A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and filtered resulting in a dc output voltage proportional to the change in differential surface stress. The differential surface stress change of the Au(111) coated silicon sensors due to chemisorbed alkanethiols is (DELTA)(sigma)_(s)approx=-0.42+-0.0028 N m~(-1) for 1-dodecanethiol (DT) and (DELTA)(sigma)_(s)approx=-0.14+-0.0028 N m~(-1) for 1-butanethiol (BT). The estimated measurement resolution (1 Hz bandwidth) is approx=0.12 mN m~(-1) (DT: 0.2 pg mm~(-2) and BT: 0.8 pg mm~(-2)) and as high as approx=3.82 (mu)N m~(-1) (DT: 8 fg mm~(-2) and BT: 24 fg mm~(-2)) with system optimization.
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