Optical gas sensing using Langmuir-Blodgett films

A polysiloxane with sidechain azobenzene chromophores has been deposited as Langmuir-Blodgett films on silicon. Using interference-enhanced reflectometry with films selected to give low reflectance of 520 nm light in air, reflectance changes of 75% were recorded on exposure to 100 ppm NO2 in air. Response and recovery times were of the order of 10 s, and recovery was effectively complete. The mechanism of response and factors such as long-term stability have yet to be fully investigated.