Prasanta Kumar Biswas

Effects of tin on IR reflectivity, thermal emissivity, Hall mobility and plasma wavelength of sol-gel indium tin oxide films on glass

Sol–gel indium tin oxide films (ITO) of various composition (In:Sn atomic ratio=90:10 to 30:70) prepared from salt-based precursors were deposited on bare and SiO2 coated (∼200 nm thickness) sheet glass substrates. The films were cured in air and then annealed under N2/H2O at ∼500 °C to obtain ITO films of thickness 250–320 nm. Directional hemispherical reflectance (Rh) and trasmittance (Th) of the films were measured in the wavelength range 0.25–18 μm. The reflectance of the films at 10 μm (near the peak wavelength of black body radiation) was in the range 0.18–0.55. The thermal emissivity (ed) was evaluated from the relation: ed=1−Rh−Th (Th≈0, for sheet glass in the wavelength range 5–18 μm) and it was in the range 0.47–0.90. Reflectance (Rh) was also evaluated from measured sheet resistance values (R□), from the relation Rh=(1+2e0c0R□)−2, where e0 and c0 are the permittivity of electron in vacuum and velocity of light, respectively. Specific resistivity of the films, measured by van-der Pauw method at ambient temperature was in the range 1.7±0.3×10−3 to 6.6±1.2×10−3 Ω cm. The sheet resistance (R□) of the films was in the range 68–212 Ω/□. Free electron carrier concentration (N) and Hall mobility (μ) of the films were in the ranges (0.66±0.18)×1020 to (3.7±1.0)×1020 cm−3 and (4.4±1.5) to (20±5) cm2/V s, respectively. These values were utilized to evaluate plasma wavelength (λP) of the conducting films which were in the range 1.72±0.24–4.07±0.58 μm. Considerable variations of the above properties were observed with increasing Sn content but minimum thermal emissivity and maximum IR reflectivity were observed in the case of In:Sn=70:30.

The effect of Sn(IV) on transformation of co-precipitated hydrated In(III) and Sn(IV) hydroxides to indium tin oxide (ITO) powder

Multicomponent metal oxide (indium tin oxide, ITO) powders were prepared by the hydrolysis of their corresponding metal salts following co-precipitation technique. Indium tin oxide powders with relatively high content of tin were prepared by the treatment of aqueous NH4OH with the mixture of aqueous In(NO3)3 and SnCl4 solution (pH=8.4–8.7) at an ambient temperature. The composition of the powders were 90:10, 70:30 and 50:50 (In/Sn atomic ratio). The air-dried powders were cured at different temperatures and also at different atmospheric conditions [air and H2(5%)–Ar(95%)]. They were characterized by FTIR spectroscopy, thermal analysis and X-ray powder diffraction studies. FTIR spectroscopy and thermal analysis of powders revealed that the air-dried powders existed as hydroxides of In3+ and Sn4+ in the solid state which transformed to ITO via some metastable intermediates after 300 °C. In addition, the formation of InOIn and SnOSn type of bonding was also predicted by FTIR. Below 200 °C, the powders predominantly existed as corresponding hydrated oxide phases which corresponded to possible formulations, In(OH)3 and SnO3H2 and transformed to ITO phases after 300 °C. The powders containing below 30% Sn showed pure cubic In2O3 phase whereas the casseterite structure of SnO2 phase was observed in the case of relatively high Sn content (Sn>30%). The crystallite size of the powders increased with temperature as well as with increase in Sn content.

Surface characterization of sol-gel derived indium tin oxide films on glass

Indium tin oxide (ITO) films containing different In : Sn atomic ratios, viz. 90 :10, 70 :30, 50 : 50, 30 :70, were deposited on two types of glass substrates by sol-gel spinning technique. XPS analysis of the films was done under as-received and after-sputtering conditions. The narrow spectra obtained for the Na1s, In3d, Sn3d and O1s have been discussed. Oxygen was found to exist in three chemical environments in as-received samples due to the existence of (i) environmental hydroxyl (-OH) group, (ii) crystalline ITO and (iii) amorphous ITO; but it was in two chemical environments, (ii) and (iii), after surface cleaning by sputtering. The presence of both tin metal and tin oxides was confirmed by the peak analysis of Sn3d. The In : Sn atomic ratio taken in the precursor sols did not change considerably in the case of developed films of low Sn content, but considerable change was observed in the films having high Sn content.

Optical and electrochromic properties of sol-gel WO3 films on conducting glass

Abstract The precursor containing peroxotungstic acid (PTA) was prepared by the reaction of tungstic acid with H 2 O 2 (30%) solution in water–ethanol mixture. This was utilized for the deposition of WO 3 · n H 2 O film on conducting (F-doped SnO 2 coated) flat glass substrate by the dipping technique. The films were cured in the temperature range of 200–300 °C in air. The optimum thickness of the film (300–500 nm) was obtained by successive operations (3–5 numbers). Films of around 500 nm thickness exhibited 60–70% transmission in the visible region. Electrochromic properties (colouration↔bleaching) of the films were studied by cyclic voltammetry (CV) using a classical three-electrode potentiostatic cell system. The cell system consists of a WO 3 -coated sample as working electrode, a platinum rod as counter electrode, Ag/AgCl as reference electrode and 0.5 M LiClO 4 in propylene carbonate as an electrolyte. Several voltammograms were recorded within the voltage range of +1.5 to −1.8 V with a scan rate of 50 mV/s. A continuous curve was observed for the films at a certain voltage sweep where a random insertion of Li + occurred reversibly in a definite crystallographic site [WO 3 (colourless)+ n Li + + n e − ↔ Li n WO 3 (blue)]. A dark blue colouration (% T =20–30% in the visible region) was observed under a constant voltage of −1.8 V whereas bleaching occurred at +1.0 V (% T =60–70%), which was studied simultaneously along with the voltage sweep of CV. The colouration time ( T col ) and the bleaching time ( T bl ) were almost equal as revealed by the simultaneous study of the second signal (photomultiplier output coupled with the electrochemistry system) during colouration↔bleaching. Coatings of about 500 nm thickness exhibited more that 500 cycles (colouration↔bleaching). The reversibility of the cycle remained good but the intensity of the colouration decreased with the number of cycles. This was possibly due to the structural deformation of WO 3 films for its long time exposure to the electrolytic solution. The cathodic current ( I c ) and anodic current ( I a ) increased with increasing thickness.

Vanadium Oxide: From Gels to Nanotubes

Vanadium oxide nanotubes (VOx-NT) have been prepared by mixing hexadecylamine with V2O5·nH2O gels. This procedure was followed by an hydrothermal treatment (150–180°C, 2–7 days) which leads to a large quantity of VOx-NT. SEM and XRD analysis have been used to optimize the temperature and reaction time required for production of VOx-Nt and morphology of the nanotubes investigated by TEM.

Characterization of oxygen deficiency and trivalent zirconium in sol-gel derived zirconia films

Abstract Zirconia films were prepared on silica glass substrates from the precursor solution of zirconium oxychloride octahydrate and acetic acid. The films were baked at 450 °C. The existence of oxygen deficiency and Zr(III) in the sol-gel derived zirconia films was characterized by UV and ESR spectral studies. The films baked in air, as well as in oxygen atmospheres, exhibited different UV absorption behaviours. The electronic transition at 5.45 eV of the air-baked film was identified with oxygen deficiency by studies of the functional dependence of the optical absorption coefficient on photon energy. The fundamental electronic transition at 5.80 eV of the films baked in different atmospheres was also identified by the same technique. The non-stoichiometric formula of zirconia (ZrO 1.63 ) was calculated from the relative change of the absorption coefficients (at 5.80 eV) of films of the same thickness 1818 ± 20 A cured in different atmospheres. The size of zirconia particles was determined by transmission electron microscopy (TEM) and found to be below 150 A. Electron diffraction patterns suggested that the structure of the metastable zirconia was cubic.

Optical characterization of in-situ generated Cu2O excitons in solution derived nano-zirconia film matrix

Abstract Cu2O excitons were generated in-situ in a nano-zirconia film matrix on silica glass substrate from the precursor solution containing Cu(II) nitrate trihydrate and zirconium oxychloride octahydrate. The films were annealed in the temperature range 200–1200 °C and characterized by transmission electron microscopy (TEM), UV-VIS-NIR and fluorescence spectroscopy. In the UV-VIS spectra of the films most of the UV and visible bands shifted towards longer wavelengths with increasing annealing temperature and the corresponding Cu2O microcrystallite size was evaluated from the shifting of the UV bands (271–371 nm). Wannier hydrogen-like excitonic transitions, e.g., blue, green, yellow series of Cu2O excitons were observed in the visible region. Excitation dependent fluorescence bands were observed in the visible region and the 400 nm excitation depicted two distinct fluorescence bands in the green (~ 525 nm) and red (~ 630 nm) regions. The intensity ratios of green and red fluorescences and vice versa were found to be dependent on the microcrystallite size. Tentative band assignments have been proposed from the excitonic absorption and fluorescence bands.

Sol-gel preparation of wavelength-selective reflecting coatings in the system ZrO2SiO2

Multilayer, wavelength-selective reflecting coatings were prepared by alternate stackings of amorphous zirconia and silica by the sol-gel spinning technique; alkoxide-derived, polymeric sols were used. A detuned, i.e. non-λ/4 stacking system was applied. The spectrum showed a transmission minimum (∼ 4%) at a wavelength of 430 nm, with a bandwidth of 72.5 nm after deposition of the 17th layer.

A sol-gel derived yellow-transmitting coating on glass

Bright yellow, transparent coatings were deposited on sheet glass by the sol-gel dip coating process. Sols were prepared from titanium tetraethoxide, ferric nitrate nonahydrate and a mixture of 1-propanol and 2-butanol. Advantage was taken of the absorption of Fe3+ and Fe2+ (a part of the ferric ion being reduced to ferrous ion during baking of the film, as confirmed by Mossbauer and UV-VIS-NIR spectroscopy) in the UV and near-IR regions, respectively, and of the absorption of Ti4+ in the UV range. The coatings show a distinct transmission maximum which shifted in position depending on the physical thickness; this indicated the role of interference in monitoring the exact yellow shade of the transmitting color. Specular reflectance and transmission spectra of the coatings were examined to elucidate their optical behavior. The coating material was used in a multilayer design to obtain selective transmission behavior.

Alkoxide-derived amorphous ZrO2 coatings

Pure and transparent ZrO2 coatings on microscopic glass slides, ranging in thickness from 250 to about 1500 A, were prepared from (i) zirconium n-propoxide in dry cyclohexane, and (ii) zirconium n-propoxide in isopropanol with additions of acetic acid and water. A dipping technique was used. A baking temperature of 450°C was chosen for the conversion of as-prepared gel films into the pure oxide state. The coatings were X-ray amorphous. The dependence of coating thickness on lifting speed and concentration of zirconium n-propoxide in solution was examined. The coating profile showed that these films were fairly smooth beyond a “trouble zone” (appearing along the boundary between the coated and non-coated parts of a slide and extending up to about 1 mm) where a relatively high and irregular profile was observed.