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.

References:

• R. Deng, G. Littlefield, O. Echt,
  Photoexcited C60: Fragmentation and Delayed Ionization,
  Z.Physik D 40,  355 - 360 (1997).
• M. Arndt, O. Nairz, J. Voss-Andreae, C. Keller, G. van der Zouw, A. Zeilinger,
  Wave-particle duality of C60 molecules,
  Nature 401,  680-682 (1999).
• O. Nairz, M. Arndt, A. Zeilinger,
  Experimental challenges in fullerene interferometry,
  Journal of Modern Optics 47,  2811-2821 (2000).
• J. O. Johansson and E. E. B. Campbell
  Probing excited electronic states and ionisation mechanisms of fullerenes
  Chem. Soc. Rev., 42, 5661 (2013)