ZO phonon of a buffer layer and Raman mapping of hydrogenated buffer on SiC(0001)

Abstract

We have measured spatial Raman maps of hydrogen intercalated quasi-free standing monolayer graphene (QFSMLG) on SiC(0001). We compare Raman spectra of QFSMLG with spectra of bare buffer layer, single-layer graphene, and bare SiC substrate. We also present the evolution of QFSMLG Raman spectra with the temperature and duration of hydrogen intercalation. We present new Raman modes, and, on the basis of polarization resolved measurements, we attribute them to the totally symmetric out-of-plane optical phonon (ZO) modes of the buffer layer at the Γ and M points. We show that these modes are eliminated by hydrogen intercalation; thus, they indicate onset of buffer layer decoupling from the SiC substrate. The spatial mapping of Raman scattering reveals details of the optimal hydrogen intercalation at elevated temperatures.Further increase of the intercalation temperature leads to etching of the buffer layer and underlying SiC substrate. Therefore, we show that interplay between temperature and intercalation time is a promising route towards increased graphene grain size with reduced lattice strain.

Raman 2D Peak Line Shape in Epigraphene on SiC

“…The characteristic distinction between the hydrogen intercalated and non-intercalated samples can be also found by the absence/presence of the peaks labeled (1), (2) and 3in inset of Figure 1. These peaks were attributed to the buffer layer [18,42]. The hydrogenated (QFMLG) and non-hydrogenated (SLG-vac, SLG-Ar) samples can be also distinguished by a low intensity background in the spectral range of the D peak.…”

“…This sp 3 bonding was switched into sp 2 bonding by hydrogen intercalation [17,38]. More details on graphene growth and hydrogen intercalation can be found in our previous works [17,18,39].…”

“…The Raman spectroscopy of graphene is a well-established technique [1][2][3] to determine number of graphene layers [4], strain [5,6], charge density [6][7][8][9], grain size [10][11][12][13][14], graphene functionalization [15], misorientation of graphene layers [16] or degree of hydrogen intercalation of epitaxial graphene on SiC [17,18]. The graphene's most prominent Raman spectral features are the D peak, G peak and 2D peak.…”

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

“…Kruskopf et al [32] have observed similar peaks at about 1235 cm -1 and 1365 cm -1 and they attributed them to the vibrational density of states of the BL and the D-related peak, respectively, following Fromm et al [51]. Rejhon et al attributed the peak observed at 1237 cm -1 to "the LO/LA phonon branches at the Γ point" of the BL [41].…”

“…These direct growth samples were synthesized at different growth temperatures ranging from 1600 to 1740°C (see table1 In the literature, a wide range of spectra have been reported for the BL from very disordered-like [28][29][30]39] to more ordered-like [20,31,34,40,41] as in the present work. Ordered-like BL can be viewed as a graphene layer sharing some sp 3 bonds with the substrate.…”