Composition profiles and adhesion evaluation of conductive diamond coatings on dielectric ceramics

Sintered silicon nitride (Si3N4) ceramic substrates were investigated as dielectric substrates for the growth of metal-like boron-doped nanocrystalline diamond (NCD) and microcrystalline diamond coatings via the Hot Filament Chemical Vapor Deposition (HFCVD) technique. The structural, electrical and chemical properties of both the ceramic substrates and the diamond coatings may potentiate their applicability in particular in harsh environments and highly demanding situations. Boron doping was achieved via a boron oxide solution in ethanol dragged into the reaction chamber with argon. The coatings were characterized by scanning electron microscopy, UV mu-Raman scattering. X-ray diffraction, time-of-flight secondary ion mass spectroscopy, Brale indentation for adhesion evaluation and two-point contact probe for resistivity measurements. The HFCVD technique led to a maximal growth rate of about 1 mu m/h. Several metal-like boron doped diamond coatings were obtained. It was found that at lower substrate temperature, lower system pressure and higher methane concentration, the resistivity of the conducting NCD coatings is about 3 orders of magnitude higher when compared with samples obtained with higher substrate temperature, higher system pressure and lower methane concentration. Nevertheless, for every metal-like boron-doped coating the use of the Si3N4 ceramic substrate guaranteed a superior adhesion level. (C) 2012 Elsevier B.V. All rights reserved.