Chemical detection based on adsorption-induced and photoinduced stresses in microelectromechanical systems devices

The recent advent of microelectromechanical systems (MEMS) devices opened u p possibilities for chemical detection. Microcantilevers respond to chemica l stimuli by undergoing changes in their bending and resonance frequency wh en molecules adsorb on their surfaces. In our present studies, we extended this concept and studied changes in both the adsorption-induced stress and photoinduced stress as molecules adsorb on the surface of microcantilevers. We found that microcantilevers that have adsorbed molecules will undergo p hotoinduced bending that depends on the number of adsorbed molecules on the surface. Furthermore, when microcantilevers undergo photoinduced bending, molecules will adsorb on their surface differently. Depending on the photon wavelength used and microcantilever material, the microcantilever can be m ade to bend by expanding or contracting the irradiated surface. By coating the surface of the microcantilever with a thin chemical layer, chemical spe cificity for the target chemicals can be achieved. Chemical selectivity can also be altered by selecting appropriate photon wavelengths due to the int roduction of surface states in semiconductor MEMS. In fact, choosing a hand ful of different photon wavelengths, tunable chemical selectivity can be ac hieved due to differentiated photoinduced response without the need for mul tiple chemical coatings. We present and discuss our results on MEMS interac tions with two isomers of dimethylnaphthalene, tetrachloroethylene, trichlo roethylene, diisopropyl methyl phosphonate, and trinitrotoluene. (C) 2001 A merican Vacuum Society.