Effect of Al doping on the conductivity type inversion and electro-optical properties of SnO2 thin films synthesized by sol-gel technique

Al doped SnO₂ thin films have been synthesized by a sol-gel dip coating technique with different percentages of Al on glass and silicon substrates. X-ray diffraction studies confirmed the proper phase formation in the films and atomic percentage of aluminium doping in the films was obtained by energy dispersive X-ray studies. SEM studies showed the particle sizes lying in the range 100–150 nm for the undoped films and it decreased with increase of Al doping. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region and the transparency increases with the increase of Al doping in the films. The direct allowed bandgap of the films have been measured for different Al concentration and they lie within the range of 3.87–4.21 eV. FTIR studies depicted the presence of Sn–O, Al–O, bonding within the films. The room temperature electrical conductivities of the films are obtained in the range of 0.21 S cm⁻¹ to 1.36 S cm⁻¹ for variation of Al doping in the films 2.31–18.56%. Room temperature Seebeck coefficients, S_RT of the films were found in the range +56.0 μVK⁻¹ to −23.3 μVK⁻¹ for variation of Al doping in the films 18.56–8.16%. It is observed that the Seebeck coefficient changes its sign at 12.05% of Al in the films indicating that below 12.05% of Al doping, SnO₂:Al behaves as an n-type material and above this percentage it is a p-type material.     

Preparation and Optical Properties of Gold-Dispersed BaTiO3, PGO (Pb5Ge3O11) and PLT (Pb1-1.5xLaxTiO3) Thin Films by Sol-Gel Process

Gold-dispersed BaTiO₃, PGO and PLT thin films, which will be used for third-order nonlinear optical devices, were prepared by sol-gel process with spin-coating using HAuCl₄4H₂O, Ba(CH₃COO)₂, Ti[O(CH₂)₃CH₃]₄, Pb(CH₃COO)₂3H₂O, Ge[O-n-C₄H₉]₄, La(CH₃COO)₃1.5 H₂O as starting materials. The thin films were heat-treated in air at temperatures ranging from 400 to 800 for 1 h. The nonlinear optical property of these thin films was measured by the degenerate four-wave mixing (DFWM) method using a frequency-doubled Nd: YAG laser with 20 ps pulse duration. Third-order nonlinear susceptibility χ⁽³⁾ of gold-dispersed BaTiO₃, PGO and PLT thin films with 5 vol% of gold were 1.410⁻⁶ esu, 3.510⁻⁷ esu respectively. The large χ⁽³⁾ may be ascribed to the high dielectric constant of the films.     

Study of third-order nonlinear susceptibility of polySchiff base containing triphenylamine

PolySchiff base containing triphenylamine has been synthesized by polycondensation and character-ized by FT-IR,NMR,UV-visible spectrometer. Measurements of the third-order optical nonlinear sus-ceptibility χ(3) by Z-scan technique have shown that the large nonlinearity is dominated by the two-photon absorption in PSB. The sign and size of real part Reχ(3) ,nonlinear refractive index n2 have been measured with the condition of 532 nm,8 ns-duration pulses to be -1.23×10-10 esu,-3.06×10-12 esu;nonlinear absorption index β and size of image part Imχ(3) to be 3.63×10-10 m/W,1.15×10-11 esu,respec-tively,so the third-order nonlinear susceptibility χ(3) is 1.19×10-11 esu. The value is larger than other polymers reported. PSB is self-focusing material and has potential application in nonlinear optic field.     

Comparative study of electrolessly deposited Pd/Ag films onto p-silicon (100)-activated seed layers of Ag and Pd

Pd/Ag films were electrolessly deposited onto p-silicon (100)-activated seed layers of Ag and Pd, respectively, in the solution of 0.005 mol l⁻¹ AgNO₃ + 0.005 mol l⁻¹ PdCl₂ + 4.5 mol l⁻¹ NH₃ + 0.16 mol l⁻¹ Na₂EDTA+0.1 mol l⁻¹ NH₂NH₂ (pH 10.5) at room temperature. The morphology and composition of the films were studied comparatively by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Cathodic polarization curves for hydrogen evolution were recorded in 0.5-mol l⁻¹ H₂SO₄ without illumination, in which the obtained films served as working electrodes. The experimental results show that the film obtained on the Ag seed layer was rather a pure Ag film and not a Pd/Ag film, and the Ag deposition rate on Pd sites was much faster than that on Ag sites.     

Amperometric enzyme electrode for glucose determination based on poly(pyrrole-2-aminobenzoic acid)

Polymerization of pyrrole and 2-aminobenzoic acid has been investigated, and a functionalized stable film of poly(pyrrole-2-aminobenzoic acid) (PP2ABA) has been obtained electrochemically onto platinum electrode. Different cyclic voltammetric behavior is obtained for polypyrrole and PP2ABA during electrosynthesis. Fourier-transformed infrared spectrometry and surface-enhanced Raman spectrometry measurements on the two films have confirmed the presence of carboxylate group in the films. The enzyme, glucose oxidase, was covalently immobilized on a conducting PP2ABA film, and amperometric response was measured as a function of concentration of glucose at a potential of 0.7 V vs Ag/AgCl in 0.1 M phosphate buffer at pH 6.2. The effect of polymeric film thickness, pH, and possible interferents were investigated. The linear range of the calibration curve is from 3 to 40 mM with a sensitivity of 0.058 μA mM⁻¹ cm⁻² and a limit of detection of 0.5 mM. The apperent Mishaelis–Menten constant K _M is calculated to be 1 × 10⁻² mM, and the response time is 5 s.     

Redox reactions of nitrite ions on the surface of colloidal magnetite particles coated with chondroitin sulfate

Colloidal magnetite particles coated with chondroitin sulfate (abbreviated as Fe/CS) were prepared under conditions of varying Fe(II) fractions at a fixed Fe concentration and a given concentration of CS. The average size of the magnetite core region was estimated as 7 nm from transmittance electron microscopy measurements, while the size of the Fe/CS particles ranged 155–175 nm, as estimated using Rayleigh scattering measurements by reference to a control size derived from the dynamic light scattering. The reaction of various Fe/CS with NO⁻ ₂ in aqueous solutions was determined by fluorometry using 2,3-diaminonaphthalene as a probe and by gas chromatography–mass spectrometry. The concentrations of NO⁻ ₂ in the reaction mixtures decreased in the presence of Fe/CS to a greater extent under Ar compared with aerobic conditions. The reactivity of Fe/CS toward NO⁻ ₂ under aerobic conditions increased with decreasing the size of Fe/CS particles or with increasing content of Fe(III) in the Fe/CS solutions, but was independent of the Fe(II) fraction in the preparation process. While CS molecules had no influence on the NO⁻ ₂ decomposition, those coated with the magnetite core may prevent the diffusion of NO⁻ ₂ to be adsorbed on the core surfaces. NO⁻ ₂ was concluded to undergo redox reactions with Fe(II) and Fe(III) located on the core surface of magnetite crystalline structures of Fe/CS. Received: 12 April 2000/Accepted: 9 August 2000     

Sol-Gel Derived Hydrated Nickel Oxide Electrochromic Films: Optical, Spectroelectrochemical and Structural Properties

Electrochromic hydrated Ni-oxide films were prepared using a dip-coating technique from a nickel sulphate heptahydrate precursor in combination with glycerol, formamide and polyvinyalcohol. In-situ monochromatic (λ=400 nm) spectroelectrochemical measurements using a potential of −0.4 V to 0.8 V in 0.1M LiOH electrolyte revealed that the electrochromic efficiency was 23.5 cm²/C. The observed colouring/bleaching transmittance of a 100 nm thick film changed during potential cycling (20 cycles) by 45%. Ex-situ FT-IR absorption/reflection measurements performed at near-grazing incidence angle conditions (80°) confirmed transformation of as-deposited α-Ni(OH)₂ phase to β-Ni(OH)₂ at cathodic (bleached state) and β-NiOOH at anodic (coloured state) potentials during extended cycling (200 cycles). Clear evidence of the OH⁻ ions insertion and release of SO ₄ ²⁻ ions from the as-deposited films when soaked (0.5 hour) in 0.1M LiOH are given. These processes are accompanied by the transformation of the residual COO⁻ groups originating from the peptisation with glacial acetic acid into CO ₃ ²⁻ species residing in the films during extensive potential cycling.     

Study on the thermodynamic properties of cholesterol

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δ_r U _m^θ(−14358.4±20.65 kJ mol⁻¹), Δ_r H _m^θ(−14385.7 kJ mol⁻¹) of combustion reaction and Δ_f H _m^θ(2812.9 kJ mol⁻¹) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.     

Preparation and Characterization of HgxCd1-xS and PbxCd1-xS Quantum Dots and Doped Thin Films

Thin silica and silica-titania films doped with sulfide nanocrystals of controlled size were fabricated by a method based on the preparation of colloidal particles and their introduction into a glassy matrix through the sol-gel method. Colloidal sols of composition Hg_xCd_1-xS and Pb_xCd_1-xS (with _x ranging from 0 to 1) were prepared and used to dope alkoxide solutions for the deposition of thin silica and silica-titania films. Optical absorption spectra were taken on both precursor colloidal sols and derived doped films. X-ray diffraction characterization gave structural information on the nature and size of particles in powders obtained by precipitation from colloidal sols and in doped films. The advantages and limits of the investigated systems are discussed in light of possible applications. The nonlinear properties of the most interesting PbS-doped planar waveguides have been investigated in the near-infrared, at 1.064 m. A reversible nonlinear effect was measured, with n ₂ values ranging from -5 to -20×10^-9 cm²/kW.     

Preparation of TeOx–SiO2 film with excellent third-order nonlinear optical properties by electrochemically induced sol–gel method

TeO_x-SiO₂ composite films having third-order nonlinearities were prepared by electrochemically induced sol-gel deposition method on ITO substrate.The third-order optical nonlinearities of the films were measured by Z-scan technique.The third-order nonlinear susceptibilities(χ^（3）) of the as-prepared films are 5.9×10^-7 to 4.29×10^-6esu.The surface morphology and composition of the films were characterized by SEM/EDX,which identified that Te metallic particles well dispersed in TeO_x-SiO₂ gel films.