Abstract
Heteroepitaxial diamond films are deposited on sapphire substrate without intermediate layer in a hot-filament chemical vapor deposition. A distance between filament and substrate, nitrogen concentrations, and filament current are three parameters with different pretreatment methods. Pretreatment methods include diamond scratching, ultrasonic abrasion and electrophoresis by diamond powders. Since the thermal expansion coefficient of sapphire is about three times higher than that of diamond, good adhesion between diamond film and sapphire substrate without intermediate layer is very hard to obtain. From the experimental results, the higher adhesion between diamond film and sapphire substrate came from the pretreatment of electrophoresis by diamond powder. For nitrogen addition, some nitrogen improved the adhesion, but too much nitrogen inhibited diamond film deposition. The optimal adhesion were obtained from the current of 40 A with a distance between filament and sapphire of 5 mm. More than 90% diamond film remained on sapphire substrate.