In recent years there has been a growing interest in sp-carbon chains as possible novel nanostructures. An example of sp-carbon chains are the so-called polyynes, characterized by the alternation of...
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 new 2D
systems with tunable properties is an important
subject for science and technology. Starting from graphene, we developed
an algorithm to systematically generate 2D carbon crystals belonging
to the family of graphdiynes (GDYs) and having different structures
and sp/sp
2
carbon ratios. We analyze how structural and
topological effects can tune the relative stability and the electronic
behavior, to propose a rationale for the development of new systems
with tailored properties. A total of 26 structures have been generated,
including the already known polymorphs such as α-, β-,
and γ-GDY. Periodic density functional theory calculations have
been employed to optimize the 2D crystal structures and to compute
the total energy, the band structure, and the density of states. Relative
energies with respect to graphene have been found to increase when
the values of the carbon sp/sp
2
ratio increase, following
however different trends based on the peculiar topologies present
in the crystals. These topologies also influence the band structure,
giving rise to semiconductors with a finite band gap, zero-gap semiconductors
displaying Dirac cones, or metallic systems. The different trends
allow identifying some topological effects as possible guidelines
in the design of new 2D carbon materials beyond graphene.
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