As-produced SWCNT materials include both metallic and semiconducting SWCNTs, the electronic structures of which are governed by tube structures (tube diameter and wrapping angle). For the application of SWCNTs to electronic and electro-optical devices, techniques to extract specific SWCNTs from the SWCNT material are important. In particular, we have focused on polymer-wrapping technique for selective extraction of specific larger-diameter SWCNTs; large diameter tubes are useful for encapsulation of other molecules into individual SWCNTs. The selective extraction was a tough issue because the large-diameter tubes not only have a variety of tube structures but also promote the bundling of SWCNTs via π-π interaction between the tube walls. However, we have revealed that poly(9,9-di-n-dodecylfluorene) (PFD) can selectively extract a variety of semiconducting SWCNTs from the mixture of metallic and semiconducting SWCNTs. In addition, we have found recently that poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy) show remarkable selectivity for specific semiconducting SWCNTs with diameters larger than 1.2 nm. In particular, PFOPy has the ability to significantly narrow tube-diameter distribution of SWCNTs owing to a characteristic wavelike conformation of PFOPy backbone. Moreover, the PFOPy-extracted SWCNTs exhibit intense emissions in a telecommunication wavelength region. The 1.5µm emissions will be especially useful for optoelectronic and photonic devices used in optical communications.

We have synthesized carbon-based composite materials for functionalized SWCNTs. For the synthesis, we can use a vapor phase process: we can insert other molecules into individual SWCNTs via the vapor phase of the molecules. For example, we have encapsulated perylene into SWCNTs; the fluorescence of encapsulated perylene is dependent on the molecular arrangement in the SWCNT.

For the quality evaluation of CNT solutions, the morphology and volume of dispersed CNT particles are important information. We have investigated the dispersion state in CNT solutions to characterize the dispersed particles of CNTs. We are looking for methods to effectively characterize them of the dispersed CNT particles.

We synthesized Bi-2212 (Bi₂Sr₂CaCu₂O_8+δ) superconducting whiskers with high quality to reveal the effect of the strip shape of the whiskers on the vortex dynamics. In addition, we have investigated the electrical transport properties under magnetic field applied along the crystal c-axis. Consequently, characteristic phenomena with respect to a low-field-induced vortex state have been revealed. For example, a zero-voltage state appears when low fields are applied to the whisker as shown in the figure. The magnitude of the field inducing the zero-voltage state can be controlled by current and the width of the whisker. This electrical transport property depending on magnetic fields will be useful for switching devices under low magnetic fields.