Katsunori Aoki

Density Control of Carbon Nanotubes through the Thickness of Fe/Al Multilayer Catalyst

The density control of vertically aligned carbon nanotubes (CNTs) has been studied using a thermal chemical vapor deposition (CVD) method in correlation with the thicknesses of the Fe/Al multilayer catalyst on a Si substrate. The density of CNTs could be controlled through the thicknesses of both the Al layer and Fe catalyst layer. The low density of the Fe catalyst grains formed by thermal treatment, caused the formation of CNTs with random orientations, and resulted in a decrease in the CNT height. The optimum film thickness of the Fe/Al multilayer catalyst for obtaining long CNTs (220 µm) was determined for the case of a substrate temperature of 700 °C.

Correlation between Field Electron Emission and Structural Properties in Randomly and Vertically Oriented Carbon Nanotube Films

We investigated the influence of the structural properties of randomly oriented carbon nanotube (R-CNT) and vertically oriented carbon nanotube (V-CNT) films on their field electron emission properties. The R-CNT and V-CNT films were synthesized using FeNi catalysts by means of thermal and dual-RF plasma-enhanced chemical vapor depositions, respectively. The structural properties of the R-CNT and V-CNT films were dependent on the initial thickness of the FeNi catalyst. As the FeNi film thickness decreased, the diameters of both types of CNTs decreased. Although the field electron emission property of the V-CNT film was improved with increasing the aspect ratio of V-CNT, the field enhancement factor, β, obtained from the Fowler–Nordheim plot was found to be 100 times larger than that obtained from the geometric properties. R-CNTs exhibited a lower threshold field than V-CNTs. These results suggest that the field emission property is markedly influenced by the surface state rather than by the geometric factors of CNTs.

Low-Temperature Growth of Carbon Nanofiber by Thermal Chemical Vapor Deposition Using CuNi Catalyst

Thermal-CVD was carried out for the low-temperature growth of carbon nanofibers (CNFs) using a CuNi alloy catalyst film with a thickness of 5 nm on Si in a gas mixture of C2H2 and He (C2H2/He=3/12 sccm). The experimental results obtained using the CuNi alloy catalyst film were compared with those obtained using the Fe, Ni, and FeNi catalyst films with the same thickness of 5 nm. It was shown that an amorphous CNF with a diameter of 20 nm can be grown even at 400 °C using the CuNi catalyst film, but not using the Fe, Ni and FeNi catalysts. A reduction in the growth temperature of CNFs was considered to be achieved using small CuNi catalyst particles with a comparatively smaller surface energy than FeNi catalyst particles.

Low-Temperature Synthesis of Aligned Carbon Nanofibers on Glass Substrates by Inductively Coupled Plasma Chemical Vapor Deposition

Vertically aligned carbon nanofiber (CNF) films were successfully grown on glass substrates at 450 °C with metal buffer layers by inductively coupled plasma chemical vapor deposition (ICP-CVD). The diameter and number density of the aligned CNFs can be controlled by changing the type and thickness of the metal buffer layers deposited on the glass substrates. The metal buffer layers play an important role in reducing the thermal expansion coefficient difference between the catalyst metal film and the glass substrate, resulting in the enhancement of the formation of catalyst nanoparticles so as to grow the aligned CNFs with high number density.

Carbon nanostructures grown on graphite substrates without catalyst by pulsed laser deposition

Standing fibrous carbon nanostructures have been synthesized from graphite substrates without a catalyst using pulsed laser deposition (PLD). Sharpened carbon nanostructures with a diameter of 2–10 nm, a length of 30–180 nm, and a tip angle of 25° were grown on the substrate surface. Transmission electron microscopy revealed that the sharpened carbon nanostructure consists of a few graphite sheets with a good crystallinity. At a low temperature of 500 °C, short and conical carbon nanostructures, which are similar to carbon nanohorns, were densely grown at the surface of the graphite substrate.

Formation of Nanoscale Diamond Particles without Substrate Heating by Cathodic Arc Deposition

A carbon film grown at room temperature using a cathodic arc process in ambient gases such as N2 and He was investigated by Raman spectroscopy and scanning electron microscopy (SEM). Diamond particles were found to be formed at a constant total pressure of 10-2 Pa, while graphite-like carbon was grown at a lower pressure of around 10-3 Pa in the lower P(He)/P(Total) region and tetrahedral amorphous carbon was grown at a higher pressure such as 10-1 Pa. The diamond particles were randomly distributed in the film and had sizes in the range of 50–200 nm.