Tin-doped Indium Oxide Substrates Research Articles

An electrografted monolayer of polyaniline as a tuneable platform for a glucose biosensor.

Polyaniline (PANI), a nanostructured conducting polymer, has shown significant potential in optical and bioelectrochemical devices. However, its performance and stability on various substrates are hindered by weak adhesion to the surface. In this study, a strongly adherent polyaniline conducting polymer layer with a thickness of five nanometers was electrografted onto an initiating monolayer on gold and tin-doped indium oxide substrates. These electrografted monolayers consist of vertically oriented fully oxidized-protonated (pernigraniline salt) and deprotonated (pernigraniline base) forms of polyaniline. The monolayer exhibits pH-dependent colour changes and it is suitable for enzyme compatibility. In light of these findings, we have developed and characterized an electrochemical glucose biosensor based on the monolayer of polyaniline on a gold electrode. The biosensor utilizes glucose oxidase as the biorecognition element for the selective detection of glucose concentrations in real blood plasma samples.

Piezoelectricity-enhanced multifunctional applications of hydrothermally-grown p-BiFeO3–n-ZnO heterojunction films

This paper reports the fabrication of p-BiFeO3 (BFO)–n-ZnO composite films on tin-doped indium oxide substrates through a facile hydrothermal method and the tuning of various functional properties of single-crystalline BFO and ZnO for piezoelectricity-enhanced multiapplications. BFO microplates were embedded in ZnO nanorod arrays; the clear interfaces indicated the robust formation of the heterojunction, which was also confirmed through X-ray photoelectron spectroscopy. The conductivity type of the BFO and ZnO was determined through Mott–Schottky, open-circuit potential, and photoelectrochemical measurements. Moreover, the induced piezopotential distributions of the samples were theoretically simulated, and the piezotronics, piezophototronics, and Schottky behavior of the composites were determined. The composite-based piezoelectric nanogenerators exhibited durable output and excellent sensitivity, enabling practical sensor applications. Excellent piezophotodegradation with a rate constant of approximately 3 × 10−2 min−1 for the composite was attributable to predominant ·O2− radicals. The maximum applied bias photon-to-current efficiency and piezophotoelectrochemical current density were approximately 0.86% (at 0.63 V vs. Ag/AgCl) and 1.4 mA cm−2, respectively. The multiapplications of the p–n junction composites were primarily attributable to the enhanced piezoelectric coefficient (d33 ≈ 27.3 pm·V−1), favorable electrochemical surface area (≈69.8 mF cm−2 mg−1), prolonged charge carrier lifetime, weak photoluminescence, and suitable band positions and piezopotential-induced band bending.

Photoelectric properties of low temperature solution‐processed three‐dimensional Bi 2 S 3 crystals

Three-dimensional Bi2S3 with different morphology of flower-like, waxberry like and hydrangea like on the tin-doped indium oxide substrate has been produced from one-step aqueous solution at low temperature (40–70°C) and fixed pH of 0.81 for 24 h. The UV–vis measurement showed that the absorption spectrums of obtained Bi2S3 crystals were occurred blue shift compared to the bulk orthorhombic Bi2S3(1.3 eV). With the increase in temperature, the crystallinity of Bi2S3 films was gradually improved. When the temperature went to 55°C, the best conductivity was obtained.

Nucleation and growth mechanism of tellurium electrodeposited on tin-doped indium oxide substrate

The mechanism of electrochemical deposition of tellurium on tin-doped indium oxide (ITO) substrate from a nitric acid solution containing telluryl ion (HTeO2+) has been studied in this work. The investigation, using cyclic voltammetry and chronoamperometry, shows that the electrodeposition of Te at a negative potential around − 0.42 V versus saturated calomel electrode (SCE) is a quasi-reversible reaction controlled by the diffusion process. Furthermore, by chronoamperometry, the measured current transient curves were compared with the theoretical models, proposed by Scharifker–Hills and Heerman–Tarallo models. It was found that the nucleation and growth mechanism of Te on ITO substrate changed with increasing the concentration of HTeO2+, it can be instantaneous for 2.10−2 mol L−1 or progressive for 2.10−3 mol L−1. The quantitative analysis (nonlinear fitting) shows that the diffusion coefficient remains between 7.10−6 and 9.10−6 cm2 s−1, the nucleation rate constant A and the number density of active sites N0 were growth with the increase of the concentration and the deposition potential. The thin tellurium layers, electrodeposited by chronoamperometry, are characterized by X-ray diffraction. It has been identified that all the films were polycrystalline type hexagonal crystal structure with preferred orientation of (1 0 0) and (1 1 0) planes to growth. The SEM analysis reveals that the morphology of the resulting deposits is depending on the type of electrodeposition mechanism.

Enhanced photoelectrochemical activity of electrochemically deposited ZnO nanorods for water splitting reaction

This paper reports the development of zinc oxide films electrodeposited at different potentials on tin-doped indium oxide substrates. The effect of deposition potential on ZnO microstructure, optical absorption, and photocatalytic activity for water splitting reaction were studied in detail. The films were potentiodynamically grown by applying different deposition potentials, such as − 0.7, − 0.8, and − 0.9 V at constant temperature (70 °C) for 30 min. The pH of precursor solution was maintained around 6 during the electrodeposition process. X-ray diffraction study revealed the hexagonal wurtzite crystal structure of the ZnO. The field emission scanning electron microscopy (FESEM) demonstrated a significant variation in the microstructure with changing deposition potential. UV–Visible spectroscopy demonstrated a significant change in the optical band gap values for the ZnO films deposited at different deposition potentials. The highest photocatalytic activity of water splitting was recorded for the films deposited at − 0.8 V under AM. 1.5 G solar light illumination.

Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO3 films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO3 films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50–700cm−1 were identified based on group theory. The symmetries of the high order Raman modes in 900–1500cm−1 of BiFeO3 are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400–700cm−1 in return. Moreover, the lattice structures of BiFeO3 films are identified consequently on the basis of Raman spectroscopy. BiFeO3 films on SrRuO3 coated SrTiO3 (001) substrate, CaRuO3 coated SrTiO3 (001) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO3 film on SrRuO3 coated Nb: SrTiO3 (001) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO3 films.

The effect of linker of electrodes prepared from sol–gel ionic liquid precursor and carbon nanoparticles on dioxygen electroreduction bioelectrocatalysis

The effect of linker of three-dimensional, hydrophilic-carbon-nanoparticle film-electrodes prepared by layer-by-layer method on redox probe accumulation and bioelectrocatalytic dioxygen reduction was studied and compared for two different electrode scaffolds. The linker in both of these scaffolds was based on the same ionic liquid sol–gel precursor, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium bis(trifluoromethyl-sulfonyl)imide. The first electrode type was prepared by alternative immersion of tin doped indium oxide substrate in an aqueous suspension of carbon nanoparticles modified with phenyl sulphonic groups and a sol composed of ionic liquid sol–gel precursor and tetramethoxysilane. For the second electrode type sol was replaced by a methanolic suspension of silicate submicroparticles with appended imidazolium functional groups. In both films 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) anions accumulate irreversibly. In the case of the first electrode electrostatic attraction plays the more important role in comparison to the case of the second where stable adsorption of the redox probe takes place. After adsorption of bilirubin oxidase, electrodes obtained from sol and carbon nanoparticles exhibit modest bioelectrocatalytic activity towards dioxygen reduction at pH 4.8, however those obtained from oppositely charged particles are much more efficient. The magnitude of the associated catalytic current in both cases depends on the number of immersion and withdrawal steps. Interestingly, mediatorless catalysis at electrodes obtained from oppositely charged particles is more efficient than mediated catalysis.

Sol–gel processed ionic liquid – hydrophilic carbon nanoparticles multilayer film electrode prepared by layer-by-layer method

Multilayer hydrophilic carbon nanoparticles modified electrodes are prepared by a layer-by-layer method combined with sol–gel processing. A tin doped indium oxide substrate is alternatively immersed in sulfonated carbon nanoparticles solution and a sol containing the ionic liquid precursor 1-methyl-3-(3-trimethoxysilylpropyl)imidazolium bis(trifluoromethyl-sulfonyl)imide together with tetramethyl orthosilicate. The thickness of the film is proportional to the number of immersion and withdrawal steps. Scanning electron microscopy image reveals relatively uniform distribution of carbon nanoparticles within the film. The resistance of the electrode increases only slightly after film deposition. More importantly the electrochemical behaviour of the electrode connected with double layer charging, irreversible hydrogen peroxide reduction and oxidation–reduction of the immobilised redox liquid – t-butyloferrocene and the simple redox reaction of 1,1′-ferrocenedimethanol correlates with the number of immersion and withdrawal steps. Clearly the subsequent immobilisation of a larger number of carbon nanoparticles increases the electrochemically active surface and provides an extended solid|organic liquid|aqueous solution boundary. The electrode also acts as a reversible sponge for Fe ( CN ) 6 3 - anions due to an excess of imidazolium functional groups. 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) anion – a popular enzyme mediator is irreversibly accumulated on the electrode. The electrode modified with it exhibits catalytic behaviour in dioxygen saturated aqueous solution in the presence of laccase.

Liquid-phase synthesized mesoporous electrochemical supercapacitors of nickel hydroxide

Electrochemical supercapacitive (ES) properties of liquid-phase synthesized mesoporous (pore size distribution centered ∼12 nm) and of 120 m 2/g surface area nickel hydroxide film electrodes onto tin-doped indium oxide substrate are discussed. The amounts of inner and outer charges are calculated to investigate the contribution of mesoporous structure on charge storage where relatively higher contribution of inner charge infers good ion diffusion into matrix of nickel hydroxide. Effect of different electrolytes, electrolyte concentrations, deposit mass and scan rates on the current–voltage profile in terms of the shape and enclosed area is investigated. Specific capacitance of ∼85 F/g at a constant current density of 0.03 A/g is obtained from the discharge curve.

Introducing hydrophilic carbon nanoparticles into hydrophilic sol-gel film electrodes

A hydrophilic carbon nanoparticle–sol-gel electrode with good electrical conductivity within the sol-gel matrix is prepared. Sulfonated carbon nanoparticles with high hydrophilicity and of 10–20 nm diameter (Emperor 2000) are co-deposited onto tin-doped indium oxide substrates employing a sol-gel technique. The resulting carbon nanoparticle-sol-gel composite electrodes are characterized as a function of composition and salt (KCl) additive. Scanning electron microscopy and voltammetry in the absence and in the presence of a solution redox system suggest that the composite electrode films can be made electrically conducting and highly porous to promote electron transport and transfer. The effect of the presence of hydrophilic carbon nanoparticles is explored for the following processes: (1) double layer charging, (2) diffusion and adsorption of the electrochemically reversible solution redox system 1,1′-ferrocenedimethanol, (3) electron transfer to the electrochemically irreversible redox system hydrogen peroxide, and (4) electron transfer to the redox liquid tert-butylferrocene deposited into the porous composite electrode film. The extended electrochemically active hydrophilic surface area is beneficial in particular for surface sensitive processes (1) and (3), and it provides an extended solid|organic liquid|aqueous solution boundary for reaction (4). The carbon nanoparticle–sol-gel composite electrodes are optimized to provide good electrical conductivity and to remain stable during electrochemical investigation.

Chemical synthesis of p-type nanocrystalline copper selenide thin films for heterojunction solar cells

Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200°C for 1h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV–vis spectrophotometry techniques, respectively. Cu2−xSe phase was confirmed by XRD pattern and spherical grains of 30±4 – 40±4nm in size aggregated over about 130±10nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80mW/cm2 light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.

Characterisation of hydrophobic carbon nanofiber–silica composite film electrodes for redox liquid immobilisation

Carbon (50–150 nm diameter) nanofibers were embedded into easy to prepare thin films of a hydrophobic sol–gel material and cast onto tin-doped indium oxide substrate electrodes. They promote electron transport and allow efficient electrochemical reactions at solid|liquid and at liquid|liquid interfaces. In order to prevent aggregation of carbon nanofibers silica nanoparticles of 7 nm diameter were added into the sol–gel mixture as a “surfactant” and homogeneous high surface area films were obtained. Scanning electron microscopy reveals the presence of carbon nanofibers at the electrode surface. The results of voltammetric experiments performed in redox probe—ferrocenedimethanol solution in aqueous electrolyte solution indicate that in the absence of organic phase, incomplete wetting within the hydrophobic film of carbon nanofibers can cause hemispherical diffusion regime typical for ultramicroelectrode like behaviour. The hydrophobic film electrode was modified with two types of redox liquids: pure tert-butylferrocene or dissolved in 2-nitrophenyloctylether as a water-insoluble solvent and immersed in aqueous electrolyte solution. With a nanomole deposit of pure redox liquid, stable voltammetric responses are obtained. The presence of carbon nanofibers embedded in the mesoporous matrix substantially increases the efficiency of the electrode process and stability under voltammetric conditions. Also well-defined response for diluted redox liquids is obtained. From measurements in a range of different aqueous electrolyte media a gradual transition from anion transfer dominated to cation transfer dominated processes is inferred depending on the hydrophilicity of the transferring anion or cation.

Effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide substrates for polymer LEDs

The effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide (ITO) substrates and the changes in surface properties of treated ITO substrates with ageing time were investigated by X-ray photoelectron spectroscopy (XPS), contact angle and surface free energy measurements. Experimental results show that oxygen plasma treatment increases the oxygen concentration, decreases the carbon concentration, and enhances the surface free energy and polarity, and thereby improves the surface properties of ITO substrates. However, the improved ITO surface properties tended to decay and the surface free energy decreased, with ageing time. In addition, the ageing effect of treated ITO substrates on the performance of polymer light-emitting diodes (LEDs) was studied with respect to the driving voltage, electroluminescent luminance and efficiency. We observe that the ITO substrates aged for various times result in significant differences in optical and electrical characteristics which become worse as the ageing time increases. The optical and electrical performance of polymer LEDs is closely related to the surface properties of ITO substrate and the interface characteristics of ITO/polymer.

Ion transfer processes at the room temperature ionic liquid|aqueous solution interface supported by a hydrophobic carbon nanofibers – silica composite film

A thin film of carbon nanofibers embedded into a hydrophobic sol–gel material and deposited onto tin-doped indium oxide substrate electrodes is employed as a support for liquid|liquid redox systems. The system 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide|aqueous electrolyte is studied with t -butylferrocene as an electrochemically active component in the ionic liquid phase. Redox processes within the ionic liquid are coupled to ion transfer processes at the ionic liquid|water interface. The carbon nanofiber electrode material provides an ideal porous support and allows both high Faradaic and high capacitive currents to be achieved. The capacitive current obtained after immobilisation of 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and immersion into aqueous electrolyte indicates that most (ca 65%) of the real carbon nanofiber surface is active, electrically connected to the substrate electrode, and in direct contact with the ionic liquid. The reversible oxidation and re-reduction of t -butylferrocene in 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide occurs at a potential which depends on the composition and nature of the aqueous electrolyte as well as on the type of electrode. The position of differential pulse voltammetric oxidation peak potentials is shown to depend on the type of anion present in the aqueous solution phase with most significant effects for the hydrophobic ClO 4 - and PF 6 - anions. Although only the Faradaic voltammetric response allows the ion transfer mechanism to be analysed, anion transfer is proposed to be coupled to both Faradaic and capacitive charge transfer.