Creation of novel structured carbon nanotubes using different-polarity ion plasmas

Abstract

In order to develop novel functional carbon-based nanomaterials, an original approach using plasma technology has been performed. When positive or negative bias voltages are applied to a substrate that is covered with single-walled carbon nanotubes (SWNTs) and immersed in alkali–fullerene plasmas, accelerated negative fullerene or positive alkali-metal ions are irradiated on the SWNTs through plasma sheaths in front of the substrate. Field emission gun transmission electron microscopy (FEG-TEM) images clearly show that drastic structural modifications such as severe bending of SWNT bundles and tube tip termination take place after the ion irradiation. Energy dispersive x-ray spectrometry confirms the existence of the elements Na, K and Cs in the samples after alkali-metal irradiation. In particular, Cs encapsulation inside the SWNTs is directly observed, the configuration of which is demonstrated to comprise three varieties by FEG-TEM and scanning TEM. In the case of irradiation by positive bias application, on the other hand, SWNTs encapsulating fullerene molecules are clearly observed. Furthermore, the fullerene encapsulation yield within the SWNTs linearly increases with an enhancement of the plasma density used. Finally, a sequential bias application with polarity change gives the possibility of formation of a nanojunction structure composed of Cs rows and C60 chains. It is worth emphasizing that our results open a new possibility for novel structured material synthesis using plasma technology.