<I>In Situ</I> Observation of Diamond Gasification and the Crystallographic Relationship of Graphite Formed on the Surface of Diamond

Abstract

Recently, a property of diamond as a semiconductor is focused on by many researchers. For the mass production, it is important to develop the manufacturing process. As it is thought that the ionic milling process has limitations, the application of gasification reactions with oxidizing gases such as CO 2 , H 2 O and O 2 is the best option.In this study, reaction behaviors of diamond at temperatures of more than 1273 K were investigated under a wide range of oxygen potentials, and the crystallographic relationship from diamond to graphite was clarified.A graphite layer was formed on the surface of diamond under both Ar gas with an oxygen potential of less than 100 ppm, and a CO 2 -Ar mixture (30 vol%). The Raman spectrum consisted of the amorphous carbon and graphite. However, the graphite formed differed from ordinary graphite in the reactivity. Furthermore, the crystallographic relationship between diamond and graphite was determined to be ð111Þ D == ð002Þ G .

Kinetic Analysis of the Gasification of Diamond

“…Figure 2(c) shows the image from the optical microscope after the experiment at 1773 K under an argon atmosphere (P O2 < 20 ppm). The slightly oxidized surface, which was confirmed as a kind of graphite layer, 8) can be observed. Figure 2(d) shows the diamond image after the experiment at 1473 K under Ar-30 vol%CO 2 for 1800 s. The gasification degree seen in Fig.…”

“…16. As mentioned above and in reference, 8) the original diamond surface had many triangular defects consisting of {111}. When the surface was gasified, a pit formed at the center of the triangle as shown in Fig.…”

“…The diamond was not spherical in shape. The surface of the natural diamond consisted of {111} as the habit plane; 8) the length of an edge of the equilateral triangle was about 750 mm. Figure 2 shows the morphology of the diamond samples used before and after the experiment.…”

“…The present authors carried out the gasification of natural diamond 8) and clarified the behavior of gasification, both under a low oxygen partial pressure in an argon (<20 ppm) and under an argon-CO 2 mixture, specifically Ar-30 vol%CO 2 . The gasification behaviors of diamond were different from the reaction gas composition; however, the transformation from diamond to graphite during gasification was the same.…”

“…The crystallographic orientation between the diamond and the formed graphite was presented in the previous study. 8) As mentioned above, there have been many studies on the gasification of various kinds of carbon. However, no gasification study has been conducted for the diamond.…”