Abstract

CVD (Chemical Vapor Deposition) diamond deposition on different materials requires surface treatment such as diamond particles seeding on the substrate dispersed in an appropriate solvent by using ultrasonic agitation. On the other hand, seeding process by electrostatic attraction of nanodiamond particle have produced films with higher nucleation density compared to that obtained from ultrasonic treatment. In addition, nucleation and growth of micro/nanocrystalline boron doped diamond films (BDD/NBDD) on titanium (Ti) substrates represent a complex process, mainly due to the poor film adhesion related to the difference in the thermal expansion coefficients between the film and the substrate. Thus, the substrate morphology associated to the seeding process can be determinant for this adhesion. In this context, the adhesion of BDD and NBDD films on Ti substrate was systematically considered in five different Ti surface roughness associated to two different seeding processes: ultrasonic agitation with 0.25μm diamond particle and electrostatic seeding with 4nm diamond particle in potassium chloride. Thus, twenty different diamond film sample sets were grown by CVD technique following the combinations of BDD and NBDD morphologies, Ti roughnesses, and seeding methodologies. The samples were characterized by scanning electron microscopy, Raman scattering spectroscopy, and X-ray diffraction (XRD). The adhesion tests were performed by the Rockweel hardness test according to VDI 3198. The results showed that the BDD and NBDD films grown with electrostatic seeding with 4nm diamond particle presented the best adhesion regardless of substrate roughness while only the Ti substrates with higher roughness presented good adhesion for ultrasonic agitation pre-treatment with 0.25μm diamond particle. These results indicate that the electrostatic seeding pre-treatment associated with greater surface roughness have an important role in improving diamond films adhesion for the two studied morphologies.

Keywords: Micro/nanocrystalline boron doped diamond; HFCVD; Diamond seeding; Titanium; Adhesion