Naoto Ohtake

Diamond Film Preparation by Arc Discharge Plasma Jet Chemical Vapor Deposition in the Methane Atmosphere

Diamond films are synthesized by arc discharge plasma jet chemical vapor deposition in the methane atmosphere. The apparatus developed generates a stabilized plasma jet continuously for more than 12h. The plasma jet consists of hydrogen and argon. is used as an atmospheric gas and is mixed into the plasma jet. The plasma jet is sprayed onto a cool‐down substrate, and a diamond film is deposited on the substrate surface. By means of this method, a diamond film is deposited on a molybdenum substrate at the growth rate of 930 μm/h. The crystallinity of the diamond film measures well by means of x‐ray diffraction and Raman spectroscopy. The weight of diamond obtained by this method in a unit time seems to be almost the same as that obtained by high‐temperature and high‐pressure synthesis method.

Measurement of Young’s modulus of carbon nanotubes by nanoprobe manipulation in a transmission electron microscope

A method for quantifying the nanomechanics of nanomaterials was developed using a nanoprobe manipulator fitted into a transmission electron microscope. Apparent Young’s moduli of various carbon nanotubes (CNTs) were measured using this method. The apparent Young’s modulus of an arc-grown CNT is as large as approximately 3.3TPa, which is close to the theoretical Young’s modulus (5.5TPa) of the single-walled CNT simulated using molecular dynamics. The relationship between the apparent Young’s modulus and the crystallinity of CNTs is demonstrated using the crystallinity parameter ID∕IG derived by Raman spectroscopic analysis. The apparent Young’s modulus is higher for better crystallinity of CNT.

Characterization of Head Overcoat for 1 Tb/in

To achieve a 1 Tb/in2 system, diamond-like carbon (DLC) on head and disk have to meet the criteria of corrosion- and wear-resistance at thicknesses of less than 2 nm. This paper will assess the performance of head and disk overcoat for a 1 Tb/in2 system and beyond, with focus on the influence of DLC forming technologies, thickness, and substrate materials. To evaluate DLC film, sp3 fraction was measured by X-ray photoelectron spectroscopy (XPS). It was shown that DLC films fabricated by filtered cathodic vacuum arc (FCVA) would have less sp3 fraction with decreasing thickness. To evaluate corrosion- and wear-resistance, coverage and critical loads were measured by XPS and atomic force microscopy scratch test. XPS revealed that DLC films prepared by both FCVA and ion-assisted sputtering had sufficient coverage at thickness of down to 1 nm. Atomic force microscopy scratch test showed that critical load depends on substrate materials and DLC thickness, not on DLC forming methods.

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The deposition of diamond-like carbon (DLC) films at atmospheric pressure is a promising technique of achieving in-process coatings regardless of work size. In this study, we aimed at the synthesis of DLC films at atmospheric pressure by nanopulse chemical vapor deposition (CVD) using a unique power source system consisting of a static induction (SI) thyristor and an inductive energy strage (IES). Then, we realized the synthesis of DLC films in open air (101 kPa). The deposition rate was as high as 0.4 µm/min, and the hardness of the film was 20.6 GPa. From Raman spectroscopic analysis results, the quality of films was found to significantly depend on input voltage and deposition time.

Magnetic Recording

The deposition of diamond-like carbon (DLC) films at subatmospheric pressure has been achieved by the nanopulse plasma chemical vapor deposition (CVD) method. To realize this process, a high ion density and non-arcing plasma at subatmospheric pressure are required. A static induction (SI) thyristor with an inductive energy storage (IES) circuit was used. The DLC film was obtained under the conventional low-pressure process at 6 Pa, and the characteristics of the high electron temperature and the exponential relationship between pulse frequency and growth rate were observed. Deposition of the DLC film was also achieved at the subatmospheric pressure of 26.7 kPa (200 Torr) using this nanopulse plasma CVD method.

Synthesis of Diamond-Like Carbon Films by Nanopulse Plasma Chemical Vapor Deposition in Open Air

Polypropylene matrix carbon nanofiber composites were obtained by injection molding after kneading with a batch-type twin-screw kneader. The thermal conductivity of the composites in the thickness direction was evaluated, with particular focus on the effects of carbon nanofiber (CNF) content and filler orientation. The thermal conductivity of the composites increased with increasing CNF content, and was obtained as 3.46 W/(mK) when the CNF content was 50% in weight fraction and the CNFs were highly oriented along the measuring direction of thermal conductivity. This value is approximately seventeenfold higher than that of neat polypropylene.

Synthesis of diamond-like carbon films by nanopulse plasma chemical vapor deposition at subatmospheric pressure

Abstract In this report, we discuss nucleation effects, and characteristics of diamond film synthesized by arc discharge plasma jet chemical vapor deposition in a methane atmosphere with a high growth rate. To observe the internal structure of the diamond film, we cut the diamond film with a YAG laser, polished the cut surface with a diamond film polishing apparatus using a hot metal plate, then observed and analyzed the polished surface. The structure of the diamond film is different between the {100} and {111} sectors; the {100} sector is clear except for marks of step growth, whereas the {111} sector consists of numerous flaky crystallites. The surface ratio of the {100} sector is similar to that of the {111} sector, when the thickness is within 50 μm; however, the proportion of {100} sector increases with increasing distance from the substrate. The crystallinity of the {100} sector is better than that of the {111} sector. The contamination of hydrogen in the {111} growth sector is twice as large as that in the {100} sector. In addition, the effects of surface treatment of the substrate and methane concentration on the surface unevenness and porosity were investigated. Diamond film with small surface unevenness and no porosity is fabricated under fluctuating methane concentrations in the range 3.5%–7%.

Effect of Filler Orientation on Thermal Conductivity of Polypropylene Matrix Carbon Nanofiber Composites

Abstract High-density dislocations (∼5 × 108 cm−2) in diamond crystallites synthesized by a chemical vapour deposition method have been studied by electron microscopy. Most of the dislocations, having the Burgers vector of ½ , are seen undissociated by the weak-beam observation and are often zigzag in shape on a climb-plane. Some dislocations lying on {111} glide planes are dissociated into Shockley partials. The stacking fault energy estimated from the separation of the partials is 290 ± 40 mJm−2, which is substantially the same as that reported for natural diamond. In some crystallites, high-density twins are observed instead of dislocations.

Nucleation effects and characteristics of diamond film grown by arc discharge plasma jet chemical vapor deposition

We investigated the influence of substrate materials on bonding structure of diamond-like carbon (DLC) films, fabricated by filtered cathodic vacuum arc, by using X-ray photoelectron spectroscopy and secondary ion mass spectroscopy. Two kinds of substrate materials, Si and NiFe, were evaluated. The results showed that sp3 ratio of DLC films on NiFe was lower than that on Si by approximately 10%, and implies that the diffusion of Ne and Fe into DLC films inhibits sp3 bonding formation.

Electron microscopy studies of dislocations in diamond synthesized by a cvd method

A surface acoustic wave (SAW) linear motor, which is a kind of ultrasonic motors, has many merits such as thin structure, large force, high speed, precise positioning and so on. On the other hand, wear is one of problems in the motor due to friction drive principle. Diamond-like carbon (DLC) films have been recognized as a wear resistant material. In this research, segment structured DLC films are focused to avoid the DLC property of easy damage. Installation of the films to friction surface of the motor is reported. Measurement result of its driving characteristics is also described.