  Artificial diamond is created by exposing graphite to pressures on the order
of 10GPa and temperatures of about 2000 K. Here, we provide evidence that the
pressure exerted by the tip of an atomic force microscope onto graphene over
the carbon buffer layer of silicon carbide can lead to a temporary transition
of graphite to diamond on the atomic scale. This transition is accompanied by
local rehybridization from an sp2-bonded to an sp3-bonded local structure. We
perform atomic force microscopy with a CO terminated tip to image graphene and
to induce the structural transition. Experimental evidence for this transition
is provided by the observation of third harmonics in the cantilever oscillation
and an asysmmetry between the two basis atoms of the graphene lattice that
unfolds for large repulsive tip forces. Density functional theory (DFT)
calculations show that inducing a simultaneous transformation of mesoscale
sheets of graphite into diamond by pushing with one CO tip on every 1x1 unit
cell requires a pressure of 41GPa. However, the average pressure reduces to
36GPa for a graphene mesh with a 2x2 unit cell and to 20GPa for a graphene mesh
with a 2 sqrt(3) x 2 sqrt(3) unit cell. From this observation of decreased
transition pressures for larger unit cells, it appears reasonable that a large
enough unit cell would indeed require 10GPa to induce the transition. We thus
propose that the artificial diamond creation does not involve the simultaneous
transition of large sheets of graphite into diamond simultaneously, but by
local transitions that occur sequentially.
