Approach to Multigas Sensing and Modeling on Nanostructure Decorated Porous Silicon Substrates

An approach to multiple gas sensing on decorated porous silicon (PS) substrates is presented. The simple microelectromechanical systems/nanoelectromechanical systems platform that we have developed facilitates the modeling of the interaction of nanostructured metal oxide islands with the analytes of interest, which are exemplified by NO and NH₃. These conductometric sensors operate at room temperature and atmospheric pressure and, as they are forgiving, do not require film-based technology or lithography for their construction. We show that diffusion dominates the conductometric response. The direct response and the derivatives of this response are considered. The first derivative allows a quick evaluation of sensor response and the derivative is linear with concentration. The spectral simulations have been refined to include adsorption/desorption effects of the analyte gas and assess subsequent non-linear interface sensitivities. By including the physics of adsorption/desorption, the simulated sensor response is now a non-linear function of concentration. We model the absorption/diffusion through the use of the Langmuir absorption isotherm and find substantial agreement with experiment for the mixed analyte interactions of NH₃ and NO combinations on several metal oxide decorated PS interfaces.