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

Alabdullah, Furqan, Singh, Vikramdeep, Payne, Lukas, Regan, David ORCID: https://orcid.org/0000-0003-0420-3481, Masia, Francesco ORCID: https://orcid.org/0000-0003-4958-410X, Rocha, Victoria G. ORCID: https://orcid.org/0000-0001-6125-8556, Langbein, Wolfgang ORCID: https://orcid.org/0000-0001-9786-1023 and Borri, Paola ORCID: https://orcid.org/0000-0002-7873-3314 2024. Radially polarized light in single particle optical extinction microscopy identifies silver nanoplates. Applied Physics Letters 124 , 181105. 10.1063/5.0188860

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Abstract

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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering Physics and Astronomy Biosciences
Publisher:	American Institute of Physics
ISSN:	0003-6951
Funders:	EPSRC
Date of First Compliant Deposit:	1 May 2024
Date of Acceptance:	12 April 2024
Last Modified:	24 Jun 2024 09:07
URI:	https://orca.cardiff.ac.uk/id/eprint/168571

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