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  • 1. Abid, Jean-Pierre
    et al.
    Abid, Mohamed
    Uppsala University, Disciplinary Domain of Science and Technology.
    Bauer, Christophe
    Girault, Hubert H.
    Brevet, Pierre-Francois
    Controlled reversible adsorption of core: Shell metallic nanoparticles at the polarized water/1,2-dichloroethane interface investigated by optical second-harmonic generation2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 25, p. 8849-8855Article in journal (Refereed)
    Abstract [en]

    We report the observation of the reversible adsorption of core-shell gold-silver nanoparticles at the polarized water/1,2-dichloroethane interface using the nonlinear optical technique of surface second-harmonic generation. This study unambiguously demonstrates the excellent stability against aggregation of these core-shell nanoparticles, namely, gold core nanoparticles coated with silver layers of variable thickness, in the presence of an electrolyte salt like lithium chloride. Furthermore, it is also demonstrated that the adsorption of the nanoparticles is reversible by modulating the applied potential at water/1,2-dichloroethane interface. The analysis of these results is performed within the Debye-Huckel approximation of the electrostatic interactions between the nanoparticles. This approach shows that the stability of core-shell nanoparticles can be attributed to the formation of a silver oxide layer at the Surface of the particles.

  • 2.
    Agrios, Alexander G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Low-temperature TiO2 Films for Dye-sensitized Solar Cells: Factors Affecting Energy Conversion Efficiency2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 27, p. 10021-10026Article in journal (Refereed)
    Abstract [en]

    Semiconductor films prepd. by electrostatic layer-by-layer deposition can be used to fabricate dye-sensitized solar cells after low-temp. treatment (150 DegC). However, the resulting photocurrent is much less than when the film is sintered at 500 DegC. The difference in short-circuit current is a factor of 2.2 with the Ru-based dye N719 and is 3.5 with the org. dye D5. The photocurrent at a given wavelength is proportional to the light-harvesting efficiency, charge injection effciency, and charge collection efficiency. Sintered films take up more than 60% more of either dye than unsintered films and therefore absorb more photons. Electron injection is hindered in unsintered films due to a conduction band edge potential 100 mV more neg. than in a sintered electrode. Addnl. injection effects could be due to adsorption of the dye to polymer rather than to TiO2 in unsintered films, although our measurements were inconclusive on this point. Kinetic studies show electron transport times (ttr) an order of magnitude faster then electron lifetimes (te) in both sintered and unsintered electrodes. Furthermore, a Li+ insertion expt. shows that both films have good elec. connectivity between TiO2 nanoparticles. Unsintered films thus exhibit efficient charge transport despite the presence of polymer and the lack of heat treatment to induce necking.

  • 3. Ahmad, Y.
    et al.
    Dubois, M.
    Guerin, K.
    Hamwi, A.
    Fawal, Z.
    Kharitonov, A. P.
    Generalov, A. V.
    Klyushin, A. Yu.
    Simonov, K. A.
    V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504, Russia.
    Vinogradov, Nikolay A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics. V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504, Russia.
    Zhdanov, I. A.
    V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504, Russia.
    Preobrajenski, A. B.
    MAX-lab, Lund University, Box 118, 22100 Lund, Sweden.
    Vinogradov, A. S.
    V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504, Russia.
    NMR and NEXAFS Study of Various Graphite Fluorides2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 26, p. 13564-13572Article in journal (Refereed)
    Abstract [en]

    Graphite fluorides with different structural types (CyF)(n) (y = 2.5, 2, and 1) and room temperature graphite fluorides were studied by solid state,NMR and NEXAFS. Data extracted from those two techniques are complementary, providing information about the C-F bonding and the hybridization character of the carbon atom valence states. The comparison of data obtained by different methods such as NMR, Raman, and X-ray absorption leads to similar conclusions regarding the chemical bonding in fluorographites. Several major configurations of fluorinated graphites are discussed, that is, planar sheets with mainly sp(2) hybridization in room temperature graphite fluorides and corrugated sheets with sp(3) hybridization in covalent high temperature graphite fluoride. Different references such as highly oriented pyrolytic graphite (HOPG), graphitized carbon nanodiscs (graph-CNDs) and nanodiamonds (NDs) have also been investigated for comparison.

  • 4.
    Ahmed, Taha
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Optical Quantum Confinement in Ultrasmall ZnO and the Effect of Size on Their Photocatalytic Activity2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 11, p. 6395-6404Article in journal (Refereed)
    Abstract [en]

    Zinc oxide is a well-known metal oxide semiconductor with a wide direct band gap that offers a promising alternative to titanium oxide in photocatalytic applications. ZnO is studied here as quantum dots (QDs) in colloidal suspensions, where ultrasmall nanoparticles of ZnO show optical quantum confinement with a band gap opening for particles below 9 nm in diameter from the shift of the band edge energies. The optical properties of growing ZnO QDs are determined with Tauc analysis, and a system of QDs for the treatment and degradation of distributed threats is analyzed using an organic probe molecule, methylene blue, whose UV/vis spectrum is analyzed in some detail. The effect of optical properties of the QDs and the kinetics of dye degradation are quantified for low-dimensional ZnO materials in the range of 3-8 nm and show a substantial increase in photocatalytic activity compared to larger ZnO particles. This is attributed to a combined effect from the increased surface area as well as a quantum confinement effect that goes beyond the increased surface area. The results show a significantly higher photocatalytic activity for the QDs between 3 and 6 nm with a complete decolorization of the organic probe molecule, while QDs from 6 nm and upward in diameter show signs of competing reduction reactions. Our study shows that ultrasmall ZnO particles have a reactivity beyond that which is expected because of their increased surface area and also demonstrates size-dependent reaction pathways, which introduces the possibility for size-selective catalysis.

  • 5.
    Aktekin, Burak
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lacey, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nordh, Tim
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Younesi, Reza
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Tengstedt, Carl
    Scania CV AB, SE-15187 Sodertalje, Sweden.
    Zipprich, Wolfgang
    Volkswagen AG, D-38436 Wolfsburg, Germany.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Understanding the Capacity Loss in LiNi0.5Mn1.5O4-Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 21, p. 11234-11248Article in journal (Refereed)
    Abstract [en]

    The high-voltage spinel LiNi0.5Mn1.5O4, (LNMO) is an attractive positive electrode because of its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LNMO parallel to Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells, and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass loss from LNMO or increases in internal cell resistance were minor. A comparison of cell formats constructed with and without the possibility of cross-talk indicates that the parasitic reactions on LTO occur because of the transfer of reaction products from the LNMO side. The efficiency of LTO is more sensitive to temperature, causing a dramatic increase in the fading rate at 55 degrees C. These observations show how important the electrode interactions (cross-talk) can be for the overall cell behavior. Additionally, internal resistance measurements showed that the positive electrode was mainly responsible for the increase of resistance over cycling, especially at 55 degrees C. Surface characterization showed that LNMO surface layers were relatively thin when compared with the solid electrolyte interphase (SEI) on LTO. The SEI on LTO does not contribute significantly to overall internal resistance even though these films are relatively thick. X-ray absorption near-edge spectroscopy measurements showed that the Mn and Ni observed on the anode were not in the metallic state; the presence of elemental metals in the SEI is therefore not implicated in the observed fading mechanism through a simple reduction process of migrated metal cations.

  • 6. Alarcón, H.
    et al.
    Hedlund, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics I.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics I.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics I.
    Hagfeldt, Anders
    KTH, Fysikalisk kemi / Physical Chemistry.
    Boschloo, Gerrit K.
    KTH, Fysikalisk kemi / Physical Chemistry.
    Modification of nanostructured TiO2 electrodes by electrochemical Al3+ insertion: Effects on dye-sensitized solar cell performance2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 35, p. 13267-13274Article in journal (Refereed)
    Abstract [en]

    Nanostructured TiO2 films were modified by insertion with aluminum ions using an electrochemical process. After heat treatment these films were found suitable as electrodes in dye-sensitized solar cells. By means of a catechol adsorption test, as well as photoelectron spectroscopy (PES), it was demonstrated that the density of Ti atoms at the metal oxide/electrolyte interface is reduced after Al modification. There is, however, not a complete coverage of aluminum oxide onto the TiO2, but the results rather suggest either the formation of a mixed Al−Ti oxide surface layer or formation of a partial aluminum oxide coating. No new phase could, however, be detected. In solar cells incorporating Al-modified TiO2 electrodes, both electron lifetimes and electron transport times were increased. At high concentrations of inserted aluminum ions, the quantum efficiency for electron injection was significantly decreased. Results are discussed at the hand of different models:  A multiple trapping model, which can explain slower kinetics by the creation of additional traps during Al insertion, and a surface layer model, which can explain the reduced recombination rate, as well as the reduced injection efficiency, by the formation of a blocking layer.

  • 7.
    Ali, Ehesan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Tuning the Magnetic Interaction between Manganese Porphyrins and Ferromagnetic Co Substrate through Dedicated Control of the Adsorption2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 32, p. 14381-14383Article in journal (Refereed)
    Abstract [en]

    We report, on the basis of density-functional theory+U (DFT+U) calculations that metalloporphyrins can adsorb on ferromagnetic metal surfaces in two distinct configurations. Two separate adsorption minima are obtained for manganese porphyrin (MnP) on Co from our DFT+U total energy calculations, which correspond to strong and weak adsorption strengths, respectively. By steering the nature of adsorption, we find that distinct chemical interactions as well as magnetic exchange interactions between the metalloporphyrin and the metal surface can be realized. We furthermore show that a switching of the MnP molecule's spin state can occur even for the weakly adsorbed case. This new discovery opens up prospects for engineering the chemical and magnetic exchange interaction in new functionalized spintronic materials.

  • 8. Amft, M.
    et al.
    Walle, L. E.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Uvdal, P.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO22013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed)
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

  • 9.
    Amidani, Lucia
    et al.
    Rossendorf Beamline ESRF European Synchrotron, F-38043 Grenoble, France.;Inst Resource Ecol, Helmholtz Zent Dresden Rossendorf, D-01328 Dresden, Germany..
    Dumas, Thomas
    Univ Montpellier, CEA, DES, ISEC, F-30207 Bagnols Sur Ceze, France..
    Shuh, David K.
    Lawrance Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Sahle, Christoph J.
    ESRF, European Synchrotron, F-38043 Grenoble, France..
    Longo, Alessandro
    ESRF, European Synchrotron, F-38043 Grenoble, France..
    Kvashnina, Kristina O.
    Rossendorf Beamline ESRF European Synchrotron, F-38043 Grenoble, France.;Inst Resource Ecol, Helmholtz Zent Dresden Rossendorf, D-01328 Dresden, Germany..
    Oxygen K-Edge X-ray Absorption Spectra of ThO2 and CeO2: Experiment, Interpretation, and Structural Effects2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 6, p. 3077-3084Article in journal (Refereed)
    Abstract [en]

    Experimental oxygen K-edge spectra of ThO2 and CeO2 are presented and interpreted based on density functional theory (DFT). The contribution of d and f orbitals to the O Kedge spectrum is identified as well-distinguished peaks, the presence of which evidences the strong hybridization of Th and Ce metal centers with O orbitals. The sensitivity of the O K-edge to both f- and d-states in the absence of a core-hole on the metal ion results in an insightful overview of the electronic structure involved in the chemical bond. In particular, the large bandwidth of the Th 5f band as compared to the Ce 4f band is observed as a set of wider and more substantial set of peaks in the O K-edge, confirming the stronger hybridization of the former with O orbitals. The peak ascribed to the 5f band of ThO2 is found at higher energy than the 6d band, as predicted from DFT calculations on actinide dioxides. To highlight the sensitivity and the potential use of the O K-edge for the characterization of ThO2-based systems, the sensitivity of the spectrum to structural changes such as lattice expansion and size reduction are calculated and discussed.

  • 10.
    Amorim, Rodrigo G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Fed Fluminense, Dept Fis, ICEx, Volta Redonda, RJ, Brazil..
    Rocha, Alexandre R.
    Univ Estadual Paulista, UNESP, Inst Fis Teor, Sao Paulo, Brazil..
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Boosting DNA Recognition Sensitivity of Graphene Nanogaps through Nitrogen Edge Functionalization2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 34, p. 19384-19388Article in journal (Refereed)
    Abstract [en]

    One of the challenges for next generation DNA sequencing is to have a robust, stable, and reproducible nanodevice. In this work, we propose how to improve the sensing of DNA nucleobase using functionalized graphene nanogap as a solid state device. Two types of edge functionalization, namely, either hydrogen or nitrogen, were considered. We showed that, independent of species involved in the edge passivation, the highest-to-lowest order of the nucleobase transmissions is not altered, but the intensity is affected by several orders of magnitude. Our results show that nitrogen edge tends to p-dope graphene, and most importantly, it contributes with resonance states close to the Fermi level, which can be associated with the increased conductance. Finally, the translocation process of nucleobases passing through the nanogap was also investigated by varying their position from a certain height (from +3 to -3 angstrom) with respect to the graphene sheet to show that nitrogen-terminated sheets have enhanced sensitivity, as moving the nucleobase by approximately 1 angstrom reduces the conductance by up to 3 orders of magnitude.

  • 11.
    Andersson, M.
    et al.
    Chalmers University of Technology.
    Kiselev, A.
    Umeå University.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Palmqvist, A E C
    Chalmers University of Technology.
    Microemulsion-mediated room-temperature synthesis of high-surface-area rutile and its photocatalytic performance2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 18, p. 6789-6797Article in journal (Refereed)
    Abstract [en]

    Nanosized titania having the rutile crystalline structure was synthesized at room temperature using a microemulsion-mediated system. The formed rutile particles had a diameter of 3 nm, which corresponds well with the droplet size of the water-in-oil microemulsion used for their preparation. The crystallinity was monitored by both X-ray diffraction (XRD) and electron diffraction, together with dark-field electron microscopy (TEM) and high-resolution TEM. The rutile had a high specific surface area (similar to 300 m(2)/g) according to N-2 adsorption and the BET equation. To our knowledge, this is the highest specific surface area ever reported for rutile. The rutile crystals aligned in a specific crystallographic direction forming elongated aggregates 200-1000 nm in size, as observed by TEM and high-resolution TEM. The titania formation was followed in situ using dynamic light scattering and UV-vis spectroscopy, and together with TEM and XRD performed on samples collected throughout the duration of the titania synthesis, the results gave support for a formation scheme involving the initial formation of amorphous titania followed by crystallization of rutile. The photocatalytic performance of the formed material was evaluated by in situ Fourier transform infrared spectroscopy and compared to that of a rutile sample having a lower specific surface area (similar to 40 m(2)/g). The TEM and formate adsorption experiments revealed that the high-surface-area rutile had a much higher fraction of (101) facets than the low-surface-area sample, which predominantly exposed (110) facets. In particular, a new bidentate formate (mu-formate) species bridge-bonded to the (101) facet could be identified with characteristic bands at 1547 and 1387 cm(-1). The photodegradation rate of this species was found to be similar to the mu-formate species on the (110) facet. However, the overall formate degradation rate was larger on the high-surface-area rutile sample because of a high concentration of the more readily photodegradable monodentate formate (eta(1)-formate) on that sample.

  • 12. Andersson, Mikael
    et al.
    Grinderslev, J. B.
    Chen, X. -M
    Chen, X.
    Häussermann, U.
    Zhou, W.
    Jensen, T. R.
    Karlsson, M.
    Udovic, T. J.
    Interplay between the Reorientational Dynamics of the B3H8– Anion and the Structure in KB3H82021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 7, p. 3716-3724Article in journal (Refereed)
  • 13.
    Andersson, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 USA.;Chalmers Univ Technol, Dept Chem & Chem Engn, SE-41296 Gothenburg, Sweden..
    Stavila, Vitalie
    Sandia Natl Labs, Energy Nanomat, Livermore, CA 94551 USA..
    Skripov, Alexander, V
    Russian Acad Sci, Ural Branch, Inst Met Phys, Ekaterinburg 620108, Russia..
    Dimitrievska, Mirjana
    NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 USA.;Natl Renewable Energy Lab, Golden, CO 80401 USA.;Ecole Polytech Fed Lausanne, Inst Mat, Lab Semicond Mat, CH-1015 Lausanne, Switzerland..
    Psurek, Malgorzata T.
    NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 USA.;Univ Maryland, Dept Chem, College Pk, MD 20742 USA..
    Leao, Juscelino B.
    NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 USA..
    Babanova, Olga A.
    Russian Acad Sci, Ural Branch, Inst Met Phys, Ekaterinburg 620108, Russia..
    Skoryunov, Roman, V
    Russian Acad Sci, Ural Branch, Inst Met Phys, Ekaterinburg 620108, Russia..
    Soloninin, Alexei, V
    Russian Acad Sci, Ural Branch, Inst Met Phys, Ekaterinburg 620108, Russia..
    Karlsson, Maths
    Chalmers Univ Technol, Dept Chem & Chem Engn, SE-41296 Gothenburg, Sweden..
    Udovic, Terrence J.
    NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 USA.;Univ Maryland, Dept Mat Sci & Engn, College Pk, MD 20742 USA..
    Promoting Persistent Superionic Conductivity in Sodium Monocarba-closo-dodecaborate NaCB11H12 via Confinement within Nanoporous Silica2021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 30, p. 16689-16699Article in journal (Refereed)
    Abstract [en]

    Superionic phases of bulk anhydrous salts based on large cluster-like polyhedral (carba)borate anions are generally stable only well above room temperature, rendering them unsuitable as solid-state electrolytes in energy-storage devices that typically operate at close to room temperature. To unlock their technological potential, strategies are needed to stabilize these superionic properties down to subambient temperatures. One such strategy involves altering the bulk properties by confinement within nanoporous insulators. In the current study, the unique structural and ion dynamical properties of an exemplary salt, NaCB11H12, nanodispersed within porous, high-surface-area silica via salt-solution infiltration were studied by differential scanning calorimetry, X-ray powder diffraction, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and impedance spectroscopy. Combined results hint at the formation of a nanoconfined phase that is reminiscent of the high-temperature superionic phase of bulk NaCB11H12, with dynamically disordered CB11H12-anions exhibiting liquid-like reorientational mobilities. However, in contrast to this high-temperature bulk phase, the nanoconfined NaCB11H12 phase with rotationally fluid anions persists down to cryogenic temperatures. Moreover, the high anion mobilities promoted fast-cation diffusion, yielding Na+ superionic conductivities of similar to 0.3 mS/cm at room temperature, with higher values likely attainable via future optimization. It is expected that this successful strategy for conductivity enhancement could be applied as well to other related polyhedral (carba)borate-based salts. Thus, these results present a new route to effectively utilize these types of superionic salts as solid-state electrolytes in future battery applications.

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  • 14.
    Anikina, Ekaterina
    et al.
    South Ural State Univ, Inst Nat Sci & Math, Chelyabinsk 454014, Russia.;Uppsala Univ, Dept Phys & Astron, Mat Theory Div, S-75120 Uppsala, Sweden..
    Hussain, Tanveer
    Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia..
    Beskachko, Valery
    South Ural State Univ, Inst Nat Sci & Math, Chelyabinsk 454014, Russia..
    Bae, Hyeonhu
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Lee, Hoonkyung
    Konkuk Univ, Dept Phys, Seoul 05029, South Korea..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala UniKTH Royal Inst Technol, Appl Mat Phys, Dept Mat & Engn, S-10044 Stockholm, Sweden..
    Tunning Hydrogen Storage Properties of Carbon Ene-Yne Nanosheets through Selected Foreign Metal Functionalization2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 31, p. 16827-16837Article in journal (Refereed)
    Abstract [en]

    In this study, we have employed density functional theory with a range of van der Waals corrections to study geometries, electronic structures, and hydrogen (H-2) storage properties of carbon ene-yne (CEY) decorated with selected alkali (Na, K) and alkaline-earth metals (Mg, Ca). We found that all metals, except Mg, bind strongly by donating a major portion of their valence electrons to the CEY monolayers. Thermal stabilities of representative systems, Ca-decorated CEY monolayers, have been confirmed through ab initio molecular dynamics simulations (AIMD). We showed that each metal cation adsorbs multiple H-2 with binding energies (E-bind) considerably stronger than on pristine CEY. Among various metal dopants, Ca stands out with the adsorption of five H-2 per each Ca having E-bind values within the desirable range for effective adsorption/desorption process. The resulting gravimetric density for CEY@Ca has been found around 6.0 wt % (DFT-D3) and 8.0 wt % (LDA), surpassing the U.S. Department of Energy's 2025 goal of 5.5 wt %. The estimated H-2 desorption temperature in CEY@Ca exceeds substantially the boiling point of liquid nitrogen, which confirms its potential as a practical H-2 storage medium. We have also employed thermodynamic analysis to explore the H-2 adsorption/desorption mechanism at varied conditions of temperature and pressure for real-world applications.

  • 15.
    Araujo, Rafael Barros Neves de Araujo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2 : A High Voltage Organic2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455Article in journal (Other academic)
  • 16.
    Araujo, Rafael Barros Neves de
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 26, p. 14027-14036Article in journal (Refereed)
    Abstract [en]

    In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds NaxC6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds.

  • 17.
    Arruda, Lucas M.
    et al.
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany;Minist Educ Brazil, CAPES Fdn, BR-70040020 Brasilia, DF, Brazil.
    Ali, Md. Ehesan
    Inst Nano Sci & Technol, Phase 10,Sect 64, Mohali 160062, Punjab, India.
    Bernien, Matthias
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany.
    Nickel, Fabian
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany.
    Kopprasch, Jens
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany.
    Czekelius, Constantin
    Heinrich Heine Univ Dusseldorf, Inst Organ Chem & Makromol Chem, Univ Str 1, D-40225 Dusseldorf, Germany.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kuch, Wolfgang
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany.
    Modifying the Magnetic Anisotropy of an Iron Porphyrin Molecule by an on-Surface Ring-Closure Reaction2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 23, p. 14547-14555Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of adsorbed metalloporphyrin molecules can be altered or tuned by the substrate, additional axial ligands, or changes to the molecules' macrocycle. These modifications influence the electronic configuration of the fourfold-coordinated central metal ion that is responsible for the metalloporphyrins' magnetic properties. We report a substantial increase in the effective spin moment obtained from sum-rule analysis of X-ray magnetic circular dichroism for an iron metalloporphyrin molecule on Au(111) through its conversion from iron(II)-octaethylporphyrin to iron(II)-tetrabenzoporphyrin in a surface-assisted ring-closure ligand reaction. Density functional theory calculations with additional strong Coulomb correlation (DFT+U) show that the on-surface reaction alters the conformation of the molecule, increasing its planarity and the ion-surface distance. A spin-Hamiltonian fit of the magnetization as a function of field reveals a substantial increase in the intra-atomic magnetic dipole term (T-z) and a decrease in the magnitude of the easy-plane anisotropy upon ring closure. This consequence of the ring closure demonstrates how new magnetic properties can be obtained from on-surface reactions, resulting here in significant modifications to the magnetic anisotropy of the Fe ion, and sheds light onto the molecule-substrate interaction in these systems.

  • 18. Asano, Kohta
    et al.
    Westerwaal, Ruud J.
    Anastasopol, Anca
    Mooij, Lennard P. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Boelsma, Christiaan
    Ngene, Peter
    Schreuders, Herman
    Eijt, Stephan W. H.
    Dam, Bernard
    Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg-Ti System2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 22, p. 12157-12164Article in journal (Refereed)
    Abstract [en]

    Mg is an attractive hydrogen storage material not only because of its high gravimetric and volumetric hydrogen capacities but also because of it low material costs. However, the hydride of MgH2 is too stable to release hydrogen under moderate conditions. We demonstrate that the formation of nanometer-sized clusters of Mg reduces the stability of MgH2 by the interface energy effect in the immiscible Mg-Ti system. Ti-rich MgxTi1-x (x < 0.5) thin films deposited by magnetron sputtering have a hexagonal close packed (HCP) structure, which forms a face-centered cubic (FCC) hydride phase upon hydrogenation. Positron Doppler broadening depth profiling demonstrates that after hydrogenation, nanometer-sized MgH2 clusters are formed which are coherently embedded in an FCC TiH2 matrix. The P (pressure)-T (optical transmission) isotherms measured by hydrogenography show that these MgH2 clusters are destabilized. This indicates that the formation of nanometer-sized Mg allows for the development of a lightweight and cheap hydrogen storage material with a lower desorption temperature.

  • 19.
    Babucci, Melike
    et al.
    Department of Chemicaland Biological Engineering and ‡Koç University TÜPRAŞEnergy Center (KUTEM), Koç University Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey.
    Balci, Volkan
    Department of Chemicaland Biological Engineering and ‡Koç University TÜPRAŞEnergy Center (KUTEM), Koç University Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey.
    Akçay, Aslı
    Department of Chemicaland Biological Engineering and ‡Koç University TÜPRAŞEnergy Center (KUTEM), Koç University Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey.
    Uzun, Alper
    Department of Chemicaland Biological Engineering and ‡Koç University TÜPRAŞEnergy Center (KUTEM), Koç University Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey.
    Interactions of [BMIM][BF4] with Metal Oxides and Their Consequences on Stability Limits2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 36, p. 20089-20102Article in journal (Refereed)
    Abstract [en]

    Interactions between 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and high-surface-area metal oxides, SiO2, TiO2, Fe2O3, ZnO, gamma-Al2O3, CeO2, MgO, and La2O3, covering a wide range of point of zero charges (PZC), from pH = 2 to 11, were investigated by combining infrared (IR) spectroscopy with density functional theory (DFT) calculations. The shifts in spectroscopic features of the ionic liquid (IL) upon coating different metal oxides were evaluated to elucidate the interactions between IL and metal oxides as a function of surface acidity. Consequences of these interactions on the short- and long-term thermal stability limits as well as the apparent activation energy (Ea) and rate constant for thermal decomposition of the supported IL were evaluated. Results showed that stability limits and Ea of the IL on each metal oxide significantly decrease with increasing PZC of the metal oxide. Results presented here indicate that the surface acidity strongly controls the IL surface interactions, which determine the material properties, such as thermal stability. Elucidation of these effects offers opportunities for rational design of materials which include direct interactions of ILs with metal oxides, such as solid catalysts with ionic liquid layer (SCILL), and supported ionic liquid phase (SILP) catalysts for catalysis applications or supported ionic liquid membranes (SILM) for separation applications.

  • 20.
    Babucci, Melike
    et al.
    Department of Chemical Engineering, University of California, Davis, California 95616, United States.
    Hoffman, Adam S.
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
    Bare, Simon R.
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
    Gates, Bruce C.
    Department of Chemical Engineering, University of California, Davis, California 95616, United States.
    Characterization of a Metal–Organic Framework Zr6O8 Node-Supported Atomically Dispersed Iridium Catalyst for Ethylene Hydrogenation by X-ray Absorption Near-Edge Structure and Infrared Spectroscopies2021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 31, p. 16995-17007Article in journal (Refereed)
    Abstract [en]

    The catalytic properties of atomically dispersed supported metals depend on the supports as ligands. We report metal-organic frameworks in the UiO-66 family, synthesized with various ligands that influence the electron-donor properties of the Zr6O8 nodes, including benzene-1,4-dicarboxylate linkers (some with substituents) and formate, acetate, benzoate, and trifluoroacetate. Catalytically active iridium species on the nodes were made by chemisorption of Ir(CO)(2)(acetylacetonato), giving Ir(CO) 2 groups, identified by infrared (IR) and extended X-ray absorption fine structure spectroscopies. The electronic properties of the iridium centers, which are sensitive to the supports as ligands, were characterized with high-energy-resolution fluorescence detection X-ray absorption near-edge spectroscopy (HERFD XANES), distinguishing the supports and giving results correlated with the nu(CO) IR spectra and catalytic activities of partially decarbonylated iridium sites for ethylene hydrogenation at 313 K and atmospheric pressure. The IR spectra of the working catalyst incorporating linkers with NH2 substituents show an initial induction period as reactants changed the iridium ligand environment, after which the catalyst operating in a once-through flow reactor underwent no measurable deactivation for 48 h. Among the results, we emphasize the value of HERFD XANES spectroscopy for the sensitive assessment of the effects of supports as ligands that determine the catalytic properties of atomically dispersed metals.

  • 21.
    Bajaj, Ashima
    et al.
    Inst Nano Sci & Technol, Mohali 160062, Punjab, India..
    Kaur, Prabhleen
    Inst Nano Sci & Technol, Mohali 160062, Punjab, India..
    Sud, Aakanksha
    Inst Nano Sci & Technol, Mohali 160062, Punjab, India..
    Berritta, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ali, Md Ehesan
    Inst Nano Sci & Technol, Mohali 160062, Punjab, India..
    Anomalous Effect of Quantum Interference in Organic Spin Filters2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 44, p. 24361-24371Article in journal (Refereed)
    Abstract [en]

    The molecular topology in the single-molecule nanojunctions through which the de Broglie wave propagates plays a crucial role in controlling the molecular conductance. The enhancement and reduction of the conductance in para- and meta-connected molecules due to constructive and destructive quantum interference (QI), respectively, are quite well established. Herein, we investigated the effect of localized spin centers on spin transportation using organic radicals as molecular junctions. The role of the localized spins on the QI as well as on spin filtering capability is investigated employing density functional theory in combination with nonequilibrium Green's function (NEGF-DFT) techniques. Various organic radicals including nitroxy (NO center dot), phenoxy (PO center dot), and methyl (CH2 center dot) attached to the central benzene ring of pentacene with different terminal connections (para and meta) to gold electrodes are examined. Due to more obvious QI effects, para-connected pentacene is found to be more conductive than the meta one. Surprisingly, on incorporating a radical center, along with spin filtering, a significant reversal of QI effects is observed which manifests itself in such a way that the conductance of meta-coupled radicals is found to be more than para-coupled ones by 2 orders of magnitude. The anomaly in QI patterns induced by the radical center is analyzed and discussed in terms of orbital and structural perspectives.

  • 22.
    Barcaro, Giovanni
    et al.
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Sernenta, Luca
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Monti, Susanna
    CNR, ICCOM, Inst Chem Organometall Cpds, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Carravetta, Vincenzo
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Dynamical and Structural Characterization of the Adsorption of Fluorinated Alkane Chains onto CeO22018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 41, p. 23405-23413Article in journal (Refereed)
    Abstract [en]

    The widespread use of ceria-based materials and the need to design suitable strategies to prepare eco-friendly CeO2 supports for effective catalytic screening induced us to extend our computational multiscale protocol to the modeling of the hybrid organic/oxide interface between prototypical fluorinated linear alkane chains (polyethylene-like oligomers) and low-index ceria surfaces. The combination of quantum chemistry calculations and classical reactive molecular dynamics simulations provides a comprehensive picture of the interface and discloses, at the atomic level, the main causes of typical adsorption modes. The data show that at room temperature. a moderate. percentage` of fluorine atoms (around 25%) can enhance the interaction of the organic chains by anchoring strongly pivotal fluorines to the channels of the underneath ceria (100) surface, whereas an excessive content can remarkably reduce this interaction because of the repulsion between fluorine and the negatively charged oxygen of the surface.

  • 23. Barrabes, Noelia
    et al.
    Foettinger, Karin
    Llorca, Jordi
    Dalinov, Anton
    Medina, Francesc
    Sa, Jacinto
    Hardacre, Christopher
    Rupprechter, Guenther
    Pretreatment Effect on Pt/CeO2 Catalyst in the Selective Hydrodechlorination of Trichloroethylene2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 41, p. 17675-17682Article in journal (Refereed)
  • 24.
    Bayrak Pehlivan, Ilknur
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, Miguel A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 39, p. 23890-23897Article in journal (Refereed)
    Abstract [en]

    Hydrogen production by splitting water using electrocatalysts powered by renewable energy from solar or wind plants is one promising alternative to produce a carbon-free and sustainable fuel. Earth-abundant and nonprecious metals are, here, of interest as a replacement for scarce and expensive platinum group catalysts. Ni–Mo is a promising alternative to Pt, but the type of the substrate could ultimately affect both the initial growth conditions and the final charge transfer in the system as a whole with resistive junctions formed in the heterojunction interface. In this study, we investigated the effect of different substrates on the hydrogen evolution reaction (HER) of Ni–Mo electrocatalysts. Ni–Mo catalysts (30 atom % Ni, 70 atom % Mo) were sputtered on various substrates with different porosities and conductivities. There was no apparent morphological difference at the surface of the catalytic films sputtered on the different substrates, and the substrates were classified from microporous to flat. The electrochemical characterization was carried out with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in the frequency range 0.7 Hz–100 kHz. LSV measurements were carried out at direct current (DC) potentials between 200 and −400 mV vs the reversible hydrogen electrode (RHE) in 1 M NaOH encompassing the HER. The lowest overpotentials for HER were obtained for films on the nickel foam at all current densities (−157 mV vs RHE @ 10 mA cm–2), and the overpotentials increased in the order of nickel foil, carbon cloth, fluorine-doped tin oxide, and indium tin oxide glass. EIS data were fitted with two equivalent circuit models and compared for different DC potentials and different substrate morphologies and conductivities. By critical evaluation of the data from the models, the influence of the substrates on the reaction kinetics was analyzed in the high- and low-frequency regions. In the high-frequency region, a strong substrate dependence was seen and interpreted with a Schottky-type barrier, which can be rationalized as being due to a potential barrier in the material heterojunctions or a resistive substrate–film oxide/hydroxide. The results highlight the importance of substrates, the total charge transfer properties in electrocatalysis, and the relevance of different circuit components in EIS and underpin the necessity to incorporate high-conductivity, chemically inert, and work-function-matched substrate–catalysts in the catalyst system.

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  • 25.
    Bender, Philipp
    et al.
    Univ Cantabria, E-39005 Santander, Spain..
    Fock, Jeppe
    Tech Univ Denmark, DK-2800 Lyngby, Denmark..
    Frandsen, Cathrine
    Tech Univ Denmark, DK-2800 Lyngby, Denmark..
    Hansen, Mikkel F.
    Tech Univ Denmark, DK-2800 Lyngby, Denmark..
    Balceris, Christoph
    TU Braunschweig, D-38106 Braunschweig, Germany..
    Ludwig, Frank
    TU Braunschweig, D-38106 Braunschweig, Germany..
    Posth, Oliver
    Phys Tech Bundesanstalt, D-10587 Berlin, Germany..
    Wetterskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bogart, Lara K.
    UCL, London W1S 4BS, England..
    Southern, Paul
    UCL, London W1S 4BS, England..
    Szczerba, Wojciech
    Bundesanstalt Mat Forsch & Prufung, D-12205 Berlin, Germany.;AGH Univ Sci & Technol, PL-30059 Krakow, Poland..
    Zeng, Lunjie
    Chalmers Univ Technol, S-41296 Gothenburg, Sweden..
    Witte, Kerstin
    Univ Rostock, D-18059 Rostock, Germany.;Micromod Partikeltechnol GmbH, D-18119 Rostock, Germany..
    Grüttner, Cordula
    Micromod Partikeltechnol GmbH, D-18119 Rostock, Germany..
    Westphal, Fritz
    Micromod Partikeltechnol GmbH, D-18119 Rostock, Germany..
    Honecker, Dirk
    Inst Laue Langevin, F-38042 Grenoble, France..
    Gonzalez-Alonso, David
    Univ Cantabria, E-39005 Santander, Spain..
    Fernandez Barquin, Luis
    Univ Cantabria, E-39005 Santander, Spain..
    Johansson, Christer
    RISE Acreo, S-40014 Gothenburg, Sweden..
    Relating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 5, p. 3068-3077Article in journal (Refereed)
    Abstract [en]

    We investigated, in depth, the interrelations among structure, magnetic properties, relaxation dynamics and magnetic hyperthermia performance of magnetic nanoflowers. The nanoflowers are about 39 nm in size, and consist of densely packed iron oxide cores. They display a remanent magnetization, which we explain by the exchange coupling between the cores, but we observe indications for internal spin disorder. By polarized small-angle neutron scattering, we unambiguously confirm that, on average, the nano flowers are preferentially magnetized along one direction. The extracted discrete relaxation time distribution of the colloidally dispersed particles indicates the presence of three distinct relaxation contributions. We can explain the two slower processes by Brownian and classical Neel relaxation, respectively. The additionally observed very fast relaxation contributions are attributed by us to the relaxation of disordered spins within the nanoflowers. Finally, we show that the intrinsic loss power (ILP, magnetic hyperthermia performance) of the nanoflowers measured in colloidal dispersion at high frequency is comparatively large and independent of the viscosity of the surrounding medium. This concurs with our assumption that the observed relaxation in the high frequency range is primarily a result of internal spin relaxation, and possibly connected to the disordered spins within the individual nanoflowers.

  • 26.
    Beniwal, Shivang
    et al.
    Indian Inst Technol Roorkee, Adv Res Electrochem Impedance Spect Lab, Roorkee 247667, India..
    Kumar, Ankush
    Indian Inst Technol Roorkee, Adv Res Electrochem Impedance Spect Lab, Roorkee 247667, India.;Nanyang Technol Univ Singapore, Sch Phys & Math Sci, Singapore 637371, Singapore..
    Kumar, Ramesh
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Indian Inst Technol Roorkee, Adv Res Electrochem Impedance Spect Lab, Roorkee 247667, India.
    Suhail, Atif
    Indian Inst Technol Roorkee, Adv Res Electrochem Impedance Spect Lab, Roorkee 247667, India.;Indian Inst Technol Roorkee, Ctr Nanotechnol, Roorkee 247667, India..
    Bag, Monojit
    Indian Inst Technol Roorkee, Adv Res Electrochem Impedance Spect Lab, Roorkee 247667, India.;Indian Inst Technol Roorkee, Ctr Nanotechnol, Roorkee 247667, India..
    Tuning Conductivity of Lead-Free Cs2AgBiBr6 Double Perovskite Ternary Composite with PEDOT:PSS and Carbon Black for Supercapacitor Application2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 27, p. 12874-12881Article in journal (Refereed)
    Abstract [en]

    Lead-based halide perovskites have been widely used as efficient energy materials due to their superior optoelectronic properties and mixed electronic–ionic conductivity. However, lead toxicity has been one of the key challenges for commercialization. Recently Cs2AgBiBr6, a lead-free double perovskite, has garnered significant interest due to its exceptional stability, nontoxic nature, and promising optoelectronic properties. But because of the low electronic and ionic conductivity of bismuth-based double perovskites, there is a challenge for their use in energy storage applications. To resolve this issue, we have incorporated carbon black and a conducting polymer poly(2,3-dihydrothieno-1,4-dioxin)-poly (styrene sulfonate) (PEDOT:PSS) as electronic and ionic conductivity agents respectively into the Cs2AgBiBr6 porous electrode. This ternary composite exhibits over 40% enhancement in specific capacitance as well as specific energy density compared with a binary composite of carbon black with a perovskite electrode. There is no significant change in the power density. However, only PEDOT:PSS as charge transporting materials in perovskite matrix results in lower energy density and power density despite lower charge transfer resistance (Rct) at the electrode/electrolyte interface and higher dc ionic conductivity compared to perovskite/carbon composite electrodes. From the electrochemical impedance spectroscopy analysis, it is evident that balanced ionic and electronic conductivities are necessary to achieve optimal performance in lead-free perovskite-based supercapacitors. We also fabricated a solid-state symmetric supercapacitor using a quasi-solid-state gel electrolyte.

  • 27.
    Berggren, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Weng, Yi-Chen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Li, Qifan
    Linköping Univ, Dept Sci & Technol, Lab Organ Elect, SE-60174 Norrköping, Sweden..
    Yang, Chi-Yuan
    Linköping Univ, Dept Sci & Technol, Lab Organ Elect, SE-60174 Norrköping, Sweden..
    Johansson, Fredrik O. L.
    KTH Royal Inst Technol, Dept Chem, Div Appl Phys Chem, SE-10044 Stockholm, Sweden.;Sorbonne Univ, Inst Nanosci Paris, CNRS, INSP, F-75005 Paris, France..
    Cappel, Ute B.
    KTH Royal Inst Technol, Dept Chem, Div Appl Phys Chem, SE-10044 Stockholm, Sweden..
    Berggren, Magnus
    Linköping Univ, Dept Sci & Technol, Lab Organ Elect, SE-60174 Norrköping, Sweden..
    Fabiano, Simone
    Linköping Univ, Dept Sci & Technol, Lab Organ Elect, SE-60174 Norrköping, Sweden..
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Charge Transfer in the P(g42T-T):BBL Organic Polymer Heterojunction Measured with Core-Hole Clock Spectroscopy2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 49, p. 23733-23742Article in journal (Refereed)
    Abstract [en]

    The conductivity of organic polymer heterojunction devices relies on the electron dynamics occurring along interfaces between the acceptor and donor moieties. To investigate these dynamics with chemical specificity, spectroscopic techniques are employed to obtain localized snapshots of the electron behavior at selected interfaces. In this study, charge transfer in blends (by weight 10, 50, 90, and 100%) of p-type polymer P(g(4)2T-T) (bithiophene-thiophene) and n-type polymer BBL (poly(benzimidazo-benzo-phenanthroline)) was measured by resonant Auger spectroscopy. Electron spectra emanating from the decay of core-excited states created upon X-ray absorption in the donor polymer P(g(4)2T-T) were measured in the sulfur KL2,3L2,3 Auger kinetic energy region as a function of the excitation energy. By tuning the photon energy across the sulfur K-absorption edge, it is possible to differentiate between decay paths in which the core-excited electron remained on the atom with the core-hole and those where it tunneled away. Analyzing the competing decay modes of these localized and delocalized (charge-transfer) processes facilitated the computation of charge-transfer times as a function of excitation energy using the core-hole clock method. The electron delocalization times derived from the measurements were found to be in the as/fs regime for all polymer blends, with the fastest charge transfer occurring in the sample with an equal amount of donor and acceptor polymer. These findings highlight the significance of core-hole clock spectroscopy as a chemically specific tool for examining the local charge tunneling propensity, which is fundamental to understanding macroscopic conductivity. Additionally, the X-ray absorption spectra near the sulfur K-edge in the P(g(4)2T-T) polymer for different polymer blends were analyzed to compare molecular structure, orientation, and ordering in the polymer heterojunctions. The 50% donor sample exhibited the most pronounced angular dependence of absorption, indicating a higher level of ordering compared to the other weight blends. Our studies on the electron dynamics of this type of all-polymer donor-acceptor systems, in which spontaneous ground-state electron transfer occurs, provide us with critical insights to further advance the next generation of organic conductors with mixed electron-hole conduction characteristics suitable for highly stable electrodes of relevance for electronic, electrochemical, and optoelectronic applications.

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  • 28.
    Bernes, E.
    et al.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Fronzoni, G.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Stener, M.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Guarnaccio, A.
    ISM CNR, Inst Struct Matter, Tito, PZ, Italy.;ISM CNR, Inst Struct Matter, Trieste, Italy..
    Zhang, T.
    Beijing Inst Technol BIT, Sch Informat & Elect, MIIT Key Lab Low Dimens Quantum Struct & Devices, Beijing 100081, Peoples R China.;Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Grazioli, C.
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Basovizza, Italy..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Coreno, M.
    ISM CNR, Inst Struct Matter, Tito, PZ, Italy.;ISM CNR, Inst Struct Matter, Trieste, Italy..
    de Simone, M.
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Basovizza, Italy..
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Toffoli, D.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    S 2p and P 2p Core Level Spectroscopy of PPT Ambipolar Material and Its Building Block Moieties2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 127, p. 14510-14520Article in journal (Refereed)
    Abstract [en]

    The near-edge X-ray absorption fine structure (NEXAFS and X-ray photoelectron (XP) spectra of gas-phase 2,8-bis-(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) and triphenylphosphine oxide (TPPO) have been measured at the S and P L-II,L-III-edge regions. The time-dependent density functional theory (TDDFT) based on the relativistic two-component zeroth-order regular approximation approach has been used to provide an assignment of the experimental spectra, giving the contribution of the spin-orbit splitting and of the molecular-field splitting to the sulfur and phosphor binding energies. Computed XP and NEXAFS spectra agree well with the experimental measurements. In going from dibenzothiophene and TPPO to PPT, the nature of the most intense S 2p and P 2p NEXAFS features are preserved; this trend suggests that the electronic and geometric behaviors of the S and P atoms in the two building block moieties are conserved in the more complex system of PPT. This work enables us to shed some light onto the structure of the P-O bond, a still highly debated topic in the chemical literature. Since the S 2p and P 2p NEXAFS intensities provide specific information on the higher-lying localized sigma*(C-S) and sigma*(P-O) virtual MOs, we have concluded that P 3d AOs are not involved in the formation of the P-O bond. Moreover, the results support the mechanism of negative hyperconjugation, by showing that transitions toward sigma*(P-O) states occur at lower energies with respect to those toward it pi*(P-O) states.

  • 29.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Penazzi, Gabriele
    Univ Bremen, BCCMS, D-28359 Bremen, Germany..
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Frauenheim, Thomas
    Univ Bremen, BCCMS, D-28359 Bremen, Germany..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Controlling Electronic Structure and Transport Properties of Zigzag Graphene Nanoribbons by Edge Functionalization with Fluorine2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 36, p. 21227-21233Article in journal (Refereed)
    Abstract [en]

    In this work, we report a detailed study of the electronic structure and transport properties of mono- and difluorinated edges of zigzag graphene nanoribbons (ZGNR) using density functional theory (DFT). The calculated formation energies at 0 K indicate that the stability of the nanoribbons increases with the increase in the concentration of difluorinated edge C atoms along with an interesting variation of the energy gaps between 0.0 to 0.66 eV depending on the concentration. This gives a possibility of tuning the band gaps by controlling the concentration of F for terminating the edges of the nanoribbons. The DFT results have been reproduced by density functional tight binding method. Using the nonequilibrium Green functional method, we have calculated the transmission coefficients of several mono- and difluorinated ZGNR as a function of unit cell size and degree of homogeneous disorder caused by the random placement of mono and difluorinated C atoms at the edges.

  • 30.
    Bidermane, Ieva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahmadi, S.
    Materialfysik, KTH-Electrum.
    Grazioli, C.
    CNR-IOM, Laboratorio TASC.
    Bouvet, M.
    Institut de Chimie Moléculaire de l’Université de Bourgogne.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mårtensson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Witkowski, N.
    Institut des Nanosciences de Paris, UPMC.
    When the Grafting of Double Decker Phthalocyanines on Si(100)-2 × 1 Partly Affects the Molecular Electronic Structure2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 26, p. 14270-14276Article in journal (Refereed)
    Abstract [en]

    A combined X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the adsorbate interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 × 1 surface. Large molecule–substrate adsorption energies are computed and are found to compete with the molecule–molecule interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.

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  • 31.
    Björneholm, Olle
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ottosson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Öhrwall, Gunnar
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Winter, Bernd
    Unger, Isaak
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Deeper Insight into Depth-Profiling of Aqueous Solutions Using Photoelectron Spectroscopy2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 50, p. 29333-29339Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) is widely used to probe properties such as molecular stoichiometry, microscopic distributions relative to the surface by so-called "depth-profiling", and molecular orientation. Such studies usually rely on the core-level photoionization cross sections being independent of molecular composition. The validity of this assumption has recently been questioned, as a number of gas-phase molecules have been shown to exhibit photon-energy-dependent nonstochiometric intensity oscillations arising from EXAFS-like modulations of the photoionization cross section. We have studied this phenomenon in trichloroethanol in both gas phase and dissolved in water. The gas-phase species exhibits pronounced intensity oscillations, similar to the ones observed for other gas-phase molecules. These oscillations are also observed for the dissolved species, implying that the effect has to be taken into account when performing depth-profiling experiments of solutions and other condensed matter systems. The similarity between the intensity oscillations for gas phase and dissolved species allows us to determine the photoelectron kinetic energy of maximum surface sensitivity, ~100 eV, which lies in the range of pronounced intensity oscillations.

  • 32.
    Björnson, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wills, John Michael
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Alouani, Mebarek
    Univ Strasbourg, Inst Phys & Chim Mat Strasbourg, UMR 7504 CNRS UNISTRA, Strasbourg, France..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ong, Chin Shen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    In Situ Pseudopotentials for Electronic Structure Theory2021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 27, p. 15103-15111Article in journal (Refereed)
    Abstract [en]

    We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn-Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn-Sham equation, to extract the pseudopotential that produces the state generated in steps i-iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na.

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  • 33. Blomquist, J.
    et al.
    Walle, L. E.
    Uvdal, P.
    Borg, A.
    Sandell, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Water Dissociation on Single Crystalline Anatase TiO2(001) Studied by Photoelectron Spectroscopy2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 42, p. 16616-16621Article in journal (Refereed)
    Abstract [en]

    The adsorption of water on the anatase TiO2(001)-(4 x 1) surface is studied using synchrotron radiation-excited core level photoelectron spectroscopy. The coverage-dependent adsorption of water at low temperature is monitored and compared to the sequence obtained after heating of a water multilayer. Two adsorption phases of submonolayer coverage can be defined: Phase 1 consists only of dissociated water, observed as OH-groups. This phase is found at low coverage at low temperature (190 K) and is the only state of adsorbed water above similar to 230 K. The saturation coverage of phase 1 is consistent with dissociation on the 4-fold-coordinated Ti ridge atoms of the (4 x 1) surface reconstruction. Phase 2 is found at higher coverage, reached at lower temperature. It consists of a mixture of dissociated and molecular water with a ratio of 1:1 at 170 K. The molecular water is found to bond to the hydroxyl groups. The hydroxyl coverage of phase 2 is approximately 2 times that of phase 1. The results suggest that the OH and H2O species of phase 2 are confined to the ridges of the surface.

  • 34.
    Borges, J.
    et al.
    Univ Minho, Ctr Fis, Campus Gualtar, P-4710057 Braga, Portugal.;Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, Prague 6, Czech Republic.;Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, Rua Pedro Nunes, P-3030199 Coimbra, Portugal.;Univ Coimbra, SEG CEMUC, Mech Engn Dept, P-3030788 Coimbra, Portugal..
    Pereira, R. M. S.
    Univ Minho, Ctr Fis, Campus Gualtar, P-4710057 Braga, Portugal.;Univ Minho, Ctr Matemat, Campus Gualtar, P-4710057 Braga, Portugal.;Univ Minho, Dept Matemat & Aplicacoes, Campus Gualtar, P-4710057 Braga, Portugal..
    Rodrigues, M. S.
    Univ Minho, Ctr Fis, Campus Gualtar, P-4710057 Braga, Portugal.;Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, Rua Pedro Nunes, P-3030199 Coimbra, Portugal..
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kumar, Saroj
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cavaleiro, A.
    Univ Coimbra, SEG CEMUC, Mech Engn Dept, P-3030788 Coimbra, Portugal..
    Polcar, T.
    Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, Prague 6, Czech Republic.;Univ Southampton, Natl Ctr Adv Tribol Southampton nCATS, Southampton SO17 1BJ, Hants, England..
    Vasilevskiy, M. I.
    Univ Minho, Ctr Fis, Campus Gualtar, P-4710057 Braga, Portugal.;City Univ Hong Kong, Dept Phys & Mat Sci, Hong Kong, Hong Kong, Peoples R China.;City Univ Hong Kong, CFP, Hong Kong, Hong Kong, Peoples R China..
    Vaz, F.
    Univ Minho, Ctr Fis, Campus Gualtar, P-4710057 Braga, Portugal..
    Broadband Optical Absorption Caused by the Plasmonic Response of Coalesced Au Nanoparticles Embedded in a TiO2 Matrix2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 30, p. 16931-16945Article in journal (Refereed)
    Abstract [en]

    The effect of Au nanopattides' (NPs) concentration, site, and spatial distribution within a TiO2 dielectric matrix on the localized surface plasmon resonance (LSPR) band characteristics was experimentally and theoretically studied. The results of the analysis of the Au NPs' size distributions allowed us to conclude that isolated NPs grow only up to 5 to 6 nm in site, even for the highest annealing temperature used. However, for higher volume fractions of Au, the coalescence of closely located NPs yields elongated clusters that are much larger in size and cause a considerable broadening of the LSPR band. This effect was confirmed by Monte Carlo modeling results. Coupled dipole equations were solved to find the electromagnetic modes of a supercell, where isolated and coalesced NPs were distributed, from which an effective dielectric function of the nanocomposite material was calculated and used to evaluate the optical transmittance and reflectance spectra. The modeling results suggested that the observed LSPR band broadening is due to a wider spectral distribution of plasmonic modes, caused by the presence of coalesced NPs (in addition to the usual damping effect). This is particularly important for detection applications via surface-enhanced Raman spectroscopy (SERS), where it is desirable to have a spectrally broad LSPR band in order:to favor the fulfillment of the conditions of resonance matching, to electronic transitions in detected species.

  • 35.
    Boström, Hanna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Max Planck Inst Solid State Res, D-70569 Stuttgart, Germany..
    Kieslich, Gregor
    Tech Univ Munich, Dept Chem, D-85748 Garching, Germany..
    Influence of Metal Defects on the Mechanical Properties of ABX(3) Perovskite-Type Metal-formate Frameworks2021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 2, p. 1467-1471Article in journal (Refereed)
    Abstract [en]

    Defects are emerging as a key tool for fine-tuning the stimuli-responsive behavior of coordination polymers and metal-organic frameworks. Here, we study the ramifications of defects on the mechanical properties of the molecular perovskite [C(NH2)(3)]Mn-II(HCOO)(3) and its defective analogue [C(NH2)(3)]Fe-2/3(III)square(1/3)(HCOO)(3), where q = vacancy. Defects reduce the bulk modulus by 30% and give rise to a temperature-driven phase transition not observed in the nondefective system. The results highlight the opportunities that come with defect-engineering approaches to alter the mechanical properties and underlying thermodynamics, with important implications for the research on stimuli-responsive materials.

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  • 36.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ojamae, Lars
    Surface effects and quantum confinement in nanosized GaN clusters: Theoretical predictions2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 35, p. 13516-13523Article in journal (Refereed)
    Abstract [en]

    The structure and the electronic properties of stoichiometric (GaN)(n) clusters (with 6 < ;= n < ;= 48) were investigated by means of quantum-chemical hybrid density functional theory (DFT) using the B3LYP functional. Particular emphasis was put on the investigation of the evolution of the physical properties of the clusters as a function of their size. Two types of model clusters were studied. Cage-type structures were found to be the most stable for smaller cluster sizes, whereas for larger sizes conformations cut out from the GaN wurtzite crystal were favorable. The study of the electronic structure shows that the energy gap of the clusters tends to become larger as the dimensions of the clusters increase. The vertical electronic absorption energies were calculated by means of time-dependent (TD) DFT. For such small clusters, probably due to the predominant amount of surface atoms, well-defined quantum confinement effects, as commonly observed in crystalline quantum dots, are not apparent.

  • 37.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chemical Switching of the Magnetic Coupling in a MnPc Dimer by Means of Chemisorption and Axial Ligands2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 49, p. 27185-27193Article in journal (Refereed)
    Abstract [en]

    We present an ab initio density functional theory study of the magnetic properties of manganese phthalocyanine dimers, where we focus on the magnetic coupling between the Mn centers and on how it is affected by external factors like chemisorption or atomic axial ligands. We have studied several different configurations for the gas phase dimers, which resulted in ferromagnetic couplings of different magnitudes. For the bare dimer we find a significant ferromagnetic coupling between the Mn centers, which decreases by about 20% when a H atom is adsorbed on one of the Mn atoms and is reduced to about 7% when a Cl atom is adsorbed. The magnetic coupling is almost fully quenched when the dimer, bare or with the H ligand, is deposited on the ferromagnetic substrate Co(001). Our calculations indicate that the coupling between the two Mn atoms principally occurs via a superexchange interaction along two possible paths within a Mn-N-Mn-N four-atom loop. When these electrons get involved in chemical bonding outside the dimer itself, an appreciable alteration of the overlap between Mn and N molecular orbitals along the loop occurs, and consequently, the magnetic interaction between the Mn centers varies. We show that this is reflected by the electronic structure of the dimer in various configurations and is also visible in the structure of the atomic loop. The chemical tuning of the magnetic coupling is highly relevant for the design of nanodevices like molecular spin valves, where the molecules need to be anchored to a support.

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  • 38.
    Brnovic, Andjela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Tian, Haining
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Mechanistic Insights into the Photocatalytic Hydrogen Production of Y5 and Y6 Nanoparticles2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 26, p. 12631-12639Article in journal (Refereed)
    Abstract [en]

    Utilization of solarenergy in organic semiconductorsrelies oncomplicated photophysical processes due to the strong electron-holeinteractions. To gain a better understanding of these processes andtheir effect on the photocatalytic performance of non-fullerene acceptors(NFAs) within nanoparticles (NPs), we compared the excited-state dynamicsand photocatalytic hydrogen production activity of two NFA-based NPs,Y5 and Y6. Our results show that under LED light irradiation, Y5 NPsexhibit 14 times better hydrogen production activity than Y6 NPs.The hydrogen production activity was also evaluated under Xenon lightirradiation (AM1.5G, 100 mW & BULL;cm(-2)) for Y5 NPs,yielding 410 mmol/g after 24 h. Time-resolved spectroscopy experimentsrevealed a longer triplet lifetime for Y5 compared to Y6 NPs, andthe lifetime was reduced upon addition of the electron donor ascorbate.This suggests the involvement of the triplet state in reductive quenchingand better hydrogen evolution reaction performance for Y5 NPs. Thegood agreement between fluorescence and triplet lifetimes observedfor Y5 NPs was attributed to reverse intersystem crossing, which repopulatesthe excited singlet state through thermally activated delayed fluorescence(TADF). The absence of TADF in Y6 NPs could limit its efficiency forhydrogen evolution reaction, in addition to the intrinsically shortertriplet lifetime and reduction potential difference, making it animportant factor to consider in Y series-based NPs.

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  • 39.
    Broqvist, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    van Duin, Adri C. T.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    ReaxFF Force-Field for Ceria Bulk, Surfaces, and Nanoparticles2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 24, p. 13598-13609Article in journal (Refereed)
    Abstract [en]

    We have developed a reactive force-field of the ReaxFF type for stoichiometric ceria (CeO2) and partially reduced ceria (CeO2-x). We describe the parametrization procedure and provide results validating the parameters in terms of their ability to accurately describe the oxygen chemistry of the bulk, extended surfaces, surface steps, and nanoparticles of the material. By comparison with our reference electronic structure method (PBE+U), we find that the stoichiometric bulk and surface systems are well reproduced in terms of bulk modulus, lattice parameters, and surface energies. For the surfaces, step energies on the (111) surface are also well described. Upon reduction, the force-field is able to capture the bulk and surface vacancy formation energies (E-vac), and in particular, it reproduces the E-vac variation with depth from the (110) and (111) surfaces. The force-field is also able to capture the energy hierarchy of differently shaped stoichiometric nanoparticles (tetrahedra, octahedra, and cubes), and of partially reduced octahedra. For these reasons, we believe that this force-field provides a significant addition to the method repertoire available for simulating redox properties at ceria surfaces.

  • 40.
    Butorin, Sergei. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Modin, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vegelius, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Kvashnina, Kristina O.
    European Synchrotron, CS40220, F-38043 Grenoble 9, France.;HZDR, Inst Resource Ecol, POB 510119, D-01314 Dresden, Germany..
    Shuh, David K.
    Lawrence Berkeley Natl Lab, Div Chem Sci, MS 70A1150,One Cyclotron Rd, Berkeley, CA 94720 USA..
    Probing Chemical Bonding in Uranium Dioxide by Means of High- Resolution X-ray Absorption Spectroscopy2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 51, p. 29397-29404Article in journal (Refereed)
    Abstract [en]

    A systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d(3/2) edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the 5f localization in UO2. The results support the covalent character of UO2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.

  • 41.
    Böhme, Solveig
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Photoelectron Spectroscopic Evidence for Overlapping Redox Reactions for SnO2 Electrodes in Lithium-Ion Batteries2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 9, p. 4924-4936Article in journal (Refereed)
    Abstract [en]

    In-house and synchrotron-based photoelectron spectroscopy (XPSand HAXPES) evidence is presented for an overlap between the conversion andalloying reaction during the cycling of SnO2 electrodes in lithium-ion batteries(LIBs). This overlap resulted in an incomplete initial reduction of the SnO2 as wellas the inability to regenerate the reduced SnO2 on the subsequent oxidative scan.The XPS and HAXPES results clearly show that the SnO2 conversion reactionoverlaps with the formation of the lithium tin alloy and that the conversion reactiongives rise to the formation of a passivating Sn layer on the SnO2 particles. The latterlayer renders the conversion reaction incomplete and enables lithium tin alloy toform on the surface of the particles still containing a core of SnO2. The results alsoshow that the reoxidation of the lithium tin alloy is incomplete when the formationof tin oxide starts. It is proposed that the rates of the electrochemical reactions andhence the capacity of SnO2-based electrodes are limited by the lithium masstransport rate through the formed layers of the reduction and oxidations products.In addition, it is shown that a solid electrolyte interphase (SEI) layer is continuously formed at potentials lower than about 1.2 VLi+/Li during the first scan and that a part of the SEI dissolves on the subsequent oxidative scan. While the SEI was found tocontain both organic and inorganic species, the former were mainly located at the SEI surface while the inorganic species werefound deeper within the SEI. The results also indicate that the SEI dissolution process predominantly involves the organic SEIcomponents.

  • 42.
    Cappel, Ute B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Gibson, Elizabeth A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Dye regeneration by spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry.2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 15, p. 6275-6281Article in journal (Refereed)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy is presented as a tool for the systematic study of dye regeneration and pore filling in solid state dye-sensitized solar cells (DSC). Oxidn. potentials and extinction coeffs. for oxidized species of the perylene dye, ID28, on TiO2 and of the hole conductor, 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), were detd. by spectroelectrochem. The onset of oxidn. of a solid film of spiro-MeOTAD was found to be 0.15 V vs. Fc/Fc+ and extinction coeffs. of spiro-MeOTAD+ were found to be 33 000 M-1 cm-1 at 507 nm and 8500 M-1 cm-1 at 690 nm. Electrons in TiO2 films were shown to alter the ground-state absorption spectra of ID28 attached to TiO2. PIA measurements indicated a good contact between ID28 and spiro-MeOTAD for different spiro-MeOTAD concns. for both 2- and 6-micro m thick TiO2 films. We discuss the possibility of estg. the quality of pore filling from the positions of absorption peaks. Results suggested that with a spiro-MeOTAD concn. of 300 mg mL-1 in chlorobenzene, a uniform distribution of spiro-MeOTAD in the pores of the 6-micro m thick TiO2 film could be achieved.

  • 43.
    Cappel, Ute B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Karlsson, Martin H.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Pschirer, G
    Eickemeyer, Felix
    Schoeneboom, Jan
    Erk, Peter
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    A broadly absorbing perylene dye for solid-state dye-sensitized solar cells.2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 33, p. 14595-14597Article in journal (Refereed)
    Abstract [en]

    We present a new perylene sensitizer, ID 176, for dye-sensitized solar cells (DSCs). The dye has the capability for very high photocurrents due to strong absorption from 400 to over 700 rim. Photocurrents Of LIP to 9 mA cm(-2) were achieved in solid-state DSCs employing the hole conductor 2,2'7,7'-tetrakis-(NN-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD), with a conversion efficiency of 3.2%. In contrast, the sensitizer did not perform well in conjunction with liquid iodide/tri-iodide electrolytes, suggesting a difference in the injection and regeneration mechanisms in these two types of dye-sensitized solar cells.

  • 44.
    Cappel, Ute B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Smeigh, Amanda L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Plogmaker, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 10, p. 4345-4358Article in journal (Refereed)
    Abstract [en]

    We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2-,7,7-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.

  • 45.
    Castleton, Christopher W. M.
    et al.
    Nottingham Trent Univ, Sch Sci & Technol, Nottingham NG11 8NS, England;Malardalen Univ, Div Phys & Math Nat Sci Didact, Box 883, SE-72123 Vasteras, Sweden.
    Lee, Amy
    Nottingham Trent Univ, Sch Sci & Technol, Nottingham NG11 8NS, England.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Benchmarking Density Functional Theory Functionals for Polarons in Oxides: Properties of CeO22019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 9, p. 5164-5175Article in journal (Refereed)
    Abstract [en]

    We examine methods for studying polarons in metal oxides with density functional theory (DFT), using the example of cerium dioxide and the functionals, local density approximation + U (LDA+U), generalized gradient approximation + U (GGA+U) in the Perdew-Burke-Ernzerhof parametrization (PBE+U), as well as the hybrid functionals B3LYP, Heyd Scuseria Ernzerhof (HSE)03, HSE06, and PBEO. We contrast the four polaron energies commonly reported in different parts of the literature: formation energy, localization/relaxation energy, density-of-states level, and polaron-hopping activation barrier. Qualitatively, all these functionals predict "small" (Holstein) polarons on the scale of a single lattice site, although LDA +U and GGA+U are more effective than the hybrids at localizing the Ce 4f electrons. The improvements over pure LDA/GGA appear because of changes in the filled Ce 4f states when using LDA/GGA+U but due to changes in the empty Ce 4f states when using the hybrids. DFT is shown to have sufficient correlation to predict both adiabatic and (approximate) diabatic hopping barriers. Overall, LDA+U = 6 eV provides the best description in comparison to the experiment, followed by GGA+U = 5 eV. The hybrids are worse, tending to overestimate the gap and significantly underestimate the polaron-hopping barriers.

  • 46. Chaudhary, Shilpi
    et al.
    Head, Ashley R.
    Sanchez-de-Armas, Rocio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tissot, Heloise
    Olivieri, Giorgia
    Bournel, Fabrice
    Montelius, Lars
    Ye, Lei
    Rochet, Francois
    Gallet, Jean-Jacques
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schnadt, Joachim
    Real-Time Study of CVD Growth of Silicon Oxide on Rutile TiO2(110) Using Tetraethyl Orthosilicate2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 33, p. 19149-19161Article in journal (Refereed)
    Abstract [en]

    The interaction of the ruffle TiO2(110) surface with tetraethyl orthosilicate (TEOS) in the pressure range from UHV to 1 mbar as well as the TEOS-based chemical vapor deposition of SiO2 on the TiO2(110) surface were monitored in real time using near-ambient pressure X-ray photoelectron spectroscopy. The experimental data and density functional theory calculations confirm the dissociative adsorption of TEOS on the surface already at room temperature. At elevated pressure, the ethoxy species formed in the adsorption process undergoes further surface reactions toward a carboxyl species not observed in the absence of a TEOS gas phase reservoir. Annealing of the adsorption layer leads to the formation of SiO2, and an intermediate oxygen species assigned to a mixed titanium/silicon oxide is identified. Atomic force microscopy confirms the morphological changes after silicon oxide formation.

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  • 47.
    Chen, Xin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Liu, Yuhang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Calif Riverside, Dept Elect & Comp Engn, Riverside, CA 92521 USA.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Manipulation of Electronic and Magnetic Properties of 3d Transition Metal (Cr, Mn, Fe) Hexamers on Graphene with Vacancy Defects: Insights from First-Principles Theory2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 7, p. 4270-4278Article in journal (Refereed)
    Abstract [en]

    One of the possible ways to introduce magnetism in graphene is to trap highly mobile transition metal atoms at defect sites in graphene. In this paper, based on Born-Oppenheimer molecular dynamics simulations, we investigated the self-assembly of transition metal hexamers X-6 (X = Cr, Mn, and Fe) on graphene with mono/divacancy defects and studied the fundamental electronic and magnetic properties of the resulting X-6 clusters on graphene. Interestingly, the ground state Cr-6 and Fe-6 hexamers on divacancy defects in graphene show quite small energy differences between in-plane and out-of-plane magnetism. By applying external electric fields, the easy axis of magnetization can be switched between in-plane and out-of-plane, which demonstrates potential applications in electric field-assisted magnetic recording and quantum computing.

  • 48.
    Chien, Yu-Chuan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Menon, Ashok S.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brant, William
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lacey, Matthew
    Scania CV AB.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Understanding the Impact of Precipitation Kinetics on the Electrochemical Performance of Lithium–Sulfur Batteries by Operando X-ray Diffraction2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 6, p. 2971-2979Article in journal (Refereed)
    Abstract [en]

    The complex reaction mechanism of the lithium–sulfur battery system consists of re-petitive dissolution and precipitation of the sulfur-containing species in the positiveelectrode. In particular, the precipitation of lithium sulfide (Li2S) during discharge hasbeen considered a crucial factor for achieving a high degree of active material utiliza-tion. Here, the influence of electrolyte amount, electrode thickness, applied current andelectrolyte salt on the formation of Li2S is systematically investigated in a series ofoperando X-ray diffraction experiments. Through a combination of simultaneous dif-fraction and resistance measurements, the evolution of the intensity from Li2S is di-rectly correlated to the variation in internal resistance and transport properties insidethe positive electrode. The correlation indicates that at different stages, the Li2S precip-itation both facilitates and impedes the discharge process. The kinetic information ofLi2S formation offers mechanistic explanations for the strong impact of different elec-trochemical cell parameters on the performance and thus, directions for holistic optimi-zations to achieve high sulfur utilization.

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  • 49.
    Choi, Jae Won
    et al.
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Lee, Won-Yong
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Solid-State Electronics.
    Kim, Yun-Ho
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Park, No-Won
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Kang, Min-Sung
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Kim, Gil-Sung
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Yoon, Young-Gui
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Lee, Sang-Kwon
    Department of Physics and Center for Berry Curvature Based New Phenomena, Chung-Ang University, Seoul06974, Republic of Korea.
    Observation of a Strong Decoupling Phenomenon in Pt/Si Hybrid Structures for In-Plane Thermoelectric Properties2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 40, p. 17283-17290Article in journal (Refereed)
    Abstract [en]

    The performance of thermoelectric (TE) materials is limited by the intrinsic coupling of the Seebeck coefficient and the electrical conductivity such that an increase in one leads to a decrease in the other with respect to the carrier concentration. This coupling makes it particularly difficult to enhance the TE power factor in TE materials. In this study, we added a Pt top layer over a silicon wafer, forming a hybridized Pt/Si structure to drive a strong decoupling of the Seebeck coefficient and electrical conductivity. The results show that the electrical resistance in the Pt/Si hybrid structure decreased by ∼94 times compared to that of a single-layer lightly doped Si substrate at 300 K, while the Seebeck coefficient in the hybrid structure decreased slightly compared to that of the single layer. The remarkably high TE performance of the Pt/Si hybrid structure is brought about by the hybridization of the intrinsic high-conductivity Pt layer and the high-Seebeck coefficient Si substrate. In addition, we demonstrate that this novel and effective decoupling method enables the assessment of the in-plane intrinsic Seebeck coefficient of a lightly doped Si wafer, which typically has an electrical resistance that is extremely high to measure the Seebeck coefficient even with a high-resolution voltmeter. These results represent a significant advancement in the understanding of electrical transport in TE materials, which will invigorate further research on Si-based devices for realizing large-area watt-scale TE generation at room temperature.

  • 50.
    Choudhuri, Indrani
    et al.
    Indian Inst Technol, Sch Basic Sci, Discipline Chem, Indore 452020, Madhya Pradesh, India..
    Patra, Nandini
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Indian Inst Technol, Ctr Mat Sci & Engn, Indore 452020, Madhya Pradesh, India..
    Mahata, Arup
    Indian Inst Technol, Sch Basic Sci, Discipline Chem, Indore 452020, Madhya Pradesh, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat Sci & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Pathak, Biswarup
    Indian Inst Technol, Sch Basic Sci, Discipline Chem, Indore 452020, Madhya Pradesh, India.;Indian Inst Technol, Ctr Mat Sci & Engn, Indore 452020, Madhya Pradesh, India..
    B-N@Graphene: Highly Sensitive and Selective Gas Sensor2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 44, p. 24827-24836Article in journal (Refereed)
    Abstract [en]

    We have performed density functional theory (DFT) calculations to study the gas (CO, CO2, NO, and NO2) sensing mechanism of pure and doped (B@, N@, and B-N@) graphene surfaces. The calculated adsorption energies of the various toxic gases (CO, CO2, NO, and NO2) on the pure and doped graphene surfaces show, doping improves adsorption energy and selectivity. The electronic properties of the B-N@graphene surfaces change significantly compared to pure and B@ and N@graphene surfaces, while selective gas molecules are adsorbed. So, we report B-N codoping on graphene can be highly sensitive and selective for semiconductor-based gas sensor.

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