Radially polarized light in single particle optical extinction microscopy identifies silver nanoplates

Quantifying the optical extinction cross section of a single plasmonic nanoparticle (NP) has recently emerged as a powerful method to characterize the NP morphometry, i.e., size and shape, with a precision comparable to electron microscopy while using a simple optical microscope. Here, we enhance th...

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Bibliographic Details
Published in:Applied physics letters 2024-04, Vol.124 (18)
Main Authors: Alabdullah, Furqan, Singh, Vikramdeep, Payne, Lukas, Regan, David, Masia, Francesco, Rocha, Victoria G., Langbein, Wolfgang, Borri, Paola
Format: Article
Language:English
Subjects:
Absorption cross sections
Algorithms
Cluster analysis
Electron microscopy
Extinction
Machine learning
Microscopy
Nanoparticles
Numerical aperture
Optical microscopes
Polarization
Polarized light
Scattering cross sections
Triangles
Unsupervised learning
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Summary:Quantifying the optical extinction cross section of a single plasmonic nanoparticle (NP) has recently emerged as a powerful method to characterize the NP morphometry, i.e., size and shape, with a precision comparable to electron microscopy while using a simple optical microscope. Here, we enhance the capabilities of extinction microscopy by introducing a high numerical aperture annular illumination coupled with a radial polarizer to generate a strong axial polarization component. This enables us to probe the NP response to axial polarized light, and, in turn, to distinguish flat-lying nanoplates from other geometries. Polarization-resolved optical extinction cross sections were acquired on 219 individual colloidal silver NPs of a nominally triangular nanoplate shape but, in practice, exhibiting heterogeneous morphometries, including decahedrons and non-plate spheroids. An unsupervised machine learning cluster analysis algorithm was developed, which allowed us to separate NPs into different groups, owing to the measured differences in cross sections. Comparison of the measurements with a computational model of the absorption and scattering cross section accounting for nanoplates of varying geometries beyond simple triangles provided insight into the NP shape of each group. The results provide a significant improvement of polarization-resolved optical extinction microscopy to reconstruct NP shapes, further boosting the utility of the method as an alternative to electron microscopy analysis.
ISSN:0003-6951
1077-3118
DOI:10.1063/5.0188860