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Surface Applications of Cavity Ring-Down Spectroscopy

Published

Author(s)

A C. Pipino, Curtis Meuse, J P. Hoefnagels, Vitalii I. Silin, John T. Woodward IV

Abstract

We report preliminary results describing two new applications of cavity ring-down spectroscopy (CRDS): 1) detection of non-absorbing species by refractive-index change using surface-plasmon-resonance (SPR)-enhanced CRDS, and 2) C-H overtone detection by evanescent wave CRDS with a determination of absolute adsorbate surface coverage. Detection of tri- and tetra-chloroethylene (TCE and PCE), which are major environmental contaminants, is explored. The SPR-enhanced CRDS measurements show a minimum detectable concentration of 7x10-8 mole/liter and 2x10-8 mole/liter for TCE and PCE, respectively, based on a 1 minute response time at 555 nm, where neither species possesses a significant absorption cross section. A conventional linear resonator is employed with an intra-cavity flow cell consisting of a pair of low-loss optical flats at Brewster s angle. The surface plasmon resonance is provided by an ultra-thin Au film (nominal thickness .0.2 nm), which creates a sparse distribution of approximately spherical Au particles. The EW-CRDS measurements exploit the first C-H overtone of TCE occurring around 1640 nm. Spectra for both surface and gas-phase species are obtained in the evanescent wave. Employing the absolute absorption cross section for the C-H overtone of TCE obtained from gas-phase CRDS measurements, the adsorbate spectrum and corresponding absolute surface number density are determined. The requisite measure of molecular orientation is provided by the polarization dependence of the surface spectrum.
Citation
NIST Interagency/Internal Report (NISTIR) - 6957
Report Number
6957

Keywords

absolute surface coverage, absorption, cavity ring-down spectroscopy, evanescent waves, surface plasmon resonance

Citation

Pipino, A. , Meuse, C. , Hoefnagels, J. , Silin, V. and Woodward IV, J. (2008), Surface Applications of Cavity Ring-Down Spectroscopy, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD (Accessed February 29, 2024)
Created October 16, 2008