Optical properties of nanostructure boron doped NiO thin films

Boron doped NiO films were prepared by sol–gel method. The effects of B content on the morphological and optical properties of NiO films were studied with atomic force microscopy, and optical characterization method. The average transmittance at the visible region is reached to 75 % for lower doped films (0.1 and 0.2 % B), whereas, the recorded average value of transmittance was about 62 % for doped film with 1 % B throughout the region. The optical energy gap value for pure NiO film was found to be 3.73 eV. These values were affected by B doping with non-monotonic variation and reached to 3.64 eV for 0.1 % B doped NiO. Also, the refractive index dispersion and dielectric constants of the NiO films were studied throughout the investigated range of wavelengths. The obtained results indicate that the optical parameters of the NiO film are controlled with boron doping.     

Polyaniline thin film optical waveguides for integrated optics and VLSI prepared by vacuum evaporation technique

Polyaniline is emerging as an important polymer material which offers challenging opportunities for both fundamental research and new technological applications in waveguides. Metal doped polyaniline has been prepared initially in the form of powder by a solution growth technique. The emeraldine salt with doped metal was also prepared by solution growth technique. This powder was used for vacuum evaporation on optically flat glass substrate. The dark green doped (Fe, Al) polyaniline thin films were prepared by vacuum evaporation technique (10^?4 torr). Deposited waveguide thin films have been characterized structurally, using X‐ray diffraction (XRD), optically etc. Effective refractive index of the thin film waveguide was also calculated theoretically and experimentally. Waveguide parameters, namely refractive index, propagation loss and depth of vacuum deposited polyaniline thin films optical waveguide have been determined. The optical spectra and structure and waveguide parameters of vacuum deposited polyaniline thin films are strongly affected by the type of doping. It is possible to reduce the losses by addition of Fe to the vacuum deposited polyanine thin film and modify the effective refractive index (O_eff) according to particular requirements. Results are compared with the results in the literature. Copyright © 2002 John Wiley & Sons, Ltd.     

Band gap tailoring of chemically synthesized lead sulfide thin films by in situ Sn doping

In the present report, undoped and tin (Sn)‐doped lead sulfide thin films were synthesized via chemical bath deposition method. The effects of Sn molar concentration on the optical, structural, and morphological properties were systematically studied. The concentration of Sn in the chemical bath was characterized by the ratio of [Sn⁺²]/[Pb⁺²] and varied from 0 to 15 at.%. Both doped and undoped thin films were polycrystalline in nature with a face‐centered cubic crystal structure; however, the preferred orientations of the crystallites were varied along the (111) and (200) planes with Sn‐doping concentration. The X‐ray powder diffraction results also showed that peak intensities and the crystalline size were decreased with increasing Sn concentration. The lattice constant varied with Sn concentration and found in the range of 6.020 to 5.944 Å. The variation of Sn concentration in PbS:Sn thin films were confirmed by energy dispersive X‐ray analyses study. The scanning electron microscope and atomic force microscopy studies revealed that Sn doping had a critical role on the surface roughness and morphology of the PbS:Sn thin films. The optical band gap study showed that the band gap of PbS:Sn thin films were engineered from 0.676 to 1.345 eV because of incorporation of Sn⁺² ions via cost‐effective chemical route. Room temperature photoluminescence spectra showed a well‐defined peak at 427 nm and shoulders at 405 and 462 nm for all Sn‐doped and undoped PbS samples.     

Improved optical and electrical properties of sol–gel-derived boron-doped zinc oxide thin films

Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films.     

Photocatalytic Degradation of Glyphosate in Water by N‐Doped SnO2/TiO2 Thin‐Film‐Coated Glass Fibers

Photocatalytic degradation of glyphosate contaminated in water was investigated. The N‐doped SnO₂/TiO₂ films were prepared via sol–gel method, and coated on glass fibers by dipping method. The effects of nitrogen doping on coating morphology, physical properties and glyphosate degradation rates were experimentally determined. Main variable was the concentration of nitrogen doping in range 0–40 mol%. Nitrogen doping results in shifting the absorption wavelengths and narrowing the band gap energy those lead to enhancement of photocatalytic performance. The near optimal 20N/SnO₂/TiO₂ composite thin film exhibited about two‐ and four‐folds of glyphosate degradation rates compared to the undoped SnO₂/TiO₂ and TiO₂ films when photocatalytic treatment were performed under UV and solar irradiations, respectively, due to its narrowest band gap energy (optical absorption wavelength shifting to visible light region) and smallest crystallite size influenced by N‐doping.     

Investigation of structural,optical and luminescent properties of sprayed N-doped zinc oxide thin films

N-doped ZnO (NZO) thin films are synthesized via spray pyrolysis technique in aqueous medium treating zinc acetate and N,N-dimethylformamide as precursors. Influence of N doping on structural, optical and luminescence properties have been investigated. Films are nanocrystalline having hexagonal crystal structure. Raman analysis depicts an existence of NZnO structure in NZO thin film. XPS spectrum of N 1s shows the 400 eV peak terminally bonded, well screened molecular nitrogen (γ-N₂). Lowest direct band gap of 3.17 eV has been observed for 10 at% NZO thin film. The UV, blue, and green deep-level emissions in photoluminescence of NZO films are due to Zn interstitials and O vacancies.     

Enhanced lithium electrochemical performance and optical properties of CeO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> nanocomposite thin films by transition metal (TM: Ni,Mn, and Co) doping

Undoped and transition metal (TM: Ni, Mn, Co)-doped CeO₂–SnO₂ nanocomposite thin films were prepared by sol-gel dip coating (SGDC) technique. The grazing incidence X-ray diffraction (GIXRD) patterns indicated that CeO₂–SnO₂ film has a cubic structure of CeO₂ and the crystallinity deteriorated with incorporation of dopant. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that the surface morphology of the films was affected by TM incorporation. The surface roughness and fractal dimensions of CeO₂–SnO₂ films increased with doping. The average transmittance of CeO₂–SnO₂ thin film is found nearly 80% in the visible region and increased with doping. The absorption edge revealed a blue shift toward shorter wavelengths after incorporation of TM ions. The compositional dependence of optical parameters such as refractive index, extinction coefficient, and optical conductivity were also investigated. Cyclic voltammetry measurements showed that ion storage capacity was decreased significantly with increasing scan rate. The undoped and doped CeO₂–SnO₂ films showed good reversible cycle of intercalation/deintercalation of Li⁺ ions. The ion storage capacity and electrochemical stability were enhanced with transition metal doping. The Mn-doped CeO₂–SnO₂ composite thin film had better ion storage capacity rather than other samples due to its special porous morphology. The Li diffusion toward electrode surface was described in terms of self-similar fractal dimension. A quenching in blue-green photoluminescence (PL) intensity of CeO₂–SnO₂ films was occurred by transition metal doping.

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Open air annealing effect on the electrical and optical properties of tin doped ZnO nanostructure

Transparent conducting undoped and tin doped ZnO multilayer films were deposited by sol-gel method. Effect of open air annealing on different parameters like grain size, carrier density, band gap, resistivity, refractive index and extinction coefficient were investigated. Films were deposited on glass and silicon substrate by keeping doping concentration 4 at%. It was observed that tin doping reduces resistivity from 194.6 Ω cm to 3.11 Ω cm. Optical transmission spectra exhibit transmittance above 88% in visible range. Maximum carrier density of 11.9 × 10¹⁸ cm⁻³ and band gap of 3.24 eV was estimated at 375 °C. Scanning Electron Microscopy showed homogenous worm like morphology. Atomic force microscopy revealed pyramid shaped nanostructure of tin doped ZnO.     

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.     

Sol-gel processing and properties of cerium doped Barium Strontium Titanate thin films

A stock solution sol-gel based method for making Barium Strontium Titanate (BST) thin films has been developed. A modified titanium alkoxide was combined with a barium and/or strontium inorganic salt in methoxyethanol and ethylene glycol to form the solution. The effect of chemistry on the stability of this BST solution is discussed. The crystallization temperature of 700–725°C for rapid thermally processed films dropped by 100°C using cerium doping. The permittivity for undoped films was 250 and doping by 3 at. % Ce increased the dielectric constant by 20%. A remanent polarization of approximately 0.5 C/cm² and coercive field of 28 kV/cm were measured for the undoped films. The leakage current densities were <10 nA/cm² at E=60 kV/cm and improved for cerium concentrations up to 3 at. %. The charge storage density was 50 fF/m² at 200 kV/cm and the DC breakdown voltage was 300 kV/cm for Ce doped films.     

Influence of nickel incorporation on structural,optical and electrical characteristics of SILAR synthesized CuO thin films

In this report, we have primarily studied the influence of nickel (Ni) incorporation on ac electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of copper oxide (CuO) thin films synthesized by successive ion layer adsorption and reaction (SILAR) technique. The materials has been characterized using X-ray diffraction and UV–VIS spectrophotometric measurements. Reduction in grain size in doped films up to a certain extent of doping (tentatively 6%) were confirmed from XRD analysis, beyond which there is a reverse tendency. Increase in band gap in doped films were observed up to 6% doping level which could be associated with enhanced carrier density in doped films. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for doped samples. The results are useful for capacitive application of the films. Beyond 6% doping level, AC conductivity and dielectric constant shows a reverse tendency indicating reduced density of charge carriers. Nyquist plot shows contribution of both grain and grain boundary towards total resistance and capacitance. Imaginary part of complex modulus and imaginary part of complex impedance was used to find the migration/activation energy to electrical conduction process. Nearly identical result was obtained from relaxation frequency/relaxation time approach suggesting hopping mechanism of charge carriers.

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Preparation and characterization of nanorods Sb doped CdO films by sol–gel technique

Pure and antimony (Sb) doped CdO films were grown using sol–gel spin coating technique. The structural properties of the films were investigated using atomic force microscopy. The structure of CdO film is converted from microrods to nanorods with Sb dopant. The analysis of optical absorption revealed that optical bandgap of the films changes with doping. The optical bandgap for 0.1, 0.5, 1.0, and 2.0% Sb doped CdO was determined to be 2.28, 2.30, 2.56, and 2.42 eV, respectively. Other optical constants such as refractive index, extinction coefficient, and dielectric constants were calculated using the optical data. The refractive index dispersion of the films obeys the single oscillator model. The volume and surface energy loss functions were calculated and observed to increase with increase in the photon energy.     

Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films

Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.     

Preparation and nonlinear optical properties of Au nanoparticles doped TiO2 thin films

Nano-sized noble metal nanoparticles doped dielectric composite films with large third-order nonlinear susceptibility due to the confinement and the enhancement of local field were considered to be applied for optical information processing devices, such as optical switch or all optical logical gates. In this paper, sol–gel titania thin films doped with gold nanoparticles (AuNPs, ~10 nm in average size) were prepared. AuNPs were firstly synthesized from HAuCl₄ in aqueous solution at ~60 °C, using trisodium citrate as the reducing agent, polyvinylpyrrolidone as the stable agent; then the particle size and optical absorption spectra of the AuNPs in aqueous solutions were characterized by transmitting electron microscopy and UV–Vis–NIR spectrometry. Sol–gel 2AuNPs–100TiO₂ (in %mol) thin films (5 layers, ~1 μm in thickness) were deposited on silica glass slides by multilayer dip-coating. After heat-treated at 300–1,000 °C in air, the AuNPs–TiO₂ thin films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The nonlinear optical properties of the AuNPs–TiO₂ thin films were measured with the Z-scan technique, using a femtosecond laser (200 fs) at the wavelength of 800 nm. The third-order nonlinear refractive index and nonlinear absorption coefficient of 2AuNPs–100TiO₂ films were at the order of 10^?12 cm²/W, and the order of 10^?6 cm/W, respectively, and the third-order optical nonlinear susceptibility χ⁽³⁾ was ~6.88 × 10^?10 esu.     

Azo dye doped polymer films for nonlinear optical applications

Azo dye doped polymer films were prepared on glass substrates using spin-coating technique. FTIR, UV-Vis spectra and PL measurements were recorded to characterize the structure of the metanil yellow doped PVA films. Surface morphology and thickness of the films were studied using AFM and FESEM. The magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ3 of metanil yellow were determined by the Z-scan technique. The nonlinear refractive index n2 and the nonlinear absorption coefficient β of the azo dye doped polymer films were calculated respectively. The real part of the third-order susceptibility χ3 is much larger than its imaginary part indicating that the third-order optical response of the metanil yellow doped PVA films is dominated by the optical nonlinear refractive behavior.     

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.     

Ellipsometric investigations of Fe3+-doped polyvinyl alcohol films

In this work, we study the inclusion mechanism of Fe³⁺ ions in a polyvinyl alcohol (PVA) matrix. Thin films of pure and FeCl₃-doped PVA on silicon substrates, prepared by the spin-coating method, are investigated using spectroscopic ellipsometry (SE) and Fourier transform infrared (FT-IR) spectroscopy. SE measurements of PVA and Fe³⁺-doped thin films are carried out at an incidence angle of 75° over the wavelength range of 0.24–1.1 μm. An optical model is used to obtain the refractive index (n) and the extinction coefficient (k). The gap energy E _g is afterwards evaluated. The Fe³⁺ doping is found to affect strongly the optical parameters of the polymer films. In fact, an increase in the refractive index with doping is observed, resulting from the intermolecular hydrogen bonding between Fe³⁺ ions with the adjacent OH group of PVA. The increase of the thin films' absorption with doping is estimated by the k spectral profile analysis. The gap energy is then calculated and shows an important decrease with the Fe³⁺ filling, more pronounced for low doped samples. Such a behavior is confirmed by FT-IR analysis.     

The optical properties of a novel metal-free phthalocyanine

In the present work, 4-(4′-dodecyloxycarbonyl) phenoxy phthalonitrile was synthesized and then this phthalonitrile derivative was cyclotetramerized in dodecanol resulting a new metal-free phthalocyanine. The optical properties of this phthalocyanine were investigated. Novel metal-free phthalocyanine thin films were deposited on indium tin oxide-coated glass substrates by spinning method. Surface and microstructural properties of the films were characterized by atomic force microscopy and scanning electron microscopy. Both the transmittance and reflectance spectra of the deposited films were recorded using an NKD analyser. The optical band gap energy, the thickness of thin films, refractive index (n) and extinction coefficient (k) were calculated as 2.7 eV, 300 nm, 1.47 and 0.02, respectively.     

The influence of diffusion temperature on the structural, optical and magnetic properties of manganese-doped zinc oxysulfide thin films

We investigated the structural, optical and magnetic properties of Mn-doped zinc oxysulfide films. Zn(O,S) films were deposited by a spray pyrolysis method on glass substrate. A thin Mn layer evaporated on these films served as the source for the diffusion doping. The XRD pattern of undoped films revealed the presence of two wurtzite phases corresponding to ZnS and ZnO with a strong preferred orientation along the ZnS (0 0 2) hexagonal plane direction. SEM showed a similar surface morphology for the undoped and Mn-doped films, displaying regular arrays of hexagonal micro-rods perpendicular to the substrate. The optical transmission measurements showed that both undoped and Mn diffusion-doped films had a low average transmittance less than about 10%. The gap energy is decreased from 3.42 to 3.33 eV upon annealing at 400 °C. Photoluminescence studies at 300 K show that the incorporation of manganese leads to a decrease of deep level band intensity compared to undoped sample. Clear ferromagnetic loops were observed for the Mn-doped Zn(O,S) films, which might be due to the presence of point defects.     

Effect of Fluorine Doping on Semiconductor to Metal-Like Transition and Optical Properties of Cadmium Oxide Thin Films Deposited by Sol–Gel Process

Highly conducting fluorine doped n-type cadmium oxide thin films have been synthesized by sol–gel dip coating process on glass and Si substrates for various fluorine concentrations in the films. X-ray diffraction pattern confirmed the cubic CdO phase formation and SEM micrograph showed fine particles of CdO with size ~0.3 m. F concentration in the films was varied from 1.8% to 18.7% as determined from energy dispersive X-ray analysis (EDX). The resistivity of the CdO films decreased with increase of F doping and increase of temperature below 14.6% of F, as usual for semiconductors. Above this F concentration the resistivity increased with increase of temperature like metals. Hall measurement showed very high carrier concentrations in the films lying in the range of ~2.93 × 10²⁰ cm^–3 to 4.56 × 10²¹ cm^–3. UV-VIS-NIR spectrum of the films showed the optical bandgap energy increased with increase of F doping and corresponding carrier concentrations obtained from Burstein-Moss shift also support the Hall measurement results.