Atomic Scale Imaging and Energy Loss Spectroscopy of Epitaxial Graphene
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Atomic Scale Imaging and Energy Loss Spectroscopy of Epitaxial Graphene Giuseppe Nicotra1, Quentin M. Ramasse2, Mario Scuderi1, Paolo Longo3, Ioannis Deretzis1, Antonino La Magna1, Filippo Giannazzo1, and Corrado Spinella1
1 Istituto
per la Microelettronica e Microsistemi (CNR-IMM), VIII strada 5, I-95121 Catania, Italy
2 SuperSTEM 3 Gatan,
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Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, UK
Inc., 5794 W Las Positas Blvd, Pleasanton, CA, 94588, USA
ABSTRACT Atomic-resolution structural and spectroscopic characterization techniques (scanning transmission electron microscopy and electron energy loss spectroscopy) are combined with nanoscale electrical measurements (conductive atomic force microscopy) to study at the atomic scale the properties of graphene grown epitaxially through the controlled graphitisation of Si-face and C-face hexagonal SiC(0001) substrates by high temperature annealing. A scanning transmission electron microscopy analysis, carried out at 60KeV of beam energy, below the knock-on threshold for carbon to ensure no damage is imparted to the film by the electron beam, demonstrates that the buffer layer present on the planar SiC(0001) Si-face delaminates from it on the (11-2n) facets of SiC surface steps, In addition, electron energy loss spectroscopy reveals that the delaminated layer has a similar electronic configuration to purely sp2-hybridized graphene. A thin amorphous film is found on the C-face, instead, which strongly suppresses epitaxy with the SiC substrate. Structurally, the amorphous area is inhomgeneous, as its Si-concentration gradually decreases while approaching the first graphene layer, which is purely sp2-hybridized. Based on these features, we discuss differences and similarities between the C-only buffer layer that forms on the Si-face of SiC with respect to the thicker C/Si amorphous film of the C-face. INTRODUCTION Graphitization of SiC, is attracting particular research interest since it is a very promising way to produce uniform graphene films over large areas. Graphene is a planar one-atom-thick layer of sp2bonded carbon atoms with remarkable electronic transport properties that make it a potential candidate for future electronic applications. However, graphene presents specific structural and electronic properties depending on the growth substrate and mechanism, which consequently have an impact on its macroscopic electrical behavior. In the case of epitaxial graphene (EG) grown on Si-polarized SiC, a crucial role is played by the presence of a so-called carbon “buffer layer” or “0 layer”. Such layer has been shown to present a certain degree of sp3 hybridization since it is partially bound to the outmost Si atoms of the SiC (0001) surface [1]. On the contrary, even under similar growth conditions, graphitization over the C-face of SiC shows structural and electronic inhomogeneity [2], which affects the number of graphene layers, their orientation, the stacking order and doping concentration. Even though the presence of this apparent disorder, graphene
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