Plasmonic and Diffractive Coupling in 2D Arrays of Nanoparticles produced by Electron Beam Lithography

Abstract

Nanofabrication is one of the driving forces leading to developments in a variety of fields including microelectronics, medicine, and sensors. Precise control over nanoscale architecture is an essential aspect in relating new size-dependent material properties. Both direct write methods and natural lithography's offer a unique opportunity to fabricate "user-defined" writing of nanostructures in a wide range of materials. Electron Beam Lithography (EBL) and Nanosphere Lithography (NSL) provide the opportunity to fabricate precise nanostructures on a wide variety of substrates with a large range of materials. Using electrodynamics calculations, Schatz and coworkers have discovered one and two dimensional array structures that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicularly to the array axis. In order to investigate these interactions, precise control of nanoparticle orientation, size, shape and spacing is necessary. If the overall structures have excessive defects then the effect may not be seen. For the two dimensional arrays, to have the best control over array fabrication and to look at these interactions experimentally, EBL was used to construct both hexagonal arrays of circular cylinders and the Kagome lattice. The interparticle spacing in each of these structures was varied systematically. Dark field microscopy was used to look at overall sample homogeneity and collect the single particle plasmon resonance spectrum. Additionally, both dark-field and extinction spectroscopies were used to look at the bulk spectral properties of each array type and each spacing. In investigating of the two dimensional arrays, the Kagome structure was also compared to samples produced by traditional NSL to study the optical interaction of defects, domains, and overall sample uniformity on the shape and location of the plasmon resonance. This work illustrates a deeper understanding in the nature of the optical coupling in nanostructures and this knowledge can be utilized in the future to fabricate designer (tailor made) substrates for plasmonic and surface-enhanced raman applications.Mater. Res. Soc. Symp. Proc. Vol. 951

Hybrid Semiconductor Nanoparticles: π-Conjugated Ligands and Nanostructured Films

“…The optical properties of these materials are known to be dependent on their transparency and refractive index modulation. − For example, the simple blending of SiO 2 NPs and polymers decreases the transparency of nanocomposites, because of the scattering of light triggered by the SiO 2 NPs. − The transparency of a polymer (e.g., polyimide, polypropylene, poly(methyl methacrylate)) and silica nanocomposites can also be controlled in the matrix by preparing the hybrid materials using the sol–gel method. Organic surfactant-capped noble metallic NPs can be prepared in a similar manner, e.g., nanowires, nanoshells, and nanocages. − They are very popular and much investigated, giving interesting plasmonic and scattering behavior, which can be identified visible at specific regions of the absorption spectrum. − The emerging field of plasmonics with interesting theoretical and experimental studies on their size, shape, polarization, localized distance dependence, and field-gradient properties are worth examining carefully. − However, they will not be the subject of this current review article, in terms of their hybrid properties, because of the limited space and focus on semiconductor materials.…”

Uniting Top-Down and Bottom-Up Strategies Using Fabricated Nanostructures as Hosts for Synthesis of Nanomites

“…In particular, gold nanostars have attracted attention due to the branched features ending in sharp tips with the potential for generating a high density of surface regions with enhanced local fields for spectroscopy applications. − However, gold nanostars have challenges associated with the need for complex purification protocols, a tendency to aggregate, and a short storage life because of structural changes. − As an alternative approach to synthetic methods, top-down fabrication strategies offer rationally designed plasmonic substrates with control of the structural characteristics of individual particles and organization of particles into arrays. Though generally less sensitive compared to synthetically produced nanostars, fabricated particles have several advantages, including tunable localized surface plasmon resonance (LSPR) wavelengths spanning broad spectral ranges, reproducibility of particles with different shapes using direct-write and template methods, and no aggregation problems due to solution conditions or exposure to complex matrices for applications. − …”

Plasmonic nanospherical dimers for color pixels

“…Far-field diffractive coupling enhances the scattering intensity and reduces the plasmon linewidth of the array. [31][32][33][34][35][36][37][38] Note that the glass substrate has the effect of redshifting the resonance and making the farfield diffractive coupling less efficient due to the inhomogeneous environment around the dimers. [39][40][41][42][43] However, it was shown that for large particles, diffractive coupling could still occur.…”