Single molecular spectroscopy: identification of individual fullerene molecules.

We report the molecule-by-molecule spectroscopy of individual fullerenes by means of electron spectroscopy based on scanning transmission electron microscopy. Electron energy-loss fine structure analysis of carbon 1s absorption spectra is used to discriminate carbon allotropes with known symmetries. C(60) and C(70) molecules randomly stored inside carbon nanotubes are successfully identified at a single-molecular basis. We show that a single molecule impurity is detectable, allowing the recognition of an unexpected contaminant molecule with a different symmetry. Molecules inside carbon nanotubes thus preserve their intact molecular symmetry. In contrast, molecules anchored at or sandwiched between atomic BN layers show spectral modifications possibly due to a largely degraded structural symmetry. Moreover, by comparing the spectrum from a single C(60) molecule and its molecular crystal, we find hints of the influence of solid-state effects on its electronic structure.