Methane sensing at room temperature using photothermal cantilever deflection spectroscopy

Detection of methane at room temperature using adsorption-based chemical sensing is a challenge since methane is inert and does not adsorb on surfaces. We demonstrate that nanomechanical photothermal spectroscopy is capable of detecting femtogram level physisorbed methane on a thermally sensitive microcantilever. Even though the residence time of methane is in sub nanoseconds, it is enough for a vibrationally excited methane molecule to transfer its energy to the cantilever through a non-radiative decay process. The variation of cantilever deflection as a function of excitation wavelength shows the characteristic vibrational spectrum of methane. Photothermal cantilever deflection spectroscopy, therefore, offers a powerful technique for chemical characterization of physisorbed molecules which are chemically inert.