Scientific Publications 2005
2005. "Design, Fabrication and Characterization of a Miniaturized Series-Connected Potentiometric Oxygen Sensor." Sensors and Actuators. B, Chemical 105(2):312–321. Abstract Miniaturization of potentiometric sensors facilitates connecting many sensors in series to amplify the output. Miniaturized series-connected potentiometric sensors were developed on a silicon wafer by microfabrication techniques. The sensors consist of a thin film yttria stabilized zirconia (YSZ) electrolyte and Pt electrodes. The reference oxygen partial pressure is determined by a nickel - nickel oxide (Ni-NiO) mixture. The open circuit voltage (OCV) was tested in air at 300oC and was found to be lower than expected. The output of the net sensor increased almost linearly by connecting 10 sensors in series. Impedance spectroscopy was used to investigate the electrolyte and electrolyte/electrode interfaces using a two electrode configuration.
2005. "18O Effects on the Infrared Spectrum and Skeletal Tunneling of Tropolone." Journal of Chemical Physics 122:224311. Abstract Infrared absorption profiles observed for vibrational transitions of gaseous tropolone often show sharp Q branch peaks, some of them ultra-narrow spikes, indicative of the band origins for vibrational state-specific spectral tunneling doublets. In this work oxygen isotope effects for two CH wagging fundamentals, the COH torsion fundamental, and the skeletal contortion fundamental are reported. They allow considerations to be given: (1) oxygen isotope effects on the vibrational frequencies and state-specific tunneling splittings; (2) the asymmetry offset of the potential energy minima for 16O, 18O-tropolone; and (3) additional details concerning previously proposed high J rotation-contortion fundamental. The new results help to characterize the skeletal contortion fundamental and support the jo9nt participation of skeletal tunneling with H tunneling in the vibrational state-specific tautomerization processes of tropolone in its ground electronic state.
2005. "Temperature-Dependent Infrared Absorption Cross Sections of Methyl Cyanide (Acetonitrile)." Journal of Quantitative Spectroscopy and Radiative Transfer 96(2):271-280. Abstract Pressure broadened (1 atm. N2) absorption cross sections and integrated band intensities have been derived from laboratory spectra of CH3CN, recorded at 276,298, and 323 K, covering 600-6500 cm-1. The spectra were recorded at a resolution of 0.112cm-1 using a commercial Fourier transform spectrometer and a custom flowing sample delivery system. We report integrated absorption cross sections for intervals corresponding to the most prominent bands, compare the results with previously reported values, and discuss error sources, which are estimated as ~7% with systematic error the largest error source.
2005. "Ferromagnetic Cr-doped ZnO for Spin Electronics via Magnetron Sputtering." Journal of Applied Physics 97:10D310. doi:10.1063/1.1847914 Abstract Through nonequilibrium rf magnetron co-sputtering of ZnO and Cr metal on a-plane Al₂O₃ we find ferromagnetic ordering with a room-temperature saturation moment of 1.4 mB per Cr ion at a doping concentration of ,9.5 at. % after UHV postanneal. No secondary phases are detected in the films via x-ray diffraction sXRDd. Increased Cr doping causes disorder within the films resulting in decreased overall, and per Cr, moment. The Curie temperature exceeds 365 K, the maximum temperature reached in our experiment. All films are dielectric with a resistivity higher than 10₆ V cm at room temperature. The lack of carriers indicates that the ferromagnetic mechanism is not carrier mediated.
2005. "Physical and Chemical Properties of Ce₁-xZrxO₂ Nanoparticles and Ce₁-xZrxO₂ (111) Surfaces: Synchrotron-based Studies." Journal of Molecular Catalysis. A, Chemical. 228(1-2):11-19. Abstract In this article, we review a series of studies that use synchrotron-based techniques (high-resolution photoemission, time-resolved x-ray diffraction, and x-ray absorption near-edge spectroscopy) to investigate the physical and chemical properties of Ce₁-xZrxO₂ nanoparticles and Ce₁-xZrxO₂ (111) surfaces (x ≤ 0.5). Ce O₂ and Ce₁-xZrxO₂ particles in sizes between 3 and 7 nm were synthesized using a novel microemulsion method. The results of XANES (O K-edge, Ce and Zr LIII-edges) indicate that the Ce₁-xZrxO₂ nanoparticles and Ce₁-xZrxO₂ (111) surfaces have very similar electronic properties. For these systems, the lattice constant decreased with increasing Zr content, varying from 5.40 Å in CeO₂ to 5.27 Å in Ce₀․₅Zr₀․₅O₂. Within the fluorite structure, the Zr atoms exhibited structural perturbations that led to different types of Zr-O distances and non-equivalent O atoms in the Ce₁-xZrxO₂ compounds. The Ce₁-xZrxO₂ nanoparticles were more reactive towards H₂ and SO₂ than the Ce₁-xZrxO₂ (111) surfaces. The Ce₁-xZrxO₂ (111) surfaces did not reduce in hydrogen at 300 °C. At temperatures above 250 °C, the Ce₁-xZrxO₂ nanoparticles reacted with H₂ and water evolved into gas phase. XANES showed the generation of Ce³⁺cations without reduction of Zr⁴⁺. There was an expansion in the unit cell of the reduced nanoparticles probably as a consequence of a partial Ce⁴⁺→ Ce³⁺ transformation and the sorption of hydrogen into the bulk of the material. S K-edge XANES spectra pointed to SO₄ as the main product of the adsorption of SO₂ on the Ce₁-xZrxO₂ nanoparticles and Ce₁-xZrxO₂ (111) surfaces. Full dissociation of SO₂ was seen on the nanoparticles but not on the Ce₁-xZrxO₂ (111) surfaces. The metal cations at corner and edge sites of the Ce₁-xZrxO₂ nanoparticles probably play a very important role in interactions with the H₂ and SO₂ molecules.
2005. "1H, 13C, and 15N resonance assignments for the protein coded by gene locus BB0938 of Bordetella bronchiseptica." Journal of Biomolecular NMR 33(3):197. Abstract The product of gene locus BB0938 from Bordetella bronchiseptica (Swiss-Prot ID: Q7WNU7_BORBR; NESG target ID: BoR11; Wunderlich et al., 2004; Pfam ID: PF03476) is a 128-residue protein of unknown function. This broadly conserved protein family is found in eubacteria and eukaryotes. Using triple resonance NMR techniques, we have determined 98% of backbone and 94% of side chain 1H, 13C, and 15N resonance assignments. The chemical shift and 3J(HN–Ha) scalar coupling data reveal a b topology with a seven-residue helical insert, ββββββββ∞β. BMRB deposit with accession number 6693. Reference: Wunderlich et al. (2004) Proteins, 56, 181–187.
2005. "Effects of Compositional Defects on Small Polaron Hopping in Micas." Journal of Chemical Physics 122(24):244709 (9 pages). Abstract Hartree-Fock calculations and electron transfer (ET) theory were used to model the effects of compositional defects on ET in the brucite-like octahedral sheet of mica. ET was modeled as a FeII/III valence interchange reaction across shared octahedral edges of the M2-M2 iron sublattice. The model entails the hopping of localized electrons and small polaron behavior. Hartree-Fock calculations indicate that substitution of F for structural OH bridges increases the reorganization energy l, decreases the electronic coupling matrix element VAB, and thereby substantially decreases the hopping rate. The l increase arises from modification of the metal‑ligand bond force constants, and the VAB decrease arises from reduction of superexchange interaction through anion bridges. Deprotonation of an OH bridge, consistent with a possible mechanism of maintaining charge neutrality during net oxidation, yields a net increase in the ET rate. Although substitution of Al or Mg for Fe in M1 sites distorts the structure of adjacent Fe-occupied M2 sites, the distortion has little net impact on ET rates through these M2 sites. Hence the main effect of Al or Mg substitution for Fe, should it occur in the M2 sublattice, is to block ET pathways. Collectively, these findings pave the way for larger-scale oxidation/reduction models to be constructed for realistic, compositionally diverse micas
2005. "Molecular Dynamics Simulation of the Titration of Polyoxocations in Aqueous Solution." Geochimica et Cosmochimica Acta 69(18):4397-4410. doi:10.1016/j.gca.2005.05.007 Abstract The aqueous complex ion Al30O8(OH)56(H2O)26 18+(Al30) has a variety of bridging and terminal amphoteric surface functional groups which deprotonate over a pH range of 4–7. Their relative degree of protonation is calculated here from a series of molecular dynamics simulations in what appear to be the first molecular dynamics simulations of an acidometric titration. In these simulations, a model M30O8(OH)56(H2O)26 18+ ion is embedded in aqueous solution and titrated with hydroxide ions in the presence of a charge-compensating background of perchlorate ions. Comparison with titration of a model M13O4(OH)24(H2O)12 7+ reveals that the M30 ion is more acidic than the M13 ion due to the presence of acidic nH2O functional groups. The higher acidities of the functional groups on the M30 ion appear to result from enhanced hydration. Metal–oxygen bond lengths are calculated for the ion in solution, an isolated ion in the gas phase, and in its crystalline hydrate sulfate salt. Gas-phase and crystalline bond lengths do not correlate well with those calculated in solution. The acidities do not relate in any simple way to the number of metals coordinating the surface functional group or the M-O bond length. Moreover, the calculated acidity in solution does not correlate with proton affinities calculated for the isolated ion in the absence of solvent. It is concluded that the search for simple indicators of structure–reactivity relationships at the level of individual reactive sites faces major limitations, unless specific information on the hydration states of the functional groups is available.
2005. "The Influence of Edge Sites on the Development of Surface Charge on Goethite Nanoparticles: A Molecular Dynamics Investigation." Geochimica et Cosmochimica Acta 69(6):1405-1411. Abstract Large-scale molecular simulation of proton accumulations were carried out on (i) (110) and (021) slabs immersed in aqueous solution and (ii) a series of model goethite nanoparticles of dimension 2-8 nm with systematically varying acicularity and (110)/(021) surface areas. In the slab systems, the (021) surface exhibits 15 percent more proton charge/unit area than the (110) surface. In the particulate systems, the acicular particles, having the highest (110)/(021) ratio accumulate the most charge, opposite to the trend expected from the slab simulations, indicating that, at length scales on the order of 10 nm, the slab results are not a good indicator of the overall charging behavior of the particles. The primary reason for the discrepancy between the particulate systems and slab systems is the preferential accumulation of protons at acute (110)-(110) intersections. Charge accumulates preferentially in this region because excess proton charge at an asperity is more effectively solvated than at a flat interface.