Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Effect of annealing time on the structural,optical and electrical characteristics of DC sputtered ITO thin films

Using an Indium tin oxide (ITO) ceramic target (In₂O₃:SnO₂, 90:10 wt%), ITO thin films were deposited by conventional direct current magnetron sputtering technique onto glass substrates at room temperature. The obtained ITO films were annealed at 400 °C for different annealing times (1, 2, 5, 7, and 9 h). The effect of annealing time on their structural, optical and electrical properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM), ultra violet–visible (UV–Vis) spectrometer, and temperature dependence Hall measurements. XRD data of obtained ITO films reveal that the films were polycrystalline with cubic structure and exhibit (222), (400) and (440) crystallographic planes of In₂O₃. AFM and Scanning Electron Microscopy SEM have been used to probe the surface roughness and the morphology of the films. The refractive index (n), thickness and porosity (%) of the films were evaluated from transmittance spectra obtained in the range 350–700 nm by UV–Vis. The optical band gap of ITO film was found to be varying from 3.35 to 3.47 eV with the annealing time. The annealing time dependence of resistivity, carrier concentration, carrier mobility, sheet resistance, and figure of merit values of the films at room temperature were discussed. The carrier concentration of the films increased from 1.21 × 10²⁰ to 1.90 × 10²⁰ cm^?3, the Hall mobility increased from 11.38 to 18 cm² V^?1 s^?1 and electrical resistivity decreased from 3.97 × 10^?3 to 2.13 × 10^?3 Ω cm with the increase of annealing time from 1 to 9 h. Additionally, the temperature dependence of the carrier concentration, and carrier mobility for the as-deposited and 400 °C annealed ITO films for 2 and 9 h were analysed in the temperature range of 80–350 K.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Rutile TiO<Subscript>2</Subscript> films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO₂) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO₂ films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO₂ films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO₂ films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO₂ layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm^?2 for TiO₂ layer heat-treated at 600 °C.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Structural and optical properties of SnS nanoparticles and electron-beam-evaporated SnS thin films

SnS nanoparticles were synthesised by the precipitation method using SnCl₂.2H₂O and Na₂S.xH₂O and the nanoparticles were characterised by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. From the particles’ XRD pattern, a strong peak at 2θ = 31.5? was observed, which confirms the Herzenbergite orthorhombic crystal structure of SnS. The FTIR result also confirmed the SnS nanoparticles at 2354 cm^?1 and 615 cm^?1. Second, thin SnS films were prepared on a glass substrate by the electron beam evaporation technique at room temperature and annealed at 100°C, 200°C and 300°C. The effect of the annealing temperature on structural and optical properties of the SnS films was characterised by XRD and ultraviolet–visible (UV–Vis) analysis. From the experimental studies, optical absorption of SnS films increases with respect to the annealing temperature, while the values of band gap energy (E_g) get reduced from 1.77 to 1.57 eV.     

Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films prepared by sol–gel method through a cycle

Mg_0.05Zn_0.95O thin films were prepared on silicon substrates by a sol–gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm^?1 is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of Mg_0.05Zn_0.95O thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation.     

Structural,optical and magnetic properties of the Fe2TiO5 nanopowders

Iron titanate nanopowders with a particle size range of 48–70?nm could be obtained after calcinations of the dried gel at 900°C for 2?h. Fe₂TiO₅ indicates a ferrimagnetic–paramagnetic behaviour, as evidenced by using vibrating sample magnetometer at room temperature. In the temperature range of 25–300°C the empirical equation of the heat capacity C _p (J/mol?K)?=??692.328?+?1.39?T?+?3.757?×?10⁷/T ² for Fe₂TiO₅ was determined from differential scanning calorimetry. Direct optical band gap of Fe₂TiO₅ was calculated using the Tauc model by UV-Vis diffuse reflectance spectroscopy. Band gap energy of Fe₂TiO₅ was determined as 1.95?eV.     

Broad band optical characterization of sol-gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO₂) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO₂ thin films was studied in the range of 0.62 to 4.96 eV photon energy (250-2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol-gel precursors and the creation of dense layers of TiO₂. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol-gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.     

Effects of annealing on the formation of Mg2Si film prepared by resistive thermal evaporation method

The effects of annealing time and temperature on the formation and structure of magnesium silicide (Mg₂Si) films were investigated. Magnesium films of 380 nm thickness were deposited on Si (111) substrates using resistive thermal evaporation method. The films were then annealed in an annealing furnace under a low vacuum atmosphere of 10^?1–10^?2 Pa. The results showed that the crystallization quality of Mg₂Si films was strongly affected by the annealing time and temperature. Annealing at 400 °C for 4 h was the optimal preparation conditions for Mg₂Si films.     

Microstructure and properties of ZrO2-, TiO2-doped Ca–Si–B based ceramics

The microstructure, sintering and dielectric properties of ZrO₂-, TiO₂-doped Ca–Si–B based ceramics prepared by solid-phase process were investigated, and the effects of ZrO₂, TiO₂ content on these performances were analyzed. The Ca–Si–B based ceramics without additive (ZrO₂ or TiO₂) showed a high sintering temperature (1,100?°C) and had the dielectric properties: dielectric constant (ε_r) of 8.38, dielectric loss (tanδ) of 1.51?×?10^?3 at 1?MHz, and volume density of 2.47?g/cm³. The addition of ZrO_2, TiO₂ was revealed to lower the sintering temperature of Ca–Si–B based ceramics to 1,000?°C and enhance the sintering and dielectric properties: ρ?=?2.61?g/cm³, ε_r?=?5.85, tanδ?=?1.59?×?10^?4 (1?MHz) with ZrO₂ addition, and ρ?=?2.65?g/cm³, ε_r?=?6.12, tanδ?=?6.4?×?10^?4 (1?MHz) with TiO₂ addition, which are superior to the pure Ca–Si–B. The results show that ZrO₂, TiO₂ as nucleating agents, are conducive to the precipitation of crystals, thus decrease the sintering temperature and improve the dielectric properties of Ca–Si–B based ceramics.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Effects of 200 keV Ar-ions irradiation on the structural and optical properties of reactively sputtered CrN films

Modification in structural and optical properties of chromium-nitride (CrN) films induced by argon ion irradiation and thermal annealings were investigated using various experimental techniques. CrN films deposited by d. c. reactive sputtering on Si substrate were implanted with 200 keV argon ions, at fluences of 5–20 × 10¹⁵ ions/cm². As-implanted samples were then annealed in vacuum, for 2 h at 700 °C. Rutherford backscattering spectrometry, X-ray diffraction, cross-sectional (high-resolution) transmission electron microscopy and spectroscopic ellipsometry (SE) measurements were carried out in order to study structural and optical properties of the layers. After irradiation with 200 keV Ar ions a damaged surface layer of nanocrystalline structure was generated, which extended beyond the implantation profile, but left an undamaged bottom zone. Partial loss of columnar structure observed in implanted samples was recovered after annealing at 700 °C and CrN started to decompose to Cr₂N. This layer geometry determined from transmission electron microscopy was inferred in the analysis of SE data using the combined Drude and Tauc-Lorentz model, and the variation of the optical bandgap was deduced. The results are discussed on the basis of the changes induced in the microstructure. It was found that the optical properties of the layers are strongly dependent on the defects' concentration of CrN.     

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500?°C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400–2000?nm continuously increases as the annealing temperature increases from 500?°C to 700?°C, whilst it decreases first and then increases as the annealing temperature increases from 800?°C to 1000?°C. When the film is excited with a laser of 980?nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho³⁺: ⁵S₂/⁵F₄?→?⁵I₈?and ⁵F₅?→?⁵I₈ transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900?°C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.     

Optimising the crystallinity of anatase TiO2 nanospheres for the degradation of Congo red dye

Anatase TiO₂ nanospheres having a high degradation efficiency are prepared through hydrothermal method employing titanium (IV) isopropoxide as precursor. The effects of hydrothermal temperature on structural, morphological and optical properties of TiO₂ nanospheres are investigated. X-ray diffraction (XRD) results show that, the TiO₂ nanospheres crystallise in the anatase phase, the tetragonal crystal system. The crystallite size increases with the increase in hydrothermal temperature and the values are in the range of 10–19 nm. On the other hand, the spherical particles evenly distributed on the surface are observed in the scanning electron microscope (SEM) images. The band gap of the nanospheres is determined from the reflectance spectra using Kubelka–Munk function. The band gap energy decreases from 3.189 (2) to 3.023 (5) eV with the increase in hydrothermal temperature. The decrease in band gap values well agree with the XRD results of higher crystallite size and enhanced crystallinity. The removal of Congo red dye under dark condition varies with the hydrothermal temperature and it is maximum for the higher crystallinity anatase TiO₂ synthesised at 160 °C having a lower band gap of 3.023 (5) eV. Maximum efficiency of 96.9% and rate constant value of 0.01413 g mg^?1 min^?1 are observed for the sample hydrothermally synthesised at 160 °C.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Role of annealing temperature on microstructural and electro-optical properties of ITO films produced by sputtering

This study probes the effect of annealing temperature on electrical, optical and microstructural properties of indium tin oxide (ITO) films deposited onto soda lime glass substrates by conventional direct current (DC) magnetron reactive sputtering technique at 100 watt using an ITO ceramic target (In₂O₃:SnO₂, 90:10 wt%) in argon atmosphere at room temperature. The films obtained are exposed to the calcination process at different temperature up to 700 °C. X–ray diffractometer (XRD), ultra violet-visible spectrometer (UV–vis) and atomic force microscopy (AFM) measurements are performed to characterize the samples. Moreover, phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. The results obtained show that all the properties depend strongly on the annealing temperature. XRD results indicate that all the samples produced contain the In₂O₃ phase only and exhibit the polycrystalline and cubic bixbite structure with more intensity of diffraction lines with increasing the annealing temperature until 400 °C; in fact the strongest intensity of (222) peak is obtained for the sample annealed at 400 °C, meaning that the sample has the greatest ratio I ₂₂₂/I ₄₀₀ and the maximum grain size (54 nm). As for the AFM results, the sample prepared at 400 °C has the best microstructure with the lower surface roughness. Additionally, the transmittance measurements illustrate that the amplitude of interference oscillation is in the range from 78 (for the film annealed at 400 °C) to 93 % (for the film annealed at 100 °C). The refractive index, packing density, porosity and optical band gap of the ITO thin films are also evaluated from the transmittance spectra. According to the results, the film annealed at 400 °C obtains the better optical properties due to the high refractive index while the film produced at 100 °C exhibits much better photoactivity than the other films as a result of the large optical energy band gap.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

The temperature dependence of stresses in aluminum films on oxidized silicon substrates

In situ measurements were carried out of stress at the AlSiO₂ interface at various temperatures (25–500 °C) and for various film thicknesses (0.2–1.6 microm). These data are complemented with microstructural studies by transmission electron microscopy.For the aluminum films studied, the intrinsic structural component was very small (less than 2 × 10⁸ dyn cm^?2). On heating, thermal mismatch led to a compressive stress, with dσ/dT ≈ ?2 × 10⁷ dyn cm^?2 °C; these films yielded at 6σ6 ; ? 5 × 10⁸ dyn cm^?2, primarily through diffusion creep and grain growth. On cooling from about 450–500 °C, thermal mismatch led to a tensile stress which was limited mainly by dislocation slip. The final room temperature value after thermal cycling ranged from 0.5 × 10⁹ dyn cm^?2 for a 1.5 microm film to 8 × 10⁹ dyn cm^?2 for a 0.2 microm film; these values are believed to represent the critical stress for the generation of dislocation loops within the grains.The grain size of cold-deposited aluminum films ranged from about 0.2 microm for films 0.45 microm thick to about 2 microm for films 1.5 microm thick. Thermal cycling led to an order-of-magnitude increase in the grain size together with the formation of dislocation networks within the grains.