Masoud Berahman

Publications (3) View all

• Article: Optical Properties of Chiral Graphene Nanoribbons: a First Principal Study

  M. Berahman, M. Asad, M. H. Sheikhi
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  ABSTRACT: In this paper, optical properties of Chiral Graphene Nanoribbons both in longitude and transverse polarization have been studied using density functional theory calculation. It has been shown that the selection rule which have been reported before for Armchair and Zigzag Graphene Nanoribbons are no longer valid due to breaking symmetry on these new categorize of graphene nanoribbons. However, still the edge states play a critical role in optical absorption. It have been illustrated that depending on the polarization of incident beam the absorption peaks are different while it is spread in the same energy range. It is also suggested that the absorption of light is sensitive to the chiral vector on the edges and direction of the light polarization. Due to breaking symmetry in chiral graphene nanoribbons, absorption peak is changed and it would be around 1000nm, introducing a new potential of graphene nanoribbons for optoelectronic devices.
  05/2012;
• Article: Optical Excitations of Finite Length Graphene Nanoribbons

  Berahman, Sheikhi
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  ABSTRACT: In this paper, influences of finite length on optical properties of graphene nanoribbons have been investigated. Discrete electronic states, which created by finite length barriers, are calculated using third nearest neighbor tight binding jointed with quantum confinement of Bloch theory. Fermi Golden rule within Gradient approximation has been used to study optical properties of zigzag and armchair graphene nanoribbons as a result of these discrete states. It is shown that the absorption spectra strongly have depended on length and edge structures of graphene nanoribbons. Our calculation has shown the threshold excitation frequency decrease to its infinite length value as length increases in metallic armchair, while in nonmetallic armchair and zigzag; this frequency does not change sensitively. Number of absorption peaks in different structures of graphene nanoribbons has been investigated and shown these absorption peaks group together as length increased. Maximum absorption and stop band frequencies have investigated in different lengths and edges structures. It has shown that these frequencies have little shift with length. The predicted results can be verified by the experimental measurements, which have been done for infinite GNRs and as length increases, results converge to previous reports on optical absorption spectrum of infinite length graphene nanoribbons.
  Journal of Computational and Theoretical Nanoscience. 01/2011; 8(1):90-96.
• Article: The Numerical Modeling for Electrical Behavior of Graphene Nanoribbon in the Present of Optical Detection

  Mohammad Hosein Sheikhi, Masoud Berahman, Reza Alaei
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  ABSTRACT: A physical model is presented for GNR based photo detector. The photo detector structure is photodiode in which GNR is inserted between two electrodes as a tool for changing pick frequency of absorption. Optical properties of GNR discussed using tight-binding approximation and DOS coupled with conductivity. Our calculations have shown that GNR based photo detectors have better characteristics than semiconductor devices and they have appropriate characteristic for communication applications.
  Computer and Electrical Engineering, International Conference on. 12/2009; 2:20-22.