AVS 60th International Symposium and Exhibition
    Scanning Probe Microscopy Focus Topic Thursday Sessions
       Session SP+AS+BI+NS-ThP

Paper SP+AS+BI+NS-ThP2
Rapid Near-Field Infrared Spectroscopy Using an External Cavity Quantum Cascade Laser

Thursday, October 31, 2013, 6:00 pm, Room Hall B

Session: Scanning Probe Microscopy Poster Session
Presenter: A.S. Lea, Pacific Northwest National Laboratory
Authors: I.M. Craig, Pacific Northwest National Laboratory
M.S. Taubman, Pacific Northwest National Laboratory
M.C. Phillips, Pacific Northwest National Laboratory
A.S. Lea, Pacific Northwest National Laboratory
M.B. Raschke, University of Colorado at Boulder
Correspondent: Click to Email
Scattering scanning near-field optical microscopy (s-SNOM) is an apertureless superfocusing technique that uses the antenna properties of a conducting atomic force microscope (AFM) tip to achieve infrared spatial resolution below the diffraction limit. The instrument can be used either in imaging mode, where a fixed wavelength light source is tuned to a molecular resonance and the AFM raster scans an image, or in spectroscopy mode where the AFM is held stationary over a feature of interest and the light frequency is varied to obtain a spectrum. In either case, a strong, stable, coherent infrared source is required. Here we demonstrate the integration of a broadly tunable external cavity quantum cascade laser (ECQCL) into a s-SNOM and use it to obtain infrared spectra of microcrystals adsorbed onto gold substrates.

Residues of explosive compounds PETN, RDX, and tetryl were deposited onto gold substrates. s-SNOM experiments were performed in the 1260–1400 cm−1 tuning range of the ECQCL, corresponding to the NO2 vibrational fingerprint region. Chemical imaging with fixed wavelength tuned to a molecular resonance allows mapping of species distributions a spatial resolution of 25 nm. Vibrational infrared spectra are then collected on individual chemical domains with a collection area of 500 nm2. Acquisition times of less than 6 min with SNR of >50 and 0.2 cm−1 spectral resolution are possible. Spectra are compared to ensemble averaged far-field infrared reflection-absorption spectroscopy (IRRAS) results.