Sensitive and selective detection of hydrocarbon/water vapor mixtures with a nanoporous silicon microcantilever

We have developed a sensitive and selective sensor for hydrocarbon/water vapor mixtures using nanomechanical infrared (IR) spectroscopy with a porous silicon (P-Si) microcantilever. Facile and direct anodization process is utilized to fabricate vertically aligned nanopores of 20-50 nm diameters on a plain silicon microcantilever. The effective Young's modulus and surface area of a P-Si microcantilever can be easily controlled by the thickness of the anodized P-Si layer. Here we demonstrate the detection of 1 wt% naphtha/water vapor mixtures using nanoporous cantilever IR spectroscopy. Nanoporous nature of the cantilever surface enhances its thermomechanical sensitivity. In addition, trapping the volatile hydrocarbon molecules in the nanowells increases the analyte concentration on the surface. Nanomechanical IR spectra of adsorbed vapors were obtained by plotting the deflection amplitudes of the microcantilever as a function of the illuminating IR wavenumber. The mass of the adsorbed vapors was determined from variations in the resonance frequency of the cantilever.