There is a need to measure ammonia gas concentrations under clinical and industrial conditions, and for environmental protection.

Now researchers at the C.S.I.C, Spain, have developed a new ammonia gas sensor device based on Schottky platinum/n -gallium arsenide barrier diodes with discontinuous platinum films which have excellent sensitivity between room temperature and 150°C (L. M. Lechuga, A. Calle, D. Golmayo and F. Briones, J. Appl. Pkys., 1991, 70, (6), 3348–3354).

The devices have a dual metallic configuration consisting of a thick deposited platinum circular dot and a thin porous platinum film evaporated over and outside the contact dot. Gas-induced modification in Schottky diode electrical properties are monitored by measuring changes in the diode capacitance as a function of time.

In synthetic air it was possible to measure ammonia concentrations above 150 ppm with response times lower than one minute.