  Infrared (IR) spectroscopy, a well established tool for chemical analysis of
diverse materials, has significant potential in biomedical applications. While
the spatial resolution of traditional IR spectroscopy is limited by the
wavelength of the IR light to the few micrometres, it has been shown that
nanoscale chemical analysis can be obtained by detecting IR induced local
heating photothermal response via Scanning Thermal Microscopy (SThM) or local
thermomechanical expansion using Atomic Force Microscopy (AFM). This paper
explores the potential of a pulsed ps pulse duration high power free electron
laser (FEL) light source for AFM-IR and SThM-IR spectroscopy employing standard
AFM and SThM probes. The SThM-IR response was found to have a detrimental
strong background signal due to the direct heating of the probe, whereas the
AFM IR thermomechanical response allowed to eliminate such a problem for both
top down and bottom up illuminations with the FEL IR source. The SThM IR
characteristic response time was approximately half that of AFM-IR, in line
with finite element analysis simulations. Finally, the advantages and drawbacks
of AFM-IR wavelength sensitive spectroscopic response using a ps duration FEL
vs a high repetition quantum cascade laser IR source in studies of nanoscale
dimension amyloid peptide fibres were explored both experimentally and via
finite elements analysis.
