[extropy-chat] Interstellar Dust

[Amara Graps]

Robert Bradbury:

>But the most interesting thing that caught my eye answers a question
>that I think may have come up on the list before though I'm not sure
>whether or not we answered it (perhaps I might have missed it).

>"... Other Fullerenes are also common, particularly C_70, C_76 and
>C_84, and have been found to exist in interstellar dust as well as in
>geological formations on Earth. ..."

>So yes folks there are Fullerenes in space (too bad the references aren't
>cited).

Didn't we talk about this ?  I sent some paper references on
this topic to the list last March. A. Rotundi et al.'s paper
should have appeared in _Fullerenes, Nanotubes and Carbon
Nanostructures_ but I don't know if that is the paper of which
you and others were thinking.

Here is my message again:

http://www.lucifer.com/pipermail/extropy-chat/2004-March/004832.html



>Next question is are there Fullerenes with caged atoms or molecules
>inside???  Now those would be really interesting.

The structures look complicated.. From the text, the authors write:

"A transmission electron microscope study of individual soot grains
forming fluffy carbon particles produced using the arc-discharge
technique revealed close-packed arrangements of single -wall ring
structures with average diameters of 0.7, 1.1, 3.0, 5.5 and 8.2
nanometers."


"Soot Grains. Field emission scanning electron microscope (FESEM)
analyses showed a considerable degree of fusion of individual soot
grains arranged in chain-like aggregates."
[...]
"The soot grains have a typical internal texture of densely packed,
single -wall rings [Figure 2]. In addition to these grains, the ACAR
and ACH2(0.8) samples also contain rare, irregularly-shaped aggregates
of similar rings."

"Single -wall spheres. There is generally no ordering of rings in soot
grains that are thus crystallographically amorphous. Tilting
experiments during TEM imaging confirmed that the rings are hollow
spheres. The ring diameters from 0.7 nm to ~10 nm define the
populations I to IV in Table 2. The one-standard deviations [Table 2]
are similar to the error of measurement (see above) but each
population is accepted as a statistically-relevant distribution of
sphere diameters. We cannot exclude the possibility that each measured
diameter corresponds to a unique hollow carbon sphere. These
individual diameters then defining a continuous range of different
single -wall, hollow spheres. We do not think it was the case although
noting that a similar situation was found [20] for the range of single
-shell carbon nanotube diameters between ~0.7 nm and 1.6 nm that
included two significant peaks at 0.8 nm and 1.05 nm."
[...]
"The overwhelming majority of single -wall structures are spheres but
there are rare ellipsoidal shapes with their longest semi-major axis
parallel to the ultra-thin section [Figure 3]. The ellipsoidal single
-wall rings occur as isolated structures or in small clusters that are
randomly distributed within the amorphous soot grains. Single -wall
spheres can also be organized into rare "bunch-of-grape" domains both
within soot grains and as isolated structures among the other carbon
forms in the samples. Some "bunch-of-grape" 'domains are
cross-sections of small stacks of hollow, parallel-stacked,
ellipsoidal rings. "

"Carbon onions. Other soot grains contain spherical structures ~10 nm
to ~25 nm in diameter that have either a central single -wall sphere,
or a cluster of spheres. Concentric circular fringes without the
proto-fringe structure surround these spheres and clusters. These
unique structures are only a very small fraction of features found in
soot grains. The spacing of these particular fringes corresponds to
those of proto-fringes and single -wall spheres diameters [Table 2].
The origin of the resultant carbon onion domains is uncertain. They
could be a primary feature when condensed single-wall spheres acted as
nucleation centers for condensation of amorphous carbon. Lattice
fringe formation [Table 2] could be an experimental artifact caused by
exposure to the incident electron beam reminiscent of the formation of
nested-fullerenes [21]."


So, I don't know. Alessandra told me that these fullerene structures
are unstable, in any case.

Amara





-- 

***********************************************************************
Amara Graps, PhD
Istituto di Fisica dello Spazio Interplanetario, INAF - ARTOV,
Via del Fosso del Cavaliere, 100, I-00133 Roma, ITALIA
tel: +39-06-4993-4375       |fax:  +39-06-4993-4383
Amara.Graps at ifsi.rm.cnr.it  | http://www.mpi-hd.mpg.de/dustgroup/~graps
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I'M SIGNIFICANT!...screamed the dust speck. -- Calvin