Abstract:

Thin films consisted of iron phosphate nanopaticles were prepared by spincoating mixed solutions of iron nitrate, methanol and phosphate acid. The effects of coater speed and drying temperature on film thickness and refractive index were studied. It was found that when the thin films were dried at 150 ℃ or higher, the thickness(130 nm) and refractive index(1.7) of the thin films remained nearly unchanged. A composite optical waveguide sensing unit for ammonia vapor was fabricated by spin coating iron phosphate precursor on a single-mode potassium ion exchanged glass followed by spin coating a thin film of a pH indicator dye(bromothymol bule,BTB) onto the composite film. The experimental results show that the sensing unit has a ammonia vapor detection concentration limit of 0.35 mg/m³. It also has unique features such as fast response(10 s), short recovery time(90 s) and good reversibility and reusability.

Key words: optical waveguide gas sensor, iron phosphate thin film, bromothymol blue, ammonia