G. Jungnickel et al., GRAPHITIZATION EFFECTS ON DIAMOND SURFACES AND THE DIAMOND GRAPHITE INTERFACE, Physica status solidi. a, Applied research, 154(1), 1996, pp. 109-125
Graphitic layers have previously been conjectured to play an active ro
le in diamond nucleation by Lambrecht et al. and may also be involved
in a mechanism for homoepitaxial diamond growth since the surfaces of
diamond may partially graphitize under high-temperature conditions typ
ical of growth processes. Recent molecular dynamics simulations of the
diamond {111} surface, briefly reviewed and discussed here, indicate
a progressive graphitization with increasing temperature which is stro
ngly facilitated by any kind of surface perturbation or roughness such
as step-like adsorbates. Here we show specifically that also twin bou
ndaries promote graphitization. The process of debonding of the surfac
e layer which is a simple displacive motion of the outer layer is also
shown to be closely related to the delamination of the tetrahedrally
bonded icosahedral C-100 molecule into two concentric C-20 and (fuller
ene-like) C-80 fragments. In contrast, the tetrahedrally bonded icosah
edral C-300 molecule which contains one more concentric shell, does no
t spontaneously graphitize into a bucky onion (consisting of concentri
c C-80 and C-240 fullerenes) although the latter has lower energy. Pro
gressive graphitization at a surface towards deeper lagers before the
top layer is delaminated can occur under certain conditions and then m
ay lead to graphite/diamond prism plane interfaces similar to those pr
eviously investigated in connection with nucleation. The structural st
ability of the prism plane interface between graphite and diamond is r
e-investigated here. While the initial calculations with a classical p
otential underestimated the interface energy: the structural stability
of the models previously presented is confirmed by the present quantu
m mechanical simulations.