title: Broadband near-field infrared spectromicroscopy using photothermal probes and synchrotron radiation.
abstract: In this paper, we experimentally demonstrate the use of infrared synchrotron radiation (IR-SR) as a broadband source for photothermal near-field infrared spectroscopy. We assess two methods of signal transduction; cantilever resonant thermal expansion and scanning thermal microscopy. By means of rapid mechanical chopping (50-150 kHz), we modulate the IR-SR at rates matching the contact resonance frequencies of atomic force microscope (AFM) cantilevers, allowing us to record interferograms yielding Fourier transform infrared (FT-IR) photothermal absorption spectra of polystyrene and cyanoacrylate films. Complementary offline measurements using a mechanically chopped CW IR laser confirmed that the resonant thermal expansion IR-SR measurements were below the diffraction limit, with a spatial resolution better than 500 nm achieved at a wavelength of 6 μm, i.e. λ/12 for the samples studied. Despite achieving the highest signal to noise so far for a scanning thermal microscopy measurement under conditions approaching near-field (dictated by thermal diffusion), the IR-SR resonant photothermal expansion FT-IR spectra measured were significantly higher in signal to noise in comparison with the scanning thermal data.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Donaldson
authors.forename: Chris S
authors.initials: CS
authors.lastname: Kelley
authors.forename: Mark D
authors.initials: MD
authors.lastname: Frogley
authors.forename: Jacob
authors.initials: J
authors.lastname: Filik
authors.forename: Katia
authors.initials: K
authors.lastname: Wehbe
authors.forename: Gianfelice
authors.initials: G
authors.lastname: Cinque