We report on DNA translocations through nanopores created in graphene membranes. Devices consist of 1-5 nm thick graphene membranes with electron-beam sculpted nanopores from 5 to 10 nm in diameter. Due to the thin nature of the graphene membranes, we observe larger blocked currents than for traditional solid-state nanopores. However, ionic current noise levels are several orders of magnitude larger than those for silicon nitride nanopores. These fluctuations are reduced with the atomic-layer deposition of 5 nm of titanium dioxide over the device. Unlike traditional solid-state nanopore materials that are insulating, graphene is an excellent electrical conductor. Use of graphene as a membrane material opens the door to a new class of nanopore devices in which electronic sensing and control are performed directly at the pore.

Single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy. Samples loaded with 1 wt% unpurified SWNT material show a 70% increase in thermal conductivity at 40K, rising to 125% at room temperature; the enhancement due to 1 wt% loading of vapor grown carbon fibers is three times smaller. Electrical conductivity data show a percolation threshold between 0.1 and 0.2 wt% SWNT loading. The Vickers hardness rises monotonically with SWNT loading up to a factor of 3.5 at 2 wt%. These results suggest that the thermal and mechanical properties of SWNT-epoxy composites are improved, without the need to chemically functionalize the nanotubes. a) present address:

Graphene is a two-dimensional material with extremely favorable chemical sensor properties. Conventional nanolithography typically leaves a resist residue on the graphene surface, whose impact on the sensor characteristics has not yet been determined. Here we show that the contamination layer chemically dopes the graphene, enhances carrier scattering, and acts as an absorbent layer that concentrates analyte molecules at the graphene surface, thereby enhancing the sensor response. We demonstrate a cleaning process that verifiably removes the contamination on the device structure and allows the intrinsic chemical responses of the graphene monolayer to be measured. These intrinsic responses are surprisingly small, even upon exposure to strong analytes such as ammonia vapor.

We report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction. The data suggest a gapping of the two-dimensional electronic system by removal of π-electrons. We discuss possible gapping mechanisms, and propose that a Kekule pattern of bond distortions may account for the observed behavior.

DNA-carbon nanotube hybrids (DNA-CN) are novel nanoscale materials that consist of single-wall carbon nanotubes (SWCN) coated with a self-assembled monolayer of single-stranded DNA (ssDNA). Recent experiments on DNA-CN have shown that this material offers a remarkable set of technologically useful properties such as facilitation of SWCN sorting, chemical sensing, and detection of DNA hybridization. Despite the importance of DNA-CN, a detailed understanding of its microscopic structure and physical properties is lacking. To address this, we have performed classical all-atom molecular dynamics (MD) simulations exploring the self-assembly mechanisms, structure, and energetic properties of this nanomaterial. MD reveals that SWCN induces ssDNA to undergo a spontaneous conformational change that enables the hybrid to self-assemble via the pi-pi stacking interaction between ssDNA bases and SWCN sidewall. ssDNA is observed to spontaneously wrap about SWCN into compact right- or left-handed helices within a few nanoseconds. Helical wrapping is driven by electrostatic and torsional interactions within the sugar-phosphate backbone that result in ssDNA wrapping from the 3' end to the 5' end.

We demonstrate a method by which few-layer graphene samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. The technique results in long (>1 µm) crystallographic edges etched through to the insulating substrate, making the process potentially useful for atomically precise graphene device fabrication. This advance could enable atomically precise construction of integrated circuits from single graphene sheets with a wide range of technological applications.Due to its remarkable electronic properties, few layer graphene is emerging as a promising new material for use in a vast array of postsilicon nanoelectronic devices incorporating quantum size effects.1,2 Of particular interest would be the construction of atomically precise graphene nanoribbons, in which charge carriers are confined in the lateral dimension whereby the electronic properties are controlled by the width and specific crystallographic orientation of the ribbon.3−14 Such structures hold enormous promise as nanoscale devices similar to those recently developed using carbon nanotubes 2,11,15 with the added advantage that graphenes two-dimensionality lends itself to existing device architectures based on planar geometries.However, these structures have so far been impossible to achieve because of the rough noncrystalline edges of the graphene that result from current state-of-the-art nanolithography techniques.2,16,17 These rough edges are thought to be the crucial limiting factor to attaining useful performance and on/off current ratios from nanoscale graphene devices. 13,18,19 As a step toward band gap engineering of this material, we have developed a means by which fewlayer graphene (FLG) samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. 20 The technique results in long (>1 µm) trenches commensurate with the crystal lattice that are etched through to the supporting insulating substrate, making the process potentially useful for atomically precise graphene device fabrication, as well as indicating a possible method by which entire circuits could be carved out from single graphene sheets. Our initial samples (before etching) consisted of pristine few-layer graphene sheets transferred onto highly doped Si substrates with 300 nm thermally grown SiO 2 by mechanical exfoliation under ambient conditions, similar to the technique described in ref 21. Flakes of few-layer graphene are identified using optical microscopy. Height imaging of our samples is done using a Veeco Dimension 3100 atomic force microscope (AFM) operating in intermittent contact mode, with Si 3 N 4 -coated tips (NSC15, Mikromasch) of curvature * E-mail: drstrach@sas.upenn.edu † E-mail: cjohnson@physics.upenn.edu 1 radius ≤ 20 nm. Samples are also characterized using a JEOL JSM6400 scanning electron microscope (with a LaB 6 filament).The FLG on SiO 2 /Si substrates are uniformly spin-coated with ∼15 mL solution of 50 mg/L Fe(NO 3 ) 3 ·9H 2 O in isopropyl alcohol (HPLC grade). The samples are th...

We demonstrate a new, versatile class of nanoscale chemical sensors based on singlestranded DNA (ss-DNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (swCN-FETs) as the electronic read-out component. SwCN-FETs with a nanoscale coating of ss-DNA respond to gas odors that do not cause a detectable conductivity change in bare devices. Responses of ss-DNA/swCN-FETs differ in sign and magnitude for different gases, and can be tuned by choosing the base sequence of the ss-DNA. Ss-DNA/swCN-FET sensors detect a variety of odors, with rapid response and recovery times on the scale of seconds. The sensor surface is selfregenerating: samples maintain a constant response with no need for sensor refreshing through at least 50 gas exposure cycles. This remarkable set of attributes makes sensors based on ss-DNA decorated nanotubes very promising for "electronic nose" and "electronic tongue" applications ranging from homeland security to disease diagnosis.The one-dimensional carbon cage structure of semiconducting single-walled carbon nanotubes (swCNs) makes their physical properties exquisitely sensitive to variations in the surrounding electrostatic environment, whether the swCNs are suspended in liquid or incorporated into field effect transistor (FET) circuits on a substrate.

Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite.