Structural properties of oligomeric Langmuir-Blodgett films for second-order nonlinear optics

Neutron reflection and infrared spectroscopy have been used to investigate molecular ordering in Langmuir-Blodgett films of oligomers for second-order nonlinear optical applications. The results are compared to those from a previous ellipsometric study. A high degree of order for the chromophores in the multilayer films is revealed by these experiments. In contrast, the hydrocarbon tails are either randomly oriented or highly tilted with respect to the substrate normal. To account for the reduced nonlinear optical activity in thick films, we suggest that some chromophores have become inverted during the deposition process.