Development of the Creation Method of New Functional Evolved-Nanotubes by Using Plasma Ion Irradiation

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1. When a substrate covered with dispersed single-walled carbon nanotubes (SWNTs) is immersed in an alkali-fullerene plasma of Cs^+ -C_<60>^-, both of C_<60> and Cs encapsulated SWNTs (C_<60>@SWNT, Cs@SWNT) are formed as a result of accelerated-ion irradiation in an energy-controlled manner through the plasma sheath. Furthermore, the SWNT encapsulating a junction of Cs atoms on one side and C_<60> molecules on the other [(Cs/I)@SWNT] is observe to be formed in the case of applying bias voltages with polarity change.2. For the purpose of creating an ideal nano-pn junction, an alkali-halogen plasma such as Cs^+ -I^- is successfully generated using a magnetron discharge method with alkali salts. The substrate bias method leads to the generation of both the I@SWNT and junction encapsulated SWNT, (Cs/I)@SWNT.3. Electronic transport measurements reveal that C_<60>@SWNTs give rise to a p-type semiconducting property, but that Cs@SWNTs exhibit air stable n-type transport characteristics changing from p-type transport behavior via ambipolar behavior as the Cs-injection quantity inside SWNTs is increased. Moreover, Coulomb oscillations are observed under low temperatures, which is derived from the electronic structure modulated mainly by the encapsulated Cs atoms.4. In the case of I@SWNTs the threshold gate voltage of FET, which shows the p-type conductivity, is found to shift to a more positive value as the I-injection quantity is increased, indicating the strong enhancement of p-type property. Finally, the electronic transport property of (Cs/I)@SWNT is observed to behave as a diode, suggesting the formation of nano-pn junction. Thus, our evolved carbon nanotubes created by plasma ion irradiation are considered in principle to be provided with hidden potential as an ultra-super nonlinear-electronic microdevice.