Second-order nonlinear optical thin films fabricated from ionically self-assembled monolayers

Ionic self-assembled monolayers (ISAM) are a recently developed, revolutionary class of materials that allows detailed structural control at the molecular level combined with ease of manufacturing and low cost. The ISAM method involves the alternate dipping of a charged substrate into an aqueous solution of a cation followed by dipping in an aqueous solution of an anion at room temperature. Because the adsorption is based on the electrostatic attraction of interlayer charges, each layer is self-limiting in thickness and uniform at the molecular level. We have recently demonstrated through second-harmonic generation (SHG) measurements with fundamental wavelengths of 1064 and 1200 nm that the ISAM technique can produce a noncentrosymmetric arrangement of NLO chromophores to yield thin films with /spl chi//sup (2)/ values at least four times larger than that of quartz. The development of ISAM /spl chi//sup (2)/ thin films provides significant advantages over the production of organic /spl chi//sup (2)/ thin films by alternative methods. For example, ISAM films can exhibit long-term stability of /spl chi//sup (2)/ in contrast to electric field poling of glassy polymers, can provide thicker films (upwards of 10 /spl mu/m) than the Langmuir-Blodgett technique, and can be fabricated much more rapidly than covalent self-assembly methods.