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Graphene nanoribbon based spaser  [PDF]
Oleg L. Berman,Roman Ya. Kezerashvili,Yurii E. Lozovik
Physics , 2013, DOI: 10.1103/PhysRevB.88.235424
Abstract: A novel type of spaser with the net amplification of surface plasmons (SPs) in doped graphene nanoribbon is proposed. The plasmons in THz region can be generated in a dopped graphene nanoribbon due to nonradiative excitation by emitters like two level quantum dots located along a graphene nanoribbon. The minimal population inversion per unit area, needed for the net amplification of SPs in a doped graphene nanoribbon is obtained. The dependence of the minimal population inversion on the surface plasmon wavevector, graphene nanoribbon width, doping and damping parameters necessary for the amplification of surface plasmons in the armchair graphene nanoribbon is studied.
The unique chemical reactivity of a graphene nanoribbon's zigzag edge  [PDF]
De-en Jiang,Bobby G. Sumpter,Sheng Dai
Physics , 2007, DOI: 10.1063/1.2715558
Abstract: The zigzag edge of a graphene nanoribbon possesses a unique electronic state that is near the Fermi level and localized at the edge carbon atoms. We investigate the chemical reactivity of these zigzag edge sites by examining their reaction energetics with common radicals from first principles. A "partial radical" concept for the edge carbon atoms is introduced to characterize their chemical reactivity, and the validity of this concept is verified by comparing the dissociation energies of edge-radical bonds with similar bonds in molecules. In addition, the uniqueness of the zigzag-edged graphene nanoribbon is further demonstrated by comparing it with other forms of sp2 carbons, including a graphene sheet, nanotubes, and an armchair-edged graphene nanoribbon.
Modelling of Graphene Nanoribbon Fermi Energy  [PDF]
Zaharah Johari,Mohammad Taghi Ahmadi,Desmond Chang Yih Chek,N. Aziziah Amin,Razali Ismail
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/909347
Abstract: Graphene nanoribbon (GNR) is a promising alternative to carbon nanotube (CNT) to overcome the chirality challenge as a nanoscale device channel. Due to the one-dimensional behavior of plane GNR, the carrier statistic study is attractive. Research works have been done on carrier statistic study of GNR especially in the parabolic part of the band structure using Boltzmann approximation (nondegenerate regime). Based on the quantum confinement effect, we have improved the fundamental study in degenerate regime for both the parabolic and nonparabolic parts of GNR band energy. Our results demonstrate that the band energy of GNR near to the minimum band energy is parabolic. In this part of the band structure, the Fermi-Dirac integrals are sufficient for the carrier concentration study. The Fermi energy showed the temperature-dependent behavior similar to any other one-dimensional device in nondegenerate regime. However in the degenerate regime, the normalized Fermi energy with respect to the band edge is a function of carrier concentration. The numerical solution of Fermi-Dirac integrals for nonparabolic region, which is away from the minimum energy band structure of GNR, is also presented. 1. Introduction Single layer of graphite which is also known as graphene has been discovered as a material with attractive low-dimensional physics, and possible applications in electronics [1–6]. A single-wall carbon nanotube (SWCNT) is a piece of rolled-up graphene sheet while a nanoribbon is an unrolled nanotube. Band-gap opening is expected by patterning narrow ribbons [7, 8] from Graphene which can be achieved by chemical means [9]. This Graphene nanoribbon (GNR) with quasi-one-dimensional structures and narrow widths ( ~10?nm ) is predicted to be used as a channel for field effect transistors with high switching speed and excellent carrier mobility with ballistic transport behavior [9–14]. Armchair and zigzag GNRs show metallic or semiconducting electronic properties depending on the number of dimer lines, N which gives the width of the nanoribbon as depicted in Figures 1 and 2. The semiconducting property in armchair GNRs occurs when or , where p is an integer [15]. The width of the GNR, , is proportional to N given by the expression where is the lattice constant [16]. Quantum confinement effect results in similarity of semiconducting and metallic behaviors in both nanotube and nanoribbon configurations. A nanoribbon can be assumed as an unrolled single-wall nanotube that results in two different classes of GNRs depending on SWNTs unfolded way. One is by unzipping the
Quantum computation with graphene nanoribbon  [PDF]
Guo-Ping Guo,Zhi-Rong Lin,Xiao-Peng Li,Tao Tu,Guang-Can Guo
Physics , 2008, DOI: 10.1088/1367-2630/11/12/123005
Abstract: We propose a scalable scheme to implement quantum computation in graphene nanoribbon. It is shown that electron or hole can be naturally localized in each zigzag region for a graphene nanoribbon with a sequence of Z-shaped structure without exploiting any confined gate. An one-dimensional graphene quantum dots chain is formed in such graphene nanoribbon, where electron or hole spin can be encoded as qubits. The coupling interaction between neighboring graphene quantum dots is found to be always-on Heisenberg type. Applying the bang-bang control strategy and decoherence free subspaces encoding method, universal quantum computation is argued to be realizable with the present techniques.
Ferromagnetism in armchair graphene nanoribbon  [PDF]
Hsiu-Hau Lin,Toshiya Hikihara,Horng-Tay Jeng,Bor-Luen Huang,Chung-Yu Mou,Xiao Hu
Physics , 2009, DOI: 10.1103/PhysRevB.79.035405
Abstract: Due to the weak spin-orbit interaction and the peculiar relativistic dispersion in graphene, there are exciting proposals to build spin qubits in graphene nanoribbons with armchair boundaries. However, the mutual interactions between electrons are neglected in most studies so far and thus motivate us to investigate the role of electronic correlations in armchair graphene nanoribbon by both analytical and numerical methods. Here we show that the inclusion of mutual repulsions leads to drastic changes and the ground state turns ferromagnetic in a range of carrier concentrations. Our findings highlight the crucial importance of the electron-electron interaction and its subtle interplay with boundary topology in graphene nanoribbons. Furthermore, since the ferromagnetic properties sensitively depends on the carrier concentration, it can be manipulated at ease by electric gates. The resultant ferromagnetic state with metallic conductivity is not only surprising from an academic viewpoint, but also has potential applications in spintronics at nanoscale.
Resistivity of Graphene Nanoribbon Interconnects  [PDF]
Raghunath Murali,Kevin Brenner,Yinxiao Yang,Thomas Beck,James D. Meindl
Physics , 2009, DOI: 10.1109/LED.2009.2020182
Abstract: Graphene nanoribbon interconnects are fabricated, and the extracted resistivity is compared to that of Cu. It is found that the average resistivity at a given line-width (18nm
Bends and splitters in graphene nanoribbon waveguides  [PDF]
Xiaolong Zhu,Wei Yan,N. Asger Mortensen,Sanshui Xiao
Physics , 2012, DOI: 10.1364/OE.21.003486
Abstract: We investigate the performance of bends and splitters in graphene nanoribbon waveguides. Although the graphene waveguides are lossy themselves, we show that bends and splitters do not induce any additional loss provided that the nanoribbon width is sub-wavelength. We use transmission line theory to qualitatively interpret the behavior observed in our simulation. Our results pave a promising way to realize ultra-compact devices operating in the terahertz region.
Graphene Nanoribbon and Graphene Nanodisk  [PDF]
Motohiko Ezawa
Physics , 2007, DOI: 10.1016/j.physe.2007.09.031
Abstract: We study electronic properties of graphene derivatives which have closed edges. They are finite-length graphene nanoribbons and graphene nanodisks. No metallic states are found in finite-length zigzag nanoribbons though all infinite-length zigzag nanoribbons are metallic. We also study hexagonal, parallelogrammic and trigonal nanodisks with zigzag or armchair edges. No metallic states are found in these nanodisks either except trigonal zigzag nanodisks. It is interesting that we can design the degeneracy of the metallic states arbitrarily in trigonal zigzag nanodisks by changing the size.
Measuring the local quantum capacitance of graphene using a strongly coupled graphene nanoribbon  [PDF]
D. Bischoff,M. Eich,A. Varlet,P. Simonet,T. Ihn,K. Ensslin
Physics , 2015, DOI: 10.1103/PhysRevB.91.115441
Abstract: We present electrical transport measurements of a van-der-Waals heterostructure consisting of a graphene nanoribbon separated by a thin boron nitride layer from a micron-sized graphene sheet. The interplay between the two layers is discussed in terms of screening or, alternatively, quantum capacitance. The ribbon can be tuned into the transport gap by applying gate voltages. Multiple sites of localized charge leading to Coulomb blockade are observed in agreement with previous experiments. Due to the strong capacitive coupling between the ribbon and the graphene top layer sheet, the evolution of the Coulomb blockade peaks in gate voltages can be used to obtain the local density of states and therefore the quantum capacitance of the graphene top layer. Spatially varying density and doping are found which are attributed to a spatial variation of the dielectric due to fabrication imperfections.
Graphene Nanoribbon Conductance Model in Parabolic Band Structure  [PDF]
Mohammad Taghi Ahmadi,Zaharah Johari,N. Aziziah Amin,Amir Hossein Fallahpour,Razali Ismail
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/753738
Abstract: Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR) with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel. 1. Introduction Graphene consist of a single sheet of cabon atom bonded in sp2 of hexagonal lattice structure offers a numbers of fascinating possibilities in electronics application [1, 2]. Graphene is a gapless two dimensional material which its confinement introduce one dimensional Graphene nanoribbon with a width less than the De-Broglie wavelength as illustrated in Figure 1. The formation of band gap in GNR resulted from the confinement of electron that form standing waves along the chiral vector [3, 4]. The band gap of the GNR formed that depends on its width and chirality leads to different carrier transport phenomena [5, 6]. GNR band structure shows electronic properties of metallic and semiconducting just like the CNT [7]. GNR also share similar properties with single wall CNTs (SWNTs) [8] that have a mean free path in a range of micrometer [9, 10] as well as carrying higher carrier densities. Unlike CNTs, GNRs has simpler fabrication process owing to excellent future electronic devices like transistor and interconnect [11, 12]. Theoretical study on GNR [13–15] is still at the beginning stage and the conductance phenomena based on band structure are still unexplored. In this paper, physical model of GNR conductance presented as a function of normalized Fermi energy. Figure 1: A prototype one-dimensional GNR with and for rectangular cross-section. 2. Conductance Modeling Applying the Taylor expansion on graphene band energy near the Fermi point, the relation of the GNR is obtained as [16] where is quantized wave vector given by [17] here is the subband index and is the number of dimmer lines which determine the width of
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