title: Molecular orientation in self-assembled multilayers measured by second harmonic generation using femtosecond pulses.
abstract: 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 layer-by-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 the second harmonic signal, without interference fringes usually present in nanosecond experiments. We found that the first bilayer, in contact with the substrate, presents a broad distribution 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 surface normal. 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.
authors: Departamento de Física, FCEN, UBA. catalina@df.uba.ar
authors: Catalina
authors: C
authors: von Bilderling
authors: Mario
authors: M
authors: Tagliazucchi
authors: Ernesto J
authors: EJ
authors: Calvo
authors: Andrea V
authors: AV
authors: Bragas
mesh_terms: D004573:Electrolytes; D007477:Ions; D008567:Membranes, Artificial; D015394:Molecular Structure; D055095:Optics and Photonics; D011073:Polyamines / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D015203:Reproducibility of Results; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry
chemical_list: D004573:Electrolytes; D007477:Ions; D008567:Membranes, Artificial; D011073:Polyamines; D011108:Polymers; C063994:polyallylamine; D014025:Titanium