  Growth of $>$100 $\mu$m thick diamond layer adherent on aluminium nitride is
presented in this work. While thick films failed to adhere on untreated AlN
films, hydrogen/nitrogen plasma treated AlN films retained the thick diamond
layers. Clear differences in zeta potential measurement confirms the surface
modification due to hydrogen/nitrogen plasma treatment. Areal Raman maps showed
an increase in non-diamond carbon in the initial layers of diamond grown on
pre-treated AlN. The presence of non-diamond carbon has minimal effect on the
interface between diamond and AlN. The surfaces studied with x-ray
photoelectron spectroscopy (XPS) revealed a clear distinction between
pre-treated and untreated samples. The surface aluminium goes from nitrogen
rich environment to an oxygen rich environment after pre-treatment. Cross
section transmission electron microscopy shows a clean interface between
diamond and AlN. Thermal barrier resistance between diamond and AlN was found
to be in the range of 16 m$^2$K/GW which is a large improvement on the current
state-of-the-art.
