Bulk and surface electronic structures of potassium fullerides

Photoemission spectra from thin films of ${\mathrm{K}}_{\mathit{x}}$ ${\mathrm{C}}_{60}$ prepared by vapor-phase reaction of ${\mathrm{C}}_{60}$ with K vapor consist of superpositions of distinct bulk and surface contributions. The spectra of ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and ${\mathrm{K}}_6$ ${\mathrm{C}}_{60}$ are identified and shown to be in very good agreement with band-structure calculations. The surface layer of molecules does not contribute to the metallic conductivity for any bulk composition.