Electric gating induced bandgaps and enhanced Seebeck effect in zigzag bilayer graphene ribbons

Superlattices and Microstructures

Huy

et al. 2017

Self Cite

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..

Section: Introductionsupporting

confidence: 42%

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

Superlattices and Microstructures

Huy

et al. 2017

Self Cite

“…[14][15][16][17][18][19] It has shown that the bandgap in bilayer ribbon structures is strongly modulated under the impact of electric fields. [18,19] In bilayer zigzag graphene nanoribbons (BL-ZGNRs), [18] an energy gap up to 600 meV has been achieved in narrow ribbon structures and under the simultaneous influence of vertical and transverse electric fields. This bandgap induced by the presence of electric fields in BL-ZGNRs is much higher than that obtained by the same effect in 2D bilayer graphene sheets which is about 250 meV.…”

Section: Introductionmentioning

confidence: 99%

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

Superlattices and Microstructures

et al. 2018

Self Cite

The Seebeck coefficient in single and bilayer graphene sheets has been observed to be modest due to the gapless characteristic of these structures. In this work, we demonstrate that this coefficient is significantly high in quasi-1D structures of bilayer armchair graphene nanoribbons (BL-AGNRs) thanks to the open gaps induced by the quantum confinement effect. We show that the Seebeck coefficient of BL-AGNRs is also classified into three groups 3p, 3p + 1, 3p + 2 as the energy gap. And for the semiconducting BL-AGNR of width of 12 dimer lines, the Seebeck coefficient is found as high as 707 µV/K and it increases up to 857 µV/K under the impact of the vertical electric field. While in the semimetallic structure of width of 14 dimer lines, the Seebeck coefficient remarkably enhances 14 times from 40 µV/K to 555 µV/K. Moreover, it unveils an appealing result as the Seebeck coefficient always increases with the increase of the applied potential. Such BL-AGNRs appear to be very promising for the applications of the next generation of both electronic and thermoelectric devices applying electric gates. Modeling and Methodologies 2.1 Modeling

“…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).…”

Section: Introductionmentioning

confidence: 79%

“…In particular, the gap size for the armchair edge is Egap_max = 400 meV under the effect of |𝑉 𝑡 | = 0.96 V for M = 16 or Egap_max = 350 meV with |𝑉 𝑡 | = 1.3 V for M = 17 (Vũ et al, 2017). For the zigzag edge, the energy gaps of M = 16 and M = 19 have peaks of approximately 450 meV and 369 meV at |𝑉 𝑠 | = 1.14 V and |𝑉 𝑠 | = 0.92 V, respectively (Vũ & Trần, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…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). In particular, the gap size for the armchair edge is Egap_max = 400 meV under the effect of |𝑉 𝑡 | = 0.96 V for M = 16 or Egap_max = 350 meV with |𝑉 𝑡 | = 1.3 V for M = 17 (Vũ et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Nguyễn

Phạm

et al. 2021

DLU JOS

We employed tight-binding calculations and Green’s function formalism to investigate the effect of applied electric fields on the energy band and electronic properties of bilayer armchair graphene nanoribbons (BL-AGNRs). The results show that the perpendicular electric field has a strong impact on modifying and controlling the bandgap of BL-AGNRs. At the critical values of this electric field, distortions of energy dispersion in subbands and the formation of new electronic excitation channels occur strongly. These originate from low-lying energies near the Fermi level and move away from the zero-point with the increment of the electric field. Phase transitions and structural changes clearly happen in these materials. The influence of the parallel electric field is less important in changing the gap size, resulting in the absence of the critical voltage over a very wide range [–1.5 V; 1.5 V] for the semiconductor-insulator group. Nevertheless, it is interesting to note the powerful role of the parallel electric field in modifying the energy band and electronic distribution at each energy level. These results contribute to an overall picture of the physics model and electronic structure of BL-AGNRs under stimuli, which can be a pathway to real applications in the future, particularly for electronic devices.