Fullerene detection by Thermionic Emission

Fullerenes are particularly stable carbon molecules which can be heated to surprisingly high microcanonical temperatures for a short period of time. This is the basis for a trick to photo-ionize fullerene, essentially back-ground free in high vacuum.

Every C60 molecule is internally heated by about 130 K per absorbed photon. After absorption of 30-50 green photons, or 60-100 eV of internal energy, the energy distributed in internal vibrations suffices to induce an electronic excitaion into the ionization continuum beyond 7.6 eV above the ground state.

A tightly focused green laser beam thus allows us to ionize fullerenes with high mass-selectivity, even without the need for any mass spectrometer,with about 10% detection efficiency and with high spatial resolution (a few µm).

This was the basis for the detection of the successful first diffraction of C60 at a nanomechanical grating.


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