Yoichi Hirose

Misting-free diamond surface created by sheet electron beam irradiation

We developed a diamond surface that does not mist near the room temperature under a saturated humidity atmosphere, by sheet electron beam irradiation (SEBI) treatment. SEBI treatment decreased the time to clear vision of the diamond surface. Following SEBI treatment for 1.91 s (= 0.72 MGy) to a diamond surface, the time to clear vision was less than 2 s. The effective duration time was a few hours. Based on the results of the size distribution of the drops on the misting-free diamond surface following blowing for 3 s, we proposed an explanation for the short time to clear vision of the diamond surface treated by SEBI.

Synthesis and growth mechanism of flattened diamond crystals by chemical vapor deposition

Abstract Flattened diamond crystals were synthesized under high oxygen gas concentration and low substrate temperature conditions using the oxy-acetylene flame method. The flattened morphology appeared because preferential growth occurred along side faces owing to the presence of twin re-entrant corners. This “re-entrant corner effect” can be expected only under the condition of a low two-dimensional nucleation rate. Therefore, the flattened diamond crystals are synthesized only under the condition of a high oxygen gas concentration because when the oxygen to carbon ratio is increased, the two-dimensional nucleation rate is suppressed by the decrease in supersaturation of the source gas. Also, the twin re-entrant corners are formed as hexagonal diamond nuclei moving on the substrate coalesce together.

Growth mechanism of flattened diamond crystals synthesized by chemical vapor deposition

Abstract Flattened diamond crystals were synthesized under high oxygen gas concentration and low substrate temperature conditions. Preferential growth occurred along side faces due to the presence of twin re-entrant corners. The flattened morphology appears because a {111} face is oriented parallel to the substrate surface due to texture growth in the early stage of nucleation. Scanning electron microscopy (SEM) observations and Raman spectroscopy measurements indicate that the flattened diamond crystals show good crystallinity and high quality.

Etching of Nondiamond Carbon in Diamond Thin Films Synthesized by Hot-Filament Chemical Vapor Deposition with Ultraviolet Irradiation.

The etching of nondiamond carbon present in diamond thin films which were grown using the CVD method has been studied with UV irradiation in air. The etching of nondiamond carbon was accelerated by UV irradiation, and hence the temperature required was lowered from 600 °C to 250 °C. On the other hand, the temperature required to etch diamond in the film did not change even with UV irradiation. Selective etching of nondiamond carbon in diamond thin films can be achieved at temperatures between 250 °C and 550 °C. These etching effects are caused by excited atomic oxygen produced by the UV irradiation and not by the direct excitation of the film by UV irradiation.

Effect of Oxidation due to Ultraviolet-Light Irradiation on Diamond Thin Films Synthesized by Hot-Filament Chemical Vapor Deposition

The effect of oxidation due to ultraviolet (UV) irradiation in air on diamond thin film synthesized by hot-filament chemical vapor deposition (CVD) has been investigated. A low-pressure mercury lamp is used as the UV light source. With UV irradiation, removal of graphite contained in the film begins at a temperature of 350° C due to the oxidation. This temperature is 250° C lower than that reported to yield the same effect without UV irradiation. UV irradiation enables the selective removal of graphite while maintaining the idiomorphic structure of diamond. It is clarified that direct UV irradiation on the film is critical in this process.