posted on 2017-02-16, 00:00authored byMark W. Kelly, Sarah C. Halliwell, W. Jeff Rodgers, Jason D. Pattle, Jeremy N. Harvey, Michael N. R. Ashfold
Quantum
mechanical and hybrid quantum mechanical/molecular mechanical
cluster models were used to investigate possible reaction mechanisms
whereby gas-phase NHx (x = 0–2), CNHx (x = 0, 1), and OH radicals can add to, and incorporate in, a C–C
dimer bond on the C(100):H 2 × 1 diamond surface during chemical
vapor deposition (CVD) from microwave-activated C/H containing gas
mixtures containing trace amounts of added N or O. Three N incorporation
routes are identified, initiated by N, NH, and CN(H) addition to a
surface radical site, whereas only OH addition was considered as the
precursor to O incorporation. Each is shown to proceed via a ring-opening/ring-closing
reaction mechanism analogous to that identified previously for the
case of CH3 addition (and CH2 incorporation)
in diamond growth from a pure C/H plasma. On the basis of the relative
abundances of N atoms and NH radicals close to the growing diamond
surface, the former is identified as the more probable carrier of
the N atoms appearing in CVD grown diamond, but fast H-shifting reactions
postaddition encourage the view that NH is the more probable migrating
and incorporating species. CN radical addition is deemed less probable
but remains an intriguing prospect, since, if the ring-closed structure
is reached, this mechanism has the effect of adding two heavy atoms,
with the N atom sitting above the current growth layer and thus offering
a potential nucleation site for next-layer growth.