Combined in situ micromechanical cantilever-based sensing and ellipsometry

Two cantilever-based chemical sensors are reported. First, a differential cantilever-based chemical sensor capable of sensitive surface stress measurements has been designed and implemented. The system uses two commercially available atomic force microscope cantilevers. The surface of one cantilever is functionalized to make it receptive to specific target analytes, while the second, passivated cantilever is used as a reference by subtracting undesired signals, resulting from mechanical and thermal noise, from the signal of interest. The second system is a combined cantilever-based sensor and ellipsometer capable of simultaneous in situ surface stress and film thickness measurements. Both sensors, operated in static mode, achieve a cantilever deflection measurement sensitivity of 0.2 nm and a surface stress resolution of 5x10(-5) N/m. Molecular monolayer thicknesses are measured simultaneously with a 0.1 nm resolution. The real-time formation process of alkanethiol self-assembled monolayers on gold was investigated as a model system to characterize these instruments. (C) 2003 American Institute of Physics.