Alkyl Imidazolium Ionic-Liquid-Mediated Formation of Gold Particle Superstructures

The development of new methodologies for controlling the organization of quantum materials in multiple dimensions is crucial to the advancement of device fabrication. By using a self-assembly route using selected imidazolium ionic liquids bearing long alkyl chains (C_<i>n</i>Imida, <i>n</i> = 8, 10, 12) as ligands, we have achieved a tunable assembly of quantum-sized gold nanoparticles. The initial stabilizer of the gold nanoparticles was partially or wholly substituted depending on the concentration and alkyl chain length. π–π interactions between imidazolium rings also promote the generation of spatially controlled aggregates from the nanometer to micrometer size regimes. In particular, in the case of an imidazolium ionic liquid with decyl chains, gold particles assemble into a core–shell spherical superstructure induced by the aggregation of imidazolium ionic liquid molecules during ligand exchange. Conceptually, the assemblies of nanoparticles mimic biological systems and provide strategies for the organization of single-component nanomaterials into functional assemblies for potential applications. Our approach is general and can be applied to other types of nanomaterials for facile manipulation of the assembly processes, permitting an exploration of physicochemical properties as well as technological applications

Gold Nanoparticle Chains: Synthesis, Characterization, and Modeling Using Spectroscopic Ellipsometry

In this paper, we explore the ability of ellipsometry to characterize colloidal suspensions composed of gold nanoparticle (NP) chains. The complex effective index of these suspensions is deduced from ellipsometric measurement by using a wavelength-by-wavelength inversion without any dispersion law. We show that the effective refractive index of these colloids is defined by the nature of the solvent, whereas their effective extinction coefficient is mainly sensitive to the plasmonic properties of NP chains. The influence of the NP radius distribution and arrangement on the effective extinction coefficient of NP chain are investigated through simulations based on the coupled point dipole method (CDM). We clearly show that this coefficient is mainly sensitive to the interparticle distance and the number of NPs in the longest segment of chains. We demonstrate that the distribution of the number of NPs in the longest segment of chains and their volume fractions can be directly deduced from the ellipsometry by using the CDM