Femtosecond Optical Annealing Induced Polymer Melting and Formation of Solid Droplets.

Interaction between femtosecond laser pulses with polymeric thin films induced transient optical annealing of the polymer molecules. Melting of the polymer films took place during the transient annealing process, so that a solid-liquid-solid phase transition process was observed. Ultrafast cooling of the melting polymer produced solidified droplets. Microscopic and spectroscopic characterization revealed that the polymer molecules were rearranged with preferable H-aggregation to reach the lowest formation energy during the melting process. Intermolecular coupling was enhanced due to the modified molecular arrangement. This observation of melting of polymeric semiconductors due to the interaction with femtosecond light pulses is potentially important for better understanding laser-matter interactions and for exploring organic optoelectronic devices through special material processing.