2D Assembly of Atomically Oriented Gold Nanodisks Leads to Tunable Plasmonic Resonance

Abstract

Nanocrystals (NCs) are extensively used to create self-assembled nanostructures; however, little has been achieved on the assembly of NCs with an anisotropic shape. A key challenge with the anisotropic NCs is assembling them into positional order with preferential atomic crystallographic orientations. Here, we use the air–liquid interface to prepare two-dimensional (2D) assemblies of crystalline gold nanodisks (AuNDs) with preferentially oriented atomic lattices and report on the in situ structural and optical properties of the nanostructures. The structure of 2D assemblies driven by in-plane surface pressure was monitored using grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence X-ray diffraction (GIXD), and optical properties were monitored using UV–vis spectroscopy. We observe that the preferentially oriented atomic lattice of the NDs leads to the formation of 2D hexagonal superlattices, exhibiting a continuous blue shift of the plasmonic band with increasing surface pressure. We quantify the packing by X-ray scattering to understand the plasmonic properties induced by the surface pressure. This controlled process to tune the plasmon resonance property paves a novel way to establish the essential correlation between the structure and properties of anisotropic NCs and opens door to the rational design of programmable NC networks.

Highly Ordered Monolayers of μm-Sized Polystyrene Spheres Studied by Grazing-Incidence Small-Angle X-ray Scattering, Simulations, and Geometrical Calculations

“…The supports used here are not sufficiently transparent for X-rays as they are relatively thick, which is needed for their use as catalyst model systems. GISAXS, on the other hand, is a well-established technique for studying the structure of self-assembled 2D nanoobjects that does not suffer from X-ray absorption due to the use of an X-ray reflection geometry. − Earlier GISAXS studies on self-assembled systems were mainly focused on the determination of structural parameters on the nanoscale. − However, 2D structures with long-range order made of μm-sized particles have been explored barely by GISAXS. In this work, a hexagonally ordered 2D porous template has been prepared from a monolayer of μm-sized, almost monodisperse polystyrene (PS) spheres on the surface of a TiO 2 /ITO-coated glass substrate , and has been studied by GISAXS.…”