POLYMER-FILMS ON METALS INVESTIGATED BY OPTICAL 2ND-HARMONIC GENERATION

In two different types of experiments, polymer films on gold substrate s were investigated by optical second harmonic generation (SHG). Thick ness dependent ex situ measurements on Langmuir-Blodgett films of the octadecylammonium salt of polyamic acid (PACS) show a preferential ori entation of the polymer molecules. In situ SHG experiments were perfor med to monitor the growth of polyamic acid films deposited from the ga s phase. Pyromellitic dianhydride (PMDA), 4,4'-oxydianiline (ODA), and 4,4'-diaminodiphenyl disulfide (DAPS) served as monomers. Similar to the Langmuir-Blodgett films, an oriented growth is observed. The thick ness dependence of the SHG signal is strongly dependent on the interfa cial chemistry which is very different for the two amines used as mono mers. Based on a comprehensive three layer model, the relation between the structure of the films and the SHG signal is discussed.