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

The recent advent of microelectromechanical systems (MEMS) devices opened up possibilities for chemical detection. Microcantilevers respond to chemical stimuli by undergoing changes in their bending and resonance frequency when 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 photoinduced 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 made to bend by expanding or contracting the irradiated surface. By coating the surface of the microcantilever with a thin chemical layer, chemical specificity for the target chemicals can be achieved. Chemical selectivity can also be altered by selecting appropriate photon wavelengths due to the introduction of surface states in semiconductor MEMS. In fact, choosing a handful of different photon wavelengths, tunable chemical selectivity can be achieved due to differentiated photoinduced response without the need for multiple chemical coatings. We present and discuss our results on MEMS interactions with two isomers of dimethylnaphthalene, tetrachloroethylene, trichloroethylene, diisopropyl methyl phosphonate, and trinitrotoluene. (C) 2001 American Vacuum Society.