Theoretical Investigation and Simulated Imaging of Halogenated Tetracenes on Coinage Metal (111) Surfaces

Energetics, geometry, mobility, and imaging of halogenated tetracenes on Cu, Ag, and Au(111) substrates are simulated from first principles. The adsorption energies grow with the atomic number of the halogen species and are, in general, larger on the Cu substrate than on Ag and Au. The Cu surface is nearly commensurate with the benzene rings, leading to distinct adsorption sites and limited mobility. Ag and Au substrates are characterized by larger lattice parameters, exceeding the size of the benzene rings. This leads to less distinct adsorption sites and to a large tetracene mobility parallel to the ⟨11̅0⟩ directions. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are modeled within the Tersoff-Hamann approximation and within the probe particle model (PPM), respectively. The simulated images match available experimental results and allow us to explain the contrast mechanism.