References of "Wirtz, Ludger 50003339"
     in
Bookmark and Share    
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)

Detailed reference viewed: 105 (2 UL)
Full Text
Peer Reviewed
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 B (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 ▲]

Detailed reference viewed: 136 (1 UL)
See detailOptical and vibrational properties of M0S2
Wirtz, Ludger UL

Presentation (2012, November 26)

Detailed reference viewed: 94 (2 UL)
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 ▲]

Detailed reference viewed: 91 (4 UL)
See detailOptical and vibrational properties of layered materials
Wirtz, Ludger UL

Presentation (2012, June 13)

Detailed reference viewed: 102 (4 UL)
See detailSubstrate dependence of the Raman 2D line of graphene
Wirtz, Ludger UL; Allard, Adrian; Molina-Sanchez, Alejandro UL

Scientific Conference (2012)

Detailed reference viewed: 59 (2 UL)
See detailTheory of Raman spectroscopy of graphene on different substrates
Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 58 (0 UL)
See detailSpectroscopie expérimentale et théorique du graphène fonctionnalisé
Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 49 (0 UL)
Full Text
See detailTheoretical Spectroscopy of single-layer and few-layers MoS2
Molina-Sanchez, Alejandro UL; Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 76 (1 UL)
See detailPhonons in single-layer and few-layer MoS2
Molina-Sanchez, Alejandro UL; Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 214 (3 UL)
See detailThe phonon dispersion of graphene in interaction with different substrates
Wirtz, Ludger UL

Scientific Conference (2012)

Detailed reference viewed: 58 (2 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 128 (7 UL)
Full Text
Peer Reviewed
See detailVariations in the work function of doped single- and few-layer graphene assessed by Kelvin probe force microscopy and density functional theory
Ziegler, D.; Gava, P.; Guettinger, J. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 83(23),

We present Kelvin probe force microscopy measurements of single-and few-layer graphene resting on SiO2 substrates. We compare the layer thickness dependency of the measured surface potential with ab ... [more ▼]

We present Kelvin probe force microscopy measurements of single-and few-layer graphene resting on SiO2 substrates. We compare the layer thickness dependency of the measured surface potential with ab initio density functional theory calculations of the work function for substrate-doped graphene. The ab initio calculations show that the work function of single-and bilayer graphene is mainly given by a variation of the Fermi energy with respect to the Dirac point energy as a function of doping, and that electrostatic interlayer screening only becomes relevant for thicker multilayer graphene. From the Raman G-line shift and the comparison of the Kelvin probe data with the ab initio calculations, we independently find an interlayer screening length in the order of four to five layers. Furthermore, we describe in-plane variations of the work function, which can be attributed to partial screening of charge impurities in the substrate, and result in a nonuniform charge density in single-layer graphene. [less ▲]

Detailed reference viewed: 194 (2 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 135 (4 UL)
Full Text
Peer Reviewed
See detailPhonons in single-layer and few-layer MoS2 and WS2
Molina-Sanchez, Alejandro UL; Wirtz, Ludger UL

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84

Detailed reference viewed: 353 (24 UL)
Full Text
Peer Reviewed
See detailRumpling of LiF(001) surface from fast atom diffraction
Schueller, A.; Wethekam, S.; Blauth, D. et al

in Physical Review. A (2010), 82(6), 062902

Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces ... [more ▼]

Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces. From comparison of measured and calculated diffraction patterns we deduce the rumpling of the topmost surface layer of LiF(001) (i.e., an inward shift of Li(+) ions with respect to F(-) ions). The effect of thermal vibrations on the measurement of rumpling is accounted for by ab initio calculations of the mean-square vibrational amplitudes of surface ions. At room temperature this leads to a reduction of the apparent rumpling by 0.008 angstrom. We then obtain a rumpling of ( 0.05 +/- 0.04) angstrom, which improves its accuracy achieved in previous work. [less ▲]

Detailed reference viewed: 120 (2 UL)
Full Text
Peer Reviewed
See detailDoped Graphene as Tunable Electron-Phonon Coupling Material
Attaccalite, Claudio; Wirtz, Ludger UL; Lazzeri, Michele et al

in Nano Letters (2010), 10(4), 1172-1176

we present a new way to tune the electron phonon coupling (EPC) in graphene by changing the deformation potential with electron/hole doping. We show the EPC for highest optical branch at the high symmetry ... [more ▼]

we present a new way to tune the electron phonon coupling (EPC) in graphene by changing the deformation potential with electron/hole doping. We show the EPC for highest optical branch at the high symmetry point K acquires a strong dependency on the doping level due to electron electron correlation not accounted in mean-field approaches. Such a dependency influences the dispersion (with respect to the laser energy) of the Raman D and 2D lines and the splitting of the 2D peak in multilayer graphene. Finally this doping dependence opens the possibility to construct tunable electronic devices through external control of the EPC. [less ▲]

Detailed reference viewed: 82 (5 UL)