Evolution and properties of adherent diamond films with ultra high nucleation density deposited onto alumina

In this work, we report on adherent diamond films with thickness of up to 4.5 mum grown on polycrystalline alumina substrates. Prior to deposition, alumina substrates were ultrasonically abraded with mixed poly-disperse slurry that allows high nucleation density of values up to similar to5 x 10(10) particles/cm(2). It was estimated that the minimal film thickness achieved for continuous films was similar to320 nm, obtained after a deposition time of 15 min with diamond particles density (DPD) of similar to4 x 10(9) particles/cm,. Continuous adherent diamond films with high DPD (similar to10(9) particles/cm(2)) were obtained also on sapphire surface after abrasion with mixed slurry and IS min of deposition. However, after longer deposition time, diamond films peeled off from the substrates during cooling. The poor adhesion between the diamond and sapphire is attributed to the weak interface interaction between the film and the substrate and to difference in coefficient of thermal expansion. On the other hand, it is suggested that the reason for good adhesion between diamond film and alumina substrate is that high carbon diffusivity onto alumina grain boundaries allows strong touch-points at the grooves of alumina grains, and this prevents the delamination of diamond film. This adhesion mechanism, promoted by sub-micron diamond grain-size, is allowed by initial high nucleation density. The surface properties, phase composition and microstructure of the diamond films deposited onto alumina were examined by electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and high-resolution scanning electron microscopy (HR-SEM). The residual stress in the diamond films was evaluated by diamond Raman peak position and compared to a theoretical model with good agreement. Due to the sub-micron grain-size, the intrinsic tensile stress is high enough to partially compensate the thermal compressive stress, especially in diamond films with thickness lower than 1 mum. (C) 2004 Elsevier B.V. All rights reserved.