Raman and IR spectra of graphdiyne nanoribbons

Abstract

γ-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp 2 carbon atoms organized as hexagonal rings connected by linear links, and it is predicted to be a semiconductor. The lateral confinement of γ-graphdiyne nanoribbons significantly affects the electronic and vibrational properties. By means of periodic Density Functional Theory (DFT) calculations we here investigate the electronic band structure, the Raman and IR spectra of γ-graphdiyne 2D crystal and related nanoribbons. We discuss the effect of the functional and basis set on the evaluation of the band gap, highlighting the reliability of hybrid functionals. By joining DFT calculations with a symmetry analysis, we assign in detail the IR and Raman spectra of γ-graphdiyne. On this basis we show the modulation of the gap in nanoribbons of increasing width and different edges (armchair, zigzag). We assess how confinement affects the Raman and IR spectra by comparing vibrational modes with phonons of the parent 2D crystal. Our symmetry-based classification allows identifying the marker bands sensitive to the edge structure and lateral confinement of nanoribbons of increasing width. These results show the effectiveness of vibrational spectroscopy for the characterization of such nanostructures.

Designing All Graphdiyne Materials as Graphene Derivatives: Topologically Driven Modulation of Electronic Properties

“…As also demonstrated in our previous work on y-GDY (6-hT 2 ), this functional can indeed give a more accurate quantitative evaluation of the band gap, in agreement with benchmark GW-computed values, even if the qualitative trends are the same obtained with PBE0. 31 The comparison between the band structure/DOS computed with these two functionals is reported in the Supporting Information (Table S1). As expected, HSE06 band gap values are lower: 1.11 versus 1.63 eV for 6-hT 2 (y-GDY), 0.34 versus 0.83 eV for 6-hT 2 R, and 0.68 versus 1.14 eV for 6-HT 2 (β-GDY); however, they still confirm that these structures are finite-band gap semiconductor.…”

“… 52 This level of theory has been chosen according to our previous investigations of the structural and vibrational properties of γ-GDY and related nanoribbons, where the results obtained using different functionals and basis sets have been compared. 31 When using the 6-31G(d) basis set in PBC-DFT simulations with the CRYSTAL code, the exponent of the diffuse sp orbitals of carbon atoms has been increased from 0.1687144 to 0.187 bohr –2 to avoid convergence problems in the SCF, due to basis set linear dependencies. 53 Considering the other simulation parameters, the tolerance on integral screening has been fixed to 9,9,9,9,80 (TOLINTEG parameters), while the shrink parameters defining Monkhorst–Pack and Gilat sampling points have been fixed to 100 and 200 for the calculation of the band structure and DOS, respectively.…”

“…Even if a further improvement could be obtained by employing the HSE06 functional, 54 in our previous investigation on γ-GDY and its nanoribbons, we verified if both PBE0 and HSE06 are able to describe the same trends for band gaps, with a larger overestimation of PBE0 ones with respect to benchmark values computed by the GW method. 31 For some peculiar structures, full geometry optimization and band structure and DOS calculations have been carried out also using the HSE06 functional and compared with PBE0 results.…”

“…These structures are a part of a larger family of two-dimensional π-conjugated Covalent Organic Frameworks (COF) showing the occurrence of Dirac cones [19,20], flat bands, tunable bands gap. Such phenomena observed in the electronic structure of COFs have been explained based on peculiar topological effects also in connection to their influence on the charge transport behavior [21][22][23][24].Several papers report on the prediction of properties of γ-GDY mainly through Density Functional Theory (DFT) calculations [5,6,[25][26][27][28]29]. From the experimental side, synthetic bottom-up approaches have been successfully employed to produce sub-fragments of GDY of different topology and dimensions in particular by .…”

Structural, Electronic, and Vibrational Properties of a Two-Dimensional Graphdiyne-like Carbon Nanonetwork Synthesized on Au(111): Implications for the Engineering of sp-sp2 Carbon Nanostructures

“…The characteristic Raman signal of sp carbon and its structure-related behavior allows a detailed investigation of sp and sp-sp 2 carbon systems. 18 , 19 …”