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A transformerless multicellular dc-dc converter has been newly proposed. The capacitively isolated dc-dc cell converters have been applied to develop the multicellular converter without using high frequency transformers. The high voltage transformation ratio is achieved by the ISOP (Input Series Output Parallel) connection topology of the cell converters and the realization of the highly efficient cell converter is expected because of no transformers. A 144 V-24 V, 200 W prototype of the multicellular dc-dc converter using 3 cell converters based on the capacitive isolation has been developed, and the feasibility of the transformerless multicellular converter has been confirmed.

Plasma is a useful tool to synthesize carbon nanomaterials, including diamonds, fullerenes, nanotubes, and graphenes. This review gives an overview of these carbon nanomaterials produced by thermal or nonthermal plasmas and of the authors' work related to plasma-enhanced chemical vapor deposition of carbon nanotubes, along with an analysis and numerical simulation of CH4/H2 feedstock gas plasmas. The amount of carbon atoms in the grown carbon nanotubes and that calculated by simulation showed good agreement. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(6): 1–8, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11504

Electromagnetically pulled-out gas plasma (EPOP) gun was developed, which will be applied to the filtered arc deposition system in order to enhance the nitriding of preparing thin film under medium vacuum. A hot cathode of tungsten (W) filament was employed and DC discharge was generated between the cathode and anode (SUS304). The distance of electrodes was 100 mm. Electromagnetic coils were placed around the cathode, anode and plasma pulled-out duct, separately. Experimental pressure was 0.1 Pa. The following results were obtained. Ignition voltage became lower when the same direction magnetic field was axially applied to the cathode and anode. Minimum voltage for sustaining the discharge became lower when the magnetic filed was applied to the anode. With increasing discharge voltage, the discharge current increased dramatically for the discharge voltage less than 50 V and increased gradually for the voltage more than that. The plasma between the cathode and anode was able to be pulled out to the process chamber by applying magnetic field perpendicular to the discharge axis. The amount of pulled-out plasma increased with increasing the filament current and magnetic flux density for plasma pulling-out.

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.

A new technique to etch a substrate as a pre-treatment prior to functional film deposition was developed using a filtered vacuum arc plasma. An Ar-dominated plasma beam was generated from filtered carbon arc plasma by introducing appropriate flow rate of Ar gas in a T-shape filtered arc deposition (T-FAD) system. The radiation spectra emitted from the filtered plasma beam in front of a substrate table were measured. The substrate was etched by the Ar-dominated plasma beam. The principal results are summarized as follows. At a high flow rate of Ar gas (50 ml/min), when the bias was applied to the substrate, the plasma was attracted toward the substrate table and the substrate was well etched without film formation on the substrate. Super hard alloy (WC), bearing steel (SUJ2), and Si wafer were etched by the Ar-dominated plasma beam. The etching rate was dependent on the kind of substrate. The roughness of the substrate increased, when the etching rate was high. A pulse bias etched the substrate without roughening the substrate surface excessively.

A Y-shape filtered-arc-deposition system, which has two arc sources and a common plasma-transport-duct, was operated under nitrogen gas, and a titanium aluminum nitride (TiAlN) thin film was prepared with Ti and Al cathodes. Two filtered-arc plasma beams were not completely combined into one beam even at the exit of the common duct. Thus, TiAlN film with composition-uniform distribution was not obtained at the fixed substrate position. However, different composition films were easily obtained at one time. Then various-composition films of TiAlN with different arc currents were prepared and film properties were measured. The surface roughness in arithmetical mean roughness was less than 3 nm on a 1.5-nm roughness substrate. The density of TiAlN increased with the Ti-content ratio, and its hardness tended to weakly increase with Al-content ratio. The maximum hardness was 36 GPa. Ti-rich film has internal compression stress and Al-rich film has internal tensile stress.

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.

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.

The Young’s modulus of buckypaper (BP) was improved via the addition of carbon nanocoils (CNCs). The Young’s modulus was the highest when the added amount of CNCs of the mass of the bucky paper was 11.9%. It is likely that the improved Young’s modulus was due to the higher Young’s modulus of the CNCs, compared with the multi-walled carbon nanotube (MWCNT) bundles. The helical structure of the CNCs also contributed to the improvement in the Young’s modulus. In the BP containing CNCs, the CNCs were anchored in the MWCNT matrix with superior entanglement, and this effect improved the Young’s modulus of the BP.

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.

The fabrication of diamond-like carbon (DLC) micro-gear by room temperature curing nanoimprint lithography (RTC-NIL) using glass-like carbon (GC) molds as applications to the DLC-based medical MEMS (Micro Electronic Mechanical Systems) was investigated. The DLC film which has excellent properties similar to chemical vapor deposited (CVD) diamond films was used as the patterning material. We propose GC as mold material because GC has higher etching selectivity than a diamond film. The etching selectivity of polysiloxane film against a GC substrate is about 5 times as high as that of a diamond film. Therefore we fabricated the GC molds that have micro-gear patterns with 30 µm-tip diameter and 500 nm-tooth thickness. We carried out the RTC-NIL process using the GC micro-gear molds under the following optimum conditions. 1 min-time from spin-coating to imprint: t1, 0.5 MPa-imprinting pressure: P and 5 min-holding time: t2, and then the imprinted polysiloxane pattern on DLC film was processed with an electron cyclotron resonance (ECR) oxygen ion shower. However, we were not able to fabricate micro-gear patterns in high accuracy because of a remaining residual layer on the DLC film. Therefore we propose the removing process for the residual layer with trifluoromethane (CHF3) ion shower under the optimum conditions of 300 eV-ion energy and 4 min-etching time. As a result, we succeeded to fabricate concave DLC-based micro-gear patterns in high accuracy which has 30 µm-tip diameter and 1 µm-depth.

The microfabrication technologiesfor organic light-emitting devices (OLEDs) are essential to the fabrication of the next generation of light-emitting devices. The micro-OLEDs fabricated by room-temperature curing nanoimprint lithography (RTC-NIL) using diamond molds have been investigated. However, light emissions from 10 μm-square-dot OLEDs fabricated by the RTC-NIL method have not been uniform. Therefore, we proposed the fabrication of micro-OLEDs by room-temperature curing nanocontact-print lithography (RTC-NCL) using the diamond-like carbon (DLC) mold. The DLC molds used in RTC-NCL were fabricated by an electron cyclotron resonance (ECR) oxygen ion shower with polysiloxane oxide mask in electron beam (EB) lithography technology. The mold patterns are square and rectangle dots which has 10 µm-width, 10 µm-width and50 µm-length, respectively. The height of the patterns is 500 nm. The DLC molds were used to form the insulating layer of polysiloxane in RTC-NCL. We carried out the RTC-NCL process using the DLC mold under the following optimum conditions: 0.1 MPa-pressure for coating DLC mold with polysiloxane film, 2.1 MPa-pressure for transferring polysiloxane from DLC mold pattern to indium tin oxide (ITO) glass substrate. We deposited N, N'-Diphenyl -N, N'-di (m-tolyl)benzidine (TPD) [40 nm-thickness] as hole transport layer / Tris(8-quinolinolato)aluminum (Alq3) [40 nm-thickness] as electron transport layer / Al [200 nm-thickness] as cathode on ITO glass substrateas anode in this order. We succeeded in formation of the insulating layer with square and rectangle dots which has 10 µm-width,10 µm-width and 50 µm-length, and operation of micro-OLEDs by RTC-NIL using DLC molds.

Helical carbon nanofibre (HCNF) is spiral-shaped carbon nanofibre (CNF) with coil and fibre diameters in the range of 20—1000 nm and 5—400 nm, respectively. The unique three-dimensional structure of HCNFs induces a lot of researches to apply HNCFs to electrical and electronic engineering as well as mechanical engineering. Carbon nanotubes (CNTs) were first discovered in the soot produced by an arc discharge and laser ablation has been one of the most reliable methods to prepare high-quality CNTs. On the other hand, HCNFs has been almost entirely grown by chemical vapour deposition (CVD) using hydrocarbon feedstock gases. In this chapter, we describe the history, classification, synthesis, and application of HCNFs. We mainly introduce our research results including the latest topics, comparing with the other group’s work. The problems that still remain in the CVD growth and the future researches of HCNFs we intend are also discussed.

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.

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.

In this study, we used two types of carbon nanomaterials, arc-black (AcB) which has an amorphous structure and carbon nano-balloon (CNB) which has a graphitic structure as electrochemical capacitor electrodes. We made a coin electrode from these carbon materials and fabricated an electric double-layer capacitor (EDLC) that sandwiches a separator between the coin electrodes. On the other hand, RuO2 was loaded on these carbon materials, and we fabricated a pseudo-capacitor that has an ion insertion mechanism into RuO2. For comparison with these carbon materials, activated carbon (AC) was also used for a capacitor electrode. The electrochemical properties of all the capacitors were evaluated in 1M H2SO4 aqueous solution. As a result of EDLC performance, AcB electrode had a higher specific capacitance than AC electrode at a high scan rate (≥ 100 mV/s). In the evaluation of pseudo-capacitor performance, RuO2-loaded CNB electrode showed a high specific capacitance of 734 F/g per RuO2 weight.

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.