Sharif Digital Repository

We present two compact analytic formulae for calculating the channel number in graphene nanoribbons (GNRs), in terms of GNRs' width and Fermi energy. Numerical data obtained from these analytic formulae fit those obtained numerically from the exact formula, with accuracies within 1%. Using appropriate fit parameters, the compact formulae are valid for zigzag, armchair-metallic, and armchair-semiconducting GNRs, at room, liquid nitrogen, and liquid helium temperatures (i.e. 300, 77 and 4.2 K)  

Here, SnO2 nanoribbons (NRs) synthetized on the catalyst-free stainless steel (SS) substrate as a possible anode for Li-ion batteries (LIBs) have been reported. SnO2 NRs were synthesized on catalyst-free SS substrate via vapor-solid (VS) growth approach. Morphological and structural characterizations of the SnO2 NRs were confirmed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) microscopes and x-ray diffraction (XRD) respectively. The prepared binder-free electrode demonstrated high initial discharge/charge capacities of 1818/929 mAh g-1 at current density of 300 mA g-1. A reversible capacity of 676 mAh g-1 with a coulombic efficiency of 98.5% has been... 

Time domain analysis of multilayer graphene nano ribbon (MLGNR) interconnects, based on transmission line modeling (TLM) using a six-order linear parametric expression, has been presented for the first time. We have studied the effects of interconnect geometry along with its contact resistance on its step response and Nyquist stability. It is shown that by increasing interconnects dimensions their propagation delays are increased and accordingly the system becomes relatively more stable. In addition, we have compared time responses and Nyquist stabilities of MLGNR and SWCNT bundle interconnects, with the same external dimensions. The results show that under the same conditions, the... 

Graphene nanoribbons (GNRs) fabricated using electron beam lithography are investigated using tip-enhanced Raman spectroscopy (TERS) with a spatial resolution of 5 nm under ambient conditions. High-resolution TERS imaging reveals a structurally modified 5-10 nm strip of disordered graphene at the edge of the GNRs. Furthermore, hyperspectral TERS imaging discovers the presence of nanoscale organic contaminants on the GNRs. These results pave the way for nanoscale chemical and structural characterisation of graphene-based devices using TERS. © The Royal Society of Chemistry 2021  

In this study, sandwich beam model (SM) is proposed for free vibration analysis of bilayer graphene nanoribbons (BLGNRs) with interlayer shear effect. This model also takes into account the intralayer (in-plane) stretch of graphene nanoribbons. The molecular dynamics (MD) simulations using the software LAMMPS and Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential are done to validate the accuracy of the sandwich model results. The MD simulation results include the two first frequencies of cantilever BLGNRs with different lengths and two interlayer shear moduli, i.e., 0.25 and 4.6GPa. These two interlayer shear moduli, 0.25 and 4.6GPa, can be obtained by sliding a small... 

In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin... 

Electronic and transport properties of 11 zigzag graphene nanoribbons (11-z-GNRs) with two types of 3D-paired pentagon-heptagon defects (3D-PPHDs) are studied using density functional theory combined with non-equilibrium Green's function method. The C ad-dimers that have been introduced to z-GNRs to form these 3D-PPHDs have induced local strains forcing the C-bonds in the ad-dimers to hybridize in sp3-like rather than sp2-like orbitals. Such transformations that cause extra electrons to accumulate around the 3D-PPHDs are responsible for the variations in the electronic and transport properties of the defected z-GNRs. Density of states (DOS) for 11-z-GNRs containing either type of 3D-PPHDs,... 

In this paper the band structure of spin polarized zigzag graphene nanoribbons(ZGNRs) and armchair graphene nanoribons(AGNRs) with Stone-Wales defect are investigated. The results show when the spin effect is considered, the band structures of ZGNRs and AGNRs will be changed and modified. A larger gap will be created and the degenerate bands in ZGNRs will become far from each other. Tight-binding and hubard model were used to simulate the band structures  

Graphene nanogrids (fabricated by graphene nanoribbons obtained through oxidative unzipping of multi-walled carbon nanotubes) were used as two-dimensional selective templates for accelerated differentiation of human mesenchymal stem cells (hMSCs), isolated from umbilical cord blood, into osteogenic lineage. The biocompatible and hydrophilic graphene nanogrids showed high actin cytoskeleton proliferations coinciding with patterns of the nanogrids. The amounts of proliferations were found slightly better than proliferation on hydrophilic graphene oxide (GO) sheets, and significantly higher than non-uniform proliferations on hydrophobic reduced graphene oxide (rGO) sheets and... 

We present a Nyquist stability criterion based on transmission line modeling for graphene nanoribbon (GNR) interconnects. This is the first instance that such an analysis has been presented for GNR, so far. In this analysis, the dependence of the degree of relative stability for multilayer GNR (MLGNR) interconnects on the geometry of each ribbon has been acquired. It is shown that, increasing the length and width, MLGNR interconnects become more stable  

We report a first principles study on the electronic and transport properties of bilayer armchair graphene nanoribbons (BLAGNRs) containing Stone-Wales (SW) defect. It is shown that in the presence of SW defect in BLAGNRs, some electron localization occurs in defect atoms and degradation of transmission is observed in specific energy regions. The strength of electron localization is dependent on the symmetry of SW defect. In case of symmetric SW defect, stronger electron localization leads to sharper dip in its transmission spectrum in comparison with the broad dip in the transmission spectrum of the BLAGNR containing asymmetric SW defect. The effect of electron localization is also evident... 

The present paper demonstrates the capability of narrow graphene nanoribbons (GNRs) in constructing new sensing platforms. Graphene nanoribbons have been synthesized via a simple solvothermal route through unzipping of carbon nanotubes, which was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy analysis. These narrow carbon sheets were used to form a composite film by in-situ electro-polymerization with aniline. The produced graphene nanoribbon/polyaniline (GNR/PANI) composite film showed impressive performance in electrochemical determination of dobutamine (DBT). Under optimal conditions, in comparison to... 

Using non-equilibrium Green’s function method and density functional theory, we study the effect of line structural defects on the electron transport of zigzag molybdenum disulfide (MoS 2 ) nanoribbons. Here, the various types of non-stoichiometric line defects greatly affect the electron conductance of MoS 2 nanoribbons. Although such defects would be lead to the electron scattering, they can increase the transmission of charge carriers by creating new channels. In addition, the presence of S bridge defect in the zigzag MoS 2 nanoribbon leads to more the transmission of charge carriers in comparison with the Mo–Mo bond defect. Also, we find that the different atomic orbitals and their... 

Our aim is to improve the switching performance of the graphene nanoribbon field-effect transistors (GNRFETs), exploiting the concept of energy filtering. Within the proposed scheme, a superlattice (SL) structure is used in the source of the transistor for filtering high-energy electron tail by engineering the density of states (DOS). According to simulation results, this can significantly decrease the OFF-current and the subthreshold swing (SS). A comparison of the proposed device with a conventional GNRFET and a graphene nanoribbon (GNR) tunneling field-effect transistor (GNRTFET) demonstrates a significant improvement. Therefore, a typical SL-GNRFET can reduce the average and the minimum... 

A triboelectric nanogenerator (TENG) electrode sensitive to the adsorption of water molecules has been introduced to create a self-powered humidity sensor. Graphene oxide (GO) nanosheets and graphene oxide nanoribbon (GONR) possessing oxygenated functional groups, as well as high dielectric constants, have been proposed as appropriate candidates for this purpose. GO papers have been fabricated in three forms, i.e. pure GO paper, uniform composites of GONR and GO, and double-layer structures of GONR on top of GO. Results showed that all of the prepared paper-based TENGs revealed excellent performances by maximum output voltage above 300 V. As active humidity sensors, the maximum voltage... 

Graphene nanogrids (crossed graphene nanoribbons synthesized by the oxidative unzipping of multi-walled carbon nanotubes) on a SiO2 matrix containing TiO2 nanoparticles (NPs) were applied as a photocatalytic stimulator in the accelerated differentiation of human neural stem cells (hNSCs) into two-dimensional neural networks. The hydrophilic graphene nanogrids exhibited patterned proliferations of hNSCs (consistent with patterns of the nanogrids), in contrast with the usual random growths occurring on quartz substrates. The number of cell nuclei differentiated on reduced graphene oxide nanoribbon (rGONR) grid/TiO2 NPs/SiO2 increased ∼5.9 and 26.8 fold compared to the number of cells on quartz... 

A nanoscale logic NOR gate has been theoretically designed by magnetic flux inputs in a Z-shaped graphene nanoribbon composed of an armchair ribbon device sandwiched between two semi-infinite metallic zigzag ribbon leads. The calculations are based on the tight-binding model and iterative Green's function method, in which the conductance as well as current-voltage characteristics of the nanosystem are calculated, numerically. We show that the current and conductance are highly sensitive to both the magnetic fluxes subject to the device and the size of the system. Our results may have important applications for building blocks in the nanoelectronic devices based on graphene nanoribbons  

In this paper, for the first time, we present a computational study on electrical characteristics of field effect tunneling transistors based on a vertical graphene-WS2 heterostructure and vertical graphene nanoribbon (GNR)-WS2 heterostructure (VTGNRFET). Our model uses the nonequilibrium Green's function formalism along with an atomistic tight binding (TB) method. The TB parameters are extracted by fitting the bandstructure to first principles results. We show that, due to the advantage of switching between tunneling and thermionic transport regimes, an improvement can be achieved in the electrical characteristics of the device. We find that the increase of the number of WS2 layers enhances... 

In this paper, using first principle calculation and non-equilibrium Green's function, the thermally induced spin current in Hydrogen terminated Zigzag-edge Germanene Nanoribbon (ZGeNR-H) is investigated. In this model, because of the difference between the source and the drain temperature of ZGeNR device, the spin up and spin down currents flow in the opposite direction with two different threshold temperatures (Tth). Hence, a pure spin polarized current which belongs to spin down is obtained. It is shown that, for temperatures above the threshold temperature spin down current increases with the increasing temperature up to 75 K and then decreases. But spin up current rises steadily and in... 

We are proposing a next-generation graphene nanoribbon field-effect transistor (GNRFET) with superlattice source, channel, and drain (SLSCD-GNRFET), with significantly improved switching performance. The presence of superlattice in each region is for energy filtering. The simulation results indicate that the addition of an appropriate superlattice in the channel region, it reduces the subthreshold swing. Also, using proper superlattice in the drain region leads to an increase of more than a decade in the ION/IOFF ratio by intensely reducing the OFF-current. These improvements make the proposed transistor potentially suitable for the next-generation logical digital applications. Comparison of...