Shape-Selective Deposition and Assembly of Anisotropic Nanoparticles

Abstract

We report the large-area assembly of anisotropic gold nanoparticles into lithographically defined templates with control over their angular position using a capillary force-based approach. We elucidate the role of the geometry of the templates in the assembly of anisotropic nanoparticles consisting of different shapes and sizes. These insights allow us to design templates that immobilize individual triangular nanoprisms and concave nanocubes in a shape-selective manner and filter undesired impurity particles from a mixture of triangular prisms and other polyhedra. Furthermore, by studying the assembly of two particles in the same template, we elucidate the importance of interparticle forces in this method. These advances allow for the construction of face-to-face and edge-to-edge nanocube dimers as well as triangular nanoprism bowtie antennas. As an example of the fundamental studies enabled by this assembly method, we investigate the surface-enhanced Raman scattering (SERS) of face-to-face concave cube dimers both experimentally and computationally and reveal a strong polarization dependence of the local field enhancement.

Insights into mechanisms of capillary assembly

“…20,21 By designing the templates appropriately, both spherical and anisotropic objects can be assembled; 22,23 hereby the directionality of the final structure is encoded in the geometry of the traps. In addition, careful design of the traps makes it possible to assemble specific sizes out of a polydisperse 30 mixture selectively, 23 indicating the robustness of the method against variations in the particle properties. The limitations of the method are in principle linked to the limitations of the technology used to fabricate the templates: depending on the size range of interest, different strategies are used to fabricate the templates, including photolithography, electron-beam lithography, and thermal scanning probe 35 lithography (tSPL).…”

A high-performance and low cost SERS substrate of plasmonic nanopillars on plastic film fabricated by nanoimprint lithography with AAO template

“…23 However, the sparse hot-spots and lack of the uniformity and reproducibility in EF for the random nanostructures limit their practical applications. 24 Alternatively, to control and immobilize the SERS-active sites, various types of ordered nanostructure such as nanodots and nanoholes arrays have been purposed, which could improve the reliability and reproducibility of the SERS measurement. The top-down approaches such as electronbeam lithography (EBL) and focused-ion-beam (FIB) offer high fidelity and high controllability to produce the metallic nanostructure arrays with patterned SERS hot-spots, but its high cost hinders the fabrication over a large-area for practical application in SERS.…”

Evaporative gold nanorod assembly on chemically stripe-patterned gradient surfaces

“…Impressive achievements in terms of well-accessible, reproducible synthesis procedures have led to the availability of a large diversity of monodisperse colloidal metallic, semiconducting and insulating particles with sizes ranging from micrometers to nanometers. Active and reproducible control over orientation and mutual alignment of nanoparticles in suspension as well as during adsorption at surfaces has mainly been limited to (controlled) drying experiments, in which hydrodynamic attractive forces compete with steric and/or electrostatic repulsive forces [7][8][9][10][11][12][13][14][15][16]. Additionally, the application of external stimuli, such as electric, magnetic and optical fields have been explored [17][18][19][20][21][22][23][24].…”