Hyperspectral Analysis of Enhanced Extinction in Micrometer-Thin Polymer Films Containing Nanoparticles at High Volume Fraction

Extinction in thin polymer films containing nanoparticles is important to photovoltaics, sensors, and interconnects. Extinction measured in 1-millimeter-thin films containing plasmonic nanoparticles increased with nanoparticle density to levels higher than predicted. Yet, enhancement of extinction was not measured in <100-nanometer-thin films containing high-density plasmonic nanoparticles. The present study examined extinction in 80 micrometer films that contained plasmonic nanoparticles at increasing volume fractions. Optical images and spectra were integrated in a new hyperspectral method to quantitate visual attributes to use nanoparticle-containing films in e.g., colorimetric assays. Measured extinction was compared with values predicted by the exact Mie solution to Maxwell's equation and by the Maxwell-Garnett effective medium theory. Extinction measured in 80-micron films was found to increase with nanoparticle volume fraction from a low value predicted by Mie theory to a high value predicted by Maxwell-Garnett effective medium theory. Results of the present study are useful to specify the volume fraction of nanoparticles in thin polymer films to obtain desired spectral characteristics for photovoltaics, sensors, interconnects, and colorimetric point-of-care assays.