Arsenic diffusion from doped anodic oxide films to silicon

The effect of H₃AsO₄ concentration in ethylene glycol on the electrical properties of p-n junctions in silicon has been studied. The results can be used to select the orthoarsenic acid concentration for producing arsenic diffusion layers with a predetermined junction depth, sheet resistance, and arsenic concentration. The maximum value of N _{s As}, 4.1 × 10¹⁹ cm⁻³, is lower than the surface phosphorus concentration, N _{s P} ∼ 2 × 10²⁰ cm⁻³, which is tentatively attributed to the significant arsenic vaporization from anodic oxide films and also to the fact that the arsenic concentration in doped anodic oxide films is lower than the phosphorus concentration because, in the case of phosphate electrolytes, the sorption capacity of a monolayer is a factor of 2.7 higher. Original Russian Text ? L.P. Mileshko, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 135–136.     

Electrochemical polymerization of 9-phenylcarbazole in mixed electrolytes of boron trifluoride diethyl etherate and sulfuric acid

Poly(9-phenylcarbazole) (P9PC) films were synthesized electrochemically by direct anodic oxidation of 9-phenylcarbazole in boron trifluoride diethyletherate (BFEE) containing additional 2% sulfuric acid (by volume). The oxidation potential onset of 9-phenylcarbazole in this medium was measured to be 0.9 V vs. SCE, which was much lower than that in acetonitrile containing 0.1 mol L⁻¹ Bu₄NBF₄ (1.1 V vs. SCE). P9PC films obtained from this medium showed good electrochemical behavior and good thermal stability with an electrical conductivity of 0.09 S cm⁻¹. The structure and morphology of the polymer were investigated by UV–visible spectroscopy, infrared spectroscopy, and scanning electron microscopy (SEM), respectively. The results of quantum chemistry calculations of 9-phenylcarbazole monomer indicated that the polymerization mainly occurred at C₃ and C₆ positions. Fluorescent spectral studies indicated that P9PC was a blue-light emitter.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Preparation and characterizations of tungsten oxide electrochromic nanomaterials

Nanoscaled tungsten oxide thin films were fabricated by galvanostatic electrodeposition. The effect of preparation parameters such as tungsten ions concentration, pH, current density and annealing on the properties and performance of WO₃ thin films electrochromic materials was investigated. XRD, SEM–EDS, TEM, FTIR, UV–VIS spectrophotometry, and electrochemical measurements were utilized to characterize the structural and compositional properties as well as the electrochromic behaviour of the prepared thin films. Triclinic WO₃ structure was prepared at 0.1 M W⁺ and current density of 0.5 mA cm⁻², while at 0.2 M W⁺ and 1 mA cm⁻², orthorhombic structure was revealed. High energy gap of 3.5 eV with diffusion coefficient of 6.81 × 10⁻¹¹ cm² S⁻¹ and coloration efficiency of 62.68 cm² C⁻¹ were obtained for the films prepared at pH 2, 1 mA cm⁻², and 0.1 M W⁺.     

Anodic oxidation of tantalum in water and biological solutions using current limiting constant voltage method

A reliable method is developed for preparing tantalum pentoxide film targets in natural water and biological fluids (urine, blood plasma and serum) by the anodization of tantalum metal using a current limiting constant voltage method. Tantalum pentoxide film targets are successfully prepared at a current density of 10 mA cm⁻² at an anodic voltage ranging from 20 V to 100 V without any oxide breakdown. The results show that for the same applied voltage, more ionic concentration in biological solutions leads to a higher rate of oxide growth than in water and a darker interference color. The analysis shows that anodic oxidation is more likely to breakdown in a biological environment than in pure water for the same oxidation time and applied voltage. The oxide film capacitance is found to be only slightly dependent on pH and anodic voltage with higher capacitive films in biological solutions than for water.     

Influence of sputtering power on the physical properties of magnetron sputtered molybdenum oxide films

Thin films of molybdenum oxide were formed on glass and silicon substrates by sputtering of molybdenum target under various sputtering powers in the range 2.3–6.8 W/cm², at a constant oxygen partial pressure of 2 × 10⁻⁴ mbar and substrate temperature 523 K employing DC magnetron sputtering technique. The effect of sputtering power on the core level binding energies, chemical binding configurations, crystallographic structure, surface morphology and electrical and optical properties was systematically studied. X-ray photoelectron spectroscopic studies revealed that the films formed at sputtering powers less than 5.7 W/cm² were mixed oxidation states of Mo⁵⁺ and Mo⁶⁺. The films formed at 5.7 W/cm² contained the oxidation state Mo⁶⁺ of MoO₃. Fourier transform infrared spectra contained the characteristic optical vibrations. The presence of a sharp absorption band at 1,000 cm⁻¹ in the case of the films formed at 5.7 W/cm² was also conformed the existence of α-phase MoO₃. X-ray diffraction studies also confirmed that the films formed at sputtering powers less than 5.7 W/cm² showed the mixed phase of α-and β-phase of MoO₃ where as at sputtering power of 5.7 W/cm² showed single phase α-MoO₃. The electrical conductivity of the films increased from 8 × 10⁻⁶ to 1.2 × 10⁻⁴ Ω⁻¹ cm⁻¹, the optical band gap decreased from 3.28 to 3.12 eV and the refractive index decreased from 2.12 to 1.94 with the increase of sputtering power from 2.3 to 6.8 W/cm², respectively.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

Characterization of CuAlO2 films prepared by dc reactive magnetron sputtering

Thin films of copper aluminum oxide (CuAlO₂) were prepared on glass substrates by dc magnetron sputtering at a substrate temperature of 523 K under various oxygen partial pressures in the range 1 × 10⁻⁴–3 × 10⁻³ mbar. The dependence of cathode potential on the oxygen partial pressure was explained in terms of oxidation of the sputtering target. The influence of oxygen partial pressure on the structural, electrical and optical properties was systematically studied. p-Type CuAlO₂ films with polycrystalline nature, electrical resistivity of 3.1 Ω cm, Hall mobility of 13.1 cm² V⁻¹ s⁻¹ and optical band gap of 3.54 eV were obtained at an oxygen partial pressure of 6 × 10⁻⁴ mbar.     

Solution synthesis of crystallized AMO4 (A=Ba, Sr, Ca; M=W, Mo) film at room temperature

A well-crystallized AMO₄ (A=Ba, Ca, Sr; M=W, Mo) films have been prepared at room temperature through a simple solution reaction in respective alkaline solution at higher pH ranging from 12–14. Adopting the corrosion principle for oxidation of metal substrate, these double oxide films were carried out in presence of chemical driving force without any special apparatus or devices. Hydrogen peroxide was used to enhance the dissolution rate of metal substrates. The driving force for the film formation and growth were high concentration of A²⁺, MO₄²⁻ ions with high pH conditions. Average grain sizes of 8–10 μm with bipyramidal shaped particle were grown to the thickness of about 10–14 μm after 3–6 hours treatment. The crystallization of AMO₄ was characterized by three-dimensional nucleation. This work demonstrates the possibility of fabrication of functional ceramic films directly from the aqueous solution in a single step by solution reactions.     

The Poole-Frenkel conduction mechanismin Mo-Cu2O-Au thin film structures

Thin films of cuprous oxide (4.6 μm) were electrodeposited on molybdenum. Gold contacts were vacuum evaporated on the films to form devices. These films showed relatively low electrical resistivities at around 10⁶ Ω cm and a charge transport mechanism which is different from the space charge limited current conduction previously reported for the 10¹¹ Ω cm films. The charge transport mechanism in these films was determined by isothermal measurements of the devices current-voltage (I–V) characteristics at some selected temperatures in the range of 78–321 K. In this temperature range the dominant transport mechanism can be explained by the Poole-Frenkel effect through the relation I = VG₀exp(−φ_0L/kT)exp(B_LV^1/2)+I₀exp(−φ_0H/kT)exp(B_HV^1/2) where the numerical values of the parameters are measured. φ_0L = 0.12 eV is the zero-field ionization energy of a shallow acceptor-type level (measured from the edge of the valence band) which has the dominant effect in the range of 78–230 K. Similarly φ_0H = 0.70 eV corresponds to a deep level dominant in the high-temperature range 230–321 K. In the high-temperature region a 2.7 μm thick hole accumulation layer forms beneath the oxide-gold interface, assuming the ionized deep level is doubly charged. This revised version was published online in July 2006 with corrections to the Cover Date.     

Properties of GaAs films deposited by pulse periodic technique

GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV , making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared at room temperature by plating an aqueous solution containing GaCl₃ and As₂O₃ at a pH of 2. The current density was kept as 50 mA cm⁻² and the duty cycle was varied in the range 10–50%. The films were deposited on titanium and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. The surface roughness of the films varied from 3 nm to 6 nm as the duty cycle increased. Raman spectra indicated both the LO and TO phonons for the films deposited at duty cycles above 25%. Photoelectrochemical studies indicated that the current and voltage output are higher than earlier reports on thin film electrodes.     

Photoelectrochemical solar cell studies on electroplated cuprous oxide thin films

Cuprous oxide (Cu₂O) is an interesting p-type semiconductor with a band gap of 2 eV suitable for solar cell applications. Deposition of Cu₂O thin films by electrodeposition from aqueous solutions is a low temperature and inexpensive technique. in the present work, Cu₂O thin films were cathodically deposited on Cu and tin oxide coated glass substrates by the cathodic reduction of copper (II) lactate solution. The optimized deposition conditions to synthesize cuprous oxide thin films were experimentally identified as; Deposition potential: −0.555 V versus SCE, pH: 9.0 ± 0.1, Bath temperature: 70^∘C. X-ray diffraction studies revealed the formation of single phase cubic Cu₂O films. The effect of annealing on the structure and morphology of Cu₂O thin films are studied. The dielectric susceptibility, optical conductivity and packing density are evaluated. Photoelectrochemical solar cells based on p-Cu₂O films are constructed. Spectral response studies indicate a peak in photo current density around 600 nm corresponding to the band gap of Cu₂O thin films. The effects of annealing, chemical etching and photo etching on the solar cell parameters are studied.     

Titanium-doped indium oxide films prepared by d.c. magnetron sputtering using ceramic target

Polycrystalline thin films of Ti-doped indium oxide (indium–titanium-oxide, ITiO) were prepared by d.c. magnetron sputtering and their electrical and optical properties were investigated. Doping of Ti was effective in improvement of the electroconductivity of the indium oxide: the electrical resistivity of 1.7 × 10⁻³ Ω cm of non-doping decreased to minimum value of 1.8 × 10⁻⁴ Ω cm at 2.4 at.% Ti-doping when the films were deposited at 300 °C. The polycrystalline ITiO films of 0.8–1.6 at. % Ti-doping showed the high Hall mobilitiy (82–90 cm² V⁻¹ s⁻¹) and the relatively low carrier density (2.4–3.5 × 10²⁰ cm⁻³) resulting in characteristics of both low resistivity (2.1–3.0 × 10⁻⁴ Ω cm) and high transmittance in the near-infrared region (over 80% at 1550 nm), which cannot be shown in the conventional Sn-doped indium oxide (ITO) films.     

Voltammetric and chronoamperometric studies of silver electrodeposition from a bath containing HEDTA

The electrodeposition of silver on platinum from ammonium-buffered solutions containing HEDTA (N-(2-hydroxyethyl)ethylenediaminetriacetic acid) at various concentrations was investigated. Potentiometric titration and voltammetric studies indicated that in the presence of 2.0 × 10⁻¹ M HEDTA, the deposited silver was reduced from a mixture of [AgHEDTA]²⁻ and [Ag(NH₃)₂]⁺ complexes, whereas at 2.0 × 10⁻² M and 2.0 × 10⁻³ M HEDTA in the electrolyte, the silver was reduced from the [Ag(NH₃)₂]⁺ complexes alone. Hydrodynamic studies showed variation in the diffusion coefficient for the electroactive species in solution, depending on the HEDTA concentration. Chronoamperometric study in a solution containing 2.0 × 10⁻¹ M HEDTA at low overpotential (0.000 V to –0.050 V) showed a transition from progressive to instantaneous nucleation in a single current transient, whereas, at −0.200 V only 3D-progressive nucleation controlled by mass transport was observed. Scanning electron microscope images showed that the silver films produced in silver baths with HEDTA were uniform, without cracks, and fine-grained, regardless of its concentration, while in the absence of HEDTA the morphology was rough and dendritic. X-ray diffraction analysis of the films obtained at various HEDTA concentrations revealed polycrystalline silver, similar to film obtained in cyanide and EDTA/ammonia baths.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Supercapacitive performance of hydrous ruthenium oxide (RuO<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) thin films deposited by SILAR method

The amorphous hydrous ruthenium oxide (RuO₂·nH₂O) thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. These films were characterized for their structural, surface morphological, and compositional study by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX) techniques. The wettability test was carried out by measuring the water contact angle. The scanning electron microscopy study showed small RuO₂ particles are grouped together to form porous agglomerates. The FT-IR study confirmed the formation of hydrous ruthenium oxide films. The hydrophilic nature of ruthenium oxide (RuO₂·nH₂O) thin films was observed from water contact angle measurement. The presence of Ru and O in the film was confirmed by EDAX analysis. The supercapacitor behavior of these films studied in 0.5 M H₂SO₄ electrolyte showed maximum specific capacitance of 162 F g⁻¹ at 10 mV s⁻¹ scan rate. These films exhibit 80% cycling performance after 2,000 cycles. The charge–discharge studies carried at 1 mA cm⁻² current density revealed the specific power of 3.5 KW kg⁻¹ and specific energy of 29.7 W Kg⁻¹ with 93% coulombic efficiency.     

The influence of substrate temperature on the properties of aluminum-doped zinc oxide thin films deposited by DC magnetron sputtering

Transparent, conducting, aluminum-doped zinc oxide (AZO) thin films were deposited on Corning 1737 glass by a DC magnetron sputter. The structural, electrical, and optical properties of the films, deposited using various substrate temperatures, were investigated. The AZO thin films were fabricated with an AZO ceramic target (Al₂O₃:2 wt%). The obtained films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The lowest resistivity was 6.0 × 10⁻⁴Ω cm, with a carrier concentration of 2.7 × 10²⁰ cm⁻³ and a Hall mobility of 20.4 cm²/Vs. The average transmittance in the visible range was above 90%.     

Optical and electrical properties of SnO2 films prepared by chemical vapour deposition

Transparent and conducting SnO₂ films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl₂. The effect of oxygen gas flow rate on the properties of SnO₂ films is reported. Oxygen with a flow rate from 0·8–1·35 lmin⁻¹ was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films obtained have a resistivity between 1·72 × 10⁻³ and 4·95 × 10⁻³ ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the maximum figure of merit value of 2·03 × 10⁻³ ohm⁻¹ was obtained with the films deposited at the flow rate of 1·16 lmin⁻¹.     

Surface tuning for promoted charge transfer in hematite nanorod arrays as water-splitting photoanodes

Hematite (α-Fe₂O₃) nanorod films with their surface tuned by W⁶⁺ doping have been investigated as oxygen-evolving photoanodes in photoelectrochemical cells. X-ray diffraction, field emission scanning electron microscopy, UV-visible absorption spectroscopy, and photoelectrochemical (PEC) measurements have been performed on the undoped and W⁶⁺-doped α-Fe₂O₃ nanorod films. W⁶⁺ doping is found to primarily affect the photoluminescence properties of α-Fe₂O₃ nanorod films. Comparisons are drawn between undoped and W⁶⁺-doped α-Fe₂O₃ nanorod films, WO₃ films, and α-Fe₂O₃-modified WO₃ composite electrodes. A close correlation between dopant concentration, photoluminescence intensity, and anodic photocurrent was observed. It is suggested that W⁶⁺ surface doping promotes charge transfer in α-Fe₂O₃ nanorods, giving rise to the enhanced PEC performance. These results suggest surface tuning via ion doping should represent a viable strategy to further improve the efficiency of α-Fe₂O₃ photoanodes.      

Diffusion of americium in aqueous solutions

The diffusion coefficients of Am in lanthanum and barium nitrate solutions of various concentrations in the pH range 2–12 at 25°C were determined. The secondary hydrate shell of the ion does not participate in the Am migration in the solution. The Am hydrolysis is stepwise and occurs via intermediate species according to the scheme Am(H₂O)₉³⁺ → Am(OH)(H₂O)₉²⁺ or Am(OH)(H₂O)₈²⁺ → Am(OH)₂(H₂O)₅⁺ → Am(OH)₃. The diffusion coefficients of Am at infinite dilution were determined: D ₀ = 6.2 × 10⁻⁶ cm² s⁻¹ at pH 2 and D ₀ = 6.15 × 10⁻⁶ cm² s⁻¹ at pH 3. The limiting concentrations at which the Onsager law is still observed are 0.1 g-equiv l⁻¹ at pH 3 and 0.3 g-equiv l⁻¹ at pH 2.