Toshiki Sugai

Bulk production of quasi-aligned carbon nanotube bundles by the / catalytic chemical vapour deposition CCVD method

Abstract The large-scale production of quasi-aligned carbon nanotube bundles is reported. The method includes catalytic decomposition of acetylene over well-dispersed metal particles embedded in commercially available zeolite at a lower temperature (700°C). In-depth studies of this nanotube through scanning electron microscopy and transmission electron microscopy reveal their homogeneity as well as perfect graphitization, along with inner (2.5–4 nm) and outer diameters (10–12 nm) of the tubes. Details of the optimum conditions for producing these nanotubes are also described.

Growing carbon nanotubes

The discovery of ‘fullerenes’ added a new dimension to the knowledge of carbon science 1 ; and the subsequent discovery of ‘carbon nanotubes’ (CNTs, the elongated fullerene) added a new dimension to the knowledge of technology 2 ;. Today, ‘nanotechnology’ is a hot topic attracting scientists, industrialists, journalists, governments, and even the general public. Nanotechnology is the creation of functional materials, devices, and systems through control of matter on the nanometer scale and the exploitation of novel phenomena and properties of matter (physical, chemical, biological, electrical, etc.) at that length scale. CNTs are supposed to be a key component of nanotechnology. Almost every week a new potential application of CNTs is identified, stimulating scientists to peep into this tiny tube with ever increasing curiosity.

Production and characterization of boron- and silicon-doped carbon clusters

Abstract Boron- and silicon-doped carbon clusters of the type BmCn (m = 1−4) and SimCn (m = 1, 2) have been produced via the laser-vaporization cluster beam technique. The observed features of the intensity distribution in mass spectra suggest that B atoms can be incorporated into the clusters with much higher efficiency than Si atoms. The mass spectral evidence is also consistent with the idea that SiCn(n ⩾ 30) and BCn(n ⩾ 30) clusters have a silicon- and boron-heterofullerene structure, respectively.

Ambipolar field-effect transistor behavior of Gd@C82 metallofullerene peapods

Transport properties of C60 fullerene peapods and Gd@C82 metallofullerene peapods are investigated by using the field effect in a gated structure. The results show that C60 peapods exhibit unipolar p-type characteristics, whereas Gd@C82 peapods show ambipolar both p- and n-type characteristics. This difference in transport behavior can be explained in terms of a bandgap narrowing of the peapods. One of the important findings is that tunable electronic properties of peapods are achieved by using the different types of encapsulated fullerene molecules.

Double-wall carbon nanotube field-effect transistors: Ambipolar transport characteristics

Double-wall carbon nanotubes (DWNTs) have been used as channels of field-effect transistors (FETs) to obtain information on their transport characteristics. DWNTs-FETs show metallic or semiconducting behavior depending on the tube diameters. All the semiconducting DWNTs have exhibited both p- and n-type characteristics, the so-called ambipolar behavior which is absent in normal SWNTs-FETs. Comparisons between the subthreshold swing (S) factor of DWNTs and that of SWNTs indicate that DWNTs are better FET channels than SWNTs.

Enhanced 1520 nm Photoluminescence from Er3+ Ions in Di-erbium-carbide Metallofullerenes (Er2C2)@C82 (Isomers I, II, and III)

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.

High-Performance Thin-Film Transistors with DNA-Assisted Solution Processing of Isolated Single-Walled Carbon Nanotubes

2010 WILEY-VCH Verlag Gmb Two-dimensional networks of single-walled carbon nanotubes (SWNTs) have attracted much attention because of their excellent transport properties and expected scalable integration into devices such as thin-film transistors (TFTs) and chemical/ biological sensors. To realize these promising applications in such electronics, it is essential to develop sophisticated fabrication processes of the networks. Until now the networks of SWNTs have been fabricated by mainly using two different processes: dry and wet processes. The former includes direct synthesis and deposition of SWNTs on substrates using the chemical vapor deposition (CVD) method,, and the latter includes drop casting, spin coating, inkjet printing, and dip coating by using a solution of dispersed SWNTs. Even though the TFTs fabricated by the CVD process oftentimes show high device performance, the solution processes, in particular, receive increasing interests in recent years because of their low manufacturing cost and of high scalability. However, virtually all of the present solution processes have shown fatal drawbacks of aggregation of individual nanotubes during the network making. The aggregation basically causes i) a wide variation in bundle size and network morphology and ii) a bundling of metallic and semiconducting SWNTs. These obviously will degrade the device performance such as an on/ off current ratio, sensitivity and reproducibility. So far, most of the solution processes have incorporated the dispersion of bundled SWNTs. Since SWNT bundles may contain metallic SWNTs serving as a conductive wire, the network of bundled SWNTs tends to have conducting paths. Even though the enrichment of high-purity semiconducting SWNTs has been achieved, the TFT characteristics can still be degraded by a small number of metallic SWNTs which oftentimes creeps into bundled SWNT networks. To avoid the use of the bundles, several research groups have utilized aqueous solution of surfactant-wrapped individual SWNTs. However, the transistor characteristics of these individual SWNTs have never exceeded those of the bundled SWNTs for non-separated SWNTs. This is presumably because of the fact that such solution normally contains a large amount of free surfactants (usually hundreds times larger than SWNTs in weight) resulting in an inability to achieve effective inter-nanotube contacts. The development of a new and effective solution process of isolated SWNTs is, therefore, highly required to realize high performance TFT devices. One of the most promising candidates for realizing highperformance TFTdevices is to incorporate DNA-wrapped SWNTs as TFTchannels. It has been reported that individual SWNTs can easily be dispersed in water using DNA in the form of DNAwrapped SWNT hybrids (DNA-SWNTs). Importantly, they are completely stable without unbound and free DNA molecules unlike the surfactant-wrapped SWNTs case. Furthermore, the DNA-SWNTs can be sorted by chirality and length of nanotubes, which provides major advantages in the device applications. Here, we show that the DNA-SWNTs can provide an effective way to fabricate the uniform networks of highly isolated and structure-sorted nanotubes for TFTs of high performance. We have prepared a high purity aqueous solution of DNA-SWNTs using sonication, ultracentrifugation, and size-exclusion liquid chromatography (SEC). The SWNTs were wrapped by DNA molecules during the sonication in water. After removing unwrapped SWNTs through ultracentrifugation, the supernatant was collected. This supernatant contains the DNA-SWNTs and excessive amount of free DNA molecules (approximately 100 times the total weight of DNA-SWNTs), which disturb the inter-nanotube contacts. To remove the free DNA, the DNA-SWNTs were purified using SEC incorporating a newly developed HPLC column. Figure 1a shows typical SEC chromatograms of the supernatant, where the detecting UV wavelengths at 260 and 350 nm are used to trace DNA and SWNTs fraction, respectively. The DNA-SWNTs were completely separated from the free DNA because of their difference in size. The broad absorption band of DNA-SWNTs derives from a wide variety of their lengths. In SEC separations, the chromatographic retention time increases as the size of the molecule decreases. The DNA-SWNT hybrids, therefore, can be separated by their length. Figure 1b shows a histogram on the length distribution for a fraction of the retention time corresponding from 20 to 21min (hereafter refer to as fraction 20), which

Production of fullerenes and single-wall carbon nanotubes by high-temperature pulsed arc discharge

Fullerenes and single-wall carbon nanotubes (SWNTs) have been produced for the first time by the high-temperature pulsed arc-discharge technique, which has developed in this laboratory. Fullerenes are identified quantitatively by high-performance liquid chromatography (HPLC), and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal a significant amount of production of bundles of SWNTs in soot. The pulse arc production of fullerenes and SWNTs favors the high-temperature (⩾1000 °C), long pulses (⩾1 ms) and a heavy rare gas such as Ar or Kr as a buffer gas. We have found that fullerenes and SWNTs have complementary relationships in their early stage of production. The details of the pulsed arc discharge have been obtained by observing the transition from the pulsed arc discharge to the steady arc discharge while increasing the pulse width.

Preferential arc-discharge production of higher fullerenes

Abstract A new method for efficiently generating higher fullerenes is reported. By utilizing the arc-discharge of boron-doped graphite (bulk boronized graphite) electrodes, we have found that the yield of higher fullerenes (C 76 C 96 ) in toluene extracts becomes 35–40 wt% with an optimum boron doping, which is more than twice as large as that obtained in the conventional arc-discharge of 100% graphite rods. A typical absolute yield of the higher fullerenes in soot is 5–6 wt%. The results suggest that some boron-carbon binary clusters play an important role in an early stage of the formation of higher fullerenes.

Fullerenes found in the Permo-Triassic mass extinction period

Fullerenes have been identified by high-performance liquid chromatography with UV-visible spectroscopic analysis of toluene extracts of deep sea claystones from Permo-Triassic (P/T) boundary sections in the Inuyama area, central Japan. The analysis reveals the presence of 10–20 parts per trillion of C60 only in the dark-colored rock samples, suggesting the anoxia at the time of the P/T boundary 250 million years ago, when the greatest Phanerozoic mass extinction occurred. The fullerenes were likely synthesized within locally anoxic zone in the extensive wildfires on the supercontinent Pangea and deposited on an anoxic deep-sea floor of the superocean Panthalassa.