Chemical bath deposition of different phases of copper selenide thin films by controlling bath parameters

In the preparation of copper selenide thin films using chemical bath deposition (CBD) technique, it is observed that the pH of the final reacting mixture is the major factor controlling the composition of the film. Thin films of cubic Cu_2−xSe and tetragonal Cu₃Se₂, of band gaps 2.20 and 2.83 eV, respectively, have been prepared using the CBD technique by adjusting the bath parameters like pH, temperature and the ratio between copper and selenium atoms in the reaction bath. X-ray diffraction analysis is used as the major tool for identification of these phases. The results have been confirmed using XPS, ICP and absorption studies.     

The study of polystyrene surface swelling by quartz crystal microbalance and Rutherford backscattering techniques

A quartz crystal microbalance technique (QCM) was used to measure the mass gain of a glassy polystyrene film as 1 -iodo-n-hexane (IOH) was diffused into it. We present a technique by whichØ _s(t), the time dependent volume fraction of IOH at the surface of the PS film, can be obtained from the QCM data. The surface swelling data thus obtained are shown to be in good agreement with values ofØ _s(t) measured independently by Rutherford backscattering spectrometry (RBS). The QCM method has the advantage that the data are obtained continuously from one sample rather than requiring the tedious exposure and analysis of the multiple samples that the RBS method does; it is, however, sensitive to small errors in determining the mass gain rate.     

Poly(BCB)/Au-nanoparticles hybrid film modified electrode: Preparation, characterization and its application as a non-enzymatic sensor

We report electrochemical preparation and characterization of poly-brilliant cresyl blue (Poly(BCB))/gold nanoparticles (Au-NPs) modified electrode. The Poly(BCB)/Au-NPs modified electrode has been used as an electrochemical sensor for the detection of hydrogen peroxide (H₂O₂) at lower potential (− 0.2 V). The Poly(BCB)/Au-NPs film was characterized by scanning electron microscopy, Uv-visible spectroscopy (Uv-vis) and cyclic voltammetry. We have observed that, Au-NPs attached glassy carbon electrode (Au-NPs/GCE) significantly enhanced the polymerization of BCB compared to bare GCE. The Poly(BCB) film was irreversibly attached onto the Au-NPs modified electrode, the resulting hybrid film modified electrode was electrochemically active in the pH range from 2 to 11. Attachment of Poly(BCB)/Au-NPs hybrid film on the electrode surface was confirmed by Uv-vis spectra. In addition, electrocatalytic properties of the Poly(BCB)/Au-NPs/GCE towards reduction of H₂O₂ have been investigated, and it was found that the sensitivity, reduction potential as well as the corresponding detection limit were improved as compared to the voltammetric response of the Poly(BCB)/GCE and Au-NPs/GCE. Based on this study, a non-enzymatic electrochemical sensor for the determination of H₂O₂ has been reported. Moreover, analysis of commercial H₂O₂ samples was performed using the proposed method and satisfactory results were obtained.     

Lead incorporation in thin iron garnet films produced by LPE and chemical analysis by the radioactive tracer technique

The mode of incorporation of lead ions into Y₃Fe₅O₁₂ single crystal thin films grown by the LPE technique from lead containing fluxes has been carefully studied using radioactive tracers as the analysis technique. In particular, the variation of lead content with film thickness has been studied. It has confirmed the existence of a lead rich layer at the interface of the substrate and the film. The formation of this layer is connected with the transient period during which stable growth is established. The variation of lead with film growth rate is established. The misfit with the substrate lattice parameter has an influence on the grown film, whereas the species of the substrate does not have an effect. There is evidence that rare-earth ions enter the octahedral sites in the garnet.     

Determination of optical constants and inhomogeneity of optical films by two-step film envelope method

A simple two-step film envelope method has been proposed to determine the optical constants and small inhomogeneity of the optical films, which uses maximum envelopes and minimum envelope of the normal incidence transmittance of the two-step film. The two-step films were prepared by stopping the deposition process in the middle of the designed sputtering time, and then, after a full cooling down to room temperature, repeating the same deposition process again to complete the whole preparation of the films. The optical constants of Nb₂O₅-TiO₂ mixed films were calculated by two-step film envelope method and traditional envelope method. The experimental results demonstrate that the average refractive index and extinction coefficient calculated by two-step film envelope method are more accurate than those calculated by the traditional envelope method.     

Contact potential difference measurement using a single-junction breakdown field method

A technique for measuring contact potential differences using single-junction breakdown has been developed from evidence that recovery of a broken-down junction takes place after breakdown has occurred. Experiments have been performed with Al-Al₂O₃-metal thin film sandwiches. The aluminium oxide film was grown thermally on vacuum-deposited thin aluminium films. The present method appears to be superior to the usual two-junction breakdown method of Simmons.     

Study of Size Distribution in Nanostructured Se<Subscript>58</Subscript>Ge<Subscript>39</Subscript>Pb<Subscript>3</Subscript> Glass Using Various Characterization Methods

The present paper aims at the study of size distribution of particles in nanostructured Se₅₈Ge₃₉Pb₃ glass using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and UV–visible spectrophotometer. The thin film sample has been prepared using melt quenching technique and inert gas consolidation method. The particle size distribution obtained from XRD and UV–Vis spectrophotometer shows more uncertainty than the results obtained from TEM measurements. The absorption spectra recorded on UV–Vis spectrophotometer is employed to get band gap values corresponding to different size distribution in sample. Further, it is concluded that TEM is the best measurement technique for size distribution as it has less uncertainty in the obtained results.     

Simultaneous measurement of resistivity and temperature coefficient of resistivity of metallic thin films with the transient hot-strip method

The recently described transient hot-strip method for measuring thermal transport properties of solid insulators has been developed for simultaneously measuring the resistivity ?_F and the temperature coefficient of resistivity (TCR) α_F of metallic thin films. The experimental arrangement is similar to the well-known four-probe technique but the constant current pulse passed through the thin film is sufficiently high to increase its mean temperature by about 1 K. By measuring the time-varying increase or decrease in the resistance, information is obtained not only about the resistivity but also about the TCR.The main advantage of the method is the possibility to measure ?_F and α_F simultaneously without increasing or decreasing the temperature of the film by more than 1 K, i.e. without measurably changing the properties of the film.The method has been tested on unannealed copper films at room temperature.     

Electrodeposition of graphene layers doped with Brϕnsted acids

A simple and fast method is demonstrated for the preparation of a thin film of graphene layers by the electrodeposition of positively doped graphene dispersion onto desired electrode substrates. A thin film of graphene layers was obtained by applying negative potentials according to the electrophoretic deposition mechanism. The doped graphene dispersion was prepared from expanded graphite treatment with various acids (HCl, HNO₃, and H₂SO₄) and an ultrasonication process. The doping and deposition processes are strongly dependent on the type of acid and the applied potential, which were monitored by Raman spectroscopy and quartz crystal microbalance, respectively. The morphology and electrochemical properties of the graphene film were characterized by scanning electron microscopy and cyclic voltammetry. The electrochemical performance of graphene film obtained using nitric acid or hydrochloric acid dopant is superior to that obtained with sulfuric acid doping. This technique could be a facile tool for the fabrication of a thin film of graphene layers on a desired substrate.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.     

Characterization of ZrO2 and SiC ceramic thin films prepared by electrostatic atomization

ZrO₂ and SiC ceramic thin films and their bilayer have been successfully prepared by a newly developed electrostatic atomization technique. This technique can generate fine spray of ceramic suspensions in a micrometer sized range with a narrow size distribution which is crucial for preparation of uniform thin films of these ceramic materials. Compared to some other thin film deposition techniques, such as Chemical vapour deposition (CVD), physical vapour deposition (PVD) and plasma spray (PS) etc. the thin film deposition process using electrostatic atomization is not only cheap but also controllable. The prepared ZrO₂ and SiC thin films were investigated using scanning electron microscopy (SEM) and energy dispersion analysis (EDA) techniques. These thin films were observed to be homogenous with a particle size less than 10 m. The ZrO₂-SiC bilayer was found to have an abrupt interface, implying that the deposition process is controllable and also that functionally graded ceramic/ceramic materials can be prepared in this way if the thickness of each layer is accurately controlled.     

In situ, real-time thickness measurement techniques for bath-deposited CdS thin films on Cu(In,Ga)Se2

A technique has been developed that can measure the thickness of a 30-70 nm thin film of cadmium sulfide on a Cu(In,Ga)Se₂ substrate, in real time, as it grows in a chemical bath. The technique does not damage the film, and can be used to monitor batch depositions and roll-to-roll depositions with equal accuracy. The technique is based on reflectance spectroscopy through the chemical bath.     

Synthesis and electrochemistry of LiMn2O4 prepared using succinic acid as complexing agent

Single phase spinel-LiMn₂O₄ has been synthesized from the methanolic solution of metal acetates and succinic acid as a complexing agent by soft-chemistry technique. Shorter heat-treatment time, narrow particle size distribution, smaller crystallite size, better control of morphology, and low formation temperature of the synthesized materials are the advantages of this technique. The formation temperature of LiMn₂O₄ has been found to be as low as 300°C in this method of preparation. The dependence of crystallinity of LiMn₂O₄ with heat treatment temperature has been studied. The physical properties of the synthesized product have been investigated by structural (XRD), spectroscopic (FTIR and Raman) and thermal (DTA/TG) analyses. The electrochemical performance of the material has been evaluated by employing it as cathode in Li//LiMn₂O₄ cells. LiMn₂O₄ synthesized by the soft-chemistry method shows a two step delithiation process, which is explained by the change of phases during delithiation, a first step in a single phase and in a second step in a mixed phase.     

Preparation of lead iodide films by iodination of chemically deposited lead sulphide films

A method of preparation of PbI₂ films by iodination of chemically deposited PbS films is described. The X-ray characterization of these films show that they are poly-crystalline in nature and the crystallites are preferentially oriented with c-axis perpendicular to the plane of the substrates. The analysis of the diffuse reflectance measurements performed on material scraped off the substrates yielded a forbidden energy gap of 2.34 eV in conformation with the results of pure PbI₂ powder. The transmittance spectra of these films, in the wavelength range 400 to 600 nm, revealed a characteristic strong absorption edge at about 510 nm and a hump at about 490 nm. On the basis of the changes in conductance of PbS film during iodine treatment a mechanism of iodination has been proposed.     

Advantages of transparent conducting oxide thin films with controlled permittivity for thin film photovoltaic solar cells

Our recent investigations have identified a pathway to produce transparent conducting oxide (TCO) films that demonstrate higher infrared transparency. The technique involves controlling the dielectric permittivity of the TCO film such that the electrical properties are maintained, but the plasma frequency (ω_p) is shifted to longer wavelength. This has the effect of reducing free-carrier absorption in the visible and near-infrared spectral region, thus producing a TCO film with higher optical transmission. The technique has been demonstrated for sputtered films of indium tin oxide by adding small amounts of ZrO₂ to a ceramic sputtering target, and for SnO₂:F films deposited by chemical vapor deposition using a metalorganic Zr source.     

Selective detection of hydrogen sulfide using copper oxide-doped tin oxide based thick film sensor array

In this work, copper oxide-doped (1, 3 and 5 wt%) tin oxide powders have been synthesised by sol–gel method and thick film sensor array has been developed by screen printing technique for the detection of H₂S gas. Powder X-ray diffraction pattern shows that the tin oxide (SnO₂) doped with 3 wt% copper oxide (CuO) has smaller crystallite size in comparison to 0, 1 and 5 wt% CuO-doped SnO₂. Furthermore, field emission scanning electron microscopy manifests the formation of porous film consisting of loosely interconnected small crystallites. The effect of various amounts of CuO dopant has been studied on the sensing properties of sensor array with respect to hydrogen sulfide (H₂S) gas. It is found that the SnO₂ doped with 3 wt% CuO is extremely sensitive (82%) to H₂S gas at 150 °C, while it is almost insensitive to many other gases, i.e., hydrogen (H₂), carbon monoxide (CO), sulphur dioxide (SO₂) and liquefied petroleum gas (LPG). Moreover, at low concentration of gas, it shows fast recovery as compared to response time. Such high performance of 3 wt% CuO-doped SnO₂ thick film sensor is probably due to the diminishing of the p–n junction and the smallest crystallite size (11 nm) along with porous structure.     

Alcohol sensing of tin oxide thin film prepared by sol-gel process

The present paper describes the alcohol sensing characteristics of spin coated SnO₂ thin film deposited by using sol-gel process. The sensitivity of the film was measured at different temperatures and different concentrations of alcohol at ppm level. Alcohol detection result shows peak sensitivity at 623 K. The variation of sensitivity and ethanol concentration has shown a linear relationship up to 1150 ppm and after that it saturates. The response time measurement of the sensor was also observed and it was found that the response time is 30 sec. The results obtained favour the sol-gel process as a low cost method for the preparation of thin films with a high sensing characteristic.     

Metal silicide-templated growth of quality Si films for Schottky-diodes

Quality Si films were grown on a metal silicide template and fabricated for a Schottky-diode. The thin metal was firstly deposited and reacted to the supplying Si and then formed the silicide layer, which is a template to grow quality Si film above it due to the lattice affinity to Si. Various types of metal (Co, Ni, and mixture of Co and Ni) were used as catalyst species. The morphological changes of Si grain sizes were systematically investigated. Two steps of Si supply condition were applied and revealed the formation of metal silicide phases and Si film growth.During the Si supply, Co was stable to form CoSi₂ and grew a crystalline Si (c-Si) film above it. However Ni firstly formed Ni rich silicide phases at low Si supply due to the fast Ni diffusion in Si. By increasing the Si supply, Ni diffusion has been staggered and formed NiSi₂ layer to grow a c-Si film above it. It has been also revealed that the NiSi₂ migration produced a c-Si film behind. Mixing of Co with Ni showed a stable silicide phase without a serious metal migration and improved the Si crystallinity providing an enhanced Schottky-diode performance.The investigation of silicide formation and quality Si film growth is presented. Transmission electron microscope analysis proves the volume growth of c-Si film above a metal disilicide of NiSi₂ or CoSi₂.     

Effect of calcination conditions on phase formation and particle size of nickel niobate powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb₂O₆) powders. The formation of the NiNb₂O₆ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb₂O₅ precursors and the Ni₄Nb₂O₉ phase tend to form together with the columbite NiNb₂O₆ phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb₂O₆ in an orthorhombic phase.     

Preparation and humidity-sensitive properties of nanocrystalline BaTiO3 thick film fabricated on Teflon substrate by using pressing method

Nanocrystalline BaTiO₃ precursor has been synthesized by using the stearic acid gel (SAG) method. After calcining the precursor at above 600 °C for 0.5 h, nanocrystalline BaTiO₃ powder with cubic perovskite structure is obtained. The powder is compacted further into solid material under a pressure of 0.1 to 2.0 GPa or fabricated into thick film by pressing on a Teflon substrate at room temperature and 200 °C. The powder and film samples are characterized by XRD, TEM and SEM. The results show that the average grain size of the powder is between 20 and 60 nm, and the thickness of the compacted film is about 56 μm. The investigation on the humidity-sensitive properties of nanocrystalline BaTiO₃ thick film shows that a compacted thick-film sample possesses higher humidity sensitivity, simpler preparation process, and enhanced adhesion strength on the Teflon substrate in comparison with a coated sensor, and the grain size and pressing pressure have obvious influence on its properties. In addition, the solid reaction mechanism and pressure effect on the material in the course of processing are also discussed.