Fullerene Propellants

sanman

I'd read about the investigation into using C60 fullerenes as propellant in an ion engine, due to their high molecular weight and low ionization energy:

http://linkinghub.elsevier.com/retri...94576502001157

By this reasoning, shouldn't buckyonions be even better candidates as propellant, since they have many layers, each of which would be influenced/polarized by the ionization/polarization of the adjacent layers?

Furthermore, I'd also read about Silicon fullerenes, like Si60, which not only have even higher molecular weight, but also have high magnetic spin properties as well.

http://www3.interscience.wiley.com/j...13554/abstract

Wouldn't it be possible to use Silicon fullerenes as propellant under Lorentz force, for even better thrust performance?
What would be the main challenges or obstacles to doing so?