Studying the Adsorption of Fluorofullerene Molecules on the Surfaces of Solids at the Atomic Scale

The initial stages of the adsorption of fluorinated fullerenes C₆₀F₁₈ at the Si(111)-7 × 7, Si(001)-2 × 1, and Cu(001)-1 × 1 surfaces are studied by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy in ultra-high vacuum. By combining STM imaging of individual molecules and ab initio calculations of the total energy, we demonstrate that polar C₆₀F₁₈ molecules interact with the surface with their fluorine atoms facing toward the surface. Molecules of the investigated fluorofullerenes enable surface modification at the nanoscale by local etching. By analyzing the experimental STM images and their computer-simulated counterparts, we show that the adsorbed fullerene molecules give up their F atoms to the Si surface. The binding energy between the fluorine atom and the Si surface is almost twice as high as that between the fluorine atom and the C₆₀ molecule. The rate of disintegration of the fluorofullerene molecules adsorbed at the Cu(001) surface depends on the initial surface coverage. Initially, adsorbed C₆₀F₁₈ molecules lose some of their fluoride atoms, giving rise to two-dimensional islands consisting of C₆₀ and C₆₀F_n molecules.