Diamond synthesis by CO 2 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 CO 2 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.