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Reliable determination of sub-nanometer gaps in plasmonic gold dimers for correlation to their optical properties

Francesca Scalerandi1, Alexander Skorikov2, Nathalie Claes3, Sara Bals3, Guillermo González-Rubio4, Nick Sokov5, and Wiebke Albrecht1,*

  • *Contact author: w.albrecht@amolf.nl
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Phys. Rev. Materials 9, 105202 – Published 10 October, 2025

DOI: https://doi.org/10.1103/9jvw-qdsx

Abstract

Accurately characterizing sub-nanometer gaps in plasmonic nanoparticle dimers is essential for understanding their optical properties, particularly in the transition from classical to quantum plasmonic behavior. While two-dimensional (scanning) transmission electron microscopy imaging provides high spatial resolution, it lacks the three-dimensional (3D) morphological information needed to reliably extract gap sizes. In this work, we combine electron tomography with a robust data analysis workflow to quantify interparticle gaps in gold nanosphere dimers with sub-nanometer precision. We show that gap size estimates are highly sensitive to reconstruction algorithms, segmentation thresholds, and meshing parameters. To overcome this, we introduce a model-fitting approach based on convolving a step function with a Gaussian, enabling consistent and accurate gap measurements even in the absence of a known ground truth. Validation on simulated datasets confirms pixel-level accuracy, and application to experimental data demonstrates the robustness and general applicability of the method. The resulting 3D reconstructions are directly integrated into electromagnetic simulations, allowing reliable interpretation of the optical response of the dimer. This workflow offers a broadly applicable strategy for correlating morphology and optical function in plasmonic systems and provides a crucial step toward resolving quantum effects in nanoscale light-matter interactions.

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Corrections

21 October, 2025

Correction: An error in the order of author names has been fixed and the presentation of the bylines has been adjusted to accommodate for the change.

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New Insights into Functional Materials through Advanced Electron Microscopy

The Editors of Physical Review Materials are pleased to present the Collection on New Insights into Functional Materials through Advanced Electron Microscopy, highlighting cutting-edge microscopy techniques and the extraordinary advances in materials science and engineering that they enable. The Collection is being guest-edited by Joanne Etheridge from Monash University (Australia) and Yimei Zhu from Brookhaven National Laboratory (USA). Every article published in this collection underwent a rigorous peer review process, adhering to the same high standards applied to all papers. The Physical Review Materials editorial team managed the peer review and made all editorial decisions.

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Phys. Rev. Materials 9, 105202– Published 10 October, 2025
  • Received 28 March 2025
  • Revised 16 July 2025
  • Accepted 20 August 2025
  • Corrected 21 October 2025
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