Monte carlo simulation of phase separation in KxC60

Kinetic Monte-Carlo methods have been used to simulate phase transformations in K x C 6 0 layers. It has been found that the phase composition is controlled by a balance between the Madelung energy and the energy of the electronic-shells interaction. A density-functional calibrated tight-binding method is used to calculate electronic effects. Our calculations point out a phase separation in the fulleride layer into K-rich (K 3 C 6 0 ) and K-depleted areas at room temperature. The two-phase system is formed as a fine mixture which is shown to be stable against aggregation. The average diameter of K 3 C 6 0 particles is about 20 to 40 nm and depends on the K content. This phase separation explains nanostructuring effects observed in electrochemically doped potassium fulleride layers. The size of the simulated K 3 C 6 0 particles correlates with the size of experimentally observed clusters. Since K 3 C 6 0 particles are metallic, the system considered can serve as an array of nanoelectrodes.