Plasmon-enhanced vibrational spectroscopy, including surface-enhanced infrared absorption spectroscopy (SEIRA) and surface-enhanced Raman scattering (SERS), has attracted great attention in molecular sensing and nano-spectroscopy. In this work, we present a facile <i>in situ</i>-controlled method for the chemical synthesis of patchy SiO<sub>2</sub>@Au core-shell nanoparticles with multiple plasmonic nanogaps. The multiple sizes and shapes of Au nano-islands on patchy Au nanoshells and their plasmonic coupling exhibit broadband resonances ranging from the near infrared (NIR) region to the middle infrared (MIR) region, making patchy Au particles ensemble suitable for both SEIRA and SERS applications. In the SEIRA application, we demonstrate <i>in situ</i> and real-time monitoring of monolayer of reduced glutathione molecules (GSH) adsorbed on the plasmonic Au surface. By using GSH as the molecular linker, we also demonstrate <i>in situ </i>detection of trace amount of mercuric ions in water at nanomolar level. In the SERS application, we show the applicability of patchy Au nanoparticles for SERS at 785 nm excitation.
We demonstrate the development of colloidal lithography technique to fabricate large-area plasmonic perfect absorbers using Al, which is an earth abundant low-cost plasmonic material in contrast to Au and Ag. Using numerical electromagnetic simulations, we optimize the geometrical parameters of Al perfect absorbers (AlPAs) with resonances at desired wavelengths depending on the applications. The fabricated AlPAs exhibit narrowband absorptions with high efficiency up to 98 %. By tuning AlPAs parameters, the resonance of AlPAs can be tuned from the visible to the middle infrared region. The AlPAs can be applied for spectrally selective infrared devices such as selective thermal emitters, selective surface-enhanced vibrational spectroscopy (SEIRA) for molecular sensing and selective IR detectors. In this report, we demonstrate applications of AlPAs for selective thermal emitters and SEIRA. The results obtained here reveal a simple technique to fabricate scalable plasmonic perfect absorbers as well as their potential applications in optoelectronic and photonic devices.
Nanosphere lithography (NSL) uses self-assembled layers of monodisperse micro-/nano-spheres as masks to fabricate
plasmonic metal nanoparticles. Different variants of NSL have been proposed with the combination with dry etching
and/or angled-deposition. These techniques have employed to fabricate a wide variety of plasmonic nanoparticles or
nanostructures. Here we report another promising extension - moiré nanosphere lithography (MNSL), which
incorporates in-plane twisting between neighboring monolayers, to extend the patterning capability of conventional
NSL. In conventional NSL, the masks, either a monolayer or bilayer, are formed by spontaneous self-assembly.
Therefore, the resulted colloidal crystal configurations are limited. In this work we used sequential stacking of
polystyrene nanosphere monolayers to form a bilayer crystal at the air/water interfaces. During this layer-by-layer
stacking process, a crystal domain in the top layer gains the freedom to positon itself in a relative angle to that in the
bottom layer allowing for the formation of moiré patterns. Subsequent O<sub>2</sub> plasma etching results in a variety of complex
nanostructures that have not been reported before. Using etched moiré patterns as masks, we further fabricated the
corresponding gold nanostructures and characterized their scattering optical properties. We believe this facile technique
provides a new strategy to fabricate novel and complex plasmonic nanostructures or metasurfaces.