Elucidating the Equilibrium States of C60 molecules on Ag(111)

The properties of C$_{\mathrm{60}}$ on surfaces depend strongly on their local geometries, but until recently there were few quantitative studies for these structures. The interactions of C$_{\mathrm{60}}$ molecules on Ag(111) surface produce an interesting structural complexity that manifests as a competition between two geometrical states. We studied the most stable (2$\surd $3x2$\surd $3)R30$^{\mathrm{o}}$ phase of C$_{\mathrm{60}}$ on Ag(111) by using STM, LEED, and DFT. This phase consists of molecules in two different geometrical states - one sitting on a C-C bond on the top site and one sitting on a hex face on a vacancy. By measuring the dynamical equilibrium behavior of the system, we obtained detailed information on the energetics of two states.