α-6T on Ag(1 1 0): The formation of the wetting layer

The growth of thin films of α-sexithiophene (α-6T) on a Ag(1 1 0) surface was studied by means of scanning tunneling microscopy (STM) and photoelectron emission microscopy (PEEM). In contrast to (1 1 0) surfaces of other metals, α-6T molecules deposited on Ag(1 1 0) do not align exclusively along the close-packed atomic rows but also perpendicular to them. The mixture of molecules arranged with their long axis parallel to the [0 0 1] and [ 1 1 ¯ 0 ] directions leads to a strained checkerboard pattern. Besides the checkerboard phase, small α-6T domains of a hitherto unreported well ordered homochiral phase were found. STM images show that the molecules in the second layer are exclusively aligned along the [0 0 1] direction but their arrangement is strongly influenced by the checkerboard phase of the first layer. For coverages above two monolayers of α-6T, 3D island nucleation and growth was observed.