Integrating Scanning Tunneling Microscopy with Fourier-Transform Infrared Spectroscopy

The scanning tunneling microscope (STM) has revolutionized our ability to observe surface features at the scale of atoms and molecules on a variety of conductive substrates. Conventional STM images contain limited chemical information, generally related to electronic structural variations of surfaces and adsorbates. We propose to expand the capabilities of the STM by simultaneously exciting the surface with an evanescent wave of infrared radiation and measuring the changes in apparent conductance with the probe tip. Due to the local nature of scanning probe microscopies, we investigate vibrational structure below the diffraction limit. An interferometer source enables us to probe the surface at a variety of frequencies simultaneously. We are using cyanide monolayers on Au{111}, because of its stability, simple absorption spectra distinct from water and CO₂ absorption spectra, and its theoretical vibronic coupling to the surface electronic states of Au{111}. This methodology will serve as the framework for future experiments on a wide variety of systems.