Charge transfer from potassium into thet1gband ofC60

Depositing ${\mathrm{C}}_{60}$ on potassium multilayers creates a K-rich environment for low coverages of ${\mathrm{C}}_{60}$ and photoemission spectra show that not only the ${\mathit{t}}_{1\mathit{u}}$ but also the ${\mathit{t}}_{1\mathit{g}}$ band is occupied. This is direct evidence for the formation of ${\mathrm{K}}_{\mathit{x}}$ ${\mathrm{C}}_{60}$ with 6<x<12, which could not be achieved in previous studies where K was evaporated onto solid ${\mathrm{C}}_{60}$ surfaces. However, less than one electron can be transferred to ${\mathrm{C}}_{60}$ from submonolayer coverages of K on Rh(111) and hence even the ${\mathit{t}}_{1\mathit{u}}$ band is mostly unoccupied, despite the large K-induced drop in work function from 5.4 to 1.8 eV.