Properties Of Armchair Graphene Nanoribbons Research Articles

Enhanced thermoelectric figure of merit in graphene nanoribbons by creating a distortion and transition-metal doping

Thermoelectric (TE) materials have the exceptional ability to directly convert waste heat into electricity and theoretical studies-based guidance is an effective way to investigate high-performance nanostructured TE materials throughout a range of temperatures. Herein, we studied the influence of distortion and transition metal (TM) atoms (V, Cr, Co and Pt) on the electronic and TE properties of armchair graphene nanoribbons (AGNRs) at various temperatures. The results showed that TM-doping and distortion might significantly alter the electronic structure of AGNRs. The band gap and valence band convergence are reduced as a result of the synergistic effect. A higher TE figure of merit results from a combination of decreased heat conductivity and increased electrical conductivity brought about by the electronic structural change. This study proposes that by doping and distortion-induced TE characteristics engineering of AGNR, high-performance nanostructured TE materials may be produced that have a wide range of TE applications.

Adsorption of cadmium selenide clusters: A novel approach to enhance solar energy conversion using armchair graphene nanoribbons

Tailoring the electronic, optical, and transport properties of low-dimensional semiconductor materials is essential to improve the light-conversion efficiency of thin-film solar cell materials. Here, using first-principles calculations and non-equilibrium Green functions, we investigate the enhancement of optoelectronic and transport properties of armchair graphene nanoribbons (AGNRs) upon adsorption of cadmium selenide clusters. Upon adsorption of a CdSe diatomic molecule on an AGNR, the most energetically favorable configuration is the cadmium end sitting on top of a carbon atom. The corresponding electronic bandgap reduces ∼5 times with respect to that of the pristine system, thanks to the formation of a polaron state formed by the p-orbital of the selenide atom. Upon adsorption of CdSe cyclohexane molecules, the bandgap of this system slightly shrinks by 0.121 eV with respect to the pristine system. The charge accumulation induced by these clusters significantly enhances the absorption coefficient of the adsorbed systems, resulting in a red shift of the optical spectra toward the infrared region. More interestingly, by solving the Bethe–Salpeter equations with the Tamm–Dancoff approximation, we provide a direct link between the first-principles optical prediction and experimental observations. In addition, the electron transfer from these molecules to the hosted systems increases the transmission spectra in the vicinity of the Fermi level, leading to a remarkable electronic current passing through these scattering regions. These results highlight the role of cadmium selenide clusters in enhancing the light-to-energy conversion efficiency of next-generation solar cell devices.

Thermoelectric properties of armchair graphene nanoribbons: importance of quantum confinement

Thermoelectric properties of armchair graphene nanoribbons: importance of quantum confinement

Thermoelectric properties of armchair graphene nanoribbons with array characteristics.

The thermoelectric properties of armchair graphene nanoribbons (AGNRs) with array characteristics are investigated theoretically using the tight-binding model and Green's function technique. The AGNR structures with array characteristics are created by embedding a narrow boron nitride nanoribbon (BNNR) into a wider AGNR, resulting in two narrow AGNRs. This system is denoted as w-AGNR/n-BNNR, where 'w' and 'n' represent the widths of the wider AGNR and narrow BNNR, respectively. We elucidate the coupling effect between two narrow symmetrical AGNRs on the electronic structure of w-AGNR/i-BNNR. A notable discovery is that the power factor of the 15-AGNR/5-BNNR with the minimum width surpasses the quantum limitation of power factor for 1D ideal systems. The energy level degeneracy observed in the first subbands of w-AGNR/n-BNNR structures proves to be highly advantageous in enhancing the electrical power outputs of graphene nanoribbon devices.

An investigation of the role of line defects on the transport properties of armchair graphene nanoribbons

An investigation of the role of line defects on the transport properties of armchair graphene nanoribbons

Electronic properties and reactivity of oxidized graphene nanoribbons and their interaction with phenol.

The effect of the oxidized functional groups on the structural, electronic, and reactivity properties of armchair graphene nanoribbons has been investigated in the framework of the density functional theory. The presence of functional groups near the edges stabilizes the oxidized graphene nanoribbons (OGNRs) more than substituting near the center. Overall, we found slight differences in the electronic properties of OGNRs concerning the pristine ones. The oxygen contribution of functional groups to the DOS is found in the conducting energy bands far from the Fermi level. Consequently, the semiconducting behavior is maintained after doping. Based on the reactivity of OGNRs, the most promising nanostructures were proposed as adsorbents studying the interaction and complexation with phenol, a critical pollutant removed mainly by hydrotreating processes (HDO) to produce bio-oil. Parallel and perpendicular phenol conformations were found towards the OGNRs in the optimized complexes driven by a physisorption process. These results provide significant insights for catalytic processes that use biomass derivatives containing phenolic compounds. The physisorption of streams containing pollutants on OGNRs could be adapted to new technological applications for the remotion of aromatic compounds under environmentally friendly operational conditions.

Role Played by Edge-Defects in the Optical Properties of Armchair Graphene Nanoribbons.

We explore the implementation of specific optical properties of armchair graphene nanoribbons (AGNRs) through edge-defect manipulation. This technique employs the tight-binding model in conjunction with the calculated absorption spectral function. Modification of the edge states gives rise to the diverse electronic structures with striking changes in the band gap and special flat bands at low energy. The optical-absorption spectra exhibit unique excitation peaks, and they strongly depend on the type and period of the edge extension. Remarkably, there exist the unusual transition channels associated with the flat bands for selected edge-modified systems. We discovered the special rule governing how the edge-defect influences the electronic and optical properties in AGNRs. Our theoretical prediction demonstrates an efficient way to manipulate the optical properties of AGNRs. This might be of importance in the search for suitable materials designed to have possible technology applications in nano-optical, plasmonic and optoelectronic devices.

Novel hydrogen cyanide gas sensor: A simulation study of graphene nanoribbon doped with boron and phosphorus

Hydrogen Cyanide (HCN) gas is a toxic gas generated by burning of material. In the present study, the sensing material for this gas is optimized with simulation software. The adsorption analysis, stability analysis, structural and electronic properties of armchair graphene nanoribbon (ArGNR) and its doped system has been examined for sensing of HCN using Density Functional Theory with Non Equilibrium Green's Function. The BP co-doped ArGNR is explored for the first time for sensing of HCN gas in this work. The ArGNR studied is in the form of Pristine, Defective state, Boron doped, Phosphorus doped and Boron Phosphorus co-doped. The pristine ArGNR is not much sensitive to HCN gas molecule, whereas on introducing dopants, the sensitivity increased considerably. The changes are observed in optimized geometry and electronic properties of different variants. Among all the variants, Phosphorus doped and BP co-doped ArGNR results in strong adsorption and is most sensitive to the Cyanide molecule, showing adsorption energy 15 and 12 times more as compared to pristine ArGNR. It is proposed that Phosphorus doped and BP co-doped ArGNR may be considered for HCN gas sensor applications. • Boron–Phosphorus co-doped graphene nanoribbon as HCN gas sensing reported for the first time. • DFT analysis of pristine, defective and co-doped armchair graphene nanoribbon carried out. • Boron-Phosphorous co-doped armchair graphene nanoribbon emerges as promising material for sensing. • The large band gap variation from 1.91eV to 1.58eV shows sensitivity towards HCN gas. • The co-doped system shows adsorption energy of -1.23eV which is nearly 12 times higher than its pristine structure.

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.

The Effect of 555-777 Defect on Mechanical Properties of Graphene Nanoribbon

In this study, the effects of 555-777 defect on Young’s modulus, fracture strength and fracture strain of armchair graphene nanoribbons (AGNRs) and zigzag graphene nanoribbons (ZGNRs) were investigated by using Molecular Dynamics simulations under uniaxial tension. The simulation results show that 555-777 defect significantly reduces the fracture strength and fracture strain of AGNRs and ZGNRs, but has little effect on Young's modulus. The influence of 555-777 defect on the mechanical properties of AGNRs is greater than that of ZGNRs. This study provides a better understanding of mechanical properties of graphene nanoribbons.

Phosphorus doped armchair graphene nanoribbon as a sensing platform of NH3 detection: A DFT investigation

The variation in geometrical and electronic properties of armchair graphene nanoribbon (AGNR) along with pristine and phosphorus (P-AGNR) doped configuration in the presence of ammonia gas (NH3) have been identified in this work. The density functional theory based calculations have been performed in order to detect and equate the sensitivity of modified armchair graphene nanoribbon towards NH3 sensing. Further, the variation in geometrical and electronic properties of AGNR and P-AGNR have been analyzed by considering the cohesive energy, band structure, density of states, and conductance. Hence, our findings shows that P doped AGNR can upsurge its sensitivity towards NH3 gas by the order of 106 times owing to the enhancement in the conductance. Overall, results shows the great potential in the area of designing the graphene nanoribbon based sensors.

Multi-orbital tight binding model for the electronic and optical properties of armchair graphene nanoribbons in the presence of a periodic potential

The influences of an external electric field with uniform or modulated potential on the electronic and optical properties of armchair graphene nanoribbons (GNRs) are explored using the multi-orbital tight-binding Hamiltonian. The interplay between an electric field and interaction between (s, p x , p y , p z ) orbitals remarkably enriches the main features of band structures and absorption spectra. The applied electric field can notably alter the energy dispersions of π and σ bands, leading to the deformation of band-edge states, open and close of a band gap, and modification of the Fermi energy. The vertical optical excitations happen among the π bands, while their available channels depend on the Fermi level which is controlled by the σ-edge bands and a finite potential. With the rich and unique properties, GNRs are suitable candidates for applications in the fields of photodetectors, nanoelectronics, and spintronics. The calculated results are expected to be examined by the angle-resolved photoemission spectroscopies and optical spectroscopies.

Electron transport in boron functionalised armchair graphene nanoribbons: Potential interconnects

Density functional theory (DFT) coupled with non-equilibrium Green's function (NEGF) formalism is employed to explore the electronic and transport properties of armchair graphene nanoribbons (AGNR) doped with Boron (B) at 6.25%, 12.5%, 18.75% and 25% doping concentrations. The modeled (3,0) AGNR exhibit a semiconducting behaviour with a band gap of 1.06eV and as a effect of Boron doping (6.25%, 12.5% and 18.75%) shows fluctuating semiconducting or metallic behaviour. However, at around the boron concentration of 25% AGNR remains metallic it exhibit relatively better conductance than silver, gold, copper and its other B doped counterparts. Further, the interesting linear Current-Voltage characteristics and conductance of boron doped AGNR may lead to its application as interconnects.

Electronic and transport properties of armchair graphene nanoribbons with defects

Density-functional theory (DFT) in combination with the nonequilibrium Green’s function formalism is performed to study the electronic and transport properties of armchair graphene nanoribbons with defects. The results show that the electronic and transport properties vary with different type of defects. The binding energy indicate that single-defect AGNRs are the most stable structure and line-defect AGNRs are the most unstable structure. The transmission spectra show that the defective AGNRs become disorder and the value decreases. The energy gap at the Fermi level become wider. These results would guide the experiments in real applications.

The influences of boron doping in various defect sites on the thermo-mechanical properties of armchair graphene nanoribbons

In this study, the influences of boron (B) atom doping for various sites of Stone-Wales (SW) defects on the thermal conductivity (TC) and mechanical properties of armchair graphene nanoribbon (AGNR) are systematically examined at room temperature using molecular dynamics (MD) simulations. Firstly, the effects of SW defect and B doping with different concentrations on the TC and mechanical properties are investigated randomly. Additionally, it is observed that as SW defect and B doping exist together in AGNR, the effect of B doping on the TC and mechanical properties is far less than others. Secondly, the influences of four different B doping sites, which are located at the edge and center sites of SW defect, on the TC and mechanical properties of AGNR are examined. MD simulation results show that B doping in the central sites of SW defect indicates higher mechanical properties and TC than those in the edge sites of SW defect. In addition, B doping in the central sites of SW defect further improved the TC and mechanical properties of AGNR compared to random SW defect with B doping. On the other hand, B doping in the edge sites of defective AGNR indicates lower TC and mechanical properties than those in random B doping in defective AGNR. The results of this study may be considered helpful for future works of thermal and mechanical management of AGNRs based nanodevices and to develop thermoelectric applications of AGNRs.

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.

Tuning the Energy Band Structures and Optical Properties of Armchair Graphene Nanoribbons Using Oxygen Adsorption

The electronic properties and optical properties of bare and H-terminated armchair graphene nanoribbons (AGNRs), with adsorption of single and double oxygen atoms, are investigated using density functional theory. Our results suggest that the number of adsorbed atoms and modification of atomic edge configuration cause an indirect-to-direct band gap and a metal-to-semiconductor transition. In addition, our results demonstrate that a change in the number of adsorbed atoms leads to N-semiconductor-to-P-semiconductor transition in H-terminated AGNRs. Single oxygen atom adsorption on the bare AGNRs results in an indirect-band-gap semiconductor with an energy gap of 0.212 eV. The band structures near the Fermi level are mainly dominated by C-2s, 2p and O-2s, 2p electronic states, which are strongly hybridized in the conduction and valence bands. We also find that H-terminated AGNRs with single O adsorption and double O adsorption become n-type and p-type semiconductors, respectively. By increasing adsorption of O atoms and modifying the edge H atoms, the peaks of the optical absorption tend to be redshifted. Furthermore, the number of peaks is reduced as edge H atom concentration is modified, for the same number of adsorbed atoms. Electron energy loss spectroscopy (EELS) is redshifted for single and double O atoms adsorbed on bare and H-terminated AGNRs.

Magnetic properties of armchair graphene nanoribbons: A Monte Carlo study

The magnetic properties of armchair graphene nanoribbons have been studied using a Monte Carlo study. The ground state phase diagrams have been determined for mixed spins S={±2; ±1; 0} and σ={±5/2; ±3/2; ±1/2}. The topologies of the phase diagrams depend on the values of the parameters in the Hamiltonian such as exchange interactions, crystal field and external magnetic field. The some diagrams show some coexistence between regions. The Néel temperature tN is obtained for different values of layer (n). The effect of reduced exchange interactions between the mixed spins σ and S and reduced crystal field on total magnetization has been given. Magnetic hysteresis cycles are given for different values of n, reduced exchange interactions and reduced temperatures. The double hysteresis loop and superparamagnetism were observed.

Structural and electronic properties of armchair graphene nanoribbons functionalized with fluorine

The interaction of armchair graphene nanoribbons (AGNR) with F has been investigated by considering it as a passivating element as well as adatom impurity. The adsorption of F at three different sites viz. bridge (B), top (T) and hole (H) is examined to determine the most stable configuration. It is revealed that F passivation is slightly more favorable than the H passivation of AGNR and it also affects the band gap. Interestingly, F adsorbed AGNR exhibit magnetic ground state which is about 70 meV more favourable over nonmagnetic state. Further, F passivated AGNR exhibit linear I-V characteristic which indicates potential for interconnect applications.

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.