Parts-per-billion level chlorine sensors with fast kinetics using ultrathin cobalt phthalocyanine films

Ultrathin cobalt phthalocyanine films grown on (0 0 0 1) sapphire substrates were investigated for ppb-level gas sensing. For 5 ppb Cl2, 20 nm films show faster response times (18 s), higher base-line stabilities (<5% drift) and enhanced sensitivity (80%). In contrast, 100 nm films exhibit low sensitivity as well as sluggish response and recovery. Twenty nanometer films owing better crystallinity have high carrier mobility (8 × 10−4 m2 V−1 s−1), and therefore, even ppb level Cl2 chemisorption leads to a large change in conductance. Cl2 chemisorption obeys Elovich equation that permits quantitative determination of Cl2 concentration from response rate of sensor.