Synthesis, Separation, and Hypermethod Characterization of Gold Nanoparticle Dimers Connected by a Rigid Rod Linker

Bonding individual metallic nanoparticles at small separation distances to let them form dimers and making them available in large quantities is a key requirement for various applications that wish to exploit the tremendous enhancement of electromagnetic fields in plasmonic junctions. Although progress has been witnessed in the past concerning the fabrication of dimers mediated by rigid molecular linkers, the exact bonding mechanism remains unclear. Here, we describe the fabrication of a rigid linker molecule and demonstrate its feasibility to achieve dimers made from closely spaced metallic nanoparticles in large quantities. Although the topography of the dimers proves the success of the fabrication method, we use what we call a hypermethod characterization approach to study the optical properties of dimers from various perspectives. Measuring the surface-enhanced Raman scattering signal of the linker molecule enables direct tracing of the optical environment it perceives. By reaching a strong field enhancement in the gap of the dimers, we are able to investigate optical and geometrical properties of the linker. Moreover, upon isolation of the dimers, we use single-particle extinction spectroscopy to study the optical response of a fabricated dimer directly. Full wave numerical simulations corroborate the experimental results and provide insights into quantities which cannot be accessed directly in experiments. The ability to fabricate and to characterize rigidly linked nanoparticles will pave the way toward various plasmonic applications such as sensors, photocatalysis, and plexcitonics.