Hidetoshi Miyashita

Mass sensing of adsorbed molecules in sub-picogram sample with ultrathin silicon resonator

Ultrathin single-crystalline silicon cantilevers with a thickness of 170 nm as a resonating sensor are applied to mass sensing. The hydrogen storage capacity of a small amount of carbon nanotubes (CNTs), which were mounted on an ultrathin resonator by a manipulator, is measured from the resonant frequency change. The resonator is annealed in ultrahigh vacuum to clean the surface and increase the quality factor, and exposed to oxygen gas to oxidize the surface for long-term stability. The resonator can be electrostatically actuated, and the vibration is measured by a laser Doppler vibrometer in ultrahigh vacuum. The mass of the CNTs is determined by the difference of resonant frequencies before and after mounting the CNTs, and the hydrogen storage capacity is determined from the frequency change after exposure to high-pressure hydrogen as well. The obtained hydrogen storage capacitance is 1.6%–6.0%. The available mass resolution and the achieved stability of the resonance of the 170-nm-thick resonator are ...

Electric-field-enhanced growth of carbon nanotubes for scanning probe microscopy

The influence of an electric field on carbon nanotube?(CNT) growth using hot-filament chemical vapour deposition is investigated. Acetylene (C2H2) gas diluted with hydrogen is used as the source gas for the growth of CNTs, and a bias voltage of -300?V is applied to the sample stage during growth. The silicon substrate onto which the CNT is grown is prepared by sputtering a thin catalysed metal (Ni) film onto the surface, and the CNT is selectively grown from the tip of a silicon protrusion on the substrate. It is found that the application of a high electrostatic field with a negative substrate bias enhances the growth of CNTs in this situation. This effect is successfully applied to the fabrication of a CNT tip supported by a silicon cantilever for use in scanning probe microscopy.

Pattern Transfer of Self-Ordered Structure with Diamond Mold

A diamond mold patterned into self-ordered honeycomb structures was fabricated and pattern transfer was demonstrated with this mold. A diamond film was deposited onto a silicon substrate by hot-filament chemical vapor deposition and bonded with Pyrex glass by an anodic bonding technique. By removing the silicon substrate, the diamond film with a flat surface was formed on the Pyrex glass. The high aspect ratio of the pattern with 100 nm-pitch honeycomb structures was formed on the diamond thin film by a fast-atom beam of oxygen using an ordered porous alumina film as a mask. A dot pattern was transferred onto a polymethylmethacrylate (PMMA) film by an imprinting technique.

Precise control of epitaxy of graphene by microfabricating SiC substrate

Epitaxial graphene (EG) on SiC is promising owing to a capability to produce high-quality film on a wafer scale. One of the remaining issues is microscopic thickness variation of EG near surface steps, which induces variations in its electronic properties and device characteristics. We demonstrate here that the variations of layer thickness and electronic properties are minimized by using microfabricated SiC substrates which spatially confines the epitaxy. This technique will contribute to the realization of highly reliable graphene devices.

Site-Selective Epitaxy of Graphene on Si Wafers

The fusion of graphene with silicon may provide an effective solution to the problem of scale in electronic devices. This approach will allow the excellent electronic properties of graphene to be combined with known Si device technologies. We review the epitaxial growth of graphene on Si substrates (GOS) for fabricating transistors. GOS has been multifunctionalized by controlling the orientation of the Si substrate. The site-selective epitaxy of GOS has also been developed by controlling the base SiC thin films. These results demonstrate that GOS is suitable for integrated devices.

Selective growth of carbon nanotubes for nano electro mechanical device

In this paper, we present the growth techniques of carbon nanotubes and its application for nano-electromechanical devices. Several methods were attempted for the selective growth of the carbon nanotubes. Catalyzed metal (Ni) patterning and the following hot-filament chemical vapor deposition enable to grow carbon nanotubes on the metal pattern formed on quartz glass. However, no carbon nanotubes are grown on a flat silicon substrate using this method. It is found that the high electrostatic field with a negative substrate bias enhances the growth of the carbon nanotubes. This growth enhancement effect is applied to fabricate single carbon nanotube tip on silicon for scanning probe microscopy.

Nanomechanical Structure with Integrated Carbon Nanotube

In this paper, we report on the fabrication method of a freestanding carbon nanotube (CNT) bridged between opposing silicon electrodes with a narrow gap (0.5?5 ?m) that was fabricated by a silicon micromachining technique. After the metallization of nickel (Ni) or iron (Fe) as a catalyst for CNT growth, the CNT was grown between these electrodes with the application of a voltage of 30V during the growth by hot-filament chemical vapor deposition (HF-CVD) using acetylene diluted by hydrogen, as a source gas. The CNT was grown from the negative electrode to the other electrode. From the measurement of current?voltage (I?V) characteristics, the contact between the CNT and the silicon electrode shows ohmic behavior and the resistivity of the CNT was estimated to be approximately 4?10-5 ??cm. This nanofabrication technique will be applicable to the nanomechanical elements integrated an individual CNT.

Mechanical Energy Dissipation of Multiwalled Carbon Nanotube in Ultrahigh Vacuum

Mechanical elements composed of an individual multiwalled carbon nanotube was fabricated and its mechanical energy dissipation was evaluated in an ultrahigh vacuum. The carbon nanotube was oscillated by applying a voltage between the carbon nanotube and a metal electrode, and its vibration was detected by a laser Doppler vibrometer. Heating in vacuum desorbed contaminants from the carbon nanotube surface and decreased mechanical energy loss. However, the Q factor, i.e., the reciprocal number of the energy loss, was still low (~800). This result suggests that the dominant energy dissipation relies on the bulk defect of the carbon nanotube.

Nanometric Sensing and Processing with Micromachined Functional Probe

Ultrathin single crystal silicon cantilevers with the thickness of 170 nm and 20 nm for a resonating sensor are successfully fabricated. Flash annealing in ultra-high vacuum results in the increase of the quality factor of these cantilevers, which enables to vibrate the cantilevers electrostatically with a low actuation voltage and senses a small mass change and a weak force gradient. In this paper, we apply these cantilevers to a gravimetry and a magnetometry on a small quantity of objects that are attached on the end of the cantilever beam using a manipulator. Hydrogen storage capacity of a carbon nanotube bundle, and magnetic force acting on an iron particle are successfully measured. The available mass resolution and force gradient resolution are about 5×10−18 g and 8×10−10 N/m, respectively.

Fabrication of high aspect ratio carbon nanotube-carbon composite microstructures based on silicon molding technique

This paper reports the fabrication and characterization of carbon nanotube (CNT)/carbon composite microstructures with higher Youngs modulus than that of pyrolysis carbon. Hybrid microstructures consisted of CNT composite and Si are successfully fabricated by micromolding and pyrolysis of a resist (SU-8) mixed with CNTs. The photoresist mixed with CNTs is filled into a Si micromold fabricated by deep reactive ion etching (deep RIE), then the CNT/resist is converted to CNT/carbon microstructures using two-step high temperature pyrolysis process in an inert gas. Then, the Si substrate is patterned by deep RIE. The maximum aspect ratio of the composite structures is approximately 40