Formation of Fullerides and Fullerene-Based Heterostructures

Two potassium fulleride phases, metallic K$_3$C$_{60}$ and nonmetallic K$_6$C$_{60}$, are formed when potassium is incorporated into thin C$_{60}$ films under ultrahigh vacuum conditions. Phase separation is observed for intermediate stoichiometries. Results obtained for the C$_{60}$-K$_3$C$_{60}$ heterostructure demonstrate that it is stable against potassium migration from the K$_3$C$_{60}$ phase. In contrast, the C$_{60}$-K$_6$C$_{60}$ interface is not stable and K$_3$C$_{60}$ is formed.