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Tip-Enhanced Infrared Nanospectroscopy via Molecular Expansion Force Detection

January 19, 2014

Feng Lu, Mingzhou Jin & Mikhail A. Belkin

Key points

  • AFM-IR collects spectra of molecular monolayers and monolayer islands with high spatial resolution
  • Comparison of AFM-IR and s-SNOM techniques
  • Achieving sub-monolayer sensitivity


The ability to perform mid-infrared spectroscopy with nanometer spatial resolution is highly desirable for applications in materials and life sciences. At present, scattering near-field scanning optical microscopy is considered to be the most sensitive technique for nanoscale mid-infrared spectroscopy under ambient conditions. We demonstrate that nanoscale mid-infrared spectra can be obtained with comparable or higher sensitivity by detecting mechanical forces exerted by molecules on the atomic force microscope tip on light excitation. This approach results in a simple optical set-up that requires no cryogenically cooled mid-infrared detectors, is easy to align, and is not affected by sample scattering.

(a) Topography of PEG monolayer islands. (b) Height of monolayer islands measured by a topographical line scan along blue arrow in (a). (c) Spectra taken at points shown in (b).