  We present an experimental study on the etching of detonation nanodiamond
(DND) seeds during typical microwave chemical vapor deposition (MWCVD)
conditions leading to ultra-thin diamond film formation, which is fundamental
for many technological applications. The temporal evolution of the surface
density of seeds on Si(100) substrate has been assessed by scanning electron
microscopy (SEM). The resulting kinetics have been explained in the framework
of a model based on the effect of particle size, according to the Young-Laplace
equation, on both chemical potential of carbon atoms in DND and activation
energy of reaction. We found that seeds with size smaller than a critical
radius, r*, are etched away while those greater than r* can grow. Finally, the
model allows to estimate the rate coefficients for growth and etching from the
experimental kinetics.
