2019 Volume 64 Issue 11 Pages 661-666
Infrared (IR) spectroscopy is one of the major methods for chemical structural characterization. However, its spatial resolution is limited to a few micrometers at most due to diffraction limit. Recently, several kinds of nanoscale infrared spectroscopy have been developed based on the combination of a pulsed IR laser illumination and atomic force microscopy (AFM). Among them, AFM-IR (AFM-based IR) spectroscopy has been applied to various kinds of materials from organic to inorganic. In AFM-IR, local infrared absorption is detected through an AFM probe oscillation induced by thermal expansion of a sample after IR laser illumination. Another method named O-PTIR (optical photothermal IR) spectroscopy which utilizes a visible laser instead of an AFM probe to detect IR absorption also has nanoscale, or more correctly sub-micron spatial resolution. Its ability of non-contact signal detection has a potential applicability to in-situ measurements. The principles and applications of AFM-IR and O-PTIR spectroscopy are introduced.
