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Papers by Thomas Mion

Research paper thumbnail of Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa2Cu3O7-x/La0.7Ca0.3MnO3 heterostructures

Nature communications, 2016

Recent developments in high-temperature superconductivity highlight a generic tendency of the cup... more Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa2Cu3O7-x (YBCO) thin films grown epitaxially on La0.7Ca0.3MnO3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, with long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO2 plane. Our finding sheds light on the nature of charge...

Research paper thumbnail of Photoresponse: Highly Sensitive Detection of Polarized Light Using Anisotropic 2D ReS2(Adv. Funct. Mater. 8/2016)

Advanced Functional Materials, 2016

Research paper thumbnail of Highly Sensitive Detection of Polarized Light Using Anisotropic 2D ReS2

Advanced Functional Materials, 2016

Research paper thumbnail of X-Ray diffraction analysis of B-site dipole-like substitutions in Barium Titanate

An investigation of phase transitions in dipole like B-site substituted perovskites is reported. ... more An investigation of phase transitions in dipole like B-site substituted perovskites is reported. Several doped Barium Titanite materials were examined over a temperature range of 173 k to1200 K. Their structural changes were examined by X-Ray diffraction as a function of temperature. Several phase transitions of the doped Barium Titanate have noted and characterized. This material is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U.S. Army Research Office under contract/grant number W911NF-08-1-0353.

Research paper thumbnail of Radiation Effects on Polypropylene Carbon Nanofibers Composites: Spectroscopic Investigations

Dispersion of carbon nanostructures within polymeric matrices affects their physical and chemical... more Dispersion of carbon nanostructures within polymeric matrices affects their physical and chemical properties (increased Young modulus, improved thermal stability, faster crystallization rates, higher equilibrium degree of crystallinity, modified glass, melting, and crystallization temperatures, enhanced thermal and electrical conductivity). Nevertheless, little is known about the radiation stability of such nanocomposites. The research is focused on spectroscopic investigations of radiation-induced modifications in isotactic polypropylene (iPP)-vapor grown nanofiber (VGCNF) composites. VGCNF were dispersed within iPP by extrusion at 180^oC. Composites containing various amounts of VGCNFs ranging from 0 to 20 % wt. were prepared and subjected to gamma irradiation, at room temperature, at various integral doses (10 MGy, 20 MGy, and 30 MGy). Raman spectroscopy, ATR, and WAXS were used to assess the radiation-induced modifications in these nanocomposites. Acknowledgements: This research...

Research paper thumbnail of Thermal Features and Glass Transition in Polystyrene-Nanodiamond Composites

Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta ... more Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta solvent (cyclohexane) followed by the addition of diamond nanoparticles from Aldrich (with a particle size ranging between 3 and 8 nm) and subsequent sonication for about 100 minutes by using a Hielscher high power (1 kW) sonicator. The homogeneous solution was poured onto microscope slides and the solvent has been removed by heating in an oven at 125 ^oC for about 3 hours. Composites containing various amounts (from 0 % to 25 % nanodiamonds within polystyrene) have been investigated. The physical properties of the as obtained nanocomposites were investigated by DSC, TGA, Raman, and WAXS. Glass transition temperature was shifted to higher temperatures and the thermal stability was enhanced by the addition of nanodiamonds. A phenomenological model for the observed changes is proposed (within the free volume approximation) and discussed in detail. Acknowledgements: This research was suppor...

Research paper thumbnail of Glass Transition in Polystyrene -- TiO2 Nanocomposites

Polystyrene is a typical amorphous polymer with almost no crystallinity degree. The addition of v... more Polystyrene is a typical amorphous polymer with almost no crystallinity degree. The addition of very small particles to polystyrene is expected to change significantly the mechanical and thermal features of this polymer due to the competition between the macromolecular chains and the nanofiller for the same cluster of free volumes. The shift of the glass transition temperature and of the associated mechanical properties is expected to increase as the particle size is reduced. Anatase nanoparticles from Aldrich, with an average diameter of 15 nm have been dispersed within PS. To achieve a homogeneous distribution of nanoparticle the polymer was dissolved within a theta solvent (cyclohexene), the solution has been sonicated for about 100 minutes, and the solvent has been evaporated by heating at 125 ^oC for few hours. Thermal characteristics of composites containing various fractions of anatase were measured by TGA, DSC, and DMA. The research was focused on the shift in the glass tran...

Research paper thumbnail of Radiation-Induced Changes of Thermal Properties of Polypropylene Carbon Nanofibers Composites

Dispersion of nanostructures within polymeric matrices affects their thermal properties and stabi... more Dispersion of nanostructures within polymeric matrices affects their thermal properties and stability. Shifts, convolutions, and splitting of the main transitions (glass transition, melting transition, and crystallization temperature) were reported. In most cases, the thermal decomposition of the polymeric matrix is delayed or shifted towards higher temperatures. Nevertheless, little is known about the effect of ionizing radiation on the thermal stability and phase transitions in such nanocomposites. Spectroscopic investigations of radiation-induced modifications in isotactic polypropylene (iPP)-vapor grown nanofiber composites (VGCNF) are reported. VGCNFs were dispersed within iPP by extrusion at 180^oC. Composites containing various amounts of VGCNFs ranging from 0 to 20 % were prepared and subjected to gamma irradiation, at room temperature, at various integral doses (10 MGy, 20 MGy, and 30 MGy). Thermal characteristics were of iPP-VGCNF composites were measured by TGA, DSC, and ...

Research paper thumbnail of Radiation Effects on Polypropylene Carbon Nanofibers

Dispersion of carbon nanostructures within polymeric matrices affects most physical and chemical ... more Dispersion of carbon nanostructures within polymeric matrices affects most physical and chemical properties of the polymeric matrix (increased Young modulus, improved thermal stability, faster crystallization rates, higher equilibrium degree of crystallinity, modified glass, melting, and crystallization temperatures, enhanced thermal and electrical conductivity). Such changes have been reported and explained by thorough spectroscopic investigations. Nevertheless, little is known about the radiation

Research paper thumbnail of Ensemble Site Requirements for Oxidative Adsorption of Methanol and Ethanol on Pt Membrane Electrode Assemblies

ACS Catalysis, 2012

ABSTRACT The ensemble site requirements for the oxidative adsorption of methanol and ethanol on p... more ABSTRACT The ensemble site requirements for the oxidative adsorption of methanol and ethanol on platinum based membrane electrode assemblies in operating liquid feed fuel cells were measured by CO stripping voltammetry. At 30 degrees C and 0.2 V vs reference hydrogen electrode (RHE), the COads, coverage from directly dosed CO (COCO), methanol (COMeOH), and ethanol (COEtOH) are 94%, 49%, and 39%, respectively. At 50 degrees C the COMeOH and COEtOH COEtOH approach equality. The ratio of COEtOH/COMeOH was simulated with assumed ensemble site requirements of 3 and 2 for ethanol and methanol respectively. Experimental and simulated ratios of 0.79 and 0.78 suggest that high surface area fuel cell Pt catalysts at 30 degrees C have adsorption properties similar to that of a Pt (100) surface. Potential dependent infrared spectroscopy of COMeOH and COEtOH from flash evaporated aqueous alcohols delivered to a 50 degrees C fuel cell show lower COEtOH relative to COMeOH with Stark tuning rates below 10 cm(-1)/V.

Research paper thumbnail of Fermi Arcs vs. Fermi Pockets in Electron-doped Perovskite Iridates

Scientific reports, 2015

We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite irid... more We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)3Ir2O7. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected "Fermi arcs", reminiscent of those reported recently in surface electron-doped Sr2IrO4. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

Research paper thumbnail of Dielectric and X-ray Diffraction Analysis of Ba(Ga,Ta) 0.05 Ti 0.90 O 3

Ferroelectrics, 2014

Ba (Ga,Ta) 0.05 Ti 0.90 O 3 , a B-site dipole-like substituted material is investigated for struc... more Ba (Ga,Ta) 0.05 Ti 0.90 O 3 , a B-site dipole-like substituted material is investigated for structural phase transitions over the temperature range 30 to 900 • C using x-ray diffraction. Rietveld refinement of the data suggests the material to be Pm3m (cubic) from 200 to 900 • C, P4/mmm (tetragonal) from 30 to 200 • C with phases similar to those of BaTiO 3 [12]. Average grain size determined using scanning electron microscopy is 650 nm. Measurements of dielectric properties from −50 to 120 • C and over a frequency range of 10 Hz to 2 MHz show a relatively flat dielectric constant that is electric-field tunable indicating that Ba(Ga,Ta) 0.05 Ti 0.90 O 3 is a reasonable candidate for frequency agile components.

Research paper thumbnail of Polyvinylchloride-Single-Walled Carbon Nanotube Composites: Thermal and Spectroscopic Properties

Journal of Nanomaterials, 2012

Nanocomposites of single-walled carbon nanotubes dispersed within polyvinylchloride have been obt... more Nanocomposites of single-walled carbon nanotubes dispersed within polyvinylchloride have been obtained by using the solution path. High-power sonication was utilized to achieve a good dispersion of carbon nanotubes. Thermogravimetric analysis revealed that during the synthesis, processing, or thermal analysis of these nanocomposites the released chlorine is functionalizing the single-walled carbon nanotubes. The loading of polyvinylchloride by single-walled carbon nanotubes increases the glass transition temperature of the polymeric matrix, demonstrating the interactions between macromolecular chains and filler. Wide Angle X-Ray Scattering data suggested a drop of the crystallite size and of the degree of crystallinity as the concentration of single-walled carbon nanotubes is increased. The in situ chlorination and amorphization of nanotube during the synthesis (sonication step) is confirmed by Raman spectroscopy.

Research paper thumbnail of Polyoctenamer - Single Walled Carbon Nanotube Composites: Spectroscopic Investigations

MRS Proceedings, 2009

ABSTRACT Composites of single walled carbon nanotube dispersed within polymeric matrices have bee... more ABSTRACT Composites of single walled carbon nanotube dispersed within polymeric matrices have been investigated by spectroscopic techniques (Raman and Wide Angle X-Ray Spectroscopy). Raman investigations included an in depth analysis of the radial breathing mode (for single wall carbon nanotubes) and a brief analysis of the lines originating from the polymeric matrix. Raman spectra were successfully simulated by computer assuming that the as recorded spectrum is a convolution of lines whose line shape is well described by a modified Breit-Wigner-Fano equation. The dependence of the position of the lines belonging to the radial breathing mode on the concentration of single walled carbon nanotube has been investigated, with emphasis on information pertinent to the stress transfer from the macromolecular matrix to the filler and to the coating of single walled carbon nanotube by polymeric chains. Complementary Wide Angle X-Ray Spectroscopy measurements provided information about the effect of the loading with single walled carbon nanotube on the crystal structure of the polymeric matrix. The research aims to a better understanding of the interactions between polymeric matrices and nanofillers.

Research paper thumbnail of A Density Functional Theory Study on Carbon Monoxide Adsorption on Platinum–Osmium and Platinum–Ruthenium–Osmium Alloys

The Journal of Physical Chemistry C, 2012

Research paper thumbnail of Carbon Monoxide Adsorption Coverage Study on Platinum and Ruthenium Surfaces

The Journal of Physical Chemistry C, 2014

ABSTRACT Periodic density functional theory calculations elucidate carbon monoxide coverage effec... more ABSTRACT Periodic density functional theory calculations elucidate carbon monoxide coverage effects on platinum and ruthenium surfaces. As expected the CO stretching frequencies increase with coverage. Unexpectedly, overlap population calculations show that increased stretching frequencies may not always correspond to stronger bonds. A theoretical framework is established based on a modified π-attraction σ-repulsion scheme. This phenomenological model directly relates the internal adsorbate bond strength to the net change of the carbon 2s and 2pxy contributions to the π- and σ-components, respectively. The variation of the metal–surface bond is examined by using the charges, polarizations, and electron densities of the adsorbate CO orbitals. For the systems studied here, the traditional frontier orbital model of the 5σ-donation/2π*-back-donation with the metal substrate bands is not always sufficient to explain the relative C–O and C–Metal bonds strengths.

Research paper thumbnail of XAFS Debye-Waller factors for deformed hemes and metal substituted hemes

Journal of Physics: Conference Series, 2009

We present an efficient and accurate method for calculating XAFS Debye-Waller factors for deforme... more We present an efficient and accurate method for calculating XAFS Debye-Waller factors for deformed active sites of hemoproteins and metal substituted hemes. Based on the Normal Coordinate Structural Decomposition scheme, the deformation of the porphyrin macrocycle is expressed as a linear combination of the normal modes of the planar species. In our approach, we identify the modes that contribute most to the deformation. Small metal-porphyrin structures which match the macrocycle structural deformation of the deformed hemoprotein site are used to calculate the Debye-Waller parameters at sample's temperature. The Debye-Waller factors are directly obtained by calculating the normal mode spectrum of the corresponding metalporphyrin structure using Density Functional Theory. Our method is tested on Ni-tetraadamantyl porphyrin and cytochrome c structures with more than 500 available scattering paths.

Research paper thumbnail of Single and multiple scattering XAFS Debye-Waller factors for crystalline materials using periodic Density Functional Theory

Journal of Physics: Conference Series, 2009

ABSTRACT We present an accurate and efficient technique for calculating thermal X-ray absorption ... more ABSTRACT We present an accurate and efficient technique for calculating thermal X-ray absorption fine structure (XAFS) Debye-Waller factors (DWFs) applicable to crystalline materials. Using Density Functional Theory on a 3×3×3 supercell pattern of MnO structure, under the nonlocal hybrid B3LYP functional paired with Gaussian local basis sets, we obtain the normal mode eigenfrequencies and eigenvectors; these parameters are in turn used to calculate single and multiple scattering XAFS DWFs. The DWFs obtained via this technique are temperature dependent expressions and can be used to substantially reduce the number of fitting parameters, when experimental spectra are fitted with a hypothetical structure. The size of the supercell size limits the R-space range that these parameters could be used. Therefore corresponding DWFs for paths outside of this range are calculated using the correlated Debye model. Our method is compared with prior cluster calculations and with corresponding values obtained from fitting experimental XAFS spectra on manganosite with simulated spectra.

Research paper thumbnail of Electrical and Structural Properties of Ba(Y 3+ , Sb 5+ ) 0.05 Ti 0.90 O 3

Integrated Ferroelectrics, 2013

The microwave ceramic Ba(Y,Sb) 0.05 Ti 0.90 O 3, based upon random B-site dipole-like substitutio... more The microwave ceramic Ba(Y,Sb) 0.05 Ti 0.90 O 3, based upon random B-site dipole-like substitutions is structurally and electrically characterized over the temperature range −55 • C to 120 • C. X-ray diffraction information coupled together with scanning electron microscopy reveals that the material is single phase and has submicron grain sizes. Results show the tetragonal phase ranges from −30 • C to 200 • C, which is a broader temperature range than that of the parent material BaTiO 3 , 0 • C to 120 • C. The material Ba(Y,Sb) 0.05 Ti 0.90 O 3 also has a diffuse relative high dielectric constant of about 10,000 that peaks at the orthorhombic-tetragonal structural phase transition around −30 • C.

Research paper thumbnail of Thermal Features and Glass Transition in Polystyrene-Nanodiamond Composites

Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta ... more Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta solvent (cyclohexane) followed by the addition of diamond nanoparticles from Aldrich (with a particle size ranging between 3 and 8 nm) and subsequent sonication for about 100 minutes by using a Hielscher high power (1 kW) sonicator. The homogeneous solution was poured onto microscope slides and the solvent has been removed by heating in an oven at 125 ^oC for about 3 hours. Composites containing various amounts (from 0 % to 25 % nanodiamonds within polystyrene) have been investigated. The physical properties of the as obtained nanocomposites were investigated by DSC, TGA, Raman, and WAXS. Glass transition temperature was shifted to higher temperatures and the thermal stability was enhanced by the addition of nanodiamonds. A phenomenological model for the observed changes is proposed (within the free volume approximation) and discussed in detail. Acknowledgements: This research was supported by US Army Research Laboratory (W911NF-08-1-0353) and LSAMP -UTPA.

Research paper thumbnail of Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa2Cu3O7-x/La0.7Ca0.3MnO3 heterostructures

Nature communications, 2016

Recent developments in high-temperature superconductivity highlight a generic tendency of the cup... more Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa2Cu3O7-x (YBCO) thin films grown epitaxially on La0.7Ca0.3MnO3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, with long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO2 plane. Our finding sheds light on the nature of charge...

Research paper thumbnail of Photoresponse: Highly Sensitive Detection of Polarized Light Using Anisotropic 2D ReS2(Adv. Funct. Mater. 8/2016)

Advanced Functional Materials, 2016

Research paper thumbnail of Highly Sensitive Detection of Polarized Light Using Anisotropic 2D ReS2

Advanced Functional Materials, 2016

Research paper thumbnail of X-Ray diffraction analysis of B-site dipole-like substitutions in Barium Titanate

An investigation of phase transitions in dipole like B-site substituted perovskites is reported. ... more An investigation of phase transitions in dipole like B-site substituted perovskites is reported. Several doped Barium Titanite materials were examined over a temperature range of 173 k to1200 K. Their structural changes were examined by X-Ray diffraction as a function of temperature. Several phase transitions of the doped Barium Titanate have noted and characterized. This material is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U.S. Army Research Office under contract/grant number W911NF-08-1-0353.

Research paper thumbnail of Radiation Effects on Polypropylene Carbon Nanofibers Composites: Spectroscopic Investigations

Dispersion of carbon nanostructures within polymeric matrices affects their physical and chemical... more Dispersion of carbon nanostructures within polymeric matrices affects their physical and chemical properties (increased Young modulus, improved thermal stability, faster crystallization rates, higher equilibrium degree of crystallinity, modified glass, melting, and crystallization temperatures, enhanced thermal and electrical conductivity). Nevertheless, little is known about the radiation stability of such nanocomposites. The research is focused on spectroscopic investigations of radiation-induced modifications in isotactic polypropylene (iPP)-vapor grown nanofiber (VGCNF) composites. VGCNF were dispersed within iPP by extrusion at 180^oC. Composites containing various amounts of VGCNFs ranging from 0 to 20 % wt. were prepared and subjected to gamma irradiation, at room temperature, at various integral doses (10 MGy, 20 MGy, and 30 MGy). Raman spectroscopy, ATR, and WAXS were used to assess the radiation-induced modifications in these nanocomposites. Acknowledgements: This research...

Research paper thumbnail of Thermal Features and Glass Transition in Polystyrene-Nanodiamond Composites

Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta ... more Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta solvent (cyclohexane) followed by the addition of diamond nanoparticles from Aldrich (with a particle size ranging between 3 and 8 nm) and subsequent sonication for about 100 minutes by using a Hielscher high power (1 kW) sonicator. The homogeneous solution was poured onto microscope slides and the solvent has been removed by heating in an oven at 125 ^oC for about 3 hours. Composites containing various amounts (from 0 % to 25 % nanodiamonds within polystyrene) have been investigated. The physical properties of the as obtained nanocomposites were investigated by DSC, TGA, Raman, and WAXS. Glass transition temperature was shifted to higher temperatures and the thermal stability was enhanced by the addition of nanodiamonds. A phenomenological model for the observed changes is proposed (within the free volume approximation) and discussed in detail. Acknowledgements: This research was suppor...

Research paper thumbnail of Glass Transition in Polystyrene -- TiO2 Nanocomposites

Polystyrene is a typical amorphous polymer with almost no crystallinity degree. The addition of v... more Polystyrene is a typical amorphous polymer with almost no crystallinity degree. The addition of very small particles to polystyrene is expected to change significantly the mechanical and thermal features of this polymer due to the competition between the macromolecular chains and the nanofiller for the same cluster of free volumes. The shift of the glass transition temperature and of the associated mechanical properties is expected to increase as the particle size is reduced. Anatase nanoparticles from Aldrich, with an average diameter of 15 nm have been dispersed within PS. To achieve a homogeneous distribution of nanoparticle the polymer was dissolved within a theta solvent (cyclohexene), the solution has been sonicated for about 100 minutes, and the solvent has been evaporated by heating at 125 ^oC for few hours. Thermal characteristics of composites containing various fractions of anatase were measured by TGA, DSC, and DMA. The research was focused on the shift in the glass tran...

Research paper thumbnail of Radiation-Induced Changes of Thermal Properties of Polypropylene Carbon Nanofibers Composites

Dispersion of nanostructures within polymeric matrices affects their thermal properties and stabi... more Dispersion of nanostructures within polymeric matrices affects their thermal properties and stability. Shifts, convolutions, and splitting of the main transitions (glass transition, melting transition, and crystallization temperature) were reported. In most cases, the thermal decomposition of the polymeric matrix is delayed or shifted towards higher temperatures. Nevertheless, little is known about the effect of ionizing radiation on the thermal stability and phase transitions in such nanocomposites. Spectroscopic investigations of radiation-induced modifications in isotactic polypropylene (iPP)-vapor grown nanofiber composites (VGCNF) are reported. VGCNFs were dispersed within iPP by extrusion at 180^oC. Composites containing various amounts of VGCNFs ranging from 0 to 20 % were prepared and subjected to gamma irradiation, at room temperature, at various integral doses (10 MGy, 20 MGy, and 30 MGy). Thermal characteristics were of iPP-VGCNF composites were measured by TGA, DSC, and ...

Research paper thumbnail of Radiation Effects on Polypropylene Carbon Nanofibers

Dispersion of carbon nanostructures within polymeric matrices affects most physical and chemical ... more Dispersion of carbon nanostructures within polymeric matrices affects most physical and chemical properties of the polymeric matrix (increased Young modulus, improved thermal stability, faster crystallization rates, higher equilibrium degree of crystallinity, modified glass, melting, and crystallization temperatures, enhanced thermal and electrical conductivity). Such changes have been reported and explained by thorough spectroscopic investigations. Nevertheless, little is known about the radiation

Research paper thumbnail of Ensemble Site Requirements for Oxidative Adsorption of Methanol and Ethanol on Pt Membrane Electrode Assemblies

ACS Catalysis, 2012

ABSTRACT The ensemble site requirements for the oxidative adsorption of methanol and ethanol on p... more ABSTRACT The ensemble site requirements for the oxidative adsorption of methanol and ethanol on platinum based membrane electrode assemblies in operating liquid feed fuel cells were measured by CO stripping voltammetry. At 30 degrees C and 0.2 V vs reference hydrogen electrode (RHE), the COads, coverage from directly dosed CO (COCO), methanol (COMeOH), and ethanol (COEtOH) are 94%, 49%, and 39%, respectively. At 50 degrees C the COMeOH and COEtOH COEtOH approach equality. The ratio of COEtOH/COMeOH was simulated with assumed ensemble site requirements of 3 and 2 for ethanol and methanol respectively. Experimental and simulated ratios of 0.79 and 0.78 suggest that high surface area fuel cell Pt catalysts at 30 degrees C have adsorption properties similar to that of a Pt (100) surface. Potential dependent infrared spectroscopy of COMeOH and COEtOH from flash evaporated aqueous alcohols delivered to a 50 degrees C fuel cell show lower COEtOH relative to COMeOH with Stark tuning rates below 10 cm(-1)/V.

Research paper thumbnail of Fermi Arcs vs. Fermi Pockets in Electron-doped Perovskite Iridates

Scientific reports, 2015

We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite irid... more We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)3Ir2O7. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected "Fermi arcs", reminiscent of those reported recently in surface electron-doped Sr2IrO4. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

Research paper thumbnail of Dielectric and X-ray Diffraction Analysis of Ba(Ga,Ta) 0.05 Ti 0.90 O 3

Ferroelectrics, 2014

Ba (Ga,Ta) 0.05 Ti 0.90 O 3 , a B-site dipole-like substituted material is investigated for struc... more Ba (Ga,Ta) 0.05 Ti 0.90 O 3 , a B-site dipole-like substituted material is investigated for structural phase transitions over the temperature range 30 to 900 • C using x-ray diffraction. Rietveld refinement of the data suggests the material to be Pm3m (cubic) from 200 to 900 • C, P4/mmm (tetragonal) from 30 to 200 • C with phases similar to those of BaTiO 3 [12]. Average grain size determined using scanning electron microscopy is 650 nm. Measurements of dielectric properties from −50 to 120 • C and over a frequency range of 10 Hz to 2 MHz show a relatively flat dielectric constant that is electric-field tunable indicating that Ba(Ga,Ta) 0.05 Ti 0.90 O 3 is a reasonable candidate for frequency agile components.

Research paper thumbnail of Polyvinylchloride-Single-Walled Carbon Nanotube Composites: Thermal and Spectroscopic Properties

Journal of Nanomaterials, 2012

Nanocomposites of single-walled carbon nanotubes dispersed within polyvinylchloride have been obt... more Nanocomposites of single-walled carbon nanotubes dispersed within polyvinylchloride have been obtained by using the solution path. High-power sonication was utilized to achieve a good dispersion of carbon nanotubes. Thermogravimetric analysis revealed that during the synthesis, processing, or thermal analysis of these nanocomposites the released chlorine is functionalizing the single-walled carbon nanotubes. The loading of polyvinylchloride by single-walled carbon nanotubes increases the glass transition temperature of the polymeric matrix, demonstrating the interactions between macromolecular chains and filler. Wide Angle X-Ray Scattering data suggested a drop of the crystallite size and of the degree of crystallinity as the concentration of single-walled carbon nanotubes is increased. The in situ chlorination and amorphization of nanotube during the synthesis (sonication step) is confirmed by Raman spectroscopy.

Research paper thumbnail of Polyoctenamer - Single Walled Carbon Nanotube Composites: Spectroscopic Investigations

MRS Proceedings, 2009

ABSTRACT Composites of single walled carbon nanotube dispersed within polymeric matrices have bee... more ABSTRACT Composites of single walled carbon nanotube dispersed within polymeric matrices have been investigated by spectroscopic techniques (Raman and Wide Angle X-Ray Spectroscopy). Raman investigations included an in depth analysis of the radial breathing mode (for single wall carbon nanotubes) and a brief analysis of the lines originating from the polymeric matrix. Raman spectra were successfully simulated by computer assuming that the as recorded spectrum is a convolution of lines whose line shape is well described by a modified Breit-Wigner-Fano equation. The dependence of the position of the lines belonging to the radial breathing mode on the concentration of single walled carbon nanotube has been investigated, with emphasis on information pertinent to the stress transfer from the macromolecular matrix to the filler and to the coating of single walled carbon nanotube by polymeric chains. Complementary Wide Angle X-Ray Spectroscopy measurements provided information about the effect of the loading with single walled carbon nanotube on the crystal structure of the polymeric matrix. The research aims to a better understanding of the interactions between polymeric matrices and nanofillers.

Research paper thumbnail of A Density Functional Theory Study on Carbon Monoxide Adsorption on Platinum–Osmium and Platinum–Ruthenium–Osmium Alloys

The Journal of Physical Chemistry C, 2012

Research paper thumbnail of Carbon Monoxide Adsorption Coverage Study on Platinum and Ruthenium Surfaces

The Journal of Physical Chemistry C, 2014

ABSTRACT Periodic density functional theory calculations elucidate carbon monoxide coverage effec... more ABSTRACT Periodic density functional theory calculations elucidate carbon monoxide coverage effects on platinum and ruthenium surfaces. As expected the CO stretching frequencies increase with coverage. Unexpectedly, overlap population calculations show that increased stretching frequencies may not always correspond to stronger bonds. A theoretical framework is established based on a modified π-attraction σ-repulsion scheme. This phenomenological model directly relates the internal adsorbate bond strength to the net change of the carbon 2s and 2pxy contributions to the π- and σ-components, respectively. The variation of the metal–surface bond is examined by using the charges, polarizations, and electron densities of the adsorbate CO orbitals. For the systems studied here, the traditional frontier orbital model of the 5σ-donation/2π*-back-donation with the metal substrate bands is not always sufficient to explain the relative C–O and C–Metal bonds strengths.

Research paper thumbnail of XAFS Debye-Waller factors for deformed hemes and metal substituted hemes

Journal of Physics: Conference Series, 2009

We present an efficient and accurate method for calculating XAFS Debye-Waller factors for deforme... more We present an efficient and accurate method for calculating XAFS Debye-Waller factors for deformed active sites of hemoproteins and metal substituted hemes. Based on the Normal Coordinate Structural Decomposition scheme, the deformation of the porphyrin macrocycle is expressed as a linear combination of the normal modes of the planar species. In our approach, we identify the modes that contribute most to the deformation. Small metal-porphyrin structures which match the macrocycle structural deformation of the deformed hemoprotein site are used to calculate the Debye-Waller parameters at sample's temperature. The Debye-Waller factors are directly obtained by calculating the normal mode spectrum of the corresponding metalporphyrin structure using Density Functional Theory. Our method is tested on Ni-tetraadamantyl porphyrin and cytochrome c structures with more than 500 available scattering paths.

Research paper thumbnail of Single and multiple scattering XAFS Debye-Waller factors for crystalline materials using periodic Density Functional Theory

Journal of Physics: Conference Series, 2009

ABSTRACT We present an accurate and efficient technique for calculating thermal X-ray absorption ... more ABSTRACT We present an accurate and efficient technique for calculating thermal X-ray absorption fine structure (XAFS) Debye-Waller factors (DWFs) applicable to crystalline materials. Using Density Functional Theory on a 3×3×3 supercell pattern of MnO structure, under the nonlocal hybrid B3LYP functional paired with Gaussian local basis sets, we obtain the normal mode eigenfrequencies and eigenvectors; these parameters are in turn used to calculate single and multiple scattering XAFS DWFs. The DWFs obtained via this technique are temperature dependent expressions and can be used to substantially reduce the number of fitting parameters, when experimental spectra are fitted with a hypothetical structure. The size of the supercell size limits the R-space range that these parameters could be used. Therefore corresponding DWFs for paths outside of this range are calculated using the correlated Debye model. Our method is compared with prior cluster calculations and with corresponding values obtained from fitting experimental XAFS spectra on manganosite with simulated spectra.

Research paper thumbnail of Electrical and Structural Properties of Ba(Y 3+ , Sb 5+ ) 0.05 Ti 0.90 O 3

Integrated Ferroelectrics, 2013

The microwave ceramic Ba(Y,Sb) 0.05 Ti 0.90 O 3, based upon random B-site dipole-like substitutio... more The microwave ceramic Ba(Y,Sb) 0.05 Ti 0.90 O 3, based upon random B-site dipole-like substitutions is structurally and electrically characterized over the temperature range −55 • C to 120 • C. X-ray diffraction information coupled together with scanning electron microscopy reveals that the material is single phase and has submicron grain sizes. Results show the tetragonal phase ranges from −30 • C to 200 • C, which is a broader temperature range than that of the parent material BaTiO 3 , 0 • C to 120 • C. The material Ba(Y,Sb) 0.05 Ti 0.90 O 3 also has a diffuse relative high dielectric constant of about 10,000 that peaks at the orthorhombic-tetragonal structural phase transition around −30 • C.

Research paper thumbnail of Thermal Features and Glass Transition in Polystyrene-Nanodiamond Composites

Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta ... more Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta solvent (cyclohexane) followed by the addition of diamond nanoparticles from Aldrich (with a particle size ranging between 3 and 8 nm) and subsequent sonication for about 100 minutes by using a Hielscher high power (1 kW) sonicator. The homogeneous solution was poured onto microscope slides and the solvent has been removed by heating in an oven at 125 ^oC for about 3 hours. Composites containing various amounts (from 0 % to 25 % nanodiamonds within polystyrene) have been investigated. The physical properties of the as obtained nanocomposites were investigated by DSC, TGA, Raman, and WAXS. Glass transition temperature was shifted to higher temperatures and the thermal stability was enhanced by the addition of nanodiamonds. A phenomenological model for the observed changes is proposed (within the free volume approximation) and discussed in detail. Acknowledgements: This research was supported by US Army Research Laboratory (W911NF-08-1-0353) and LSAMP -UTPA.