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 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.

Magnetic nanomaterials record information as fast as picoseconds in computer memories but retain it for millions of years in ancient rocks. This exceedingly broad range of times is covered by hopping over a potential energy barrier through temperature, ultrafast optical excitation, mechanical stress, or microwaves. As switching depends on nanoparticle size, shape, orientation, and material properties, only single-nanoparticle studies can eliminate the ensemble heterogeneity. Here, we push the sensitivity of photothermal magnetic circular dichroism down to individual 20 nm magnetite nanoparticles. Single-particle magnetization curves display superparamagnetic to ferromagnetic behaviors, depending on the size, shape, and orientation. Some nanoparticles undergo thermally activated switching on time scales of milliseconds to minutes. Surprisingly, the switching barrier varies with time, leading to dynamical heterogeneity, a phenomenon familiar in protein dynamics and supercooled liquids. Our observations will help to identify the external parameters influencing magnetization switching and, eventually, to control it, an important step for many applications.

We demonstrate how to measure scattering spectra of single plasmonic nanoparticles using a confocal darkfield setup. We give an overview of considerations and problems we encountered when employing a darkfield technique based on filtering illumination under low angles instead of the conventional high-angle filtering by darkfield objectives.

The nanoscale morphology of metal nanostructures directly defines their optical, catalytic and electronic properties and even small morphological changes can cause significant property variations. On the one hand, this dependence allows for precisely tuning and exploring properties by shape engineering; next to advanced synthesis protocols, post-synthesis modification through tailored laser modification has become an emerging tool to do so. On the other hand, with this interconnection also comes the quest for detailed structure-property correlation and understanding of laser-induced reshaping processes on the individual nanostructure level beyond ensemble averages. With the development of single-particle (ultrafast) optical spectroscopy techniques and advanced electron microscopy such understanding can in principle be gained at the femtosecond temporal and atomic spatial scale, respectively. However, accessing both on the same individual nanostructure is far from straightforward as it requires the combination of optical spectroscopy and electron microscopy. In this Minireview, we highlight key studies from recent years that performed such correlative measurements on the same individual metal nanostructure either in a consecutive ex situ manner or in situ inside the electron microscope. We demonstrate that such a detailed correlation is critical for revealing the full picture of the structure-property relationship and the physics behind light-induced nanostructure modifications. We put emphasis on the advantages and disadvantages of each methodology as well as on the unique information that one can gain only by correlative studies performed on the same individual nanostructure and end with an outlook on possible further development of this field in the near future.