The influence of CO on the response of hydrogen sensitive Pd-MOS devices

In order to understand and correctly interpret the response of chemical sensors under measurement conditions, detailed studies of molecule-sensor interactions under well-controlled conditions are needed. In this work, the influence of CO on the response of a hydrogen sensitive Pd-metal-oxide-semiconductor (Pd-MOS) device with a dense Pd Sim is studied in ultrahigh vacuum (UHV). The results show that although CO by itself does not induce any response of the device, CO may have a significant influence on the hydrogen response, especially so in the presence of oxygen. It is also shown that high CO coverages on the Pd surface increases the time needed to obtain equilibrium between the gas phase hydrogen pressure and the response of the Pd-MOS device. This is due to a CO induced increase of the activation energies of the dissociation and association processes for hydrogen. The effect on the hydrogen response is small for CO coverages below 0.2 monolayers and increases dramatically above this coverage. (C) 1997 Elsevier Science S.A.