Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Synthesis,structure, and optical properties of Au–TiO2 composite thin films

Titanium dioxide (TiO₂) films with varying concentrations of gold particles were synthesized using pulsed DC magnetron sputtering, with the intent to develop infrared reflecting films for use on cars and planes to reduce solar heat load. Under our deposition conditions, the films are smooth (RMS roughness on the order of 1.0–2.0 nm) and consist of rutile TiO₂ with embedded gold. The average gold particle diameter on the sample surface was found to change from 60 to 200 nm as the volume fraction of gold in the films increased from 1.9 to 4.3% (3.5 to 7.9 mol% Au). The maximum reflectance of these films in the infrared region (800–2500 nm) is > 50%, compared with 30% for pure TiO₂. The Maxwell–Garnett equation does not model the reflectance data very well, due to the relatively large gold particle size. Instead, by assuming that the contribution of gold particles to the reflectance response is proportional to their projected areal fraction in an effective medium approximation, we were able to fit the observed reflectance data quite well.     

Mechanical properties and microstructure of ZrO2–SiO2 composite

ZrO2–SiO2 composite powder has been prepared by a wet chemical route using zirconyl chloride and fumed silica as starting materials and subsequently sintered by the hot-pressing method to obtain a ZrO2–SiO2 ceramic. The mechanical properties of the silica matrix have been much increased by the addition of 20 vol% zirconia. The microstructural features of the composite are observed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The stabilibity of tetragonal zirconia in the matrix is attributed to the particle-size effect, and to the constraint effect of the silica matrix and that of the interphasic reaction layer. The increase in mechanical properties is discussed in relation to the residual stress and the enhanced elastic modulus caused by the incorporated ZrO2 particles.     

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.     

Growth, electrical and structural characterization of β-GaSe thin films

GaSe thin films were deposited onto the glass substrates kept at 200° and 300°C by the thermal evaporation of GaSe crystals under the pressure of 10^–5 Torr. X-ray analysis of the films revealed that films grown at 200°C are amorphous in nature while the films grown at 300°C are polycrystalline -GaSe. The temperature dependent electrical conductivity measurements in the region of 320–100 K for the films grown at 300°C showed that the transport mechanisms are the thermionic emission of charged carriers and the variable range hopping above and below 180 K, respectively. Space charge limited current (SCLC) studies have also been performed on these films through the current-voltage measurements at different temperatures and a dominant hole trap at 0.233 eV from the top of the valance band with a trap density of 1.6 × 10¹¹ cm^–3 is identified.     

Enhanced dielectric and electrical properties of three-component PMMA–NaNbO3–starch percolative composite films

Journal of Materials Science: Materials in Electronics - Three-component PMMA–NaNbO3–starch percolative composites with starch and sodium niobate (NaNbO3; NN) particles embedded into...     

Structural,optical and electrical properties of Bi2−xMnxTe3 thin films

Journal of Materials Science: Materials in Electronics - Undoped and Mn doped Bi2Te3 (x = 0, 0.05 and 0.10 at%) thin films were prepared via thermal evaporation method from their bulk alloys. X-ray...     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.     

Dielectric,mechanical and thermal properties of novel core–shell CuPc@MWCNTs/PEN composite films

In this work, multiwalled carbon nanotubes (MWCNTs) were successfully enwrapped by a thin layer of tetra-nitrophthalocyanine copper (CuPc) via solvent-thermal method. EDS spectrum shows that the hybrid materials are mainly composed of C, Cu, N and O elements. TEM images exhibit that the MWCNT was wholly coated with a layer of CuPc and micro-nanoscale core–shell CuPc@MWCNTs were formed. FTIR reveals the detailed chemical groups of micro-nanoscale core–shell CuPc@MWCNTs. Thereafter, CuPc@MWCNTs/polyarylene nitrile ethers (PEN) composite films were prepared via solution-casting method. The CuPc@MWCNTs/PEN composite films possess excellent thermal and mechanical properties endowed by PEN matrix. The glass transition temperature of the composite films is about 175 °C and the initial decomposition temperature is in the range of 494–499 °C. Besides, the tensile modulus of the composite films is above 70 MPa. Furthermore, the dielectric constant of the composite film with 5.0 wt% CuPc@MWCNTs loading is 31 at 50 Hz while the dielectric loss is 0.58 at 50 Hz.     

Phase and structural evolution of sol–gel synthesized ZrO2/Si thin films under heat treatment

ZrO₂/Si thin films were fabricated using a sol–gel technique, and the chemical state change and structural evolution from sol to gel to Zr oxide by heat treatment were investigated. The precursor sol was synthesized using a Zr-acetylacetonate (Zr-acac) precursor, spin-coated, dried on Si(100) substrates, and then annealed at 300–700 °C in air. With increased annealing temperature of the sol–gel-derived layer, Zr-acac decomposed into Zr-acetate, an amorphous ZrO₂ phase formed, and crystallization into a tetragonal phase occurred. In addition, the ZrO₂ layer became denser and the interfacial layer between ZrO₂ and Si thickened, whereas the surface morphology was nearly unaffected and remained smooth with root-mean-square values < 4.5 ?.     

Dielectric behaviors of PHBHHx–BaTiO3 multifunctional composite films

Multifunctional polymeric composites were investigated for potential use in high energy storage capacitors and tissue engineering. The polymeric composites were fabricated by employing biodegradable polyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), as the matrix. Ferroelectric BaTiO₃ ceramic powders were added to the composites as fillers. The dielectric spectroscopy of the composites was measured over a wide frequency range (10⁰–10⁷ Hz) from −100 to 60 °C. The composition dependent dielectric behavior was modeled by a self-consistent effective medium theory. A percolation threshold of 0.367 was observed in the composites. The glass transition relaxation of the composite was also discussed by comparing the popular Vögel–Fulcher–Tammann law with a new glass model. The composites show attractive ferroelectricity and piezoelectricity for biomedical applications.     

ZrO2–TiO2Materials

The magnetic, electrical, catalytic, and photocatalytic properties of ZrO₂–TiO₂materials were studied. The ZrO₂–TiO₂system was shown to contain ZrO₂-, TiO₂, and ZrTiO₄-based solid solutions. Procedures for the preparation of high-activity ZrO₂–TiO₂photocatalysts and photostable pigments were developed.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

Determination of the optical constants of HfO2–SiO2 composite thin films through reverse fitting of transmission spectra

Composite thin films of HfO₂:SiO₂ with wide range of relative composition from 100:0 (pure HfO₂) to 10:90 have been deposited on fused silica substrates by co-evaporation technique and the optical properties of the films have been studied by measuring the transmission spectra of the samples by spectrophotometer. Different important optical parameters viz., band gap, refractive index and absorption coefficients of the samples have been obtained by fitting the measured optical spectra with theoretically generated spectra and the variation of the optical constants as a function of SiO₂ content in the films have been obtained. Two different dispersion models viz., the single effective oscillator model and the Tauc–Lorentz model have been used to generate the theoretical spectra in the above fitting procedure. X-ray reflectivity (XRR) measurement technique has been used to find the densities of the films in order to explain the observed variation in optical properties of the films with increase in SiO₂ content.     

Morphology-wettability relations in artificially structured superhydrophilic TiO2–SiO2 composite films

Naturally superhydrophilic TiO₂–SiO₂ composite films were deposited through a sol–gel route and the morphology of these films was artificially modified by nanosphere lithography using polystyrene spheres. Morphology changes induced by this structuration were studied by optical, scanning electron, and atomic force microscopy. The water wettability of the so-obtained films over aging under ambient atmosphere was then studied with respect to the sol composition and morphological features. This study i/confirms the assumption of a natural superhydrophilicity of composite films intrinsically induced by TiO₂–SiO₂ granular interfaces and ii/shows that this property can be greatly improved by artificially induced morphology features. Such features are discussed on the basis of well-established surface thermodynamic models.     

Dielectric relaxation and ac conductivity of polyaniline–zinc ferrite composite

In situ polymerization of aniline is carried out in the presence of zinc ferrite to synthesize polyaniline/ZnFe₂O₄ composites (PANI/ZnFe₂O₄) by chemical oxidation method. The composite has been synthesized with various compositions (10, 20, 30, 40 and 50 wt.%) of zinc ferrite in PANI. From the infrared spectroscopy (FTIR) studies on polyaniline/ZnFe₂O₄ composites, the peak at 1140 cm^?1 is considered to be measure of the degree of electron delocalization. The surface morphology of these composites is studied with scanning electron micrograph (SEM). The ac conductivity and dielectric properties are studied in the frequency range from 10² to 10⁶ Hz. The results obtained for these composites are of scientific and technological interest.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

Origin of photoluminescence peaks in Ge–SiO2 thin films

Ge–SiO₂ thin films were prepared by the RF magnetron sputtering technique on p–Si substrates from a Ge–SiO₂ composite target. The asdeposited films were annealed in the temperature range of 300–10000C under nitrogen ambience. The structure of films was evaluated by X–ray diffraction, X-ray photoemission spectroscopy and Fourier transform infrared absorption spectroscopy. Results show that the content of Ge and its oxides in thefilms change with increasing annealing temperature (Ta), the photoluminescence (PL) characteristics are closely dependent on the contents of Ge and its oxides in SiO₂ matrix. The dependence observed strongly suggests that the PL peak at 394 nm is related to the existenceof GeO and 580 nm to that of Ge nanocrystal (nc-Ge) in the films. © 2002 Elsevier Science Ltd. All rights reserved.