Enhancement of optical conductivity in the ultra-violet region of Cs doped ZnO sol gel thin films

Nano crystalline cesium (Cs) doped ZnO thin films were deposited on glass substrate by sol gel spin coating method with 1–3 mol.% doping concentration and different annealing temperatures. The deposited films were characterized by X-ray diffraction (XRD), Hall Effect, Photoluminescence (PL) and UV–Visible studies. XRD measurements reveal that all the samples abound in the wurtzite structure with polycrystalline nature. An increase in crystalline size from 19.60 to 44.54 nm is observed with the increase of doping concentration. Electrical conductivity of Cs doped ZnO films were observed from Hall effect measurements and the maximum carrier concentration obtained is 7.35 × 10¹⁸ cm^?3. The near band emission (384 nm) peak intensity increases with the increase of Cs doping concentration and a maximum intensity 55,280 was observed for CZ3 film from PL spectrum. Also a low energy near infrared (NIR) emission peak centered at 1.62 eV appears for the Cs doped ZnO films. The average transmission of CZ film is 88 % and the absorption edge is red shifted with the increase of Cs doping concentration and also the optical conductivity increases in the UV region.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Structural and optical properties of Na doped ZnO nanocrystalline thin films synthesized using sol–gel spin coating technique

Sodium (Na) doped Zinc oxide (ZnO) thin films have been deposited on a glass substrate by the sol–gel spin coating method. Effect of doping with various percentages of Na at a particular annealing temperature of 500 °C is studied. The samples were characterized by X-ray diffraction (XRD), micro-photoluminescence, Raman and Polarized Raman spectroscopy. The X-ray diffraction and micro-Raman spectroscopy confirmed the presence of Na substitution in zinc oxide and the wurtzite structure of the lattice is retained. An enhancement of resonant Raman scattering processes as well as longitudinal optical phonon overtones up to the fifth order were observed in the micro Raman spectra. The similar values of depolarization ratios obtained from Polarized Raman studies recommend no change in the symmetry. Photoluminescence showed a strong emission peak in the near UV at 3.2 eV and negligible visible emission.     

Nanocrystalline Zn1−x−yBexMgyO thin films synthesized by the sol–gel method: structural and near infrared photoluminescence properties

In this paper, we reports on the structural and optical properties of Zn_1?x?yBe_xMg_yO thin films prepared by sol–gel method, which are new materials for optoelectronic and ultraviolet-light-emitting devices. The crystal structure and core level spectra of these films are studied by X-ray diffraction and X-ray photoelectron spectroscopy. Surface morphology of the films is analyzed by scanning electron microscope images and the surface is composed of spherical shaped grains. Micro-photoluminescence shows a near edge band emission and the peak values tuned from 3.26 eV for the undoped to 3.4 eV for the doped ZnO film. Near infrared emission is observed in the region 1.64–1.67 eV for pure and co-doped ZnO films. In micro-Raman spectra, multiple-order Raman bands originating from ZnO-like longitudinal optical (LO) phonons are observed. A Raman shift of about 5–18 cm^?1 is observed for the first-order LO phonon. A comparative study was made on Raman band for BeZnO, MgZnO and BeMgZnO nanocrystals with the LO phonon band of bulk ZnO. The ultraviolet resonant Raman excitation at room temperature shows multi-phonon LO modes up to the fourth order. Deformation energy of all the films is calculated and BeMgZnO film has the minimum deformation energy.     

Active carbon supported S-promoted Bi catalysts for acetylene hydrochlorination reaction

We synthesized a S doped Bi/AC catalyst for acetylene hydrochlorination. The addition of H₂SO₄ changes the structure of the Bi atoms in the catalyst, resulting in the improvement of the specific surface areas and catalytic efficiency of the Bi-based catalyst under reaction conditions.     

Electrochemical polymerization of polyaniline doped with Zn2+ as the electrode material for electrochemical supercapacitors

Polyaniline doped with Zn²⁺ (PANI/Zn²⁺) films was synthesized by cyclic voltammetric method on stainless steel mesh substrates in 0.2 mol L^?1 aniline and 0.5 mol L^?1 sulfuric acid electrolyte with various concentrations of zinc sulfate (ZnSO₄·7H₂O). The structure and morphology of PANI and PANI/Zn²⁺ films were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques, respectively. The electrochemical properties of PANI and PANI/Zn²⁺ films were investigated by cyclic voltammetry, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy in 0.5 mol L^?1 H₂SO₄ electrolyte in a three-electrode system. The results show that the surface morphology of PANI/Zn²⁺ is more rough than that of pure PANI. The specific capacitance of the PANI/Zn²⁺ film displays a larger specific capacitance of 738 F g^?1, lower resistance, and better stability as compared with the pure PANI film. Thus, good capacitive performance demonstrates its potential superiority for supercapacitors.     

Improved electrochemical properties of Sn-doped TiO2 nanotube as an anode material for lithium ion battery

Anatase TiO₂ nanotube was doped with different contents of Sn (3, 5, and 7 at.%) through sol-gel method and subsequent hydrothermal process. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller (BET), and Hall effect measurement are utilized to characterize the structures, components, chemical environments, morphologies, specific areas, and electronic conductivities of the samples. The investigation in cycling performances demonstrates that 5 at.% Sn-doped TiO₂ nanotube exhibits the best cycling stability, with specific capacity of 386 mAh g^?1 and coulombic efficiency of 99.2 % after 50 cycles at 0.1 C, much higher than those of the other Sn-doped samples and pristine TiO₂ nanotube. The improved electrochemical performances of Sn-doped TiO₂ nanotube are attributed to the increase of electronic conductivity and therefore enhance the reversible capacity of the material.     

Sol–gel preparation of pure and doped TiO2 films for the photocatalytic oxidation of ethanol in air

Stable sols of TiO₂ were synthesized by a non-aqueous sol–gel process using titanium (IV) isopropoxide as precursor. The microstructure, optical and morphological properties of the films obtained by spin-coating from the sol, and annealed at different temperatures, were investigated using scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy and ellipsometry. The crystalline structure of the films was characterized by X-ray diffraction and their photocatalytic activity was evaluated for the oxidation of ethanol in air. The influence of the calcination temperature, pre-heat treatment and the number of layers was studied. Simultaneous thermo-gravimetric and differential thermal analysis measurements were carried out to ascertain the thermal decomposition behavior of the precursors. In order to obtain a higher photoresponse in the visible region, a series of vanadium-, niobium- and tantalum-doped TiO₂ catalysts was synthesized by the same sol–gel method. For V doping two different precursors, a vanadium alkoxide and V₂O₅, were used. The effect on the crystallization and photocatalytic activity of the doped TiO₂ films was investigated. Furthermore, to identify the effective composition of the samples, they were characterized by X-ray photoelectron spectroscopy and the surface area of the powders was measured by N₂ adsorption. The 10 wt.% doped catalysts exhibit high photocatalytic activity under visible light and among them the best performance was obtained for the sample containing Ta as dopant. The crystallite sizes are closely related to the photocatalytic activity.     

Multiscale study on hydrogen storage based on covalent organic frameworks

In this paper, we performed a multiscale study on the hydrogen storage capacity of Li–Sc doped and Li-C₆₀ injected covalent organic frameworks (COFs)-based phthalocyanine, porphyrin and TBPS COFs. We combined the first-principles studies of hydrogen adsorption and grand canonical Monte Carlo (GCMC) simulations of hydrogen adsorption in nine designed COFs. The first-principles calculations revealed that the Li atoms can be doped on the surface of the Sc-doped COFs with binding energy from ?83.9 to ?160.2 kJ/mol. Each Li atom can bind three H₂ molecules with the adsorption energy between ?16.8 and ?20.0 kJ/mol. The GCMC simulations have predicted that all the nine designed COFs can reach the Department of Energy’s 2015 target (5.5 wt% and 40 g/L) at T = 77 K and P = 100 bar. The optimum conditions of hydrogen storage for Li-C₆₀@Li–Sc-PR-TBPS2, the promising materials, are T = 193 K (?80 °C) and P = 100 bar with a gravimetric H₂ density of 8.19 wt% and volumetric H₂ uptake of 42.6 g/L. Finally, we further convinced the importance of Sc in improving H₂ uptake in doped COFs.     

Influence of insertion of a noble gas atom on halogen bonding in H2O···XCCNgF and H3N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes

The H₂O···XCCNgF and H₃N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes have been studied with quantum chemical calculations at the MP2/aug-cc-pVTZ level. The results show that the inserted noble gas atom has an enhancing effect on the strength of halogen bond, and this enhancement is weakened with the increase of noble gas atomic number. The methyl and Li substituents in the electron donor strengthen the halogen bond. The interaction energy increases from ?3.75 kcal/mol in H₃N–BrCCF complex to ?9.66 kcal/mol in H₂LiN–BrCCArF complex. These complexes have been analyzed with atoms in molecules, natural bond orbital, molecular electrostatic potentials, and energy decomposition calculations.     

High efficiency ZnO nano sensor,fabrication and characterization

Ultra fine thin films of pure and SnO doped ZnO nanosensor were grown on gold digitated ceramic substrate from bis(2, 4- pentanedionate)dimethylethanolamine zinc (II) using bis(2, 4-pentanedionate) tin(II) chloride as a dopant by ultrasonic aerosol assisted chemical vapor deposition technique (UAACVD) at temperature range of 400–450 °C under oxygen atmosphere at 5 Pa pressure. The sensitivity, selectivity, fast recovery, and reliability test performed on nanosensor suggested that both doped and undoped ZnO thin films are suitable for detecting ethanol vapor in the temperature range of at 60 to 150 °C, whereas at room temperature (25 °C) response and recovery time of the sensor increases many folds compared to 60 °C. Sensitivity of the ZnO sensor shows linear relationship with the increase of gas concentration. Electrical properties show that 1 % SnO doped ZnO enhanced the sensitivity of the film drastically and thus improved its detecting efficiency. Physico-chemical techniques like, CHNS-O, atomic absorption analyzer, and infra red and multinuclear nuclear magnetic resonance spectrometers were used for precursor characterization. X-ray diffractometer, scanning electron microscope, sigma scan analyzer and energy dispersive x-ray techniques were used for thin film characterization.     

50 keV H+ ion beam irradiation of Al doped ZnO thin films: Studies of radiation stability for device applications

Thin films of Al doped ZnO (Al:ZnO) were deposited on two substrates (Si and glass) at room temperature and 300°C using DC magnetron sputtering. These films were bombarded with 50 keV H⁺ beam at several fluences. The pristine and ion beam irradiated films were analysed by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and UV‐Vis spectroscopy. The X‐ray diffraction analysis, Hall measurements, Raman and UV‐Vis spectroscopy confirm that the structural and transport properties of Al:ZnO films do not change substantially with beam irradiation at chosen fluences. However, in comparison to film deposited at room temperature, the Al:ZnO thin film deposited at 300°C shows increased transmittance (from 70% to approximately 90%) with ion beam irradiation at highest fluence. The studies of surface morphology by scanning electron microscopy reveal that the ion irradiation yields smoothening of the films, which also increases with ion fluences. The films deposited at elevated temperature are smoother than those deposited at room temperature. In the paper, we discuss the interaction of 50 keV H⁺ ions with Al:ZnO films in terms of radiation stability in devices.     

Synthesis and properties of Mo and W ions co-doped porous nano-structured VO2 films by sol–gel process

Porous nano-structured vanadium dioxide (VO₂) films doped with Mo and W ions had been synthesized by sol gel process by employing a sol containing ammonium molybdate and ammonium tungstate with the addition of cetyltrimethyl ammonium bromide (CTAB). The effects of molybdenum and tungsten co-doping and CTAB addition on the structure, morphologies, crystalline and optical properties of VO₂ films were investigated systematically in this study. The composition and microstructure were detected by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The Mo and W ions co-doped porous nano-structured VO₂ films showed excellent infrared transmittance (nearly 70 %), large transmittance difference (55 %) before and after the phase transition, low transition temperature (35 °C), wide hysteresis width (22 °C) and fast phase transition. The results suggest that such Mo and W ions co-doped porous nano-structured VO₂ film is an ideal fundamental material for optical data storage.     

Different morphologies of ZnO nanostructures via polymeric complex sol–gel method: synthesis and characterization

Various morphologies of ZnO nanostructures, such as nanoparticles, nanorods and nanoflowers have been achieved controllably by polymeric sol–gel method. In this approach, zinc nitrate Zn(NO₃)₂·6H₂O, citric acid and ethylene glycol were used as the source of Zn²⁺, the chelating agent and the solvent agent, respectively. The microstructure of the ZnO nanostructures was characterized by X-ray diffractometry, scanning electron microscopy with the energy dispersive X-ray spectroscopy, transmission electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. The effect of ethylene glycol to citric acid mole ratio on the morphology and structure of the products was discussed. The ZnO nanoparticles with diameter between 24 ± 2 nm was obtained with EG:CA mole ratio equal to 2:1. The optical properties of as-obtained power were investigated by ultraviolet–visible spectroscopy.     

Effect of lithium doping on the photoluminescence of Sm:ZnO powders

ZnO co-doped with 2 at.% Sm and different Li concentration (0–7 at.%) powders were fabricated by the sol–gel method with 700 °C annealing. The effect of Li doping concentration on the structure and photoluminescence (PL) of ZnO powders doped with 2 at.% Sm was investigated. Based on the balance of structure and valence, with the help of Li doping (1, 2 at.%) into ZnO powders doped with 2 at.% Sm, Sm³⁺ ions enter ZnO crystal lattice and induce the characteristic Sm³⁺ emission peaks by the ultra-violet (UV) excitation (278 nm). Especially, when the Li doping concentration is 2 at.%, the sample has the most efficient Sm characteristic emission line. However, Li will hinder the substitution of zinc location by Sm³⁺ when the Li doping concentration is above 3 at.%, which results in the disappearance of the characteristic samarium emission lines.     

Microstructure and optical properties of Ag-doped ZrO2 thin films prepared by sol gel method

Ag doped ZrO₂ thin films were deposited on quartz substrates by sol–gel dip coating technique. The effect of Ag doping on tetragonal to monoclinic phase transformation of ZrO₂ at a lower temperature (500 °C) was investigated by X-ray diffraction. It is found that the Ag doping promotes the phase transformation. The phase transformation can be attributed to the increase in the tetragonal grain size and concentration of oxygen vacancies in the presence of the Ag dopant. Accumulation of the Ag atoms at the film surface and surface morphology changes in the films were observed by AFM as a function of varying Ag concentration. X-ray photoelectron spectroscopy gave Ag 3d and O 1s spectra on Ag doped thin film. The chemical states of Ag have been identified as the monovalent state of Ag⁺ ions in ZrO₂. The Ag doped ZrO₂ thin films demonstrated the tailoring of band gap values. It is also found that the intensity of room temperature photoluminescence spectra is suppressed with Ag doping.     

Co doped ZnO nanowires as visible light photocatalysts

High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10⁻³ min⁻¹ in case of nanoparticles and 4.2·10⁻³ min⁻¹ in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn_0.95Co_0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.     

Electrochemical fabrication and characterization of p-CuSCN/n-ZnO heterojunction devices

p-CuSCN/n-ZnO heterojunction devices were prepared by depositing CuSCN electrochemically over a ZnO film previously deposited. The compact and smooth surface films of n-ZnO on FTO substrate were deposited electrochemically from a nonaqueous bath. The CuSCN films were characterized by cyclic voltammetry, chronoamperometry, SEM, energy-dispersive X-ray spectroscopy, and XRD measurements. The pure crystalline films of CuSCN with intrinsic trigonal pyramidal morphology over the ZnO films were obtained electrochemically by fixing the SCN/Cu ratio in the electrolytic bath 1.5:1 at 60 °C with ?0.4 V deposition potential. Photocurrent measurements showed the increase of intrinsic surface states or defects in ZnO/CuSCN interface. The I–V characteristic of p-CuSCN/n-ZnO heterojunctions shows good rectification behavior with a rectification ratio of 250 at ±2 V. The value of 2.81 of the ideality factor calculated by fitting the semilogarithmic I–V data with the ideal diode equation revealed the better electrical contact between the smooth ZnO and CuSCN films than that of ZnO nano-rods and CuSCN crystallites.     

Direct electrochemistry of hemoglobin on graphene/Fe3O4 nanocomposite-modified glass carbon electrode and its sensitive detection for hydrogen peroxide

Graphene/Fe₃O₄ nanocomposite was prepared for the immobilization of hemoglobin (Hb) to improve the electron transfer between Hb and glass carbon electrode (GCE). The characterization of nanocomposites was described by transmission electron microscopy, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemistry of Hb on the graphene/Fe₃O₄-based GCE was investigated by cyclic voltammetry and amperometric measurement. The modified electrode showed a wide linear range from 0.25 μmol/L to 1.7 mmol/L with a correlation coefficient of 0.9967. The detection limit of the H₂O₂ biosensor was estimated at 6.0?×?10^?6?mol/L at a signal-to-noise ratio of 3.     

Degradation of 2-Nitrophenol by Dielectric Barrier Discharge System: The Influence of Carbon Doped TiO<Subscript>2</Subscript> Photocatalyst Supported on Stainless Steel Mesh

This study investigated the degradation of 2-nitrophenol (2-NP) in aqueous solution by dielectric barrier discharge (DBD) system alone and its combination with supported TiO₂ photocatalysts. The TiO₂ photocatalyst supported on a stainless steel mesh was synthesised using sol–gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide/TiCl₄ followed by pyrolysis in the furnace under N₂ atmosphere at temperatures of 300, 350, or 400 °C for 3 h holding time. The supported catalysts were characterized for their morphologies, functional groups, crystallinity, surface areas and elemental chemical states by high resolution scanning electron microscope (HRSEM), Fourier transform infrared, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray photoelectron spectroscopy. The influence of solution pH on the degradation of 2-NP was investigated. The residual concentration of 2-NP and the intermediate compounds were quantified and identified using high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS). The concentration of the dissolved ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using ultraviolet–visible spectroscopy and photoluminescence spectroscopy. The HRSEM, HRTEM, XRD and BET analysis revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO₂ catalysts with high specific surface area was 350 °C at a 3 h holding time in N₂ atmosphere with a flow rate of 20 mL/min. The supporting procedure simultaneously carbon doped the photocatalyst. The DBD system alone without catalysts successfully mineralised 58.6% of 2-NP within 60 min while combined DBD/supported TiO₂ nanocrystals achieved 77.5% mineralisation within the same treatment time. The increase in mineralisation rate was attributed to the existence of a synergistic effect between the DBD system and the supported catalysts. 2-NP degradation proceeded via hydroxylation, nitration and denitration using DBD alone and combined DBD/Supported TiO₂ photocatalyst. Catechol, hydroquinone, hydroxyl-1,4-benzoquinone, 2-nitrohydroquinone, and 2,4-dinitrophenol were identified as major intermediate products. The order of production of free reactive species by DBD alone and combined DBD with supported photocatalyst was OH° > H₂O₂ > O₃.The results showed that the combined system was more than effective than DBD alone for the degradation of the 2-NP in aqueous solution.