Molecular orientation in self-assembled multilayers measured by Second Harmonic generation using femtosecond pulses

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

OPTICS EXPRESS

OPTICAL SOC AMER

Año: 2009 vol. 17 p. 10642 - 10647

1094-4087

We present measurements of the optical second-harmonicgeneration in self assembled multilayer films of PAZO/PAH polymers withthe aim to investigate molecular order in the layer-by-layer architecture. Theexperiments are performed in transmission, using a femtosecond Ti:Sapulsed laser, which allows a more accurate determination of the amplitudeof the second harmonic signal, without interference fringes usually presentin nanosecond experiments. We found that the first bilayer, in contact withthe substrate, presents a broad distribution of the orientation of themolecules, while the addition of successive bilayers (up to 12) producesordering of the molecules with a small tilt angle respect to the surfacenormal. This result, together with the monotonic increment of the secondharmonic signal with the number of layers indicates that the moleculesgrow orderly assembled in these films.