Open AccessBroadband near-field infrared spectromicroscopy using photothermal probes and synchrotron radiation
Author(s) -
Paul M. Donaldson,
Chris S. Kelley,
Mark D. Frogley,
Jacob Filik,
Katia Wehbe,
Gianfelice Cinque
Publication year - 2016
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.24.001852
Subject(s) - materials science , photothermal therapy , optics , infrared , microscopy , infrared microscopy , photothermal spectroscopy , near field scanning optical microscope , synchrotron radiation , optoelectronics , analytical chemistry (journal) , optical microscope , scanning electron microscope , nanotechnology , chemistry , physics , chromatography
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.