Anisotropic ordered planar growth of a-Sexithienyl thin films

We show how the anisotropy of the (1 x 2) reconstructed Au(110) surface can be effectively used to achieve spontaneous ordered planar growth of rodlike conjugated oligomers uniaxially oriented on the substrate. The growth of the first few monolayers of alpha-sexithienyl (T6) films on the (1 x 2) reconstructed Au(110) surface in ultrahigh vacuum has been investigated by He atom scattering (HAS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). T6 molecules lie flat on the substrate forming long chains along the [110] direction of the Au rows. The interchain spacing is coverage dependent and uniaxially commensurate with the substrate along [001]. Three ordered structures with 12, 16, and 20 Angstrom periods are formed during the deposition of the first two T6 monolayers. This T6 overlayer acts as a template for the growth of at least five monolayers which are still planar and orientationally ordered.