CONSTANT CURRENT CORONA CHARGING AS A TECHNIQUE FOR POLING ORGANIC NONLINEAR OPTICAL THIN-FILMS AND THE EFFECT OF AMBIENT GAS

Poling, which involves the alignment of nonlinear optical (NLO) dipolar molecules in the direction of the applied electric field, was carried out using constant current char developed corona charging technique. Using this technique, the sample surface voltage buildup, and hence the efficiency of the dipole alignment, can be monitored during the poling process. In addition, it will be shown that this capability also provides a way to detect the end point of the dipolar orientation. Corona charging of the organic NLO film used in this study, however, needs to be done in an inert atmosphere. Results from in situ IR spectroscopy measurement during corona charging of the NLO film, ultraviolet and visible absorption spectroscopy and electron scattering for chemical analysis of this film before and after poling, indicated that exposing it to corona discharge in air ambient caused oxidation of the polymer surface. Various types of nitrogen oxides and carboxylic acids were found to be the products of this oxidation reaction. Finally, we also obtained evidence showing that the surface charging process of the organic NLO film is affected by this newly grown oxidized layer.