Artificial photosynthesis by using chloroplasts from spinach adsorbed on a nanocrystalline TiO2 electrode for photovoltaic conversion

Photovoltaic conversion has been achieved by use of chloroplasts (photosynthetic organs) from spinach adsorbed on a nanocrystalline TiO₂ film on an indium tin oxide (ITO) glass electrode (chloroplast/TiO₂ electrode). The shape of the absorption spectrum of the chloroplast/TiO₂ electrode is almost the same that of a dispersion of the chloroplasts. Absorption maxima of the chloroplast/TiO₂ electrode observed at 430, 475, and 670 nm were attributed to carotenoid and chlorophyll molecules, suggesting that chloroplasts have been adsorbed by the nanocrystalline TiO₂ film on the ITO electrode. The photocurrent responses of chloroplast/TiO₂ electrodes were measured by using a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water and 100 mW cm^?2 irradiation. The photocurrent of the chloroplast/TiO₂ electrode was increased by adding water to the redox electrolyte. The photocurrent responses of chloroplast/TiO₂ electrodes irradiated with monochromatic light (680 nm, the absorption band of photosystem II complexed with evolved oxygen) were measured by use of a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water. A chloroplast/TiO₂ electrode photocurrent was observed only when the redox electrolyte containing water was used, indicating that the oxygen evolved from water by photosystem II in chloroplasts adsorbed by a nanocrystalline TiO₂ film on an ITO electrode irradiated at 680 nm is reduced to water by the catalytic activity of the platinum electrode. The maximum incident photon-to-current conversion efficiency (IPCE) was 0.8 % on irradiation at 670 nm.     

Tuning percolation speed in layer-by-layer assembled polyaniline–nanocellulose composite films

Polyaniline of low molecular weight (ca. 10 kDa) is combined with cellulose nanofibrils (sisal, 4–5 nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4 nm per layer. Stable and strongly adhering films are formed with thickness-dependent coloration. Electrochemical measurements in aqueous H₂SO₄ confirm the presence of two prominent redox waves consistent with polaron and bipolaron formation processes in the polyaniline–nanocellulose composite. Measurements with a polyaniline–nanocellulose film applied across an ITO junction (a 700 nm gap produced by ion beam milling) suggest a jump in electrical conductivity at ca. 0.2 V vs. SCE and a propagation rate (or percolation speed) two orders of magnitude slower compared to that observed in pure polyaniline This effect allows tuning of the propagation rate based on the nanostructure architecture. Film thickness-dependent electrocatalysis is observed for the oxidation of hydroquinone.

     

Ag nanoparticles deposited onto silica,titania, and zirconia mesoporous films synthesized by sol–gel template method

A variety of Ag nanoparticles/oxide mesoporous films with templated silica, titania, and zirconia was synthesized by sol–gel method at glass, aluminum, and silicon substrates using metal alkoxides (tetraethoxysilane, titanium tetraisopropoxide, and zirconium tetrapropoxide) and AgNO₃ as precursors of oxide films and Ag nanoparticles, respectively, and Pluronic P123 as a template agent. Oxide films alone and Ag/oxide composites were characterized using hexane adsorption, X-ray diffraction (XRD), Raman and ultraviolet (UV)/vis spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. The distribution of Ag nanoparticles within the films, their sizes, intensity, and position of surface plasmon resonance (SPR) absorbance band at λ = 400 nm, as well as the textural and structural characteristics of whole films depend on treatment temperature, types of substrates and oxide matrices, oxide crystallization, and Ag content. Ag nanoparticles form preferably on the outer surface of the films under lower sintering temperatures if the amount of loaded silver is low. Oxide crystallization (e.g., TiO₂) promotes silver embedding into the outer film layer. At higher silver content (≥10 at.%) and higher calcination temperature (873 K), silver nanoparticles could be entrapped more uniformly along the film profile because of more intensive evaporation of silver droplets from the outer surface of the films on heating.     

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

Heat treatment of Zr-24 at% Ti alloy with barrier-type dielectric anodic oxide films was conducted at 473 K in air to examine the thermal stability of the dielectric oxide films for possible electrolytic capacitor application. The anodic oxide film was formed by anodizing of the alloy at 50 V for 30 min in 0.1 mol dm^?3 ammonium pentaborate electrolyte. The anodic oxide film of 125 nm thickness was crystalline, containing both monoclinic and tetragonal ZrO₂ phase. It was found that marked thickening of the oxide film with generation of cracks occurred during heat treatment at 473 K. Thus, the dielectric loss was largely increased along with the capacitance increase. In contrast, the anodic oxide film formed on the oxygen-incorporated alloy remained uniform, and no significant increase in dielectric loss was observed even after the heat treatment. The capacitance of the anodic film became as high as 4.8 mF m^?2, which was nearly twice that on Ta. The high capacitance was associated with the preferential formation of tetragonal ZrO₂ phase in the anodic oxide film on the oxygen-incorporated alloy. Findings indicated that the oxygen-incorporated Zr-Ti alloy is a promising novel material for capacitor application.     

Use of a precursor solution to fill the gaps between indium tin oxide nanorods, for preparation of three-dimensional CuInGaS2 thin-film solar cells

We have fabricated a three-dimensional (3D) nanostructured indium tin oxide (ITO) film in which the spaces were filled by use of a Cu, In, and Ga precursor solution. This solution has potential for use in bulk heterojunction CuIn _x Ga_1?x S₂ (CIGS) thin-film solar cells. ITO nanorod films ~700 nm thick on glass substrates were synthesized by radio-frequency magnetron sputtering deposition. To ensure complete filling of the gaps in ITO nanorod films, a polymeric binder-free precursor solution was used. In addition, a two-step heating process (oxidation and sulfurization) was used after coating of the precursor solution to make a CIGS absorber film with a minimum of carbon impurities. Superstrate-type solar cell devices with 3D nanostructured films (CIGS–ITO) had a photovoltaic efficiency of 1.11 % despite the absence of a buffer layer (e.g. CdS) between the CIGS and ITO.     

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i _ph and photopotential E _ph measurements, the n-type conductivity of Ag₂O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i _ph ~L and E _ph ~L ². The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X _Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag₂O. The parameters of Ag₂O film (optical absorption coefficient α, donor defects concentration N _D, space charge region W, and Debye’s length of screening L _D) depend on the index of a crystal face of silver, volume concentration of gold X _Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag₂O formed on Ag_poly, Ag_hkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Ag_poly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag₂O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.     

Superhigh-Rate Epitaxial Silicon Thick Film Deposition from Trichlorosilane by Mesoplasma Chemical Vapor Deposition

Homoepitaxial Si thick films have been deposited by mesoplasma chemical vapor deposition (CVD) with SiHCl₃ (TCS)–H₂–Ar gas mixtures. The addition of a small amount of H₂ has been found to not only modify the film structure from polycrystalline to epitaxial but also effectively improve the deposition efficiency and film purity by removing Cl in the form of HCl. However, an excess introduction of H₂ decreases the deposition efficiency owing to the shrinkage of the plasma flame. On the other hand, an increase in TCS flow rate increases the epitaxial deposition rate despite exhibiting a saturating tendency, while the material yield tends to decrease gradually due possibly to an increase in the Cl atoms. Also, we observed a critical limit in the TCS flow rate for epitaxial growth, beyond which a polycrystalline film resulted. However, when RF input power was increased, not only the upper limit of TCS flow rate for epitaxy was extended but also the deposition yield was improved so that the deposition rate reached ~700 nm/s with the material yield of >50 % at 30 kW input power with an H₂/TCS ratio of 1.5. Additionally, high input power is found to be beneficial to decrease Cl atom incorporation into the film and improve the Hall mobility of the films. An epitaxial film with a Cl atom concentration of less than 3 × 10¹⁶ cm^?3 and a Hall mobility as high as 250 cm²/(V·s) was obtained at 30 kW input power.     

Magnetron formation of Ni/YSZ anodes of solid oxide fuel cells

Physico-chemical and structural properties of nanocomposite NiO/ZrO₂:Y₂O₃ (NiO/YSZ) films applied using the reactive magnetron deposition technique are studied for application as anodes of solid oxide fuel cells. The effect of oxygen consumption and magnetron power on the discharge parameters is determined to find the optimum conditions of reactive deposition. The conditions for deposition of NiO/YSZ films, under which the deposition rate is maximum (12 μm/h), are found and the volume content of Ni is within the range of 40–50%. Ni-YSZ films reduced in a hydrogen atmosphere at the temperature of 800°C have a nanoporous structure. However, massive nickel agglomerates are formed in the course of reduction on the film surface; their amount grows at an increase in Ni content in the film. Solid oxide fuel cells with YSZ supporting electrolyte and a LaSrMnO₃ cathode are manufactured to study electrochemical properties of NiO/YSZ films. It is shown that fuel cells with a nanocomposite NiO/YSZ anode applied using a magnetron sputtering technique have the maximum power density twice higher than in the case of fuel cells with an anode formed using the high-temperature sintering technique owing to a more developed gas-anode-electrolyte three-phase boundary.     

Oxygen reduction on electrodeposited silver catalysts in alkaline solution

In this study, silver was electrochemically deposited onto glassy carbon (GC) substrate using constant potential regime and tested for oxygen reduction reaction (ORR) in alkaline media. The surface morphology of Ag/GC electrodes was studied by scanning electron microscopy (SEM). It was established that after 10 s of deposition, a number of Ag nanoparticles with the size of 15 nm are produced that grow to about 45 nm after 300 s of electrodeposition. The ORR studies were conducted in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. The Tafel slope at low current densities for electrodeposited silver is in the range from ?70 to ?80 mV. The RDE measurements showed that the electron transfer number (n) is 3.5 for smaller amounts of electrodeposited Ag, and it increases with increasing the loading of Ag on the GC surface. These n values suggest that the electroreduction of oxygen on Ag/GC electrodes proceeds mainly to water.     

Nano silver coated patterned silica thin film by sol–gel based soft lithography technique

We report the fabrication of nano silver coated patterned silica thin film by sol–gel based soft lithography technique. Initially, silica gel film on soda lime silica glass was prepared by dipping technique from a silica sol of moderate silica concentration. A PolydimethylSiloxane elastomeric stamp containing the negative replica of the patterns of commercially available compact disc was used for embossing the film and the embossed film was cured up to 450 °C in pure oxygen atmosphere for oxide film. Finally, a precursor solution of AgNO₃ in water containing polyvinyl alcohol as an organic binder was made and used for coating on the patterned silica film by dipping technique and cured the sample up to 450 °C in reducing gas atmosphere to obtain nano silver layer. The formation of only cubic silver (~4.0 nm) and both cubic silver (~5.2 nm) and silver oxide (~3.6 nm) crystallites at 350 and 450 °C film curing temperatures respectively were confirmed by XRD measurements. The % of nano silver metal and silver oxide were 75.4 and 24.6 respectively. The nano-structured surface feature was visualized by FESEM whereas AFM revealed the high fidelity grating structure of the films. Presence of both spherical and rectangular structure (aspect ratio, 2.37) of nano silver/silver oxide was confirmed by TEM. The films were also characterized by UV–Vis spectral study. The patterned film may find application in chemical sensor devices.     

Facile synthesis of a porous network-like silver film for electrocatalytic detection of nitrate

We have developed a method for in-situ construction of a porous network-like silver film on the surface of a glassy carbon electrode (GCE). It is based on a galvanic replacement reaction where a layer of copper nanoparticles is first electrodeposited as a sacrificial template. The silver film formed possesses a porous network-like structure and consists of an assembly of numerous nanoparticles with an average size of 200 nm. The electrode displays excellent electrocatalytic activity, good stability, and fast response (within 2 s) toward the reduction of nitrate at a working potential of ?0.9 V. The catalytic currents linearly increase with the nitrate concentrations in the range of 0.08–6.52 mM, with a detection limit of 3.5 μM (S/N?=?3) and a repeatability of 3.4 % (n?=?5).

Electrodeposition of silver nanoparticles on a zinc oxide film: improvement of amperometric sensing sensitivity and stability for hydrogen peroxide determination

A strategy to fabricate a hydrogen peroxide (HP) sensor is developed by electrodepositing silver nanoparticles (Ag NPs) on a modified glassy carbon electrode (GCE) with a zinc oxide (ZnO) film. The Ag NPs/ZnO/GCE has been characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. It has been found that the Ag NPs synthesized in the presence of ZnO film provide an electrode with enhanced sensitivity and excellent stability. The sensitivity to HP is enhanced 3-fold by using Ag NPs/ZnO/GCE compared to Ag NPs/GCE. The HP sensor exhibits good linear behavior in the concentration range 2 µM to 5.5 mM for the quantitative analysis of HP with a detection limit of 0.42 µM (S/N?=?3).     

Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Composite thin films of poly(phenylene oxide)/poly(styrene) and PPO/silver via vapor phase deposition

We report fabrication of thin (100～300 nm) poly(phenylene oxide) (PPO) films and their composites with poly (styrene) (PS) and silver (Ag) nanoparticles using a one‐step electron beam‐assisted vapor phase co‐deposition technique. Surface morphology and the structure of the deposited polymer thin film composites were characterized by FTIR, Raman, X‐ray spectroscopy, and contact angle measurements. As‐deposited PPO films and PPO/Ag composites were of porous nature and contrary to solvent casting techniques were free from nodular growth. In the case of PPO/PS thin film polymer composites, however, film morphology displayed nodular growth of PPO with nodule diameters of about ～200 nm and height of approximately 50 nm. Unique morphological changes on the porous PPO thin film surface were noticed at different Ag filling ratios. Further, the capacitance of PPO/Ag composites (<16 wt%) were measured under radio‐frequency conditions and they were functional up to 100 MHz with an average capacitance density of about 2 nF/cm². The fabricated PPO‐based composite systems are discussed for their potential applications including embedded capacitor technology. Copyright © 2008 John Wiley & Sons, Ltd.     

A galvanic gas sensor using poly (ethylene oxide) complex of silver trifluoromethane sulphonate electrolyte

Summary A galvanic sensor for monitoring nitrogen dioxide was developed by using a poly(ethylene oxide) complex of silver trifluoromethanesulphonate electrolyte. The sensor, which is expressed as Au/P(EO)_4.5 AgCF₃SO₃/Ag, is a small disk (i.d. 13 mm). The polymeric electrolyte film was made by casting the mixture of acetonitrile solutions of both P(EO) (MW 6×10⁵) and AgCF₃SO₃. The working electrode was made by sputtering of gold in argon. The thicknesses of the desposited gold, polymeric electrolyte film and silver are 25 nm, 30 m and 1 mm, respectively. When the sample gas containing nitrogen dioxide impinges at 20 ml min^–1 on the gold cathode, the current flowing in the external circuit was linearly related to the concentration of nitrogen dioxide from 20 ppb to about 10 ppm. The current efficiency of the cell was 0.051%. The cell's response time was about 2 min for 0.5 ppm of nitrogen dioxide.     

Preparation and characterization of nanocomposite ZnO–Ag thin film containing nano-sized Ag particles: influence of preheating,annealing temperature and silver content on characteristics

Nanocomposite ZnO–Ag thin film containing nano-sized Ag particles have been grown on glass substrate by spin-coating technique using zinc acetate dihydrate as starting precursor in 2-propanol as solvent and monoethanolamine as stabilizer. Silver nanoparticles were added in the ZnO sol using silver nitrate dissolved in ethanol-acetonitrile. Their structural, electrical, crystalline size and optical properties were investigated as a function of preheating, annealing temperature and silver content. The results indicated that the crystalline phase was increased with increase of annealing temperature up to 550 °C at optimum preheating temperature of 275 °C. Thermal gravimetric differential thermal analysis results indicated that the decomposition of pure ZnO and nanocomposite ZnO–Ag precursors occurred at 225 and 234 °C, respectively with formation of ZnO wurtzite crystals. The scanning electron microscopy and atomic force microscopy revealed that the surface structure (the porosity and grain size) of the ZnO–Ag thin film (the film thickness is about 379 nm) was changed compared to pure ZnO thin film. The result of transmission electron microscopy showed that Ag particles were about 5 nm and ZnO particles 58 nm with uniform silver nanoclusters. Optical absorption results indicated that optical absorption of ZnO–Ag thin films decreased with increase of annealing temperature. Nanocomposite ZnO–Ag thin films with [Ag] = 0.068 M and [Ag] = 0.110 M showed an intense absorption band, whose maximum signals appear at 430 nm which is not present in pure ZnO thin films. The result of X-ray photoelectron spectroscopy revealed that the binding energy of Ag 3d_5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.     

Thin films of vanadium oxide grown on vanadium metal: oxidation conditions to produce V2O5 films for Li‐intercalation applications and characterisation by XPS,AFM, RBS/NRA

Thin films of vanadium oxide were grown on vanadium metal surfaces (i) in air at ambient conditions, (ii) in 5 mM H₂SO₄ (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10^?5 mbar) at temperatures between 350 and 550 °C and (iv) at near‐atmospheric oxygen pressure (750 mbar) at 500 °C. The oxide films were investigated by atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed of V₂O₃. In air and in aqueous solution at RT, the oxide films are ultra‐thin and hydroxylated. At 500 °C, nearly atmospheric oxygen pressure is required to form crystalline V₂O₅ films. The oxide films grown at pO₂ = 750 mbar for 5 min are about 260‐nm thick, and consist of a 115‐nm outer layer of crystalline V₂O₅. The inner oxide is mainly composed of VO₂. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 °C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well‐crystallized V₂O₅ film, formed by oxidation for 5 min at 500 °C and 750 mbar O₂, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright © 2005 John Wiley & Sons, Ltd.     

Formation of solid electrolyte films on porous supporting electrodes

In this work, the method of chemical deposition from the gas phase of organometallic compounds (CVDOM) was used to obtain thin electrolyte films of zirconia stabilized by yttria (YSZ) on a supporting electrode. Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium often termed as zirconium (IV) Zr(dpm)₄ and yttrium (III) Y(dpm)₃ dipivaloylmethanates were used as precursors for film deposition. Gas-tight electrolyte films were obtained on a supporting anode with a thickness of 4–10 μm at moderate deposition temperatures of 500–700°C. An electrochemical cell was prepared and tested using the obtained films. The cell allowed obtaining the power density values of 680, 360, and 175 mW/cm² at the temperatures of 800, 700, and 600°C, accordingly.     

Polyethylene glycol assisted direct deposition of rutile TiO2 nanocrystals on transparent conducting oxide substrate for dye-sensitized solar cell applications

Rutile TiO₂ nanocrystals having rectangular faces were directly deposited on fluorine-doped tin oxide coated glass substrates. Using polyethylene glycol-400 as the surfactant, we succeeded in growing a porous rutile layer having maximum thickness of 4.8 μm and containing nanocrystals with lateral dimensions of at least 30 nm. We observed that polyethylene glycol not only controlled the sizes of the nanocrystals but also enhanced the rate of deposition. The nanocrystals had rutile structure and the film was strongly textured with preferential orientation along {002} direction. The dye adsorption properties of the nanocrystalline films depended on their microscopic surface areas which were determined by the sizes of the nanocrystals. A dye-sensitized solar cell, fabricated with a 4.8 μm thick nanocrystalline rutile thin film photoanode, exhibited a light-to-electricity conversion efficiency of 5.02 % under 1.0 sun illumination. The internal resistance, interface capacitance and electron lifetime of dye sensitized solar cell were estimated by electrochemical impedance spectroscopy and an electron lifetime of 0.19 s was recorded.     

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In₂O₃ (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)₃, formed on the surface of the nm-sized ITO particles. This revised version was published online in August 2006 with corrections to the Cover Date.