Graphene films grown on Cu foils have been fluorinated with xenon difluoride (XeF(2)) gas on one or both sides. When exposed on one side the F coverage saturates at 25% (C(4)F), which is optically transparent, over 6 orders of magnitude more resistive than graphene, and readily patterned. Density functional calculations for varying coverages indicate that a C(4)F configuration is lowest in energy and that the calculated band gap increases with increasing coverage, becoming 2.93 eV for one C(4)F configuration. During defluorination, we find hydrazine treatment effectively removes fluorine while retaining graphene's carbon skeleton. The same films may be fluorinated on both sides by transferring graphene to a silicon-on-insulator substrate enabling XeF(2) gas to etch the Si underlayer and fluorinate the backside of the graphene film to form perfluorographane (CF) for which calculated the band gap is 3.07 eV. Our results indicate single-side fluorination provides the necessary electronic and optical changes to be practical for graphene device applications.

Macroscopic and nanoscopic current−voltage measurements reveal asymmetries in the DC electrical conductivity through Langmuir−Blodgett multilayers and even monolayers of γ-(n-hexadecyl)quinolinum tricyanoquinodimethanide, C16H33Q-3CNQ (5). These asymmetries are due to a transition of the ground-state zwitterion to an excited-state conformer which is probably neutral. Unimolecular electrical rectification by monolayers of 5 is unequivocally confirmed.

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( =185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit ( f x Q>10(11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite.

Asymmetries were observed across a monolayer of dimethylanilinoaza[C 60 ]fullerene, (DMA-NC 60 , 1) sandwiched between gold electrodes of relatively large size (0.265 mm 2 ). Two modes of behavior are observed: (1) a sigmoidal and slightly asymmetric behavior, bespeaking of a moderate unimolecular rectifier (rectification ratio of about 2), and (2) above a threshold voltage V 1 (≈0.6 to 1.0 V), a dramatic increase of current to 0.3 to 1 A (as high as 1.36 × 10 7 electrons molecule -1 s -1 at 1.5 V), followed by ohmic behavior from V 1 to a relatively smaller negative bias V 2 (≈ -0.5 V to -0.6 V). At more negative potentials (e.g., at -1.5 V) the current is very small (a few µA). This high asymmetry in current persists for between 10 and 20 cycles of voltage scan. This increased, but ohmic conductivity is probably due to defects that grow at domain boundaries, since this behavior is not seen when very small electrodes (1 µm 2 area) are used. The defects could be stalagmitic filaments of gold which grow from the bottom electrode above V 1 but are broken at the negative bias V 2 , or else they could be due to some unknown electrochemical couple. This device is vaguely reminiscent of Zener diodes or varistors: if operated between, say, + 2 V and -2 V, it is a super-rectifier, with a rectification ratio of up to 20 000 at 1.5 V.

The design of predictable multichromophoric supramolecular arrays of freebase and metallo porphyrins constitutes an essential first step toward the synthesis of light-harvesting complexes. We now report crystal engineering strategies to achieve the synthesis of controllable and predictable porphyrinic multichromophores in the solid state. The coordination complexes of metal halides, MX2 (M = Cd, Hg, Pb; X = Br, I), with freebase tetrapyridylporphyrin (TPyP) form either 1D, [(HgX2)2TPyP]·2TCE, 1, or 2D, [(MX2)TPyP]·4TCE, (M = Pb, 2; Cd, 3) polymeric networks. The porphyrin cavities in these crystalline networks can be selectively populated with various metal cations to generate ordered multiporphyrinic supramolecular arrays without distorting the coordination networks, either by (a) crystallizing the metal halides and TPyP in the presence of suitable metal salts or by (b) reacting metal halides with a mixture of freebase and metallo porphyrins in specific stoichiometric ratios. A design limit has been reached following approach b, synthesis of the complexes using 100% metalated TPyP results in a change in structure due to intermolecular MTPyP coordination. The UV/vis and fluorescence spectra recorded on partially metalated complexes indicate the presence of the expected absorption and emission bands. Additionally, complex 1 reveals an unusual clathration behavior, wherein the stacking features perpendicular to the porphyrin plane adjust to allow inclusion of variable amounts of identical guest solvent molecules without modification of the layered structure.

We have developed a simple, efficient process for solubilization of single-wall carbon nanotubes (SWNTs) with amylose in aqueous DMSO. This process requires two important conditions, presonication of SWNTs and subsequent amylose treatment in an optimum mixture of DMSO/H2O. The former step separates SWNT bundles, and the latter step provides a maximum cooperative interaction of SWNTs with amylose, leading to the immediate and complete solubilization. The best solvent condition for this is around 10-20% DMSO, in which amylose assumes a random conformation or an interrupted helix. This indicates that the amylose helix is not the prerequisite for encapsulation of SWNTs. The SEM and AFM images of the encapsulated SWNTs manifest loosely twisted ribbons wrapping around SWNTs, which are locally intertwined as a multiple twist, but no clumps of the host amylose are seen on SWNT capsules.

We report the first observation of the n-type nature of hydrogenated graphene on SiO(2) and demonstrate the conversion of the majority carrier type from electrons to holes using surface doping. Density functional calculations indicate that the carrier type reversal is directly related to the magnitude of the hydrogenated graphene's work function relative to the substrate, which decreases when adsorbates such as water are present. Additionally, we show by temperature-dependent electronic transport measurements that hydrogenating graphene induces a band gap and that in the moderate temperature regime [220-375 K], the band gap has a maximum value at the charge neutrality point, is tunable with an electric field effect, and is higher for higher hydrogen coverage. The ability to control the majority charge carrier in hydrogenated graphene, in addition to opening a band gap, suggests potential for chemically modified graphene p-n junctions.

No abstract