Commensurate Surface Structures And Concerted Cis-Trans-Isomerization Within Ordered Monolayers Of Alpha-Sexithiophene On Ag(001)

The monolayer of alpha-sexithiophene on Ag(001) has been studied by scanning tunneling microscopy and low-energy electron diffraction. Upon deposition at room temperature four well-ordered and commensurate molecular structures have been identified where the molecules adsorb flat lying with their long axis parallel to the [110] and [1 (1) over bar0] high-symmetry directions. Whereas three structures consist of straight molecules in all-trans configuration, one long-range ordered structure is observed where all molecules have undergone a trans-cis isomerization process between the second and third thiophene ring.