Aufsatz in einer Fachzeitschrift
Large-amplitude coherent phonons and inverse Stone-Wales transitions in graphitic systems with defects interacting with ultrashort laser pulses
Details zur Publikation
Autor(inn)en: | Garcia, M. |
Publikationsjahr: | 2006 |
Zeitschrift: | Physical Review B |
Seitenbereich: | 0 |
Abkürzung der Fachzeitschrift: | Phys. Rev. |
Jahrgang/Band : | 74 |
ISSN: | 1098-0121 |
Zusammenfassung, Abstract
The mechanical response of a defective graphene layer to an ultrafast laser pulse is investigated through nonadiabatic molecular dynamics simulations. The defects are pentagon-heptagon pairs introduced by a single Stone-Wales transformation in the simulation cell. We found that when the fraction of excited electrons xi is below 6%, the layer exhibits strong transversal displacements in the neighborhood of the defect. The amplitude of these movements increases with the amount of energy absorbed until the threshold of xi=6% is reached. Under this condition the layer undergoes a subpicosecond inverse Stone-Wales transition, healing the defect. The absorbed energy per atom required to induce this mechanism is approximately 1.3 eV, a value that is below the laser damage thresholds for the pristine layers. The transition is lead by the electronic entropy and follows a path with strong out-of-plane contributions; it differs from the predicted path for thermally activated transitions, as calculated using standard transition state approaches. The same phenomenon is observed in defective zig-zag and armchair nanotubes. In contrast, for a defective C-60 fullerene the mechanism is hindered by the presence of edge-sharing pentagons.
The mechanical response of a defective graphene layer to an ultrafast laser pulse is investigated through nonadiabatic molecular dynamics simulations. The defects are pentagon-heptagon pairs introduced by a single Stone-Wales transformation in the simulation cell. We found that when the fraction of excited electrons xi is below 6%, the layer exhibits strong transversal displacements in the neighborhood of the defect. The amplitude of these movements increases with the amount of energy absorbed until the threshold of xi=6% is reached. Under this condition the layer undergoes a subpicosecond inverse Stone-Wales transition, healing the defect. The absorbed energy per atom required to induce this mechanism is approximately 1.3 eV, a value that is below the laser damage thresholds for the pristine layers. The transition is lead by the electronic entropy and follows a path with strong out-of-plane contributions; it differs from the predicted path for thermally activated transitions, as calculated using standard transition state approaches. The same phenomenon is observed in defective zig-zag and armchair nanotubes. In contrast, for a defective C-60 fullerene the mechanism is hindered by the presence of edge-sharing pentagons.
