Surface structure of poly(3-alkylthiophene) films studied by atomic force microscopy

Tapping mode atomic force microscopy (AFM) was employed to study the surface structure of spin-coated and solvent-cast films of the newly synthesized electroluminescent copolymer TT9 and its fractions A and B. Fraction A is well soluble in chloroform while fraction B forms aggregates of high molecular weight in the same solvent. TT9 and fraction A are photoluminescent; fraction B is not. TT9 spin-coated and solvent-cast films show similar morphologies characterized by wormlike structures. Solvent-cast films formed by fraction A have a large density of defects. Fraction B forms larger structures, giving rise to more corrugated surfaces. These structures are formed by grains of rather uniform size, likely to be related to the aggregates already present in solution. For all the examined films, the surface roughness scales in the same way with the linear dimension of the surface, suggesting similar growth mechanisms.