We have produced alkali-metal encapsulated single-walled carbon nanotubes using a method of alkali-metal plasma ion irradiation. After plasma ion irradiation, alkali-metal encapsulated single-walled carbon nanotubes are sonicated for several hours in N,N-dimethylformamide to make well dispersed solution, then applied on a field-effect transistor substrate. As a result of measurements, pristine semiconducting single-walled carbon nanotubes show p-type conductivity, but Cs-encapsulated single-walled carbon nanotubes show n-type transport properties. This drastic change can be explained by electron transfer from encapsulated Cs atoms toward the surrounding SWNTs. At 11 K, the Coulomb oscillation is observed, implying that an inhomogeneous encapsulation profile of Cs atoms form several quantum dots. Thus, the electronic properties of SWNTs are found to be successfully controlled by plasma ion irradiation.
We report the preparation, properties and biocompatibility of multi-walled carbon nanotube (MWCNT) disk. Sintered Multi-walled carbon nanotube disk was fabricated by spark plasma sintering the MWCNT and phenol resin mixture by using the Spark Plasma System (SPS) under 1273 K and 80 MPa in vacuum. As the concentration of phenol resin in the sintered MWCNT disk increases, the bending strength and Young’s modulus increased. However, the inflammatory response was observed in the tissue exposed to the surface of the sintered MWCNT disk. This was believed due to the residual phenol resin in the disk. The result indicates that the disk has to be annealed at higher temperatures under inert gas atmosphere to perfectly convert phenol resin to graphitic materials.
In this paper, we report the results of an attempt to disperse MWCNTs in water and determine their biocompatibilities. The length of the MWCNTs was reduced by treating the acidic nanotube suspension with ultrasonic irradiation. Then, the cut nanotubes were size-separated into 670, 550 and 220 nm length by filtration using polycarbonate membrane filters. The neutrophils activity (TNF-α) of size-separated MWCNTs was low and confirmed biocompatible.