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HL: Fachverband Halbleiterphysik

HL 103: Graphene: Adsorption, intercalation, doping (organized by O)

HL 103.6: Vortrag

Donnerstag, 3. April 2014, 17:15–17:30, WIL C107

Charge doping induced phase transitions in hydrogenated and fluorinated graphene — •Tim Wehling^1,2, Bernhard Grundkötter-Stock², Bálint Aradi², Thomas Niehaus³, and Thomas Frauenheim² — ¹Institute for Theoretical Physics, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany — ²Bremen Center for Computational Material Science, Universität Bremen, Am Fallturm 1, 28359 Bremen, Germany — ³Department of Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany

We show that charge doping can induce transitions between three distinct adsorbate phases in hydrogenated and fluorinated graphene. By combining ab initio, approximate density functional theory and tight binding calculations we identify a transition from islands of C₈H₂ and C₈F₂ to random adsorbate distributions around a doping level of ± 0.05 e/C-atom. Furthermore, in situations with random adsorbate coverage, charge doping is shown to trigger an ordering transition where the sublattice symmetry is spontaneously broken when the doping level exceeds the adsorbate concentration. Rehybridization and lattice distortion energies make graphene which is covalently functionalized from one side only most susceptible to these two kinds of phase transitions. The energy gains associated with the clustering and ordering transitions exceed room temperature thermal energies.