Tip-Enhanced Infrared Nanospectroscopy via Molecular Expansion Force Detection

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.