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Elucidating the dynamical equilibrium of C 60 molecules on Ag(111)

2012; American Physical Society; Volume: 86; Issue: 20 Linguagem: Inglês

10.1103/physrevb.86.205406

1550-235X

K. Pussi, H. I. Li, Heekeun Shin, L. N. Serkovic Loli, A. K. Shukla, J. Ledieu, V. Fournée, L. L. Wang, S. Su, Kristin Marino, M Snyder, Renee D. Diehl,

Graphene research and applications

We have used scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) to elucidate the structure and thermodynamics of the (2$\sqrt{3}$ \ifmmode\times\else\texttimes\fi{} 2$\sqrt{3}$)$R$30\ifmmode^\circ\else\textdegree\fi{} phase of C${}_{60}$ on Ag(111), which consists of a mixture of molecules in two different site/orientation states. The structure analysis identifies the two types of molecules as (1) sitting on a vacancy with a hexagon face down and (2) sitting on a top site with a C-C bond down. The molecules flip between the two states at a temperature-dependent rate. We show using a thermodynamic analysis that the two states differ by 0.07 eV and are separated by an energy barrier of 0.84 eV. Their dynamical equilibrium involves the diffusion of surface vacancies between C${}_{60}$ molecules, producing spatially and temporally correlated flipping events.