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  • 1.
    Antonio Ribeiro, Luiz
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Polaron stability in molecular semiconductors: theoretical insight into the impact of the temperature, electric field and the system dimensionality2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 14, 8973-8982 p.Article in journal (Refereed)
    Abstract [en]

    A semi-empirical Holstein-Peierls model is used to study the temperature effects on the polaron stability in organic semiconductors at a molecular scale. The approach takes into account both intra- and intermolecular electron-lattice interactions and is aimed at describing charge transport in the system. Particularly, we present a systematic numerical investigation to characterize the influence of both temperature and electric field on the stability as well as mobility of the polaron. It is found that the parameter space for which the polaron is dynamically stable is quite limited and the variations in some of these parameters strongly depend on the temperature. The electric field can play a role in further localizing the charge causing a compression of the lattice distortions associated with the polaron, increasing thereby its stability, up to a field strength of approximately 2.0 mV angstrom(-1). Considering field strengths higher than this critical value, the polaron is annihilated spreading charge through the lattice. Furthermore, we have studied the polaron mobility as a function of the anisotropy of the system, going from a one-dimensional system via a highly anisotropic two-dimensional system to a uniform two-dimensional system. There is a clearly observed mobility edge for the polaron; it exhibits a high mobility in the one-dimensional system but as the coupling in the second dimension is turned on the polaron slows down and becomes immobile in the uniform system. The results provided by this transport mechanism are in good agreement with experimental observations and may provide guidance to improve the charge transport in organic optoelectronic devices.

  • 2.
    Barta, P.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zagórska, M.
    Department of Chemistry, Technical University of Warsaw, PL‐00 664 Warsaw, Poland.
    Pron, A.
    Department of Material Science and Ceramics, Academy of Mining and Metallurgy, PL‐30 059 Kraków, Poland.
    Temperature evolution of the electronic band structure of the undoped and doped regioregular analog of poly(3‐alkylthiophenes): A spectroscopic and theoretical study1994In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 100, no 2, 1731-1741 p.Article in journal (Refereed)
    Abstract [en]

    The undoped and ferric chloride p‐doped ‘‘head‐to‐head’’ ‘‘tail‐to‐tail’’ analog of poly(3‐decylthiophene) obtained from substituted bithiophenes, i.e., poly(4,4’didecyl‐2,2’bithiophene)‐PDDBT has been investigated. The samples were studied by means of ultraviolet photoelectron spectroscopy,optical absorption measurements, and polymerbands structure calculations. Experiments were carried out at different temperatures between 100 °C and −180 °C. The results indicate that PDDBT is nonplanar in the undoped state. No temperature effects have been observed in the π‐electron properties. In the doped state, however, lowering of the temperature results in an increase of the system planarity that modifies the electronic band structure. This effect has been shown to be fully reversible with temperature.

  • 3.
    Baughman, R.H.
    et al.
    Honeywell International, Honeywell Technology Center, Morristown, NJ 07962-1021, United States.
    Dantas, S.O.
    Departamento de Física, Universidade Federal de Juiz de Fora, Juiz de Fora, 36036-330, Mina Gerais, Brazil.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Zakhidov, A.A.
    Honeywell International, Honeywell Technology Center, Morristown, NJ 07962-1021, United States.
    Mitchell, T.B.
    Natl. Inst. of Std. and Technology, Boulder, CO 80303, United States.
    Dubin, D.H.E.
    Department of Physics, Univ. of California at San Diego, San Diego, CA 92093, United States.
    Negative Poisson's ratios for extreme states of matter2000In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 288, no 5473, 2018-2022 p.Article in journal (Refereed)
    Abstract [en]

    Negative Poisson's ratios are predicted for body-centered-cubic phases that likely exist in white dwarf cores and neutron star outer crusts, as well as those found for vacuumlike ion crystals, plasma dust crystals, and colloidal crystals (including certain virus crystals). The existence of this counterintuitive property, which means that a material laterally expands when stretched, is experimentally demonstrated for very low density crystals of trapped ions. At very high densities, the large predicted negative and positive Poisson's ratios might be important for understanding the asteroseismology of neutron stars and white dwarfs and the effect of stellar stresses on nuclear reaction rates. Giant Poisson's ratios are both predicted and observed for highly strained coulombic photonic crystals, suggesting possible applications of large, tunable Poisson's ratios for photonic crystal devices.

  • 4.
    Berggren, Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fagerström, Jan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Andersson, Mats
    Chalmers Tekniska Högskola.
    Weman, Helge
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Granström, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Wennerström, O
    Chalmers Tekniska Högskola.
    Hjertberg, T
    Chalmers Tekniska Högskola.
    Controlling inter-chain and intra-chain excitations of a poly(thiophene) derivative in thin films1999In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 304, no 1-2, 84-90 p.Article in journal (Refereed)
    Abstract [en]

    The decay of photoexcitations in polythiophene chains has been studied in solid solutions of the polymer from room temperature to 4 K. A strong blue shift of the emission spectrum is observed in the polymer blend, as compared to the homopolymer. Dispersion of the polythiophene suppresses the non-radiative processes, which are suggested to be correlated to close contacts of polymer chains. Quantum chemistry modeling of the excited state distributed on two chains corroborate this conclusion.

  • 5.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hanke, Felix
    Surface Science Research Centre, University of Liverpool, UK.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Mechanisms of halogen-based covalent self-assembly on metal surfaces2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 15, 5768-5775 p.Article in journal (Refereed)
    Abstract [en]

    We computationally study the reaction mechanisms of halogen-based covalent self-assembly, a major route for synthesizing molecular nanostructures and nanographenes on surfaces. Focusing on biphenyl as a small model system, we describe the dehalogenation, recombination, and diffusion processes. The kinetics of the different processes are also investigated, in particular how diffusion and coupling barriers affect recombination rates. Trends across the periodic table are derived from three commonly used close-packed (111) surfaces (Cu, Ag, and Au) and two halogens (Br and I). We show that the halogen atoms can poison the surface, thus hindering long-range ordering of the self-assembled structures. Finally, we present core-level shifts of the relevant carbon and halogen atoms, to provide reference data for reliably detecting self-assembly without the need for atomic-resolution scanning tunneling microscopy.

  • 6.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Adsorption of large hydrocarbons on coinage metals: a van der Waals density functional study2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 13, 2851-2858 p.Article in journal (Refereed)
    Abstract [en]

    The adsorption of organic molecules onto the close-packed facets of coinage metals is studied, and how accurately adsorption heights can be described by using recent advances of the van der Waals density functional (vdWDF), with optPBE/vdWDF, optB86b/vdWDF, vdWDF2, and rev/vdWDF2 functionals is illustrated. The adsorption of two prototypical aromatic hydrocarbons is investigated, and the calculated adsorption heights are compared to experimental literature values from normal incident X-ray standing wave absorption and a state-of-the-art semi-empirical method. It is shown that both the optB86b/vdWDF and rev/vdWDF2 functionals describe adsorption heights with an accuracy of 0.1 Å, compared to experimental values, and are concluded as reliable methods of choice for related systems.

  • 7.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hanke, Felix
    University of Liverpool.
    Zipping Up: Cooperativity Drives the Synthesis of Graphene Nanoribbons2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 38, 14884-14887 p.Article in journal (Refereed)
    Abstract [en]

    We investigate the cooperative effects controlling the synthesis of a graphene nanoribbon on the Au(111) surface starting from an anthracene polymer using density functional calculations including van der Waals interactions. We focus on the high-temperature cyclodehydrogenation step of the reaction and find that the reaction proceeds by simultaneously transferring two H-atoms from the anthracene units to the Au surface, leaving behind a C C bond in the process. This step is significantly more favorable than the three other potential reaction paths. Moreover, we find that successive dehydrogenations proceed from one end of the polyanthracene and propagate step-by-step through the polymer in a domino-like fashion.

  • 8.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Zhang, Yi-Qi
    Technische Universität München, Garching, Germany.
    Klappenberger, Florian
    Technische Universität München, Garching, Germany.
    Barth, Johannes V.
    Technische Universität München, Garching, Germany.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Unraveling the Mechanism of the Covalent Coupling Between Terminal Alkynes on a Noble Metal2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 6, 3181-3187 p.Article in journal (Refereed)
    Abstract [en]

    The mechanism of the newly reported route for surface-assisted covalent coupling of terminal alkynes on Ag(111) is unraveled by density functional theory based transition state calculations. We illustrate that the reaction path is fundamentally different from the classical coupling schemes in wet chemistry. It is initiated by the covalent coupling between two molecules instead of single-molecule dehydrogenation. The silver substrate is found to play an important role stabilizing the intermediate species by chemical bonds, although it is hardly active electronically in the actual coupling step. The dimer intermediate is concluded to undergo two subsequent dehydrogenation processes expected to be rate-limiting according to the comparatively large barriers, which origin is discussed.

  • 9.
    Brede, Jens
    et al.
    University of Hamburg.
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Kuck, Stefan
    University of Hamburg.
    Schwoebel, Joerg
    University of Hamburg.
    Scarfato, Alessandro
    University of Hamburg.
    Chang, Shih-Hsin
    University of Hamburg.
    Hoffmann, Germar
    University of Hamburg.
    Wiesendanger, Roland
    University of Hamburg.
    Lensen, Roy
    Radboud University Nijmegen.
    Kouwer, Paul H J
    Radboud University Nijmegen.
    Hoogboom, Johan
    Radboud University Nijmegen.
    Rowan, Alan E
    Radboud University Nijmegen.
    Broering, Martin
    University of Marburg.
    Funk, Markus
    University of Marburg.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Zerbetto, Francesco
    University of Bologna.
    Lazzaroni, Roberto
    University of Mons.
    Dynamics of molecular self-ordering in tetraphenyl porphyrin monolayers on metallic substrates2009In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 20, no 27, 275602- p.Article in journal (Refereed)
    Abstract [en]

    A molecular model system of tetraphenyl porphyrins (TPP) adsorbed on metallic substrates is systematically investigated within a joint scanning tunnelling microscopy/molecular modelling approach. The molecular conformation of TPP molecules, their adsorption on a gold surface and the growth of highly ordered TPP islands are modelled with a combination of density functional theory and dynamic force field methods. The results indicate a subtle interplay between different contributions. The molecule-substrate interaction causes a bending of the porphyrin core which also determines the relative orientations of phenyl legs attached to the core. A major consequence of this is a characteristic (and energetically most favourable) arrangement of molecules within self-assembled molecular clusters; the phenyl legs of adjacent molecules are not aligned parallel to each other (often denoted as pi-pi stacking) but perpendicularly in a T-shaped arrangement. The results of the simulations are fully consistent with the scanning tunnelling microscopy observations, in terms of the symmetries of individual molecules, orientation and relative alignment of molecules in the self-assembled clusters.

  • 10.
    Broitman, E.
    et al.
    Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.
    Furlan, Andrej
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zs.
    Res Inst Tech Phys and Mat Sci, H-1525 Budapest, Hungary.
    Tarditi, A M
    Univ Nacl Litoral, RA-3000 Santa Fe, Argentina.
    Gellman, A J
    Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Water adsorption on phosphorous-carbide thin films2009In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 204, no 6-7, 1035-1039 p.Article in journal (Refereed)
    Abstract [en]

    Amorphous phosphorous-carbide films have been considered as a new tribological coating material with unique electrical properties. However, such CPx films have not found practical use until now because they tend to oxidize/hydrolyze rapidly when in contact with air. Recently, we demonstrated that CPx thin films with a fullerene-like structure can be deposited by magnetron sputtering, whereby the structural incorporation of P atoms induces the formation of strongly bent and inter-linked graphene planes. Here, we compare the uptake of water in fullerene-like phosphorous-carbide (FL-CPx) thin films with that in amorphous phosphorous-carbide (a-CPx), and amorphous carbon (a-C) thin films. Films of each material were deposited on quartz crystal substrates by reactive DC magnetron sputtering to a thickness in the range 100-300 nm. The film microstructure was characterized by X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. A quartz crystal microbalance placed in a vacuum chamber was used to measure their water adsorption. Measurements indicate that FL-CPx films adsorbed less water than the a-CPx and a-C ones. To provide additional insight into the atomic structure of defects in the FL-CPx and a-CPx compounds, we performed first-principles calculations within the framework of density functional theory. Cohesive energy comparison reveals that the energy cost formation for dangling bonds in different configurations is considerably higher in FL-CPx than for the amorphous films. Thus, the modeling confirms the experimental results that dangling bonds are less likely in FL-CPx than in a-CPx and a-C films.

  • 11.
    Broitman, E
    et al.
    Carnegie Mellon University.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Furlan, Andrej
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Son, Tien Nguyen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gellman, A J
    Carnegie Mellon University.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman , Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Water adsorption on fullerene-like carbon nitride overcoats2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 3, 1106-1110 p.Article in journal (Refereed)
    Abstract [en]

    Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous carbon nitride (a-CNx) films, widely used as protective overcoats in computer disk drive systems, with fullerene-like carbon nitride (FL-CNx) and amorphous carbon (a-C) films. Films with thickness in the range 10-300 run were deposited on quartz crystal substrates by reactive DC magnetron sputtering. A quartz crystal microbalance placed in a vacuum chamber was used to measure the water adsorption. Electron paramagnetic resonance (EPR) has been used to correlate water adsorption with film microstructure and surface defects (dangling bonds). Measurements indicate that the amount of adsorbed water is highest for the pure a-C films and that the FL-CNx films adsorbed less than a-CNx. EPR data correlate the lower water adsorption on FL-CNx films with a possible lack of dangling bonds on the film surface. To provide additional insight into the atomic structure of defects in the FL-CNx, a-CNx and a-C compounds, we performed first-principles calculations within the framework of Density Functional Theory. Emphasis was put on the energy cost for formation of vacancy defects and dangling bonds in relaxed systems. Cohesive energy comparison reveals that the energy cost formation for dangling bonds in different configurations is considerably higher in FL-CNx than for the amorphous films. These simulations thus confirm the experimental results showing that dangling bonds are much less likely in FL-CNx than in a-CNx and a-C films.

  • 12.
    Böhlin, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hansson, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics.
    Electronic structure calculations of the phenalenyl-based neutral radical conductor bis(9-cyclohexylimino-1-phenalenyl) boron2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 15Article in journal (Refereed)
    Abstract [en]

    The solid state of free radicals of bis(9-cyclohexylimino-1-oxyphenalenyl) boron is one of few neutral molecular systems which exhibit high conductivity at room temperature. The system is crystalline but highly anistotropic. We have performed band structure calculations based on the density functional theory on this system. It is evident from these studies that the system is quasi-one-dimensional with strong intermolecular interactions along one crystal direction. The bandwidth is 0.424 eV along this direction as compared to 0.055 eV perpendicular to it. Despite the quasi-one-dimensional character of the system, no signature of a Peierls distortion towards a dimerized state is observed. We argue that this is due to the fact that the Fermi energy lies slightly below the middle of the conduction band. In this case the electronic driving force for the distortion to occur is weakened and overcome by the restoring force of the lattice. Also the optical properties of the system have been investigated and the origin of the low lying excitations in the system has been clarified.

  • 13.
    Böhlin, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Linares, M
    Royal Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Effect of dynamic disorder on charge transport along a pentacene chain2011In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 83, no 8, 085209- p.Article in journal (Refereed)
    Abstract [en]

    The lattice equation of motion and a numerical solution of the time-dependent Schrodinger equation provide us with amicroscopic picture of charge transport in highly ordered molecular crystals. We have chosen the pentacene single crystal as a model system, and we study charge transport as a function of phonon-mode time-dependent fluctuations in the intermolecular electron transfer integral. For comparison, we include similar fluctuations also in the intramolecular potentials. The variance in these energy quantities is closely related to the temperature of the system. The pentacene system is shown to be very sensitive to fluctuation in the intermolecular transfer integral, revealing a transition from adiabatic to nonadiabatic polaron transport for increasing temperatures. The extension of the polaron at temperatures above 200 K is limited by the electron localization length rather than the interplay between the electron transfer integral and the electron-phonon coupling strength.

  • 14.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Boman, Magnus
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Fredriksson, C.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Zamboni, R.
    Istituto di Spettroscopia Molecolare, CNR, Bologna, Italy.
    Taliani, C.
    Istituto di Spettroscopia Molecolare, CNR, Bologna, Italy.
    The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors1993In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 99, no 1, 664-672 p.Article in journal (Refereed)
    Abstract [en]

    We have investigated the chemical nature and the electronic structure of the interface between a low work function metal,aluminum, and a conjugated polymersemiconductor, polythiophene. We have studied the initial stages of the interface formation by depositing the metal onto the surface of a polymer film. Charge transfer processes between the metal and the polymer are analyzed using core‐level x‐ray photoelectron spectroscopy (XPS); the evolution upon metallization of the valence electronic levels directly related to the polymerelectronic structure is followed with ultraviolet photoelectron spectroscopy (UPS). With these techniques, we investigate the deposition of aluminum on two polythiophene systems (i) the alkyl‐substituted poly‐3‐octylthiophene and (ii) the α‐sexithiophene oligomer. The experimental data are compared to the results of a recent quantum chemical study on model systems consisting of thiophene oligomers (up to sexithiophene) interacting with a few Al atoms. The interaction of polythiophene with Al atoms is found to modify dramatically the structure of the conjugated backbone, as strong carbon–aluminum bonds are formed in the α positions of the thiophene rings. A large charge transfer takes place from the Al atoms to the polymer chain, and the upper π levels of the polymer are strongly affected. The metallization is contrasted to the doping of conjugated polymers with alkali metals

  • 15.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Boman, Magnus
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Fredriksson, C.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Graham, S.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Friend, R. H.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Holmes, A. B.
    University Chemical Laboratory, Lensfield road, Cambridge, UK.
    Zamboni, R.
    Instituto di Spettroscopia Molecolare, Bologna, Italy.
    Taliani, C.
    Instituto di Spettroscopia Molecolare, Bologna, Italy.
    Proceedings of the International Conference on Science and Technology of Synthetic Metals The chemical and electronic structure of the interface between aluminum and conjugated polymers or molecules1993In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 55, no 1, 212-217 p.Article in journal (Refereed)
    Abstract [en]

    The interaction between aluminum and α-ω-diphenyltetradecaheptaenee (DP7), α-sexithienyl (6T), and poly(p-phenylenevinylene) (PPV), respectively have been studied using both X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The UPS valence band spectra, are interpreted with the help of quantum chemical calculations based upon Modified Neglect of Diatomic Overlap (MNDO), Valence Effective Hamitonian (VEH) and ab initio Hartree-Fock methods. DP7 is a model molecule for polyacetylene, while 6T is a model molecule (an oligomer) of polythiophene. The results indicate that aluminum reacts strongly with the surfaces of all of the materials studied. The π-electronic structure of each material was strongly modified. Furthermore, aluminum reacts preferentially with the polyene partof DP7, with the vinylene part of PPV, and with the α-carbons of the thiophene nits of 6T.

  • 16.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lögdlund, Michael
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Fauquet, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Spangler, C. W.
    Department of Chemistry, Northern Illinois University, Dekalb, Illinois 60115, USA.
    Bredás, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Reactions of low work function metals Na, Al, and Ca on α,ω-€diphenyltetradecaheptaene. Implications for metal/polymer interfaces1994In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 100, no 9, 6765-6771 p.Article in journal (Refereed)
    Abstract [en]

    The interactions between different low work function metals aluminium,calcium and sodium, and α,ω‐diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π‐electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic‐like defect for Ca/DP7.

  • 17.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holmes, A. B.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Brown, A.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Graham, S.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Friend, R. H.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Lhost, O.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    New Results on Metal-Polymer Interfaces1993In: Molecular Crystals and Liquid Crystals, ISSN 1542-1406, E-ISSN 1563-5287, Vol. 228, no 1, 43-48 p.Article in journal (Refereed)
    Abstract [en]

    New results on studies of the early stages of formation of the aluminum-poly(p-phenylenevinylene) interface are presented.

  • 18.
    Demeyu, Lemi
    et al.
    Department of Physics Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics.
    Monte Carlo simulation of controlled charge carriers diffusion in highly ordered iodine doped pentacene film2007In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 204, no 10, 3545-3555 p.Article in journal (Refereed)
  • 19.
    Fauquet, C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bourée, J. E.
    CNRS, Laboratoire de Meudon, Meudon, France.
    Brillaud, P.
    SMI Organometallics Division, 13 000 Marseille, France.
    Bouanah, N.
    SMI Organometallics Division, 13 000 Marseille, France.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electronic structure of trimethylamine alane in the solid state1995In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 235, no 5-6, 528-534 p.Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of ultrathin molecular films of trimethylamine alane (TMAA), condensed in UHV at − 100°C, have been studied in the solid state, using both X-ray and ultraviolet photoelectron spectroscopy. The results are analyzed with the help of quantum chemical calculations at the ab initio Hartree-Fock 6-31G∗ level. Based upon the good agreement between theory and experimental, it is determined that clean, oxygen-free, condensed molecular solid films consist of the 2:1 adduct of TMAA, which was previously uncertain. In addition, based upon the electronic structure results, it is clear that the mechanism of the photodecomposition of TMAA can be explained in terms of the wavefunction of electrons photoexcited into the first unoccupied molecular orbital.

  • 20.
    Freitas, R R Q.
    et al.
    University of Federal Bahia, Brazil .
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    de Brito Mota, F
    University of Federal Bahia, Brazil .
    de Castilho, C M C.
    University of Federal Bahia, Brazil .
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Reactivity of adducts relevant to the deposition of hexagonal BN from first-principles calculations2013In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 583, 119-124 p.Article in journal (Refereed)
    Abstract [en]

    First-principles calculations, which also implement the nudged elastic band (NEB) code, are performed to investigate (i) the stability of the (C2H5)(3)B:NH3 adduct formed by the initial precursor molecules triethylborane (C2H5)(3)B and ammonia NH3 in the metal-chemical-vapor-deposition (MOCVD) of hexagonal BN, and (ii) the energy barrier to the first ethane elimination through consistent unimolecular, ammonia-assisted, and adduct-assisted reaction pathways. Comparison is done with the reference case of the (CH3)(3)Al:NH3 adduct, notoriously known for its high degree of stability and reactivity, which determines an overall severe parasitic gas-phase chemical reaction mechanism in the deposition of AlN.

  • 21.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Pickholz, M.
    Keil, M.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    High intercalation levels in lithium perylene stoichiometric compounds2002In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 354, no 5-6, 389-394 p.Article in journal (Refereed)
    Abstract [en]

    Both amorphous and polycrystalline films of the aromatic hydrocarbon perylene are found to accept as high as one lithium per 3.3±0.1 carbon atoms. Phases composed of stoichiometric compounds with two, four and six lithium atoms per molecule are observed. The intercalation involves a substantial charge transfer from the lithium atoms to the molecules. Moreover, a high binding energy of the dopant-induced valence band electronic states is observed by photoelectron spectroscopy. Those observations suggest a high energy storage capacity for small- and medium-size aromatic hydrocarbons and their potential use in batteries. © 2002 Elsevier Science B.V. All rights reserved.

  • 22.
    Furlan, Andrej
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigány, Zsolt
    Research Institute for Technical Physics and Materials Science, P.O. Box 49, Budapest, Hungary.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Synthesis of phosphorus-carbide thin films by magnetron sputtering2008In: physica status solidi (RRL) - Rapid Research Letters, ISSN 1862-6254, Vol. 2, no 4, 191-193 p.Article in journal (Refereed)
    Abstract [en]

    Phosphorus-carbide, CPx (0.025≤x≤0.1) thin films have beensynthesized by magnetron sputtering from pressed graphite-phosphorustargets. The films were characterized by X-ray photoelectron spectroscopy,transmission electron microscopy and diffraction, andnanoindentation. CP0.02 exhibits C-P bonding in an amorphous structure with elements of curved grapheneplanes, yielding a material with unique short range order. These features are consistent with what has been predicted by our results of theoreticallymodeled synthetic growth of CPx. The films are mechanicallyresilient with hardness up to 24 GPa and elastic recovery upto 72%.

  • 23.
    Furlan, Andrej
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Fullerene–like CPx: A first–principles study of the relative stability of precursors and defect energetics during synthetic growth2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 3, 1028-1032 p.Article in journal (Refereed)
    Abstract [en]

    Inherently nanostructured CPx compounds were studied by first-principles calculations. Geometry optimizations and cohesive energy comparisons show stability for C3P, C2P, C3P2, CP, and P4 (P2) species in isolated form as well as incorporated in graphene layers. The energy cost for structural defects, arising from the substitution of C for P and intercalation of P atoms in graphene, was also evaluated. We find a larger curvature of the graphene sheets and a higher density of cross-linkage sites in comparison to fullerene-like (FL) CNx, which is explained by differences in the bonding between P and N. Thus, the computational results extend the scope of fullerene-like thin film materials with FL-CPx and provide insights for its structural properties.

  • 24. Gisslen, L.
    et al.
    Johansson, Agneta
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Molecular genetics .
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Charge and energy dynamics in photo-excited poly(para-phenylenevinylene) systems2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 3, 1601-1608 p.Article in journal (Refereed)
    Abstract [en]

    The results from simulations of charge and energy dynamics in poly(para-phenylenevinylene) (PPV) and PPV interacting with C60 were reported. The time-dependent Schrödinger equation and the lattice equation of motion simultaneously and nonadiabatically solved for performing these simulations. The electronic system and the coupling of the electrons to the lattice were described by an extended three-dimensional version of the Su-Schrieffer-Heeger model. The simulation of electron and lattice dynamics following an electronic excitations at different energies was also presented. The results show that both exciton diffusion and transitions from high to lower lying excitations were stimulated by increasing the lattice energy.

  • 25.
    Goyenola, Cecilia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Fullerene-like CSx: A first-principles study of synthetic growth2011In: CHEMICAL PHYSICS LETTERS, ISSN 0009-2614, Vol. 506, no 1-3, 86-91 p.Article in journal (Refereed)
    Abstract [en]

    Fullerene-Like (FL) Sulpho-Carbide (CSx) compounds have been addressed by first principles calculations. Geometry optimization and cohesive energy results are presented for the relative stability of precursor species such as C2S, CS2, and C2S2 in isolated form. The energy cost for structural defects, arising from the substitution of C by S is also reported. Similar to previously synthesized FL-CNx and FL-CPx compounds, the pentagon, the double pentagon defects as well as the Stone-Wales defects are confirmed as energetically feasible in CSx compounds.

  • 26.
    Goyenola, Cecilia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Structural Patterns Arising during Synthetic Growth of Fullerene-Like Sulfocarbide2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 39, 21124-21131 p.Article in journal (Refereed)
    Abstract [en]

    Carbon-based fullerene-like (FL) solid compounds are a new class of materials with extraordinary mechanical properties, which can be tuned by the dopant choice and its concentration. In this work, FL sulfocarbide (CSx) was studied by DFT simulations during synthetic growth with CmSn (m, n andlt;= 2). The energetic and structural effects of S atoms at C sites in a graphene-like network were addressed by geometry optimizations and cohesive energy calculations. Results showed that for S concentrations lower than 10 at. %, smoothly bent pure hexagonal networks predominate. For higher S concentrations, the higher defect concentration leads to stronger deformation of the graphene-like sheets. It was determined that FL-CSx is well-structured (not amorphous) for S contents between 10 and 20 at. %. In contrast to other FL materials, bond rotation mechanisms are not expected to play any significant role during FL-CSx formation, and cross-linking sites are less frequent and may be assimilated in the planar structure during growth. Both quasi-planar networks and cage-like conformations were found to form during the synthetic growth of CSx. The detailed analysis of how CSx structural patterns form during its synthetic growth provides a realistic picture for the deposition of this novel compound by magnetron sputtering.

  • 27.
    Goyenola, Cecilia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Carbon Fluoride, CFx: Structural Diversity as Predicted by First Principles2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 12, 6514-6521 p.Article in journal (Refereed)
    Abstract [en]

    Fluorinated carbon-based thin films offer a wide range of properties for many technological applications that depend on the microstructure of the films. To gain a better understanding of the role of fluorine in the structural formation of these films, CFx systems based on graphene-like fragments were studied by first-principles calculations. Generally, the F concentration determines the type of film that can be obtained. For low F concentrations (up to similar to 5 at. %), films with fullerene-like as well as graphite-like features are expected. Larger F concentrations (greater than= 10 at. %) give rise to increasingly amorphous carbon films. Further increasing the F concentration in the films leads to formation of a polymer-like microstructure. To aid the characterization of CFx systems generated by computational methods, a statistical approach is developed.

  • 28.
    Gueorguiev, G.K.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Neidhardt, Jörg
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    First-principles calculations on the role of CN precursors for the formation of fullerene-like carbon nitride2005In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 401, no 1-3, 288-295 p.Article in journal (Refereed)
    Abstract [en]

    First-principles calculations were utilized to study the formation mechanisms of the fullerene-like structure in carbon nitride compounds in the context of aligned incorporation of CN precursors along edges of evolving sheets during vapor phase synthesis. The incorporation of CN dimers and cyanogen molecules promotes an initial stabilization of pentagon defects, necessary for the observed bending of graphene multilayers in these compounds. The theoretical results corroborate recent experimental findings suggesting that preformed CxNy species, besides C and N atoms and ions, play an important role during the growth of FL CNx thin films by reactive magnetron sputtering. © 2004 Elsevier B.V. All rights reserved.

  • 29.
    Gueorguiev, Gueorgui Kostov
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Furlan, Andrej
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    First–principles calculations on the structural evolution of solid fullerene–like CPx2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 426, no 4-6, 374-379 p.Article in journal (Refereed)
    Abstract [en]

    The formation and structural evolution of fullerene-like (FL) carbon phosphide (CPx) during synthetic growth were studied by first-principles calculations. Geometry optimizations and comparison between the cohesive energies suggest stability for solid FL-CPx compounds. In comparison with fullerene-like carbon nitride, higher curvature of the graphene sheets and higher density of cross-linkages between them is predicted and explained by the different electronic properties of P and N. Cage-like and onion-like structures, both containing tetragons, are found to be typical for fullerene-like CPx. Segregation of P is predicted at fractions exceeding ~20 at.%.

  • 30.
    Gueorguiev, Gueorgui Kostov
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Neidhardt, Jörg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    First-principles calculations on the curvature evolution and cross-linkage in carbon nitride2005In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 410, no 4-6, 228-234 p.Article in journal (Refereed)
    Abstract [en]

    First-principles calculations were utilized to study the formation mechanisms and structural features of fullerene-like carbon nitride (FL CN x). Cohesive energy comparisons reveal the energy cost for different defects arising from substitution of C for N as a function of the nitrogen concentration. In FL CNx, combinations of pentagons and heptagons compete in causing graphene sheet curvature during the addition of CN-precursors and single species. Also, cross-linkage between graphene layers in FL CNx can be explained by the bond rotation due to incorporated N atoms. The computational results agree with recent experimental observations from the growth of FL CNx thin films. © 2005 Elsevier B.V. All rights reserved.

  • 31.
    Gueorguiev, Gueorgui Kostov
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Pacheco, J.M.
    Centro de Física Teórica e Computacional, Departamento de Física, Faculdade de Ciências, Av. Prof. Gama Pinto 2, P-1649-003 Lisboa Codex, Portugal.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Silicon-metal clusters: Nano-templates for cluster assembled materials2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 3, 1192-1196 p.Article in journal (Refereed)
    Abstract [en]

    The structure, cohesive energy and electronic properties of MSin clusters were studied by first-principles calculations as a function of size (n) and species (M). We investigated 168 different clusters, containing from 1 to 14 Si atoms together with one transition metal atom among 12 different elements: Ti, Zr, Hf, V, Nb, Ta, Ni, Pd, Pt, Cu, Ag, Au. Clusters with n = 7, 10, 12 appear as local maxima in cohesive energy, independently of the metal involved. This, together with our previous findings for MSin (containing 12 other transition metal elements), establishes a systematic behavior. For most metals, MSi12 and MSi10 (the smallest endohedral species) are highly symmetric and exhibit local (with respect to their neighbors in size) stability. Thus, besides practically all MSi12 clusters (exceptions being HfSi12, ZrSi12), also some MSi10 such as VSi10, NiSi10, PdSi10, NbSi10 and AgSi10, are promising candidates as building blocks for cluster assembled materials. Electronic properties of structurally equivalent clusters depend markedly on the transition metal involved, providing the means to tailor pre-defined properties when designing extended phases. © 2006 Elsevier B.V. All rights reserved.

  • 32.
    Gueorguiev, Gueorgui Kostov
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Nano-wire formation by self-assembly of silicon-metal cage-like molecules2008In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 458, no 1-3, 170-174 p.Article in journal (Refereed)
    Abstract [en]

    By using DFT calculations we show that nano-wires consisting of endohedral MSi12 cage-like molecules are stable especially for light transition metal elements (M = Fe, Ni, Co, Ti, V, and Cu). The nano-wire assemblies are stabilized by the metal atoms located along their principal axes and can be seen as close Si-based analogues of C nanotubes, but with hexagonal cross-section due to the D6h-symmetry of their MSi12 building blocks. Independently on M, with the increase in the length of a (MSi12)m nano-wire, its HOMO-LUMO gap decreases gradually. The metallic behavior of (MSi12)m defines them as possible conductive components for self-assembled nano-devices. © 2008 Elsevier B.V. All rights reserved.

  • 33.
    Hansson, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Böhlin, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Structural and electronic transitions in potassium doped pentacene2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 18Article in journal (Refereed)
    Abstract [en]

    We calculate the ground state geometrical structure of potassium-intercalated pentacene lattices using molecular mechanics and the density-functional theory. Both methods result in a structural phase transition in going from the pristine form to the intercalated state with one potassium ion per pentacene molecule. The phase transition is characterized by a sliding of adjacent pentacene molecules relative to each other. The electronic properties of this phase is studied with the density-functional theory. As a result of the geometrical changes, the - overlap in the direction perpendicular to the molecular planes of the layered pristine pentacene structure increases substantially and many of the electronic bands show strong dispersion in this direction. The Fermi energy of the doped phase appears in the middle of the conduction band where the density of states is maximum. The bandwidth of the conduction band is 0.7  eV.

  • 34.
    Hansson, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Paulsson, Magnus
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Effect of bending and vacancies on the conductance of carbon nanotubes2000In: Physical Review B, ISSN 1050-2947, Vol. 62, no 11, 7639-7644 p.Article in journal (Refereed)
    Abstract [en]

    Electron transport through nanotubes is studied theoretically using the Landauer formalism. The studies are carried out for finite metallic nanotubes that bridge two contacts pads. The current is observed to increase stepwise with the applied voltage. Each step corresponds to resonance tunneling including one single-particle eigenstate of the nanotube. Moderate bending of the nanotube results in a shift of the single-particle levels but the overall current remains essentially unaffected. For large bending, however, the π electron system becomes more disturbed, which introduces backscattering and a marked decrease in the conductivity along the tube. A single carbon vacancy in the nanotube is shown to have very small effect on the conductivity in the center of the metallic band whereas, by increasing the defect concentration the conductivity decreases in the same way as for the strongly bent tubes.

  • 35.
    Hansson, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Electronic structure calculations of potassiumintercalated single-walled carbon nanotubes2005In: Physical Review B, ISSN 1050-2947, Vol. 72, no 12, 125420-125428 p.Article in journal (Refereed)
    Abstract [en]

    We present results from density-functional theory calculations on the geometrical and electronic structure of potassium-intercalated (4,4) armchair and (7,0) zigzag single-walled carbon nanotubes. Intercalation of potassium results in notable changes in the geometrical structure, in particular in the zigzag system in which the carbon–carbon bond lengths in the unit cell vary between 1.40 Å and 1.45 Å. The most prominent effect of K intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from potassium to the carbon nanotube. In the case of the potassium-intercalated (7,0) nanotube the band structure and the position of the Fermi energy indicate a very good metallic conductor. The (4,4) nanotube has the potential to become superconducting due to the very high density of states at the Fermi energy which is obtained at high intercalation densities.

  • 36.
    Hansson, Anders
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Elwctronic structure calculations of potassium intercalated single-wall carbon nanotubes - Poster2005In: International Conference on the Science and Application of Nanotubes,2005, 2005Conference paper (Other academic)
  • 37.
    Hansson, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Intershell conductance in multiwall carbon nanotubes2003In: Physical Review B, ISSN 1050-2947, Vol. 67, no 7, 075406- p.Article in journal (Refereed)
    Abstract [en]

    A computational study of the electron transport properties of multiwall carbon nanotubes (MWNT’s) is presented. The study is focused on the role of intershell interactions and the resistance associated with transport between neighboring shells. The tight-binding approximation is used to describe finite double-wall nanotubes [(10,10)@(5,5)] connected to two semi-infinite metallic leads. The current-voltage characteristics are calculated from the multichannel Landauer formula. When contact is made to the outer shell the calculations show that the current is distributed over both coaxial NT’s but the overall resistance is independent if the inner tube is present or not. A device in which the leads are contacted to different coaxial shells of the MWNT (telescopic junction) is also investigated. The resistance of this system depends crucially on the extent of delocalization of the wave functions over several NT’s.

  • 38.
    Hellgren, Niklas
    et al.
    Intel Corporation, Portland Technology Development, RA3-301, 5200 NE Elam Young Parkway, Hillsboro, OR 97124, USA.
    Berlind, Torun
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui K.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Johansson, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Fullerene-like B C N thin films a computational andexperimental study2004In: Materials Science and Engineering B, Vol. 113, no 3, 242-247 p.Article in journal (Refereed)
    Abstract [en]

    Ab initio calculations show that the energy cost for incorporating lattice defects such as pentagons and heptagons is significantly reduced for BCN compared to BN, thus promoting bending of basal planes in these compounds. Boron–carbon–nitride (Bsingle bondCsingle bondN) thin films with a fullerene-like (FL) microstructure were then deposited by dual cathode magnetron sputtering from C and B4C targets. Up to 1 μm thick films were grown at a total gas pressure of 3 mTorr (0.4 Pa) in varying Ar/N2 ratios, and substrate temperatures between 225 and 350 °C. Compositional and microstructural studies were performed using RBS, SEM and HREM, respectively. Depending on the deposition condition, ternary BxCyNz films with fullerene-like microstructure could be prepared in agreement with the calculations within the composition range 0 ≤ x ≤ 53, 15 ≤ y ≤ 62, and 24 ≤ z ≤ 50 at.%. Fullerene-like structures also tend to form at lower temperatures in the case of BCN compared to CN. Nanoindentation measurements show that all BxCyNz films exhibited a highly elastic response independent of elemental composition. In addition, the calculations suggest a driving force for C and BN phase separation.

  • 39. Hjort, M
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Band resonant tunneling in DNA molecules2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 87, no 22, art. no.-228101 p.Article in journal (Refereed)
    Abstract [en]

    The charge migration process in DNA is subject to a lively debate among researchers at the moment, We have performed calculations on poly(G)-poly(C) DNA which substantiate a recent report indicating bandlike conduction for this particular form of DNA. Our results show that both guanine and cytosine give rise to conducting channels along the DNA strands. The conductivity results from the overlap of the pi orbitals along the base stacks. We also demonstrate that the measured increase of the threshold voltage with temperature in poly(G)-poly(C) DNA is the result of electron localization due to the structural disorder following high temperature.

  • 40. Hjort, M
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Disorder-induced electron localization in metallic carbon nanotubes2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 11Article in journal (Refereed)
    Abstract [en]

    Anderson localization in carbon nanotubes has been studied using the transfer matrix method. A new method was developed for which transfer matrices could be obtained for both chiral and achiral tubes. The localization length scales Linearly with the tube diameter but shows no dependence on tube chirality. The conductance in the nanotubes can be significantly altered by functionalization, an effect that could make them applicable as sensors. DOI: 10.1103/PhysRevB.63.113406.

  • 41. Hjort, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Localization in defected chiral carbon nanotubes2001In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 121, no 1-3, 1239-1240 p.Article in journal (Refereed)
    Abstract [en]

    Defects in metallic carbon nanotubes have been studied within the tight binding model using the transfer matrix approach. A newly developed method for obtaining transfer matrices in a general way has been utilized, enabling us to compare nanotubes with various chiralities. The localization length was calculated for a random disorder in the onsite potentials, as well as for a functionalization type of disorder.

  • 42.
    Hjort, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Localization in quasi-one-dimensional systems2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 8, 5245-5250 p.Article in journal (Refereed)
    Abstract [en]

    A general method for obtaining transfer matrices in quasi-one-dimensional systems is presented. We used the method to study Anderson localization in trans-polyacetylene, polyparaphenylene, polyparaphenylene vinylene, and polythiophene. The electron localization length for the polymers as a function of disorder was calculated from the Lyapunov exponents. The polymers are shown to exhibit different sensitivity to disorder, which could be explained in terms of different dimensionality of the polymeric systems. We also give an explanation to the recently observed differences between electron and hole intrachain mobilities in alkoxy derivatives of polyparaphenylene-vinylene, as being a result of the electron-donating nature of the alkoxy substituents.

  • 43.
    Hjort, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Modeling vacancies in graphite via the Huckel method2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 20, 14089-14094 p.Article in journal (Refereed)
    Abstract [en]

    It is known that when irradiating a graphite surface with ions the predominant source of defects are vacancies, Vacancies are also formed in a growing graphite sheer and cannot be filled. The theoretical work that has been carried out so far on the properties of these defects has only involved quite small model systems. Calculations on graphite, or closely related carbon phases like nanotubes, with randomly distributed vacancies require very large systems allowing only the simplest model to be used. We have used the Huckel method to model vacancies, both ordinary and hydrogenated, by fitting the Huckel energy levels to those resulting from a valence effective Namiltonian calculation. The three atoms neighboring a vacancy are treated as pseudo-pi orbitals and our calculations suggest that they together contribute with one extra electron to the system. Using this model optical and electronic properties of a graphite sheet as a function of vacancy density have been calculated.

  • 44.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström , Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Impact of ring torsion dynamics on intrachain charge transport in conjugated polymers2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, 014302- p.Article in journal (Refereed)
    Abstract [en]

    Based on an approach including both the time-dependent Schrodinger equation and an effective Newtons equation for the ionic motion, we study the impact of ring torsion dynamics on the intrachain charge transport process in conjugated polymers. As model systems we have used single chains of poly(para-phenylene-vinylene). Without any external electric field, the dynamics of the phenyl ring torsion is the dominant property controlling intrachain charge propagation. The charge is coupled to both ring torsions and bond lengths distortions, which results in a significantly more localized polaron state than in a planar chain. In the presence of an electric field, the charge can breach the barriers caused by ring torsions, a process that involves nonadiabatic effects and a temporary delocalization of the polaron state.

  • 45.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Impact of ring torsion on the intrachain mobility in conjugated polymers2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 10, 104304- p.Article in journal (Refereed)
    Abstract [en]

    Wehave developed a fully three-dimensional model based on the solutionof the time-dependent Schrödinger equation for studies of polaron mobilityin twisted polymer chains. Variations in ring torsion angles alonga conjugated polymer chain are shown to have a strongeffect on the intrachain charge carrier mobility. An increase inring torsion between two neighboring monomers can cause electron localizationand then result in a transition of the type oftransport from adiabatic polaron drift to nonadiabatic polaron hopping. Inparticular, we show the sensitivity for such a transition inthe case of random variations in the ring torsion anglesalong a poly(phenylene vinylene) chain. The effective energy barrier associatedwith the change in torsion angle also depends on theapplied electric-field strength, and by increasing the field strength atransition back to adiabatic transport can be obtained.

  • 46.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Nonradiative relaxation processes in molecular crystals2008In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 128, no 12, 2019-2026 p.Article in journal (Refereed)
    Abstract [en]

    Internal conversion is the dominant relaxation channel from higher lying excited states in molecular crystals and involves the transfer of energy from the electronic system to the lattice. In this work, we present results from simulations of the nonradiative relaxation process with an emphasis on both intra- and interband transitions. We find the internal conversion process to be strongly nonadiabatic and the associated relaxation time in the case of large energy excitations to be limited by the transitions made between states of different bands.

  • 47.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Polaron dynamics in highly ordered molecular crystals2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 428, no 4-6, 446-450 p.Article in journal (Refereed)
    Abstract [en]

    From a numerical solution of the time-dependent Schrödinger equation and the lattice equation of motion we obtain a microscopic picture of polaron transport in highly ordered molecular crystals in the presence of an external electric field. We have chosen the pentacene single crystal as a model system, but study the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaronic drift process over the regime 20 < J < 120 meV. For intermolecular interaction strengths above 120 meV the polaron is no longer stable and the transport becomes band like.

  • 48.
    Hultman, Lars
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Czigany, Z
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA Meijo Univ, Dept Phys, Japan Sci & Technol Corp, Nagoya, Aichi 4688502, Japan Univ Paris 11, Phys Solides Lab, F-91405 Orsay, France Univ Paris 11, Aime Cotton Lab, F-91405 Orsay, France.
    Neidhardt, Jörg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hellgren, N
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA Meijo Univ, Dept Phys, Japan Sci & Technol Corp, Nagoya, Aichi 4688502, Japan Univ Paris 11, Phys Solides Lab, F-91405 Orsay, France Univ Paris 11, Aime Cotton Lab, F-91405 Orsay, France.
    Brunell, IF
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA Meijo Univ, Dept Phys, Japan Sci & Technol Corp, Nagoya, Aichi 4688502, Japan Univ Paris 11, Phys Solides Lab, F-91405 Orsay, France Univ Paris 11, Aime Cotton Lab, F-91405 Orsay, France.
    Suenaga, K
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA Meijo Univ, Dept Phys, Japan Sci & Technol Corp, Nagoya, Aichi 4688502, Japan Univ Paris 11, Phys Solides Lab, F-91405 Orsay, France Univ Paris 11, Aime Cotton Lab, F-91405 Orsay, France.
    Colliex, C
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA Meijo Univ, Dept Phys, Japan Sci & Technol Corp, Nagoya, Aichi 4688502, Japan Univ Paris 11, Phys Solides Lab, F-91405 Orsay, France Univ Paris 11, Aime Cotton Lab, F-91405 Orsay, France.
    Cross-linked nano-onions of carbon nitride in the solid phase: Existence of a novel C48N12 aza-fullerene2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 87, no 22, art. no.-225503 p.Article in journal (Refereed)
    Abstract [en]

    We report a new fullerenelike material consisting of cross-linked nano-onions of C and N. Growth of the onion shells takes place atom by atom on a substrate surface and yields thin solid films during magnetron sputter deposition. Electron microscopy and energy loss spectroscopy show that the core shell contains up to 20 at. % N corresponding to C48N12 aza-fullerene composition. Nanoindentation of this nanostructured material gives high resilience with hardness 7 GPa, Young's modulus 37 GPa, and complete elastic recovery after loading with 0.5 mN to a depth of 75 nm. Total energy calculations show the stability Of C60-2nN2n aza-fullerenes and suggest the existence of a novel C48N12 molecule.

  • 49.
    Iavicoli, Patrizia
    et al.
    CSIC.
    Xu, Hong
    Katholieke University Leuven.
    Feldborg, Lise N.
    CSIC.
    Linares, Mathieu
    University of Mons.
    Paradinas, Markos
    CSIC.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Ocal, Carmen
    CSIC.
    Len Nieto-Ortega, Be
    University Malaga.
    Casado, Juan
    University Malaga.
    Lopez Navarrete, Juan T.
    University Malaga.
    Lazzaroni, Roberto
    University of Mons.
    De Feyter, Steven
    Katholieke University Leuven.
    Amabilino, David B.
    CSIC.
    Tuning the Supramolecular Chirality of One- and Two-Dimensional Aggregates with the Number of Stereogenic Centers in the Component Porphyrins2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 27, 9350-9362 p.Article in journal (Refereed)
    Abstract [en]

    A synthetic strategy was developed for the preparation of porphyrins containing between one and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds reveal the profound effects of this varying molecular chirality on their supramolecular structure and optical activity. The number of stereogenic centers influences significantly the self-assembly and chiral structure of the aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen bonds induce the formation of an H-aggregate, and circular dichroism measurements and theoretical studies indicate that the compounds self-assemble into helical structures. Both the chirality and stability of the aggregates depend critically on the number of stereocenters. The chiral porphyrin derivatives gelate methylcyclohexane at concentrations dependent on the number and position of chiral groups at the periphery of the aromatic core, reflecting the different aggregation forces of the molecules in solution. Increasing the number of stereogenic centers requires more material to immobilize the solvent, in all likelihood because of the greater solubility of the porphyrins. The vibrational circular dichroism spectra of the gels show that all compounds have a chiral environment around the amide bonds, confirming the helical model proposed by calculations. The morphologies of the xerogels (studied by scanning electron microscopy and scanning force microscopy) are similar, although more fibrous features are present in the molecules with fewer stereogenic centers. Importantly, the presence of only one stereogenic center, bearing a methyl group as the desymmetrizing ligand, in a molecule of considerable molecular weight is enough to induce single-handed chirality in both the one- and two-dimensional supramolecular self-assembled structures.

  • 50.
    Jakobsson, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    A Monte Carlo study of charge transfer in DNA2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 12, 125102- p.Article in journal (Refereed)
    Abstract [en]

    A model describing charge (hole) transport in DNA has been developed. The individual charge transfer steps in the transport process are described by Marcus theory modified to account for electron delocalization over adjacent identical nucleobases. Such a modification, as well as introducing a distance dependence in the reorganization energy, is necessary in order to reach an agreement with the observed transfer rates in well defined model systems to DNA. Using previously published results as a reference for the reorganization energy and with the delocalization described within the Hückel model we obtain an excellent agreement with experimental data.

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