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See detailManifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds
Wirtz, Ludger UL; Chacon, Julio; Pichler, Thomas

Scientific Conference (2013)

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See detailManifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds.
Chacon-Torres, Julio C.; Wirtz, Ludger UL; Pichler, Thomas

in ACS Nano (2013), 7(10), 9249

We present detailed multifrequency resonant Raman measurements of potassium graphite intercalation compounds (GICs). From a well-controlled and consecutive in situ intercalation and high-temperature ... [more ▼]

We present detailed multifrequency resonant Raman measurements of potassium graphite intercalation compounds (GICs). From a well-controlled and consecutive in situ intercalation and high-temperature deintercalation approach the response of each stage up to stage VI is identified. The positions of the G and 2D lines as a function of staging depend on the charge transfer from K to the graphite layers and on the lattice expansion. Ab initio calculations of the density and the electronic band structure demonstrate that most (but not all) of the transferred charge remains on the graphene sheets adjacent to the intercalant layers. This leads to an electronic decoupling of these "outer" layers from the ones sandwiched between carbon layers and consequently to a decoupling of the corresponding Raman spectra. Thus, higher stage GICs offer the possibility to measure the vibrations of single, double, and multilayer graphene under conditions of biaxial strain. This strain can additionally be correlated to the in-plane lattice constants of GICs determined by X-ray diffraction. The outcome of this study demonstrates that Raman spectroscopy is a very powerful tool to identify local internal strain in pristine and weakly charged single and few-layer graphene and their composites, yielding even absolute lattice constants. [less ▲]

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See detailDielectric screening of the Kohn anomaly of graphene on hexagonal boron nitride
Forster, F.; Molina-Sanchez, Alejandro UL; Engels, S. et al

in Physical Review. B, Condensed Matter and Materials Physics (2013), 88

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See detailTowards an ab initio description of the charge transfer between a proton and a lithium fluoride surface: A quantum chemistry approach
Tiwald, Paul; Gräfe, Stefanie; Burgdörfer, Joachim et al

in Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2013), 317, Part A

We study the non-adiabatic charge transfer dynamics during the collision of a slow proton with a lithium fluoride surface employing a quantum-chemistry based dynamics approach. The surface is modeled by ... [more ▼]

We study the non-adiabatic charge transfer dynamics during the collision of a slow proton with a lithium fluoride surface employing a quantum-chemistry based dynamics approach. The surface is modeled by an Li5F1+ H+ cluster embedded in a large matrix of point charges. Going beyond the adiabatic (or Born–Oppenheimer) approximation, we apply multi-reference configuration-interaction methods that allow for the calculation of ground and excited states of the embedded cluster as well as of the non-adiabatic couplings between them. This information serves as input for the determination of the neutralization probability of a proton scattered off a LiF surface using Tully’s semi-classical surface hopping algorithm. [less ▲]

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See detailOptical and vibrational properties of M0S2
Wirtz, Ludger UL

Presentation (2012, November 26)

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See detailLight emitting source and method for emitting light based on boron nitride nanotubes
Rubio, Angel; Attacalite, Claudio; Wirtz, Ludger UL

Patent (2012)

The invention relates to a controllable frequency, broad spectrum light emitting source that includes boron nitride nanotubes with defects produced by the absence of a boron atom in the tubular structure ... [more ▼]

The invention relates to a controllable frequency, broad spectrum light emitting source that includes boron nitride nanotubes with defects produced by the absence of a boron atom in the tubular structure and wherein the source is additionally provided with a means for generating an electrical field perpendicular to the tube. The invention may be used as a field effect transistor (adding electrodes) or as a source of conversion of energy of an incident bundle. [less ▲]

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See detailOptical and vibrational properties of layered materials
Wirtz, Ludger UL

Presentation (2012, June 13)

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See detailTheory of Raman spectroscopy of graphene on different substrates
Wirtz, Ludger UL

Scientific Conference (2012)

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See detailThe phonon dispersion of graphene in interaction with different substrates
Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 63 (2 UL)
See detailSpectroscopie expérimentale et théorique du graphène fonctionnalisé
Wirtz, Ludger UL

Scientific Conference (2012)

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See detailTheoretical Spectroscopy of single-layer and few-layers MoS2
Molina-Sanchez, Alejandro UL; Wirtz, Ludger UL

Scientific Conference (2012)

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See detailPhonons in single-layer and few-layer MoS2
Molina-Sanchez, Alejandro UL; Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 221 (3 UL)
See detailSubstrate dependence of the Raman 2D line of graphene
Wirtz, Ludger UL; Allard, Adrian; Molina-Sanchez, Alejandro UL

Scientific Conference (2012)

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See detailCoupling of excitons and defect states in boron-nitride nanostructures
Attaccalite, C.; Bockstedte, M.; Marini, A. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 83(14), 144115

The signature of defects in the optical spectra of hexagonal boron nitride (BN) is investigated using many-body perturbation theory. A single BN-sheet serves as a model for different layered BN ... [more ▼]

The signature of defects in the optical spectra of hexagonal boron nitride (BN) is investigated using many-body perturbation theory. A single BN-sheet serves as a model for different layered BN nanostructures and crystals. In the sheet we embed prototypical defects such as a substitutional impurity, isolated boron and nitrogen vacancies, and the divacancy. Transitions between the deep defect levels and extended states produce characteristic excitation bands that should be responsible for the emission band around 4 eV, observed in luminescence experiments. In addition, defect bound excitons occur that are consistently treated in our ab initio approach along with the "free" exciton. For defects in strong concentration, the coexistence of both bound and free excitons adds substructure to the main exciton peak and provides an explanation for the corresponding feature in cathodo- and photoluminescence spectra. [less ▲]

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See detailAnisotropic excitonic effects in the energy loss function of hexagonal boron nitride
Galambosi, S.; Wirtz, Ludger UL; Soininen, J. A. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 83(8), 081413

The anisotropy of the valence energy-loss function of hexagonal boron nitride (hBN) is shown to be largely enhanced by the highly inhomogeneous character of the excitonic states. The energy loss with ... [more ▼]

The anisotropy of the valence energy-loss function of hexagonal boron nitride (hBN) is shown to be largely enhanced by the highly inhomogeneous character of the excitonic states. The energy loss with momentum transfer parallel to the BN layers is dominated by strongly bound, quasi-two-dimensional excitons. In contrast, excitations with momentum transfer perpendicular to the layers are influenced by weakly bound three-dimensional excitons. This striking phenomenon is revealed by a combined study using high-precision nonresonant inelastic x-ray scattering measurements supported by ab initio calculations. The results are relevant in general to layered insulating systems. [less ▲]

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