Two-dimensional dynamic perylene ordering on Ag(110)

We present a room temperature STM study of dynamics of the quasi-liquid perylene monolayer formed on Ag(110) under thermal equilibrium. We observe that the thermodynamic balance of the molecule–molecule and molecule–substrate interactions generates a compact two-dimensional (2D) quasi-liquid state established by mobile perylene molecules dynamically distributed into three distinct motion modes. Monitoring of the quasi-liquid monolayer indicates that each motion mode is triggered by spontaneous recognition of specific locations of the substrate lattice into which transient locking occurs. Analysis of the STM topographies shows that the substrate lattice guides the whole molecule ensemble and provides each of the modes with a distinct register. In each mode, the substrate registry forces the transiently immobile molecules to alternate with the transiently mobile ones. The dynamic interminglement of the modes prevents segregation of the dynamically active and inactive molecules. The substrate provides memory to the intermingled molecules and eliminates ergodicity of the quasi-liquid state. Fourier transform of the topographies unravels the long-range spatial correlations and epitaxial character of the quasi-liquid state. Analysis of the short-range mode coupling allows us to understand the mechanism of the long-range mode coupling. The substrate force field induces the dynamical ergodic–non-ergodic phase transition giving rise to the stationary long-range ordered −12.532 quasi-liquid state.