Toru Harigai

Improvement of adhesion of hydrogen-free DLC film by employing an interlayer of tungsten carbide

Materials with poor adhesion present a problem for the application of diamond-like carbon (DLC) films. As a method for solving this problem, there is a technique that deposits an interlayer of metal between the DLC film and substrate. A tungsten carbide film (W-C film) is used as the interlayer. In this study, the effect of introducing the W-C interlayer on the adhesion of the DLC film was investigated. The W-C films were deposited using two types of cemented tungsten carbides (WCs) as the cathode, one containing Co (WC-Co) and the other containing Ti (WC-Ti), as a binder for forming the cathode shape. It is necessary to control the film thickness of the interlayer to introduce the interlayer to the DLC film. The film thickness control of W-C films became possible by using a discharge counter. DLC films were deposited using a bias voltage of -100 V. The film thicknesses of the W-C interlayer and DLC film at the time of investigating adhesion were 30 nm and 300 nm, respectively. The result of the tape-peel...

Electromagnetic wave absorption properties of carbon nanocoil composites in the millimeter waveband

Carbon nanocoil (CNC) is a carbon nanofiber with helical shape. In this study, we fabricated CNC-based composites endowed with electromagnetic wave absorption property. CNCs were synthesized by chemical vapor deposition using acetylene as a precursor and Fe and SnO2 particles as catalysts. The composites were produced by dispersing CNCs into epoxy resin or paraffin by ultrasonication, and then hardening a droplet of the solution on an aluminum substrate with ca. 2mm in specimen thickness. Paraffin was used as a solvent when producing the composites with the CNC concentration higher than or equal to 5wt.%; otherwise epoxy was used. The reflection ratio of the composites with different concentrations were measured by the free space method using lens antennas in frequency ranges of 5.6–40 and 67–110 GHz. The CNCs/epoxy composites of 0.1–1.0 wt.% showed poor reflection losses. The 10 wt.% CNCs/paraffin composite achieved a reflection loss of −32 dB at 79.2 GHz. Its bandwidth corresponding to the reflection lo...

Diamond-like carbon films from CO source gas by RF plasma CVD method

Diamond-like carbon (DLC) films were fabricated by RF CO plasma chemical vapor deposition (CVD) to avoid hydrogen incorporation into the deposited films. Broadband optical emissions confirmed a hydrogen-free process without atomic hydrogen emissions. The fabricated films were characterized by Raman scattering spectroscopy, Rutherford backscattering spectrometry (RBS) with elastic recoil detection analysis (ERDA) methods, and FT-IR spectroscopy with comparison to conventional DLC films fabricated from C2H2 gas. The hydrogen concentration in the DLC films was reduced to 4 at. % using a CO source while the conventional DLC films prepared from C2H2 contained 27 at. %. The DLC films made from CO gas contained a large amount of oxygen, approximately 20 at. %, a larger number of graphite structures than the conventional DLC film, and characteristic triple bonds (C≡C) of carbon atoms in the FT-IR spectrum.

Hydrophilic DLC Surface Induced by Nanostructures Formed by RF O 2 Plasma Etching With Metal Micromasks

Long pillar- and tip-shaped nanostructures were formed on diamond-like carbon (DLC) surfaces by RF O2 plasma etching after deposition of a small amount of metal as a micromask by the dc magnetron sputtering method. Ni, Pt, Fe, Au, and Cu were examined as metal micromasks for deposition on the DLC surface. During the initial etching stage, nanostructures appeared on all of the DLC surfaces with each of the metal micromasks. The initial nanostructures were induced by anisotropic etching with the micromasks of aggregated metal. As the etching duration was increased, the nanostructures grown with Ni and Fe micromasks appeared to be lengthened, while the nanostructures induced by Pt, Au, and Cu completely disappeared. O2 plasma etching for 5 min after deposition of a 0.15-nm thick Ni layer resulted in complete coverage of the DLC surface with fine nanostructures around 30 nm in diameter, 60 nm in height, and an areal number density of 1500 μm-2. The resultant surface had hydrophilic characteristics with a small water contact angle of 13°.

Fabrication of nitrogen-containing diamond-like carbon film by filtered arc deposition as conductive hard-coating film

Diamond-like carbon (DLC) films, which are amorphous carbon films, have been used as hard-coating films for protecting the surface of mechanical parts. Nitrogen-containing DLC (N-DLC) films are expected as conductive hard-coating materials. N-DLC films are expected in applications such as protective films for contact pins, which are used in the electrical check process of integrated circuit chips. In this study, N-DLC films are prepared using the T-shaped filtered arc deposition (T-FAD) method, and film properties are investigated. Film hardness and film density decreased when the N content increased in the films because the number of graphite structures in the DLC film increased as the N content increased. These trends are similar to the results of a previous study. The electrical resistivity of N-DLC films changed from 0.26 to 8.8 Ω cm with a change in the nanoindentation hardness from 17 to 27 GPa. The N-DLC films fabricated by the T-FAD method showed high mechanical hardness and low electrical resistivity.

Multi-spark discharge system for preparation of nutritious water

The nitrogen compound concentration in water is increased by atmospheric-pressure plasma discharge treatment. A rod-to-water electrode discharge treatment system using plasma discharge has been developed by our group to obtain water with a high concentration of nitrogen compounds, and this plasma-treated water improves the growth of chrysanthemum roots. However, it is difficult to apply the system to the agriculture because the amount of treated water obtained by using the system too small. In this study, a multi-spark discharge system (MSDS) equipped multiple spark plugs is presented to obtain a large amount of plasma-treated water. The MSDS consisted of inexpensive parts in order to reduce the system introduction cost for agriculture. To suppress the temperature increase of the spark plugs, the 9 spark plugs were divided into 3 groups, which were discharged in order. The plasma-treated water with a NO3− concentration of 50 mg/L was prepared using the MSDS for 90 min, and the treatment efficiency was about 6 times higher than that of our previous system. It was confirmed that the NO2−, O3, and H2O2 concentrations in the water were also increased by treating the water using the MSDS.The nitrogen compound concentration in water is increased by atmospheric-pressure plasma discharge treatment. A rod-to-water electrode discharge treatment system using plasma discharge has been developed by our group to obtain water with a high concentration of nitrogen compounds, and this plasma-treated water improves the growth of chrysanthemum roots. However, it is difficult to apply the system to the agriculture because the amount of treated water obtained by using the system too small. In this study, a multi-spark discharge system (MSDS) equipped multiple spark plugs is presented to obtain a large amount of plasma-treated water. The MSDS consisted of inexpensive parts in order to reduce the system introduction cost for agriculture. To suppress the temperature increase of the spark plugs, the 9 spark plugs were divided into 3 groups, which were discharged in order. The plasma-treated water with a NO3− concentration of 50 mg/L was prepared using the MSDS for 90 min, and the treatment efficiency was abo...

Preparation of multi-layer film consisting of hydrogen-free DLC and nitrogen-containing DLC for conductive hard coating

Conductive hard-coating films have potential application as protective films for contact pins used in the electrical inspection process for integrated circuit chips. In this study, multi-layer diamond-like carbon (DLC) films were prepared as conductive hard-coating films. The multi-layer DLC films consisting of DLC and nitrogen-containing DLC (N-DLC) film were prepared using a T-shape filtered arc deposition method. Periodic DLC/N-DLC four-layer and eight-layer films had the same film thickness by changing the thickness of each layer. In the ball-on-disk test, the N-DLC mono-layer film showed the highest wear resistance; however, in the spherical polishing method, the eight-layer film showed the highest polishing resistance. The wear and polishing resistance and the aggressiveness against an opponent material of the multi-layer DLC films improved by reducing the thickness of a layer. In multi-layer films, the soft N-DLC layer between hard DLC layers is believed to function as a cushion. Thus, the tribolog...

Influences of internal resistance and specific surface area of electrode materials on characteristics of electric double layer capacitors

We fabricated electric double layer capacitors (EDLCs) using particulate and fibrous types of carbon nanomaterials with a wide range of specific surface areas and resistivity as an active material. The carbon nanomaterials used in this study are carbon nanoballoons (CNBs), onion-like carbon (OLC), and carbon nanocoils (CNCs). A commercially used activated carbon (AC) combined with a conductive agent was used as a comparison. We compared the EDLC performance using cyclic voltammetry (CV), galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy (EIS). OLC showed a poor EDLC performance, although it has the lowest resistivity among the carbon nanomaterials. CNB, which has a 1/16 lower specific surface area than AC but higher specific surface area than CNC and OLC, had a higher specific capacitance than CNC and OLC. Moreover, at current densities of 1.5 Ag−1 and larger, the specific capacitance of the EDLC using CNB was almost the same as that using AC. Electrochemical impedance spe...

Second by second prediction of solar power generation based on cloud shadow behavior estimation near a power station

Photovoltaic (PV) power generation has a particular problem for grid cooperation in that output can fluctuate due to the shadows created by clouds. If we can grasp the behavior of cloud shadows beforehand, then it may be possible to forecast output fluctuations. In this study, we want to prove if it is possible to calculate power output variation from the accumulated cloud shadow data. Cloud shadow behavior was measured from the ground by photodiodes (PDs) and the cloud shadow vector was calculated from the position and time difference. The time from the calculated cloud shadow vector to the arrival of the cloud shadow and the power generation output was calculated and compared with the actual solar power generation output. Thus, we confirmed that we can predict power generation output from a high correlation of two outputs. We found that prediction is possible, with high precision, at a short distance.

Effects of catalyst support and chemical vapor deposition condition on synthesis of multi-walled carbon nanocoils

Multi-walled carbon nanocoil (MWCNC) is a carbon nanotube (CNT) with helical shape. We have synthesized MWCNCs and MWCNTs hybrid by chemical vapor deposition (CVD). MWCNCs are considered to be a potential material in nanodevices, such as electromagnetic wave absorbers and field emitters. It is very important to take into account the purity of MWCNCs. In this study, we aimed to improve the composition ratio of MWCNCs to MWCNTs by changing catalyst preparation and CVD conditions. As a catalyst, Fe2O3/zeolite was prepared by dissolving Fe2O3 fine powder and Y-type zeolite (catalyst support material) in ethanol with an Fe density of 0.5wt.% and with a zeolite density of 3.5wt.%. The catalyst-coated Si substrate was transferred immediately onto a hotplate and was heated at 80°C for 5 min. Similarly, Fe2O3/Al2O3, Co/zeolite/Al2O3, Co/zeolite, and Co/Al2O3 were prepared. The effect of the difference of the composite catalysts on synthesis of MWCNCs was considered. The CVD reactor was heated in a tubular furnace ...