Toshiyuki Yasuhara

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.

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

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.

Characteristics of Diamond-Like Carbon Films Deposited on Polymer Dental Materials

Characterizations of diamond-like carbon (DLC) deposited on a polymer artificial tooth were performed. DLC films were deposited on dental parts made of poly(methyl methacrylate) (PMMA) resin by dc-pulse plasma chemical vapor deposition (CVD) from methane. Wear resistance test results revealed that a DLC-coated resin tooth has a very high wear resistance against tooth brushing, and endures 24 h brushing without a marked weight decrease. Cell cultivation test results show that DLC plays an important role in preventing cell death. Moreover, a biocompatibility test using a rabbit revealed that a connective tissue in the vicinity of DLC-coated PMMA is significantly thinner than that of noncoated PMMA. The numbers of inflammatory cells in the vicinity of DLC-coated and noncoated surfaces are 0 and 508 cells/mm2, respectively. These results led us to conclude that DLC films are an excellent material for use as the coating of a polymer artificial tooth in terms of not only high wear resistance but also biocompatibility.

Micro Free-Form Fabrication of Aluminum Nitride and Zinc Oxide

Selective growth of aluminum nitride (AlN) and zinc oxide (ZnO) has been performed by an Ar-laser-enhanced reactive vapor deposition method on Si (100) substrates. The substrate was selectively heated by laser irradiation. Al and Zn were evaporated from Ta crucibles by an electron gun in NH3 and O2 atmospheres, respectively. The metal vapor reacted with atmospheric gas on the substrate surface due to laser heating, when the temperature of the laser-irradiated part was higher than 450°C for AlN and 230°C for ZnO. Not only the substrate temperature, but also the thickness of the Al and Zn layers, which are deposited during the time interval between the first laser irradiation and subsequent laser irradiation, was an important factor for realizing the selective growth. The critical thickness was found to be 0.2 nm and 6 nm for AlN and ZnO, respectively. Two-dimensional selective growth and three-dimensional micro free-form fabrication of AlN were performed under these conditions using a two-dimensional laser scanning setup. The AlN layer was successfully deposited in accordance with a laser drawing pattern, even when the drawing pattern changed during synthesis.

Detecting Method of Bulk Defects in DLC Films Using Light Scattering

Diamond-like carbon (DLC) film has various micro-size defects like pinhole, void and particle. When DLC film is exposed to white light, light is scattered in all direction at defects in DLC film. In this paper, defects in DLC film are detected by observing scattering light from defects under dark-field microscope. DLC film has wavelength dependence of transmittance. Therefore, using its wavelength dependence allows to separate surface and inside defects of DLC film. This paper describes development of bulk defects detecting system using optical filtering and scattering light detecting. Bulk defects of DLC films were successfully separated into surface defects and inside defects. This detecting method of defect is nondestructive and easy, and applicable to DLC films as well as other coating films.