An optical ammonia (NH3) gas sensing by means of Pd/CuPc interferometric nanostructures based on white light interferometry

The monitoring of ammonia gas concentrations by means of an optoelectronic gas sensor is described in this paper. An optoelectronic gas sensor based on interferometric, gasochromic nanostructures contains Cu-phthalocyanine (CuPc) thin films and palladium (Pd) thin film. The optical changes (interferometric colour changes) that occur Pd/CuPc or CuPc are due to being exposed to different relative humidites (RH) or various ammonia concentrations (at 70 °C). The CuPc films were deposited by thermal evaporation. Additionally, to enhance the sensing performance of these CuPc thin films, the surfaces of CuPc were coated with an ultra-thin film of palladium. This metallic Pd film can act as catalyst that increasing the efficiency of dissociation of the molecular ammonia gas to its more reactive atomic form in order to enhance the surface reaction during the gas sensing. The thin films of Pd were obtained also by means of the vacuum-thermal method. physical–chemical interaction between the sensing structure and ammonia gas is taking place (on the sensing window of the measuring channel), the interferential colour of the sensing element (nanostructure) changes and colour coordinates the measuring optical signal will also change. The colour sensor TCS230 detecting the intensity and change of the colour coordinates RGB of the optical signal resulting from the exposure sensing structure to ammonia gas. An optical ammonia gas sensor displays a very fast response time and a fast regeneration time at low temperature (70 °C) in a dry and humid gaseous environment.