This paper outlines the preparation methods and feasible applications of new nano-carbon materials; helical carbon nanofiber (HCNF), carbon nanohorn (CNH), and carbon nanoballoon (CNB). The HCNF is fibrilliform carbon materials with spiral and twisted shapes. The HCNF is divided into the groups of carbon nanocoil (CNC) and nanotwist (CNTw). They are synthesized by means of catalytic chemical vapor deposition (catalytic-CVD) with different catalysts. One of their applications is field emitter for next-generation plat panel display. The CNH is a particulate-form material and is produced by the evaporation of graphite with a laser or an arc discharge. The one of possible applications is the catalyst-supported electrode for fuel cell. The CNB is synthesized from an arc soot (or called arc black) and also from a particular-type acetylene black by means of high-temperature treatment under inert gas. Its potential applications are mentioned.
Significant improvement of the Pt-electrode in polymer electrolyte fuel cells has been found by replacing the support material from carbon black to multi-walled carbon nanotube (CNT). In order to explore the origin for the better performance of the Pt/CNT catalysts, model studies using Pt nano-particles deposited on a highly oriented pyrolytic graphite (HOPG) have been carried out as a surface science approach. It is suggested that monolayer of Pt nano-particles show a quite different electronic nature, leading to very high catalytic activity.
Electric double layer capacitors (EDLCs) have excellent properties in power density and durability compared with rechargeable batteries. The single-walled carbon nanotubes have high surface area theoretically up to 2600 m2/g inside and outside of the tubes. The material is considered to be ideal for EDLC electrodes and hence the development of advanced capacitors using carbon nanotubes is active recently. On the other hand, hydrogen storage into carbon nanotubes has been a topic in last decade after some reports which showed a very high storage capacity of hydrogen. The present performance and the prospect of carbon nanotubes as capacitor electrodes and materials for hydrogen storage are introduced in the report.
Plasma sputtering technique has been widely used for thin film coating technology such as microelectronics, bioelectronics, and so on. It is possible to generate particles in the sputtering plasma and they cause a contamination to the films. The following results on particles have been obtained by the capacitively coupled radio frequency (RF) plasma sputtering without a magnetic field using a carbon target. In the case of the sputtering mode with high power of 200-300 W, particles are not formed in plasma. However, when changing from the sputtering mode to the non-sputtering mode with low power of 40W, particles were detected and then were collected near a sheath edge of the target. In the non-sputtering mode, particles were grown with time and then their position shifted from the sheath edge to plasma region. Subsequently, these particles fell because of an unbalance between gravity and electrostatic force acted on particles. It was revealed that the growth rate increases with time of the sputtering mode and, in particular with the gas pressure.
Measurement and control of high-energy Ar species in the magnetron plasma source is discussed. From energy distribution measurement of Ar+ in the plasma, existence of high-energy Ar atoms in the magnetron plasma source is confirmed. It is concluded that collision of high-energy Ar atom with background thermal Ar atom is the dominant ionization mechanism for the production of high-energy Ar+. Based on this ionization mechanism, a Monte Carlo code is developed to simulate the Ar+ energy distribution and the results are in good agreement with the experimental ones. A new technique to suppress high-energy Ar species i.e., VHF-DC superimposed magnetron sputter source, is proposed. Compared with conventional magnetron sputter sources, this new sputter source shows lower Ar energy, which is consistent with the simulation result. The VHF-DC superimposed magnetron plasma is successfully applied to the deposition of magnetic multilayer films with very thin (<1 nm) layer thickness and good magnetic anisotropy.
Low-energy sputtering is studied through molecular dynamics (MD) and binary-collision approximation (BCA) simulations. First, MD simulations as a preliminary study are performed for 5 keV Ar impacts on a Cu target. When random numbers gave the direction of the target crystal axis for each impact, the total sputtering yield almost agreed with the experimental yield of a polycrystalline Cu target. Second, we performed MD and BCA simulations for self-sputtering of W with incident energy of 100 eV and incident angles of 0°-85°. We found that the many-body collision results in high-yield sputtering at grazing incidence. The incident angle dependence of sputtering yields fade out for an MD result with a rough surface.