Nonlinear optical films by alternating polyelectrolyte deposition

Acentric films of stilbazolium-substituted polyepichlorohydrin (SPECH) and poly(sodium 4- styrenesulfonate) (PSS) were formed using alternating polyelectrolyte deposition (APD) on hydrophobic glass substrates. APD is a layer-by-layer technique for the formation of polymer films by alternately immersing a substrate in aqueous solutions of a polyanion and a polycation. APD provides precise control of the overall film thickness that through automated processing may exceed a thousand layers. The peak maximum UV-visible absorbance in transmission through the SPECH/PSS films was linear as a function of the number of bilayers. Second harmonic generation (SHG) was used as a tool to indicate acentric order to polarizable side-chain chromophores within the APD films. The SHG exhibited the expected quadratic intensity increase with film thickness after 30 bilayers had been deposited. During slow temperature ramping of the SPECH/PSS APD films on hydrophobic glass, in situ SHG measurements revealed that 90 percent of the polar order is retained at temperature well over 120 degrees C. The additional minima in the Maker fringe data, created by interference of the second harmonic waves generated at the two sides of a double-coated substrate, were found to go to zero, which is indicative of high quality films. The observed high thermal stability of the polar order makes the APD films attractive for device applications.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.