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5% error of measurement. The carbon nature for selected carbyne grains
with a hexagonal unit cell based on a c-axis electron diffraction pattern was
established by electron microprobe analyses [14], negative ion spectroscopy
[21] and energy dispersive spectroscopy (EDS) in the TEM for in situ
determination of impurity elements [24]. Ideally, all crystallographic and
chemical properties are obtained on the same carbyne grain, including
sp-hybridized bonds using electron energy-loss spectroscopy, which is possi-
ble on grains of a few nanometers using state-of-the-art HRTEM [20,60],
and new techniques such as scanning transmission x-ray microscopy and
micro-Raman and infrared micro-spectroscopy [61].
Since the first report of carbynes in meteorites, the simple question:
Carbyne forms of carbon: Do they exist? [62], initiated an enduring
discussion on the state of natural extraterrestrial carbynes. There is no need
to recapitulate this particular chapter in carbyne history [1] except to say
that Smith and Buseck [62] justifiably questioned the robustness of carbyne
identifications. Vesiculation and amorphization are known experimental
artifacts during HRTEM analysis of single-crystal
layer silicate grains
(
Figure 16.3
). Similar behavior for carbynes cannot be a diagnostic feature
unless a putative carbyne grain is first identified as a pure elemental carbon
solid. It was confusing that EDS spectra for representative carbyne crystals
showed distinct Al and Si peaks [
Reference 24
, Figure 5) and yet were
apparently not kaolinite, a layer silicate mineral [60,63]. It was recognized
FIGURE 16.3
Transmission electron microscope (TEM) image showing seven hexa-
gonal kaolinite, [Al
2
Si
2
O
5
(OH)
4
] single-crystal grains in IDP U2011C2. The crystals
show the vesicular texture of heated kaolinite, for example when exposed to the
incident electron beam in the TEM. An embedding epoxy (gray background) was
applied to prepare this ultrathin section (modified after Rietmeijer and Mackinnon).
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