KINETICS OF THE MICROMIRROR CHEMICAL SENSOR

Most chemical sensors involve a sensitizing coating that interacts with the chemical species to be detected to produce a change in some physical parameter which can then be measured. The speed of response of the sensor depends to a large extent on the nature of this chemical interaction. Here we explore the kinetics of the micromirror chemical sensor, a reflective-type optical-fiber sensor, for two different interactions: (1) the detection of hydrogen at high concentrations using palladium films; (2) organic vapor detection using a plasma-polymerized fluorocarbon film. For hydrogen detection, where the palladium films are very thin (approximately 10 nm), the kinetics are determined by the complex nature of the surface chemistry; the presence of oxygen changes the speed of the sensor response. For organic vapor detection, the fluorocarbon film is much thicker (approximately 1 mum) and the speed of response is determined by diffusion of the organic molecules through the fluorocarbon film.