Ultra High Vacuum Single Layer Formation of a-hexathienyl on the (1x2)Au(110) Surface

The formation of an alpha-hexathienyl (T6) single layer on the (1 x 2) Au(110) surface has been investigated by means of thermal He atom scattering (THAS) in ultra-high-vacuum (UHV) conditions. The monolayer (ML) structure has a rectangular surface unit cell with the T6 molecules lying flat on the surface and aligned parallel to the Au rows. The periodicity perpendicular to the Au rows is doubled with respect to the bare Au surface, while along the rows it is 27.4 +/- 0.5 Angstrom, corresponding to the molecular length. The correlation length of the overlayer structure depends upon substrate temperature during deposition and increases when the system is heated up to 653 K. The surface structure is irreversibly lost upon heating to temperatures higher than 673 K, but T6 molecules do not completely desorb up to about 773 K.