New UWB antenna design for wireless communications

The presented work in this article concerns a new ultra-wideband antenna design with an octagonal configuration and reduced dimensions. Different prototypes have been simulated and implemented in the form of monopoles. These prototypes have shown an admissible agreement between simulations and measurements and ultra-wide bands running from 3.1 to 14 GHz for wireless applications. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:692–697, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.2666

Cobalt intercalation at the graphene/iridium(111) interface: influence of rotational domains, wrinkles and atomic steps

3 figuresInternational audienceUsing low-energy electron microscopy, we study Co intercalation under graphene grown on Ir(111). Depending on the rotational domain of graphene on which it is deposited, Co is found intercalated at different locations. While intercalated Co is observed preferentially at the substrate step edges below certain rotational domains, it is mostly found close to wrinkles below other domains. These results indicate that curved regions (near substrate atomic steps and wrinkles) of the graphene sheet facilitate Co intercalation and suggest that the strength of the graphene/Ir interaction determines which pathway is energetically more favorable

Ultra-narrow metallic armchair graphene nanoribbons

Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N=3m+2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N=5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ~100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.Peer reviewe