Intrinsic structural and electronic properties of the Buffer Layer on Silicon Carbide unraveled by Density Functional Theory

Abstract

The buffer carbon layer obtained in the first instance by evaporation of Si from the Si-rich surfaces of silicon carbide (SiC) is often studied only as the intermediate to the synthesis of SiC supported graphene. In this work, we explore its intrinsic potentialities, addressing its structural and electronic properties by means of Density Functional Theory. While the system of corrugation crests organized in a honeycomb super-lattice of nano-metric side returned by calculations is compatible with atomic microscopy observations, our work reveals some possible alternative symmetries, which might coexist in the same sample. The electronic structure analysis reveals the presence of an electronic gap of ~0.7 eV. In-gap states are present, localized over the crests, while near-gap states reveal very different structure and space localization, being either bonding states or outward pointing p orbitals and unsaturated Si dangling bonds. On one hand, the presence of these interface states was correlated with the n-doping of the monolayer graphene subsequently grown on the buffer. On the other hand, the correlation between their chemical character and their space localization is likely to produce a differential reactivity towards specific functional groups with a spatial regular modulation at the nano-scale, opening perspectives for a finely controlled chemical functionalization.

Buffer layers inhomogeneity and coupling with epitaxial graphene unravelled by Raman scattering and graphene peeling

“…Moreover, a clear correlation is found between the integrated intensities in the 1260-1460 cm -1 and 1550-1710 cm -1 regions. These results could be the signature of the coexistence of different BL structures which can have close formation energies as evidenced by the theoretical work of Cavalluci et al [18], but the structure and Raman signature relationship still remains to be established.…”

“…In the literature, there is an intense debate about the BL atomic structure. Several BL structures have been proposed and investigated theoretically [17,18]. The scanning tunneling microscopy (STM) images commonly show a (6 × 6) structure of BL which do not agree with the low-energy electron diffraction (LEED) patterns showing a 6!3 × 6!3"30° reconstruction [7][8][9][10][11][12].…”

“…Interestingly, Rutter et al found "two energetically stable configurations for the first carbon layer, depending on the initial graphene-SiC distance prior to full relaxation of the atomic coordinates" [44]. More recently, Cavalluci et al have shown theoretically that several BL structures could have similar formation energies and "might appear in different experimental conditions or in different areas of the sample" [18]. They used a cubic polytype SiC in their calculations but 3C-SiC is "perfectly equivalent to 4H and 6H-SiC provided the SiC surface is planar" [17] and thus their results can be applied in our case (4H samples).…”

Ambipolar Behavior of Ge-Intercalated Graphene: Interfacial Dynamics and Possible Applications

“…The first carbon layer, which is commonly referred to as the buffer layer, undergoes a (6sqrt3x6sqrt3)R30°reconstruction and always presents between graphene and SiC. Despite the fact that the carbon atoms in the buffer layer are arranged in a graphene-like honeycomb structure, a significant number of carbon atoms in this layer are strongly bound to the silicon atoms of the SiC(0,001) surface [7,8]. As a result, in the electronic structure, the buffer layer exhibits graphenelike σ bands but fails to do so with π bands which are responsible for linear dispersion (Dirac cones) typical for graphene [9].…”

Engineering 3D Graphene-Based Materials: State of the Art and Perspectives

“…With little exceptions, however, these require some sort of manipulation of the sheet: in general nano-electronics requires doping to increase the density of states at the Fermi energy or to open a gap, which can be achieved by chemical substitutions [11], introduction of adatoms [12] or defects [13,14] or structure modulation [15,16]; for photovoltaics [9] different functionalization are required, depending on the specific use proposed (anode, cathode or photoactive layer [17]). Catalysis or environmental applications, such as water filtering, generally require sheet alteration, such as perforations of tailored size [18].…”