Electronic Structure Of Graphene Nanoribbons Research Articles

The effect of N-doping on the electronic structure of graphene nanoribbon

To analyse the effect on electronic structure of nitrogen-doped graphene nanoribbons, the parameters such as the lattice, band structure, density of states of intrinsic graphene nanoribbon, N-doped graphene nanoribbons are calculated by using first-principle method. The results demonstrate that the band gap of graphene nanoribbon mainly comes from the new surface states in the edge. The N-doping in the middle of graphene nanoribbon has less influence on the band gap performance than in the edge region, which indicates the atoms in the edge do great contribution to the band gap properties. The N-doping makes the band gap narrower; the sharp changes of the band gap also show that the N-doping is a promising candidate to make the n-type graphene structures.

Physical Insight Into Substitutional N-Doped Graphene Nanoribbons With Armchair Edges

Electronic structures of graphene nanoribbons with armchair edges (AGNRs) containing N-substitutional impurity have been investigated, using ab initio density functional theory. It is shown that the electronic structures of the doped AGNRs are different from those of doped carbon nanotubes (CNTs). N introduces an impurity level above the conduction band minimum (CBM) in the AGNRs while an impurity level introduced by N is below the CBM in the CNTs. This character can be explained as a consequence of the edge polarization effects, which ionize the impurity level so that the relevant charge carriers occupy the conduction bands, which is independent of curvature and doping site. Although the N-doped AGNR and CNT are all n-type semiconductors, an implication of the result is that edge polarization effects could make some properties of the N-doped AGNRs different from those of N-doped CNTs. It suggests the possibility to make 1-D doped structures with novel physical and device characteristics.

Effect of Layer Stacking on the Electronic Structure of Graphene Nanoribbons

The evolution of electronic structure of graphene nanoribbons (GNRs) as a function of the number of layers stacked together is investigated using ab initio density functional theory (DFT), including interlayer van der Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer AGNRs, exhibit three classes of band gaps depending on their width. In zigzag GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions plays a crucial role in determining the magnetic polarization and the band structure. The antiferromagnetic (AF) interlayer coupling is more stable compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF in-layer and AF interlayer coupling have a finite band gap, while ZGNRs with the FM in-layer and AF interlayer coupling do not have a band gap. The ground state of the bilayer ZGNR is nonmagnetic with a small but finite band gap. The magnetic ordering is less stable in multilayer ZGNRs compared to that in single-layer ZGNRs. The quasiparticle GW corrections are smaller for bilayer GNRs compared to single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs compared to single-layer GNRs.

The Influence of Out-of-Plane Deformation on the Band Gap of Graphene Nanoribbons

We performed ab initio calculations to study the effect of out-of-plane deformation on the electronic structures of graphene nanoribbons. We find that the band gap of severely curved GNR is significantly modified and a semiconductor−metal transition can be observed under the radial deformation. The band gap changes mainly arise from the hybridization of σ and π orbitals and the modification of orbital interactions. It is possible that good geometry control can result in semiconductor−metal transition in deformed graphene nanoribbons.

The Effects of the Modulated Magnetic Fields on Electronic Structures of Graphene Nanoribbons

The low-energy magnetoelectronic structures of nanographene ribbons under a modulated magnetic field are investigated by the Peierls tight-binding model. They are dominated by the field strength, period, phase, the ribbon width, and edge structure. The modulated magnetic field could add state degeneracy, modify energy dispersions, alter subband spacings, affect carrier-density distributions, create additional band-edge states, and cause semiconductor-metal transitions. The main features of energy bands are directly reflected in density of states, such as the position, height, structure, and number of the prominent peaks. These results immensely differ from those in a uniform magnetic field. Significant differences between a 1D graphene ribbon and a 2D electron gas are also found.

The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons

Graphene shows promise as a future material for nanoelectronics owing to its compatibility with industry-standard lithographic processing, electron mobilities up to 150 times greater than Si and a thermal conductivity twice that of diamond. The electronic structure of graphene nanoribbons (GNRs) and quantum dots (GQDs) has been predicted to depend sensitively on the crystallographic orientation of their edges; however, the influence of edge structure has not been verified experimentally. Here, we use tunnelling spectroscopy to show that the electronic structure of GNRs and GQDs with 2-20 nm lateral dimensions varies on the basis of the graphene edge lattice symmetry. Predominantly zigzag-edge GQDs with 7-8 nm average dimensions are metallic owing to the presence of zigzag edge states. GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width, and the magnitudes of the measured GNR energy gaps agree with recent theoretical calculations.

Tight binding studies on the electronic structure of graphene nanoribbons

Based on the π-electron energy dispersion relation of general compound lattices derived from the tight-binding model, and assuming that the transverse confinement potential of graphene nanoribbon is a infinite hard-wall potential，we obtain the energy dispersion relation of graphene nanoribbon and the conditions that determine whether it is metallic or semi-conducting. The results presented here show that the electronic structure of graphene nanoribbon is intimately related to its geometric structure （symmetry and width），so graphene nanoribbon can be modified as metallic or semi-conducting materials only by controlling its geometric configurations，which suggests that it is highly promising to use graphene nanoribbon to develop novel nano-scale devices.

The electronic structure and transport properties ofgraphene nanoribbons with divacancies defects

Based on first-principles calculation of the electronic structure and transport properties, we study the electronic structure and transport properties of graphene nanoribbons （GNRs） with 585 divacancies defects. It is shown that because of the existence of 585 divacancies defects, there are defected band belts in the energy gap located at the defects for the zigzag graphene nanoribbon （ZGNRs） and their energy gaps will increase. The spatial orientations of the divacancies defects have effect on the electronic structure of the system. In addition, the influences of 585 divacancies defects on the transport properties of the ZGNRs with small energy gaps are great, while that on the transport properties of the ZGNRs with large energy gaps are small. And the spatial orientations of the defects have no obvious influence on the transport properties.

Strain effect on electronic structures of graphene nanoribbons: A first-principles study

We report a first-principles study on the electronic structures of deformed graphene nanoribbons (GNRs). Our theoretical results show that the electronic properties of zigzag GNRs are not sensitive to uniaxial strain, while the energy gap modification of armchair GNRs (AGNRs) as a function of uniaxial strain displays a nonmonotonic relationship with a zigzag pattern. The subband spacings and spatial distributions of the AGNRs can be tuned by applying an external strain. Scanning tunneling microscopy dI/dV maps can be used to characterize the nature of the strain states, compressive or tensile, of AGNRs. In addition, we find that the nearest neighbor hopping integrals between pi-orbitals of carbon atoms are responsible for energy gap modification under uniaxial strain based on our tight binding approximation simulations.

Tuning the electronic structure of graphene nanoribbons through chemical edge modification: A theoretical study

We report combined first-principle and tight-binding (TB) calculations to simulate the effects of chemical edge modifications on structural and electronic properties. The C-C bond lengths and bond angles near the graphene nanoribbon (GNR) edge have considerable changes when edge carbon atoms are bounded to different atoms. By introducing a phenomenological hopping parameter ${t}_{1}$ for nearest-neighbor hopping to represent various chemical edge modifications, we investigated the electronic structural changes of nanoribbons with different widths based on the tight-binding scheme. Theoretical results show that addends can change the band structures of armchair GNRs and even result in observable metal-to-insulator transition.