Kim F. Ferris

Infrared transparent spinel films with p-type conductivity

Spinel oxide films containing at least two transition metal cations were found to exhibit p-type conductivity with high optical transparency from the visible to wavelengths near 15 μm. Resistivities as low as 0.003 Ω cm were measured on 100-nm thick rf sputter deposited films that contained nickel and cobalt. Optical spectra, Raman scattering and XPS measurements indicated the valency of nickel localized on octahedral sites within the spinel lattice determines these properties. A resistivity minimum was found at the composition NiCo 2 O 4 deposited from aqueous or alcoholic solutions followed by subsequent annealing at 400°C in air. Solution deposited films richer in nickel than this stoichiometry, were always found to phase separate into nickel oxide and a spinel phase with concomitant loss in conductivity. However, the phase stability region could be extended to higher nickel contents when rf-sputter deposition techniques were used. Sputter deposited spinel films having a cobalt to nickel ratio <2 were found to exhibit the highest conductivity. Results suggest that the phase stability region for these materials can be extended through appropriate choice of deposition conditions. A possible mechanism that promotes high conductivity in this system is thought to be charge transfer between the resident di- and trivalent cations that may be assisted by the magnetic nature of the oxide film.

Synthesis and Characterization of Transparent Conducting Oxide Cobalt-Nickel Spinel Films

Cobalt–nickel oxide films of nominal 100 nm thickness, and resistivity on the order of 10−2 Ω cm have been deposited by spin casting from both aqueous and organic precursor solutions followed by annealing at 450 °C in air. Films deposited on sapphire substrates exhibit a refractive index of about 1.7 and are relatively transparent in the wavelength region from 0.6 to 10.0 μm. They are also magnetic. The electrical and spectroscopic properties of the oxides have been studied as a function of the x=Co/(Co+Ni) ratio. An increase in film resistivity was found upon substitution of other cations (Zn2+, Al3+,…) for Ni in the spinel structure. However, some improvement in the mechanical properties of the films resulted. A combination of x-ray diffraction, x-ray photoelectron spectroscopy, UV/Vis, and Raman spectroscopy indicated that NiCo2O4 is the primary conducting component and that the conductivity reaches a maximum at this stoichiometry. When x 0....

Interactions of HCOOH with stoichiometric and defective TiO2(110) surfaces

Abstract Interactions of HCOOH with stoichiometric (nearly defect-free) and defective TiO2(110) surfaces have been studied experimentally using X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and theoretically using electronic structure calculations. The HCOOH saturation coverages were 0.58 ML, 0.77 ML, and 0.92 ML (1 ML ≈ 5.2 × 1014 cm−2) for nearly defect-free surfaces, for electron-beam exposed surfaces, and for Ar+ ion bombarded surfaces, respectively. The excess formic acid adsorption quantitatively corresponds to the number of newly exposed sites created by electron-beam exposure. Electronic structure calculations show a strong adsorptive interaction for formate on cation sites on both stoichiometric and defective TiO2 surfaces, consistent with the experimental observations. In spite of adsorption at defect sites, little or no defect healing (defect healing means a reduction in defect signal observed by the photoemission measurements) was observed for either electron-beam exposed or Ar+ bombarded surfaces by HCOOH exposure up to 104L at room temperature. However, some healing will occur if extra energy provided by electrons is introduced to breakdown formate species. In contrast to water adsorption, electronic structure calculations on defective TiO2 have found that formate is located in an asymmetric position with respect to the Ti3+ sites with a potential additional interaction with the Ti4+ site.

Chemisorption geometry of formate on Ti2(110) by photoelectron diffraction

Abstract We have combined photoelectron diffraction in both scanned-angle and scanned-energy modes with Hartree-Fock calculations to investigate the interface structure of HCOO− on TiO2(110). Formate anions bind through the oxygens to Ti cation rows along [001] with a 2× periodicity and an OCO bond angle of 126 ± 4°. Each anion binds to two Ti cations with an adsorbate-substrate bond distance of 2.0 ± 0.1 A.

The Structure and Orientation of the C-Terminus of LRAP

Amelogenin is the predominant protein found during enamel development and is thought to be the biomineralization protein controlling the unique elongated hydroxyapatite crystals that constitute enamel. The secondary structure of biomineralization proteins is thought to be important in the interaction with hydroxyapatite. Unfortunately, very little data are available on the structure or the orientation of amelogenin, either in solution or bound to hydroxyapatite. The C-terminus contains the majority of the charged residues and is predicted to interact with hydroxyapatite; thus, we used solid-state NMR dipolar recoupling techniques to investigate the structure and orientation of the C-terminus of LRAP, a naturally occurring splice variant of full-length amelogenin. Using (13)C{(15)N} Rotational Echo DOuble Resonance (REDOR), the structure of the C-terminus was found to be largely random coil, both on the surface of hydroxyapatite as well as lyophilized from solution. The orientation of the C-terminal region with respect to hydroxyapatite was investigated for two alanine residues (Ala(46) and Ala(49)) using (13)C{(31)P} REDOR and one lysine residue (Lys(52)) using (15)N{(31)P} REDOR. The residues examined were found to be 7.0, 5.7, and 5.8 A from the surface of hydroxyapatite for Ala(46), Ala(49), and Lys(52), respectively. This provides direct evidence that the charged C-terminus is interacting closely with hydroxyapatite, positioning the acidic amino acids to aid in controlling crystal growth. However, solid-state NMR dynamics measurements also revealed significant mobility in the C-terminal region of the protein, in both the side chains and the backbone, suggesting that this region alone is not responsible for binding.

Lagrangian particle model for multiphase flows

Abstract A Lagrangian particle model for multiphase multicomponent fluid flow, based on smoothed particle hydrodynamics (SPH), was developed and used to simulate the flow of an emulsion consisting of bubbles of a non-wetting liquid surrounded by a wetting liquid. In SPH simulations, fluids are represented by sets of particles that are used as discretization points to solve the Navier–Stokes fluid dynamics equations. In the multiphase multicomponent SPH model, a modified van der Waals equation of state is used to close the system of flow equations. The combination of the momentum conservation equation with the van der Waals equation of state results in a particle equation of motion in which the total force acting on each particle consists of many-body repulsive and viscous forces, two-body (particle–particle) attractive forces, and body forces such as gravitational forces. Similar to molecular dynamics, for a given fluid component the combination of repulsive and attractive forces causes phase separation. The surface tension at liquid–liquid interfaces is imposed through component dependent attractive forces. The wetting behavior of the fluids is controlled by phase dependent attractive interactions between the fluid particles and stationary particles that represent the solid phase. The dynamics of fluids away from the interface is governed by purely hydrodynamic forces. Comparison with analytical solutions for static conditions and relatively simple flows demonstrates the accuracy of the SPH model.

Interactions of methanol with stoichiometric and defective TiO2(110) and (100) surfaces

Interactions of CH3OH with stoichiometric (nearly defect-free) and defective TiO2(110) and (100) surfaces have been studied using x-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy. The CH3OH saturation coverage was increased by increasing the number of defects created by electron-beam exposure or Ar+ ion bombardment. A small percentage of any defects produced were healed upon the saturation exposure (defect healing means a reduction in defect signal observed by the photoemission measurements). The structural influence on the adsorption and surface defect reactivity was found to be less significant for CH3OH than for H2O. The CH3OH coverages at a given exposure and defect reactivity were comparable for both the (100) and (110) surfaces.

Interaction of HCOOH with stoichiometric and reduced SrTiO3(100) surfaces

Interaction of formic acid with stoichiometric (TiO2-terminated) and reduced SrTiO3(100) surfaces has been investigated using temperature programmed desorption (TPD), and x-ray photoelectron spectroscopy (XPS). Formic acid was dissociated to form formate and a surface proton below 250 K on both stoichiometric and reduced SrTiO3(100) surfaces. Formate was decomposed primarily through dehydration to produce CO and H2O, instead of through dehydrogenation to produce CO2 and H2, on both surfaces. Formaldehyde produced from decomposition of formate was also observed on both surfaces. On stoichiometric surfaces, formaldehyde was produced through bimolecular coupling of two formates on low-coordination Ti cation sites. However, on the reduced surface, formaldehyde formation involves the reduction of surface formates through the oxidation of reduced Ti cations. XPS results show that surface defects on reduced SrTiO3(100) surfaces were reoxidized significantly upon exposure to 30 L HCOOH at 300 K, in contrast to de...

Dimension reduction method for ODE fluid models

We develop a new dimension reduction method for large size systems of ordinary differential equations (ODEs) obtained from a discretization of partial differential equations of viscous single and multiphase fluid flow. The method is also applicable to other large-size classical particle systems with negligibly small variations of particle concentration. We propose a new computational closure for mesoscale balance equations based on numerical iterative deconvolution. To illustrate the computational advantages of the proposed reduction method, we use it to solve a system of smoothed particle hydrodynamic ODEs describing single-phase and two-phase layered Poiseuille flows driven by uniform and periodic (in space) body forces. For the single-phase Poiseuille flow driven by the uniform force, the coarse solution was obtained with the zero-order deconvolution. For the single-phase flow driven by the periodic body force and for the two-phase flows, the higher-order (the first- and second-order) deconvolutions were necessary to obtain a sufficiently accurate solution.

A theoretical study of the aromaticity of hypervalent sulfur heterocycles

Abstract In this paper we report on the heteroaromaticity of 1,2,5-thiadiazole-1,1-dioxide (I) and its isomers 1,2,4-thiadiazole-1,1-dioxide (II), 1,3,4-thiadiazole-1,1-dioxide (III) and 1,2,3-thiadiazole-1,1-dioxide (IV) by calculating their electronic structures and estimating their aromatic character in terms of our previously developed criteria: N , MDQ, ΔE πL (NLMO) and ΔE πL (Boys) as well as comparing their total energies. (I) is shown to be the most aromatic isomer in good agreement with chemical reasoning and experimental evidence. The 1,1-dioxides of thiazole and isothiazole were predicted to be intermediate in aromaticity between thiophene-1,1-dioxide and the isomers, (I)–(IV). N value measures indicate that thiophene-1,1-dioxide would retain a small measure of aromatic character relative to thiophene ( N (thiophene) = 0.868, N (thiophene-1,1-dioxide) = 0.389).