Physical and chemical characterizations of nanometric indigo layers as efficient ozone filter for gas sensor devices

The relevance of nanometric indigo layers as integrated ozone filters on chemical gas sensors has been established. Indigo can be considered as a selective filter because it ensures a complete removal of ozone in air while being very weakly reactive with CO and NO2. The nanometric layers have been realized by thermal evaporation and their chemical structures have been consecutively determined by FT-IR and XPS analyses. Studies about their morphology have been realized by means of SEM and AFM. Results underline the homogeneity and the low roughness of the samples. Electrical characterizations have revealed the high electronic resistivity of nanometric indigo layers. Current–voltage characterizations have put in obviousness that the integration of indigo layer has no effect on the electrical characteristics of sensitive element, even for material exhibiting a very low intrinsic electronic conductivity like metallophthalocyanines. The selective and reproducible measurements of NO2 concentrations by an original sensing device which takes advantage of on the one hand, the sensitivity and the partial selectivity of copper phthalocyanine (CuPc) to oxidizing gases and on the other hand, the filtering selectivity of indigo toward O3 have been successfully performed. Optimization of sensing performances as well as the scope of indigo nanolayers will be finally discussed.