Chemistry Reference
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FIGURE 16.4
Transmission electron microscope (TEM) image of a cluster of thin
hexagonal plates formed after thermal annealing (8 h at 1073K) in a sample of
condensed carbons that included fullerenes in amorphous soot grains, carbon nano-
tubes and anions, amorphous carbon, poorly graphitized carbon loops and pre-
graphitic carbon ribbons [4].
in the form of [C
C] and/or [C
¼
C] units, or as larger (-C
C
C
C-)
n
,
and/or (
)
n
, chains, these units and chains incorporated in an
amorphous (sp
2
) carbon matrix might bridge two graphene sheets during
thermal annealing to form hexagonal carbyne crystals.
¼
C
¼
C
¼
C
¼
16.10 A NEW CARBYNE STRUCTURE
The c-axis dimension of graphite defines the separation of two parallel
graphene sheets determined by the size of the carbon atoms and inter-atomic
interactions between stacked carbon atoms in a hexagonal arrangement.
Increasing the distance between two adjacent graphene sheets could be
achieved by ''in-plane'' addition of heteroatoms (H, N, O, S). The carbyne
c
0
dimension appears to be determined by the length of a linear chain of 6 up
to 12 carbon atoms [51]. An interesting situation emerges when two adjacent
graphene units were to be bridged by a polyyne or cumulene chain
determining the separation of the units. Such a chain connecting to the
center of each sheet would lead to an ''empty'' crystal without a physical
meaning. For the sake of argument, assuming a molecular chain of eight
carbon atoms would yield a carbon solid with twenty C atoms. All carbynes
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