Selective detection of physisorbed hydrocarbons using photothermal cantilever deflection spectroscopy

We have used photothermal cantilever deflection spectroscopy (PCDS) for selective and sensitive detection of complex hydrocarbons such as naphtha physisorbed on a bi-material cantilever. In the PCDS, molecules physisorbed on a bi-material microcantilever are illuminated with mid-infrared (IR) light from a monochromator. The resonant vibrational excitation of the molecules and the resultant nonradiative decay processes increase the temperature of the bi-material cantilever giving rise to a readily observable deflection. The nanomechanical deflection of the cantilever as a function of illumination wavelength corresponds to the IR absorption spectrum of the adsorbed molecules. Here, we report on detection and molecular discrimination of nanogram quantities of hydrocarbons on the cantilever using the PCDS technique. The obtained PCDS spectra show excellent agreement with the traditional IR spectroscopic results.