Macroscopic Strain-Induced Transition from Quasi-infinite Gold Nanoparticle Chains to Defined Plasmonic Oligomers

Abstract

We investigate the formation of chains of few plasmonic nanoparticles-so-called plasmonic oligomers-by strain-induced fragmentation of linear particle assemblies. Detailed investigations of the fragmentation process are conducted by in situ atomic force microscopy and UV-vis-NIR spectroscopy. Based on these experimental results and mechanical simulations computed by the lattice spring model, we propose a formation mechanism that explains the observed decrease of chain polydispersity upon increasing strain and provides experimental guidelines for tailoring chain length distribution. By evaluation of the strain-dependent optical properties, we find a reversible, nonlinear shift of the dominant plasmonic resonance. We could quantitatively explain this feature based on simulations using generalized multiparticle Mie theory (GMMT). Both optical and morphological characterization show that the unstrained sample is dominated by chains with a length above the so-called infinite chain limit-above which optical properties show no dependency on chain length-while during deformation, the average chain length decrease below this limit and chain length distribution becomes more narrow. Since the formation mechanism results in a well-defined, parallel orientation of the oligomers on macroscopic areas, the effect of finite chain length can be studied even using conventional UV-vis-NIR spectroscopy. The scalable fabrication of oriented, linear plasmonic oligomers opens up additional opportunities for strain-dependent optical devices and mechanoplasmonic sensing.

Mechanotunable Plasmonic Properties of Colloidal Assemblies

“…This simple example shows that mechanoplasmonic tuning is achievable via facile methods. Yet, it features a polarization‐dependent optical response which is of interest for strain sensing and color tuning …”

“…The FDTD method is especially useful to calculate the response of plasmonic particles, as there is a wide range of geometries accessible through wet‐chemical synthesis. For instance, spherical particles, anisotropic particles such as rods, hollow as well as multilayered core/shell particles can be achieved via scalable synthesis methods. In a periodic array of plasmonic particles, the lattice period, and thus the nearest‐neighbor interparticle distance, crucially determines the plasmonic SLR properties, since pronounced SLRs require an energetic overlap between the single particle LSPR and the Bragg mode.…”

“…Suitable templates can be obtained by using mechanical instabilities (wrinkling), by laser‐interference lithography, or by soft‐lithographic molding . The dielectric spacer materials, in turn, can be exchanged with functional or flexible materials such as electrochromic polymers or polydimethylsiloxane (PDMS) so that the assemblies become electrically or mechanically tunable. Considering the multitude of available polymers, this opens up a wide range of possibilities to harness collective plasmonic properties for the next generation of large‐area flexible devices.…”

“…In optical analogy, the deformation of plasmonic particle assemblies leads to changes in the lattice constant and the resulting plasmonic response. However, within this arising field of mechanoplasmonics, the practical demonstrations of colloid‐based arrays featuring SLRs with tunable properties are still rare. A proof of concept was recently realized by the Odom group, using top‐down lithographic methods .…”

Shaping Metallic Nanolattices: Design by Microcontact Printing from Wrinkled Stamps

“…[ 30–33 ] These patterns can be used to guide particle assembly, thereby avoiding the utilization of expensive masters, which are usually fabricated by the already mentioned methods of photo or non‐photo lithography. In recent years, PDMS wrinkle templates have been widely used to directly assemble organic [ 34–36 ] and inorganic particles [ 37–39 ] as well as biomaterials, [ 40,41 ] which led to functional nano‐ or micro‐structures applicable for, e.g., plasmonics, [ 37–39 ] or wetting switches. [ 42 ] Nevertheless, up to now there are only a limited number of studies about chemical patterns fabricated by using PDMS wrinkles to guide self‐assembly of particles.…”