Pristine Armchair Graphene Nanoribbons Research Articles

A new insight into transition metal doped graphene nanoribbon for hydrogen sulfide gas adsorption: First principle investigation

Detection of toxic gases is critical for the protection of human health and preserving nature's creation. This study uses armchair graphene nanoribbon (AGNR) and modified derivatives of AGNR to examine the hydrogen sulfide (H2S) gas adsorption using density functional theory (DFT). The modified derivatives considered are Cu and Pt doped AGNR. The feasibility and effectiveness of the modified AGNR optimized structures for H2S adsorption have been investigated along with geometrical variation, binding distance and binding energies. Furthermore, the electronic characteristics such as band gap (Eg) and density of states (DOS) have been computed. After adsorption of H2S, the semiconducting nature of AGNR has been changed by observing variation in band gap as a parameter of H2S binding distance from the AGNR surface. After Cu and Pt atom doping, the adsorption energy for H2S gas enhanced to -3.30 and -4.19 eV respectively, which is more than 7 times as compared to pristine AGNR surface. The substantial increase in the adsorption characteristics after Pt doping shows that Pt has a significant effect on improving AGNR's sensing capabilities for the adsorption of H2S gas. Thus, Pt-doped AGNR is a promising material for H2S gas adsorption and detection.

First-principles calculations of electrical conductivities of edge-modified graphene nanoribbons: Strain effect

We investigate the influence of strain on the electrical properties of graphene nanoribbons that have potential applications in making sensors and other optoelectronic devices. In particular, we chose pristine armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH), boron doped armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH-B) and armchair graphene nanoribbons with 7 zigzag edges that have one carbon atom vacancy (7aGNRsH-V). Based on first-principles calculations, results show that pristine unstrained 7aGNRsH is electrically nonconductive but turns to be electrically conductive in a wide range of energy spectrum , e.g., from IR to visible to UV, due to the application of strain engineering. In metallic unstrained and strained 7aGNRsH-B and 7aGNRsH-V, non-vanishing electrical conductivity in the IR, visible and UV energy spectrum regimes are observed. We also investigate the influence of strain on the Berry curvature of 7aGNRsH, 7aGNRsH-B and 7aGNRsH-V nanoribbons. The results show that fermions are spread through out the Brillouin zone in the reciprocal space for semiconducting unstrained 7aGNRsH but localized near the Γ -point for strained 7aGNRsH that have out-of-plane deformations due to strain engineering. For metallics 7aGNRsH-B and 7aGNRsH-V, Berry curvature plots show that fermions are localized far away from the Γ -point. In two atom boron doped p-type armchair graphene nanoribbons with 7 zigzag edges (7aGNRsH-2B), large peaks in electrical conductivity at IR energy spectrum regimes can be observed. These peaks of electrical conductivities in 7aGNRSH-2B may be detectable in experimentally synthesized structure in Cloke et al. (2015) [1] . • In Figs. 2 , 3 , 4 , we have provided results for band structures calculations obtained from pw.x and maximally localized wannier 90 method that are in excellent agreement. This provides foundation for investigation of influence of strain on the Berry curvature and electrical conductivity. Note that 7 boron doped armchair graphene nanoribbons in Fig. 3 and one carbon vacancy in 7 armchair graphene nanoribbons in Fig. 4 are metallic in nature. • When we apply strain, we have a relaxed shape armchair graphene nanoribbon and thus we expect localization of fermions near Gamma-point which can be clearly seen in Fig. 8 . • Since Fermi energy stays below the top of the valence band in metallic boron doped and vacancy of one carbon atom in graphene nanoribbon, we see the cut-off point in Berry curvature in Fig. 5 . • Most importantly in Figs. 6 , 11 and 12 , we see that intrinsic 7 armchair graphene nanoribbon is not conductive but metallic boron doped and vacancy created nanoribbon are conductive in the wide range of energy spectrum regimes, e.g., from IR to visible to UV.

Thermoelectric transport properties of armchair graphene nanoribbon heterostructures

In this paper, we numerically analyze the thermoelectric (TE) properties of recently synthesized graphene nanoribbon (GNR) heterostructures that are obtained as extensions of pristine armchair graphene nanoribbons (AGNRs). After simulating their band structure through a nearest-neighbor tight-binding model, we use the Landauer formalism to calculate the necessary TE coefficients, with which we obtain the electrical conductance G, thermopower S, thermal conductance K e , linear-response thermocurrent , and figure of merit ZT (using literature results for the phonon thermal conductance K ph ), at room temperature. We then compare the results for the nanoribbon heterostructures with those for the pristine AGNR nanoribbons. The comparison shows that the metallic AGNRs become semiconducting (with much higher ZT values) after the inclusion of the extensions that transform them into heterostructures and that some heterostructures have higher values of ZT when compared to the semiconducting pristine AGNRs from which they have originated.

Adsorption chemistry of co-doped graphene nanoribbon and its derivatives towards carbon based gases for gas sensing applications: Quantum DFT investigation

Sensing of the toxic gases plays a vital role in the human life to improve their health aspects and the quality of life. Using the first-principles calculations combined with density functional theory (DFT), the authors in this research work have explored the adsorption energy and electronic features of co-doped armchair graphene nanoribbon (ArGNR) and its derivatives, such as the co-doped armchair graphene oxide nanoribbon (ArGONR) and co-doped armchair reduced graphene oxide nanoribbon (ArRGONR) with boron and phosphorus (BP) atoms. A comparative study of detection of toxic carbon based gases (CO, CO2, CH4) on co-doped graphene nanoribbon (BP-ArGNR), and its derivatives such as BP-ArGONR (addition of more oxygen atoms in pristine ArGNR) and BP-ArRGONR (addition of less oxygen atoms in pristine ArGNR) has been performed. To evaluate the sensing of carbon based gases, their adsorption energies, binding distances, charge transfer, band structures and density of states have been studied for different variants. Before modification, adsorption energies for BP-ArGNR have been found to be smaller than the BP-ArGONR for CO, CO2 and CH4 molecules, thereby showing physisorption mechanism. Our computational results also revealed that after modification with oxygen atoms, BP-ArGONR shows relatively more negative value of adsorption energy in comparison to the pristine ArGNR (PR-ArGNR) for CO, CO2 and CH4 molecules, thereby showing chemisorption phenomenon. Band structure analysis predicts large band gap variations for BP-ArGONR as compared to PR-ArGNR. Thus, the authors concluded that after modification of graphene surface, enormous changes are observed in adsorption energies and band gap for BP-ArGONR towards all carbon based gases under study and hence significantly enhance the sensing performance of pristine graphene.

Electron Transport in N-functionalised Armchair Graphene Nanoribbons: Computational Insight

Density functional theory (DFT) theoryhas been used to explore the electronic and transport properties of (3, 0) pristine armchair graphene nanoribbons (AGNR) and its Nitrogen (N) doped counterparts. The analysis has been performed for four different Nitrogen doping concentrations i.e., 6.25%, 12.5%, 18.75% and 25% by replacing the carbon atoms of the pristine AGNR. The computed formation energy (Eform) confirms that the stability of N-doped AGNR is comparable to pristine AGNR. Band structure and density of states profile shows that pristine AGNRs havea band gap of 1.06 eV and introduction of N doping changes its behavior to n-type semiconductor. Interestingly, in N doped AGNR, its metallic character remains intact with increasing concentration of N and shows superior current-voltage characteristics compared to linear atomic chains of metals, with 25% doping concentration. This interesting behavior of N doped AGNR can be exploited for its application as electrodes or interconnects in electronic devices.

Density functional theory study of carbon monoxide adsorption on transition metal doped armchair graphene nanoribbon

Density Functional Theory calculations are used to study adsorption of carbon monoxide gas on transition metal doped armchair graphene nanoribbon. Sensing behaviour of pristine armchair graphene nanoribbon (Pr-AGNR) and different geometries of osmium doped AGNR such as one-edge doped AGNR, center doped AGNR and both-edge doped AGNR have been investigated. Most stable adsorption geometry, adsorption energy, binding distance, band structure and density of states of different geometries using in our work have been discussed. Electronic properties of different sensing materials can be interpreted in terms of band structure and density of states. It was studied that a weak type of physical adsorption process took place when CO molecule interacts with pristine AGNR with a very small amount of adsorption energy of amount −0.22 eV. This suggests that pristine graphene is not a good adsorber for CO adsorption. In contrast, doping of graphene with osmium atom enhances the adsorption energy of Pr-AGNR to greater extent. Computational results concluded that osmium doping in graphene nanoribbon at one-edge and both-edge position increases the adsorption energies with values −6.77 eV and −9.53 eV respectively which is 30 times and 43 times greater than in comparison to Pr-AGNR. Energy gap calculations proves that large band gap variations are observed for both-edge doped graphene nanoribbon. Sharp and intense peaks at various energy levels from density of states analysis of both-edge doped geometry confirms adsorption of CO. Our results predicts that both-edge osmium doped sensing material can be considered as promising sensing material for CO adsorption.

Bandgap engineering in Ga and P doped armchair graphene nanoribbons: DFT analysis

The paper reports a study, on calculations performed through plane wave Density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) formalism, to analyze the electronic and structural properties of armchair graphene nanoribbons (AGNR) doped with Phosphorous (P) (N type), and Gallium (Ga) (P type), with two different doping concentration viz 6.25% and 12.5%. It has been observed that (3, 0) Pristine AGNR exhibit a band gap of 1.06 eV. While, on doping with P, and Ga induce metallicity in AGNR, where with increasing doping concentration current increases linearly in Ga doped AGNR whereas, with increasing concentration of P, current decreases in P doped AGNR but AGNR remains Metallic. AGNRs with 6.25% doping concentration can be used as interconnect application due to linear rise in current and other counterparts can be used in electrode of transistor.

Antidote-induced armchair graphene nanoribbon based resonant tunneling diodes

Resonant tunneling phenomena are explored using armchair graphene nanoribbon (AGNR), which eliminates the lattice mismatch and electron mobility degradation problems of conventional heterostructure resonant tunneling diodes (RTDs). Eight antidote topologies are proposed in this paper. These antidote topologies significantly increase or decrease the band gap of AGNR. Both double barrier quantum well and single barrier quantum well structures have been achieved by putting the antidote-induced AGNRs and pristine AGNRs. A numerical approach with a tight binding model and non-equilibrium Green’s function formalism has been used to simulate the quantum phenomena of the device. Current–voltage characteristics of these proposed RTDs show a high peak to valley ratio and low power dissipation with respect to different antidote topologies. Channel length variation effects are investigated in the proposed RTDs, and it is found that the peak to valley ratio, valley current, valley voltage, and power dissipation can be improved by tuning the channel length. These graphene-based RTDs are easy to fabricate and offer more flexibility in terms of peak to valley ratio, valley current, valley voltage, and power dissipation.

Graphene nanoribbon as HBr sensor: An ab-initio analysis

The present paper reports the suitability of 3,0 armchair graphene nanoribbon (AGNR) for hydrogen bromide (HBr) sensing, by analysing its band gap variation in vacuum as well as HBr gas environment. The hydrogen bromide sensing ability of pristine AGNR has been analysed by using a DFT based ab-initio approach, applied through Generalized Gradient Approximation with Perdew, Burke and Ernzerhof type parameterization. It has been observed that out of three possible sites, the centre of the benzene has been found as the best adsorption site, measured through calculation of binding energy of the HBr adsorbed system. The presence of HBr molecule near the surface of GNR reduces the bandgap of pristine AGNR, remarkably. The surface sensitivity has also been verified through increasing the number of HBr molecule on the small surface of AGNR and found beyond three HBr molecule, the change in bandgap energy is almost negligible and hence decides the limit of detection. The zero bias sensitivity has also been verified through large drop in current as a function of voltage in HBr adsorbed AGNR at different HBr distances from AGNR surface.

Carbon-dioxide gas sensor using co-doped graphene nanoribbon: A first principle DFT study

First Principle calculations along with non equilibrium Green’s Function (NEGF) have been performed to sense CO2 gas molecule using armchair graphene nanoribbon (ArGNR) and its co-doped system. CO2 is one of the toxic gas produced from various sources. The development of more efficient gas sensor for detection of CO2 gas is required. Different sensing nanomaterials are optimized viz pristine ArGNR (Pr-ArGNR) and ArGNR co-doped with Boron-Phosphorus (BP-ArGNR), Boron–Nitrogen (BN-ArGNR), Boron–Arsenic (BAs-ArGNR) & Boron– Antimony (BSb-ArGNR). The transfer of charge between CO2 and these variants is analyzed in terms of adsorption energy, band structures and density of states (DOS). Computational Results show that Pr-ArGNR is not much sensitive to CO2 gas molecule in comparison to other variants. Whereas BP-ArGNR shows adsorption energy of −1.19 eV which is nearly eight times greater than Pr-ArGNR and BN-ArGNR. Large band gap variations are observed for BP-ArGNR from 1.91 eV to 1.56 eV. The DOS study confirms the interaction of CO2 molecule with different sensing materials used in our work. Significant changes are observed in density of states of BP-ArGNR. Therefore it is concluded that BP-ArGNR can be a promising sensing material for detection of CO2 gas.

Spin-polarized electron transmission through B-doped graphene nanoribbons with Fe functionalization: a first-principles study

In this study, we investigate the electron transport properties of a B-doped armchair graphene nanoribbon (AGNR) suspended between graphene electrodes based on first-principles calculations. Our calculations reveal that one of the electron transmission channels of a pristine AGNR junction is closed by the B-doping. We then proceed to explore the effect of the B-doping on the spin-polarized electron transport behavior of a Fe-functionalized AGNR junction. As a result, transmission channels for majority-spin electrons are closed and the spin polarization of the electron transmission is enhanced from 0.60 for the Fe-functionalized AGNR junction to 0.96 for the B- and Fe-codoped one. This observation implies that the codoped AGNR junction can be employed as a spin filter. In addition, we investigate the electronic nature of the transmission suppression caused by the B-doping. A detailed analysis of the scattering wave functions clarifies that a mode modulation of an incident wave arises in the B-doped AGNR part and the incident wave connects to an evanescent wave in the transmission-side electrode. For pristine and Fe-functionalized AGNR junctions, such a mode modulation is not observed and the incident wave connects to a propagating wave in the transmission-side electrode. Tuning of electron transport property by exploiting such a mode modulation is one of promising techniques for designing functionality of spintronics devices. We also discuss the general correspondence between the electron transmission spectrum and the density of states of a junction.

First-principles study of the electronic structure and transport properties of armchair graphene nanoribbons with adsorbed super-halogen LiF2 and super-alkali Li3 clusters

The electronic structure and quantum transport properties of pristine armchair graphene nanoribbons (AGNRs) and AGNRs adsorbing super-halogen LiF2 and super-alkaline Li3 clusters (Li3/AGNRs/LiF2) were investigated using density functional theory and non-equilibrium Green's function calculations. It was found that LiF2 and Li3 clusters are stably adsorbed on the AGNRs, and the adsorption of Li3 and LiF2 endows AGNRs with the characteristics of n-type and p-type semiconductors, respectively. The Li3/AGNRs/LiF2 structure reduces the band gap and the turn-on voltage, and improves the transmission coefficient of the ANGRs device. This structure also exhibit the rectification characteristics of a pn junction with the forward bias current greater than the reverse bias current. This shows that adsorption of super-alkali and super-halogen clusters in different regions of AGNRs is a feasible approach for obtaining AGNRs with pn junction characteristics.

Modeling of lightly-doped drain and source contact with boron and nitrogen in graphene nanoribbon

Graphene, a monolayer carbon atoms arranged in hexagonal honeycomb lattice possesses impressive electronic properties. It is utilized as channel, source and drain contact in graphene nanoribbon field-effect transistor (GNRFET). Zigzag graphene nanoribbon (ZGNR) is used as semi-metallic drain and source terminal to a pristine armchair graphene nanoribbon (AGNR) that acts as a semiconducting channel. In addition, a single dopant, either nitrogen or boron is added to create lightly-doped drain and source contact. The electronic properties of graphene nanoribbon (GNR) with lightly-doped drain and source contacts are obtained from tight-binding approach. With self-energy matrices, the lightly-doped contacts Hamiltonian matrices are combined with the pristine channel Hamiltonian matrix. The density of states (DOS) are simulated based on the non-equilibrium Green's Function (NEGF) formalism. Our findings are then compared with published research work. Furthermore, it is demonstrated that the DOS of the overall GNR structure still retain a small band gap and possess semiconducting properties when the channel is connected to semi-metallic contact at the drain and source terminal.

Improving gas sensing properties of armchair graphene nanoribbons by oxygen–hydrogen terminated edges

This work is focused on the effects of doping and neutralizing edges of armchair graphene nanoribbon (AGNR) on its gas sensing behavior. Four types of structures, pristine AGNR, boron doped AGNR, nitrogen doped AGNR and defective AGNR, when the ribbons edges are terminated by both hydrogen and oxygen atoms at the same time, are investigated in detail. First, interaction of the aforementioned structures with three gases molecules, CO, O2 and CO2, are investigated by using the density functional theory, then their applications as gas sensors are studied. An AGNR structure depending on its edge termination and type of the adsorbed gas illustrates different atomic configurations. Different atomic configurations show different physical structure, chemical behavior and electronic properties. Our results have shown that the adsorptions of the three gases molecules have stronger interaction with the defective AGNR than with the other three AGNR structures. Therefore, based on quantum analysis of energy and calculation of current flow, the defective AGNR neutralized by both H and O at edges, concurrently, shows high sensitivities to CO, O2 and CO2 gases molecules. In fact, the strong interactions between adsorbed gases molecules and AGNR cause significant changes in electronic properties of edge terminated AGNR. It is worth mentioning that the sensitivity of graphene based gas sensors could be significantly improved by introducing suitable dopants and defects. The results presented in this work indicate that the defective AGNR terminated by both hydrogen and oxygen atoms can operate as a selective CO, O2 and CO2 gas sensor.

A transport isolation by orbital hybridization transformation toward graphene nanoribbon-based nanostructure integration

Among feature-rich graphene-related materials, graphene nanoribbon (GNR)-based nanostructures are particularly attractive because they can provide tunable and excellent electronic properties. However, the integration of high-quality GNR-based nanostructures on a large scale is still an open area. In this paper, a novel idea is proposed: transport isolation. By a construction of different orbital hybridizations of the carbon atoms in graphene, the GNR regions and functionalized graphene regions are integrated. In the hybrid system, the functionalized graphene regions play the role of the isolation barrier. Based on the first principle calculation, it is demonstrated that about 0.6 nm wide hydrogenated graphene is enough to reliably isolate the GNR regions. Besides, it is revealed that once the armchair GNRs (AGNRs) are fully isolated by functionalized graphene, their band gaps are basically maintained and are weakly dependent on the width of functionalized graphene regions. In addition, the transport characteristics of those isolated AGNRs are verified to be similar to the pristine AGNRs at the device level. The above virtues infer our method can effectively produce a reliable isolation, verified by a simulation of device integration demo. We hope it can provide an intriguing option for the integration of GNR-based nanostructures.

Simulations of Propane and Butane Gas Sensor Based on Pristine Armchair Graphene Nanoribbon

Over the last decade graphene and its derivatives have gained a remarkable place in research field. As silicon technology is approaching to its geometrical limits so there is a need of alternate that can replace it. Graphene has emerged as a potential candidate for future nano-electronics applications due to its exceptional and extraordinary chemical, optical, electrical and mechanical properties. Graphene based sensors have gained significance for a wide range of sensing applications like detection of biomolecules, chemicals and gas molecules. It can be easily used to make electrical contacts and manipulate them according to the requirements as compared to the other nanomaterials. The intention of the work presented in this article is to contribute in this field by simulating a novel and cheap graphene nanoribbon sensor for the household gas leakage detection. QuantumWise Atomistix (ATK) software is used for the simulations of propane and butane gas sensor. Projected device density of the states (PDDOS) and the transmission spectrum of the device in the proximity of gas molecules are calculated and discussed. The change in the electric current through the device in the presence of the gas molecules is used as a gas detection mechanism for the simulated sensor.

Strain-Induced Armchair Graphene Nanoribbon Resonant-Tunneling Diodes

The electronic properties of armchair graphene nanoribbons (AGNRs) can be changed and modified under the uniaxial strain. Taking this advantage, we propose a new platform of AGNR-based resonant-tunneling diode (RTD) using the effects of strain for the first time. In this RTD platform, barrier regions are composed of strained AGNR, whereas channel is made up by pristine AGNR. The calculated results show that the double barrier quantum well is performed for such device, and negative differential resistance property appears in ${I}$ – ${V}$ characteristic. In addition, performance of strain-induced 12-AGNR-RTD is explored under the variation of strain percentage ( $\varepsilon $ ). It is realized that the efficiency of such devices consist of peak to valley ratio can be engineered by setting strain percentage ( $\varepsilon $ ) to appropriate orders. Tight binding model coupled with nonequilibrium Green’s function formalism is derived for this paper.

Preferable binding site of gas molecules on graphene nanoribbon with Stone–Wales defect

The issue of sensitivity of sensing device has focused on the development of sensing devices by using new materials, such as graphene. The gas molecules in different positions such as on, near and far from the defect are placed in the same binding site in two graphene configurations for fair comparison. The interaction between two different graphene configurations such as (pristine armchair graphene nanoribbon (P-AGNR) and Stone–Wales defect on graphene surface (SW-AGNR)) with gas molecules (e.g. O2, N2 and NH3) have been investigated to observe the preferential position site of adsorbate gas molecules. The preferable position sites are investigated by using Extended-Huckel Theory. It is found that, the electronic properties of each configuration are strongly depends on the position of gas molecules and graphene system. Meanwhile, the binding site of the gas molecules on the defective site of graphene surface is a significant factor in determining the sensing behavior of graphene based gas defection device.

Armchair Graphene Nanoribbon Resonant Tunneling Diodes Using Antidote and BN Doping

Band gap size of armchair graphene nanoribbons (AGNRs) can be tuned by implementing topological antidotes or boron/nitride (BN) atoms at the middle of ribbons. By imposing such modulated patterns on certain regions of AGNRs, double barrier quantum well structures can be produced. According to this procedure, this paper proposes a new method for constructing resonant tunneling diodes (RTDs) by using AGNRs while the widths of the ribbons remain constant. Different structures of modulated AGNR-RTDs are constructed by introducing hexagonal antidotes, hexagonal BN doping atoms, and the combination of antidotes and BN doping atoms at the middle of pristine AGNRs. It is found that in general, antidote AGNR-RTDs present negative differential resistance with better performance in comparison with other modulated AGNR-RTDs. In addition, the effects of dimensional parameters such as the length of channel, the length of barrier, and the distance between antidotes on the performance of antidote AGNR-RTDs are investigated. It is extracted that the peak to valley ratio, power dissipation, and other properties can be modified by tuning the dimensional parameters to appropriate values. Numerical tight-binding model along with nonequilibrium Green's function formalism is applied to study the electronic properties of devices.

Electronic properties of NH4-adsorbed graphene nanoribbon as a promising candidate for a gas sensor

The electronic properties of NH4-adsorbed N = 7 armchair graphene nanoribbons (AGNRs) were theoretically investigated using self-consistent atomistic simulations to explore the feasibility of AGNRs as a gas sensing material. Whereas a pristine AGNR has a finite band gap and is an intrinsic semiconductor, an NH4-adsorbed AGNR exhibits heavily doped n-type properties similar to a graphene sheet with the molecules adsorbed. The electric characteristics of a back-gated AGNR gas sensor were also simulated and the drain current changed exponentially with increasing number of adsorbed molecules. We may conclude that an AGNR is promising as a highly sensitive gas-sensing material with large outputs.