Ultrabroadband Infrared Nanospectroscopy

The development of near-field infrared techniques has enabled infrared analysis to surpass the diffraction-limit and probe chemical and physical heterogeneities at the nanoscale. In infrared scanning near-field optical microscopy (IR s-SNOM), IR light is focused onto and scattered by an atomic force microscope (AFM) tip, and detected interferometrically in the far-field with an IR detector. When combined with the broad bandwidth, spatial coherence, and high brightness of synchrotron infrared radiation, IR s-SNOM enables vibrational spectroscopy spanning the infrared region with a wavelength-independent spatial resolution equivalent to the tip-apex radius, which is typically less than 25 nm. The Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory operates two of these synchrotron infrared nanospectroscopy (SINS) instruments that are available for general users to address fundamental questions that can only be answered with a chemically selective nanoscopic probe. In this talk, I will describe the technical aspects of the SINS technique and highlight representative examples of the rapidly growing range of applications in physics, chemistry, biology, materials science, geology, and atmospheric and space sciences. While most of the applications to date have been measured under ambient conditions in the mid-IR, many in situ / in operando measurements require additional environmental control (i.e. variable cryogenic temperatures, gas/vacuum, liquids) and/or increased spectral range in the far- and near- IR that push the current boundaries of our instruments and technique. I will describe efforts to address some of these challenges and offer perspectives for the future of infrared nanospectroscopy.