Showing papers on "Oxide published in 2007"

Preparation and Characterization of Graphene Oxide Paper

Abstract: Free-standing paper-like or foil-like materials are an integral part of our technological society. Their uses include protective layers, chemical filters, components of electrical batteries or supercapacitors, adhesive layers, electronic or optoelectronic components, and molecular storage. Inorganic 'paper-like' materials based on nanoscale components such as exfoliated vermiculite or mica platelets have been intensively studied and commercialized as protective coatings, high-temperature binders, dielectric barriers and gas-impermeable membranes. Carbon-based flexible graphite foils composed of stacked platelets of expanded graphite have long been used in packing and gasketing applications because of their chemical resistivity against most media, superior sealability over a wide temperature range, and impermeability to fluids. The discovery of carbon nanotubes brought about bucky paper, which displays excellent mechanical and electrical properties that make it potentially suitable for fuel cell and structural composite applications. Here we report the preparation and characterization of graphene oxide paper, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets. This new material outperforms many other paper-like materials in stiffness and strength. Its combination of macroscopic flexibility and stiffness is a result of a unique interlocking-tile arrangement of the nanoscale graphene oxide sheets.

Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets

Abstract: Individual graphene oxide sheets subjected to chemical reduction were electrically characterized as a function of temperature and external electric fields. The fully reduced monolayers exhibited conductivities ranging between 0.05 and 2 S/cm and field effect mobilities of 2−200 cm2/Vs at room temperature. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest that charge transport occurs via variable range hopping between intact graphene islands with sizes on the order of several nanometers. Furthermore, the comparative study of multilayered sheets revealed that the conductivity of the undermost layer is reduced by a factor of more than 2 as a consequence of the interaction with the Si/SiO2 substrate.

Carbon materials for supercapacitor application.

Abstract: The most commonly used electrode materials for electrochemical capacitors are activated carbons, because they are commercially available and cheap, and they can be produced with large specific surface area. However, only the electrochemically available surface area is useful for charging the electrical double layer (EDL). The EDL formation is especially efficient in carbon pores of size below 1 nm because of the lack of space charge and a good attraction of ions along the pore walls. The pore size should ideally match the size of the ions. However, for good dynamic charge propagation, some small mesopores are useful. An asymmetric configuration, where the positive and negative electrodes are constructed from different materials, e.g., activated carbon, transition metal oxide or conducting polymer, is of great interest because of an important extension of the operating voltage. In such a case, the energy as well as power is greatly increased. It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO2, conducting polymers. Substitutional heteroatoms in the carbon network (nitrogen, oxygen) are a promising way to enhance the capacitance. Carbons obtained by one-step pyrolysis of organic precursors rich in heteroatoms (nitrogen and/or oxygen) are very interesting, because they are denser than activated carbons. The application of a novel type of electrolyte with a broad voltage window (ionic liquids) is considered, but the stability of this new generation of electrolyte during long term cycling of capacitors is not yet confirmed.

Metal oxides for solid-state gas sensors: What determines our choice?

Abstract: The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

Abstract: Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide (colouring under charge insertion) and nickel oxide (colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition (by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural “smart” windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

Thin film transistors and methods of manufacturing the same

Abstract: A TFT includes a zinc oxide (ZnO)-based channel layer having a plurality of semiconductor layers. An uppermost of the plurality of semiconductor layers has a Zn concentration less than that of a lower semiconductor layer to suppress an oxygen vacancy due to plasma. The uppermost semiconductor layer of the channel layer also has a tin (Sn) oxide, a chloride, a fluoride, or the like, which has a relatively stable bonding energy against plasma. The uppermost semiconductor layer is relatively strong against plasma shock and less decomposed when being exposed to plasma, thereby suppressing an increase in carrier concentration.

Activity of CeOx and TiOx Nanoparticles Grown on Au(111) in the Water-Gas Shift Reaction

Abstract: The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO-->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO(2-x)/Au(111) and CeO(2-x)/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide.

Rapid oxygen ion diffusion and surface exchange kinetics in PrBaCo2O5+x with a perovskite related structure and ordered A cations

Abstract: As part of an investigation of new cathode materials for intermediate temperature solid oxide fuel cells, we have investigated particular perovskite oxides with ordered A cations which, in turn, localize the oxygen vacancies into layers. The oxygen exchange kinetics of polycrystalline samples of the oxygen-deficient double perovskite PrBaCo2O5+x (PBCO) have been determined by electrical conductivity relaxation (ECR) and by oxygen-isotope exchange and depth profiling (IEDP). The ECR and IEDP measurements reveal that PBCO has high electronic conductivity and rapid oxygen ion diffusion and surface exchange kinetics. Both techniques demonstrate that the oxygen kinetics in this structure type are significantly faster than in corresponding disordered perovskites.

High-Performance Ultrathin Solid Oxide Fuel Cells for Low-Temperature Operation

Abstract: Thin-film solid oxide fuel cell (SOFC) structures containing electrolyte membranes 50-150 nm thick were fabricated with the help of sputtering, lithography, and etching. The submicrometer SOFCs were made of yttria-stabilized zirconia (YSZ) or YSZ/ gadolinium-doped ceria composites electrolyte and 80 nm porous Pt as cathode and anode. The peak power densities were 200 and 400 mW/cm 2 at 350 and 400°C, respectively. The high power densities achieved are not only due to the reduction of electrolyte thickness but also to the high charge-transfer reaction rates at the interfaces between the nanoporous electrodes (cathode and/or anode) and the nanocrystalline thin electrolyte.

The reversibility of the reaction CaCO3 ⇄ CaO+CO2

Abstract: The reversibility of the reaction CaCO3 ⇌ CaO+CO2 has been examined through a large number of cycles (up to 40), mainly at 866 °C. The decomposition to the oxide is always 100% but the reactivity of the oxide so formed to carbon dioxide falls off markedly after a rapid initial reaction. There is a large increase in surface area on going from the non-porous calcium carbonate to the oxide and this is due to the formation of pores, mostly very small (< 4 nm). The fast component of the back reaction is a surface reaction and the subsequent slow reaction is controlled by the slow diffusion of carbon dioxide through the newly formed carbonate layer. The reversibility of the reaction decreases with the number of cycles, rapidly at first and then more slowly: the first effect is probably due to loss of pore volume in the oxide and the second to sintering of the carbonate.

Orbital Reconstruction and Covalent Bonding at an Oxide Interface

Abstract: Orbital reconstructions and covalent bonding must be considered as important factors in the rational design of oxide heterostructures with engineered physical properties. We have investigated the interface between high-temperature superconducting (Y,Ca)Ba(2)Cu3O7 and metallic La(0.67)Ca(0.33)MnO3 by resonant x-ray spectroscopy. A charge of about -0.2 electron is transferred from Mn to Cu ions across the interface and induces a major reconstruction of the orbital occupation and orbital symmetry in the interfacial CuO2 layers. In particular, the Cu d(3z(2)-r(2)) orbital, which is fully occupied and electronically inactive in the bulk, is partially occupied at the interface. Supported by exact-diagonalization calculations, these data indicate the formation of a strong chemical bond between Cu and Mn atoms across the interface. Orbital reconstructions and associated covalent bonding are thus important factors in determining the physical properties of oxide heterostructures.

Porous Co3O4 Nanotubes Derived From Co4(CO)12 Clusters on Carbon Nanotube Templates : A Highly Efficient Material For Li-Battery Applications

Abstract: Over the past decades, a worldwide effort has been made to search for alternative anode materials of lithium batteries for improving their energy density and safety. It has been found that 3d transition metal oxides such as nickel oxide, cobalt oxide, and iron oxide exhibit reversible capacities about three times larger than those of graphite (372 mAh g) at a relative low potential, which greatly spurs the rapid development in this field. Among them, cobalt oxides (Co3O4 and CoO) have shown the highest capacity (700 mAh g) and best cycle performance (93.4 % of initial capacity was retained after 100 cycles), compared with nickel oxide (NiO) and iron oxides (Fe2O3 and Fe3O4). [3] In recent years, the nanostructured materials have attracted great interest in the application of anode or cathode materials for lithium batteries because of their high surface-to-volume ratio and short path length for Li transport. As a result, it is believed that the Co3O4 nanomaterials can exhibit the superior Li-battery performance. Previously, several Co3O4 nanostructures such as nanoparticles, nanowires, and nanotubes were prepared by different methods. Among them, the nanotubes have been considered one of the most promising structures for lithium batteries due to their higher surface-to-volume ratio than other one-dimensional nanostructures such as nanowires and more difficult for aggregation in comparison with nanoparticles. By far, there is little literature about the synthesis and application of Co3O4 nanotubes for lithium batteries. For example, Chen et al. synthesized the Co3O4 nanotubes via the anodic aluminum oxide (AAO) template route and applied them for lithium batteries with the capacity of about 800 mAh g at the current density of 50 mA g. However, there are some disadvantages for the AAO template assisted approach to synthesize metal oxide nanotubes, which restrict their application in Libattery. Firstly, the mass production of metal oxide nanotubes prepared by such an approach is impracticable, which is one of the bottlenecks for their wide applications. Secondly, it is very difficult to completely remove the nanoporous alumina template. Thirdly, the diameters of metal oxide nanotubes prepared by such an approach are usually larger than 100 nm. Recently, carbon nanotubes (CNTs) have been considered to be an ideal template for the synthesis of metal oxide nanotubes due to the mass production, being easily removed and small diameter. For example, Liu et al. reported the synthesis of Fe2O3/CNTs core-shell nanostructures and polycrystalline Fe2O3 nanotubes by supercritical fluids approach using CNTs as templates. Unfortunately, the high temperature and pressure were needed in this approach. In addition, metal oxide/ CNTs core-shell nanostructures and metal oxide nanotubes were also achieved by CNT-template assisted chemical vapor deposition (CVD), which operated at high temperature and, moreover, only deposited oxides on the top surface of CNTs. Furthermore, metal oxide/CNTs core-shell nanostructures were also fabricated by chemical precipitation method. However, the formation of metal oxide nanoparticles in the solution or metal oxide with very large grain size on the surface of CNTs was inevitable in this approach, which made it difficult to form metal oxide nanotubes after oxidation of CNTs. Very recently, we have developed a novel approach to synthesizing the porous and polycrystalline In2O3 nanotubes by layer-by-layer assembly on CNT templates in combination with subsequent calcinations, which exhibit superior gas sensing performance. Herein, we report a novel sonochemistry method to synthesizing CNTs-CoOx nanocables derived from Co4(CO)12 clusters on CNT templates at room temperature and subsequent transformation into uniform porous Co3O4 nanotubes by the calcination. Moreover, the assynthesized porous Co3O4 nanotubes have been applied in anode materials for lithium batteries, which exhibit the superior performance and thus promising application. Firstly, Co4(CO)12 and CNTs were mixed in hexane and sonicated for 1 h at room temperature. During the sonication, Co4(CO)12 can be readily decomposed to Co and CO, as shown in Reaction 1. Secondly, Co atom can be rapidly oxidized into CoOx due to the oxygen atmosphere in the solution, as illustrated in Reaction 2. Thirdly, CoOx with positive charge can be compactly deposited on the surface of CNTs C O M M U N IC A IO N

Removal Mechanism of As(III) by a Novel Fe−Mn Binary Oxide Adsorbent: Oxidation and Sorption

Abstract: A novel Fe-Mn binary oxide adsorbent was developed for effective As(III) removal, which is more difficult to remove from drinking water and much more toxic to humans than As(V). The synthetic adsorbent showed a significantly higher As(III) uptake than As(V). The mechanism study is therefore necessary for interpreting such result and understanding the As(III) removal process. A control experiment was conducted to investigate the effect of Na2SO3-treatment on arsenic removal, which can provide useful information on As(III) removal mechanism. The adsorbent was first treated by Na2SO3, which can lower its oxidizing capacity by reductive dissolution of the Mn oxide and then reacted with As(V) or As(III). The results showed that the As(V) uptake was enhanced while the As(III) removal was inhibited after the pretreatment, indicating the important role of manganese dioxide during the As(III) removal. FTIR along with XPS was used to analyze the surface change of the original Fe-Mn adsorbent and the pretreated adsorbent before and after reaction with As(V) or As(III). Change in characteristic surface hydroxyl groups (Fe-OH, 1130, 1048, and 973 cm(-1)) was observed by the FTIR. The determination of arsenic oxidation state on the solid surface after reaction with As(III) revealed that the manganese dioxide instead of the iron oxide oxidized As(III) to As(V). The iron oxide was dominant for adsorbing the formed As(V). An oxidation and sorption mechanism for As(III) removal was developed. The relatively higher As(III) uptake may be attributed to the formation of fresh adsorption sites at the solid surface during As(III) oxidation.

Atomic layer deposition of yttria-stabilized zirconia for solid oxide fuel cells

Abstract: Yttria-stabilized zirconia (YSZ) films were synthesized by atomic layer deposition (ALD). Tetrakis(dimethylamido)zirconium and tris(methylcyclopentadienyl)yttrium were used as ALD precursors with d...

Porous Indium Oxide Nanotubes: Layer-by-Layer Assembly on Carbon-Nanotube Templates and Application for Room-Temperature NH3 Gas Sensors

Abstract: Indium oxide (In2O3), as an n-type and wide-bandgap semiconductor, is of great interest for use in toxic-gas detectors, solar cells, and light-emitting diodes because of its high electrical conductivity and high transparency. In particular, In2O3 has been extensively applied in film-based chemical sensors for a long time. However, In2O3-film-based sensing devices possess several critical limitations such as a limited maximum sensitivity and high operation temperatures (200–600 °C). In2O3 nanostructured materials, possessing ultrahigh surface-to-volume ratios, are expected to be superior gas-sensor candidates that may overcome the fundamental limitations as mentioned above. Therefore, considerable efforts have been devoted to synthesizing In2O3 nanostructures such as nanoparticles, nanowires, nanotubes, and nanobelts. Among them, nanotubes are believed to be one of the most promising structures for chemical sensors because of their higher surface-to-volume ratios and, moreover, they do not aggregate as easily as nanoparticles. Up to now, template-assisted approaches have been widely used to synthesize metal oxide nanotubes. Metal oxide nanotubes prepared by template-assisted approaches possess higher surface-to-volume ratios than those prepared by template-free approaches because of their polycrystalline and porous structure, and, therefore, may display a more superior gas-sensor performance. As a result, owing to the simplicity in the synthesis of nanotubes and their availability, quite a few metal oxide nanotubes have been fabricated by nanoporous alumina template assisted approaches such as Ga2O3, In2O3, TiO2, and Fe2O3. [8] Nevertheless, there are some disadvantages in using nanoporous alumina as a template to synthesize metal oxide nanotubes. Firstly, mass production of metal oxide nanotubes by such an approach is impractical, which is one of the bottlenecks for their wide application. Secondly, it is very difficult to completely remove the nanoporous alumina template. Thirdly, the diameters of the prepared metal oxide nanotubes by such an approach are usually larger than 100 nm. Recently, carbon nanotubes (CNTs) have been considered to be an ideal template for the synthesis of metal oxide nanotubes, which can circumvent the disadvantages of nanoporous alumina as mentioned above. For example, Rao and co-workers first fabricated ZrO2, Al2O3, V2O5, SiO2, and MoO3 nanotubes by a metal-alkoxide-based sol–gel process using CNTs as templates in combination with subsequent calcination. However, the deliquescence, toxicity, and high cost of metal alkoxides, as well as the long reaction time, restrict the practical applications of this approach. Liu and co-workers reported the synthesis of Fe2O3/CNT core–shell nanostructures and polycrystalline Fe2O3 nanotubes by a supercritical-fluid-approach using CNTs as templates. Unfortunately, this approach needed to be carried out at high temperature and pressure. In addition, metal oxide/CNT core–shell nanostructures and metal oxide nanotubes have been obtained by CNT-template-assisted chemical vapor deposition (CVD), which was also carried out at high temperature and, moreover, only resulted in the deposition of oxides on the top surface of the CNTs. Metal oxide/CNT core–shell nanostructures were also fabricated by a chemical precipitation method. However, in this route, the formation of metal oxide nanoparticles in the solution or metal oxides with a very large grain size on the surface of the CNTs was inevitable, which made it difficult to form metal oxide nanotubes after oxidation of the CNTs. We report a novel and versatile approach to synthesize metal oxide nanotubes using layer-by-layer (LBL) assembly on the CNT templates in combination with subsequent calcination. LBL assembly is based on the electrostatic attraction between charged species and it has been widely used to synthesize polymeric multicomposites, inorganic and hybrid hollow spheres, polymer nanotubes, and core–shell nanostructures. We now present its use, for the first time, to synthesize metal oxide nanotubes including In2O3, NiO, SnO2, Fe2O3, and CuO. Of these, In2O3 nanotubes are used to illustrate the basic idea underlying the approach presented in this work. The as-synthesized In2O3 nanotubes were applied in an NH3 gas sensor operated at room temperature, which exhibits improved performance and thus promising applications. C O M M U N IC A IO N

Layered perovskites as promising cathodes for intermediate temperature solid oxide fuel cells

Abstract: The suitability of GdBaCo2O5+δ as a cathode material for intermediate temperature solid oxide fuel cells has been evaluated. The 18O/16O isotope exchange depth profile (IEDP) method has been used to obtain the oxygen surface exchange and oxygen tracer diffusion coefficients yielding optimum values for applicability in fuel cells (k* = 2.8 × 10−7 cm s−1 and D* = 4.8 × 10−10 cm2 s−1 at 575 °C) especially in terms of low activation energies (EAk = 0.81(4) and EAD = 0.60(4) eV). The same material has been characterized electrically as a part of a symmetrical electrochemical system (GdBaCo2O5+δ/Ce0.9Gd0.1O2−x/GdBaCo2O5+δ), by means of impedance spectroscopy measurements, corroborating an excellent performance in the classical intermediate temperature range for solid oxide fuel cells (500–700 °C). An area specific resistance (electrode–electrolyte interface) of 0.25 Ω cm2 at 625 °C was achieved for a cell processing temperature of 975 °C. Finally, layered perovskites are presented as a promising new family of materials for cathode use in solid oxide fuel cells at low temperatures.

Fabrication of Magnetic Core@Shell Fe Oxide@Au Nanoparticles for Interfacial Bioactivity and Bio-separation

Abstract: The immobilization of proteins on gold-coated magnetic nanoparticles and the subsequent recognition of the targeted proteins provide an effective means for the separation of proteins via application of a magnetic filed. A key challenge is the ability to fabricate such nanoparticles with the desired core-shell nanostructure. In this article, we report findings of the fabrication and characterization of gold-coated iron oxide (Fe2O3 and Fe3O4) core@shell nanoparticles (Fe oxide@Au) toward novel functional biomaterials. A hetero-interparticle coalescence strategy has been demonstrated for fabricating Fe oxide@Au nanoparticles that exhibit controllable sizes ranging from 5 to 100 nm and high monodispersity. Composition and surface analyses have proven that the resulting nanoparticles consist of the Fe2O3 core and the Au shell. The magnetically active Fe oxide core and thiolate-active Au shell were shown to be viable for exploiting the Au surface protein-binding reactivity for bioassay and the Fe oxide core magnetism for magnetic bioseparation. These findings are entirely new and could form the basis for fabricating magnetic nanoparticles as biomaterials with tunable size, magnetism, and surface binding properties.

Vertically oriented Ti-Fe-O nanotube array films: toward a useful material architecture for solar spectrum water photoelectrolysis.

Abstract: In an effort to obtain a material architecture suitable for high-efficiency visible spectrum water photoelectrolysis, herein we report on the fabrication and visible spectrum (380-650 nm) photoelectrochemical properties of self-aligned, vertically oriented Ti-Fe-O nanotube array films. Ti-Fe metal films of variable composition, iron content ranging from 69% to 3.5%, co-sputtered onto FTO-coated glass are anodized in an ethylene glycol + NH4F electrolyte. The resulting amorphous samples are annealed in oxygen at 500 degrees C, resulting in nanotubes composed of a mixed Ti-Fe-O oxide. Some of the iron goes into the titanium lattice substituting titanium ions, and the rest either forms alpha-Fe2O3 crystallites or remains in the amorphous state. Depending upon the Fe content, the band gap of the resulting films ranges from about 380 to 570 nm. The Ti-Fe oxide nanotube array films are utilized in solar spectrum water photoelectrolysis, demonstrating 2 mA/cm2 under AM 1.5 illumination with a sustained, time-energy normalized hydrogen evolution rate by water splitting of 7.1 mL/W.hr in a 1 M KOH solution with a platinum counter electrode under an applied bias of 0.7 V. The surface morphology, structure, elemental analysis, optical, and photoelectrochemical properties of the Ti-Fe oxide nanotube array films are considered.

Tetrachelate Porphyrin Chromophores for Metal Oxide Semiconductor Sensitization: Effect of the Spacer Length and Anchoring Group Position

Abstract: Four Zn(II)-tetra(carboxyphenyl)porphyrins in solution and bound to metal oxide (TiO2, ZnO, and ZrO2) nanoparticle films were studied to determine the effect of the spacer length and anchoring grou ...

Hybrid polymer-metal oxide thin films for photovoltaic applications{

Abstract: We review progress in the development of organic–inorganic hybrid photovoltaic materials consisting of a conjugated polymer as an electron donor and a nanocrystalline metal oxide as the electron acceptor. We distinguish two main approaches: (1) where a rigid porous metal oxide structure is filled with polymer and (2) where metal oxide nanoparticles and polymer are co-deposited from solution to form a blend film. In the case of porous structures, performance is limited by the infiltration of polymer into the pores of the metal oxide and control of the nanostructure dimensions. In the case of blends, control of the blend morphology and transport between nanoparticles are limitations. In both cases, further improvements are possible by modifying the metal oxide organic interface to optimise charge transfer, by improving both inter- and intra-particle transport within the metal oxide phase, for example by the use of single crystalline nanorods, and by optimising the choice of electrode materials. Though unlikely to achieve the highest photocurrents, the polymer–metal oxide composites provide a model system to study the effects of interface properties and film morphology on the performance of bulk heterojunction photovoltaic devices.

Perovskite oxides for semiconductor-based gas sensors

Abstract: The oxygen partial pressure dependence of the point defect concentration, and thus conductivity, in oxide semiconductors allows for their use in high-temperature gas sensors. In addition to responding to oxygen partial pressure, the resistance of oxide semiconductors can be affected by other gases, such as carbon monoxide, hydrocarbons and ethanol, which creates opportunities for developing new sensors, but also leads to interference problems. The most common oxide used in such sensors is tin oxide, although other simple oxides, and some mixed oxides, are also used. The focus of this paper is on the use of perovskite oxides in semiconductor-based gas sensors. The perovskite structure, with two differently-sized cations, is amenable to a variety of dopant additions. This flexibility allows for control of the transport and catalytic properties, which are important for improving sensor performance.