Noribumi Kikuchi

TEM observations of diamond films prepared by microwave plasma CVD

Abstract Diamond films synthesized by microwave plasma chemical vapor deposition were studied using a high-resolution transmission electron microscope. The concentration of the reactant gas, CH 4 , was varied from 0.5 to 10% and lattice images of diamond crystals were obtained for all specimens. It was found that an increase of CH 4 concentration raised both the density of twin-boundaries and stacking faults, but reduced the grain size. In CH 4 concentrations higher than 5%, the grain size was 10–30 nm and other phases such as graphite or amorphous carbon were not detected in the grain. The grain boundaries were 0.5–1 nm in width which correspond to a few carbon atoms. These carbon atoms on grain-boundaries seemed to take a non-crystalline structure because they did not show lattice image. From results of Raman spectra, X-ray diffraction, and transmission electron microscopy observations of these films, it was concluded that the films synthesized at high CH 4 concentration consisted of fine-grained diamonds and that the broad peaks of Raman spectra are mainly due to carbon atoms on grain boundaries.

Diamond synthesis by CO2 laser irradiation

Abstract The laser-beam-induced phase transformation of graphite, amorphous carbon and glassy carbon to diamond was investigated. A selection of these carbon sources was irradiated and cut by a continuous wave CO2 laser in a vacuum chamber which was filled with helium at a pressure of 500 Torr. In vaporized fine powder from these plates, diamond, graphite, chaoite and amorphous carbon were detected. Some craters with average diameter 0.05 mm were observed on the surface of the glassy carbon plate near the cutting edges and their number increased with holding time at room temperature. At the bottom of these craters, fine powder with average size 1 μm was seen and identified as crystalline diamonds by electron beam diffraction and laser Raman spectroscopy. The number of craters on the glassy carbon plate increased progressively for 3 years after irradiation and the amount of synthesized diamond powder increased. This was not observed for other carbon sources such as graphite and amorphous carbon. From these results, we can conclude that glassy carbon is the preferred starting material for diamond synthesis by laser irradiation.

Fabrication of Diamond Membranes for X-Ray Masks by Hot-Filament Method

Diamond thin films have been grown on a Si substrate by a hot-filament method with mixtures of CH4 and H2, and properties such as stress and optical transmittance were investigated for free-standing membrane films as a function of methane concentration (0.5-2.0%) and deposition pressure (8-80 Torr). Ellipsometric and Raman scattering measurements were also carried out to evaluate the film structure, and graphite and void components. It has been found that the loss in the optical transparency is mainly due to light scattering at the surface. It is also shown that boron doping is useful for decreasing the film resistivity, which is advantageous for electron beam (EB) writing and inspections.

Diamond Coated Inserts : Characteristics and Performance

Abstract Mitsubishi Materials Corporation had announced to sell mass produced diamond coated inserts named DC46 in October 1990. These throw away inserts are made of cemented carbide substrates and thin diamond layers of about 3-5 Um. Now, they are widely being used and have favorable reactions from many users in Japan. In machining of aluminum, copper, graphite and other nonferrous materials, tool life of DC46 is 3 to 18 times longer than these of uncoated cemented carbide inserts and sintered diamond inserts. Especially, in face milling of cylinder heads of automobile engines, tool life of DC46 is 18 times longer than that of uncoated inserts. Results of many other recent machining factorys tests of DC46 are also to be presented.