  45-degree rotated epitaxial diamond nucleation on both (001) and {111} planes
of a silicon substrate was observed using chemical vapor deposition with
nucleation enhancement by electron emission. The epitaxial relationship between
diamond and Si is D(001)//Si(001) and D<100>//Si<110> in both cases. While the
case of diamond nucleation on Si(001) may be explained in Verwoerd's model, the
other case has no theoretical model as yet. The as-grown diamond was
characterized by scanning electron microscopy and Raman spectroscopy. It is
speculated that a suitable combination of low temperature and low CH_4
concentration leading to low nucleation rate favors the 45-degree rotated
epitaxy over those in parallel registry. This observation sheds light on the
mechanism of epitaxy of diamond on Si substrates, and has great significance in
parameter control in achieving single-crystal epitaxial diamond films.
