Structural Deformation of Carbon Nanotubes using Energetic Plasma Ion Irradiation

Summary form only given. Doped nanotube is a possible candidate of a nano diode for the nanoelectronic device. In order to dope the N or P type elements into a carbon nanotube (CNT), it is necessary to carry on the deformation of the tube such as opening the end of the tube or cutting the side of the tube. After filling the elements, those opening areas of the tube should be closed through the reconstruction and welding processes. Here is introduced the ion irradiation method to open and close the tubes and to fill the tubes with elements. An inductively coupled plasma (ICP) was used as the process source, operating the pressure 1 mtorr of Ar or N₂ for opening and closing the nanotubes, and adding Cs into the plasma for the doping process. Such low pressure kept the collisionless plasma condition which may help to control the direction of the irradiated ion onto the tube. Plasma density increased linearly with increasing 1 to 2 kW of the input RF power, resulting that the dose rate of the irradiated ions was controlled. Target nanotubes, the multi-walled carbon nanotubes (MWNTs) were laid on a metal substrate in the ICP, which was biased with 0~200 V DC. The irradiated ions were accelerated with the sheath potential, defined as the potential difference of the space potential and the substrate potential. The space potential was controlled with an inserted metal grid which was grounded. The energy of irradiated ions was estimated precisely by measurement of a sheath potential using the emissive probe and the ion energy analyzer (IEA). Plasma density was measured by a Langmuir probe. The morphology of ion irradiated CNT was observed with the field emission scanning electron microscope (FE-SEM). The structural analysis of filled CNTs was carried out with the high resolution transmission electron microscope (HR-TEM). Then the change of crystalline structure due to the ion irradiation was characterized by a Raman spectroscopy. Preliminary results show that the- length of MWNT decreases with increasing the energy of irradiated ions. At low energy of irradiated ions (<40 eV), MWNTs are broken and trimmed, resulting in the tip opening. The opening process is enhanced with increasing dose at the low energy. With increasing the ion energy, however, the side walls of the nanotube are sputtered out and remaining the serious sputtered damages on tubes. The tip closing occurs at high ion dose with low energy, which is caused by the reconstruction process of the dangling bond. The crossed MWNTs can be welded at high ion irradiation energy (>150 eV) and high dose. More results will be presented