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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, p. 8973-8982Article 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.
    da Cunha, Wiliam Ferreira
    et al.
    Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Quasiparticle description of transition metal dichalcogenide nanoribbons2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 3, article id 035405Article in journal (Refereed)
    Abstract [en]

    An effective two-dimensional real-space model is developed to investigate the nature of charge distribution in nanoribbons of transition metal dichalcogenides. Our description is based on a lattice relaxation endowed tight-binding Hamiltonian with spin-orbit and Hubbard interactions, which is parameterized to describe molybdenum disulfide lattices. As our main finding, we observed that electron-phonon coupling induces the creation of quasiparticles such as polarons in the same fashion as observed in conducting polymers and graphene nanoribbons. These similarities suggest that the charge transport in transition metal dichalcogenides can also be mediated by quasiparticles, which is a fundamental aspect concerning the application of these structures in electronics. We determine a range of possible electron-phonon coupling that correctly describes the system and also the critical value where quasiparticle transport is present. Our findings may have profound consequences on the understanding of the transport mechanism of transition metal dichalcogenides nanoribbons.

  • 3.
    da Cunha, Wiliam Ferreira
    et al.
    University of Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    de Almeida Fonseca, Antonio Luciano
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Brasilia, Brazil.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Reactive Scattering between Excitons and Charge Carriers in Conjugated Polymers2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 41, p. 23451-23458Article in journal (Refereed)
    Abstract [en]

    The temperature influence on the scattering process between an exciton and a positively charged carrier (polaron or bipolaron) is theoretically investigated using a version of the SuSchriefferHeeger (SSH) model modified to include temperature, Coulomb interactions, and an external electric field. In general, it is observed that the products of the reactive scattering are spin independent when thermal effects are taken into account. For the interaction between a polaron and an exciton, the polaron can be annihilated, when subjected to temperatures higher than a critical value, or pass through the exciton maintaining both their consistencies, if a lower temperature regime is considered. Regarding the recombination between a bipolaron and an exciton, it is observed that the bipolaron can be annihilated whereas the exciton dissociates into two trions or into one polaron and one trion. In all cases, the recombination mechanisms depend on a suitable balance between temperature and electric field. These results may extend the knowledge about electroluminescence process in conjugated polymers, thus being of potential use to improve internal quantum efficiency in polymer light-emitting diodes.

  • 4.
    de Sousa, Leonardo Evaristo
    et al.
    Univ Brasilia, Brazil.
    Bueno, Fernando Teixeira
    Univ Brasilia, Brazil.
    da Silva Filho, Demetrio Antonio
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Dynamical exciton decay in organic materials: the role of bimolecular recombination2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 4, p. 1711-1716Article in journal (Refereed)
    Abstract [en]

    Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the materials optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.

  • 5.
    Ferreira da Cunha, Wiliam
    et al.
    University of Brasilia, Brazil .
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Gargano, Ricardo
    University of Brasilia, Brazil .
    Magela e Silva, Geraldo
    University of Brasilia, Brazil .
    Critical temperature and products of intrachain polaron recombination in conjugated polymers2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 32, p. 17072-17080Article in journal (Refereed)
    Abstract [en]

    The intrachain recombination dynamics between oppositely charged polarons is theoretically investigated through the use of a version of the Su-Schrieffer-Heeger (SSH) model modified to include an external electric field, an extended Hubbard model, Coulomb interactions, and temperature effects in the framework of a nonadiabatic evolution method. Our results indicate notable characteristics concerning the polaron recombination: (1) it is found that there exists a critical temperature regime, below which an exciton is formed directly and (2) a pristine lattice is the resulting product of the recombination process, if the temperature is higher than the critical value. Additionally, it is found that the critical electric field regime plays the role of drastically modifying the system dynamics. These facts suggest that thermal effects in the intrachain recombination of polarons are crucial for the understanding of electroluminescence in optoelectronic devices, such as Polymer Light Emitting Diodes.

  • 6.
    Ferreira da Cunha, Wiliam
    et al.
    University of Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Brasilia, Brazil; University of Florida, FL 32611 USA; University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Impurity effects on polaron dynamics in graphene nanoribbons2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 91, p. 171-177Article in journal (Refereed)
    Abstract [en]

    The impurity effects on the dynamics of polarons in armchair graphene nanoribbons are numerically investigated in the scope of a two-dimensional tight-binding approach with lattice relaxation. The results show that the presence of an impurity changes significantly the net charge distribution associated to the polaron structure. Moreover, the interplay between external electric field and the local impurities plays the role of drastically modifying the polaron dynamics. Interestingly, nanoribbons containing mobile polarons are noted to take place even when considering high impurity levels, which is associated with the highly conductive character of the graphene nanoribbons. This investigation may enlighten the understanding of the charge transport mechanism in carbon-based nanomaterials. (C) 2015 Elsevier Ltd. All rights reserved.

  • 7.
    Ferreira Monteiro, Fabio
    et al.
    University of Brasilia, Brazil.
    Lima Azevedo, David
    University of Brasilia, Brazil; University of Brasilia, Brazil.
    Carlos da Silva, Eder
    University of Brasilia, Brazil.
    Ribeiro Jr., Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology. University of Brasilia, Brazil; University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil; University of Brasilia, Brazil.
    Encapsulated beta-carotene in ZnO nanotubes: Theoretical insight into the stabilization dynamics2015In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 636, p. 62-66Article in journal (Refereed)
    Abstract [en]

    The stabilization dynamics of a molecular dye (beta-carotene) encapsulated in single-wall zinc oxide nanotubes (ZnONTs) is theoretically investigated in the scope of molecular dynamics and density functional theory simulations. Our findings show that the beta-carotene encapsulation in ZnONTs is an energetically favorable process. Once encapsulated, this molecular dye remains close to the ZnONT wall, in accordance with recent experimental reports. Interestingly, the interaction between the beta-carotene and ZnONT can form a charge delocalization state, where an amount of charge concentrated on beta-carotene is transferred to ZnONT. (C) 2015 Elsevier B.V. All rights reserved.

  • 8.
    Passos Abreu, Ana Virginia
    et al.
    University of Brasilia, Brazil.
    Fernando Teixeira, Jonathan
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Brasilia, Brazil.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Impact of the Electron-Phonon Interactions on the Polaron Dynamics in Graphene Nanoribbons2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 27, p. 4901-4906Article in journal (Refereed)
    Abstract [en]

    The influence of the electron-phonon (e-ph) interactions on the filed-included polaron dynamics in armchair graphene nanoribbons (GNRs) is theoretically investigated in the scope of a two-dimensional tight-binding model. The results show that the localization of the polaronic charge increases when the strength of e-ph coupling also increases. Consequently, the polaron saturation velocity decreases for higher e-ph coupling strengths. Interestingly, the interplay between the e-ph coupling strength and the GNR width changes substantially the polaron dynamics properties.

  • 9.
    Pereira Junior, Marcelo Lopes
    et al.
    Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Stationary polaron properties in organic crystalline semiconductors2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 5, p. 2727-2733Article in journal (Refereed)
    Abstract [en]

    Polarons play a crucial role in the charge transport mechanism when it comes to organic molecular crystals. The features of their underlying properties - mostly the ones that directly impact the yield of the net charge mobility - are still not completely understood. Here, a two-dimensional Holstein-Peierls model is employed to numerically describe the stationary polaron properties in organic semiconductors at a molecular scale. Our computational protocol yields model parameters that accurately characterize the formation and stability of polarons in ordered and disordered oligoacene-like crystals. The results show that the interplay between the intramolecular (Holstein) and intermolecular (Peierls) electron-lattice interactions critically impacts the polaron stability. Such an interplay can produce four distinct quasi-particle solutions: free-like electrons, metastable polarons, and small and large polarons. The latter governs the charge transport in organic crystalline semiconductors. Regarding disordered lattices, the model takes into account two modes of static disorder. Interestingly, the results show that intramolecular disorder is always unfavorable to the formation of polarons whereas intermolecular disorder may favor the polaron generation in regimes below a threshold for the electronic transfer integral strength.

  • 10.
    Ribeiro Jr, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    da Silva, Gesiel Gomes
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil; Goias Federal Institute of Science and Technology, IFG, Luziânia, Brazil.
    de Sousa Jr, Rafael Timoteo
    Department of Electrical Engineering, University of Brasίlia, Brasίlia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    da Cunha, Wiliam Ferreira
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    Magela e Silva, Geraldo
    Institute of Physics, University of Brasίlia, Brasίlia, Brazil.
    Spin-Orbit Effects on the Dynamical Properties of Polarons in Graphene Nanoribbons2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 1914Article in journal (Refereed)
    Abstract [en]

    The dynamical properties of polarons in armchair graphene nanoribbons (GNR) is numerically investigated in the framework of a two-dimensional tight-binding model that considers spin-orbit (SO) coupling and electron-lattice (e-l) interactions. Within this physical picture, novel polaron properties with no counterparts to results obtained from conventional tight-binding models are obtained. Our findings show that, depending on the systems width, the presence of SO coupling changes the polarons charge localization giving rise to different degrees of stability for the charge carrier. For instance, the joint action of SO coupling and e-l interactions could promote a slight increase on the charge concentration in the center of the lattice deformation associated to the polaron. As a straightforward consequence, this process of increasing stability would lead to a depreciation in the polarons motion by decreasing its saturation velocity. Our finds are in good agreement with recent experimental investigations for the charge localization in GNR, mostly when it comes to the influence of SO coupling. Moreover, the contributions reported here provide a reliable method for future works to evaluate spin-orbit influence on the performance of graphene nanoribbons.

  • 11.
    Ribeiro Junior, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil; University of Brasilia, Brazil.
    Santiago de Brito, Sara
    University of Brasilia, Brazil.
    Henrique de Oliveira Neto, Pedro
    University of Brasilia, Brazil.
    Trap-assisted charge transport at conjugated polymer interfaces2016In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 644, p. 121-126Article in journal (Refereed)
    Abstract [en]

    The trap-assisted charge transport in conjugated polymers is numerically investigated in the framework of a one-dimensional tight-binding model. Our findings show that a polaron trapped within an interchain region can be released migrating between the chains at low temperature regimes. Conversely, a trapped bipolaron cannot be released even considering high temperature values. Interestingly, for systems containing more than one polaron, the formation of trapped states is avoided and there is no charge transfer between the chains. Considering more than one bipolaron, the generation of trapped states occurs and a bipolaron can migrates between the chains. (C) 2015 Elsevier B.V. All rights reserved.

  • 12.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Nonadiabatic dynamics of injected holes in conjugated polymers2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 15, p. 10000-10008Article in journal (Refereed)
    Abstract [en]

    The dynamics of injected holes in short transient times that precede polaron formation is numerically studied in the framework of a tight-binding electron-phonon interacting approach aimed at describing organic one-dimensional lattices. In particular, the direct impact of internal and external factors on the conversion of injected holes into polarons is carefully investigated. The results show that a hole injected at levels lower than the highest occupied molecular orbital forms self-trapped bound structures that can merge spontaneously to form a polaron after, at least, one picosecond. On the other hand, the life-time of such structures substantially decreases (up to a few hundreds of femtoseconds) when the influence of external electric fields, temperature effects and impurities is considered. Importantly, the critical values of the aforementioned factors in promoting the quenching of the self-trapped structures are obtained. These findings may enlighten the understanding of the mechanism of charge carrier generation in Polymer Light Emitting Diodes when several kinds of excitations are present.

  • 13.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    University of Brasilia, Brazil.
    Garganoc, Ricardo
    University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Concentration effects on intrachain polaron recombination in conjugated polymers2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 2, p. 1299-1308Article in journal (Refereed)
    Abstract [en]

    The influence of different charge carrier concentrations on the recombination dynamics between oppositely charged polarons is numerically investigated using a modified version of the Su-Schrieffer-Heeger (SSH) model that includes an external electric field and electron-electron interactions. Our findings show that the external electric field can play the role of avoiding the formation of excited states (polaron-exciton and neutral excitation) leading the system to a dimerized lattice. Interestingly, depending on a suitable balance between the polaron concentration and the electric field strength, the recombination mechanism can form stable polaron-excitons or neutral excitations. These results may provide guidance to improve the electroluminescence efficiency in Polymer Light Emitting Diodes.

  • 14.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Florida, FL 32611 USA; University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Temperature effects on intrachain recombination of bipolarons in conjugated polymers2014In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 614, p. 151-155Article in journal (Refereed)
    Abstract [en]

    The temperature influence over the intrachain recombination dynamics between oppositely charged bipolarons has been theoretically investigated using a version of the Su-Schrieffer-Heeger model. The results shown that, below of a critical temperature regime, these charge carriers can recombine into a biexciton. This excited state is a light emissive specie that can emit one photon and turn into an exciton state. This specie can thereafter decay to the ground state by other photon emission. This knowledge can enlighten the understanding needed to improve the internal quantum efficiency of electroluminescence in Polymer Light Emitting Diodes.

  • 15.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Bloch oscillations in organic and inorganic polymers2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 14, article id 144903Article in journal (Refereed)
    Abstract [en]

    The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations. These critical electric fields are considerably smaller for inorganic lattices in comparison to organic polymers. Interestingly, for inorganic lattices, the free electron propagates preserving charge and spin densities localization which is a characteristic of a static polaron. Moreover, in the turning points of the spatial Bloch oscillations, transient polaron levels are formed inside the band gap, thus generating a fully characterized polaron structure. For the organic case, on the other hand, no polaron signature is observed: neither in the shape of the distortion-those polaron profile signatures are absent-nor in the energy levels-as no such polaron levels are formed during the simulation. These results solve controversial aspects concerning Bloch oscillations recently reported in the literature and may enlighten the understanding about the charge transport mechanism in polymers above their mobility edge. Published by AIP Publishing.

  • 16.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Transport of Polarons in Graphene Nanoribbons2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 3, p. 510-514Article in journal (Refereed)
    Abstract [en]

    The field-induced dynamics of polarons in armchair graphene nanoribbons (GNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model with lattice relaxation. Our findings show that the semiconductor behavior, fundamental to polaron transport to take place, depends upon of a suitable balance between the GNR width and the electronphonon (eph) coupling strength. In a similar way, we found that the parameter space for which the polaron is dynamically stable is limited to an even narrower region of the GNR width and the eph coupling strength. Interestingly, the interplay between the external electric field and the eph coupling plays the role to define a phase transition from subsonic to supersonic velocities for polarons in GNRs.

  • 17.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil .
    Magela e Silva, Geraldo
    University of Brasilia, Brazil .
    Temperature Effects on the Scattering of Polarons and Bipolarons in Organic Conductors2014In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 32, p. 6272-6277Article in journal (Refereed)
    Abstract [en]

    The scattering process between an electron-polaron and a hole-bipolaron has been simulated using a version of the Su-Schrieffer-Heeger (SSH) model modified to include an external electric field, Coulomb interactions, and temperature effects in the scope of nonadiabatic molecular dynamics. The simulations reveal remarkable details concerning the polaron-bipolaron recombination reaction. It is found that there exists a critical temperature regime below which a hole-bipolaron and a mixed state composed by an electron-polaron and an exciton are formed and a hole-bipolaron and a free electron are the resulting products of the collisional process, if the temperature is higher than the critical value. In addition, it is obtained that both channels depend sensitively on the strength of the applied electric field. These significant results may provide guidance to understand processes regarding electro-luminescence in polymer diodes.

  • 18.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Monteiro, Fabio Ferreira
    Univ Brasilia, Brazil.
    da Cunha, Wiliam Ferreira
    Univ Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Charge Carrier Scattering in Polymers: A New Neutral Coupled Soliton Channel2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6595Article in journal (Refereed)
    Abstract [en]

    The dynamical scattering of two oppositely charged bipolarons in non-degenerate organic semiconducting lattices is numerically investigated in the framework of a one-dimensional tight-biding-Hubbard model that includes lattice relaxation. Our findings show that it is possible for the bipolaron pair to merge into a state composed of a confined soliton-antisoliton pair, which is characterized by the appearance of states within less than 0.1 eV from the Fermi level. This compound is in a narrow analogy to a meson confining a quark-antiquark pair. Interestingly, solitons are quasi-particles theoretically predicted to arise only in polymer lattices with degenerate ground state: in the general case of nondegenerate ground state polymers, isolated solitons are not allowed.

  • 19.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Monteiro, Fabio Ferreira
    Univ Brasilia, Brazil.
    Enders, Bernhard Georg
    Univ Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    da Cunha, Wiliam Ferreira
    Univ Brasilia, Brazil.
    Dynamic Formation of Bipolaron-Exciton Complexes in Conducting Polymers2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 15, p. 3866-3872Article in journal (Refereed)
    Abstract [en]

    The recombination dynamics of two oppositely charged bipolarons within a single polymer chain is numerically studied in the scope of a one-dimensional tight-binding model that considers electron electron and electron-phonon (e-ph) interactions. By scanning among values of e-ph coupling and electric field, novel channels for the bipolaron recombination were yielded based on the interplay between these two parameters. The findings point to the formation of a compound species formed from the coupling between a bipolaron and an exciton. Depending on the electric field and e-ph coupling strengths, the recombination mechanism may yield two distinct products: a trapped (and almost neutral) or a moving (and partially charged) bipolaron-exciton. These results might enlighten the understanding of the electroluminescence processes in organic light-emitting devices.

  • 20.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil; University of Brasilia, Brazil.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Impact of the electron-phonon coupling symmetry on the polaron stability and mobility in organic molecular semiconductors2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 3, p. 1386-1391Article in journal (Refereed)
    Abstract [en]

    The influence of the interplay between symmetric and antisymmetric inter-molecular electron-phonon (e-ph) coupling mechanisms on the polaron stability and mobility in organic semiconductors has been theoretically investigated at a molecular level. A semi-empirical Holstein-Peierls model is used which in addition to the symmetric and antisymmetric inter-molecular e-ph interactions also includes an antisymmetric intra-molecular e-ph coupling. Our results show that the symmetric e-ph coupling plays the role of destabilizing the polaron as a result of temperature induced phonons that, via the symmetric coupling, affects the charge distribution of the polaron. Considering this kind of coupling, the parameter space for which the polaron is dynamically stable is strongly temperature-dependent. For the combination of symmetric e-ph coupling strength and temperature, which results in a stable polaron, the velocity of the polaron, and therefore also the charge carrier mobility, is not affected by the symmetric e-ph coupling strength.

  • 21.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Polaron dynamics in anisotropic Holstein-Peierls systems2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 5, p. 4078-4084Article in journal (Refereed)
    Abstract [en]

    Polaron dynamics in anisotropic organic molecular semiconductors is theoretically investigated and simulated in the framework of a semi-classical Holstein-Peierls model. Our computational protocol is presented and applied to studies of a two-dimensional molecular crystal. The intermolecular (Peierls) parameters for a particular crystal direction are systematically changed in order to study the effect of anisotropy in the system. The usefulness of this methodology is highlighted by studying the polaron dynamics on a picosecond timescale, which provides a microscopic insight into the influence of the interplay between different intramolecular parameters on the charge transport mechanism. Our results show that the polaron mobility is substantially reduced in going from an anisotropic to an isotropic relationship between the Peierls parameters for different directions in the crystal. Interestingly, the molecular charge distribution presents three different signatures corresponding to a one-dimensional polaron, a two-dimensional polaron, and an intermediate state for which the polaron localization depends on the degree of anisotropy. Importantly, the two-dimensional polaron, which is present in the essentially isotropic system, is immobile whereas the other two types of polarons are mobile. This, in order for polaron transport to occur in a two-dimensional molecular based system, this system has to be anisotropic.

  • 22.
    Rivera Vila, Henrique Vieira
    et al.
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Machado de Macedo, Luiz Guilherme
    Fed Univ Para, Brazil.
    Gargano, Ricardo
    Univ Brasilia, Brazil.
    On the Angular Distribution of the H+Li-2 Cross Sections: a Converged Time-Independent Quantum Scattering Study2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 1044Article in journal (Refereed)
    Abstract [en]

    A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li-2 reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4. Such a promotion then begins to retract, eventually becoming an actual inhibition for larger j. In a straightforward manner, the concept of time-independent methods implemented in this study allowed this accurate state-to-state analysis. Furthermore, a nearly isotropic behaviour of the scattering is noted to take place from the angular point of view. Remarkably, our computational protocol is ideally suited to yield converged thermal rate coefficients, revealing a non-Arrhenius pattern and showing that J-shifting approach fails to describe this particular reaction. Our results, when compared to previous and independent ones, reinforce the latest theoretical reference for future validation in the experimental field.

  • 23.
    Silva, Gesiel Gomes
    et al.
    Goias Fed Inst Educ Sci and Technol, Brazil; Univ Brasilia, Brazil.
    da Cunha, Wiliam Ferreira
    Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Almeida Fonseca, Antonio Luciano
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Influence of quasi-particle density over polaron mobility in armchair graphene nanoribbons2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 24, p. 16712-16718Article in journal (Refereed)
    Abstract [en]

    An important aspect concerning the performance of armchair graphene nanoribbons (AGNRs) as materials for conceiving electronic devices is related to the mobility of charge carriers in these systems. When several polarons are considered in the system, a quasi-particle wave function can be affected by that of its neighbor provided the two are close enough. As the overlap may affect the transport of the carrier, the question concerning how the density of polarons affect its mobility arises. In this work, we investigate such dependence for semiconducting AGNRs in the scope of nonadiabatic molecular dynamics. Our results unambiguously show an impact of the density on both the stability and average velocity of the quasi-particles. We have found a phase transition between regimes where increasing density stops inhibiting and starts promoting mobility; densities higher than 7 polarons per 45 angstrom present increasing mean velocity with increasing density. We have also established three different regions relating electric field and average velocity. For the lowest electric field regime, surpassing the aforementioned threshold results in overcoming the 0.3 angstrom fs(-1) limit, thus representing a transition between subsonic and supersonic regimes. For the highest of the electric fields, density effects alone are responsible for a stunning difference of 1.5 angstrom fs(-1) in the mean carrier velocity.

  • 24.
    Silva, Gesiel Gomes
    et al.
    Goias Fed Inst Educ Sci and Technol, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    Pereira Junior, Marcelo Lopes
    Univ Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Bipolaron Dynamics in Graphene Nanoribbons2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 2909Article in journal (Refereed)
    Abstract [en]

    Graphene nanoribbons (GNRs) are two-dimensional structures with a rich variety of electronic properties that derive from their semiconducting band gaps. In these materials, charge transport can occur via a hopping process mediated by carriers formed by self-interacting states between the excess charge and local lattice deformations. Here, we use a two-dimensional tight-binding approach to reveal the formation of bipolarons in GNRs. Our results show that the formed bipolarons are dynamically stable even for high electric field strengths when it comes to GNRs. Remarkably, the bipolaron dynamics can occur in acoustic and optical regimes concerning its saturation velocity. The phase transition between these two regimes takes place for a critical field strength in which the bipolaron moves roughly with the speed of sound in the material.

1 - 24 of 24
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