Invited Paper SA+AS+MI+SS-WeM1
LEEM, PEEM and ARPES Studies of Epitaxial Graphene on SiC(0001)

Wednesday, October 30, 2013, 8:00 am, Room 203 C

Large area epitaxial graphene (EG) can be grown on SiC(0001) by heating in Ar atmosphere [1]. However, such graphene layers are n-doped due to the influence of a covalently bonded carbon interface layer. This influence can be completely eliminated and the graphene layers be decoupled from the substrate by atomic intercalation. The electronic structure can be tuned in various ways for these decoupled graphene layers. Detailed investigations of the π-band structure, the spatial arrangement, chemical bonding and local surface order are shown based on angle-resolved photoemission spectroscopy (ARPES), low-energy electron microscopy (LEEM), photoemission microscopy (PEEM) combined with microscopic X-ray photoelectron spectroscopy (μ-XPS) and low-energy electron diffraction (μ-LEED), as well as scanning tunneling microscopy (STM) experiments.

By annealing the EG samples in atmospheric H₂, atomic hydrogen reacts under the interface layer, so that the underlying SiC layer becomes passivated [2]. The interface layer alone transforms into a quasi-free standing monolayer while monolayers and bilayers turn into decoupled bilayers and trilayers [3,4]. As a result, charge neutral quasi-free standing graphene layers can be obtained. By intercalation of Germanium the graphene layers can also be decoupled. In this process both p- and n-doping can be produced, depending on the amount of Ge material intercalated. By preparing both phases in coexistence on the surface, lateral p-n junctions can be generated on a mesoscopic scale [5]. Intercalation of Cu induces a coincidence superstructure on top of the SiC surface, which originates from periodic regions of different bond configuration for the carbon atoms in the graphene layer. As a result, a long range periodic potential is imposed onto the graphene layer, which leads to a profound modification of its electronic spectrum. A surprisingly strong doping and the development of mini-Dirac cones are observed [6].

References:

[1] K.V. Emtsev, et al., Nat. Mater. 8, 203 (2009).

[2] C. Riedl, C. Coletti, T. Iwasaki, A.A. Zakharov, and U. Starke, Phys. Rev. Lett. 103, 246804 (2009).

[3] S. Forti, K.V. Emtsev, C. Coletti, A.A. Zakharov, C. Riedl, and U. Starke, Phys. Rev. B 84, 125449 (2011).

[4] C. Coletti, K.V. Emtsev, A.A. Zakharov, T. Ouisse, D. Chaussende, and U. Starke, Appl. Phys. Lett. 99, 081904 (2011).

[5] K.V. Emtsev, A.A. Zakharov, C. Coletti, S. Forti, and U. Starke, Phys. Rev. B 84, 125423 (2011).

[6] K.V. Emtsev, S. Forti, A.A. Zakharov, C. Coletti, and U. Starke, in preparation.