A quantitative analysis was made of the electron energy loss spectra, as a function of time, of K-doped C60 thin films in order to explore the diffusion of K at, and near to, the surface at 100K. The spectral features of K3C60, K4C60, K6C60 and pure C60 phases were observed to coexist before reaching saturation doping. The ratio of these phases could be controlled via the K deposition rate. At low deposition rates, no trace of K3C60 was found at the surface. A quantitative analysis, based upon fits of Lorentzian functions that were characteristic of each structural phase, was used to monitor the time and dose variations of the multiphase film. The analysis furnished the dissipation rates of K4C60 and K6C60 phases at the surface, together with the peak broadening of certain transitions of the K4C60 and K6C60 structures as a function of grain size. The results revealed the relative kinetic stability of KxC60 grains, as the x-value was varied.

Study of the Kinetics of Potassium Diffusion in Thin C60 Films. M.F.Luo, Z.Y.Li, W.Allison: Surface Science, 2003, 523[1-2], 168-78