Photoemission Momentum Microscopy of Graphene on Ir (111)
Anna Zaporozhchenko (Institut für Physik)

Photoemission time-of-flight (ToF) momentum microscopy has been developed to be a strong technique to observe electronic structures of materials. The method was recognized as an essential step to fast acquisition of data that highly surpasses conventional techniques such as angle resolved photoemission spectroscopy (ARPES) [1]. Thus, our new ToF momentum microscope allowed us to measure simultaneously 3D (kx,ky,EB) distributions of electronic bands of graphene grown on Ir(111).
Graphene (Gr), a two-dimensional sp2 bonded honeycomb lattice of carbon atoms, has shown remarkable properties, which make it a promising material for a number of applications [2]. For weakly bonded systems, the Dirac cone is preserved and the electronic structure is close to the one of freestanding graphene [3]. This behavior was found for graphene on Ir(111) [4], and therefore the system was intriguing for our investigation.
The measurements were performed at BESSY II, Berlin using our novel ToF momentum microscope. In such a way, complete sets of 3D dispersion of bands are obtained from Gr/Ir(111) sample at p-polarized [4] and s-polarized radiation for the first time. “Dark corridors” inherent in Dirac cones of Gr due to quantum mechanical interference [5,6] are observed and analyzed at different excitation energies in the range of 14 eV up to 23 eV with the step of 1 eV and compared to appropriate results collected at p-polarized light [4]. As expected, intensity differences in the momentum discs indicate a linear dichroism in the photoelectron angular distribution (LDAD). On K-Г-K’ section hybridization of Ge π-bands and Ir 5d-bands can be distinguished resulting in distortion and breaks of dispersion due to avoiding-crossing effects.
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