Abstract
Nanothin films of polystyrene (PS) doped with poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) by spin-coating were researched. An Interplay between phase separation and dewetting caused by the inhibition of formation of holes with increasing concentration of MEH-PPV in polystyrene was observed in the early stages of instability. With increasing concentration of MEH-PPV, the morphology is dominated by this interplay. For low concentrations of 5%-MEH-PPV, dewetting by nucleation and growth was found as evidenced by the formation of holes with rim instability, after increasing the concentration to 15%-MEH-PPV, there was no formation of holes but rather the appearance of composition waves and later formation of droplets; with a higher concentration of 30%-MEH-PPV the surface morphology evidenced the formation of composition waves rather than the formation of holes. Under the same film thickness, composition waves are induced with increasing concentration of MEH-PPV. A short-time stepwise annealing experiment exposed the evolution of the morphological features. A residual layer measured on scratched samples by the AFM was found to be thicker for a larger concentration of MEH-PPV. The effect of film thickness was analyzed for films of 5, 10, 20 and 30 nm revealing that increasing film thickness benefits the formation of the composition waves as evidenced by the early rising of the bicontinuous pattern. For concentrations of 15%-MEH-PPV and above, The PL enhancement factor was found to decrease with film thickness revealing that the PL enhancement decreases progressively with increasing film thickness as the films move from higher instability to the formation of the composition waves. The solvent effect showed that acetone usually had a different path of instability than toluene.