Nanocrystalline diamond thin film has been deposited on a graphite substrate by hot filament chemical vapor deposition system. The characteristics of diamond thin film growth on a graphite sheet were evaluated depending on the pretreatment methods which increase the nucleation density. Four kinds of pretreatments were studied including mechanical abrasion by nano-diamond powders, ultrasonication of graphite in solvents with nano-diamond powder suspension, electrophoretic deposition, and pretreatment with polyethyleneimine (PEI) to change the surface polarity, allowing the adsorption of negatively charged diamond particles onto the substrate surface. Electrophoresis and PEI pretreatment methods were found to be favorable of the diamond deposition to the graphite sheet. The serial process of the PEI-pretreatment and immersion into acetone solution of diamond nano-powders was concluded as an optimal condition, resulting in 100% film coverage of diamond film with the average grain size of 0.7-0.8 μm on the graphite sheet. It can be suggested that the diamond film deposited on graphite could replace current SiC deposited graphite carrier in MOCVD process.

Keywords: Nanocrystalline diamond (NCD), Substrate pretreatments method, PEI Pretreatment.