Our regular group meetings are on alternate Tuesday at 10:00 AM in Building 28, conference room 2.066.
Results of recent experiments performed with spin- and angle-resolved photoemission which reveal different approaches allowing for control of Rashba-type electronic states in graphene will be presented and discussed.
In the first part of the presentation it will be shown how the spin-orbit split surface state of Ir(111) can be tuned through the modulation of structural properties of a graphene overlayer grown on top of the iridium sample. A substantial binding energy shift of the Ir(111) surface state is achieved either through enhancement of the graphene corrugation by a superlattice of deposited clusters or through increasing the thickness of the graphene overlayer. The resulting effects are assigned to the alteration of the graphene-Ir separation. The magnitude of the surface state Rashba splitting, however, remains preserved in both cases.
The second part of the talk is devoted to a specific Rashba effect in graphene, which can be induced extrinsically though the contact of graphene with high-Z materials. A giant (~100 meV) spin-orbit splitting of the Dirac cone in quasifreestanding graphene intercalated with Au will be demonstrated and analysed in terms of electronic hybridization between graphene and Au atoms. A similar effect will be revealed for graphene on Ir(111), although it will be shown that the magnitude of the Rashba splitting in this system is very sensitive to even small rotational displacements of the graphene with respect to the Ir substrate. Finally, a possibility to tune the magnitude of the Rashba splitting in the Dirac cone through co-intercalation of graphene on Ni(111) with different materials will be demonstrated.
It should be possible to move adsorbed nano-objects with relative ease, in large number and simultaneously. The essential idea is not to put more effort in fighting against the prevailing surface forces but rather to utilize them - in clear contrast to current techniques of nano-manipulation with atomic force microscopy [Santer, Adv Mat 2006]. For this, the topography should be reversible switching between different states by changing the morphology at the scale of objects to be moved. In this work, we choose light for changing the polymer topography. Here we present azo thin films [Seki, Chem Soc Jpn 2007] with integrated optically active elements supposed to support and steer the response of polymer films to external illumination by acting as nano-scale antennas. During irradiation surface plasmon (SP) waves are generated on a metallic mask. The interaction of the SP waves with azo polymers results in printing of near field intensity distributions into topography with the pattern size below the diffraction limit. We found that the topography can be driven reversible by changing polarization or wavelength. We also examine how the structuring process depends on the size of the metallic patterns. The results are confirmed by FTDT simulations and compared with imprints of photolithographic mask.