UV absorption studies of undoped and fluorine-doped tin oxide films

Tin oxide films undoped and doped with fluorine are prepared by a chemical vapour deposition technique involving the oxidation of SnCl₂. For fluorine doping a mixture of trifluoroacetic acid and deionized water is used. The optical properties of these films are investigated in the UV region (225–350 nm). It is observed that for an undoped tin oxide the absorption edge lies at 3.71 eV. It is also observed that for fluorine-doped tin oxide films the absorption edge shifts towards higher energies, which is related to the Moss-Burstein shift. In the case of fluorine-doped tin oxide films, depending on the fluorine concentration, the absorption edge lies in the range 3.89–4.07 eV. Undoped and fluorine-doped tin oxide films show a direct transition at 4.03 eV and in the range 4.17–4.29 eV respectively, whereas the indirect transition for undoped and fluorine-doped tin oxide films occurs at 3.35 eV and in the range 3.55–3.67 eV respectively.     

Structural studies of poly(p-phenylene selenide) doped with sulphur trioxide

Poly(p-phenylene selenide) (PPSe) was prepared by condensation polymerization of 2,4 dibromobenzene and sodium selenide. The synthesis product in the form of powder was purified. The structure of the resulting polymer was investigated by infrared spectroscopy, wide-angle X-ray spectroscopy, electron diffraction, ultraviolet, electron spin resonance and elemental analysis.¹H-nuclear magnetic resonance (NMR) solid measurements were used to determine the molecular dynamics for undoped and SO₃-doped PPSe. The NMR investigations for undoped PPSe have shown that there are no essential differences in the structure and molecular motion between PPSe and PPS. After doping PPSe with SO₃, contrary to PPS, a third component of relaxation time,T ₁, is observed. The relaxation times for this component are connected to the interaction of protons with paramagnetic centres which are generated as a result of the doping process. The electrical conductivity of SO₃-doped PPSe at the beginning of the doping process rapidly increased to about 6 ×10^–6 S cm^–1 and then decreased more than one order of magnitude because of the chemical reaction which had occurred.     

Transparent nanoporous tin-oxide film electrode fabricated by anodization

A transparent nanoporous tin oxide film electrode was fabricated by anodizing a tin film on a fluorine-doped tin oxide (FTO) film electrode. The resulting anodized nanoporous tin oxide (ANPTO) film has columnar-type pore channels with around 50 nm in diameter and is optically transparent. Electrochemical measurements with Fe(CN)₆³⁻ as a redox probe clearly revealed that the ANPTO film could be used for a working electrode with a large internal surface area. Moreover, it was found that ANPTO film had a wider anodic potential window (> ca. 2.0 V) than conventional metal oxide electrodes, such as FTO and indium tin oxide film electrodes (> ca. 1.3 V). The wide anodic potential window improves applicability of a transparent metal oxide electrode for various electrochemical oxidation reactions, which are often interfered by oxygen evolution in water. These results conclude that the ANPTO film can be used as an advanced transparent nanoporous film electrode.     

Properties of indium oxide/tin oxide multilayered films prepared by ion-beam sputtering

The preparation and characterization of indium oxide (InO _x )/tin oxide (SnO _y ) multilayered films deposited by ion-beam sputtering are described and compared with indium tin oxide (ITO) films. The structure and the optoelectrical properties of the films are studied in relation to the layered structures and the post-deposition annealing. Low-angle X-ray diffraction analysis showed that most films retained the regular layered structures even after annealing at 500° C for 16 h. As an example, we obtained a resistivity of 6×10^–4 cm and a transparency of about 85% in the visible range at a thickness of 110 nm in a multilayered film of InO _x (2.0 nm)/SnO _y (0.2 nm)×50 pairs when annealed at 300° C for 0.5 h in air. Hall coefficient measurements showed that this film had a mobility of 17 cm² V^–1 sec^–1 and a carrier concentration (electron density) of 5×10²⁰ cm^–3.     

Properties of GaN grown on sapphire substrates

Epitaxial growth of GaN on sapphire substrates using an open-tube growth furnace has been carried out to study the effects of substrate orientation and transfer gas upon the properties of the layers. It has been found that for the (0001) substrates, surface appearance was virtually independent of carrier gas and of doping levels. For the (1 ¯102) substrates surface faceting was greatly reduced when He was used as a transfer gas as opposed to H₂. Faceting was also reduced when the GaN was doped with Zn and the best surfaces for the (1 ¯102) substrates were obtained in a Zn-doped run using He as the transfer gas. The best sample in terms of electrical properties for the (1¯102) substrate had a mobility greater than 400 cm² V^–1 sec^–1 and a carrier concentration of about 2 × 10¹⁷ cm^–3. This sample was undoped and used He as the transfer gas. The best (0001) sample was also grown undoped with He as the transfer gas and had a mobility of 300cm²V^–1 sec^–1 and a carrier concentration of 1 × 10¹⁸ cm^–3.     

Studies on micro-structural and electrical properties of spray-deposited fluorine-doped tin oxide thin films from low-cost precursor

Thin films of fluorine-doped tin oxide (SnO₂:F) on glass were prepared by spray pyrolysis technique using stannous chloride (SnCl₂) and ammonium fluoride (NH₄F) as precursors. The as-prepared films were characterized for their structural and electrical properties and are discussed in detail in this article. The surface morphology studies revealed that the films are grainy and the roughness of undoped films has been reduced on fluorine doping. X-ray diffraction (XRD) studies revealed that the films are polycrystalline. It further revealed that the undoped films grow along the preferred orientation of (211), whereas all the doped films grow along (200). The minimum sheet resistance 1.75 Ω/□ achieved in the present study for the films doped with 15 wt.% F is the lowest among the reported values for these materials prepared using SnCl₂ precursor. The electrical transport phenomenon has been analyzed in order to find out the possible scattering mechanism that limiting the mobility of charge carriers.     

Preparation and properties of sprayed undoped and fluorine doped tin oxide films

Thin films of undoped and fluorine doped tin oxide have been prepared on borosilicate glass plates by a spray pyrolysis technique. The effect of process parameters, such as tin chloride concentration in the precursor solution, substrate to nozzle distance, carrier gas (air) flow rate, substrate temperature, and doping level of fluorine in the spray solution, on the physical properties of the tin oxide thin films have been investigated. The grown films were polycrystalline in nature above 350°C, the [110] reflection having the maximum intensity in all cases. Films of about 10⁻³ Ω cm resistivity and high visible transparency of about 88% have been obtained at the optimum substrate temperature of 425°C and fluorine doping concentration of 57 at.%. The optical investigations show that the optimized films have a direct allowed bandgap of 4.25 eV and indirect allowed bandgap of 2.71 eV.     

Electrical conductivity and defect structure of polycrystalline tin dioxide doped with antimony oxide

Electrical conductivity () of tin dioxide doped with antimony has been measured as functions of temperature and oxygen partial pressure (p0_2> ). Variation of electrical conductivity is explained by assuming that the antimony oxide forms a substitutional solid solution and doubly ionized oxygen vacancies are predominant defects. Above –10^–5 atm oxygen partial pressure antimony ions are present predominantly in the pentavalent state in tin dioxide lattice. However, it is converted to the trivalent state below this oxygen partial pressure accompanied by a sudden rise in conductivity.     

FeCl3-doped polyvinylidene fluoride

Infrared (350–4000 cm^–1) and optical (1.15×10⁴–2.95×10⁴cm^–1) spectra, differential thermal analysis (DTA) and d.c. electrical resistivity of FeCl₃- doped polyvinylidene fluoride (PVDF) films, over the doping mass fraction range 0 w 0.40, have been measured. The i.r. spectra provided evidence of: (a) the presence of both and phases in the undoped, and a phase in the doped PVDF films; (b) a head-to-head content of 20%; and (c) a different doping mode beyond a 0.25 doping level. The optical spectra resulted in two induced energy bands, and a probable interband electronic transition, due to doping. Dipole relaxation and premelting endothermic peaks were identified by DTA. Electrical conduction is thought to proceed by interpolaron hopping among the polaron and bipolaron states induced by doping. The hopping distance, R _o, is calculated according to the Kuivalainen model. A numerical equation is adopted to formulate the dependence of R _oon doping level and temperature. It is found that R _o< CC separation length. This implies that, in doped PVDF, charge carrier hopping is not an intrachain process.     

Sintering and properties of SrBi2(Ta1−x V x )2O9 ceramics

The effects of vanadium doping on the sintering, microstructure, dielectric properties, and ferroelectric properties of SrBi₂(Ta_1–x V _x )₂O₉ ceramics were investigated. The densification and grain-growth processes of the vanadium doped ceramics were shifted to a lower temperature range. For the ceramics with relative density 90%, the dielectric constant is 120–125 and 100–130 for the undoped and doped ceramics, respectively, and the dielectric loss tangent is below 1%. As compared with the undoped ceramics, the ferroelectric properties can be significantly improved by doping with an appropriate amount of vanadium and sintering at 1000°C. The variations of dielectric and ferroelectric properties are influenced by the incorporation of vanadium into crystal lattice and several microstructural factors.     

The combined effects of molar concentration of the precursor solution and fluorine doping on the structural and electrical properties of tin oxide films

Undoped and fluorine doped tin oxide (FTO) films have been fabricated by employing a simplified and inexpensive spray technique using perfume atomizer at comparatively lesser substrate temperature (320 °C). The combined effects of molar concentration of the precursor solution and fluorine doping on the structural and electrical properties of tin oxide films have been reported. The X-ray diffraction studies of undoped films revealed that the interstitial incorporation of Sn atoms can be controlled by employing this simple spray pattern and process conditions. The electrical studies showed that, in governing the variation in sheet resistance, the role of substitutional incorporation of F⁻ ions is predominant over the oxygen vacancies in the case of FTO films deposited from solutions having lower precursor concentration, whereas in the case of higher concentrations the role of oxygen vacancies is predominant. The quantitative results of energy dispersive X-ray analysis (EDAX) and the variations in the Fourier transform infrared (FTIR) peaks are presented as strong evidences for the above observations.     

Doping and trap states in PPV light-emitting devices

The influence of different substrates used for the fabrication of poly-(p-phenylene-vinylene) light-emitting devices on the device characteristics is investigated. In devices prepared on indium-tin oxide substrates doping with InCl₃ leads to states with a depth of about 0.15 eV and a concentration of 10¹⁶–10¹⁷ cm⁻³. This doping is responsible for the observed Schottky diode behaviour in PPV devices on ITO but also leads to considerable photoluminescence quenching. The use of fluorine-doped tin dioxide as anode material causes much lower doping and avoids photoluminescence quenching. An improvement of device properties can be achieved by controlled doping or using partially conjugated PPV.     

Enhanced crystal grain size by bromine doping in electrodeposited Cu2O

Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu₂O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 μm² in area, or ~ 100 μm in linear dimension, while the film is only 1-5 μm thick. The enhanced grain size is explained by the effect of over-potential for the Cu²⁺/Cu⁺ redox couple on nucleation density of Cu₂O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu₂O displays a high resistivity of 100 MΩcm. Bromine doping in Cu₂O significantly reduces the resistivity to as low as 42 Ωcm after vacuum annealing. Br-doped Cu₂O shows n-type behavior.     

Enhancement of the diffusional creep of polycrystalline Al2O3 by simultaneous doping with manganese and titanium

The effect of simultaneous doping with manganese and titanium on diffusional creep was studied in dense, polycrystalline alumina over a range of grain sizes (4–80m) and temperatures (1175–1250° C). At a total dopant concentration of 0.32–0.37 cation %, diffusional creep rates were enhanced considerably such that the temperature at which cation mass transport was significant was suppressed by at least 200° C compared to that observed in undoped material. The Mn-Ti (and Cu-Ti) dopant couple was far more effective in enhancing creep rates and suppressing sintering temperatures than the Fe-Ti couple. The enhanced mass transport kinetics are believed to be caused by significant increases in both aluminium lattice and grain-boundary diffusion. When aluminium grain-boundary diffusion is enhanced by increasing the concentration of divalent impurity (Mn²⁺, Fe²⁺) or by creep testing at low temperatures, creep deformation is Newtonian viscous.     

Study of the mechanical properties of CeO2 layers with the nanoindentation technique

The mechanical properties of CeO₂ layers that are undoped or doped with other elements (e.g. Zr and Ta) are a topic of special interest specially in the manufacturing of superconductor buffer layers by pulsed electron deposition. Nowadays, the trend is to produce small devices (i.e. coated conductors), and the correct mechanical characterization is critical. In this sense, nanoindentation is a powerful technique widely employed to determine the mechanical properties of small volumes. In this study, the nanoindentation technique allow us determine the hardness (H) and Young's modulus (E) by sharp indentation of different buffer layers to explore the deposition process of CeO₂ that is undoped or doped with Zr and Ta, and deposited on Ni–5%W at room temperature. This study was carried out on various samples at different ranges of applied loads (from 0.5 to 500 mN). Scanning electron microscopy images show no cracking for CeO₂ doped with Zr, as the doping agent increases the toughness fracture of the CeO₂ layer. This system, presents better mechanical stability than the other studied systems. Thus, the H for Zr–CeO₂ is around 2.75 · 10⁶ Pa, and the elastic modulus calculated using the Bec et al. and Rar et al. models equals 249 · 10⁶ Pa and 235 · 10⁶ Pa respectively.     

A nanocrystalline hematite film prepared from iron(III) chloride precursor

This paper deals with a simple and low-cost method developed to deposit hematite (α-Fe₂O₃) layers on a fluorine-doped tin oxide (FTO/F:SnO₂) substrate by thermal decomposition of solid iron(III) chloride hexahydrate (FeCl₃⋅ 6H₂O). Deposition procedure takes place through chemical intermediate iron(III) oxide chloride (FeOCl) film. A crucial influence of atmosphere dynamics involved in the calcination process of FeOCl has been observed. As-deposited films were characterized by means of Conversion Electron Mössbauer Spectroscopy (CEMS), Grazing Angle X-Ray Diffractometry (GAXRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. Final nanocrystalline hematite film with a cactus-field-like design consists of 20 nm thick porous crystal plates. A process of hematite doping by tin atoms from substrate coating is also discussed.     

Influence of a transition metal oxide (CuO) on the superplastic behaviour of 8 mol% yttria-stabilised cubic zirconia polycrystal (8Y-CSZ)

The microstructure and superplastic deformation of fine-grained undoped 8Y-CSZ and 1 wt% CuO doped 8Y-CSZ have been investigated in tension in the temperature range 1503 to 1623 K and strain rate range 5 × 10^–5 to 1 × 10^–3 s^–1. Deformation of the undoped 8Y-CSZ was characterized by large strain-hardening with limited tensile elongations of 20%; this was mainly due to severe grain growth during deformation. The addition of a small amount of a transition metal oxide (CuO) resulted in a decrease in strain-hardening and enhanced tensile elongations up to 78%. The ductility enhancement in the CuO doped 8Y-CSZ was due to copper segregation to grain boundaries, thus facilitating grain boundary sliding. In addition, the enhanced ductility in the doped material was related to a reduction in flow stress which, in turn, suppressed cavitation and delayed fracture.     

Fabrication of high-performance fluorine doped-tin oxide film using flame-assisted spray deposition

A high-performance fluorine-doped tin oxide (FTO) film was fabricated by flame-assisted spray deposition method. By varying the NH₄F doping concentration, the optimal concentration was established as 8 at.%. X-ray diffractograms confirmed that the as-grown FTO film was tetragonal SnO₂. In addition, the FTO film was comprised of nano-sized grains ranging from 40 to 50 nm. The heat-treated FTO film exhibited a sheet resistance of 21.8 Ω/? with an average transmittance of 81.9% in the visible region (λ = 400-800 nm). The figures of merit shows that the prepared FTO film can be used for highly efficient dye-sensitized solar cells electrodes.     

Comparison of the dye-sensitized solar cells performances based on transparent conductive ITO and FTO

We investigated dye-sensitized solar cell (DSSC) performances with regard to transparent conducting oxide substrates: indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO). The DSSCs were in a standard configuration: a photoelectrode of TiO₂ nanoparticles (9 nm size, anatase phase) deposited on transparent and electrically conductive substrates, counter electrodes of Pt-coated glass, ruthenium 535 dye, and AN50 iodolyte electrolyte (Solaronix). The cells manufactured from ITO (FTO) had an open circuit voltage of 705 (763) mV and short-circuit current of 7.87 (34.3) mA/cm². A direct correlation was found between transparent conductive film resistivity and cell efficiency. Resistivities of 52 Ω/sq for ITO substrates and 8.5 Ω/sq for FTO led to major differences in internal global efficiency: from 2.24% for ITO to 9.6% for FTO.     

Zinc Doping Profile in AlGaAs/GaAs Heteroepitaxial Structures Grown by Metalorganic Chemical Vapor Deposition

The Zn profile in Al _x Ga_{1 – x} As/GaAs (x = 0.2–0.4) quantum-well heteroepitaxial structures doped during growth by metalorganic chemical vapor deposition is modeled with allowance made for the diffusional broadening of the nominal doping profile. Experimentally determined carrier distributions in the heterostructures are used to refine the diffusion coefficient of Zn at a growth temperature of 770°C. The average value of D _Zn is determined to be 6.0 × 10^–14 cm²/s. The position of the p–n junction in Al _x Ga_{1 – x} As/GaAs heterostructures is assessed as a function of the nominal Zn profile and growth rate. The ways of optimizing the doping profile are outlined.