Publication

Book Chapter
  1. Hatef Sadeghi, S. M. Mousavi, M. Rahmani, Chapter 9: Bilayer Graphene Nanoribbon Physical Concept, in An Introduction to Advanced Nanoelectronics, M. T. Ahmadi, Razali Ismail, Soheil Anwar, Editor. 2011, Taylor and Francis.

  2. S. M. Mousavi, M. Rahmani, Hatef Sadeghi, Chapter 10: BGNR Mobility and Schottky Current, in An Introduction to Advanced Nanoelectronics, M. T. Ahmadi, Razali Ismail, Soheil Anwar, Editor. 2011, Taylor and Francis.

  3. M. Rahmani, Hatef Sadeghi, S. M. Mousavi, Chapter 11: Trilayer Graphene Nanoribbon, in An Introduction to Advanced Nanoelectronics, M. T. Ahmadi, Razali Ismail, Soheil Anwar, Editor. 2011, Taylor and Francis.

Journal Papers
  1. Ballistic Conductance Model of Bilayer Graphene Nanoribbon (BGN)
    • J. Comput. Theor. Nanosci. vol. 8(10), pp. 2029-2032, 2011. (IF=0.9)
    • How to Cite this Article: Hatef Sadeghi, M. T. Ahmadi, B. I. Ishak, S. M. Mousavi and Razali Ismail, “Ballistic Conductance Model of Bilayer Graphene Nanoribbon (BGN),” J. Comput. Theor. Nanosci. vol. 8(10), pp. 1993-1998, 2011. DOI:10.1166/jctn.2011.1915

      Abstract:
      Ballistic conductance of Bilayer Graphene Nanoribbons (BGNs) is concerned in this paper. Mathematical model and numerical solution of BGNs ballistic conductance is introduced as well as its analytical model in the degeneracy limit. Our method indicates that near the neutrality point the non-degenerate approximation can be properly used. In contrast, out of this boundary condition it is estimated to work in the degenerate regime. Moreover, it confirms that BGN conductance is temperature dependence near the neutrality point also minimum conductance is depended on temperature which increases by increasing temperature but beyond the neutrality point conductance is independent of temperature. Presented model shows good agreement by published experimental data.

  2. Bilayer Graphene Nanoribbon Carrier Statistic in the Degenerate and the Non Degenerate Limit
    • J. Comput. Theor. Nanosci. vol. 8(10), pp. 1993-1998, 2011. (IF=0.9)
    • How to Cite this Article: S. Mahdi Mousavi, M. T. Ahmadi, Hatef Sadeghi, Azadeh Nilghaz, Azizah Amin, Zaharah Johari and Razali Ismail, “Bilayer Graphene Nanoribbon Carrier Statistic in the Degenerate and the Non-Degenerate Limits,” J. Comput. Theor. Nanosci. vol. 8(10), pp. 2029-2032, 2011. DOI:10.1166/jctn.2011.1921

      Abstract:
      Bilayer Graphene Nanoribbon (BGN) Carrier statistic in the non-degenerate and the degenerate limit is presented. Two dimensional BGN through AB configuration with width less than De-Broglie wave length can be understood as a one dimensional (1D) device. Based on the 1D behavior offered model illustrates exponential function of normalized Fermi energy which explains carrier concentration on low carrier regime. However on zero to 3kBT distance from and within conduction or valence bands high concentration of carriers sensitively depends on normalized Fermi energy which is independent of temperature as well. Since a BGN field effect transistor (BGNFET) can be shaped by using graphene bilayers with an external controllable voltage which is perpendicular to the layers in gates.

  3. Analysis of a Novel Full Adder Cell Designed for Implementing in Carbone Nanotube Technology
    • Journal of Nanomaterials, vol. 2011, Article ID 906237, 6 pages, 2011. doi:10.1155/2011/906237 (IF= 1.023)
    • How to Cite this Article: M. H. Ghadiry, Asrulnizam A. Manaf, M. T. Ahmadi, Hatef Sadeghi, and M. Nadi Senejani, “Design and Analysis of a New Carbone Nanotube Full Adder Cell,” Journal of Nanomaterials, vol. 2011, p. 906237, 2011. DOI:10.1155/2011/906237

      Abstract:
      In this paper, a novel full adder circuit is presented. The main aim is to reduce power delay product (PDP) in the presented full adder cell. A new method is used in order to design a full-swing full adder cell with low number of transistors.  The proposed full adder is implemented in MOSFET like Carbon nanotube technology and the layout is provided based on standard 32 nm technology from MOSIS. The simulation results using HSPICE show that, there are substantial improvements in both power and performance of the proposed circuit compared to latest designs.  In addition, the proposed circuit has been implemented in conventional 32 nm process to compare the benefits of using MOSFET like Carbon nanotubes in arithmetic circuits over conventional CMOS technology. The proposed circuit can be applied in very high performance and ultra low power applications. 

  4. Channel Conductance of ABA Stacking Trilayer Graphene Nanoribbon Field Effect Transistor
    • Modern Physics Letters B. Vol. 26, 8, 1250047, 2012. (IF=0.6)
    • How to Cite this Article: Hatef Sadeghi, M. T. Ahmadi, S. M. Mousavi, M. H. Ghadiry and Razali Ismail, “Channel Conductance of ABA Stacking Trilayer Graphene Nanoribbon Field Effect Transistor.” Modern Physics Letters B, Vol. 26, 8, 1250047, 2012. DOI:10.1142/S0217984912500479

      Abstract:
      In this paper, our focus is on ABA trilayer graphene nanoribbon (TGN), in which the middle layer is horizontally shifted from the top and bottom layers. The conductance model of TGN as a FET channel is presented based on Landauer formula. Besides the good reported agreement with experimental study lending support to our model, the presented model demonstrates that minimum conductivity increases dramatically by temperature. It also draws parallels between TGN and bilayer graphene nanoribbon, in which similar thermal behavior is observed. Maxwell–Boltzmann approximation is employed to form the conductance of TGN near the neutrality point. Analytical model in degenerate regime in comparison with reported data proves that TGN-based transistor will operate in degenerate regime like what we expect in conventional semiconductors. Moreover, our model confirms that in similar condition, the conductivity of TGN is less than bilayer graphene nanoribbon as reported in some experiments.

  5. Schottky Current in Carbon Nanotube - Metal Contact
    • J. Comput. Theor. Nanosci. vol. 9(10), pp. 1554-1557, 2012. (IF=0.9)
    • How to Cite this Article: Sara Sangtarash, Hatef Sadeghi, M. T. Ahmadi, M. H. Ghadiry, Sohail Anwar, and Razali Ismail, “Schottky Current in Carbon Nanotube-Metal Contact.” J. Comput. Theor. Nanosci. vol. 9(10), pp. 1554-1557, 2012.

      Abstract:
      Silicon based technology has received its technical limitation because of its unstable structure at nano-level. Carbon nanotube as an alternative material has attracted significant scientific efforts. Fabrication of Schottky diode using carbon nanotube is an open area of research to overcome this limit. In this study, we model the current of CNT Schottky diode under applied voltage. Parabolic band approximation on CNT induces Fermi-Dirac integral of order zero on its current voltage which is similar to the conventional one dimensional material. This model shows that its current has a weak dependence on temperature corresponding to the small applied voltage. It is quite different in high bias voltages which are independent of temperature. Based on this model, incremental effect of the carbon nanotube diameter has been explained by increasing the current with the applied voltage. The model presented in this paper is in good agreement with the reported data from experiments. This device can be used in the integrated circuit miniaturization.
Conference Papers
  1. Carrier Statistic Model for a Bilayer Graphene in the Non-degenerate Regime
    • Presented in PCO 2010
    • How to Cite this Article: Hatef Sadeghi, M. T. Ahmadi, Jeff F. Webb, S. M. Mousavi, Razali Ismail and Ishak Ismail, “Carrier Statistic Model for a Bilayer Graphene in the Non-degenerate Regime.” AIP Conference Proceedings, 2011. 1337(1): 184-187. DOI: 10.1063/1.3592464

      Abstract:
      This paper focuses on the electronic transport properties of bilayer Graphene nanoribbons (BGNRs). The electronic transport of two dimensional AB stacked BGNRs with widths less than 10 nm is investigated. Due to the small width, the BGNR can be assumed to operate as a one dimensional device.
      A mathematical model of carrier concentration in BGNRs in the nondegenerate regime is presented. The model shows that in this regime the carrier statistics of BGNRs can be expressed by an exponential function of the normalized Fermi energy, which is particularly useful in the lower carrier concentration regions.

  2. Carbon Nanotube Capacitance Model in the Degenerate and the Nondegenerate Regimes
    • Presented in PCO 2010
    • How to Cite this Article: M. T. Ahmadi, J. F. Webb, N. A. Amin, S. M. Mousavi, Hatef Sadeghi, M. R. Neilchiyan and R. Ismail, “Carbon Nanotube Capacitance Model in the Degenerate and the Non-degenerate Regimes.” AIP Conference Proceedings 1337(1): 173-176. DOI:10.1063/1.3592461

      Abstract:
      In this work, fundamental results on carrier statistics in a carbon nanotube treated as a onedimensional material are presented. Also the effect of degeneracy on the capacitance of the carbon nanotube channel in a carbon nanotube field effect transistor is discussed. A quantum capacitance as well as a classical capacitance is revealed. Furthermore it is shown that for low gate voltage, the total capacitance is equivalent to the classical capacitance but for high gate voltage it is equivalent to the quantum capacitance. We predict that in the nondegenerate regime, the total capacitance is equivalent to the classical capacitance and that the quantum capacitance can be neglected, whereas only quantum capacitance needs to be taken into account in the calculation of the total capacitance in the degenerate regime.

  3. Bilayer Graphene Nanoribbon Carrier Statistics in the Degenerate Regime
    • Presented in PCO 2010
    • How to Cite this Article: S. M. Mousavi, M. T. Ahmadi, Hatef Sadeghi, Jeff F. Webb and Razali Ismail, “Bilayer Graphene Nanoribbon Carrier Statistics in the Degenerate Regime.” AIP Conference Proceedings 1337(1): 180-183. DOI: 10.1063/1.3592463

      Abstract:
      In this paper we discuss the energy band structure of bilayer graphene nanoribbons (BGNRs) near the Fermi level between zero and 3kT away from the conduction and valence bands. BGNRs can be used as the channel in field effect transistors (FETs). A FET can be created using graphene bilayers with the gate voltage perpendicular to the layers. We focus on carrier statistics in the degenerate regime and the density of states, and consider them to be fundamental properties of BGNRs. The model presented indicates that the normalized Fermi energy in the degenerate regime strongly depends on carrier concentration and is independent of temperature. 

  4. Bilayer Graphene Nanoribbon Conductance Model in Parabolic Band Structure
    • Presented in ESciNano2010
    • How to Cite this Article: S. M. Mousavi,  M. T. Ahmadi, Hatef Sadeghi, N. Aziziah Amin Zaharah Johari, Razali Ismail and Sohail Anwar, “Bilayer Graphene Nanoribbon Conductance Model in Parabolic Band Structure.” AIP Conference Proceedings 1341(1): 388-390. DOI:10.1063/1.3587025

      Abstract:
      Considering the importance of doing conductance studies, this manuscript describes the development of an analytical model for the conductance of bilayer GNR. Even though the experimental study of bilayer GNR conductivity has been conducted previously, the work described in this manuscript focuses on conductance. The work represents an improvement in the existing conductance model of bilayer GNR. In this manuscript, the conductance model is developed based on the Landauer formula which includes the correction for a smaller size device since bilayer GNR is considered as a one-dimensional device. Based on the work carried out by the authors of this manuscript, the bilayer GNR conductance has a minimum value at gate voltage.

  5. Bilayer Graphene Conductance Model in the Degenerate Limit 
    • Presented in FISSC2011
    • How to Cite this Article: Hatef Sadeghi, Sara Sangtarash and M. T. Ahmadi “Bilayer Graphene Conductance Model in the Degenerate Limit.” The First Iranian Students Scientific Conference in Malaysia, 9-10 April 2011, University Putra Malaysia, Kuala Lumpur, Malaysia

      Abstract:
      Excellent transport properties in bilayer graphene nanoribbons (BGNs) such as high carrier mobility, bandgap tunable by external voltage and high frequency characteristic, and also ability to produce single atomic thick layer (instead of silicon which is unstable in atomic sizes) makes it a good replacement for silicon based electronic devices. The carrier mobility is related to the conductance which is governed by the conductivity theory. It will indicate the transport performance of BGN, especially for the use of BGN as a conducting channel, in BGNFET. BGNs with width less than 10 nm can be understood as one dimensional (1D) device, considering the significance of the conductance study, conductance modeling of 1D BGN is our focus. In this paper, we carry out mathematical model of 1D BGNs conductance in ballistic transportation based on Landauer formula. Also we show that the numerical model can be approximated by our analytical model in the degenerate limit.

  6. Biased Voltage Boundary Condition to Operate Bilayer Graphene in the Insulating Region 
    • Presented in ICEDSA2011
    • How to Cite this Article: Hatef Sadeghi, M. T. Ahmadi, Sara Sangtarash and Razali Ismail, “Biased Voltage Boundary Condition to Operate Bilayer Graphene in the Insulating Region.” in Electronic Devices, Systems and Applications (ICEDSA), 2011 International Conference on, 2011, pp. 50-52. DOI: 10.1109/ICEDSA.2011.5959053

      Abstract:
      Graphene has received significant attention due to its excellent transport properties. Bilayer Graphene Nanoribbon (BGN), double Bernal stacked honeycomb sheets of carbon which have quadratic dispersion relations instead of single layer Graphene Nanoribbon (GNR) by linear dispersion, provides an interesting area of research activity. In this paper, we show that isolating properties appears in the limit of external applied voltage in BGNs. The gap between conduction and valance band which is opened by an applied electric field is strongly varied by the value of the external voltage. The band gap is opened for Vext=0 to Vext,max  where the conduction and valance band meet each other and overlap through the conduction and valance band. In this boundary condition, BGNs are expected to behave as an insulator. In contrast, beyond this boundary condition it is estimated to be semi-metallic. Also we showed changing the value of interlayer hopping strongly affected the maximum band gap and it creates a wider possible external electric field which opens the band gap in BGNs.

  7. Designing Fast Fourier Transform using Verilog and Simulation by Quartus II
    • Presented in FISSC2011
    • How to Cite this Article: Hatef Sadeghi, “Designing Fast Fourier Transform using Verilog and Simulation by Quartus II.” The First Iranian Students Scientific Conference in Malaysia, 9-10 April 2011, University Putra Malaysia, Kuala Lumpur, Malaysia

      Abstract:
      A fast Fourier transform (FFT) is an efficient algorithm to compute the Discrete Fourier Transform (DFT) and its inverse. Designing the Fast Fourier Transform (FFT) of a digital input signal using Verilog program is target of this study. We demonstrate a new method to calculate FFT using verilog by some constrains. The simulation result using Quartus II is fit to mathematical calculation using Matlab platform. Also in this work, it is dedicated RTL design of a 16 bits multiplayer which must use to implement this algorithm at RTL level.

  8. Design HAPS coverage to provide a footprint for the whole state of Perak
    • Presented in FISSC2011
    • How to Cite this Article: Hatef Sadeghi, “Design HAPS coverage to provide a footprint for the whole state of Perak.” The First Iranian Students Scientific Conference in Malaysia, 9-10 April 2011, University Putra Malaysia, Kuala Lumpur, Malaysia

      Abstract:
      This paper represents a HAPS coverage design to provide a footprint for the whole state of Perak in Malaysia. 3 points are called SPP1, SPP2 and SPP3 is assumed, on the other hand using 3 HAPS which is located in specific condition in this design provide full coverage of Perak.

  9. Trilayer Graphene Nanoribbon Carrier Statistic in Degenerate and Non Degenerate Limits
    • Presented in PCO 2011
    • How to Cite this Article: Meisam Rahmani, M.T. Ahmadi, N. Shayesteh, S. M. Mousavi, Hatef Sadeghi, Razali Ismail “Trilayer Graphene Nanoribbon Carrier Statistic in Degenerate and Nondegenerate Limits.” The fifth Global Conference on Power Control and Optimization PCO 2011, 1 - 3 June 2011, Dubai, Unites Arab Emirate

      Abstract:
      A multilayer with an odd number of layers (three or more) lacks inversion symmetry, but there is another transformation imposing an approximate valley degeneracy, which arises because the low-energy Hamiltonian consists of separate monolayer like and bilayer like parts. We present trilayer graphene nanoribbon carrier statistics in the degenerate and the nondegenerate limits. Within zero to 3kBT from the conduction or valence band edges high concentrations of carriers sensitively depend on a normalized Fermi energy which is independent of temperature. The effect of different stacking orders of grapheme multilayers on the electric field induced band gap is studied. The gap for trilayer graphene with the ABC stacking is much larger than the corresponding gap for the ABA trilayer. The gap for the different types of stacking is much larger as compared to the case of Bernal stacking. A non- monotonic dependence of the true energy gap in trilayer graphene on the charge density is investigated along with the electronic low-energy band structure of ABC stacked multilayer graphene. The band structure of trilayer graphene systems in the presence of a perpendicular electric field is obtained using a tight-binding approach, using a self-consistent Hartree approximation to calculate the induced charges on the different grapheme layers.

  10. Modeling of Graphene Nanoribbon Schottky Diodes in the Parabolic Band Structure Limit
    • Presented in PCO 2011
    • How to Cite this Article: Nahid shayeste, M.T.Ahmadi, M.Rahmani, Hatef Sadeghi, S. M. Mousavi, Razali Ismail “Current – Voltage Modeling of GNR Schottky diods in parabolic band structure limit”, The fifth Global Conference on Power Control and Optimization PCO 2011, 1 - 3 June 2011, Dubai, Unites Arab Emirate

      Abstract:
      In this paper we investigate the band structure of graphene nano-ribbons and the current density. A square root approximation shows that the band energy is parabolic in the low energy limit. In this parabolic region charge transport is controlled by the saturation velocity.

  11. A Review on: Carbon Based Materials as On-chip Interconnects
    • Presented in SPIE SNMMD
    • How to Cite this Article: Hatef Sadeghi, Jean-Michel Redouté, Daniel T. H. Lai, M. T. Ahmadi and Razali Ismail, "A review on carbon-based materials as on-chip interconnects", Proc. SPIE 8204, 82042O (2011); doi:10.1117/12.903196

      Abstract:
      Interconnect wires have always been one of the major technology components of modern high-speed integrated circuits. Based on the international technology roadmap, silicon FETs technology, copper and tungsten interconnects will approach their fundamental scaling limits beyond 2020. There is a need to look for an alternate paradigm. Two promising manners are proposed: state variables and new materials such as carbon based materials. Since studies on state variables are being currently evaluated with no clear frontrunner, this survey will describe the latter approach. This paper summarizes the essential electrical properties of carbon based materials, specifically graphene nanoribbon (GNR) which shows advantageous properties compared to conventional semiconductors concerning the interconnect technology. Although bilayer graphene (BGN) shows a lower carrier mobility with respect to GNR, it might be an optimum solution as its band structure can be tuned by an external field. However, characteristics of undoped and doped multilayer GNR with high edge disorders have not been clearly demonstrated yet. Since the conduction and valence bands of trilayer graphene (TGN) overlap, it is semimetal, and therefore, it may exhibit an improved performance compared to GNR or BGN as interconnects. This paper describes the conductance model of TGN using the Launderer formula: indeed, numerical solutions illustrate that the length of the ribbon affects the conductance of TGN dramatically, and consequently, since conductance of TGN is less affected by external field, it can be a better choice for on-chip interconnects.

  12. Study the Effect of Applied Voltage on Propagation Delay of Bilayer Graphene Nanoribbon Transistor
    • Presented in ISDRS 2011
    • How to Cite this Article: Asrulnizam Abd Manaf, M. Hosseinghadiry, S. Mehdi Mousavi, H. Sadeghi, "Study the Effect of Applied Voltage on Propagation Delay of Bilayer Graphene Nanoribbon Transistor", International Semiconductor Device Research Symposium (ISDRS 2011), 7 - 9 December 2011, University of Maryland, College Park, Maryland, USA. DOI: 10.1109/ISDRS.2011.6135226

      Abstract:
      Fundamental limitations of CMOS technology and anticipations of Moore’s law have motivated researchers to find several alternatives for these devices such as nanowire, carbon nanotube and graphene nanoribbon. In this work firstly, we develop an analytical model for quantum capacitance of monolayer and bilayer graphene. Secondly, resistance of the channel is modelled based on conductance of the nanoribbon and finally propagation delay is calculated by using resistance and capacitance.

  13. Using Cognitive Radio Interference Mitigation Technique to Enhance Coexistence and Sharing Between DVB-T and LTE System
    • Presented in Future Network & Mobile Summit 2012
    • How to Cite this Article: Sara Sangtarash, Hatef  Sadeghi, Walid A. Hassan, Horace L. King, T. A. Rahman "Using Cognitive Radio Interference Mitigation Technique to Enhance Coexistence and Sharing Between DVB-T and LTE System", Future Network & Mobile Summit 2012, 4 - 6 July 2012, Berlin, Germany

      Abstract:
      Today with increasing development of wireless systems, frequency utilization is limited by the problem of insufficient spectrum. In addition with increasing the implementation of the third generation (3G) and integrated cellular phones that provide high speed packet-switching data transmission, we need more portion of spectrum. On the other hand analogue TV is moving to digital, so after this switch-over, there are some parts of the spectrum which will be free, and may be able to be  used for other services. In this study we try to use the technology that is able to sens e the spectrums over the DVB-T frequency band (primary system), and detect the existence/ absence of primary users, and based on the detection of free spectrum, use that spectrum  for LTE system as a secondary system, without harmful interference with primary users defi ned as Cognitive Radio (CR). Our study has shown that for coexistence and sharing be tween DVB-T and LTE-OFDM, at the same frequency band (662-742 MHz), the probability of interference is high and a large protection guard distance is needed. However when we apply Cognitive Radio technique, harmful interference can be avoided from secondary systems and improve spectrum efficiency.
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