Unraveling the Effects of Size, Composition, and Substrate on the Localized Surface Plasmon Resonance Frequencies of Gold and Silver Nanocubes: A Systematic Single-Particle Approach

Abstract

Localized surface plasmon resonances (LSPRs), resulting from the interaction of light with metal nanoparticles, are powerful tools for biological sensors, surface-enhanced spectroscopies, and optical devices. LSPR frequencies are strongly dependent on a nanoparticle's structure, composition, and local dielectric environment. However, these relationships are prohibitively difficult or impossible to probe from bulk solutions due to the heterogeneity of chemically synthesized products. In this study, systematic single-particle structure-property measurements, coupled with a statistical analysis and FDTD calculations, are performed on silver and gold nanocubes. The dependencies of LSPR frequencies on nanocube size, composition, and substrate dielectric constant are determined. The results obtained represent the most quantitative measurements and analysis to date, yielding predictive rules and fundamental insights into the interactions between nanoparticles and substrates.

Near-Field Localization of Single Au Cubes: A Group Theory Description

“…Note that the C 4v point group does not contain any inversion symmetry with respect to the substrate plane (normal to z axis), so top and bottom charges are to be expected of different values as found in digital simulations. 47 Photoemission experiments on nanocubes can be easily interpreted as combinations of the E and A 1 LSPR resonances as displayed in Figure 3. Indeed, any incident electrical field can be decomposed onto the SALC eigenstate vector basis.…”

Plasmon and compositional mapping of plasmonic nanostructures

“…Unlike the bulk, size and shape affect the (optical) properties of metals at the nanoscale: a large cube does not behave in the same fashion as a small cube, and assembling particles lead to complex mode hybridizing, for example. 17,18 Advances in the field of synthesis and characterization has provided much insight about those effects for simple as well as increasingly complex structures. Novel multi-step reactions now also allow multicomponent and alloy materials, which are promising for multifunctional particles, bringing together properties including magnetism, catalytic activity, optical properties, and biocompatibility, to name a few.…”

Aluminum Nanocrystals

“…For the representative 165 nm diameter Al nanocrystal studied here, three prominent modes were found: the lowest energy at 3.3 eV and intermediate energy modes at 5.5 and 7.1 eV (Figure 4a). EELS images were obtained at spectral windows corresponding to these three mode energies (Figure 4b), which provided sufficient bandwidth to allow the use of non-negative matrix factorization, a powerful and assumption-free modal decomposition approach, to generate the nanocrystal image 23,24 . The nanocrystal images consistently display 3-fold symmetry, consistent with the CL images.…”

“…The field intensity for the lowest energy dipolar 3.3 eV plasmon mode (Figure 4a, top) is strongly localized at the tips of the particle, similar to the lower energy modes of a nanocube. 23,24 The 5.5 eV mode (Figure 4a, center) is a quadrupolar surface plasmon resonance, with the field intensity localized at the faces of the structure. The 7.1 eV mode (Figure 4a, bottom) is also localized at the nanoparticle surface and is consistent with a dark higher order octupolar plasmon mode that is slightly redshifted due to the presence of the thin oxide layer at the surface of the nanocrystal.…”