Molecular Memory with Atomically-Smooth Graphene Contacts

We report the use of bilayer graphene as an atomically-smooth contact for nanoscale devices. A two-terminal Bucky ball (C60) based molecular memory is fabricated with bilayer graphene as a contact on the polycrystalline nickel electrode. Graphene provides an atomically-smooth covering over an otherwise rough metal surface. The use of graphene additionally prohibits the electromigration of nickel atoms into the C60 layer. The devices exhibit a low-resistance state in the first sweep cycle and irreversibly switch to a high resistance state at 0.8-1.2 V bias. The reverse sweep has a hysteresis behavior as well. In the subsequent cycles, the devices retain the high-resistance state, thus making it write-once read-many memory (WORM). The ratio of current in low-resistance to high-resistance state is lying in 20-40 range for various devices with excellent retention characteristics. Control sample without the bilayer graphene shows random hysteresis and switching.Comment: 13 pages and 4 figure

Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons

We report the plasmon dispersion characteristics of intrinsic and extrinsic armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight binding model with third-nearest-neighbor (3nn) coupling. The coupling parameters are obtained by fitting the 3nn dispersions to that of an extended Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g \approx 64 meV. The extrinsic plasmon dispersion relation is found to approach a common dispersion curve as the chemical potential $\mu$ increases, whereas the intrinsic plasmon dispersion relation is found to have both energy and momentum thresholds. We also report an analytical model for the extrinsic plasmon group velocity in the q \rightarrow 0 limit