Current transport across the pentacene/CVD-grown graphene interface for diode applications.

We investigate the electronic transport properties across the pentacene/graphene interface. Current transport across the pentacene/graphene interface is found to be strikingly different from transport across pentacene/HOPG and pentacene/Cu interfaces. At low voltages, diodes using graphene as a bottom electrode display Poole­Frenkel emission, while diodes with HOPG and Cu electrodes are dominated by thermionic emission. At high voltages conduction is dominated by Poole­Frenkel emission for all three junctions. We propose that current across these interfaces can be accurately modeled by a combination of thermionic and Poole­Frenkel emission. Results presented not only suggest that graphene provides low resistive contacts to pentacene where a flat-laying orientation of pentacene and transparent metal electrodes are desired but also provides further understanding of the physics at the organic semiconductor/graphene interface.

Stable hole doping of graphene for low electrical resistance and high optical transparency.

We report on the p doping of graphene with the polymer TFSA ((CF(3)SO(2))(2)NH). Modification of graphene with TFSA decreases the graphene sheet resistance by 70%. Through such modification, we report sheet resistance values as low as 129 Ω, thus attaining values comparable to those of indium-tin oxide (ITO), while displaying superior environmental stability and preserving electrical properties over extended time scales. Electrical transport measurements reveal that, after doping, the carrier density of holes increases, consistent with the acceptor nature of TFSA, and the mobility decreases due to enhanced short-range scattering. The Drude formula predicts that competition between these two effects yields an overall increase in conductivity. We confirm changes in the carrier density and Fermi level of graphene through changes in the Raman G and 2D peak positions. Doped graphene samples display high transmittance in the visible and near-infrared spectrum, preserving graphene's optical properties without any significant reduction in transparency, and are therefore superior to ITO films in the near infrared. The presented results allow integration of doped graphene sheets into optoelectronics, solar cells, and thermoelectric solar cells as well as engineering of the electrical characteristics of various devices by tuning the Fermi level of graphene.

Molecular systematics and biogeography of the bent-wing bat complex Miniopterus schreibersii (Kuhl, 1817) (Chiroptera: Vespertilionidae).

The complete mitochondrial ND2 gene (1037 bp) was sequenced to examine relationships within the bent-wing bat complex, Miniopterus schreibersii (Family Vespertilionidae). It was found that M. schreibersii is a paraphyletic assemblage comprising several species. Two major lineages were identified, one of which was restricted to the Palearctic-Ethiopian regions and the other to the Oriental-Australasian regions. This pattern of differentiation was mirrored by the genus as a whole. Speciation and differentiation within the genus Miniopterus appears to have a hierarchical geographical pattern. The earliest divergence corresponds to the Ethiopian-Palearctic and the Oriental-Australasian biogeographical zones. This early divergence is then followed by radiations within each of the Ethiopian, Oriental and Australasian regions. The study also revealed that the number of species currently recognized (11 or 13) is a gross underestimate of the number of actual species. The emerging picture is one of a relatively speciose genus with most species having relatively restricted distributions; few, if any, occur in more than one biogeographical region.