From: James Rogers (jamesr@best.com)
Date: Sun Mar 02 1997 - 21:25:14 MST
At 07:55 PM 3/2/97 +0100, Eugene Leitl wrote:
>
>It is difficult to denote a boundary between all the carbon allotropes.
>Diamond is easy, as is graphite: the sheets are planar. The most perfect
>graphite brand is HOPG (highly ordered pyro graphite, used as SPM
>standard substrate, and in xray monochromators), whereas the carbon
>in soot has a semimorphous, turbostratic order of graphite sheets.
>Buckyballs are easy to spot, but what are buckytubes? I don't think
>one can call them graphite, since curvature of the concentric sheets is
>quite large.
>
Buckyballs and bucky tubes are chemically more diamond-like than anything.
The distinction between diamond and graphite is not the shape of the
crystal/molecular structure, but the bond hybridization between atoms.
Diamond is pure sp3 while pure graphite is sp2. Bucky-* allotropes are
composed of sp3 type bonds like diamond, but have dangling single bonds
which allow the carbon atoms to connect in a fashion similar to sp2 carbon
structures. The major bonus in all this, especially in the case of
buckytubes, is that you get all the flexibility of a planar allotrope, but
the strength and stability of sp3 bonds.
Carbon atoms strongly resist conformations outside of their normal
tetrahedral bond distribution (sp3) which is the reason they don't normally
form planar surfaces that occur so frequently with sp2 hybridization. Bucky
allotropes are larger-scale carbon structures that maintain enough curvature
to generate minimal stress on the sp3 bonds, while giving a chemical
appearance of a nearly planar structure.
-James Rogers
jamesr@best.com
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