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O: Oberflächenphysik
O 9: Organic films I
O 9.3: Vortrag
Montag, 27. März 2006, 15:30–15:45, TRE Phys
Long-range order and polymerisation of sexithiophene on Ag(100) surfaces – a STM study — •Klaus Duncker, Sebastian Wedekind, Christian Hagendorf, and Wolf Widdra — Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Fb Physik
High-temperature scanning tunneling microscopy (STM) is used to study the morphology of the first few monolayers of α-sexithiophene (6T) on Ag(100) surfaces at room and elevated temperatures. The
6T molecules have been evaporated from a homebuilt Knudsen cell at
a base pressure of the UHV chamber of 1×10−10mbar.
Several molecular superstructures coexist in different domains within the monolayer. They can be devided into two groups with either one or two molecules in the unit cell. Common to all, the flat-lying
6T molecules are oriented with their long axis parallel to [011]
and [0 1 1] crystallographic directions of the Ag-substrate.
As the predominant superstructure with two molecules in the unit cell we find a
(9/0)(2/5) structure with a pair of chirally equivalent, parallel
molecules in the unit cell. Additionally, a herring bone-like
structure is found with two non-linear molecules in the unit cell forming
rows in highly-ordered domains. STM images with
submolecular resolution reveal flat molecules which have undergone
a cis-trans isomerization exclusively between the 4th and 5th
thiophene ring and which align in rows of left- and right-handed
molecules.
Whereas earlier studies indicate molecular dissociation of the first monolayer during thermal desorption, we have identified by STM polymerization to long chains and polythiophene networks after annealing to about 440 K and multilayer
desorption.