Owing to its remarkable electronic and transport properties, graphene has great potential of replacing silicon for next-generation electronics and optoelectronics; but its zero bandgap associated with Dirac fermions prevents such applications. Among numerous attempts to create semiconducting graphene, periodic patterning using defects, passivation, doping, nanoscale perforation, etc., is particularly promising and has been realized experimentally. However, despite extensive theoretical investigations, the precise role of periodic modulations on electronic structures of graphene remains elusive. Here we employ both the tight-binding modeling and first-principles electronic structure calculations to show that the appearance of bandgap in patterned graphene has a geometric symmetry origin. Thus the analytic rule of gap-opening by patterning graphene is derived, which indicates that if a modified graphene is a semiconductor, its two corresponding carbon nanotubes, whose chiral vectors equal graphene's supercell lattice vectors, are both semimetals.

We report on the band gap opening and electronic structures of graphene nanomeshes (GNMs), the defected graphene containing a high-density array of nanoscale holes, from first-principle calculations. As expected, quantum confinement at the GNM necks leads to a sizable band gap; however, surprisingly, the appearance of gap depends sensitively on the hole arrangement and periodicity. For the simplest hexagonal zigzag-edged holes passivated by hydrogen, two thirds of GNMs remain semi-metallic while the rest are semiconductors. Furthermore, we show that the energy gap opening in GNM results from the combination of quantum confinement and the periodic perturbation potential due to perforation.

This paper describes the second generation Optimized Reconfigurable Cell Array (ORCA) FieldProgrammable Gate Arrays (FPGAs). Architectural innovations combined with advanced OSpm process technology result in a family of high capacity and high speed FPGAs. New types of routing resources are included on the FPGA to ensure routing completion. The first ORCA part in the 2C series, the ATT2C15, contains approximately 2.5 million FETs and has a typical logic capability of about 15, OOO usable gates. Preliminary benchmark results confirm the speed and logic capacity of the new parts.

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