Negative differential resistance in hybrid carbon-based structures

Here we study negative differential resistance effect in hybrid carbon nanostructures composed of graphene nanoribbons and carbon nanotubes. In the coupled structure, the finite flakes of nanotubes allow the formation of resonant states in the system tuning the conductance and generating Fano antiresonances. A single-band tight-binding approximation is adopted, and the density of states and conductance of the hybrid systems are calculated within the Green's function formalism and recursive numerical approaches. Armchair and zigzag edge geometries are chosen to investigate the topology effects on the electronic and transport properties for different configurations of the hybrid systems. For nanoribbons with armchair edges we derive a multiple-mode approach to analytically calculate the transmission function for the hybrid coupled system. Large and robust negative differential resistance effects are observed in the nanotube-nanoribbon zigzag hybrids that may be used in switching electronic transport responses.

Figure 1

Schematic view of a zigzag hybrid system: a graphene nanoribbon (10-AGNR) with a finite (7,7)CNT lying on it, both with armchair edges. The tube is perfectly superposed with the ribbon.

Figure 2

DOS (left) and conductance (right) of a 6-ZGNR/(7,0)CNT (dark blue curve). The results corresponding to the DOS of the isolated ribbon and tube are shown with green and orange curves, respectively.

Figure 3

DOS (left) and conductance (right) of a 11-AGNR/(7,7)CNT (dark blue curve). The results corresponding to the DOS of the isolated ribbon and tube are shown with green and orange curves, respectively.

Figure 4

Conductance results for different ($n,n$) CNTs on an 8-AGNR. The inset shows the energy values corresponding to the conductance dips for different values of the tube index $n$.

Figure 5

(a) Conductance results of a 7-AGNR/(14,14)CNT (red curve) and the pristine 7-AGNR in a dashed line. The inset shows the nanoribbon LDOS for $E=0.8376$ eV (left) and 1.0 eV (right). (b) LDOS results at the tube for both energies: $E=0.8376$ eV and 1.0 eV in the top and bottom panels, respectively. The carbon sites connecting the AGNR and tube are shown with white symbols.

Figure 6

(a) Conductance of a 6-ZGNR/(15,0)CNT (red curve) and the pristine 6-ZGNR (dashed line) for comparison. The inset shows the nanoribbon LDOS for $E=0.144$ eV (top) and 1.0 eV (bottom). (b) LDOS results at the tube for both energies: $E=0.144eV$ and 1.0 eV in the top and bottom panels, respectively. The carbon sites connecting the ZGNR and tube are represented as white symbols.

Figure 7

Current versus bias voltage for 6-ZGNR/($n$,0)CNTs considering distinct $n$ values and $d=7$. Top and bottom panels are for even-$n$ and odd-$n$ values, respectively, and $T=1$ K.

Figure 8

Dependence of the width of the Fano antiresonance on the tube radius (given in the integer $n$). Inset: Fano fitting of the current dip observed for the current versus bias voltage for a 6-ZGNR/(9,0)CNT, $d=7$, and $T=1$ K.

Figure 9

Current versus bias voltage for an 6-ZGNR with (a) a (4,0)CNT on it for three distinct sizes of the scattering region with the potential drop ($d=3$, 5, and 7), and $T=1$ K.

Figure 10

Current versus bias voltage for $m$-AGNR/($n,n$)ACNT, with $m=6$ and $m=7$, with different central scattering conductors ($d=3$, 5, and 7), distinct armchair tubes ($n=3$ and 5) and $T=1$ K. Inset: Metallic family with $m=5$ and 8, and $d=1$, 3, 5, and 7.