Pristine Graphene Nanoribbons Research Articles

Implications of vibration characteristics towards mass detection using graphene nanoribbon-based bridge configured mass sensor

Owing to its astounding mechanical properties, graphene nanoribbon (GNR) based nano-resonator is aimed as mass sensor with doubly clamped nano beam subjected to pair of point masses adsorbed at different positions over its surface. Though pristine GNR is revealed with non-piezoelectric behaviour inherently, it can be turned into piezoelectric by suitable adatoms. The present analysis investigates the performance of monolayer based (F-, Li- and K-) doped GNRs in the form of vibration attributes such as eigen-frequencies, Q-factor and Force sensitivities. Euler-Bernoulli thin beam theory is applied to model the doped GNR. The obtained results highlight the shift in the eigen-frequency due to adsorbed masses and their positions over the surface of GNRs. Moreover, the Q-factor and Force sensitivities are also determined for the proposed mass sensors. The results indicate that the eigen-frequencies at higher modes are insignificant to the Q-factor. For the fundamental mode, the magnitude of Q-factor varies in the range of 4.39–4.52 for the proposed mass sensor with respect to the positions and magnitudes of pairs of masses. The force sensitivity for the doped GNR is attained at a level of aN/√Hz. Though, force sensitivity rises with the eigen-modes, the sensitivity with the minimum magnitude to be preferred for a sensor as it reflects to early detection of mass. This suggests the fundamental mode to operate the mass sensor. For the fundamental mode, the sensitivity of Li doped GNR is ranging from 103.60–117.58 aN/√Hz, while it is ranging from 109.67 to 124.45 aN/√Hz and 125.31–142.20 aN/√Hz for K- and F- doped GNRs, respectively. The results of the present work are compared with the available literatures. From the results, significant effect of adatom is observed on the vibration characteristics of the GNRs. The findings of the present work can significantly be used to design the GNR based bridge configured mass sensor.

1D graphene nanoribbons-mediated defect engineering in 2D MXene for high-performance supercapacitors

Carbon-based supercapacitors have been extensively explored by the virtue of their exceptional performance in terms of charge-storage capacity, electrical conductivity, and good stability. However, the rush to find potential approaches for increasing their specific capacitance and specific energy without adversely affecting the specific power is still exciting. Herein, we synthesized hierarchically structured carbon-based composites based on 2D MXene sheets with an interconnected conductive porous network of 1D graphene nanoribbons (GNRs). Synergistic effects arising due to the defect engineering of 2D MXene sheets with 1D GNRs led to high surface-area, effective ion-transport, and improved structural robustness of the composite electrodes, thereby enhancing the specific capacitance along with specific energy of device while preserving its specific power. The electrochemical studies revealed that the composites with 1 wt.% GNRs (GMX-B) outperformed when the composition of GNRs was varied from 0.5 to 1.5 wt. % in MXene (GMX-A, GMX-B, and GMX-C). In comparison to pristine MXene and pristine GNRs, GMX-B exhibited ∼2.54 and ∼2.74 folded higher capacitance of 238.96 F/g at 0.6 A/g current density, respectively, a higher capacitance retention of 72.16% for a scan rate from 10–140 mV/s as well as a good cyclic stability of 85.11% over 10 000 charge/discharge cycles. Furthermore, GMX-B electrode achieved a high specific energy of 4.066 Wh/Kg while maintaining a specific power of 210.640 W/Kg as compared to pristine MXene (1.597 Wh/Kg at 211.989 W/Kg) and pristine GNRs (1.482 Wh/Kg at 211.089 W/Kg). Thus, we anticipated that the use of hierarchically engineered 1D/2D carbon-based composites with considerable improvement in its interfacial properties holds great potential to achieve high-performing energy-storage devices.

The effect of water on gold supported chiral graphene nanoribbons: rupture of conjugation by an alternating hydrogenation pattern.

In the last few years we have observed a breakpoint in the development of graphene-derived technologies, such as liquid phase filtering and their application to electronics. In most of these cases, they imply exposure of the material to solvents and ambient moisture, either in the fabrication of the material or the final device. The present study demonstrates the sensitivity of graphene nanoribbon (GNR) zigzag edges to water, even in extremely low concentrations. We have addressed the unique reactivity of (3,1)-chiral GNR with moisture on Au(111). Water shows a reductive behaviour, hydrogenating the central carbon of the zigzag segments. By combining scanning tunnelling microscopy (STM) with simulations, we demonstrate how their reactivity reaches a thermodynamic limit when half of the unit cells are reduced, resulting in an alternating pattern of hydrogenated and pristine unit cells starting from the terminal segments. Once a quasi-perfect alternation is reached, the reaction stops regardless of the water concentration. The hydrogenated segments limit the electronic conjugation of the GNR, but the reduction can be reversed both by tip manipulation and annealing. Selective tip-induced dehydrogenation allowed the stabilization of radical states at the edges of the ribbons, while the annealing of the sample completely recovered the original, pristine GNR.

Decoupling thermoelectric parameters induces significantly enhanced thermoelectric properties of oxygen-functionalized graphene nanoribbon

The coupling of thermoelectric parameters greatly limits the improvement of thermoelectric properties, which in turns restricts their applications. In this work, we introduce a strategy for significantly enhancing the thermoelectric performance of oxygen-functionalized graphene nanoribbons (GNRs). In particular, the thermoelectric figure of merit (ZT) can be increased from 0.05 (for GNRs) to 0.16 and 0.11 for epoxide- and hydroxyl-functionalized GNRs (GPO and GPOH), respectively. This is mainly attributed to a significant decrease in thermal conductance and a slight decrease in power factor. Especially, the thermoelectric parameters of ether-functionalized GNRs (GPOV) are relatively decoupled, and the simultaneous increase in power factor and decrease in thermal conductance lead to a sharp increase in their ZT value. Notably, the room-temperature ZT value of GPOV can be increased to as high as 0.5, which is 10 times greater than that of the pristine GNRs. This work reveals the application potential of oxygen-functionalized GNRs in thermoelectric materials, and demonstrates the broad prospects of the present strategy in the field of thermoelectrics.

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.

Predicting Selective Sensing Capability of Armchair Graphene Nanoribbon toward Hydrogen Halide Gases: A Density-of-State Analysis

Nonequilibrium Green’s function formalism is used to set the chemiresistor device for analyzing the sensing ability of pristine and metal-doped (Al, Fe and Mn) armchair graphene nanoribbons (AGNRs) for the detection of hydrogen halide gases — HF, HCl and HBr. Metal doping is found to enhance the adsorptive strength and sensing ability of the ribbon. On Al-AGNR, all three halide gases follow dissociative chemisorption while on Fe-AGNR and Mn-AGNR, these gases adsorb nondissociatively. The computed current–voltage characteristics indicate selective response of Mn-AGNR toward HF and of Fe-AGNR toward HBr. The origin of this selectivity has been discussed in terms of difference in the density-of-state profiles of the studied AGNR systems.

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.

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.

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.

Critical Temperature in Zigzag Graphene Nanoribbon: a First-principles Study

The critical (Néel) temperature in the zigzag graphene nanoribbon was calculated using the mean-eld approximation within the generalized Bloch theorem. This calculation was carried out over the Brillouin zone of the magnon spectrum. We found a nearly at magnon dispersion at the high energy in one-third of the Brillouin zone. Our calculation showed the critical temperature below room temperature, in good agreement with the prediction in the previous works. Our last work (Prayitno 2021 Physica E 129 114641) revealed that the critical temperature may be enhanced by increasing the ribbon width. In this brief report, we justified that the critical temperature becomes almost constant up to a certain ribbon width. This result indicates that the critical temperature in the graphene nanoribbon will never reach room temperature for any ribbon widths, thus it is likely difficult to apply pristine graphene nanoribbon in any practical devices working near room temperature.

Improving the thermoelectric properties of graphene through zigzag graphene–graphyne nanoribbon heterostructures

Thermoelectric materials can convert thermal energy and electrical energy into each other, which have attracted extensive attention in recent years. In this paper, we systematically investigate the ballistic thermoelectric performance of four zigzag graphene–graphyne nanoribbon heterostructures M $$i(i=1{-}4)$$ through utilizing non-equilibrium Green’s function method. Our results show that heterostructures possess superior thermoelectric properties with respect to pristine graphene nanoribbon. Especially, the ZT value of M4 reaches 1.5 at 700 K, which is about 15 times that of graphene. Such improvement mainly originates from the reduction of phononic and electronic thermal conductance and the increase of Seebeck coefficient. Meanwhile, because M4 has the lowest phonon thermal conductance and favorable thermal power, its thermoelectric figure of merit is the best. These findings in this paper demonstrate that heterostructure is a viable approach to optimize the thermoelectric performance of graphene, which provides useful guidance for the design and fabrication of nanoscale thermoelectric devices.

Morphological characterization and electronic properties of pristine and oxygen-exposed graphene nanoribbons on Ag(110).

Graphene nanoribbons (GNRs) are at the frontier of research on graphene materials since the 1D quantum confinement of electrons allows for the opening of an energy gap. GNRs of uniform and well-defined size and shape can be grown using the bottom-up approach, i.e. by surface assisted polymerization of aromatic hydrocarbons. Since the electronic properties of the nanostructures depend on their width and on their edge states, by careful choice of the precursor molecule it is possible to design GNRs with tailored properties. A key issue for their application in nanoelectronics is their stability under operative conditions. Here, we characterize pristine and oxygen-exposed 1.0 nm wide GNRs with a well-defined mixed edge-site sequence (two zig-zag and one armchair) synthesized on Ag(110) from 1,6-dibromo-pyrene precursors. The energy gap and the presence of quantum confined states are investigated by scanning tunneling spectroscopy. The effect of oxygen exposure under ultra-high vacuum conditions is inferred from scanning tunneling microscopy images and photoemission spectra. Our results demonstrate that oxygen exposure deeply affects the overall system by interacting both with the nanoribbons and with the substrate; this factor must be considered for supported GNRs under operative conditions.

Strain modulated carrier mobility and optical properties of graphene nanowiggles

Recently, synthesized Chevron graphene nanoribbons (CGNRs) and its laterally extended counterpart known as extended CGNRs (ECGNR) are constructed by making alternated regular cuts in pristine graphene nanoribbons (GNRs). First-principles calculations demonstrate that these GNRs are super-ductile and possess width-dependent mechanical properties. The Young’s modulus is calculated to be 389.4 GPa and 414.6 GPa for CGNR and ECGNR, respectively. The bandgap of these nanoribbons decreases on the application of tensile strain. The carrier effective masses are found to be highly sensitive towards mechanical strains. The holes (electrons) mobility of ECGNR is calculated to be 7.68 × 104 cm2 V−1 s−1 (1.69 × 104 cm2 V−1 s−1), which is higher than that of CGNR can be further enhanced by elongation. The prominent peaks of the imaginary part of dielectric function and electron energy loss spectra show redshift on increasing the tensile strain. The electron energy loss spectra show intense plasmonic structure in low energy spectrum indicating GNRs to be more sensitive to the visible region than ultra violet spectrum. Our results provide insight about the possible applications of GNRs in the fields of high-speed transistors, sensors, photonics, and optoelectronics.

Even\u2013odd conductance effect in graphene nanoribbons induced by edge functionalization with aromatic molecules: basis for novel chemosensors

We theoretically investigate the electron transport in armchair and zigzag graphene nanoribbons (GNRs) chemically functionalized with p-polyphenyl and polyacene groups of increasing length. Our nearest-neighbor tight-binding calculations indicate that, depending on whether the number of aromatic rings in the functional group is even or odd, the resulting conductance at energies matching the energy levels of the corresponding isolated molecule is either unaffected or reduced by exactly one quantum as compared to the pristine GNR, respectively. Such an even–odd effect is shown to originate from a subtle interplay between the electronic states of the guest molecule that are spatially localized on the binding sites and those of the host nanoribbon. We next generalize our findings by employing more accurate tight-binding Hamiltonians along with density-functional theory calculations and critically discuss the robustness of the observed physical effects against the level of theory adopted. Our work offers a comprehensive understanding of the influence of aromatic molecules bound to the edge of graphene nanoribbons on their electronic transport properties, an issue which is instrumental to the prospective realization of graphene-based chemosensors.

Atomistic Modelling of Size-Dependent Mechanical Properties and Fracture of Pristine and Defective Cove-Edged Graphene Nanoribbons.

Cove-edged graphene nanoribbons (CGNR) are a class of nanoribbons with asymmetric edges composed of alternating hexagons and have remarkable electronic properties. Although CGNRs have attractive size-dependent electronic properties their mechanical properties have not been well understood. In practical applications, the mechanical properties such as tensile strength, ductility and fracture toughness play an important role, especially during device fabrication and operation. This work aims to fill a gap in the understanding of the mechanical behaviour of CGNRs by studying the edge and size effects on the mechanical response by using molecular dynamic simulations. Pristine graphene structures are rarely found in applications. Therefore, this study also examines the effects of topological defects on the mechanical behaviour of CGNR. Ductility and fracture patterns of CGNR with divacancy and topological defects are studied. The results reveal that the CGNR become stronger and slightly more ductile as the width increases in contrast to normal zigzag GNR. Furthermore, the mechanical response of defective CGNRs show complex dependency on the defect configuration and distribution, while the direction of the fracture propagation has a complex dependency on the defect configuration and position. The results also confirm the possibility of topological design of graphene to tailor properties through the manipulation of defect types, orientation, and density and defect networks.

High figure of merit in an ac driven graphene nanoribbon

Generally, pristine graphene nanoribbons show poor thermoelectric (TE) performance. Several proposals are available to enhance the TE performance, which however requires some highly structural modifications of the system. In the present work, we explore a new prescription where a favorable TE response can be achieved by irradiating the ribbon. The electronic conductance, thermopower and thermal conductance due to electron are found to be highly sensitive to the irradiation. We obtain significantly enhanced thermopower along with highly suppressed thermal conductance for typical sets of irradiation parameters. As a result of this higher figure of merit is found. Therefore, we can suggest that a graphene nanoribbon can be used as an efficient energy conversion device in the presence of irradiation and hope that it will bear a significant impact in the energy market soon.

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.

Electronic Properties of the Interface Between Metallic Doped Zigzag Graphene and Pristine Graphene Nanoribbons

The electronic properties of the interface between metallic doped zigzag graphene nanoribbons and perfect graphene nanoribbons are investigated. The density functional based tight-binding approach and a non-equilibrium Green function method are employed for our calculations. The atoms of Ni, Co, and Fe are used as doping atoms. The graphs of current–voltage, density of states, electron density, transmission spectrum, and rectification ratio are obtained. The results show that the bond lengths around the atoms of Ni, Co, and Fe are increased. Moreover, it is observed that for the graphene-based nanodevice the curves of current–voltage are linear and symmetric when no impurity exists and with the effect of impurities the curves are non-linear and asymmetric. While Ni, Co, and Fe impurities are applied into the systems we found that the maximum electron densities are located around the impurities of Ni and the current is decreased. The density of states and transmission spectrum are also examined for different systems. It is found that for certain amount of energies some resonances occur for the current, and the atoms at the edge of nanoribbon are mostly responsible for the transfer of the electrons. The obtained results can be of interest for the construction of nanoelectronic devices and can have practical applications.

First principles study of sarin nerve gas adsorption on graphene nanoribbon with single molecule resolution

Nerve gases are dangerous agents of chemical warfare and mass destruction which can cause irreversible damage to the nervous system within seconds and are fatal if exposure occurs for even a few minutes. The nerve gases or agents were developed during the second world war and thereafter were banned from production. However, despite the restrictions there have been recent events of their use which have proven life threatening for instance Salisbury incident 2018. Generally the nerve gases have high volatility causing easy spread in the environment. The absorption of the harmful gases can occur via the respiratory tract, skin etc. In this paper, we propose a first principles study of the sarin nerve agent adsorbed pristine graphene nanoribbon for a vital application of nerve gas sensing. The structural, electronic and transport properties of the gas nanoribbon complexation are analysed for its viability in sarin nerve gas nanosensing application. The results obtained clearly corroborate that the pristine graphene nanoribbon can be used for sensing the presence of sarin nerve agent in the environment.