Real-time decay of fluorinated fullerene molecules on Cu(001) surface controlled by initial coverage

In this study, the evolution of C₆₀F₁₈ molecules on a Cu(001) surface was studied by means of scanning tunneling microscopy and density functional theory calculations. The results showed that fluorinated fullerenes (tortoise-shaped polar C₆₀F₁₈) decay on Cu(001) surfaces by a step-by-step detachment of F atoms from the C₆₀ cage. The most favorable adsorption configuration was realized when the F atoms of C₆₀F₁₈ pointed towards the Cu surface and six F atoms were detached from it. The results also showed that a further decay of C₆₀F₁₂ molecules strongly depended on the initial C₆₀F₁₈ coverage. The detached F atoms initially formed a two-dimensional (2D) gas phase which then slowly transformed into F-induced surface structures. The degree of contact between the C₆₀F₁₂ molecules and the Cu(001) surface depended on the density of the 2D gas phase. Hence, the life-time of fluorinated fullerenes was determined by the density of the 2D gas phase, which was affected by the formation of new F-induced structures and the decay of C₆₀F₁₂ molecules.