Atomic Force Microscopy-Infrared Spectroscopy

AFM-based infrared spectroscopy (AFM-IR) is a rapidly emerging technique that combines the spatial resolution of atomic force microscopy (AFM) with the chemical analysis capability of infrared (IR) spectroscopy.

Advantages

  • Simultaneous morphological and chemical imaging
  • Spatial resolution around a few nm (the order of the AFM tip radius), smaller than the IR diffraction limit (which restricts the spatial resolution of conventional IR microscopy to few µm)
  • AFM-IR spectra directly comparable with FTIR ones

Principles

AFM-IR consists of a pulsed tunable infrared laser that is focused on a sample near the tip of an AFM. If the tunable IR laser is set to a wavelength that corresponds to an absorbing wavelength of the sample, the sample will be slightly heated up and will expand. This causes a transient oscillation of the probe that is proportional to the IR absorption. IR absorption spectra of nanoscale region of a sample can thus be obtained by measuring the AFM probe response to IR absorption as a function of wavelength.

Additionally, it is possible to tune the laser to a fixed wavelength and measure the absorption as a function of position across the sample to create chemical images that show the distribution of chemical species across a sample.

Applications

References:

A. Dazzi, C.B. Prater, AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging, Chem. Rev. 2017, 117, 5146–517
J. Waeytens et al., Determination of Secondary Structure of Proteins by Nanoinfrared Spectroscopy, Anal. Chem. 2023, 95, 621–62