Passive Chemiresistor Sensor Based on Iron (II) Phthalocyanine Thin Films for Monitoring of Nitrogen Dioxide

Abstract

Nitrogen dioxide gas is a common atmospheric pollutant that is hazardous to human health at concentrations as low as one part per million (ppm). Iron (II) phthalocyanine (FePc) thin films have been identified to be sensitive materials for the detection of nitrogen dioxide and other oxidizing gases. The charge carrier complex formed from the interaction between FePc and nitrogen dioxide molecules acts to liberate hole charge carriers, thereby increasing film conductivity. Traditional metal-Pc based sensors rely on substrate heating and active temperature control to achieve nitrogen dioxide detection in a reversible manner. However, the heating process causes film deterioration and limits the life of metal-Pc sensors. In this dissertation, an alternate, new approach was investigated using a non-reversible, passive, FePc thin film sensor which does not require continuous power for operation. The general response, temperature dependence, concentration dependence, specificity, and longevity of FePc thin film sensors were investigated. To characterize the effects of sensor fabrication parameters, the film thickness, substrate type, and heat treatment effects were analyzed. In attempt to understand the sensor conductivity mechanism and to model sensor response, theoretical models were developed and show good agreement with experimental data. It is also with these models that a calibration method was developed to characterize sensor performance and produce a calibration plot. In summary, sensor test results show that as-deposited FePc thin films on silicon dioxide and quartz substrates with no post-deposition heat treatment produced sensors that can reliably differentiate nitrogen dioxide concentrations as low as 0.3 ppm, via passive monitoring of resistance levels.