Accurate measurement of the optical constants for modeling organic and organophosphorous liquid layers and drops

Myers, Tanya L.; Tonkyn, Russell G.; Danby, Tyler O.; Vetter, Brent M. De; Bernacki, Bruce E.; Taubman, Matthew S.; Johnson, Timothy J.

doi:10.1117/12.2300777

Cited by 2 publications

(2 citation statements)

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“…Images for the solid samples on glass and polished aluminum are presented but not for samples on roughened aluminum since the surface roughness was too high (∼2 μm) compared to the film thickness, making it impossible to yield information regarding the uniformity. For the liquids, spin coating was used to apply thin films to the substrates but attempts to quantify the thickness of the analytes were not successful; 30 reference measurements are thus not presented for the liquids.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…11; it may be due to the surface roughness having an rms roughness of ∼2 μm. 30 Two features are of note: (i) there is a wavelength dependence to the reflectance of the roughened aluminum substrate and (ii) there is an offset between the reflectance of the bare substrate and that of the roughened substrate coated with caffeine. The additional reflective losses arise from the first and second surface reflective losses from the caffeine layer.…”

Section: Caffeine On Aluminummentioning

confidence: 99%

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Modeling thin layers of analytes on substrates for spectral analysis: use of solid/liquid n and k values to model reflectance spectra

2020

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Since solids are only sometimes seen en masse in a pure bulk form, and for liquids other than water almost never, a capability to model reflectance spectra from analytes deposited on various substrates would be highly advantageous. If available, the real, nðνÞ, and imaginary, kðνÞ, components of the complex refractive index, n ∼ ¼ n þ ik, can be used to simulate infrared spectra, accounting for reflection, refraction, and absorption phenomena as a function of wavelength. We focus on using the Pacific Northwest National Laboratory (PNNL) derived n∕k vectors for solid and liquid analytes deposited as thin layers on different types of substrates including conductors, such as aluminum, and inorganic dielectrics, such as glass. The model is an adaptation of the Monte Carlo ray trace modeling program, TracePro, extended through the use of its macrolanguage. The model is tested using thin films of organic liquids including silicone oil and no. 2 diesel fuel, as well as organic solids such as caffeine and acetaminophen on aluminum and glass. The predicted spectra for the solid films were compared to experimental hemispherical reflectance data measured using a Fourier transform spectrometer with an integrating sphere. The thickness of the calculated layer is a parameter for predicting the (transflectance) spectra and is obtained using the areal density measured from gravimetric methods to generate the thin-layer samples. Comparison of the calculated spectra with experimental hemispherical reflectance data shows excellent agreement, indicating promise for the use of measured n∕k data to synthesize reference spectral data. In particular, accounting for the inhomogeneity of the deposits greatly improved the match with experimental data. Finally, the theoretical modeling shows that for thicker layers (ca. 20 to 100 μm) of typical organics possessing moderately strong k values, the longwave infrared features are often saturated and better spectral contrast is obtained from the overtone/combination bands in the shortwave infrared. © The Authors.Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Caffeine On Aluminummentioning

confidence: 99%