Raman Spectroscopy and in Situ Raman Spectroelectrochemistry of Bilayer¹²C/¹³C Graphene

Abstract

Bilayer graphene was prepared by the subsequent deposition of a (13)C single-layer graphene and a (12)C single-layer graphene on top of a SiO(2)/Si substrate. The bilayer graphene thus prepared was studied using Raman spectroscopy and in situ Raman spectroelectrochemistry. The Raman frequencies of the (13)C graphene bands are significantly shifted with respect to those of (12)C graphene, which allows us to investigate the single layer components of bilayer graphene individually. It is shown that the bottom layer of the bilayer graphene is significantly doped from the substrate, while the top layer does not exhibit a signature of the doping from the environment. The electrochemical doping has the same effect on the charge carrier concentration at the top and the bottom layer despite the top layer being the only layer in contact with the electrolyte. This is here demonstrated by essentially the same frequency shifts of the G and G' bands as a function of the electrode potential for both the top and bottom layers. Nevertheless, analysis of the intensity of the Raman modes showed an anomalous bleaching of the Raman intensity of the G mode with increasing electrode potential, which was not observed previously in one-layer graphene.

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

“…(1), showing that isotopic mixing does not affect the force constant, but only the mean atomic mass. The observed redshifts of the Raman features with increasing 13 C concentration are in good agreement with previous results reported in the literature [11,14]. The laser energy dependences of the G * and 2D peaks are related to the Fermi velocity v F according to the following expressions [17], where (dω iTO /dq) and (dω LA /dq) are the slopes of the iTO and LA phonon dispersions near the K point.…”

“…The G * band involves one iTO and one longitudinal acoustic (LA) phonon whereas the 2D band involves two iTO phonons near the K point. As expected for isotope-enriched carbon materials [4,5,11,14], the position of the Raman peaks decreases with increasing 13 C concentration, which is due to the mass difference between the 12 C and 13 C isotopes. Figure 2 depicts the Raman frequency of the bands shown in Fig.…”

“…Significant efforts have been devoted to produce and study isotope-enriched graphene-related materials [4][5][6][7][8][9][10][11][12][13]. For instance, isotope labeling provided direct evidence that the growth mechanism of graphene is substrate dependent and, furthermore, shed light on the rational design of chemical vapor deposition (CVD) synthesis methods [4][5][6][7][8].…”

“…In the case of SWCNTs, a redshift of the G band when the 13 C concentration is increased * brunorc@fisica.ufmg.br † fantini@fisica.ufmg.br has been reported [10], and a dependence of the G band linewidth on the isotope concentration was observed [14]. Studies of bilayer graphene, where one layer is composed of 12 C atoms and the other of 13 C atoms, were performed, thus allowing the investigation of interlayer interactions in the Raman scattering process [11,15]. It was also observed in twisted bilayer graphene that the G band intensity is enhanced in regions of the sample where the separation in energy of the van Hove singularities in the density of states, which are induced by the twisted electronic band structure, match the laser excitation energy [15].…”

Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers

“…Electrochemical doping or intercalation provides an alternative way to modulate the Fermi level of graphene [41]. The later is an attractive application towards field-effect transistors (FETs).…”