Poster
Raman characterization of cove-shape graphene nanoribbons: a first principles study
1University of Modena and Reggio Emilia, Modena, Italy
2CNR-Nanoscience Institute, S3 Center, Modena, Italy
Graphene nanoribbons (GNRs), defined as nanometer-wide strips of graphene, are attracting increasing attention as highly promising candidates for nano- and opto-electronics. This interest has been boosted by the possibility to achieve ultra-narrow and structurally well-defined GNRs by bottom-up techniques, where the precise structural pattern is dictated by molecular precursors. While atomically precise GNRs on a metallic substrate can now be produced by advanced and well-established techniques [1], liquid-phase processable GNRs with atomically precise edges have been only recently obtained by solution-mediated methods [2]. Such systems are characterized by cove-shape morphology, where a C ring periodically decorates the zigzag edge. In addition, the solubility is provided by functionalizing the edges with long alkyl chains. These systems show peculiar Raman spectra [2], above all in the low-energy region, which cannot be easily interpreted in light of the previous studies on ideal armchair- and zigzag-edged GNRs [3].
Here we present an ab-initio investigation [4] of the vibrational properties and Raman spectra of such novel structures. We find that both the edge geometry and the functional groups influence the Radial-Like Breathing Mode (RLBM), which is significantly redshited with respect to the case of the zigzag backbone, in agreement with experimental observations [2]. The cove-shape morphology of the edge is instead mainly responsible for the activation of the D peak, which is not present in purely zigzag GNRs [3].
[1] Cai et al., Nature Materials 9, 611-612 (2010)
[2] Narita et al., Nat. Chem. 6, 126-132 (2014); ACS Nano 8, 11622 (2014)
[3] Gillen et al., PRB 80, 155814 (2009); PRB 81, 205426 (2010) and references therein
[4] Giannozzi et al., J. Phys. Cond. Matt. 21, 395502 (2009)