Organic materials exhibiting second-order non-linear optical (NLO) properties are a key to the development of advanced electro-optic modulators used in fiber-optic communications system. This research concerns a layer-by-layer technique used to fabricate films with useful second order NLO properties. A polycation - poly(allylamine) hydrochloride (PAH) - and a polyanion, poly{1-[4-(3-carboxy-4-hydroxyphenylazo)-benzenesulfonamido]-1,2ethandiyl} (PCBS) are self-assembled on a substrate by alternately adsorbing the two polymers. We study the film deposition process using a Quartz Crystal Microbalance (QCM), ellipsometry, and absorbance measurements.

The deposition of multiple layers of PAH and PCBS adsorption were studied at different concentrations using a silicon dioxide-coated substrate in a QCM. The results show a linear decrease in frequency with increasing number of adsorbed layer signifying a homogeneous growth of the self-assembled films. Data obtained from QCM were compared with thickness measurements from ellipsometric data and absorbance measurements to estimate the water content in these films. These findings will help us to understand this self-assembly at the molecular level in order to make a practical electro-optic modulation device.