Antimony-doped SnO2 Research Articles

Anodic oxidation of oxalic acid using WO x based anodes

The electrochemical (COOH) 2 oxidation reaction was studied at high potentials (i.e. in the region where O 2 is evolved) in acidic, aqueous solutions using conductive WO x based anodes. The WO x films used as anodes also contained Pt ‘micro’-centers. Comparative oxidation studies were also carried out using antimony doped SnO 2 anodes. More rapid (COOH) 2 oxidation rates were observed for the WO x based anodes than for the antimony doped SnO 2 anodes. The (COOH) 2 oxidation reaction studied under the conditions used in this work was shown to be activation rather than mass transport controlled. The (COOH) 2 oxidation rate constant was found to be independent of the applied potential using the WO x based anodes. This likely suggests that a chemical reaction is involved in the (COOH) 2 oxidation reaction. This chemical reaction is also suggested to be the rate determining step in the (COOH) 2 to CO 2 oxidation reaction. Furthermore, it is believed that the (COOH) 2 oxidation reaction involves adsorptive interactions of this organic with the Pt/WO x anode surface.

Preparation of antimony-doped SnO 2 nanocrystallites

The antimony-doped SnO 2 nanocrystallite was synthesised by the co-precipitation reaction and subsequent calcination from the antimony(III) chloride and tin(IV) chloride. The crystal size, pore size distribution and properties of the nanocrystalline powders were examined by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and desorption isotherm(Barrett–Joyner–Halenda method). Calcination of the precipitate powder at 650°C led to the formation of Sb–SnO 2 nanocrystallite of ∼6 nm in crystal size. Most of the pores in the nanocrystallite are about 5–10 nm in diameter. Effect of doped antimony on the crystal size of the nanocrystallite is discussed.

Structural and electrical studies on highly conducting spray deposited fluorine and antimony doped SnO 2 thin films from SnCl 2 precursor

Tin oxide thin films doped with fluorine, antimony and both have been prepared by spray pyrolysis from SnCl 2 precursor. The respective deposition temperatures of SnO 2:F, SnO 2:Sb and SnO 2:(F+Sb) are 400 °C, 350 °C and 375 °C. The as-prepared films are polycrystalline with a tetragonal crystal structure. The lattice parameter values are not changed by the addition of dopants. The films are preferentially oriented along the (200) direction. The grain sizes vary between 200 and 650 Å. The films have moderate optical transmission (up to 70% at 800 nm) and the calculated reflectivity in the infra-red region is in the range of 88–95%. The figure of merit (φ) values of SnO 2:F and SnO 2:Sb samples are 2.5×10 −3 (Ω) −1 and 1.4×10 −4 (Ω) −1, respectively. The films are heavily doped, degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance ( R sh) of 5.65 Ω/□ obtained for a SnO 2:F sample, is even lower than the values reported for the spray deposited tin oxide thin films prepared from SnCl 2 precursor. The resistivity (ρ) and mobility (μ) are in the range of 10 −4–10 −3 Ω-cm and 7–17.2 cm 2 V −1 s −1. The electron density lies between 1.3×10 20 and 13.2×10 20 cm −3. A thorough electrical investigation reveals that the film's conductivity depends only on carrier concentration. It is found that ionised impurity scattering is the dominant mechanism, which limits the mobility of the carriers.

Effect of laser treatment on the gas sensitivity of tin dioxide films

It is shown that the sensitivity of antimony-doped polycrystalline SnO2 films can be increased by treatment with laser pulses.

Synthesis of Nanocrystalline, Redispersable Antimony-Doped SnO2 Particles for the Preparation of Conductive, Transparent Coatings

Nanocrystalline, redispersable Sb-doped SnO2 with Sb contents from 0.1–10 mol% (with respect to Sn) and a primary particle size of about 5 nm was prepared from SnCl4 and SbCl3 in solution by a growth reaction. The aggregation of the particles was avoided by in situ surface modification with amino carbonic acids. The stabilizing effect of the surface modification could be maintained during the following hydrothermal crystallization step (150°C, 10 bar). The resulting nanocrystalline particles are fully redispersable in aqueous suspensions at pH ≥ 11; solid contents up to 40 wt% can be achieved.

Comparison of transparent conductive oxide thin films prepared by a.c. and d.c. reactive magnetron sputtering

Antimony-doped tin oxide and aluminum-doped zinc oxide films have been prepared by reactive a.c. and d.c. magnetron sputtering (a.c. excitation at frequency of 40 kHz; twin-cathode arrangement) from metallic targets at substrate temperature of about 573 K. The optical, electrical and structural properties of the sputtered SnO 2:Sb and ZnO:Al thin films of different dopant concentrations have been investigated by means of optical spectroscopy (UV-IR), X-ray diffraction. Hall mobility and conductivity measurements. For antimony-doped SnO 2 films a minimum resistivity of 1.5 × 10 −3 Ω cm at high transparency (larger than 88% at film thickness of 250 nm) has been observed at dopant concentrations of about 1.2 at.% Sb in the layers. Low resistivity of 4.0 × 10 −4 Ω cm and transmission in the visible spectral range of about 89% at film thickness of 550 nm has been obtained for as prepared aluminum-doped ZnO thin films. Furthermore, the investigations on a.c. plasma discharges using a planar plasma probe analyzer have revealed higher ion energies (up to some tenths of eV) and about 10 times higher ion current densities as in the case of d.c. magnetron sputtering at nearly the same deposition conditions.

Electron Injection by Photoexcited Ru(bpy)32+ into Colloidal SnO2: Analyses of the Recombination Kinetics Based on Electrochemical and Auger-Capture Models

The photosensitization of colloidal particles of antimony-doped SnO2 by electrostatically adsorbed Ru(bpy)32+ (bpy = 2,2‘-bipyridine) produced Ru(bpy)33+ and a conduction band electron (ecb-) with ...

Photooxidation of Tryptophan: O2(1Δg) versus Electron‐Transfer Pathway

Tris (2,2'-bipyridyl)ruthenium(II)chloride hexahydrate (Ru[bpy]3(2+)) free in solution and adsorbed onto antimony-doped SnO2 colloidal particles was used as a photosensitizer for a comparison of the O2(1 delta g) and electron-transfer-mediated photooxidation of tryptophan (TRP), respectively. Quenching of excited Ru(bpy)3(2+) by O2(3 sigma g-) in an aerated aqueous solution leads only to the formation of O2(1 delta g) (phi delta = 0.18) and this compound was used as a type II photosensitizer. Excitation of Ru(bpy)3(2+) adsorbed onto Sb/SnO2 results in a fast injection of an electron into the conduction band of the semiconductor and accordingly to the formation of Ru(bpy)3(2+) and was used for the sensitization of the electron-transfer-mediated photooxidation. The Ru(bpy)3(3+) is reduced by TRP with a bimolecular rate constant kQ = 5.9 x 10(8) M-1 s-1, while O2(1 delta g) is quenched by TRP with kt = 7.1 x 10(7) M-1 s-1 (chemical + physical quenching). Relative rate constants for the photooxidation of TRP (kc) via both pathways were determined using fluorescence emission spectroscopy. With Np, the rate of photons absorbed, being constant for both pathways we obtained kc = (372/Np) M-1 s-1 for the O2(1 delta g) pathway and kc > or = (25,013/Np) M-1 s-1 for the electron-transfer pathway, respectively. Thus the photooxidation of Trp is more than two orders of magnitude more efficient when it is initiated by electron transfer than when initiated by O2(1 delta g).

Time-Resolved Luminescence Investigation of the Adsorption of Ru(bpy)32+ onto Antimony-Doped SnO2 Colloidal Particles

The adsorption of Ru(bpy)32+ (bpy = 2,2‘-bipyridine) onto negatively charged antimony-doped SnO2 colloidal particles (ca. 4-nm diameter) was monitored by time-resolved luminescence. Electron injection from photoexcited Ru(bpy)32+ into the conduction band of the semiconductor particle results in luminescence quenching predominantly within the laser pulse when the complex is bound to the particle, whereas the luminescence of the unbound complex decays with a lifetime of several hundred nanoseconds. The relative concentrations of the bound and free species are thus readily obtained by determining the relative contributions of the quenched and unquenched components in the luminescence decay curve. Binding of Ru(bpy)32+ to the particles conforms to the Frumkin adsorption isotherm and suggests that the adsorbed Ru(bpy)32+ molecules self-associate with a free energy of interaction equal to −1.9 ± 0.7 kcal mol-1. The average maximal capacity of each particle for adsorbed Ru(bpy)32+ determined by the binding data, 29 ± 10, is in agreement with the value obtained by ion exchange, 30 ± 4, but is smaller than predicted for a close-packed monolayer.

In situ high-temperature x-ray diffraction studies of antimony-doped tin oxide thin films formed by metallo-organic decomposition

Thin films of antimony-doped SnO 2 coated on stainless steel were fabricated by metallo-organic decomposition (MOD) techniques. A novel method for thermal fabrication of SnO 2 type films utilizing in situ high-temperature x-ray diffraction (HTXRD) found crystallization onset occurred between 400 and 500°C. Processing at fixed temperatures of 500, 700, and 900°C provided a high degree of crystallization after approximately 2 hr. The resulting crystallites after 6 hr of heating ranged in size from 36 Å at 500°C to 205 Å at 900°C. It has been observed that prolonged thermal processing of these samples leads to oxidation of the stainless steel substrate.

Effect of dopant incorporation on structural and electrical properties of sprayed SnO2:Sb films

Antimony-doped tin oxide films were deposited by spray pyrolysis technique. The effect of antimony doping on structural and electrical properties was investigated in detail using the x-ray diffraction technique and room-temperature Hall measurements. Antimony doping did not affect the preferred growth along [200] to a considerable extent. These results were analyzed on the basis of structure factor calculations. From the Hall measurements, the lowest electrical resistivity, i.e., 5.2×10−4 Ω cm was observed for the films with a doping level of 2.3 at. % in the solution. This value of electrical resistivity is the lowest reported so far in the case of spray deposited antimony-doped SnO2 films. The grain boundary and ionized impurity scattering were observed to be prevalent in governing the electronic transport of lightly and heavily doped films, respectively.

Reactions of antimony-doped SnO2 powder with molten glass in resistive composite formation

Heat treatment of (Sn-Sb-0)-glass composites causes antimony and tin to diffuse into the glass. Around the particles, the glass acquires a diffusion profile. The diffusion coefficients of those ions at 1173 K are, respectively, 10−15 and 10−16 m2/sec.

Some electrical and photovoltaic properties of poly-Si/SnO 2 heterojunction

Thin films of antimony-doped SnO 2 deposited on polycrystalline silicon formed a heterojunction with SIS (“Semiconductor-Insulator-Semiconductor”) structure, since an interfacial layer of SiO x between Si and SnO 2 was always present. Thin films of SnO 2 were formed by a new modification of the CVD (Chemical Vapour Deposition) method. The deposition parameters and the doping by antimony (Sb) were optimized in order to obtain SnO 2 films of low sheet resistance, while maintaining high solar transmittance. DC current-voltage, (I–V) characteristics of the heterojunctions were measured in the dark at different temperatures and under sunlight, together with the output I-V curves. The experimental results indicate that multi-step tunnelling through the silicon barrier might be the predominant current transport mechanism in the dark, at least in the temperature range between 290 and 360 K. It is suggested that photovoltaic properties of these n-SnO 2/ n-Si (poly) heterojunctions could be improved by applying a metal grid front contact to SnO 2 and by using thicker SnO 2 films with lower sheet resistances.

Synthesis of hydrous SnO2 and SnO2-coated TiO2 powders by the homogeneous precipitation method and their characterization

Hydrous SnO2 and SnO2-coated TiO2 powders were synthesized by the homogeneous precipitation method using urea and the products were characterized by X-ray diffraction, thermogravimetry, differential thermal analysis, scanning electron microscopy and energy- dispersive X-ray microanalysis. Electrical conductivities were measured with an impedance analyser. Hydrous SnO2 powder prepared under conditions without SO42− ions was a bulky product containing 75 wt% of water. The addition of SO42− ions to the solution changed bulky hydrous SnO2 to a dense product; approximately spherical particles were obtained with an average particle size of 0.14 ± 0.03 μm. with 13.5 wt % of absorbed water. Antimony-doped hydrous SnO2 prepared under conditions with SO42− ions consisted of approximately spherical particles with an average particle size of 0.17 ± 0.04 μm with 15.0 wt % of absorbed water. Hydrous SnO2-coated TiO2 powders with a good dispersion state and with various Sn/Ti ratios were prepared under conditions with SO42− ions. All the as-prepared coated powders were white, but the products doped with Sb3+ ions were turned to pale blue by heat treatment at 600° C for 1 h and their electrical conductivities increased by orders of about 3.0 in comparison with those of the other two.

Electron spectroscopic studies on films of SnO 2 and SnO 2:Sb

Pure and antimony-doped SnO 2 films have been deposited by two different techniques: metal-organic chemical vapour deposition (MO-CVD) and spray pyrolysis of SnCl 4 in the presence of air with different concentrations of antimony. X-ray and UV photoelectron spectroscopic studies have been carried out on these films and the combined data from these studies provided information about the electronic properties of antimony-doped SnO 2 films and their compositions. That the binding energy of SnO is higher than that of SnO 2, contrary to expectations, is because of the fact that SnO 2 is more covalent than SnO. XPS has been used successfully to confirm the presence of Sb 3+ and Sb 5+ beyond a certain concentration of antimony (0.5 mol%) in the film, which is responsible for the decrease in conductivity and IR reflectivity. UV photoelectron spectroscopy of transparent, conducting SnO 2 films has been reported for the first time. The onset of photoemission in the valence band around 2.6 eV has been explained by invoking the idea of surface states near the valence band below the Fermi level.

Preparation and properties of antimony-doped SnO2 films by thermal decomposition of tin 2-ethylhexanoate

Transparent Sb-doped SnO2 films were prepared at 600° C on glass substrates by thermal decomposition of tin 2-ethylhexanoate and antimony tributoxide. The films 100 to 300 nm thick, which are composed of fine particles, were very smooth. The films showed no preferred orientation. The minimum resistivity (2.1×10−2Ω cm) was attained at a concentration of 8 at% Sb on the substrate precoated with SiO2. The transmission of these films was about 80% over a wavelength range from 0.4 to 2.0 μm.

Deposition of improved optically selective conductive tin oxide films by spray pyrolysis

Antimony-doped SnO2 films with a resistivity as low as 9×10−4 Ωcm were prepared by spray pyrolysis. Structural, electrical and optical properties were studied by varying the antimony concentration, film thickness and deposition temperature. About 94% average transmission in the visible region and about 87% infrared reflectance were obtained for antimony-doped SnO2 films by a systematic optimization of the preparation parameters. As the best combination, an average transmission of 88% in the visible region and an infrared reflectance of 76% was possible for the doped SnO2 films.

Electroless deposition of Sno 2 and antimony doped SnO 2 films

Thin polycrystalline films of SnO 2 and antimony doped SnO 2 have been prepared by simple economic electroless deposition technique. The transmittance in the visible range and the reflectance in the i.r. range for SnO 2 films are ∼80% and ∼70%, respectively, with resistivity ∼10 −2 Ω cm. On the other hand, antimony doped SnO 2 films have transmittance in the visible range and reflectance in the i.r. range, as good as ∼86% and ∼83%, respectively, with resistivity as low as ∼10 −3Ω cm. By vacuum annealing, the resistivity of both types of films has been brought down as low as ∼10 −3 and ∼10 −4 Ω cm, respectively.

Fabrication and Characterization of SnO2/Si Heterojunction Solar Cells

Transparent conducting SnO2 films (both undoped and antimony-doped) are deposited by oxidation of SnCl2 (SnCl2+SbCl3 in the case of doped films), at different deposition temperatures, oxygen (SnCl2 carrier gas) flow rates and nitrogen (SbCl3 carrier gas) flow rates. The structural, electrical and optical properties are studied and the deposition parameters are optimized for obtaining films with the lowest sheet resistance and highest transparency. Undoped films with the maximum figure-of-merit (transparency10/sheet resistance)=1.43×10-3 ohm-1 (sheet resistance = 420 ohm/square and per cent transparency=95) are obtained when deposited at 500°C with oxygen flow rate=l l.min-1. The figure-of-merit increases to 6.78×10-3 ohm-1 (sheet resistance =55 ohm/square and percent transparency=90.6) when antimony mole per cent in the film is 3. Solar cells are fabricated by depositing undoped and antimony doped SnO2 (ATO) films on n- and p- single-crystal silicon (1 ohm-cm) at the optimized set of deposition parameters. The open-circuit voltage, short-circuit current, fill factor and efficiency of the SnO2//n-Si cells are 0.52 V, 21 mA/cm2, 0.62 and 6.71 per cent respectively. These parameters for ATO/n-Si cell are 0.52 V, 24 mA/cm2, 0.68 and and 8.5 per cent and for ATO/p-Si cell are 0.22 V, 16 mA/cm2, 0.53 and 1.95 per cent. These experimentally-obtained results are explained theoretically.

Fluorine-doped SnO 2 films for solar cell application

Highly conductive transparent thin films of fluorine-doped SnO 2 (SnO 2:F) were prepared using spray pyrolysis. These films have a potential application in SIS-type photovoltaic solar cells because of their high transmission and low sheet resistance. The electrical resistivity is a minimum (about 5.4 × 10 −4 Ω cm) and the figure of merit is a maximum (about 10 −2) for SnO 2 films doped with 1.2 wt.% F. The optical data are interpreted to give a direct band gap of 4.27 eV and an indirect band gap of 2.73 eV. SnO 2:F films show high optical transmission in films of low sheet resistance (about 5 Ω/□) compared with the corresponding values for antimony-doped SnO 2 films.