Electronic Structure and Stability of Semiconducting Graphene Nanoribbons

Abstract

We present a systematic density functional theory study of the electronic properties, optical spectra, and relative thermodynamic stability of semiconducting graphene nanoribbons. We consider ribbons with different edge nature including bare and hydrogen-terminated ribbons, several crystallographic orientations, and widths up to 3 nm. Our results can be extrapolated to wider ribbons providing a qualitative way of determining the electronic properties of ribbons with widths of practical significance. We predict that in order to produce materials with band gaps similar to Ge or InN, the width of the ribbons must be between 2 and 3 nm. If larger bang gap ribbons are needed (like Si, InP, or GaAs), their width must be reduced to 1-2 nm. According to the extrapolated inverse power law obtained in this work, armchair carbon nanoribbons of widths larger than 8 nm will present a maximum band gap of 0.3 eV, while for ribbons with a width of 80 nm the maximum possible band gap is 0.05 eV. For chiral nanoribbons the band gap oscillations rapidly vanish as a function of the chiral angle indicating that a careful design of their crystallographic nature is an essential ingredient for controlling their electronic properties. Optical excitations show important differences between ribbons with and without hydrogen termination and are found to be sensitive to the carbon nanoribbon width. This should provide a practical way of revealing information on their size and the nature of their edges.

Structure of graphene and its disorders: a review

“…On the basis of tight binding theory, the zigzag GNRs are always metallic, while the armchair GNRs exhibit either metallic or semiconducting behaviors, depending on their width. For instance, DFT shows that the energy band gaps of semiconducting armchair GNRs increase as their width decreases [81]. This property of armchair GNRs is also evidenced from experiments [102].…”

“…Zigzag and armchair are two main types of edges along the crystallographic directions in graphene. In recent years, extensive studies were carried out to investigate the relative stability of these two edge orientations and the edge orientation-dependent physics for mechanically exfoliated monolayer graphene flakes [72–74], epitaxial graphene islands [75–77], CVD derived graphene grains [78], and graphene nanoribbons (GNRs) [79–81]. …”

Strain-activated edge reconstruction of graphene nanoribbons

“…29 Figure 2 shows the edge evolution of a typical GNR through various configurations. We find that the GNR keeps its zigzag direction for more than 10 073406-2 electron irradiation. In addition, Fig.…”

“…[10][11][12][13] Recently, strain has been suggested as another effective approach to tailor the electronic structure, as it is required for nanoelectromechanical systems. [14][15][16] Moreover, it has been predicted theoretically that bending of a ribbon in-plane into a circular arc simulates a magnetic field of 10 T. 17 Tensile (compressive) strain in graphene results in lattice modifications and corresponding phonon mode softening (hardening).…”

Bulk properties of solution-synthesized chevron-like graphene nanoribbons

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20] The resulting GNRs are very narrow (typically with widths, w < 2 nm) and have atomically precise edges, which is very important for potential applications. [3][4][5][6]21,22 One type of synthetic GNRs that has received considerable theoretical [23][24][25] and experimental attention 9,16,19,20,26 is the chevron-like GNR that has a very distinct periodic structure (Fig. 1a).…”