Takeshi Ooi

Effects of Oxidation during Synthesis on Structure and Field-Emission Property of Tungsten Oxide Nanowires

We investigated the structure and field-emission property of tungsten oxide nanowires synthesized under different oxidation degrees. We annealed a sputtered tungsten film at 800 °C, controlling the ratio of hydrogen to oxygen (RHO) using Ar/H2 (97/3%) gas in a vacuum furnace. The resulting differences in shape, number density, length, and width of the nanowires were observed by scanning electron microscopy. In the RHO range of 0 to 0.4, beltlike structures were synthesized. In the RHO range of 0.8 to 4, only thin nanowires were synthesized. In this range, length and width did not differ with RHO, but the number density decreased as RHO increased. The sample with a nanowire density of 2 µm-2, annealed with an RHO of 4, showed the highest field-emission property, i.e., a current of 1 mA/cm2 for an electric field of 22 V/µm. We demonstrated their emission by fluorescence imaging and showed that the nanowires are promising candidates for field emitters.

Real-Time Observation of Growth of Tungsten Oxide Nanowires with a Scanning Electron Microscope

We observed the growth process of tungsten oxide nanowires in real-time with a field emission scanning electron microscope (SEM). The observation was performed by a new in-situ observation system designed to perform two functions: heating of tungsten film and local supply of O2 gas. The nanowires grew after the nucleation on the surface. Their length extended with time keeping the direction constant. The growth rate decreased with exponential.

Microfabricated Channels and Fluid Control Systems for Integrated Flow Injection Analysis

An integrated flow injection analysis (FIA) system on a glass chip has been achieved in the channels with various scales. It is intended that the channels of 10 to 200 μm wide are used for analytical chemistry and that those of less than 1 μm wide for physical chemistry. The channel of 200 μm wide and 100 μm deep is fabricated by CO2 laser cutting and thermally bonding. The isotropic wet etching with HF/NH4F is used for the channel with 30 μm wide and 10 μm deep. The etched Pyrex glass and the cover Pyrex glass are thermally bonded together. Further, the anisotropic dry etching such as reactive ion etching is performed for the channel with 1 μm wide and 1 μm deep. The etched Pyrex glass is anodically bonded to the Si wafer covered with silicon oxide film (800nm thick), which is consequently used as a cover glass. A new anisotropic etching technique using fast atom beam is carried out and the channel of 50 nm wide and 360 nm deep can be obtained. In all of the FIA systems, the chelating reaction of Fe(II) and o-phenanthroline has been realized.

Cell Culture in a Closed Nano-Space

The minimum size of a closed nano-space in which cells can survive was determined using 4-nl nanowells. One or two cells could divide in the nanowell. Our results suggest that the cell division activity in the nano-space is determined by the conflict between intercellular effects and consumption of substrates.

Local Synthesis of Single-walled Carbon Nanotubes on Zeolite-covered Silicon Substrate by Laser-heating Chemical Vapor Depositon

Single-walled carbon nanotubes (SWNTs) have been locally synthesized on zeolite-covered silicon substrates by laser-heating chemical vapor deposition (CVD). We used laser irradiation as a heat source, Fe/Co nanoparticles supported on zeolite as catalysts, and ethanol vapor as a carbon source. We heated the zeolite catalysts using a Nd:YAG laser at 50 mW with a spot size of about 5mum diameter and synthesized SWNTs in a local area of about 20mum diameter at the irradiation point. We also synthesized SWNTs in a line by scanning the laser irradiation at 800mW at an average speed of 10mum/s. The synthesized SWNTs were characterized by scanning electron microscopy and Raman spectroscopy. To investigate the effect of heating SWNTs by the laser, we irradiated pure SWNTs synthesized by standard CVD in a vacuum furnace using the laser. Furthermore, we succeeded in bridging zeolite islands using SWNTs by laser-irradiating one side of the islands.

Laminated Electrodes Chip for Pulse-Immunoassay

A simple and inexpensive method to fabricate microchannel-chip with electrodes was developed for pulse-immunoassay which is a kind of latex immunoassay enhanced by an alternating-current electric field. With the electrodes chip, 3 U/ml hepatatitis B surface antigen was detected on the condition that the sample was observed at multi-point(10 points per channel x 9 channels).

In-situ single DNA manipulation with /spl phi/20 nm electron-beam-deposited probe

Proposes a novel DNA-sequencing-preprocessing that can selectively extract a specific part of a single molecular DNA fiber by in-situ manipulation. The in-situ manipulation extends DNA fibers on a glass substrate, cuts into several DNA fragments, and isolates a specific DNA fragment. In this method full-time observation of the manipulation is provided for the purpose of keeping the information about where the isolated DNA fragment used to be located in the original DNA fiber. A hook-shaped /spl phi/20 nm probe was fabricated by electron-beam-deposition for isolating the DNA fragment. With this probe, the DNA fragment, extended on a water-repellent surface with its end anchored by Au colloid, was hooked and lifted up from the glass substrate; water-repellence has an effect of preventing adsorption between the DNA fragment and the glass substrate. Finally, the specific DNA fragment was successfully isolated onto a new clean glass substrate.

Integration of Immunosorbent Assay System into a Multichannel Microchip for Clinical Diagnoses

The whole process of an immunosorbent assay system was integrated into a glass microchip. Analyte was adsorbed on polystyrene beads put in a microchannel, and then the antibody conjugated with colloidal gold was reacted. The colloidal gold bound to the beads was detected by a thermal lens microscope. By using a microchip with a multichannel system, simultaneous determination became possible. This system seems to be practically useful to clinical diagnosis. Moreover, troublesome operations required for the conventional immunosorbent assay were replaced by simple operations.