Kei Shimotani

High-purity carbon nanotubes synthesis method by an arc discharging in magnetic field

We developed a synthesis method of multiwalled carbon nanotubes (MWNTs), in which an arc discharging was controlled by a magnetic field. Using this method, we can obtain high-purity MWNTs (purity >95%) without purification which disorders walls of MWNTs. The current–voltage measurements show that the carriers would transport ballistically through our defect-free MWNTs with the maximum current density of ∼1011 A/m2. Therefore, our method provides defect-free/high-purity MWNTs as nanosized electric wires for device fabrication.

Electricity Generation from Decomposition of Hydrogen Peroxide

This paper demonstrates a direct H 2 O 2 fuel cell (DHPFC). The cell converts the energy released by H 2 O 2 decomposition with H + and OH - ions into electricity, and produces water and oxygen. In the experiment, we used amicrofluidic cell, in which acid and alkaline electrolytes contact with each other. The measured power density of the cell is comparable to that of a typical air-breathing direct-methanol fuel cell. The DHPFC emits no CO 2 , uses simply handled aqueous fuels, and requires no expensive membrane-electrolyte assemblies. These advantages may allow the DHPFC to be a promising candidate for practical fuel cells.

Single molecule DNA device measured with triple-probe atomic force microscope

We have measured the electric properties of a three-terminal single molecule DNA device with a triple-probe atomic force microscope (T-AFM). The T-AFM permits us to connect a single DNA molecule with carbon nanotube (CNT) electrodes as source, drain, and gate terminals. As the gate bias voltage is increased, the voltage gap region decreased in the current–voltage (I–V) curves. Furthermore, we can observe the clear steps in the I–V curve at crossing the DNA molecule and the CNT-gate electrode with gate biased.

Transport properties of carrier-injected DNA

We have studied electric properties of carrier-injected deoxyribonucleic acid (DNA) molecules. First, a current (ICA) through a single DNA molecule was measured by the two-probe dc method with varying a distance between a cathode and an anode (dCA). The ICA–dCA curve showed that the current rapidly decreased with increasing dCA (ICA≲0.1 nA for dCA≳6 nm) according to a hopping model. Next, we measured electric properties of DNA injected carriers by two methods; a field effect transistor (FET) arrangement and a chemical doping. In the FET arrangement, we set three electrodes on a single DNA molecule as source, drain, and gate electrodes with a source–drain distance (dDS)∼20 nm. When a voltage was applied to the gate, the source–drain current (IDS) could be detected to be 0.5–2 nA. This showed that charge injection with the FET arrangement would yield a carrier transportation through DNA at least dDS∼20 nm. In order to flow a current through DNA over a distance ∼100 μm, we synthesized the DNA-acceptor cross-...

An advanced electric probing system: Measuring DNA derivatives

We have developed an advanced electric probing system, which has two probes, with the spatial resolution of ∼1 nm and the detection limit of <1 pA in order to measure electric properties of nanometer-scale samples. This system consists of a conventional AFM system and a piezoactuator system. In electric measurements of samples, two probes must be connected to the sample with keeping an electric isolation between two probes. For a connection of probes with a nanometer-scale sample, the radiuses of curvature of the probes should be smaller than the sample size. Thus, we used carbon nanotube as one of two probes, so that we could measure current–voltage (I–V) curves of the nanometer-scale samples. We have applied our system to measuring I–V curves of a lambda phage DNA (λ-DNA) bundle. The curves showed that the current through the λ-DNA was less than ∼1 pA. In order to increase conductance of DNA molecule with chemical doping, we synthesized DNA-acceptor cross-linked derivatives (DACD). We measured I–V curve...

Electric measurements of nano-scaled devices

Molecular electronics has been wished to be the real one for many researchers. In this paper, we report the electric properties of nano-scaled transistors using a triple-probe atomic force microscope. First, we describe the electric properties of semiconductive carbon nanotube (CNT) rings and metallic ones. The semiconductive small CNT ring connected with CNT terminals can be used for a nano-scaled transistor with size of less than 20 nm. Next, we also fabricated a single DNA molecule device to measure its electric properties as a filed effect transistor. Last, we show the electric conductivity of a single DNA molecule. These results show that the triple-probe atomic force microscope would be a powerful tool for molecular electronics.

Triple-probe Atomic Force Microscope: Measuring a carbon nanotube/DNA MIS-FET

We have constructed an advanced electric probing system, which is a triple-probe atomic force microscope (T-AFM). The T-AFM consists of “Nanotweezers” and an AFM with a carbon nanotube probe. Using this system, we fabricated a single-walled carbon nanotubes (SWNTs)/deoxyribonucleic acid (DNA) three-terminal device and measured the current-voltage ( I-V ) curves of this device. In this three-terminal device, DNA strands were entangled with the SWNT bundle, and behaved as a gate-insulator-layer. This three-terminal device worked as a metal-insulator-semiconductor field effect transistor (MIS-FET) with depletion switching behavior.

Dual-probe scanning tunneling microscope and a carbon nanotube ring transistor

For measuring molecular device, we developed a dual-probe scanning tunneling microscope (D-STM) composed of two STM systems in which a carbon nanotube (NT) was used for STM tip. Using D-STM, we fabricated a NT ring device. The NT ring device showed a switching behavior with applying gate bias. Furthermore, in STM imaging for various gate biases, we could observe directly hole injection into the NT ring.