Superfulleride formation and electronic properties of C₆₀ on K/Rh(111) surfaces

Despite the high electron affinity of C₆₀, photoemission and work function measurements of C₆₀ on Rh(111) surfaces containing submonolayer amounts of K show that a low value of the work function is not sufficient to cause extensive charge transfer (> 1 electron) from the substrate to the C₆₀ molecule. However, when appropriate amounts of C₆₀ are evaporated onto potassium multilayers of controlled thickness at 100 K, interdiffusion occurs and potassium superfullerides, K_xC₆₀ with 6 < x < 12, form on the surface. The resulting phases can be purified by annealing the sample to ≈ 325 K for x → 12, or higher temperatures for lower K stoichiometries, to drive out excess K.