Individual graphene oxide sheets subjected to chemical reduction were electrically characterized as a function of temperature and external electric fields. The fully reduced monolayers exhibited conductivities ranging between 0.05 and 2 S/cm and field effect mobilities of 2-200 cm2/Vs at room temperature. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest that charge transport occurs via variable range hopping between intact graphene islands with sizes on the order of several nanometers. Furthermore, the comparative study of multilayered sheets revealed that the conductivity of the undermost layer is reduced by a factor of more than 2 as a consequence of the interaction with the Si/SiO2 substrate.

Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.

One sentence summary: Doubly suspended bilayer graphene reveals Coulomb driven broken symmetry states at large B as well as at B = 0. AbstractThe non-interacting energy spectrum of graphene and its bilayer counterpart consists of multiple degeneracies owing to the inherent spin, valley and layer symmetries. Interactions among charge carriers are expected to spontaneously break these symmetries, leading to gapped ordered states. In the quantum Hall regime these states are predicted to be ferromagnetic in nature whereby the system becomes spin polarized, layer polarized or both.In bilayer graphene, due to its parabolic dispersion, interaction-induced symmetry breaking is already expected at zero magnetic field. In this work, the underlying order of the various broken-symmetry states is investigated in bilayer graphene that is suspended between top and bottom gate electrodes. By controllably breaking the spin and sublattice symmetries we are able to deduce the order parameter of the various quantum Hall ferromagnetic states. At small carrier densities, we identify for the first time three distinct broken symmetry states, one of which is consistent with either spontaneously broken time-reversal symmetry or spontaneously broken rotational symmetry.

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We study the near-field optical behavior of Fabry-Pérot resonances in thin metal nanowires, also referred to as quasi one-dimensional plasmonic nanoantennas. From eigenmodes well beyond quadrupolar order we extract both, propagation constant and reflection phase of the guided surface plasmon polariton with superb accuracy. The combined symmetry breaking effects of oblique illumination and retardation allow the excitation of dipole forbidden, even order resonances. All measurements are supported by rigorous simulations of the experimental situation.

Five core-cyanated perylene carboxylic diimides end-functionalized with fluorine-containing linear and cyclic substituents have been synthesized and employed in the fabrication of air-stable n-channel organic thin-film field-effect transistors with carrier mobilities up to 0.1 cm2/Vs. The relationships between molecular structure, thin-film morphology, substrate temperature during vacuum deposition, transistor performance, and air stability have been investigated. Our experiments led us to conclude that the role of the fluorine functionalization in the air-stable n-channel operation of the transistors is different than previously thought.

The application of graphene in electronic devices requires large scale epitaxial growth. The presence of the substrate, however, usually reduces the charge carrier mobility considerably. We show that it is possible to decouple the partially sp 3 -hybridized first graphitic layer formed on the Si-terminated face of silicon carbide from the substrate by gold intercalation, leading to a completely sp 2 -hybridized graphene layer with improved electronic properties.Electrons in graphene -sp 2 -bonded carbon atoms arranged in a honeycomb lattice -behave like massless Dirac particles and exhibit an extremely high carrier mobility [1]. So far, the only feasible route towards large scale production of graphene is epitaxial growth on a substrate. The presence of the substrate will, however, influence the electronic properties of the graphene layer. To preserve its unique properties it is desirable to decouple the graphene layer from the substrate. Here we present a new approach for the growth of highly decoupled epitaxial graphene on a silicon carbide substrate. By decoupling the strongly interacting, partially sp 3hybridized first graphitic layer (commonly referred to as zero layer (ZL) [2]) from the SiC(0001) substrate by gold intercalation, we obtain a completely sp 2 -hybridized graphene layer with improved electronic properties as confirmed by angleresolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM) and Raman spectroscopy.There are essentially two ways for large scale epitaxial growth of graphene on a substrate: by cracking organic molecules on catalytic metal surfaces [3][4][5][6][7] or by thermal graphitization of SiC [2,[8][9][10][11]. Unfortunately, the presence of the substrate alters the electronic properties of the graphene layer on the surface and reduces the carrier mobility. Even though it has been shown that the graphene layer can be decoupled from a metallic substrate [6,[12][13][14] the system remains unsuitable for device applications. This problem can be solved by decoupling the graphene layer from a semiconducting SiC substrate [15].On both the silicon and the carbon terminated face of a SiC substrate, graphene is commonly grown by thermal graphitization in ultra high vacuum (UHV). When annealing the substrate at elevated temperatures Si atoms leave the surface whereas the C atoms remain and form carbon layers. On SiC(0001), the so-called C-face, the weak graphene-tosubstrate interaction results in the growth of rotationally disordered multilayer graphene and a precise thickness control becomes difficult [16]. On the other hand, the rotational disorder decouples the graphene layers so that the transport properties resemble those of isolated graphene sheets with room temperature mobilities in excess of 200,000 cm 2 /Vs [17].On SiC(0001), i. e. the Si-face, the comparatively strong graphene-to-substrate interaction results in uniform, long-range ordered layer-by-layer growth. The first carbon layer (=ZL) grown on the Si-face is partially sp 3 -hybridized to the substrate, wh...

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