Hideto Tanoue

Review of Cathodic Arc Deposition for Preparing Droplet-Free Thin Films

Cathodic arc plasma is one of the potential ion plating physical vapor deposition methods to prepare protective coatings on cutting tools, metal mold, etc. In particular, TiN, CrN, and TiAlN films are coated on industrial cutting tools using cathodic arc plasma. However, the cathode spot of the vacuum arc generates macrodroplets as coproducts of cathodic arc plasma containing high-energy ions. These macrodroplets may pose problems with smooth-surface films that are used for advanced high-precision applications. This paper reviews cathode phenomena particularly for a graphite cathode, the techniques for reduction of macrodroplet generation, and the techniques for macrodroplet removal from the processing plasma. The reduction technique includes steered arc, pulsed arcs, etc. The removal technique includes shielded arcs and filtered arcs. Recent filtered arc deposition systems are referred.

Plasma irradiation of artificial cell membrane system at solid-liquid interface

We provide direct evidence of plasma-induced pore formation in a cell membrane model system. We irradiated plasma on the basis of the dielectric barrier discharge onto a supported lipid bilayer (SLB). Observation with a fluorescence microscope and atomic force microscope revealed the formation of pores on the order of 10 nm–1 µm in size. Capturing these micropores in a fluid lipid membrane is a significant advantage of the SLB system, and quantitative analysis of the pores was performed. Stimulation with equilibrium chemicals (HNO3 and H2O2) indicated that other transient active species play critical roles during the poration in the SLB.

Torsion fracture of carbon nanocoils

We fix a carbon nanocoil (CNC) on a substrate in a focused ion beam instrument and then fracture the CNC with a tensile load. Using the CNC spring index, we estimate the maximum to average stress ratio on the fractured surface to range from 1.3 to 1.7, indicating stress concentration on the coil wire inner edge. Scanning electron microscopy confirms a hollow region on the inner edge of all fractured surfaces.

Development of X-Shaped Filtered-Arc-Deposition (X-FAD) Apparatus and DLC/Cr Film Preparation

An X-shaped filtered-arc-deposition (X-FAD) apparatus was developed in order to prepare hydrogen-free tetrahedral amorphous carbon (ta-C), which is a kind of diamond-like carbon (DLC), and metal film as a binding interlayer on the superhard alloy using a plasma beam irradiated from the same direction. First of all, the droplet-reduction performance was verified, and then, the appropriate duct-bias voltages and deposition rate were measured. Optima of duct biases for chromium (Cr) and DLC were found to be 25 and 15 V, respectively. From the result of X-ray diffraction analysis, it was found that Cr film that is prepared at a higher substrate-bias voltage was well crystallized and has less internal stress. The appropriate substrate bias for preparing ta-C was -100 to -200 V. DLC film was also prepared with substrate heating. It was found that ta-C could be prepared at a substrate temperature of less than 200degC, and the film was graphitized at higher temperature. By following these results, 2.5-mum-thick ta-C film was prepared on a superhard alloy with an interlayer by X-FAD.

Supporting PtRu catalysts on various types of carbon nanomaterials for fuel cell applications

PtRu catalysts were supported on five types of carbon nanomaterials of various shapes, sizes, and graphitic properties and the catalyst supports evaluated. The carbon nanomaterial used included three types of nanoparticles: Arc Black (AcB), Vulcan XC-72 (Vulcan) and graphene oxide (GO), and two types of nanofibers: carbon nanocoil (CNC) and carbon nanotube (CNT). Pt and Ru were supported by the reduction method using sodium borohydride. The metal catalyst loading was confirmed by thermo-gravimetric analysis (TGA), electron microscopy, and X-ray diffraction (XRD). Transmission electron microscopy (TEM) and XRD revealed that the diameter of PtRu catalyst nanoparticles loaded on reduced GO (rGO) and AcB were ~2 nm and was the smallest among all the samples. Shifts in Pt (111) XRD peaks of CNC and CNT were larger than those of AcB, Vulcan, and rGO. These results suggest that the diameters of catalyst nanoparticles became smaller by loading on the carbon nanoparticles with a large surface area including rGO, AcB, and Vulcan. Loading onto the carbon nanofibers enhanced the degree of PtRu alloying.

Development of Y-Shaped Filtered-Arc-Deposition System for Preparing Multielement Composition-Controlled Film

In recent years, multielement films have been required for high-performance cutting tools. In this paper, a Y-shaped filtered-arc-deposition (Y-FAD) system with two vacuum-arc sources was developed. First, an optimum magnetic coil arrangement was experimentally established to transport two plasma beams through the Y-shaped duct at the same time. Since the two plasma beams have the same electrical polarity, they naturally tend to repel each other. Therefore, in the second step, the two plasma beams were combined into one plasma beam through a mixer part by vibrating the plasma beams with a laterally oscillating magnetic field. Third, the electrical bias applied to the duct was optimized to obtain a higher transportation rate of plasma and deposition rate. After these design developments and tuning, titanium-aluminum (Ti-Al) film with a combined deposition pattern was finally obtained with Al and Ti cathodes. The controllability of the composition ratio by the arc current was verified.

Optimization of Chemical Vapor Deposition Process for Reducing the Fiber Diameter and Number of Graphene Layers in Multi Walled Carbon Nanocoils

Multi walled carbon nanocoils (MWCNCs) were synthesized by chemical vapor deposition (CVD) and the experimental parameters were optimized to reduce their fiber diameter. The conditions for the synthesis of the thinnest MWCNC in this experiment were as follows: reaction temperature, 700 °C; C2H2/N2 pressure, 0.67 kPa; and C2H2/N2 ratio, 0.01. A low C2H2 gas flow rate and a low partial gas pressure were important in reducing the fiber diameter. The reaction temperature affected both the MWCNC fiber diameter and purity, which depends on the content of MWCNCs and multi walled carbon nanotubes (MWCNTs). At high temperatures (≥750 °C), MWCNTs were predominant and their crystallinity increased, which was confirmed by the detection of the radial breathing mode and high intensity ratios of the G peak to the D peak in the Raman spectra. By contrast, MWCNCs were produced preferentially at low temperatures (approximately 700 °C). Transmission electron microscopy showed that the fiber diameter of the thinnest MWCNC was less than 5 nm at both the helix and tip and that the thinnest MWCNC had a triple walled structure. Under optimized conditions, the vacuum deposition of a thin film of Sn on a Si substrate and the mounting of Fe catalyst supported zeolite on a Sn/Si substrate effectively increased MWCNC purity. MWCNC purity was improved by up to 30%, which is the highest purity we have observed thus far.

Removal of Diamond-Like Carbon Film by Oxygen-Dominated Plasma Beam Converted from Filtered Carbon-Cathodic Arc

Diamond-like carbon (DLC) film is sometimes removed using oxygen plasma in order to reuse workpieces such as cutting tools and press molds. In this study, an oxygen-dominated plasma beam was generated by converting the cathodic carbon arc plasma beam formed in T-shaped filtered-arc-deposition (T-FAD) in order to investigate the feasibility of using the plasma beam for the removal of DLC film. When the oxygen (O2) gas flow rate was relatively high (50 ml/min) and the substrate was biased (DC -500 V), the plasma beam in front of the substrate was confirmed to contain a considerable amount of excited oxygen atoms, since an atomic oxygen spectral line (777 nm) emitted from the plasma beam had relatively strong radiation intensity. The plasma beam was irradiated on a tetrahedral amorphous carbon film, a hydrogen-free sp3-rich DLC film, prepared on a hard alloy (WC with 6 wt % Co binder) substrate. It was found that a plasma beam generated with an appropriate O2 gas flow rate and applied substrate bias was able to etch the DLC film proportionally to the treatment time. The surface was not roughened when the treatment time was 1.5 times longer than the intended time to remove a given thickness of DLC film.

Preparation of Arc Black and Carbon Nano Balloon by Arc Discharge and Their Application to a Fuel Cell

Arc black (AcB) was prepared in N2 gas using the twin-torch arc discharge apparatus, and a hollow capsule with graphite layers named a carbon nano balloon (CNB) was obtained by heat treatment of the AcB in Ar gas at 2400 °C. Transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and compressive resistivity measurement confirmed that the CNB was well graphitized. In the direct methanol fuel cell (DMFC) application of these carbon nanomaterials, catalyst metal nanoparticles were supported on the AcB, and a membrane-electrode assembly (MEA) was formed from the catalyst-supported AcB and the CNB by hotpressing them on an electrolyte film. The MEA containing the CNB resulted in a higher DMFC performance than that without the CNB, indicating that the CNB with lower compressive resistivity than the AcB works as a material for the improvement of electric conductivity in an MEA.

Use of carbon nanocoil as a catalyst support in direct methanol fuel cell

When carbon nanocoils (CNCs) are used in fuel cell electrodes, the diffusion of fuel and gas, and the removal of reaction products, becomes considerably smoother. In this paper, we used CNC as an anode or cathode catalyst support material in direct methanol fuel cells (DMFCs). Other carbon nanoparticles, Arc-Black (AcB) and Vulcan, were also used as catalyst supports to compare with the CNCs. Catalysts were loaded onto nanocarbon materials using the polyol method. We measured the methanol oxidation current of PtRu catalysts loaded on the carbon nanomaterials and the catalyst on CNC showed the highest current. Compared with the catalyst layers of AcB and Vulcan, the catalyst layer of CNCs was confirmed to have several voids. As for the cathode catalysts, the power density of Pt/CNC was 1.2 times higher than that of Pt/Vulcan and 1.6 times higher than that of Pt/AcB.