ULTRA-HIGH-VACUUM SINGLE-LAYER FORMATION OF ALPHA-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 sca ttering (THAS) in ultra-high-vacuum (UHV) conditions. The monolayer (M L) structure has a rectangular surface unit cell with the T6 molecules lying flat on the surface and aligned parallel to the Au rows. The pe riodicity 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, cor responding to the molecular length. The correlation length of the over layer structure depends upon substrate temperature during deposition a nd increases when the system is heated up to 653 K. The surface struct ure is irreversibly lost upon heating to temperatures higher than 673 K, but T6 molecules do not completely desorb up to about 773 K.