Molecular order in self-assembled multilayer films measured by optical Second Harmonic

CATALINA VON BILDERLING; MARIO TAGLIAZUCCHI; ERNESTO J. CALVO; ANDREA V. BRAGAS

San Carlos de Bariloche, Argentina

Workshop; US-Argentina Workshop on Nanomaterials; 2009

UNIVERSIDAD DE BUENOS AIRES- UNIVERSIDAD DE CALIFORNIA

We present measurements of the optical second-harmonic generation in self assembled multilayer films of PAZO/PAH polymers with the aim to investigate molecular order in the layerby-layer architecture. The experiments are performed in transmission, using a femtosecond Ti:Sa pulsed laser, which allows a more accurate determination of the amplitude of thesecond harmonic signal, without interference fringes usually present in nanosecond experiments. We found that the first bilayer, in contact with the substrate, presents a broaddistribution of the orientation of the molecules, while the addition of successive bilayers (up to 12) produces ordering of the molecules with a small tilt angle respect to the surfacenormal. This result, together with the monotonic increment of the second harmonic signal with the number of layers indicates that the molecules grow orderly assembled in these films.