Modulation of bandgap in bilayer armchair graphene ribbons by tuning vertical and transverse electric fields

Abstract

We investigate the effects of external electric fields on the electronic properties of bilayer armchair graphene nano-ribbons. Using atomistic simulations with Tight Binding calculations and the Non-equilibrium Green's function formalism, we demonstrate that (i) in semi-metallic structures, vertical fields impact more effectively than transverse fields in terms of opening larger bandgap, showing a contrary phenomenon compared to that demonstrated in previous studies in bilayer zigzag graphene nano-ribbons; (ii) in some semiconducting structures, if transverse fields just show usual effects as in single layer armchair graphene nano-ribbons where the bandgap is suppressed when varying the applied potential, vertical fields exhibit an anomalous phenomenon that the bandgap can be enlarged, i.e., for a structure of width of 16 dimer lines, the bandgap increases from 0.255 eV to the maximum value of 0.40 eV when a vertical bias equates 0.96 V applied. Although the combined effect of two fields does not enlarge the bandgap as found in bilayer zigzag graphene nano-ribbons, it shows that the mutual effect can be useful to reduce faster the bandgap in semiconducting bilayer armchair graphene nano-ribbons. These results are important to fully understand the effects of electric fields on bilayer graphene nano-ribbons (AB stacking) and also suggest appropriate uses of electric gates with different edge orientations..

Enhancement of the Seebeck effect in bilayer armchair graphene nanoribbons by tuning the electric fields

“…In contrast, without external fields applied, the structure M = 14 (group 3p + 2) exhibits as semimetallic and in agreement with the conclusions in previous studies. [19] In the presence of a vertical electric field, the bandgap of former groups becomes narrower whereas it increases in the later one.…”

“…In Fig. 3 (a) As it has been demonstrated that the bandgap in BL-AGNRs and AGNRs strongly depends on the width of the structures, [19,23] it is thus relevant to investigate the interplay of the Seebeck coefficient and the number of dimer linesM. The maximum Seebeck coefficient of BL-AGNRs was deduced as a function of M for three characteristic groups of the width 3p, 3p + 1 and 3p + 2 and shown in Fig.…”

“…The width of the BL-AGNR is characterized by number of dimer lines M along the width of each sub-ribbon. [19] The parameters   0 1 3 4 , , , t t t t are the hoping energies in which 0 t is the intra-layer nearest-neighbor interaction between carbon atoms at A and B sites while 1 t , 3 t and 4 t present the inter-layer interactions between the nearest atoms (sites A-B), the next-nearest atoms (sites A-B) and the next-nearest atoms (sites A-A, B-B) in two layers, respectively. [25][26][27] To explore the effect of the vertical electric field on the electronic structure and the transport properties of BL-AGNRs, a bottom and top gates with electrostatic potentials /2…”

The Effect of Critical Electric Fields on the Electronic Distribution of Bilayer Armchair Graphene Nanoribbons

“…Previous studies have shown that in the BL-AGNR structure, the perpendicular electric field has a significant impact on tuning the bandgap of the material. On the other hand, the parallel electric field has a greater influence on the energy dispersion of zigzag bilayer graphene (Vũ & Trần, 2016;Vũ et al, 2017). Similar analytical calculations for each dimer line corresponding to each termination state have demonstrated that the maximum magnitudes of the gap are dissimilar for different critical potential strengths (Vũ & Trần, 2016;Vũ et al, 2017;Vũ et al, 2018).…”

Ferrimagnetic and antiferromagnetic phase in bilayer graphene nanoflake controlled with external electric fields

“…In addition to the infinite, two-dimensional bilayers, bilayer graphene nanostructures constitute a class of highly promising systems due to additional possibility of shaping their edge geometry to engineer the desired properties. This concerns, for example, one-dimensional nanoribbons [21][22][23][24][25][26][27][28]. It is also notable that highly non-trivial magnetic properties of bilayer zero-dimensional nanoflakes, in particular influenced by electric field, attracted considerable attention [29][30][31][32][33][34][35].…”