Characterization of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Microstructural characterization of pulsed laser deposited Al₂O₃/ZrO₂ multilayers on Si (1 0 0) substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar and at room temperature (298 K) has been carried out. A nanolaminate structure consisting of alternate layers of ZrO₂ and Al₂O₃ with 40 bi-layers was fabricated at different zirconia layer thicknesses (20, 15 and 10 nm). The objective of the work is to study the effect of ZrO₂ layer thickness on the stabilization of tetragonal ZrO₂ phase for a constant Al₂O₃ layer thickness of 5 nm. The Al₂O₃/ZrO₂ multilayer films were characterized using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1473 K. The studies showed that the thickness of the zirconia layer has a profound influence on the crystallization temperature for the formation of tetragonal zirconia phase. The tetragonal phase content increased with the decrease of ZrO₂ layer thickness. The cross-sectional transmission electron microscope (XTEM) investigations were carried out on a multilayer thin films deposited at room temperature. The XTEM studies showed the formation of uniform thickness layers with higher fraction of monoclinic and small fraction of tetragonal phases of zirconia and amorphous alumina.     

Synthesis of SrSnO3 thin films by pulsed laser deposition: Influence of substrate and deposition temperature

SrSnO₃ thin films were prepared by pulsed laser deposition on amorphous silica and single crystal substrates of R-sapphire, (100)LaAlO₃ and (100)SrTiO₃. High quality epitaxial (100) oriented films were obtained on LaAlO₃ and SrTiO₃ while a texture was revealed for films on sapphire deposited at the same deposition temperature of 700 °C. Amorphous films were obtained on silica but a post annealing at 800 °C induced crystallization with a random orientation. The screening of deposition temperature showed epitaxial features on SrTiO₃ from 650 °C while no crystallization was observed at 600 °C. The influence of substrate and deposition temperature was confirmed by Scanning Electron Microscopy and Atomic Force Microscopy observations.     

Preparation of LaRuO3 films by microwave plasma-enhanced chemical vapor deposition

LaRuO₃ films were prepared by microwave plasma-enhanced chemical vapor deposition, and the effects of La/Ru supply ratio (R_La/Ru) and microwave power (P_M) on phase and microstructure were investigated. Amorphous films of carbonate or hydroxide of La were formed without microwave irradiation. At R_La/Ru < 1.0, RuO₂ films were obtained independent of P_M. At R_La/Ru = 1.6-3.2 and P_M = 0.6-1.2 kW (deposition temperatures of 973-998 K), LaRuO₃ single phase films were prepared. A product mixture of La₂RuO₅ and β-La₃RuO₇ was obtained at R_La/Ru = 4 and P_M = 1.2 kW, while a mixture of RuO₂ and La_4.87Ru₂O₁₂ was formed at R_La/Ru = 4.6 and P_M = 0.6 kW. LaRuO₃ single phase films showed metallic conduction with a high electrical conductivity of 1.6 × 10⁴ S m^− 1 at room temperature.     

Structural, electrical and optical properties of thermochromic VO2 thin films obtained by reactive electron beam evaporation

We present the structural and physical characterization of vanadium dioxide (VO₂) thin films prepared by reactive electron beam evaporation from a vanadium target under oxygen atmosphere. We correlate the experimental parameters (substrate temperature, oxygen flow) with the films structural properties under a radiofrequency incident power fixed to 50 W. Most of the obtained layers exhibit monocrystalline structures matching that of the monoclinic VO₂ phase. The temperature dependence of the electrical resistivity and optical transmission for the obtained films show that they present thermoelectric and thermochromic properties, with a phase transition temperature around 68 °C. The results show that for specific experimental conditions the VO₂ layers exhibit sharp changes in electrical and optical properties across the phase transition.     

Current transport mechanism in CdS thin films prepared by vacuum evaporation method at substrate temperatures below room temperature

CdS thin films were deposited by vacuum deposition method at low substrate temperatures instead of the commonly used vacuum deposition at high substrate temperatures (T_S > 300 K). The effect of low substrate temperature on the current transport mechanisms in polycrystalline CdS thin films has been studied as a function of temperature over the temperature range 100-300 K. Both thermally assisted tunneling of carriers through and thermionic emission over the grain boundary potential have contributions to the conduction in the range 250-300 K for the sample prepared at 300 K substrate temperature. The dominant conduction mechanism of the samples prepared at 200 K and 100 K is determined as thermionic emission over 200 K and Mott's hopping process below 200 K. The Mott's hopping process is not applicable for the sample prepared at 300 K.     

Enhanced ferroelectric properties in Bi-doped K0.5Na0.5NbO3 thin films prepared by pulsed laser deposition

Lead-free ferroelectric Bi-doped K_0.5Na_0.5NbO₃ (KNN) and undoped KNN films were prepared by pulsed laser deposition. Bi-doped film exhibited good crystallization and improved ferroelectric properties. The dielectric constant and loss tangent were 1038 and 0.138 at 1 kHz, respectively. The remanent polarization (P_r = 28 μC/cm²) of Bi-doped film was about four times larger than that of the undoped film, which attributed to the decrease of oxygen vacancies concentration. The coercive field (E_c = 24 kV/cm) of Bi-doped films was half of the undoped film. The conduction mechanisms of Bi-doped film determined to be Space-Charge-Limited-Current and Poole–Frenkle emission at low and high electric field, respectively.     

Synthesis of epitaxial BaZrO3 thin films by chemical solution deposition

This work reports on the low temperature preparation and characterization of BaZrO₃ (BZO) epitaxial thin films by chemical solution deposition (CSD). The X-ray θ-2θ scan and φ-scan measurements have demonstrated that the BZO films exhibit cube-on-cube epitaxy on (100) MgO substrates, with the full width at half maximum (FWHM) for the ω-scan and φ-scan of 0.35° and 0.46°, respectively. The SEM and AFM analyses revealed that the morphology of the films is strongly correlated with annealing temperature. The root mean square roughness for the film annealed at 600 °C is 3.63 nm, while for the film grown at 1000 °C is 5.25 nm.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Resistive hysteresis in BiFeO3 thin films

Capacitor-like Au/BiFeO₃/SrRuO₃ thin film with (1 1 1) orientation was grown on the SrTiO₃ (1 1 1) substrate by radio frequency magnetic sputtering. It shows a resistive switching behavior, where a stable hysteresis in current–voltage curve was well developed by applying an optimum voltage at room temperature, and it reached the saturation at a bias voltage of 8 V. The Child's law in V_max → 0 direction and the interface-limited Fowler–Nordheim tunneling in 0 → V_max direction, together with the polarization reversal in the BiFeO₃ barrier, are shown to involve in the observed resistive hysteresis.     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Electrical conductivity studies on carbazole thin films

Thin films of carbazole have been prepared using vacuum evaporation technique. The electrical conductivity studies are carried out in both low and high temperature regions and the activation energies have been determined. In the low temperature region the electrical conduction is due to hopping of charge carriers in a coulomb gap. Carbazole thin films have been used to fabricate capacitors and the variation of capacitance, dielectric constant; conductivity and dielectric loss in the frequency range between 100 Hz and 3.16 MHz are investigated. The effect of annealing on the dielectric properties is also investigated. The surface topography of the deposited films is studied using scanning electron microscopy. Film morphologies are found to change by annealing.     

Influence of substrate temperature on structural,optical, and electrical properties of flash evaporated CuIn0.81Al0.19Se2 thin films

Chalcopyrite copper indium aluminum diselenide (CuIn_0.81Al_0.19Se₂) compound is prepared by direct reaction of high purity elemental copper, indium, aluminum and selenium in their stoichiometric proportion. Structural and compositional characterizations of pulverized material confirm the formation of a single phase, polycrystalline nature. CuInAlSe₂ (CIAS) thin films are deposited on organically cleaned soda lime glass substrates using flash evaporation technique by varying the substrate temperatures in the range from 423 K to 573 K. Influence of substrate temperature observed by X-ray diffraction (XRD), scanning electron microscope (SEM), optical and electrical measurement. CIAS Films grown at different substrate temperatures are polycrystalline in nature, exhibiting a chalcopyrite structure with lattice parameters a = ∼0.576 nm and c = ∼1.151 nm. The crystallinity in the films increases with increasing substrate temperature up to 473 K, and tend to degrade at higher substrate temperatures. Optical band gap is in the range of 1.20 eV–1.38 eV and the absorption coefficient is close to 10⁵ cm⁻¹. Electrical characterization reveals p-type conductivity and the structural, morphological and optical properties indicate potential use of CIAS thin films as an absorber layer for thin film solar cell applications.     

Structural and optical characterization of Al-doped ZnO films prepared by thermal oxidation of evaporated Zn/Al multilayered films

Aluminum-doped zinc oxide (ZnO:Al) thin films (t = 68–138 nm) were prepared by thermal oxidation in air flow, at 720 K, of the multilayered metallic Zn/Al thin stacks deposited in vacuum onto glass substrates by physical vapor deposition. The effect of Al content (3.7–8.2 at.%) on the structural (crystallinity, texture, stress, surface morphology) and optical (transmittance, absorbance, energy band gap) characteristics of doped ZnO thin films was investigated. The X-ray diffraction spectra revealed that the Al-doped ZnO films have a hexagonal (wurtzite) structure with preferential orientation with c-axis perpendicular to the substrate surface. A tensile residual stress increasing with Al content was observed. The films showed a high transmittance (about 90%) in the visible and NIR regions. The optical band gap value was found to decrease with Al content from 3.22 eV to 3.18 eV. The results are discussed in correlation with structural characteristics and Al content in the films.     

Characteristics of highly orientated BiFeO3 thin films on a LaNiO3-coated Si substrate by RF sputtering

BiFeO₃ (BFO) films were grown on LaNiO₃-coated Si substrate by a RF magnetron sputtering system at temperatures in the range of 300-700 °C. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. For a substrate temperature below 300 °C and at 700 °C only partially crystalline films and completely randomly polycrystalline films were grown, whereas highly (001)-orientated BFO film was obtained for a substrate temperature in the range of 400-600 °C. The crystalline quality of BFO thin films increase as the deposition temperature increase except for the film deposited at 700 °C. The fitted result from X-ray reflectivity curves show that the densities of the BFO films are slightly less than their bulk values. For the BFO films deposited at 300-600 °C, the higher the deposition temperature, the larger the remnant polarization and surface roughness of the films present.     

Manganese oxide thin films prepared by pulsed laser deposition for thin film microbatteries

Manganese oxide thin films with various oxidation states (MnO, Mn₃O₄ and Mn₂O₃) have been prepared by pulsed laser deposition using a Mn target at different oxygen partial pressures. The structural and morphological features of the as-deposited thin films are characterized by X-ray diffraction, Raman, field emission scanning electron microscopy (FESEM). The oxidation states of Mn in different thin films are investigated by X-ray photoelectron spectroscopy for both Mn 2p and 3s levels. It is found that the structure, surface morphology, and Mn oxidation state of the thin films can be tuned by oxygen partial pressure during the deposition. As anode for thin film lithium-ion microbatteries, the Mn₃O₄ thin film electrode exhibits the largest reversible capacity up to 800 mAh g⁻¹ with good cycling stability and excellent rate capability. The promising electrochemical performance of the Mn₃O₄ thin film electrode indicates the potential application of Mn₃O₄ thin film anode in all solid-state thin film microbatteries.     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

Polycrystalline ZnO-In2O3 thin films as gas sensors

Polycrystalline ZnO-In₂O₃ thin films were prepared by thermal oxidation in air of metallic Zn-In films deposited onto glass substrates by thermal evaporation under vacuum. Different oxidation conditions (oxidation temperature, oxidation time, heating rate) were used in order to prepare homogeneous films that can be used as gas sensors. Polycrystalline structure of the as-obtained films was confirmed by X-ray and electron diffraction investigations. The electrical conductivity of various thin film samples ranged between 0.84 and 6.44 (Ω cm)^− 1.Gas sensitivity to six different gasses (ammonia, methane, LPG, acetone, ethanol and formaldehyde) was evaluated and it was found that the highest sensitivity was obtained for ammonia.     

Impact of epitaxial strain on the ferromagnetic transition temperature of SrRuO3 thin films

Epitaxially strained SrRuO₃ films were grown on SrTiO₃, DyScO₃, and NdGaO₃ oxide substrates using liquid-delivery metal-organic chemical vapour deposition. Temperature dependent resistivity measurements showed a shift in the Curie temperature (T_C) of the ferromagnetic phase transition which is suggested to be caused by the incorporated elastic lattice strain in the films. T_C increased with tensile and decreased with compressive strain, which was inferred from high resolution x-ray diffraction measurements of the in-plane and out-of-plane lattice parameters.     

Preparation and characterization of chemically deposited PbSnS3 thin films

High-quality and well-reproducible PbSnS₃ thin films have been prepared by a simple and inexpensive chemical-bath deposition method from an aqueous medium, using thioacetamide as a sulphide ion source. X-ray diffraction analysis of the deposited films revealed that the as-deposited films were amorphous, however, an amorphous-to-crystalline phase transition was observed as the result of thermal annealing at 425 K for 1 h. The X-ray structure analysis of the collected powder from the bath annealed at 425 K for 1.5 h revealed an orthorhombic phase.

Analysis of the optical absorption data of crystalline PbSnS₃ films revealed that both direct and indirect optical transitions exist in the photon energy range 1.24–2.48 eV with optical band gaps of 1.68 and 1.42 eV, respectively. However, a forbidden direct optical transition with a band gap value of 1.038 eV dominates at low energy (<1.24 eV). The refractive index changes from 3.38 to 2.16 in the range 500–1300 nm. The high frequency dielectric constant and the carrier concentration to the effective mass ratio calculated from the refractive index analysis were found to be 4.79 and 2.3×10²⁰ cm⁻³, respectively. The temperature dependence of the electrical resistivity of the deposited films follows the semiconductor behaviour with extrinsic and intrinsic conduction. The determined activation energies range are 0.35–0.42 and 0.76–85 eV, respectively.