Atsuhiko Kojima

Protein Sensor Using Carbon Nanotube Field Effect Transistor

The effect of the selective adsorption of pig serum albumin as an antigen on the electrical properties of a carbon nanotube channel field effect transistor on which anti-pig serum albumin was immobilized as an antibody by physisorption in phosphate buffer solution has been investigated. We have succeeded in real-time detection of the adsorption of pig serum albumin on anti-pig serum albumin as a decrease in the conductance of the carbon nanotube channel field effect transistor, by a label-free process.

Air Stable n-type Top Gate Carbon Nanotube Filed Effect Transistors with Silicon Nitride Insulator Deposited by Thermal Chemical Vapor Deposition

The air stable n-type carbon nanotube channel filed effect transistor (CNT-FET) with the top gate structure was successfully fabricated using the silicon nitride gate insulator deposited by the thermal chemical vapor deposition. The effects of the silicon nitride insulator on the electrical properties of the CNT-FET have been investigated. The p-type characteristics of the CNT-FET can be converted to the n-type characteristics in high yield of 90% only by depositing the silicon nitride insulator. The drain current is as high as few µA order. The n-type top gate CNT-FET stably operated even in ambient air.

Non Contact Atomic Force Microscope Electrical Manipulation of Carbon Nanotubes and Its Application to Fabrication of a Room Temperature Operating Single Electron Transistor

We demonstrate that a non-contact atomic force microscope (AFM) can be used to cut and nick carbon nanotubes (CNTs) by applying negative bias to the metal-coated AFM tip when it is very close to the CNT. The voltage needed to cut the CNT completely varied from -8 to -15 V, while the nicking voltage ranged from -6 to -8 V. This technique was applied to make a nanoscale single CNT device. Unwanted CNTs were cut first to leave only one CNT connecting the electrodes. Finally, tunneling barriers defined by two small nicks were created on the CNT to fabricate a single electron transistor. The final device shows Coulomb oscillation and Coulomb diamond characteristics at room temperature.

Growth Control of Carbon Nanotube using Various Applied Electric Fields for Electronic Device Applications

The control of the growth direction of a carbon nanotube was accomplished by applying an electric field during the growth of the carbon nanotube. The effects of two types of applied bias, one is a constant DC bias, and the other is a ramp bias, on the control of the growth direction were examined. By maintaining a constant DC bias we could control the growth direction of the carbon nanotube, however, the bridging ratio between the two electrodes was as small as 35%. We suppose that this low bridging ratio may be caused by the etching effect of hydrogen. When a ramp bias was applied, bridging ratio tended to increase with the slope of ramp bias. Under optimal conditions, the bridging ratio reached a value as high as 95%.

First Selective Detection of Proteins Using Top-Gate Carbon Nanotube Field Effect Transistor

Olympus Corporation, 2-3-1 Nishishinjuku, Shinjukiu, Tokyo 163-0914, Japan Phone: +81-29-861-5080-30059 E-mail: masu-abe@aist.go.jp NEDO, 1310 Omiyacho, Saiwai, Kawasaki, Kanagawa 212-8554, Japan CREST-JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan Mitsubishi Kagaku, 1000 Higashimamianacho, Ushiku, Ibaraki 300-1295, Japan Mitsubishi Kagaku Iatron, 1144 Ohwadashinden, Yachiyo, Chiba 276-0046, Japan AIST, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan Osaka Univ., 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan

Ballistic Transport of Hole in p type Semiconductive Carbon nanotube

We have succeeded in observing the coexistence of the Coulomb charging effect and the coherent transport of the holes in the carbon nanotube of the length of 4.5μm at 8.6K. The sample was prepared as follows. A p-type silicon wafer with a thermally grown oxide of 200nm is used as a substrate. The layered catalysts of Fe/Mo/Si (3/10/10nm) are patterned on the substrate using the conventional photo-lithography process. The distance between two catalysts for the source and drain was 4.5μm and 1.4μm. Single-walled carbon nanotube is grown between two catalysts by chemical vapor deposition using mixed gas with ethanol, hydrogen and argon. Finally, Pt/Au electrodes are deposited on the patterned catalysts for the source and drain and the back side of Si substrate for the gate. Thus, back gate type carbon nanotube field effect transistor was fabricated as shown in Fig. 1. In the drain current-gate voltage characteristics at 8.6K, the drain current of both sample monotonously decreases with increasing the gate voltage from -10V to 10V (not shown), which indicates that the measured carbon nanotube has the p type semiconductive property. In the smaller range of the gate voltage from 0V to 1V, the periodic drain current peaks are observed on the 4.5μm CNT sample suggesting the Coulomb oscillation peaks as shown in Fig. 2. The period of the Coulomb oscillation peaks is 150mV, from which the gate capacitance is estimated to be 1.1aF. The origin of the Coulomb charging effect is considered to be the carrier confinement in a single island because of the high periodicity of the Coulomb oscillation peaks. As carbon nanotube has the p type semiconductive property, the Coulomb charging effect occurs by the confinement of holes in the carbon nanotube. On the 1.4μm CNT sample, the similar results with the 4.5μm CNT sample are obtained (not shown). The period of the Coulomb oscillation peaks and the gate capacitance is 1V and 0.16aF, respectively. In the Coulomb diamond characteristics at 8.6K on the 4.5μm CNT sample as shown in Fig. 3, a Coulomb gap of ~7mV is observed around zero bias voltage. The total device capacitance and the Coulomb charging energy are estimated to be 25.8aF and 3.1meV, respectively. From the Coulomb charging energy, the length of the island Lisland is estimated to be 5.0μm, which is in good agreement with the entire length of the carbon nanotube at the channel. Hence the Coulomb charging effects occurred by the hole confinement in the whole channel of the carbon nanotube. The periodic negative differential conductance (NDC) is observed at the outside of the Coulomb gap for higher drain voltages on both 4.5μm and 1.4μm CNT sample as shown in Fig. 4 and Fig. 5. The period of NDC: D V ∆ is ~0.4meV for the 4.5μm CNT sample and ~1.2meV for the 1.4μm CNT sample, respectively. The NDC is attributed to the resonant tunneling of hole through the quantum confinement discrete energy levels of carbon nanotube as shown in Fig. 6. From the period of NDC of ~0.4mV for the 4.5μm CNT sample, the quantum confinement discrete energy levels for hole were found to form through such a long distance of 4.5μm in p type semiconductive carbon nanotube. This fact suggests the existence of the ballistic transport of the holes in the semiconductive carbon nanotube, and its phase coherent length extends over a distance of at least 4.5μm. We first succeeded in observing the coexistence of the Coulomb charging effect and the ballistic transport of the holes in semiconductive carbon nanotube. We also CNT length dependence of the separation of the quantum confinement discrete energies