Abstract

Ionic self-assembled monolayers (ISAMs) are a recently developed,¹ revolutionary class of materials that allows detailed structural control at the molecular level combined with east 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 χ⁽²⁾ values at least four times larger than that of quartz. The development of ISAM χ⁽²⁾ thin films provides significant advantages over the production of organic χ⁽²⁾ thin films by alternative methods. For example, ISAM films can exhibit longterm stability of χ⁽²⁾ in contrast to electric field poling of glassy polymers,² can provide thicker films (upwards of 10 µm) than the Langmuir-Blodgett technique, and can be fabricated much more rapidly than covalent self-assembly³ methods.

© 1998 Optical Society of America