Invited Paper PS1+NS-WeM3
Ionic Plasmas Yielding Novel-Structured and -Functional Nanocarbons

Wednesday, October 17, 2007, 8:40 am, Room 606

Nanocarbons of carbon allotropes have attracted a great deal of attention due to their high potential for novel properties and a variety of applications. Since fullerenes and carbon nanotubes among them are furnished with hollow inner nanospaces, it is a fascinating challenge to inject various kinds of atoms and molecules into the nanospaces based on plasma nanotechnology, which could lead to innovative functionalization of the pristine ones. For that purpose original approaches using nanoscopic plasma processing mainly in ionic plasmas have been performed in order to develop fullerene-, SWNT(single-walled carbon nanotube)- and DWNT(double-walled carbon nanotube)-based materials with new functions corresponding to electronic and biological appilications. Firstly, the encapsulation of charge-exploited alkali atoms inside the fullerene is realized (Li@C₆₀ etc.) using alkali-fullerene plasmas as ionic plasmas, which consist of positive alkali ions and negative C₆₀ ions. Then the atomic nitrogen as a spin-exploited atom is also encapsulated inside C₆₀ (N@C₆₀). In relation to the inner nanospace modification of the carbon nanotubes, another ionic plasmas, i.e., alkali-halogen plasma and pair-ion plasma are generated, which consist of positive alkali ions and negative halogen ions, and positive-C₆₀ and negative-C₆₀ ions with an equal mass, respectively. Furthermore, an electrolyte solution plasma including DNA negative ions is prepared. The substrate bias method is utilized mainly in these plasmas, where positive and negative ions with their energies and fluxes controlled are irradiated to an immersed substrate coated with the pristine carbon nanotubes . In addition, a thermal and plasma combined process is also devised for the treatment of both charge- and spin-exploited atoms. Consequently, we have innovatively created alkali-metals encapsulated SWNTs and DWNTs (Cs@SWNTs, Cs@DWNTs), halogen-elements encapsulated SWNTs (I@SWNTs), ferromagnetic-atoms encapsulated SWNTs (Fe@SWNTs), fullerene molecules encapsulated SWNTs and DWNTs (C₆₀@SWNTs, C₆₀@DWNTs, C₇₀@DWNTs, C₈₄@DWNTs), and DNA molecules encapsulated SWNTs (DNA@SWNTs) . Finally, their electronic and magnetic properties are intensively investigated. As a result, we have for the first time succeeded in realizing the continuous transition of air stable electronic transport from p-type to n- type semiconducting property by adjusting an amount of dosed atoms and molecules inside SWNTs and DWNTs (Cs@SWNTs, Cs@DWNTs, I@SWNTs, C₆₀@SWNTs, C₆₀@DWNTs), and in forming nano structures of magnetic semiconductor (Fe@SWNTs), nano pn junctions with rectifying characteristic [(Cs/I)@SWNTs)], and nano structures with distinct negative differential resistance of high peak-to-valley ratio (C₆₀@DWNTs, C₇₀@DWNTs, C₈₄@DWNTs) . In the case of DNA@SWNTs an experimental system utilizing an interfacial region between the gas and liquid phases has been constructed in order to enhance the DNA encapsulation rate. Here an ionic liquid consisting of only positive and negative molecules is introduced into the liquid phase, which can be regarded as an ionic plasma, i.e., fully ionized electrolyte plasma.