Use of thermally induced higher order modes of a microcantilever for mercury vapor detection

We demonstrate the use of thermally induced higher order modes of a microcantilever as an alternate detection technique by studying Au-Hg interactions. The first four thermally induced flexural modes (i.e., the fundamental and first three higher order modes) have been examined for two different Au coatings. In the first case, 50 nm thick Au is sputter deposited along the entire length of a rectangular Si microcantilever. In the second case the Au is confined to a 30 mu m length at the tip of the Si microcantilever. In both cases the microcantilever spectral response and deflection has been studied as a function of Hg concentration and total exposure time. For the low doses studied, the higher order modes show a distinct Hg sensing response whereas the fundamental mode does not. The frequency shift for the fourth order mode for a total exposure of 300 s to approximately 15 ppb Hg in N-2 is found to be -320 and -70 Hz for the first and second cases, respectively. (C) 2006 American Institute of Physics.