We report a rapid and scalable method for the separation of metallic and semiconducting single-wall carbon nanotubes (SWCNTs); the separation is performed by the selective adsorption of semiconducting SWCNTs on agarose gel. The most effective separation was realized by a simple procedure in which a piece of gel containing SWCNTs and sodium dodecyl sulfate was frozen, thawed, and squeezed. This process affords a solution containing 70% pure metallic SWCNTs and leaves a gel containing 95% pure semiconducting SWCNTs. Field-effect transistors constructed from the separated semiconducting SWCNTs have been demonstrated to function without any electrical breakdown.

Optical rotation and heat capacity measurements were made on aqueous solutions of schizophyllan, a triple-helical polysaccharide. T h e heat capacity data showed that aqueous schizophyllan, either isotropic or cholesteric, exhibited a sharp thermal transition located around 279 K, and the transition enthalpy per mole of the polysaccharide repeating unit (648.6 g) was (2.83 h 0.1) k J mol-' in H20 and 3.96 k J mol-' in D20.

Thin-film transistors (TFTs) using a random network of semiconductor-enriched single-wall carbon nanotubes (SWCNTs) were fabricated on a SiO 2 /Si substrate. Semiconductor-enriched SWCNTs were extracted from a pristine sample by centrifugation using agarose gel. Prior to depositing the SWCNTs, the substrate surface was modified by self-assembly of a monolayer of aminosilanes to produce an ideal two-dimensional network structure. As a result, all the TFTs fabricated on the substrate had on/off current ratios higher than 10 4 without electrical breakdown, while TFTs fabricated using pristine SWCNTs had a broad distribution of on/off ratios from 10 1 to 10 4 . This improvement in transfer characteristics demonstrates a major advantage of using semiconductor-enriched SWCNTs.

Fullerene has been expected to realize next generation nanoelectronics as a key element. However, although single-fullerene switch operation using scanning tunneling microscope (STM) has been developed, the structural architecture with electrodes is still needed to make progress as devices. Because the fullerenes are smaller than 1.0 nm, which is suitable for the STM approach, the subnanometer size is still too small, even with the latest device electrode fabrication techniques. Here we present the principle experiment on a self-assembling fullerene nanowire to drive single-fullerene switch. A fullerene C60-nanowire (C60NW), which was synthesized at a liquid–liquid interface, exhibited negative differential resistance (NDR) and two-state resistance switching generated by local polymerization and depolymerization among the C60 molecules. A C60NW was electrically characterized after a preset treatment to induce C60NW conductivity by electron-beam (EB) irradiation to form an initial conduction path. A current though the C60NW increased more than 100-fold after the preset treatment, whereas an as-grown C60NW exhibited a nanoampere-level current under a 20 V bias voltage. The current–voltage characteristics showed a nonlinear current increase and NDR, leading to reproducible two-state resistance switching under bias-voltage modulation. The nonlinear current increase, the NDR, and the resistance switching are explained by local energy control of the current-induced connection and disconnection of C60 molecules, leading to tunneling current modulation toward a single element of C60 in a nanomaterial switching function.

The time-dependent charging process of an insulating specimen under electron beam irradiation is calculated by taking into account the charge continuity equation, the Poisson equation, Ohm's law and the electron-beam-induced conductivity. The energy and the charge deposition distributions are calculated by the Monte Carlo simulation of electron trajectories taking into account the electric field distribution in the specimen. The time-dependent charge and potential distributions are obtained in the present calculation. As the electron beam energy is 10 keV and the specimen is a 1-mm-thick poly-methyl-methacrylate (PMMA) wafer, the surface potential increases to a positive value at first, and then becomes a negative one. This charging process agrees with experimental findings.

The size dependence of the resistance switching effect in nanogap junctions was investigated to determine the nature of the local structural changes responsible for the effect. The maximum current, during resistance switching, decreased with the total emission area across the nanogap to an average of 146 μA at a linewidth of 45 nm. This implies that the resistance switching effect stems from changes in the gap width at multiple local sites on the metal surface.

We have investigated the resistance switching effect of a silicon nanogap structure when pulse bias voltages are applied. Silicon nanogap junctions were prepared by applying large-bias voltages across a Si wire and their electrical properties were measured in a vacuum chamber. The measured current–voltage characteristics exhibited a clear negative differential resistance effect and repeated on-off cycles with a large on-off ratio of over 103. The results suggest that resistance switching effects can be generated in a nanogap junction that is composed of a covalently bonded material such as silicon.

We have investigated field emission (FE) properties of an individual multiwalled carbon nanotube (CNT) under low-vacuum regions around 10−3 Pa. Current versus voltage characteristics of the present CNT emitters were found to be explicable on the basis of the Fowler-Nordheim (F-N) formalism. Time trace of the FE current exhibited more than 30% fluctuation about the mean value, and the lifetime was less than 5 h. Scanning electron microscopy (SEM) observation elucidated that the lengths of the CNTs were reduced after prolonged field emission, plausibly because of local heating induced by the large current density at the apex. To prolong the lifetime, we attempted a type of feedback system by inserting a high ohmic resistance between the electron emitter and the power supply. As a result, the current fluctuation decreased from ∼30% to 2% at 0.1 µA, and the lifetime increased from 5 to 50 h. Finally, an SEM was equipped with both the emitter systems, with and without resistance, which were designed for the CNT field emitter. The SEM images taken by using the emitter with resistance showed consistently brighter appearance, whereas those taken without the resistance exhibited fluctuations in the image brightness.