STM investigation of large π-conjugated oligomers and tetrahydrofuran codeposited on Cu(111) by pulse injection

The π-conjugated oligomer consisting of ethynyl interlinked thiophene and benzene subunits C114H158O8S2Si2 has been deposited on clean Cu(111) substrates at room temperature using the pulse-injection method with tetrahydrofuran (THF) as solvent. Scanning tunneling microscopy measurements in ultrahigh vacuum at room temperature demonstrate that the CHOSSi and THF molecules coadsorb on the copper surface. The solvent molecules form ordered structures with distinct orientations and domain boundaries, suggesting a strong interaction of THF with the substrate. Individual and small clusters of CHOSSi molecules appear randomly distributed on the surface with no apparent correlation with the solvent molecules. Subsequent thermal treatment removing the solvent causes a degradation of the CHOSSi oligomers which aggregate forming fractal nanostructures.