Summary : Atomic force microscope-based infrared spectroscopy (AFM-IR) has been developed in recent years providing extremely high spatial resolution chemical characterization and imaging. The technique is based on the combination of a tunable infrared laser with an atomic force microscope that can locally map and measure thermal expansion of nanoscale regions of a sample resulting from the absorption of infrared radiation. The results obtained in microbiology and polymer sciences show how this approach is a powerful tool. The principle is based on detecting the local thermal expansion of the sample, irradiated at the wavelength of its absorption bands [1]. This expansion is detected by the AFM tip in contact mode. As the duration of expansion and relaxation of the sample is always shorter than the response time of the cantilever in contact, the excitation transmitted to the cantilever acts as an impulse function, exciting oscillations at resonant frequencies of the cantilever. The technique can create nanoscale IR absorption spectra by recording the amplitude of these oscillations as a function of wavelength and chemical maps by measuring the oscillation amplitude as a function of position. Because the AFM probe tip can map the thermal expansion on very fine length scales, the AFM-IR technique provides a robust way to obtain interpretable IR absorption spectra at spatial resolution scales well below the diffraction limit [2]. The technique also provides simultaneous and complementary mapping of mechanical properties and has been widely and successfully applied to applications in polymers and the life sciences [3,4,5]. Most previous AFM-IR measurements have been performed using total internal reflection illumination from below the sample, generally requiring samples to be prepared as thin sections transferred to an IR transparent prism [6,7]. We have recently extended the AFM-IR technique to work in a "top side illumination" configuration. The top side illumination enables a much broader range of samples to be measured and can in some cases dramatically simplify sample preparation and increase the resolution [8]. [1] Dazzi et al. Opt. Lett. 2005 [2] Dazzi et al. J Appl. Phys. 2010 [3] Dazzi et al. Appl. Spectrosc. 2012 [4] Deniset-Besseau et al. J. Phys. Chem. Lett. 2014 [5] Policar et al, Angewandte Chemie International Edition 2011 [6] Gosh et al. New J. Chem. 2013. [7] Felts et al. Rev. Sci. Instrum. 2013. [8] Lu et al. Nature Photonics 2014.

AFMIR : A powerful tool for Infrared Nanoscopy

249th National Meeting (2015)

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