Study on diamond films with ultra high nucleation density deposited onto alumina, sapphire and quartz

Diamond films with high nucleation density were deposited onto polycrystalline alumina, sapphire and quartz substrates. To achieve high nucleation density, the substrates were ultrasonically abraded with mixed polydispersed slurry, which allows high nucleation density of values up to similar to 5 x 10(10) particles/cm(2). Continuous adherent diamond films were obtained on alumina and quartz for deposition runs from 15 min up to 2 h(for quartz and 4 h (for alumina). After a deposition time of 15 min, the diamond particles density (DPD) on alumina is similar to 4 x 10(9) particles/cm(2) and on quartz is similar to 2 x 10(10) particles/cm(2). Continuous adherent diamond films with high DPD (similar to 10(9) particles/cm(2)) were obtained also on sapphire surface after the abrasion with mixed slurry and 15 min of deposition. However, after longer deposition times, 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 the difference in the 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 the diamond film. This adhesion mechanism, promoted by submicron diamond grain-size, is allowed due to initial high nucleation density. The Raman spectroscopy analysis shows a similar evolution tendency of diamond Raman peak frequency in the diamond films on alumina and quartz: intrinsic stress decreases as deposition time increases. (c) 2004 Elsevier B.V. All rights reserved.