Hidehiro Nishijima

Carbon-nanotube tips for scanning probe microscopy: Preparation by a controlled process and observation of deoxyribonucleic acid

We report a controlled process to make carbon-nanotube tips for scanning probe microscopes. The process consists of three steps: (1) purification and alignment of carbon nanotubes using electrophoresis, (2) transfer of a single aligned nanotube onto a conventional Si tip under the view of a scanning electron microscope, and (3) attachment of the nanotube on the Si tip by carbon deposition. Nanotube tips fabricated using this procedure exhibit strong adhesion and are mechanically robust. Finally, the performance of these tips is demonstrated by imaging the fine structure of twinned deoxyribonucleic acid with tapping-mode atomic force microscopy in air.

Carbon nanotube tips for a scanning probe microscope: their fabrication and properties

We report a well controlled method to make carbon nanotube tips for a scanning probe microscope (SPM). A multiwalled carbon nanotube, which is purified by the electrophoresis, is transferred onto a conventional Si tip for a SPM using a scanning electron microscope (SEM) equipped with two independent specimen stages. The nanotube is fixed on the Si tip by electron beam deposition of carbon. A force curve measurement of nanotubes using the nanotube tips in the SEM reveals that Youngs modulus of a nanotube of 20 nm diameter is 1.1 TPa and the fixing of nanotubes by the carbon deposit is effective. The nanotube tips are used to image plasmid deoxyribonucleic acids on mica by tapping mode. The average resolution by using the nanotube tips is about two times higher than that by the best Si tips.

Carbon-nanotube probe equipped magnetic force microscope

Metal capped carbon nanotubes, prepared by catalytic decomposition of benzene, have been applied as a magnetic force microscope tip. The particles at the end of nanotubes were about 35 nm in diameter, which were found to be Ni3C from the electron diffraction pattern. The other end of the nanotubes was attached on the tip of conventional Si probes. The magnetization of the particles was carried out parallel to the nanotube axis by applying a pulsed magnetic field of 12.5 T. We demonstrate the performance of these carbon nanotube probes by imaging the stored signal in magnetic recording media with magnetic force microscopy.

Microprocess for fabricating carbon-nanotube probes of a scanning probe microscope

We have developed microprocesses to make carbon-nanotube probes for a scanning probe microscope. The processes contain electric-field induced transportation, welding and fixation by electron-beam carbon deposition and are performed in a scanning electron microscope equipped with two individual manipulable stages. Using the nanotube probes produced, a fine structure of helical and twinned deoxyribonucleic acid and an abrupt height transition with high fidelity in a 4.7 GB digital versatile disk are imaged with tapping-mode atomic force microscopy in air.

Influence of stiffness of carbon-nanotube probes in atomic force microscopy

We report the influence of stiffness of carbon nanotubes for probes of a scanning probe microscope on images. Multiwalled carbon-nanotube probes are fabricated by manipulation under the direct view of a scanning electron microscope. Using this manipulation, it is also revealed that a Hamaker constant of 60×10-20 J for the van der Waals attraction is for a sidewall of the nanotube and the metallic surface at a vacuum of ~10-3 Pa. The force curve measurements at a steep slope in air reveal the influence of the force acting not only on the tip of the probes but also on the wall of the tip. The origin of this effect is discussed in terms of the van der Waals attraction and the adhesive energy estimated from the force curve. This phenomenon is suppressed using a nanotube probe consisting of bundled nanotubes at the base to improve the stiffness for samples of high roughness.

Carbon-Nanotube Tip for Highly-Reproducible Imaging of Deoxyribonucleic Acid Helical Turns by Noncontact Atomic Force Microscopy

A carbon nanotube (CNT) was used as a tip for a noncontact-mode atomic force microscope (NC-AFM). A CNT tip was attached to an Au/Si tip by a well-controlled procedure in a scanning-electron-microscope (SEM) chamber. The NC-AFM with the CNT tip produced highly reproducible images of right-handed helical turns of linear deoxyribonucleic acid (DNA) with a spacing of 3.5 ±1.0 nm. The full-width at half-maximum (FWHM) of the cross section of DNA measured was 3.1 ±0.6 nm.

Influence of Force Acting on Side Face of Carbon Nanotube in Atomic Force Microscopy

We have examined the nanomechanics of a carbon nanotube by a manipulation technique using a scanning electron microscope. Youngs modulus of the nanotube, estimated from the buckling under force acting on the axial direction of the nanotube, agrees well with the value estimated from the bending under force acting on the side face. This indicates that the nanotube can be treated as an isotropic material in conventional mechanics. The adhesion force between the side face of the nanotube and a pit wall in a 4.7 GB digital versatile disk is estimated to be ~10 nN using atomic force microscopy. This value is 160 times less than the value estimated using force curve measurement. This discrepancy is due to the finding that the value estimated from the force curve includes not only the adhesion but also the friction force.

Atomic Force Microscopy of Single-Walled Carbon Nanotubes Using Carbon Nanotube Tip

We succeeded in observing individual single-walled carbon nanotubes (SWNTs) using an atomic force microscope (AFM) in the tapping mode by paying attention to the preparation of both samples and AFM tips. To disentangle the bundles of SWNTs, we added a small amount of amine into N,N-dimethylformamide. To achieve a high resolution in tapping-mode AFM imaging, we used carbon nanotube (CNT) tips whose radii could be reduced. We were able to image individual SWNTs using CNT tips with widths that were half of those imaged using conventional silicon tips. With this improved resolution, we could clearly resolve the two SWNTs lying parallel on a mica substrate.

Novel process for fabricating nanodevices consisting of carbon nanotubes

Carbon nanotubes are well known to have high aspect ratios, such as nanometer order diameter and micrometer order length, and small tip radii with a sharp cone. In this work we have developed microprocesses of nanotubes for fabricating the nanotube probes and other nanotube devices. The processes involve the preparation of a nanotube cartridge and the transportation, welding and fixation by carbon deposition for nanotubes.

Nanoindentation of polycarbonate using carbon nanotube tip

Nanoindentation experiments have been widely used for probing the mechanical and high pressure behavior of small region. One can expect that the spatial resolution of the experiments is improved by using the carbon nanotube tips for an atomic force microscope (AFM), because the nanotubes are well known to have high aspect ratios, small tip radii of curvature and high stiffness. The nanotube tips open out the possibility of mechanical processing in nanometer-scale region on soft material surfaces such as organic polymer or biological samples without degradation of the tips. Recently, we have developed the reliable process for fabrication of the nanotube probe using a scanning electron microscope (SEM). This technique enables us to fabricate an appropriate nanotube tip for the nanoindentation experiments. In this study, we report the nanoindentation properties of the nanotube tips and demonstrate the nanometer processing on the organic polymer surfaces.