Epitaxial Graphene on SiC

a) zero-layer graphen (ZLG); b) monolayer graphene (MLG); c) hydrogen intercalated graphene, quasi-free monolayer graphene (QFMLG).

a) zero-layer graphen (ZLG); b) monolayer graphene (MLG); c) hydrogen intercalated graphene, quasi-free monolayer graphene (QFMLG).

Epitaxial graphene on SiC(0001) is commonly prepared by means of silicon sublimation via annealing of the SiC substrate. An initial carbon layer develops - well ordered in a (6√3x6√3)R30° superstructure on the SiC(0001) substrate, which structurally is composed of the typical carbon honeycomb lattice found in graphene. However, about one third of the carbon atoms are still covalently bound to the topmost silicon atoms in the substrate so that the delocalized π-band system cannot develop. This initial carbon layer is called buffer layer or zero layer graphene (ZLG). The covalent bonding situation is sketched with the covalent bonds between Si and C across the interface and dangling bonds (DB) on the remaining Si atoms indicated (a). We note that this bonding induces a strong buckling in the graphitic layer and leads to a very distinct and intense quasi-(6x6)-SiC(0001) diffraction pattern.

By further annealing of the SiC sample a second carbon layer is formed, which in turn adopts the role of the buffer layer. The initial ZLG transforms into a real graphene layer on top with fully developed π-bands and the system is then called monolayer graphene (MLG) (b). The ZLG carbon layer can be decoupled from the SiC substrate by an intercalated atomic layer, as first shown for hydrogen intercalation (c). The covalent bonds at the ZLG interface are broken and all Si atoms in the topmost substrate layer are saturated by hydrogen atoms. Effectively in this way, a quasi-free standing graphene monolayer is obtained exhibiting the well-known graphene Dirac cones. Besides hydrogen many other chemical elements like Ag, Au, Cu, Gd, Ge, Yb, etc. can be used to intercalate the ZLG or MLG. A plentitude of new electronic and chemical properties evolve by the intercalation of graphene with different elements.

ZLG samples with homogeneous coverage are prepared on 6H-SiC(0001) (on-axis, n-doped, purchased from SiCrystal GmbH) by annealing in our home-built RF-furnace in Ar atmosphere, which results in a superb homogeneity on a waver scale. Atomic force microscopy (AFM), low-energy electron diffraction (LEED) and photoelectron spectroscopy (PES) together with synchrotron techniques are used to investigate the chemical and electronic properties of the graphene layer and the interface.

Publications:

P. Rosenzweig, U. Starke, Phys. Rev. B 101, 201407(R) (2020). Large-area synthesis of a semiconducting silver monolayer via intercalation of epitaxial graphene.
S. Forti, S. Link, A. Stöhr, Y. Niu, A. A. Zakharov, C. Coletti, U. Starke, Nat. Commun. 11, 2236 (2020). Semiconductor to metal transition in two-dimensional gold and its van der Waals heterostack with graphene.
S. Link, S. Forti, A. Stöhr, K. Küster, M. Rösner, D. Hirschmeier, C. Chen, J. Avila, M. C. Asensio, A. A. Zakharov, T. O. Wehling, A. I. Lichtenstein, M. I. Katsnelson, U. Starke, Phys. Rev. B 100, 121407(R) (2019). Introducing strong correlation effects into graphene by gadolinium intercalation.
P. Rosenzweig, H. Karakachian, S. Link, K. Küster, U. Starke, Phys Rev B 100, 035445 (2019). Tuning the doping level of graphene in the vicinity of the Van Hove singularity via ytterbium intercalation.
A. Stöhr, S. Forti, S. Link, A.A. Zakharov, K. Kern, U. Starke, and H.M. Benia, Phys. Rev. B 94, 085431 (2016). Intercalation of graphene on SiC(0001) via ion implantation.
S. Forti, A. Stöhr, A. A. Zakharov, C. Coletti, K. V. Emtsev, and U. Starke, 2D Mater. 3, 035003 (2016). Mini-Dirac Cones in the Band Structure of a Copper Intercalated Epitaxial Graphene Superlattice.
J. Sforzini, L. Nemec, T. Denig, B. Stadtmüller, T.-L. Lee, C. Kumpf, S. Soubatch, U. Starke, P. Rinke, V. Blum, F.C. Bocquet, and F.S. Tautz, Phys. Rev. Lett. 114, 106804 (2015). Approaching Truly Freestanding Graphene: The Structure of Hydrogen-Intercalated Graphene on 6H-SiC(0001).
J. Baringhaus, A. Stöhr, S. Forti, U. Starke, and C. Tegenkamp, Sci. Rep. 5, 9955 (2015). Ballistic bipolar junctions in chemically gated graphene ribbons.
J. Baringhaus, A. Stöhr, S. Forti, S. A. Krasnikov, A. A. Zakharov, U. Starke, and C. Tegenkamp, Appl. Phys. Lett., 104, 261602 (2014). Bipolar gating of epitaxial graphene by intercalation of Ge.
S. Forti, and U. Starke, J. Phys. D: Appl. Phys. 47, 094013 (2014). Epitaxial graphene on SiC: from carrier density engineering to quasi-free standing graphene by atomic intercalation.
T. Eelbo, M. Wasniowska, M. Gyamfi, S. Forti, U. Starke, and R. Wiesendanger, Phys. Rev. B 87, 205443 (2013). Influence of the degree of decoupling of graphene on the properties of transition metal adatoms.
U. Starke, C. Coletti, K.V. Emtsev, A.A. Zakharov, T. Ouisse, and D. Chaussende, Mat. Sci. Forum 717-720, 617 (2012). Large area quasi-free standing monolayer graphene on 3C-SiC(111).
U. Starke, S. Forti, K.V. Emtsev, and C. Coletti, MRS Bulletin 37, 1177 (2012). Engineering of the electronic structure of epitaxial graphene by transfer doping and atomic intercalation.
C. Coletti, S. Forti, K.V. Emtsev, and U. Starke, in: Carbon Nanostructures: GraphITA 2011 (eds: L. Ottaviano and V. Morandi), Springer, Berlin, Heidelberg, 2012, p39-50, Tailoring the Electronic Structure of Epitaxial Graphene on SiC(0001): Transfer Doping and Hydrogen Intercalation.
S. Forti, K.V. Emtsev, C. Coletti, A.A. Zakharov, C. Riedl, and U. Starke, Phys. Rev. B 84, 125449 (2011), Large area homogeneous quasi-free standing epitaxial graphene on SiC(0001). Electronic and structural characterization.
K. Emtsev, A.A. Zakharov, C. Coletti, S. Forti, and U. Starke, Phys. Rev. B 84, 125423 (2011), Ambipolar doping in quasi-free epitaxial graphene on SiC(0001) controlled by Ge intercalation.
C. Riedl, C. Coletti and U. Starke, J. Phys. D: Appl. Phys. 43, 374009 (2010), Structural and electronic properties of epitaxial graphene on SiC(0001): a review of growth, characterization, transfer doping and hydrogen intercalation.
U. Starke, in Silicon Carbide 2010 - Materials, Processing, and Devices, edited by S.E. Saddow, E. Sanchez, F. Zhao, M. Dudley (Mater. Res. Soc. Symp. Proc. Volume 1246, Warrendale, PA, 2010), B10-01, Preprint, Bandstructure manipulation of epitaxial graphene on SiC(0001) by molecular doping and hydrogen intercalation.
I. Gierz, T. Suzuki, R.T. Weitz, D.S. Lee, B. Krauss, C. Riedl, U. Starke, H. Hochst, J.H. Smet, C.R. Ast, and K. Kern, Phys. Rev. B 81, 235408 (2010), Electronic decoupling of an epitaxial graphene monolayer by gold intercalation.
C. Coletti, C. Riedl, D.S. Lee, B. Krauss, L. Patthey, K.v. Klitzing, J.H. Smet, and U. Starke, Phys. Rev. B, 81, 235401 (2010), Band structure engineering of epitaxial graphene on SiC by molecular doping.
C. Riedl, C. Coletti, T. Iwasaki, A.A. Zakharov, and U. Starke, Mat. Sci. Forum 645-648, 623 (2010), Hydrogen intercalation below epitaxial graphene on SiC(0001).
U. Starke and C. Riedl, J. Phys.: CM 21, 134016 (2009), Epitaxial graphene on SiC(0001) and SiC(000-1): from surface reconstructions to carbon electronics.
C. Riedl, C. Coletti, T. Iwasaki, A.A. Zakharov, and U. Starke, Phys. Rev. Lett. 103, 246804 (2009), Quasi-free standing epitaxial graphene on SiC obtained by hydrogen intercalation.
I. Gierz, C. Riedl, U. Starke, C.R. Ast and K. Kern, Nano Letters 8, 4603 (2008), Atomic hole doping in graphene.
D.S. Lee, C. Riedl, B. Krauss, K. v. Klitzing, U. Starke and J.H. Smet, Nano Letters 8, 4320 (2008), Raman spectra of epitaxial graphene on SiC and of epitaxial graphene transferred to SiO2.
C. Riedl, U. Starke, J. Bernhardt, M. Franke and K. Heinz, Phys. Rev. B 76, 245406 (2007), Structural properties of the graphene-SiC(0001) interface as a key for the preparation of homogeneous large-terrace graphene surfaces.