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Understanding the uranium 5f/6d orbital mixing with oxygen 2p valence orbitals in uranium oxides is important for advancing nuclear technology. Unfortunately, U–O orbital mixing is difficult to probe experimentally. In this manuscript, U–O bonding is evaluated in U 3 O 8 using O K-edge X-ray absorption spectroscopy (XAS). To confirm that the O K-edge XAS spectra were correct and did not contain contributions from surface contamination, three different sample types were investigated using three unique detection methods. Specifically an epitaxial film of U 3 O 8 deposited on Al 2 O 3 (PAD-U 3 O 8 ) was probed using grazing-incidence fluorescence yield (GIFY) detection, a bulk powder of α-phase U 3 O 8 was analyzed with fluorescence yield (FY) detection at normal incidence, and particles of α-phase U 3 O 8 were studied in transmission mode using a scanning transmission X-ray microscope (STXM). Experimental spectra have been presented in the context of previously published computational results from DFT using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid functional. Overall, the comparative analyses of PAD-U 3 O 8 and α-phase U 3 O 8 samples enabled identification of unique signatures associated with oxygen 2p orbital mixing with both U V and U VI 5f and 6d valence orbitals.

High quality epitaxial thin films of cubic UC2 were synthesized using a solution based technique. The films were characterized using XRD, UPS, Raman, and resistivity. The substrate lattice is yttrium stabilized zirconia and serves to stabilize the high temperature cubic phaseof UC2 (>1765 °C) at room temperature. The resistivity and UPS data indicate that UC2 has relatively low electrical conductivity consistent with HSE hybrid DFT calculations showing a narrow band gap. In situ XRD measurements show that the UC2 films oxidize to U3O8 above 200 °C.

Catalyst support durability is currently a technical barrier for commercialization of polymer electrolyte membrane (PEM) fuel cells, especially for transportation applications. Degradation and corrosion of the conventional carbon supports leads to losses in active catalyst surface area and, consequently, reduced performance. As a result, the major aim of this work is to develop support materials that interact strongly with Pt, yet sustain bulk-like catalytic activities with very highly dispersed particles. This latter aspect is key to attaining the 2015 DOE technical targets for platinum group metal (PGM) loadings (0.20 mg/cm{sup 2}). The benefits of the use of carbon-supported catalysts to drastically reduce Pt loadings from the early, conventional Pt-black technology are well known. The supported platinum catalyzed membrane approach widely used today for fabrication of membrane electrode assemblies (MEAs) was developed shortly thereafter these early reports. Of direct relevance to this present work, are the investigations into Pt particle growth in PEM fuel cells, and subsequent follow-on work showing evidence of Pt particles suspended free of the support within the catalyst layer. Further, durability work has demonstrated the detrimental effects of potential cycling on carbon corrosion and the link between electrochemical surface area and particle growth. To avoid the issuesmore » with carbon degradation altogether, it has been proposed by numerous fuel cell research groups to replace carbon supports with conductive materials that are ceramic in nature. Intrinsically, these many conductive oxides, carbides, and nitrides possess the prerequisite electronic conductivity required, and offer corrosion resistance in PEMFC environments; however, most reports indicate that obtaining sufficient surface area remains a significant barrier to obtaining desirable fuel ceU performance. Ceramic materials that exhibit high electrical conductivity and necessary stability under fuel cell conditions must also exhibit high surface area as a necessary adjunct to obtaining high Pt dispersions and Pt utilization targets. Our goal in this work is to identify new synthesis approaches together with materials that will lead to ceramic supports with high surface areas and high Pt dispersions. Several strong candidates for use as PEMFC catalyst supports include: transition metal nitrides and substoichiometric titanium oxides, which hither to now have been prepared by other researcher groups with relatively low surface areas (ca. 1-50 m{sup 2}/g typical). To achieve our goals of engineering high surface area, conductive ceramic support for utilization in PEMFCs, a multi-institutional and multi-disciplinary team with experience synthesizing and investigating these materials has been assembled. This team is headed by Los Alamos National Laboratory and includes Oak Ridge National Laboratory and the University of New Mexico. This report describes our fiscal year 2010 technical progress related to applying advanced synthetiC methods towards the development of new ceramic supports for Pt catalysts for PEM fuel cells.« less

Solvothermal reactions of Zn(NO3)2·6H2O and alkali (Na, K) chloride with the trigonal-planar ligand benzene-1,3,5-tribenzoic acid (H3BTB) gave rise to two new crystalline porous metal−organic frameworks (MOFs), [Zn3Na2O(BTB)2(DMF)2](DMF)(H2O) and [Zn2K3(BTB)2(HCOO)(DMF)3](DMF)3(H2O)2, respectively. Both phases have Zn3Na2(μ4-O) and Zn2K2(HCOO) clusters as molecular building block nodes, and they form similar alkali-bridged 2-fold interpenetrated, (3,6)-connected nets with the mineral rtl-c topology. The alkali-bridged interpenetration reduces the flexibility of their interpenetrated nets, affording permanent porosity and high thermal stability. These two MOFs also exhibit high capacities of hydrogen uptake and strong solid fluorescent emissions.

The vertical connection of carbon nanotubes (CNTs) to silicon based on a chemical route at room temperature has been realized, using polyethylenimine (PEI) as a binding material between them. Chemical hydrogen bonding and electrostatic interaction between PEI, CNTs, and silicon effectively connect the CNTs to silicon. In this process, CNTs always keep their pristine structure and shape, so the unique physical properties of CNTs are maintained. Electric transport at this junction shows a tunneling behavior, which verifies PEI as a molecular link between CNT tips and the silicon. Control of both interaction and surface termination of the materials at the molecular level allows us to bind the CNTs to the silicon surface without modifying the properties of either.

Transparent conductive oxides (TCOs) are widely used in optoelectronic devices. For example, Sn-doped In2O3 (indium tin oxide, ITO), Al-doped ZnO, and F- or Sb-doped SnO2 have been practically adopted as transparent electrodes in flat panel displays, solar cells, and organic light-emitting diodes. [1] As these materials are all electron doped, the electrical conductivity of these materials is controlled by the conduction of electrons. In other words, they are n-type TCOs. In order to fully explore the potential applications of TCOs in transparent electronics, the development of p-type TCOs is critical as well. [2] For instance, the formation of active devices such as p–n junctions based on TCOs can lead to functional windows, where the junction not only transmits visible light but also generates electricity by the absorption of the ultraviolet (UV) radiation. [2] Since the discovery of p-type electrical conduction in the transparent CuAlO2 thin film, a class of delafossite AMO2 materials (A= Cu or Ag, M = Al, Ga, Fe, or In) has been extensively investigated in the last several years. [2–5] The crystal structure of delafossite CuAlO2 consists of an alternating stack of Cu ion layers and AlO2 octahedron layers. Each Cu atom is linearly coordinated with two oxygen atoms to form an O-Cu-O dumbbell unit placed parallel to the c-axis. O-atoms of O-Cu-O dumbbell link all Cu layers with the AlO2 layers. [2] Synthesizing thin film of this material is complicated due to the variety of possible Cu-Al-O phases. [6] A few attempts have been made to prepare CuAlO2 films using techniques such as pulsed laser deposition (PLD), DC- and rfsputtering, chemical vapor deposition (CVD), ion-exchange reactions, spray, and sol-gel methods. [2,5–18] The chemical solu

Polymer assisted deposition is a versatile technique to grow simple and complex metal-oxide thin films. In this paper we report the structural and electrical properties of ferroic materials, namely La0.67M0.33MnO3 (M=Sr and Ca) and Ba1 −xSrxTiO3 (x=0.3, 0.5, and 0.7) prepared using this process. The films were prepared on single crystalline LaAlO3 substrates. The films were highly c-axis oriented and epitaxial in nature. The ferromagnetic La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 films show intrinsic transport properties with maximum magnetoresistance values (at applied field of 5 T) of −50% and −88%, respectively. The highest dielectric constant (∼1010) and tunability (∼69%) of Ba1 −xSrxTiO3 film occurs at x=0.3 for films, which is at the phase boundary of tetragonal and cubic. Published by Elsevier B.V.

Highly c-axis-oriented zinc oxide (ZnO) films with nano-size grains were successfully prepared on sapphire (0001) substrates by polymer-assisted deposition, where the crystallization of the ZnO was realized by a rapid thermal process (RTP). Post-processing conditions played critical roles in the structure, surface morphology, and the photoluminescence (PL) spectra of the films. The post-thermal treatment by RTP enhances the green PL of the ZnO films. Oxygen vacancies induced by the RTP may be related to the green PL from undoped ZnO.

Metal oxides are emerging as important materials for their versatile properties such as high-temperature superconductivity, ferroelectricity, ferromagnetism, piezoelectricity and semiconductivity. Metal-oxide films are conventionally grown by physical and chemical vapour deposition. However, the high cost of necessary equipment and restriction of coatings on a relatively small area have limited their potential applications. Chemical-solution depositions such as sol-gel are more cost-effective, but many metal oxides cannot be deposited and the control of stoichiometry is not always possible owing to differences in chemical reactivity among the metals. Here we report a novel process to grow metal-oxide films in large areas at low cost using polymer-assisted deposition (PAD), where the polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal-organic films. The latter feature makes it possible to grow simple and complex crack-free epitaxial metal-oxides.

Polymer-assisted deposition (PAD) is one of the chemical solution deposition methods which have been successfully used to grow films, form coatings, and synthesize nanostructured materials. In comparison with other conventional solution-based deposition techniques, PAD differs in its use of water-soluble polymers in the solution that prevent the metal ions from unwanted chemical reactions and keep the solution stable. Furthermore, filtration to remove non-coordinated cations and anions in the PAD process ensures well controlled nucleation, which enables the growth of high quality epitaxial films with desired structural and physical properties. The precursor solution is prepared by mixing water-soluble polymer(s) with salt(s). Thermal treatment of the precursor films in a controlled environment leads to the formation of desired materials. Using BaTiO3 grown on SrTiO3 and LaMnO3 on LaAlO3 as model systems, we show the effect of filtration on the nucleation and growth of epitaxial complex metal-oxide films based on the PAD process.

We measured the thickness dependence of the superconducting properties in epitaxial δ-MoN thin films grown on α-Al2O3(001) substrates by polymer-assisted deposition. Our results indicate that the superconducting properties such as the upper critical field (μ0Hc2 ≈ 10 T) and the superconducting critical temperature (Tc = 12.5 K) are thickness independent for films thicker than ~36 nm. By measuring the critical current density (Jc) in the vortex-free state, which coincides with the depairing current density (J0), we estimate that films thicker than ~36 nm have a coherence length ξ(0) = 5.8 ± 0.2 nm and penetration depth λ(0) = 420 ± 50 nm. We found that it is possible to enhance the Hc2(0) values to close to 10 T without any appreciable reduction in Tc. Fil: Haberkorn, Nestor Fabian. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina Fil: Zhang, Y. Y.. Tsinghua University; China Fil: Kim, Jeehoon. Institute for Basic Science and Department of Physics; Corea del Norte Fil: Mccleskey, Thomas M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Burrell, Anthony K.. Argonne National Laboratory; Estados Unidos Fil: Depaula, R. F.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Tajima, T.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Jia, Q. X.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Civale, Leonardo. Los Alamos National High Magnetic Field Laboratory; Estados Unidos

Epitaxial Ba1−xSrxTiO3 (BST) thin films with different Ba∕Sr ratio (x=0.1–0.9 with an interval of 0.1) have been grown on (001) LaAlO3 substrates using polymer-assisted deposition. Dielectric measurements show that the films have dielectric properties comparable to the BST films grown by the pulsed laser deposition. Systematic changes in the lattice parameters and dielectric behavior with x values have been measured. The highest dielectric constant (∼1010) and tunability (∼69%) at 1MHz and room temperature have been obtained at x=0.3, which is at the phase boundary of tetragonal and cubic structures.

The formation of carbon nanotube and superconductor composites makes it possible to produce new and/or improved functionalities that the individual material does not possess. Here we show that coating carbon nanotube forests with superconducting niobium carbide (NbC) does not destroy the microstructure of the nanotubes. NbC also shows much improved superconducting properties such as a higher irreversibility and upper critical field. An upper critical field value of ~5 T at 4.2 K is much greater than the 1.7 T reported in the literature for pure bulk NbC. Furthermore, the aligned carbon nanotubes induce anisotropy in the upper critical field, with a higher upper critical field occurring when the magnetic field is parallel to the carbon nanotube growth direction. These results suggest that highly oriented carbon nanotubes embedded in superconducting NbC matrix can function as defects and effectively enhance the superconducting properties of the NbC. Composites of carbon nanotubes and superconductors provide technologically important new, or improved, functionalities. Here, with a chemical solution approach, well-aligned carbon nanotube forests embedded in a superconducting NbC matrix are shown to effectively enhance the superconducting properties of NbC.

Epitaxial NbC thin films were grown by a chemical solution technique, polymer assisted deposition. High quality epitaxial NbC film showed a transition temperature of 10 K and a hardness of 19.54 GPa.

Carbide films exhibit many unique properties. The development of a versatile and simple technique for the deposition of carbide films will enable a wide range of technological applications. Here we report a cost-effective chemical solution deposition or polymer-assisted deposition method for growing epitaxial carbide (including TiC, VC, and TaC) films. These epitaxial carbide films exhibit structural and physical properties similar to the films grown by vapor deposition methods.

In the last several years, metal-oxides have become the basis for many revolutionary electronic devices because they exhibit a wide range of electronic properties that conventional metallic elements and covalent semiconductors do not possess. Metal-oxide films can be grown by physical vapor deposition, chemical vapor deposition, and chemical solution deposition techniques. One of the challenges in solution-based processes of complex functional metal-oxide films has been to produce high quality films and at the same time to control the stoichiometry. In this talk, we describe a new chemical solution method called polymer-assisted deposition (PAD) to grow epitaxial complex metal-oxides such as ferroelectric Ba1-xSrxTiO3, Pb0.40Sr0.60TiO3, and BaZr0.27Ti0.73O3 films. We use a new strategy to control the distribution of metals in solution at a molecular level and a mixture of metal precursor and soluble polymer to form a solution with desired viscosity. By actively binding the metal, the polymer serves to encapsulate the metal to prevent chemical reaction while maintaining an even distribution of the metal in solution.U This ensures a homogeneous metal distribution and prevents unwanted reactivity that can lead to the formation of undesired phases. The successful growth of epitaxial ferroelectric films with desired properties by PAD suggests that PAD is a feasible alternative approach to the growth of high quality ferroelectric materials.

Nanophosphor LaF 3 :Ce has been synthesized and incorporated into a matrix to form a nanocomposite scintillator suitable for application to γ-ray detection. Owing to the small nanocrystallite size (sub-10 nm), optical emission from the γ / nanophosphor interaction is only weakly Rayleigh scattered (optical attenuation length exceeds 1 cm for 5-nm crystallites), thus yielding a transparent scintillator. The measured energy resolution is ca. 16% for 137 Cs γ rays, which may be improved by utilizing brighter nanophosphors. Synthesis of the nanophosphor is achieved via a solution-precipitation method that is inexpensive, amenable to routine processing, and readily scalable to large volumes. These results demonstrate nanocomposite scintillator proof-of- principle and provide a framework for further research in this nascent field of scintillator research.

Epitaxial ferromagnetic SrRuO3 thin films with a room-temperature resistivity of 300 microOmega.cm have been successfully grown on LaAlO3(001) substrates at a processing temperature in the range of 550-750 degrees C by a polymer-assisted deposition technique. X-ray diffraction analysis shows good epitaxial quality of SrRuO3 thin films, giving values of the full width at half-maximum (FWHM) of 0.42 degrees from the rocking curve for the (002) reflection and 1.1 degrees from the in-plane phi scan for the (204) reflection. Both the resistivity and the magnetization versus temperature measurements show that the SrRuO3 films are ferromagnetic with a transition temperature of 160 K. The spontaneous magnetization near the ferromagnetic transition follows the scaling law, and the low-temperature magnetization follows the Bloch law.

We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO(2) (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling (SOC). The computed HSE lattice constants and band gaps of AnO(2) are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO(2) is a simple band insulator (f(0)), while PaO(2), UO(2), and NpO(2) are predicted to be Mott insulators. The remainders (PuO(2) and AmO(2)) show considerable O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO(2), NpO(2), and PuO(2) with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations.

Highly aligned carbon nanotube (CNT) ribbons were sandwiched in epitaxial superconducting NbC films by a chemical solution deposition method. The incorporation of aligned long CNTs into NbC film enhances the normal-state conductivity and improves the superconducting properties of the assembly.

Alternative supports for polymer electrolyte membrane fuel cells were synthesized and catalytic activity was explored using electrochemical analysis. High surface area, molybdenum nitride supports were synthesized by rapidly heating a gel of polyethyleneimine bound molybdenum in a tube furnace under a forming gas atmosphere. Subsequent disposition of platinum through an incipient wetness approach lead to dispersed crystallites of platinum on the conductive support. All the ceramic materials were characterized with XRD, SEM, TEM and electrochemical analysis. The supports without platinum are highly stable to acidic aqueous conditions and show no signs of oxygen reduction reactivity (ORR). However, once the 20 wt % platinum is added to the material, ORR activity comparable to XC72 based materials is observed.

Water in supercritical carbon dioxide microemulsions are examined as a new medium for the extraction of metal ions from contaminated surfaces, and are shown to extract >99% of the copper from a spiked filter paper with as little as a two-fold excess of surfactant.

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We have grown epitaxial films of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) on single crystalline LaAlO3 substrates by a cost effective polymer-assisted deposition technique. Film crystallinity, microstructure, resistivity, magnetization, and magnetoresistance (MR) were highly dependent on the annealing temperature in the film processing. High negative MR values of −50% (at 305K) and −88% (at 250K) were observed at magnetic field of 5T, for high temperature annealed LSMO and LCMO films, respectively. These results are comparable to those for films grown by pulsed laser deposition and rf sputtering techniques.