|
Atom-probe
tomographic analyses of presolar silicon carbide grains and meteoritic
nanodiamonds - first results on silicon carbide
Heck P. R., Pellin M. J., Davis A. M., Martin I.,
Renaud L., Benbalagh R., Isheim D., Seidman D. N., Hiller J., Stephan
T., Lewis R. S., Savina M. R., Mane A., Elam J., Stadermann F. J., Zhao
X., Daulton T. L., and Amari S. (2010)
Lunar Planet. Sci. XLI, Abstract #2112.
ABSTRACT
The chemistry of presolar grains is studied with analytical
instruments that provide very high spatial resolution, such as the
NanoSIMS ion microprobe (~50 nm spatial resolution). Even this
resolution is not sufficient to analyze, e.g., the isotopic composition
of small subgrains (diam. of a few to tens of nm) within presolar
grains or individual meteoritic nanodiamonds (avg. diam. ~3 nm). A
knowledge of carbon isotope ratios in individual meteoritic
nanodiamonds would help to resolve a fundamental question about the
origin of nanodiamonds: What fraction of the nanodiamonds formed in the
solar nebula and what fraction is presolar? Such small samples need to
be studied with sub-nm spatial resolution. Chemical compositions at
sub-nm resolution can be acquired with an atom probe tomograph (APT)
which is basically a field-ion microscope coupled to a time-of-flight
mass spectrometer. The latest generation of APTs use
pulsed-laser-assisted field ionization and evaporation and have been
successful in analyzing non-metallic samples. Synthetic SiC whiskers
and synthetic diamond have been already successfully analyzed by APT.
Reviews of modern atom probes are available. Here, we present first APT
results of an atom-by-atom study of several presolar SiC grains.
|