Ultraviolet photoelectron spectra ofC82andKxC82

Abstract

Photoelectron spectra of ${\mathrm{C}}_{82}$, one of the newly isolated fullerene compounds, are measured with a synchrotron-radiation light source. The spectra resemble those of ${\mathrm{C}}_{84}$, and their spectral onset is at 1.15 eV below the Fermi level (${\mathit{E}}_{\mathit{F}}$). The first band is a broadband and consists of two peaks located at 2.2 and 3.3 eV. A slight structure is observed at the low-binding-energy side of the first band. The intensity of the two peaks of the band oscillates with the incident photon energy change, as is observed in ${\mathrm{C}}_{60}$, ${\mathrm{C}}_{70}$, and ${\mathrm{C}}_{84}$. The second band is located between 4 and 6.2 eV with a peak at 5.3 eV and an accompanying shoulder at the low-binding-energy side. The third band is located between 6.2 and 9 eV and consists of a peak at 7.8 eV and a distinct shoulder at 6.5 eV. Potassium dosing brings a new band between ${\mathit{E}}_{\mathit{F}}$ and the first band and its intensity grows as the potassium dosage increases. The spectral onset approaches ${\mathit{E}}_{\mathit{F}}$ in accordance with an increase of potassium dosage but it does not cross ${\mathit{E}}_{\mathit{F}}$, which indicates the semiconductive nature of the potassium-dosed ${\mathrm{C}}_{82}$ complex. The spectra of low or high potassium dosage can be understood by the rigid-band model, but the spectral change at medium potassium dosage seems to support a nonrigid-band filling of the electrons from the potassium atoms.