Chemical vapor infiltration (CVI) — Part II: Infiltration of porous substrates with diamond by using a new designed hot-filament plant

We designed a new hot-filament plant which features some new operating states for chemical vapor infiltration (CVI) with diamond. Most characteristic for the new hot-filament plant is the possibility of a forced flow of the activated gas species through a porous substrate. Separate feeding of hydrogen, methane and oxygen above or underneath the substrate ensures the production of pertinent carbon growth species like CH3 directly at or in the substrate or rather in the pore. We infiltrated porous substrates by using several operating states and compared the results with standard processes. For these first experiments we have set the addition of oxygen aside, which was viable for the infiltration experiments described in Part I of the paper. In order to achieve good infiltration results it was necessary to use very low methane concentrations between 0.2% and 0.3%. We were able to infiltrate at high growth rates (> 0.5 μm/h) combined with a good diamond quality (> 90%). Moreover it was possible to alleviate the “bottleneck” effect which we described in Part I of the paper. Raman spectroscopy and SEM were used to characterize the deposited or rather infiltrated diamond.