Takeshi Izumida

Synthesis and electronic properties of ferrocene-filled double-walled carbon nanotubes

Double-walled carbon nanotubes (DWNTs) are filled with ferrocene molecules by a vapour diffusion method for the first time. The as-synthesized ferrocene-filled DWNTs are characterized by transmission electron microscopy (TEM), energy-dispersive x-ray spectrometry (EDX) and Raman spectroscopy. Electronic properties of double-walled carbon nanotubes (DWNTs) filled with ferrocene molecules are studied by fabricating them as the channels of field-effect transistor (FET) devices. Our results reveal that electronic properties of ferrocene-filled DWNTs are greatly modified due to the charge transfer between ferrocene molecules and DWNTs. In addition, after ferrocene molecules are decomposed inside DWNTs, electronic properties of DWNTs exhibit a further change due to Fe encapsulation, and unipolar n-type semiconducting DWNTs are consequently obtained.

Electronic transport properties of Cs-encapsulated double-walled carbon nanotubes

Electronic transport properties of Cs-encapsulated double-walled carbon nanotubes (DWNTs) synthesized via a plasma irradiation method are investigated by fabricating them as field-effect transistor devices. The authors’ results indicate that Cs-encapsulated DWNTs exhibit a high performance n-type characteristic in contrast to ambipolar behavior of pristine DWNTs. Coulomb blockade oscillations are observed on the Cs-encapsulated DWNTs at low temperatures. In addition, it is found that the semiconducting characteristics of the as-synthesized Cs-encapsulated DWNTs can possibly be controllable by adjusting applied negative dc bias voltages during the plasma synthesis process.

Electrical properties of ferromagnetic semiconducting single-walled carbon nanotubes

Electrical properties of single-walled carbon nanotubes (SWCNTs) filled with Fe are studied by fabricating them as the channels of field-effect transistor devices. The synthesis of Fe-filled SWCNTs is realized by using ferrocene as the starting material. Our results reveal that ferrocene-filled SWCNTs show the interesting ambipolar behavior. In contrast, Fe-filled SWCNTs can exhibit high performance unipolar n-type semiconducting characteristics, suggesting the possibility of creating ferromagnetic semiconducting SWCNTs. Moreover, Coulomb blockade oscillations are significantly observed on Fe-filled SWCNTs, which indicates that they exhibit excellent single-electron transistor characteristics at low temperatures.

Electronic transport properties of Cs-encapsulated single-walled carbon nanotubes created by plasma ion irradiation

The electronic transport properties of Cs-encapsulated single-walled carbon nanotubes (Cs@SWNTs), which are created by a plasma ion irradiation method, are experimentally investigated at both room and low temperatures by fabricating field-effect transistor devices with these modified SWNTs. It is found that Cs@SWNTs exhibit air stable n-type transport characteristics at room temperature, where Cs atoms function as an electron donor. Moreover, Coulomb oscillations are observed under a low temperature, which is derived from the electronic structure modulated mainly by the encapsulated Cs atoms.

Measurements of electronic transport properties of single-walled carbon nanotubes encapsulating alkali-metals and C60 fullerenes via plasma ion irradiation

We report on the measurements of the electronic transport properties of Cs-encapsulated single-walled carbon nanotubes (SWNTs), Li-encapsulated SWNTs, and C60-encapsulated SWNTs synthesized by plasma ion irradiation method. After fabricating field-effect transistor (FET) configurations using pristine and plasma-ion-irradiated SWNTs, the electronic transport properties of these devices are investigated in vacuum at room temperature. As a result, C60-encapsulated SWNTs give rise to a p-type semiconducting property as pristine SWNTs do. On the other hand, it is clearly observed that Cs-encapsulated SWNTs exhibit n-type transport behavior. Moreover, Li-encapsulated SWNTs show an ambipolar transport property with both n-type and p-type characteristics. Thus, the electronic properties of SWNTs are found to be successfully controlled by plasma ion irradiation.

Modification of Double-Walled Carbon Nanotubes by Cs Plasma Ion Irradiation

The synthesis of Cs-encapsulated double-walled carbon nanotubes (DWNTs) is realized for the first time by plasma irradiation. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectrometry confirm that Cs clusters can be doped inside DWNTs. The structural deformation of Cs-encapsulated DWNTs synthesized under different applied negative DC bias voltages from -25 to -150 V during plasma irradiation is examined by Raman spectroscopy, and the obtained results indicate that DWNTs have structural merits compared with single-walled carbon nanotubes (SWNTs). In addition, the electronic transport properties of pristine and Cs-encapsulated DWNTs are investigated by their fabrication as the channels of field-effect transistor (FET) devices. We find that, in contrast to pristine ambipolar DWNTs, unipolar n-type semiconducting DWNTs can be created by Cs plasma irradiation.

Electronic transport modification of single-walled carbon nanotubes by encapsulating alkali-metal ions

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.

Electric transport properties of single-walled carbon nanotubes functionalized by plasma ion irradiation method

We report experimental results of the electric transport properties of single-walled carbon nanotubes (SWNTs) functionalized by plasma ion irradiation method, where purified SWNTs and Cs-encapsulating SWNTs are used. SWNTs bundles are well dropped between source and drain electrodes of the field effect transistor (FET) configuration. Voltage-current characteristics, gate bias dependence, and measuring temperature dependence are investigated. It is found that purified SWNTs exhibit p-type semiconducting behavior. Transport measurements for Cs encapsulating individual SWNTs have also been performed, the result of which is discussed.