Luminita Predoana

Influence of the substrate type on the microstructural, optical and electrical properties of sol–gel ITO films

AbstractIndium tin oxide (ITO) is recognized as the best transparent and conductive material [transparent conducting oxide (TCO)] until now and its properties are dependent on the preparation method. In the present work ITO films with In:Sn atomic ratio 9:1 were prepared by a sol–gel route on different substrates (microscope glass slides, microscope glass covered with one layer of SiO2 and Si wafers) for TCO applications. The multilayer ITO films were obtained by successive deposition by the dip-coating method and the films were characterized from the structural, morphological, optical, and electrical points of view using X-ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry and by Hall effect measurements, respectively. The results showed that the thickness, optical constants and carrier numbers depend strongly on the type of substrate, number of deposited layers and sol concentration. The optical properties of ITO films are closely related to their electrical properties. The enhancement of the conductivity was possible with the increase of crystallite size (which occurred after thermal treatment) and with the reduction of surface roughness.

Antimony Doped Bi2O3 Thin Films

Bismuth oxide system exhibit high oxide ionic conductivity and have been proposed as good electrolyte materials for application such as solid oxide fuel cell (SOFC) and oxygen sensor. A preliminary investigation for depositing thin and dense antimony doped Bi2O3 films based on wet chemical routes was realized. Antimony doped Bi2O3 films were deposited onto glass substrate from bismuth nitrate and antimony precursor solutions. As chelating agent polyethyleneglycol (PEG) was used and the above-mentioned precursor solutions were sufficiently viscous. Crystallization behavior and microstructure evolutions of the obtained films were investigated using spectroscopic ellipsometry (SE), polarized microscope observation, X-ray diffractometry (XRD), and infrared spectrometry (IR). The thickness and the porosity of the films were evaluated. The preparation techniques differ mainly in precursor materials and method of deposition, leading to different quality of the resulting films.

Optical properties of Na2O-TiO2-SiO2 glass films prepared by the sol-gel method

Layers based on TiO2-SiO2 systems fabricated by sol-gel method have been investigated for the preparation of planar waveguides, antireflective coatings, Bragg mirrors, etc. However, at high titania contents such materials exhibit high viscosities and tendency to phase separation. In this paper we present optical properties of films containing TiO2 which are prepared via a novel approach sol-gel on the basis of ternary Na2O-TiO2-SiO2 glasses and which can exhibit lower viscosities. Films of Na2O-TiO2-SiO2 systems were prepared from input sols mixed of silica, titania and sodium oxide sols. The silica sol was prepared from tetraethyl orthosilicate (TEOS), ethanol, hydrochloric acid and water, with a TEOS c= 2 mol/l and water/alkoxide ratio 1.75. The titania sol was mixed from titanium tetraisopropoxide (TiPr), propan-2-ol, nitric acid and water, c= 0.5 mol/l, RW= 0.42. The sodium oxide sols with c= 0.474 mol/l were prepared from sodium ethoxide and ethanol. Input sols were prepared by mixing the silica and titania sols first and then the sodium sol was added. The input sols were aged for one hour. Stable input sols were obtained. The input sols were deposited on glass and silica slides by dip-coating technique at a withdrawing speeds of 200 mm/min. Applied gel layers were thermally treated at temperatures of 450 and 900°C. Layers containing sodium oxide and titania in concentration ranges of 0-20 mol.% and 0-30 mol.% respectively have been fabricated. Optical properties of layers were determined by UV-VIS-NIR transmission and reflection spectrophotometry. Refractive indices of layers were determined by spectral ellipsometry and from transmission spectra. Optical properties were correlated with results of XRD spectroscopy, optical microscopy, and atomic force microscopy. Transparent homogenous films with a maximum refractive index of 1.61 at a wavelength of 600 nm have been obtained.

SiO 2 -TiO 2 Undoped or (Er 3+ ) Doped Thin Layers for Integrate Optics Prepared by Sol-Gel Method

The multilayer silica-titania waveguides undoped and doped with Er + were prepared by sol- gel method. The selected molar composition was 90%SiO2-10%TiO2 and the films were deposited on Si/SiO2 substrate by dip coating and by spin coating methods, followed by annealing at 900 C. The films were characterized by SE in the range of 300-700 nm. Differences were noticed depending on the method of deposition and number of layers deposited. Optical waveguides and photonic circuits (microring resonators) were obtained by patterning Er-doped SiO2-TiO2 sol-gel layers deposited on oxidized silicon wafers (oxide thickness over 1700 nm).

Monocomponent Powders and Thin Films in the Binary System SiO2–TiO2

In this work, we report the sol-gel alkoxide route preparation of nanostructured SiO2 and TiO2 powders as well as TiO2-SiO2 thin films obtained by dip-coating. Thermal analysis, morphology and structure were characterized for powders and correlation between preparation method and optical properties of binary materials (SiO2-TiO2) for thin films was approached. Spectroscopic Ellipsometry (SE), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) have been used for the physical characterization of the films.

SiO2-ZrO2 Sol-Gel Nanostructured Thin Films with Optical Properties

SiO2-ZrO2 based nanometric multilayers films have been prepared by sol-gel method from metallorganic precursors by low temperature polymerization reactions. Simultaneous gelation of both cations was realized. Homogeneous and transparent films were poduced on glass substrate at room temperature by dipping procedure. Each deposited layer was thermal treated 1h at 300°C. The coatings were characterized by XRD, spectroellipsometry (SE), UV-VIS spectroscopy and AFM method. The influence of number of coatings and thermal treatments on the optical and structural proprieties of the films was established.

Lithium Cobalt Oxide (LiCoO2) Films Obtained by Different Sol-Gel Methods

Lithium cobalt oxide (LiCoO2) synthesis was realized by sol-gel process using two — alcoholic and aqueous — routes. The chemicals 2-Co methoxyethoxide and lithium nitrate in alcoholic solutions in stoichiometric molar ratio were used in the alcoholic route. In the aqueous route, the precursors were lithium nitrate and cobalt acetate in equimolar ratio. Polyethyleneglycol (PEG)200 was added as chelating agent.