Nanocrystalline p-type-cuprous oxide thin films by room temperature chemical bath deposition method

Nanocrystalline cuprous oxide (Cu₂O) thin films were synthesized on amorphous glass substrate by using simple room temperature chemical route namely, chemical bath deposition (CBD) method. The deposition kinetics played important role to get good quality nanocrystalline films with uniform thickness. The structural, surface morphological, optical and electrical properties of the films were investigated. Crystallization and growth processes obtained micro-spherical shaped grains of Cu₂O due to agglomeration of smaller nanoparticles. An optical and electrical characterization was performed to study the optical band gap and type of electrical conductivity of the film.     

Surfactant assisted electrodeposition of MnO2 thin films: Improved supercapacitive properties

In order to obtain a high specific capacitance, MnO₂ thin films have been electrodeposited in the presence of a neutral surfactant (Triton X-100). These films were further characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and contact angle measurement. The XRD studies revealed that the electrodeposited MnO₂ films are amorphous and addition of Triton X-100 does not change its amorphous nature. The electrodeposited films of MnO₂ in the presence of the Triton X-100 possess greater porosity and hence greater surface area in relation to the films prepared in the absence of the surfactant. Wettability test showed that the MnO₂ film becomes superhydrophilic from hydrophilic due to Triton X-100. Supercapacitance properties of MnO₂ thin films studied by cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy showed maximum supercapacitance for MnO₂ films deposited in presence of Triton X-100 is 345 F g⁻¹.     

Chemical synthesis and electrochemical analysis of nickel cobaltite nanostructures for supercapacitor applications

Nickel cobaltite (NiCo₂O₄) films containing nanorods and nanoflakes are synthesized on indium tin oxide (ITO) substrates by a chemical bath deposition method and calcination process at 300 °C for 3 h. The NiCo₂O₄/ITO films are used as electrodes for supercapacitor applications, and electrochemical properties of the NiCo₂O₄ nanostructures are examined by cyclic voltammetry and charge-discharge experiments. NiCo₂O₄ nanorods exhibit the largest specific capacitance, with a value of 490 F g⁻¹at energy and power densities of 45 Wh kg⁻¹ and 2 kW kg⁻¹, respectively. This is significantly better than the performance of NiCo₂O₄ nanoflakes. Cycle-life tests show that the specific capacitance of NiCo₂O₄ is stable even after 1000 cycles, indicating its high potential for supercapacitor applications. The low cost and environmental friendliness of NiCo₂O₄ nanorods, coupled with its high supercapacitor performance, offer advantages over other transition metal oxides used for supercapacitors.     

Annealing driven performance and optical effects in nanocrystalline SnO2 thin films induced by pulsed delivery

Tin dioxide thin films were prepared successfully by pulsed laser deposition techniques on glass substrates. The thin films were then annealed for 30 min from 50 °C to 550 °C at 50 °C intervals. The influence of the annealing temperature on the microstructure and optical properties of SnO₂ thin films was investigated using X-ray diffraction, optical transmittance and reflectance measurements. Various optical parameters, such as optical band gas energy, refractive index and optical conductivity were calculated from the optical transmittance and reflectance data recorded in the wavelength range 300-2500 nm. We found that the SnO₂ thin film annealed at temperatures up to 400 °C is a good window material for solar cell application. Our experimental results indicated that SnO₂ thin films with the high optical quality could be synthesized by pulsed laser deposition techniques.     

Microwave assisted chemical bath deposited polyaniline films for supercapacitor application

In the present investigation, we are reporting the first time synthesis of polyaniline (PANI) thin films by microwave assisted chemical bath deposition (MW-CBD) method on the stainless steel substrate. The PANI thin films are prepared by the oxidation of aniline in the domestic microwave oven working with frequency 2.45 GHz. The PANI thin films are characterized for their structural, morphological and optical studies by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and UV-vis spectrophotometer. The wettability study is carried out by measuring the contact angle. The supercapacitive behavior of PANI electrode is studied in 0.5 M H₂SO₄ using cyclic voltammetric (CV) measurements. The X-ray diffraction pattern showed the films are amorphous. Morphological study revealed PANI thin film is well covered over the entire substrate surface with less overgrown fine spherical granules. The optical band gap of PANI thin film is found to be 2.5 eV. The hydrophilic nature of the PANI thin films is observed from water contact angle measurement. A maximum specific capacitance is found to be 753 F g⁻¹ at the scan rate of 5 mV s⁻¹.     

One-pot hydrothermal synthesis of ruthenium oxide nanodots on reduced graphene oxide sheets for supercapacitors

Ruthenium oxide nanodots have been deposited on reduced graphene oxide (RGO) sheets homogeneously by hydrothermal and annealing methods. Adding NaOH solution in GO colloids prevents the restack and agglomeration of GO sheets when mixed with ruthenium chloride solution. Local crystallization of RuO₂ in the composites is revealed by X-ray diffraction and transmission electron microscopy. The element mapping image demonstrates the uniform distribution of Ru on RGO sheets. Unlike the pure crystalline RuO₂ exhibiting poor electrochemical performance, the composites present superior capacitive properties. The hydrothermal time is optimized and a maximum of 471 F g⁻¹ is measured in the composites at 0.5 A g⁻¹ when loaded with 45 wt% of RuO₂. After 3000 cycles, its specific capacitance remains 92% of the maximum capacitance. Our results suggest potential application of the reduced graphene oxide/ruthenium oxide composites to supercapacitors.     

Room-temperature synthesis of crystallized LiCoO2 thin films by electrochemical technique

LiCoO₂ thin films have been directly synthesized on cobalt substrate in LiOH solution at room temperature by electrochemical method. The obtained LiCoO₂ thin films were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of electrochemical reaction time, current density and concentration of LiOH solution on the crystal structure and morphology of the obtained LiCoO₂ thin films was discussed emphatically. Our results show that the as-synthesized LiCoO₂ films all are pure hexagonal structure. The crystallinity, densification and uniformity of the films increase with increasing electrochemical reaction time, current density as well as concentration of LiOH solution and then decrease. The preferable electrochemical reaction conditions were optimized as: electrochemical reaction time is 50 h, current density is 1 mA cm⁻² and concentration of LiOH solution is 3 mol dm⁻³.     

Effect of precursor concentration on the properties of ITO thin films

Tin-doped indium oxide (ITO) thin films have been prepared by the spray pyrolysis method using indium chloride as a precursor and stannic chloride as a dopant. The effect of a precursor concentration on the structural, morphological, electrical and optical properties of films has been studied. The concentration of InCl₃ in the spraying solution is varied from 6.25 to 37.5 mM keeping doping percentage of tin fixed at its optimized value of 5 wt.%. Bare glass is used as a substrate and oxygen as the carrier and reaction gas. X-ray diffraction (XRD) patterns show that films are polycrystalline and their crystallinities are dependent on the precursor concentration. A surface morphology has been observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The typical ITO film has minimum resistivity value of 2.71 × 10⁻³ Ω cm, whose carrier concentration and mobility were 7.45 × 10¹⁹ cm⁻³ and 31 cm²/(V s), respectively. In addition, the best ITO film has optical transmittance of 94.4% and figure of merit 1.20 × 10⁻³ Ω⁻¹.     

Study on the orientation degree of Pb1 − xLaxTiO3 thin films by the rocking curve technique and its morphological aspects

Thin films of perovskite-type materials such as PbTiO₃, BaTiO₃, (Pb,La)TiO₃, (Pb, La)(Zr,Ti)O₃, KNbO₃, and Pb(Mg,Nb)O₃ have been attracting great interest for applications like non-volatile memories, ultrasonic sensors and optical devices. Thin film should be epitaxially grown or at least highly textured since the properties of this anisotropic material depend on the crystallographic orientation. For optical devices, in particular, an epitaxial thin film without defects are essential to reduce optical propagation losses. Pb_1 − xLa_xTiO₃ (PLT) where x = 0, 13 and 27% thin films were prepared by a chemical method (polymeric precursors method), and deposited by the spin coating technique onto substrates of SrTiO₃ (STO) and LaAlO₃ (LAO). The films were then heat treated at 500 °C in a controlled atmosphere of O₂. The orientation degree of the thin films was obtained from rocking curve technique, by means of X-ray diffraction analysis. A microstructural study revealed that the films were crack-free, homogeneous and have low roughness.     

Physical properties of tin oxide thin films improved by vapour chopping

The vapour chopping technique has been successfully used to lower the ambient air ageing effect on the tin oxide thin films. The films were prepared by thermal oxidation (in air) of vacuum evaporated vapour chopped and nonchopped tin thin films. The films showed SnO and SnO₂ phases with tetragonal and orthorhombic structure. All the films showed increase in optical transmittance with increase in oxidation temperature and duration. The vapour chopped films showed higher refractive index and band gap than those of nonchopped films. The refractive index was found to increase with the thickness. Due to air ageing, the refractive index of both the films was found to increase. The ageing effect was found lower on the vapour chopped (0.008) than those on nonchopped (0.02) tin oxide thin films. These films can have potential use in optical waveguides.     

Synthesis and structural characterization of undoped and Co doped zinc oxide thin films obtained by aerosol assisted chemical vapour deposition

Dilute magnetic oxides are transparent, wide-bandgap materials that behave ferromagnetically when doped with a few percent of a magnetic 3d cation. They have attracted a great deal of interest due to the integration of semiconducting and magnetic properties in a material, that is a prerequisite for successful fabrication of useful devices for the emerging technologies of spintronics. Here we report a study of growth characteristics and microstructural properties of undoped and Co doped ZnO films grown onto borosilicate glass substrates, using aerosol assisted chemical vapour deposition method. The obtained films are single phase, of Wurtzite type, some of them with a strong c-axis orientation, i.e. with the c-axis normal to the substrate surface.     

Characterization of chromium thin films by sputter deposition

In this study, a systematic investigation on the deposition of Cr-CrO_x bi-layer film was performed by magnetron DC sputtering. The X-ray photoelectron spectrometer (XPS) examining the bare Cr film showed that the peaks of Cr 2P_3/2 and Cr 2P_1/2 appeared in the Cr thin film associated with the presence of a 12 nm oxide layer. The transmission was reduced to zero as the Cr film exceeded 100 nm in thickness. The reflection saturated at a value of ≈55% when the thickness of the Cr film reached 30 nm. The optical density exceeded 3.50 with a Cr film thickness over 150 nm. In order to reduce the reflection of the film to a level of ≤4%, a Cr-CrO_x bi-layer thin film was prepared. Overall, a Cr-CrO_x bi-layer film with the Cr layer 130 nm and the CrO_x layer 40 nm in thickness reported a transmission of zero, a reflection of 3.82% and an optical density of 4.04, all meeting the requirements of anti-reflection black matrix (BM) for display applications.     

Electrical and optical properties of tantalum oxide thin films prepared by reactive magnetron sputtering

Tantalum oxide thin films were prepared by using reactive dc magnetron sputtering in the mixed atmosphere of Ar and O₂ with various flow ratios. The structure and O/Ta atom ratio of the thin films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The optical and dielectric properties of the Ta₂O₅ thin films were investigated by using ultraviolet-visible spectra, spectral ellipsometry and dielectric spectra. The results reveal that the structure of the samples changes from the amorphous phase to the β-Ta₂O₅ phase after annealing at 900 °C. The XPS analysis showed that the atomic ratio of O and Ta atom is a stoichiometric ratio of 2.50 for the sample deposited at Ar:O₂ = 4:1. The refractive index of the thin films is 2.11 within the wavelength range 300-1000 nm. The dielectric constants and loss tangents of the Ta₂O₅ thin films decrease with the increase of measurement frequency. The leakage current density of the Ta₂O₅ thin films decreases and the breakdown strength increases with the increase of Ar:O₂ flow ratios during deposition.     

Microstructure and optical absorption properties of Au-dispersed CoO thin films

Au nanoparticles dispersed cobalt monoxide (CoO) composite films were fabricated via a chemical solution approach combined with a spin-coating processing. Au particles were spherical approximately and uniformly dispersed in the amorphous CoO matrix. The mean diameters of Au particles in the Au/CoO thin films with 40 mol% Au are about 30 nm. The optical absorption peaks due to the surface plasmon resonance (SPR) of Au particles were observed in the UV-vis absorption spectra in the wavelength range of 550-650 nm. The SPR peaks exhibit a red shift and intensify with increasing Au content from 10 to 40 mol%, but show a blue shift and weaken from 40 to 60 mol%. The band gap E_g decreases with increasing Au contents from 10 to 40 mol% but increases by further increasing Au content.     

Deposition and characterization of CuInSe2 films for solar cells using an optimized chemical route

CuInSe₂ (CISe) thin films have been deposited on glass using successive ionic layer adsorption and reaction (SILAR). The as-deposited films are treated at 400 °C in argon atmosphere and etched in KCN solution to remove detrimental secondary phases. The preparation and temperature of the precursor solutions, the duration of the reaction cycles and the duration of the annealing stage have been optimized. The films have been characterized employing grazing incident X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive scanning spectroscopy. Relevant semiconductor parameters have been calculated. Photoelectrochemical tests confirm p-type conduction. The films are crystalline and the stoichiometry can be improved by renewing the precursor solution after completing half of the cycles, annealing for 90 min and later etching in KCN. The quality of the material seems to be promising for application in solar cell devices.     

Thickness dependence of crystalline state in FeZrNbCuB thin films obtained by sputter deposition

Differential scanning calorimetry, hysteresis measurements, X-ray diffraction, Mössbauer spectroscopy and transversal Kerr effect have been used to study the thickness and temperature dependence of magnetic properties and crystalline state of Fe₈₄Zr_3.5Nb_3.5B₈Cu₁ (at.%) thin films. Results indicate that a decrease of the saturation magnetization with increasing film thickness can be ascribed to the presence of a crystalline α-Fe phase at the early stages of film growth, followed by the deposition of the amorphous alloy. Thinner films, which have a significant crystalline phase in the as-prepared state, display less prominent crystallization features, whereas thicker films, with a significant amorphous phase in the as-prepared state, are characterized by much more pronounced crystallization effects, that are confirmed by Mössbauer and Transversal Kerr Effect measurements. Progressive thinning of a film by means of sputter etching allows to reduce the amorphous component, leading to the expected increase of saturation magnetization as the thickness decreases.     

Preparations and characterizations of polycrystalline PbSe thin films by a thermal reduction method

Polycrystalline PbSe thin films were deposited on Si substrates by a thermal reduction method with the carbon as the reducing agent. The X-ray diffraction (XRD) spectra show that the deposited thin films predominately crystallize with the rock-salt structures above the evaporation temperature of 600 °C, and the PbSe thin film has the optimal crystal quality at 900 °C. The scanning electron microscopy (SEM) measurements reveal that the PbSe thin film with carbon addition has uniform crystal grain sizes and dense microstructure, while the thin film without carbon consists of loosely distributed and widely size-ranged crystal grains. The optical transmittance spectrum shows that the direct band gap of the PbSe film is about 0.256 eV. By the introduction of element S, PbSe_1−xS_x (0 ≤ x ≤ 1.0) thin films could be prepared, but excess amount of S additions (>20 at.%) would cause phase segregations between PbSe and PbS phases. The deposition method presented in this paper may be useful for mass-producing polycrystalline lead chalcogenide thin films in the future.     

Synthesis mechanisms of lithium cobalt oxide prepared by hydrothermal–electrochemical method

Thermodynamic calculation method was adopted to predict the reaction mechanism of LiCoO₂ prepared by hydrothermal–electrochemical process. It was found that in the Co–LiOH–H₂O system, Co was oxidized to HCoO₂⁻, Co(OH)₂ (100 °C) or CoO (150 °C), CoOOH in sequence with the increase of electrode potential, then the ion-exchange reaction of CoOOH and lithium ion occurred and LiCoO₂ came into being. The optimum synthesis parameter was obtained through thermodynamic calculation and it was validated experimentally by cyclic voltammogram method.     

Thickness effects of Bi0.89Ti0.11FeO3 thin films deposited on PbZr0.2Ti0.79Nb0.01O3 buffer layers

Bi_0.89Ti_0.11FeO₃ thin films with the thicknesses of 200-440 nm were fabricated on the 40-nm-thick PbZr_0.2Ti_0.79Nb_0.01O₃ (PZTN)-buffered Pt(1 1 1)/Ti/SiO₂/Si substrates using a metal organic decomposition process. As a result of the good insulating property and high breakdown characteristic of the PZTN buffer layer, the leakage currents in the Bi_0.89Tb_0.11FeO₃ films are significantly reduced. All the films show well-saturated and rectangular P-E hysteresis loops without any evident leaky behavior. The remnant polarization P_r and coercive field E_c for all Bi_0.89Ti_0.11FeO₃ films are around 45-50 μC/cm² and 200 kV/cm, respectively, and show weak dependent on the film thickness. The 200-nm-thick Bi_0.89Ti_0.11FeO₃ film exhibits better fatigue-free characteristic and charge-retaining ability, and the domain backswitching is significantly restrained due to the strong anti-aging ability of the PZTN buffer layer.     

Dielectric properties of soft chemical method derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(1 0 0) substrates

Calcium copper titanate, CaCu₃Ti₄O₁₂ (CCTO), thin film has been deposited by the soft chemical method on Pt/Ti/SiO₂/Si (1 0 0) substrates at 700 °C for 2 h. The peaks were indexed as cubic phase belonging to the Im−3 space group. The film exhibited a duplex microstructure consisting of large grains of 130 nm in length and regions of fine grains (less than 80 nm). The CCTO film capacitor showed a dielectric loss of 0.031 and a dielectric permittivity of 1020 at 1 MHz. The J-V behavior is completely symmetrical, regardless of whether the conduction is limited by interfacial barriers or by bulk-like mechanisms. Based on impedance analyses, the equivalent circuit of CCTO film consisting of a resistor connected in series with two resistor-capacitor (RC) elements.