Silver Nanocrystals: Self-Organization and Collective Properties

Abstract

In this paper, the main parameters, which dictate the supracrystalline structure of silver nanocrystals self-assembled at the micrometer scale, are evidenced. They are the alkyl-chain length, the deposition temperature, the concentration of the colloidal solution and the nature of the substrate. By varying the deposition temperature (from 15° to 50 °C), from the same batch of nanocrystals (same size, same coating agent), dense (fcc and hcp) and loose (bcc) supracrystals or disordered arrangements (rcp) are produced. By tuning the nature of the substrate (HOPG or amorphous carbon) and its temperature, the final size of the supracrystals is controlled. Collective properties due to either nanocrystals ordering in 2D superlattices or in supracrystals (3D) are pointed out. These properties are either due to dipolar interactions with the appearance of coupled plasmon modes or to the attraction between nanocrystals, self-assembled via interdigitation of the alkylchains used as coating agents, which leads to coherent vibrations of nanocrystals in a supracrystal.

Low wavenumber Raman scattering of cobalt nanoparticles self‐organized in 3D superlattices far from surface plasmon resonance

“…Despite the red-shift (from 427 to 461 nm) and broadening resulting from the interparticle plasmon coupling, [33,34] the resonance remains in the visible range when the particles are deposited and self-organized. Conversely, for cobalt NPs, either dispersed in hexane or deposited on the substrate, no particular absorption is observed.…”

Tunable SERS Platforms from Small Nanoparticle 3D Superlattices: A Comparison between Gold, Silver, and Copper

“…[1] These often rely on noble metal nanoparticles (NPs) that produce al arge increase in the local electromagnetic field near their surfacet hrough excitation of their localized surfacep lasmon (LSP) modes in the visible domain [2][3][4] and, therefore, of the Raman scattered signal. When two or more nanoparticles are in close proximity,t heir LSP modesa re significantly alteredd ue to additional electromagnetic coupling across the interparticle gap, [5] the so-called "hot spot". [6][7][8] The resultingl ocal enhancement factor (EF) was found to be highly sensitivet ot he interparticle distance.…”

Metal Nanoparticles with Liquid‐Crystalline Ligands: Controlling Nanoparticle Superlattice Structure and Properties

“…[8] The latter is crucial since optical, magnetic, thermal and electric properties of the structures rely on the distant-dependent collective interactions. [15][16][17] To expand the list of available spatial arrangements one can try to introduce new interactions by changing chemical nature of ligands and thus, influencing overall nanoparticle behaviour. Nature provides clues about the types of interactions that can be utilized (electrostatic, hydrophobic, Hbonding, p-p stacking) and possible paths for future development, namely achieving dynamic or functional assemblies.…”