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How much graphene in space?
Qi Li1,2, Aigen Li2, B W Jiang1
1Department of Astronomy, Beijing Normal University, Beijing 100875, China.
Monthly Notices of the Royal Astronomical Society
|November 26, 2019
Summary
The interstellar medium likely contains very little graphene, with abundance limits significantly lower than previously estimated. Researchers also found no evidence for C24 molecules in interstellar dust, setting new upper limits on their presence.
Area of Science:
- Astrochemistry
- Materials Science
- Astrophysics
Background:
- Graphene's potential presence in the interstellar medium (ISM) is debated.
- Previous estimates of interstellar graphene abundance relied on spectroscopic ellipsometry (SE) data.
Purpose of the Study:
- To investigate the abundance of graphene and C24 in the ISM.
- To refine upper limits on interstellar graphene using electron energy loss spectroscopy (EELS).
Main Methods:
- Comparing interstellar extinction curves with graphene's UV absorption calculated from EELS-derived dielectric functions.
- Analyzing infrared emission spectra for characteristic C24 vibrational bands.
Main Results:
- The interstellar extinction curve lacks graphene's characteristic π-π* electronic interband transition.
- An upper limit of 10^-7 C/H was placed on interstellar graphene abundance, 3 times lower than SE-based estimates.
- No characteristic vibrational bands of C24 were detected in observed infrared emission.
Conclusions:
- The interstellar graphene abundance is significantly constrained, likely being very low.
- The absence of C24 vibrational features sets a new upper limit on its interstellar abundance.
- EELS provides more reliable dielectric functions for graphene than SE due to less surface contamination.
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