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1057-II10-41

A Tight-Binding Hamiltonian for Band Structure and Carrier Transport in Graphene Nanoribbons Daniel Finkenstadt1, Gary Pennington2, and Michael J Mehl1 1 Code 6390, U.S. Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC, 20375 2 U.S. Army Research Laboratory, Adelphi, MD, 20783 ABSTRACT To understand nanoribbons of graphene, we developed an ab initio parametrized fit to Carbon and Hydrogen chemical data, out to arbitrary neighbor interactions, including relaxations. Our computed band structure confirms the well-known three-family behavior of armchair band gaps but also predicts a similar familial behavior for conductance in nanoribbon transistors. The Boltzmann carrier transport simulations from calculated phonon spectra show, over a range of temperatures, the familial conductance behavior. Both the peak field-effect mobility and the "on" conductance increase with ribbon width, the later being proportional to the width and inversely proportional to the lattice temperature. We will also discuss phonon-limited scattering of charge carriers in graphene. INTRODUCTION Understanding and predicting carrier transport and scattering in graphite nanoribbons (GNRs) is important for potential nanoscale device applications, including use as ultra-small transistors and as bio/chemical sensors. Semiconducting GNRs , including armchair nanoribbons (ANRs) [1], are best suited for such applications since a gate potential may effectively turn the device current on and off by moving the Fermi level into and out of the carrier bands. Previous transport studies have focused mainly on the ballistic transport regime. Here we focus on phonon-limited semi-classical transport, a regime that has been shown to describe many transport features in carbon nanotubes [2] but has received only limited attention in nanoribbons [3]. Semiclassical transport is applicable when the carrier mean free path between scattering events is much smaller than the ribbon length L. This transport regime is of interest since: 1) it allows for the incorporation of a relatively simple and highly predictive scattering theory, 2) many of the ‘bulk’ transport features obtained are also found in other regimes and 3) it gives the limits of the ballistic and phase coherent transport regimes. Phonon scattering will be considered since this mechanism is found to be significant in similar materials such as graphite and carbon nanotubes [2]. As both transport and associated scattering mechanisms depend strongly on the low-energy electronic structure of carriers, we find that important semi-classical transport properties also vary with the three ANR families. Our approach will use a highly sophisticated tight-binding method, including arbitrary neighbor interactions, forces and relaxations, to describe the relaxed band-structure and phonon dispersions of ANRs, as a function of width. These data are then input into our transport model.

THEORETICAL METHODS We previously fit [1,4] tight-binding parameters for the C-H system to linearized augmented plan