Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 3: Graphene: Magnetic Fields (jointly with DS, HL, MA, and TT)

O 3.2: Talk

Monday, March 11, 2013, 09:45–10:00, H17

Experiments on Superlattice Graphene Structures with Patterned Top Gates — •Franz-Xaver Schrettenbrunner, Martin Drienovsky, Bastian Birkner, Sebastian Ringer, Dominik Koch, Dieter Weiss, and Jonathan Eroms — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg

We report on fabrication, finite element modelling (FEM), and the measurements of single- and bilayer graphene with structured top gates. By using micromechanically exfoliated graphene on SiO₂ surface, a Al₂O₃ dielectric was fabricated on top of the structure by either atomic layer deposition (ALD), evaporating thin aluminum films, or by combination of both methods. A digitated, patterned top gate electrode out of an AuPd alloy was fabricated by electron beam lithography (EBL). FEM yields that form and strength of the modulation strongly depend on thickness of the top gate dielectric, periodicity of the gate fingers, and applied voltage. Using both, the planar SiO₂ back gate and the patterned Al₂O₃ top gate the electric field effect creates variable modulations of the charge carrier concentration like pnp, nn’n, n0n, etc. along the whole underlying graphene. Measurements on these structures show typical behaviour for Klein-Tunneling resulting in an asymmetric curve of the Dirac Point. At high magnetic fields up to 14T unusual plateaus were observed when filling factors are mixing up in the top gated and the non top gated areas of the graphene samples.