Formation of extended straight molecular chains by pairing of thymine molecules on the Ag–Si(111) surface

Abstract

Here, we report on the assembly of thymine molecules into extended straight chains of single and multiple dimer rows on a Si(111)/Ag $\sqrt{3}\times \sqrt{3}$ R30° surface. Using variable temperature scanning tunneling microscopy, we follow the nucleation process and formation of self-assembled structures. Submonolayer coverages at 120 K are disordered and exhibit a high density of thymine dimers. Upon annealing the dimers assemble into extended dimer chains along three equivalent high-symmetry surface directions. At low coverages single dimer rows are favored. At increased coverage chains with multiple dimer rows are observed, with a preference to an even multiplicity. We show that a complex cross-talk between H-bond thymine–thymine interactions and commensurization of dimer chains to the Ag/Si surface leads to this specific layout.