Search for: graphene-nanoribbons
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    Compact formulae for number of conduction channels in various types of graphene nanoribbons at various temperatures

    , Article Modern Physics Letters B ; Volume 26, Issue 1 , 2012 ; 02179849 (ISSN) Nasiri, S. H ; Faez, R ; Moravvej Farshi, M. K ; Sharif University of Technology
    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)  

    Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

    , Article Journal of Applied Physics ; Volume 120, Issue 5 , 2016 ; 00218979 (ISSN) Chaghazardi, Z ; Babaee Touski, Sh ; Pourfath, M ; Faez, R ; Sharif University of Technology
    American Institute of Physics Inc 
    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... 

    Spin effect on band structure of zigzag and armchair graphene nanoribbones with Stone-Wales defect

    , Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 , Page(s): 1 - 4 ; 9781467356343 (ISBN) Faez, R ; Barami, S ; Sharif University of Technology
    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  

    Sandwich beam model for free vibration analysis of bilayer graphene nanoribbons with interlayer shear effect

    , Article Journal of Applied Physics ; Vol. 115, issue. 17 , May , 2014 ; ISSN: 00218979 Nazemnezhad, R ; Shokrollahi, H ; Hosseini-Hashemi, S ; Sharif University of Technology
    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... 

    A computational study of vertical tunneling transistors based on graphene-WS2 heterostructure

    , Article Journal of Applied Physics ; Volume 121, Issue 21 , 2017 ; 00218979 (ISSN) Horri, A ; Faez, R ; Pourfath, M ; Darvish, G ; Sharif University of Technology
    American Institute of Physics Inc  2017
    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... 

    Simulation of Graphene Nanoribbon based Photodetector

    , M.Sc. Thesis Sharif University of Technology Faramarzi, Vahid (Author) ; Faez, Rahim (Supervisor)
    In this work, we have simulated graphene nanoribbon based photodetector and impact of changing the width, and Boron-Nitride doping and Stone-Wales defects on the optical properties of GNR has study. The energy band structure of GNR with nearest-neighbor approximation in a tight binding model calculated. To correspond with experiment and accuracy, we need to consider the impact of third nearest neighbors and edge bond relaxation. By Using the band structure, we calculated joint density of state and optical matrix elements and obtain inter band selection rule for A-GNR and Z-GNR. Then, using the Fermi’s golden rule, we investigate optical properties of GNR such as optical conductivity and... 

    An investigation of ZGNR-based transistors

    , Article 2011 International Semiconductor Device Research Symposium, ISDRS 2011, 7 December 2011 through 9 December 2011 ; December , 2011 , Page(s): 1 - 2 ; 9781457717550 (ISBN) Karamitaheri, H ; Pourfath, M ; Faez, R ; Kosina, H ; Sharif University of Technology
    Graphene, a recently discovered form of carbon, has received much attention for possible applications in nanoelectronics, due to its excellent carrier transport properties [1]. Graphene nanoribbons (GNRs) are thin strips of graphene, where the electronic properties depend on the chirality of the edge and the width of the ribbon. Zigzag GNRs (ZGNRs) show metalic behavior, whereas armchair GNRs (AGNRs) are semiconductors and their band-gap is inversely proportional to their width [2]. Therefore, narrow AGNRs have been recently suggested as a material for transistor channels. However, line edge roughness and substrate impurities can significantly degrade the ballistic transport in AGNRs,... 

    In-situ electro-polymerization of graphene nanoribbon/polyaniline composite film: Application to sensitive electrochemical detection of dobutamine

    , Article Sensors and Actuators, B: Chemical ; Vol. 196 , June , 2014 , pp. 582-588 ; ISSN: 09254005 Asadian, E ; Shahrokhian, S ; Zad, A. I ; Jokar, E ; Sharif University of Technology
    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 superlattice structure in the source of GNRFET to improve its switching performance

    , Article IEEE Transactions on Electron Devices ; Volume 67, Issue 3 , 2020 , Pages 1334-1339 Behtoee, B ; Faez, R ; Shahhoseini, A ; Moravvej Farshi, M. K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    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... 

    Visualising structural modification of patterned graphene nanoribbons using tip-enhanced Raman spectroscopy

    , Article Chemical Communications ; Volume 57, Issue 56 , 2021 , Pages 6895-6898 ; 13597345 (ISSN) Su, W ; Esfandiar, A ; Lancry, O ; Shao, J ; Kumar, N ; Chaigneau, M ; Sharif University of Technology
    Royal Society of Chemistry  2021
    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  

    Optimal Multi-Level Interconnect Architecture for GSI Using Novel Solutions Replacing Copper

    , Ph.D. Dissertation Sharif University of Technology Kishani Farahani, Esmat (Author) ; Sarvari, Reza (Supervisor)
    Although a lot of research has been done on Carbon-based interconnect, there are many important questions unanswered. For example, there is no compact model for the resistance of bundle of CNTs at high frequencies, at which interconnects will be operating due to the scaling. Also there are many studies comparing CNT, GNR, and Cu wires but there is no study to show how much this will impact the design of a chip at today’s Giga Scale Integration. This comprehensive study should include chip performance, power dissipation and total number of metal levels. These two big questions are investigated in this dissertation. In the first part, high frequency behavior of CNT bundles is studied. A... 

    A Simulation Study of Graphene Nanoribbon Field Effect Transistor

    , M.Sc. Thesis Sharif University of Technology Samadi, Mohsen (Author) ; Faez, Rahim (Supervisor)
    In this thesis, a field effect transistor (FET) using armchair graphene nanoribbon as the channel is simulated, and the effects of changing nanoribbon width and length, as well as adding defects, are also studied. To obtain the Hamiltonian matrix and the energy band structure of graphene nanoribbon, tight binding method is used in which the first and third neighbor approximation is considered. Also, to maximize accuracy, we also considered the edge bond reconstruction. To obtain the transport characteristics of the transistor, such as the transmission coefficient and the density of states (DOS), Poisson and Schrodinger equations are solved self-consistently. We used the nonequilibrium... 

    Simulation and Comparative Study of Tunneling FETs Based on Graphene Nanoribbon and Phosphorene Monolayer

    , M.Sc. Thesis Sharif University of Technology Almasi, Hossein (Author) ; Faez, Rahim (Supervisor)
    In this thesis, we simulate and investigate two transistors which both have tunneling FET (TFET) structure but the channel in the first one is graphene nanoribbon (GNR) and in the second one is a monolayer of phosphorene (PML). To describe the quantum systems of the transistors, we use the tight binding method and its models for the channel materials. In case of the PML TFET, based on the behavior of the phosphorene nanoribbon in different widths, we obtain a proper amount for the width to model the infinite-width channel. To extract the channel quantum transport, the Schrodinger-Poisson equations are self-consistently solved. In the next step, we simulate the GNR TFET and present the... 

    Role of 3D-paired pentagon-heptagon defects in electronic and transport properties of zigzag graphene nanoribbons

    , Article Applied Physics A: Materials Science and Processing ; Volume 116, Issue 1 , July , 2014 , Pages 295-301 ; ISSN: 09478396 Fotoohi, S ; Moravvej Farshi, M. K ; Faez, R ; Sharif University of Technology
    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,... 

    Graphene nanogrids for selective and fast osteogenic differentiation of human mesenchymal stem cells

    , Article Carbon ; Volume 59 , 2013 , Pages 200-211 ; 00086223 (ISSN) Akhavan, O ; Ghaderi, E ; Shahsavar, M ; Sharif University of Technology
    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... 

    Effects of Stone-Wales defect on the electronic and transport properties of bilayer armchair graphene nanoribbons

    , Article Superlattices and Microstructures ; Volume 100 , 2016 , Pages 739-748 ; 07496036 (ISSN) Gholami Rudi, S ; Faez, R ; Morawej Farshi, M. K ; Sharif University of Technology
    Academic Press 
    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... 

    Atomistic study of the lattice thermal conductivity of rough graphene nanoribbons

    , Article IEEE Transactions on Electron Devices ; Volume 60, Issue 7 , 2013 , Pages 2142-2147 ; 00189383 (ISSN) Karamitaheri, H ; Pourfath, M ; Faez, R ; Kosina, H ; Sharif University of Technology
    Following our recent study on the electronic properties of rough nanoribbons , in this paper the role of geometrical and roughness parameters on the thermal properties of armchair graphene nanoribbons is studied. Employing a fourth nearest-neighbor force constant model in conjuction with the nonequilibrium Green's function method the effect of line-edge-roughness on the lattice thermal conductivity of rough nanoribbons is investigated. The results show that a reduction of about three orders of magnitude of the thermal conductivity can occur for ribbons narrower than 10 nm. The results indicate that the diffusive thermal conductivity and the effective mean free path are directly proportional... 

    Local impact of Stone–Wales defect on a single layer GNRFET

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 384, Issue 7 , 2020 Shamloo, H ; Nazari, A ; Faez, R ; Shahhoseini, A ; Sharif University of Technology
    Elsevier B.V  2020
    In this work, a new structure of single layer armchair graphene nanoribbon field effect transistor with the Stone–Wales (SW) defect (SWGNRFET) is studied. The simulations are solved with Poisson–Schrödinger equation self-consistently by using Non-Equilibrium Green Function (NEGF) and in the real space approach. The energy band structure is obtained by approximation tight-binding method. The results show that displacement of a defect in the width of the channel of the new structure is led to 50% increase in ION/IOFF ratio only by rotating of a C–C (Carbon–Carbon) bond with similar behavior. But, a remarkable increase of 300% in ION/IOFF ratio is obtained by a “dual center” defect. The results... 

    Investigation of Vibration and Stability of Graphene NanoRibbone under Magnetic field Effect

    , Ph.D. Dissertation Sharif University of Technology Mohammadkhani, Hasan (Author) ; Dehghani Firouzabadi, Rouhollah (Supervisor)
    This study aims at investigating the vibration analysis and stability of Graphene Nano-Ribbon (GNR) under a magnetic field using continuum mechanics approach and an efficient hybrid modal-molecular dynamics method. The force distribution on the GNR due to the magnetic field is determined by Maxwell's equations, Biot-savart law, magnetic dipoles and Lorentz force law.
    Using the continuum mechanics model, the vibration of the GNR in a magnetic field is investigated by some problems and the resonance frequencies, stability boundaries and critical load are studied.
    Furthermore, in this present study, an efficient hybrid modal-molecular dynamics method is developed for the vibration... 

    Fabrication and Characterized of Transmission Line Parametrs for GNR Interconnect

    , M.Sc. Thesis Sharif University of Technology Reihany, Omid (Author) ; Sarvari, Reza (Supervisor)
    The process of contracting the chips will lead the increasing of impurity concentration, decreasing the bias voltage and threshold voltage to make stable the electrical field. For using the advantage of lesser dimensions of the total circuit using decreasing bias voltage lead the dimension of the wires to be decrease also. Therefore, once the parasitic effects of wires, the RC delays of wires and the noise of power transmission will enhance obviously. With this contracting by process, electrical resistance of interconnect will enhance also. The reason of this matter is that the area chip will decrease significantly. While the operational frequency increases the effect of inductance should be...