_o), average oscillator wavelength (λ_o), moments M₋₁ and M₋₃, dielectric constant (ε), optical conductivity (σ), and electrical resistivity (ρ) of the BZO thin films were investigated. The transmittance spectra of the ZnO and BZO thin films show that the transmittance of the BZO thin films was significantly higher than that of the ZnO thin films in the visible region of the spectrum and that the absorption edge of the BZO thin films was blue-shifted. The BZO thin films exhibited higher E_g, E_U, and E_o and lower E_d, λ_o, M₋₁ and M₋₃ moments, S_o, n_∞, and ρ than the ZnO thin films.     

Effect of solution concentration on the structural, optical and conductive properties of ZnO thin films prepared by sol–gel method

ZnO thin films with different solution concentrations (0.1–0.9 mol/L) were prepared by a simple sol–gel dip-coating technique. X-ray diffraction, ultraviolet–visible spectroscopy, Hall effect measurements and photoluminescence (PL) spectroscopy were employed to investigate the effect of solution concentration on the structural,optical and electrical conductive properties of the ZnO thin films. The results showed that the ZnO thin films preferentially oriented along the (002) direction at higher solution concentration. The careful study of the optical and electrical conductive properties showed that the resistivity decreased monotonously, while the transmittance increased first and then decreased when solution concentrations changed from 0.1 to 0.9 mol/L. Photoluminescence spectra indicated that the defect-related blue emission was increased with the enhancement of solution concentration. The mechanism of the blue emission, and the reasons why high solution concentration was favorable for forming high c-axis oriented ZnO thin films and obtaining low resistivity were also discussed in detail.     

Structure and ferroelectric properties of barium titanate films synthesized by sol–gel method

The barium strontium titanate (Ba_0.7Sr_0.3TiO₃, BST) thin films were synthesized by a sol–gel technique on a silicon nanoporous pillar array (Si-NPA) substrate. SEM observation reveals that the as-prepared BST thin film has uniformly covered the inherited pillar-like surface of the Si-NPA substrate. X-ray diffraction analysis indicates that the perovskite phase was able to be generated in the BST film when the annealing temperature was higher than 600 °C. The remnant polarization (Pr) and coercive field (Ec) values were also found to increase with the annealing temperature, with the maxima of 4.57 μC cm⁻² for Pr and 7.61 kV mm⁻¹ for Ec at 800 °C, respectively. The measurement of leakage current density against voltage applied suggested that the BST films are excellent insulators along with fair resistance to breakdown, and the mechanism of leakage current was discussed.     

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.     

The effect of repeated annealing temperature on the structural,optical, and electrical properties of TiO<Subscript>2</Subscript> thin films prepared by dip-coating sol–gel method

In this study, we have studied the effect of repeated annealing temperatures on TiO₂ thin films prepared by dip-coating sol–gel method onto the glasses and silicon substrates. The TiO₂ thin films coated samples were repeatedly annealed in the air at temperatures 100, 200, and 300 °C for 5 min period. The dipping processes were repeated 5 to 10 times in order to increase the thickness of the films and then the TiO₂ thin films were annealed at a fixed temperature of 500 °C for 1 h period. The effect of repeated annealing temperature on the TiO₂ thin films prepared on glass substrate were investigated by means of UV–VIS spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). It was observed that the thickness, average crystallite size, and average grain size of TiO₂ samples decreased with increasing pre-heating temperature. On the other hand, thickness, average crystallite size, and average grain size of TiO₂ films were increased with increasing number of the layer. Al/TiO₂/p-Si metal–insulator–semiconductor (MIS) structures were obtained from the films prepared on p-type single silicon wafer substrate. Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the prepared MIS structures were conducted at room temperature. Series resistance (R _s) and oxide capacitance (C _ox) of each structures were determined by means of the C–V curves.