Shigekazu Ohmori

Diameter‐Dependent Performance of Single‐Walled Carbon Nanotube Thin‐Film Transistors

IO N Single-walled carbon nanotubes (SWCNTs) have attracted much attention as a printable semiconducting or metallic material in various electronic devices. In particular, the network of SWCNTs fabricated by printing techniques has been investigated for the application to SWCNT thin-fi lm transistors (SWCNT-TFTs). [ 1 ] Printed SWCNT-TFTs are promising for fl exible display devices, [ 2 ] chemical sensors, [ 3 ] and so on due to their applicability to large-area devices and facility for preparation on plastic substrates. In SWCNT-TFTs, structural properties of the SWCNTs such as their length and tube diameter can considerably affect the device performance because these should dominate the dispersing characteristic and the way of forming SWCNT networks. However, the relationship between the device performance and structural properties of SWCNTs has not yet been fully explored. Recent research on the separation extracting SWCNTs with the semiconducting-type structure have shown improvement in the device performance of SWCNT-TFTs. [ 4–6 ]

A Novel Method for Characterizing the Diameter of Single-Wall Carbon Nanotubes by Optical Absorption Spectra

The potentiality of optical absorption spectroscopy (OAS) for the estimation of mean diameter of single-wall carbon nanotubes (SWCNTs) from electronic transition energies has been explored. The observed dependence of electronic transition energies of both metallic and semiconducting SWCNTs on their mean diameters clearly showed that transition energies scale inversely with the tube diameter. In the present study, the applicability of this estimation method has been experimentally confirmed for the diameter range of 1–2 nm and is expected to be useful for the characterization of wide range of diameters of SWNCTs.

Fractionation of single wall carbon nanotubes by length using cross flow filtration method.

A novel system for fractionating single wall carbon nanotubes (SWCNTs) by length via a three-step cross-flow filtration has been developed in which three membrane filters of different pore sizes, 1.0, 0.45, and 0.2 microm, were used. SWCNTs dispersed in water with the help of sodium carboxymethylcellulose (CMC) detergents were successfully sorted into four samples, and the atomic force microscopy (AFM) observation of those samples confirmed that their length distribution peaks are within the expected ranges from pore sizes of used filters. However, the result of the similar filtration process using a different detergent, sodium dodecylbenzenesulfonate (SDBS), showed no pronounced correlation between the length distribution of SWCNTs and the pore size. The observed difference in the sorting phenomena caused by the detergent type suggests that the permeation property depends on the complex structure resulting from the dispersed SWCNTs and detergent molecules.

Wall-Number Selectivity in Single/Double-Wall Carbon Nanotube Production by Enhanced Direct Injection Pyrolytic Synthesis

The effect of methane (CH4) gas as a secondary carbon source in addition to liquid feedstock, on the number of walls and the diameter of carbon nanotubes (CNTs) produced by floating-catalyst CVD under different conditions has been investigated in this study. Transmission electron microscopy reveals that the products mainly contain single-wall (SW) and double-wall (DW) CNTs with the relative abundance of DWCNTs being 9.2–50.7%, which increases linearly with increasing CH4 gas flow rate. In contrast, the distributions of the tube diameters of SW- and DWCNTs are almost constant and are much less dependent on the CH4 gas flow rate. These results suggest that the carbon generated from the pyrolysis of CH4 mainly contributes to the formation of additional walls during the CNT growth in the present CVD system.

Low variability with high performance in thin-film transistors of semiconducting carbon nanotubes achieved by shortening tube lengths

Extremely low variability with excellent device performances in a SWCNT-TFT array has been demonstrated in SWCNT-TFTs fabricated by using a semiconducting ink of short SWCNTs with an average length of 340 nm; the field-effect mobility of 3.9 ± 0.45 cm2 V−1 s−1, on/off ratio from 105 to 106, and hysteresis of ≈0.5 V. AFM observations revealed that the nonionic surfactant, Brij 700, adopted for dispersing SWCNTs during their extraction, causes the significant and homogeneous shortening of SWCNTs compared with sodium cholate, which is frequently used for the dispersion of SWCNTs as an ionic surfactant. Thus, it has been concluded that the shortening of SWCNTs in the dispersing process using the Brij 700 surfactant contributes to the observed uniformity of performance among the devices.

Thin-film transistors using DNA-wrapped semiconducting single-wall carbon nanotubes with selected chiralities

Selected semiconducting chiralities, , , and , of DNA-wrapped single-wall carbon nanotubes (DNA-SWCNTs) were used for thin-film transistors (TFTs). Chirality separation was carried out by ion exchange chromatography (IEX) with the ssDNA of the (TAT)4 sequence. An on/off ratio of 3.8 × 106 with a carrier mobility of 11 cm2/(Vs) was successfully achieved in the fabricated SWCNT-TFTs. The comparison between the on/off ratios obtained before (101–102) and after IEX (104–107) indicated that the IEX separation process sufficiently improves the performance of SWCNT-TFTs because of the reducing metallic SWCNT pathways in the TFT channel.