3-D Plasmonic Nanoarchitectures: Fabrication, Characterization, and Applications

Abstract

Plasmonic nanostructures are known to concentrate incident light to their surfaces by collective electron oscillation, a.k.a., localized surface plasmon resonance (LSPR). Plasmonic hot-spot refers to locations where electromagnetic fields are particularly enhanced relative to the incident field. Traditional plasmonic nanomaterials are 1D (e.g., colloidal nanoparticles) or 2D (lithographically patterned nanostructure arrays) in nature, which typically result in sparse field concentration patterns. To improve efficiency and better utilization of hot-spots, 3D plasmonic nanoarchitectures are desired, where abundant hot-spots are formed in a 3D volumetric fashion, a feature drastically departing from traditional nanostructures. In this dissertation, two novel 3D plasmonic nanostructures are reported.

The first one is NPG nanoparticle, a disk shaped nanostructure with 3D pore-ligament bi-continuous network. NPG disks are made by the low-cost nanosphere lithography (NSL) technique, which is capable of wafer scale production. NPG disks possess larger surface area and high density internal plasmonic hot-spots, which are absent in its bulk counterparts. Due to these unique properties, NPG disks can be potentially used in various surface enhanced Raman spectroscopy (SERS), surface enhanced fluorescence (SEF), and photothermal based applications. To optimize the performance of NPG disks in various applications and understand its plasmonics better, two different modeling techniques, Bruggeman effective medium theory (B-EMT) model and Nanoporous (NP) model, are introduced and evaluated against the experimental data obtained by an electron beam lithography (EBL) compatible fabrication technique for NPG disks. The EBL method can provide large area 2D patterns of randomly distributed nanodisks with flexible interdisk (center to center) distance. Such flexibility is essential to obtain quasi-single NPG disk response, which typically peaks in the near infrared (NIR) spectrum beyond 1 μm, from ensemble measurements by common UV/VIS/NIR spectrometers instead of a specialized NIR spectroscopic microscope. After successful fabrication and modeling, the plasmon enhanced catalysis application of NPG disks is reported in details. The effectiveness of NPG disks in various applications depends on its LSPR peak position. Hence, optimization of an application might require the fine tuning of the peak position. A novel laser based rapid thermal annealing technique is reported to fine tune the LSPR peak position of NPG disks.

The second 3D plasmonic nanostructure, reported in this dissertation, is based on the chicken egg shell, a day-to-day waste material. The 3-dimensional (3D) submicron features on the outer shell (OS), inner shell (IS), and shell membrane (SM) regions are sputter coated with gold found to have excellent SERS performance. Moreover, the outer shell substrate is found to be capable of detecting single bacterial cell. This facile way of fabricating 3D plasmonic substrates can facilitate the adoption of 3D plasmonic substrates by researchers in less fortunate countries.