Detection of Nitrogen Dioxide Gas in Nitrogen Atmospheres via Passive Monitoring of Iron (II) Phthalocyanine Thin Films

Nitrogen dioxide (NO2) is a highly toxic oxidizing gas generally produced as a byproduct of combustion processes and also commonly stored in high concentrations as dinitrogen tetroxide (N2O4) for military and industrial use. A passive, unpowered sensor for the detection of NO2 gas was fabricated using Iron Phthalocyanine (FePc), an organometallic molecular crystal. FePc acts as an electron donor in the presence of Nitrogen Dioxide gas, forming a charge carrier complex, thus when FePc is exposed to NO2, the resulting decrease in resistivity can be monitored to determine ambient NO2 concentrations. Sensors were fabricated via physical vapor deposition of FePc powder onto gold inter-digitated electrodes patterned on oxidized silicon substrates. Gas exposure tests were conducted with sensor resistance monitored in real time. By observing normalized sensor resistance over time, NO2 concentrations in the range of 0.5 to 2 ppm under a N2 atmosphere were consistently detectable.