Diamond single crystal growth in hot filament CVD

The synthesis of diamond crystals is of particular interest due to the material's outstanding physical and mechanical properties. In hot filament CVD (HFCVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized without the use of monocrystalline substrates. These CVD parameters are far beyond growth conditions for HFCVD diamond coating processes. Extremely low methane contents in the feed gas along with high substrate temperatures allow single diamond nuclei of a sufficiently large size to grow stabile. Crystals up to 80 μm in diameter were successfully synthesized. The morphology of the crystals is cubo-octaedric. According to our proposed growth model [S. Schwarz, C. Rottmair, J. Hirmke, S. Rosiwal, R.F. Singer, J. Cryst. Growth 271 (2004) 425.], the observed growth defects are primarily caused by the gas phase conditions during the CVD process. The aim of this work was to exclude a further possible formation of growth defects due to the employed diamond seed particles. The early growth stage was investigated by tracking distinct monocrystalline diamond seeds. It is shown that cubo-octaedric crystals with CVD typical smooth faces of high quality can be grown from micrometer-sized particles. Seed imperfections are therefore not considered as a major reason for growth defects of the larger crystals.