Surface morphology study of corona-poled thin films derived from sol–gel processed organic–inorganic hybrid materials for photonics applications

Abstract

Dye-doped and a dye-attached sol–gel films using the chromophore (E)-N-butyl-(4-{2-[4-bis(2-hydroxyethyl)amino]phenyl}-ethenyl)pyridinium tetraphenylborate (BPTP) and N,N-bis(2-hydroxyethyl)amino-N′-methylstibazoliumtoluene-p-sulfonate (BAST) were fabricated by sol–gel processing. Surface morphology of the films was studied using an atomic force microscope. In the dye-doped film, many surface defects were observed. The morphology of the surface defects varied as a function of chromophore concentration. The shapes of the defects became more complicated as the chromophore concentration increased. On the other hand, no evidence of such defects was present in the dye-attached film and the quality of the film was high. Also for the dye-attached film, the surface was optically flat and smooth, and the surface roughness was measured to be less than 4 nm. It was found that corona poling processes also affected the quality of the dye-attached film significantly. Corona poling with a needle electrode resulted in many irregular shaped defects in the film. However, poling with a tungsten wire stabilized the corona discharge and thus prevented the formation of defects, which led to films of excellent quality. The electro-optic coefficient, r₃₃ , of the BPTP dye-attached film was measured to be 5.0 pm V^–1 and this value was maintained even after 54 days at room temperature.