Structural order in plasmonic superlattices

Abstract

The assembly of plasmonic nanoparticles into ordered 2D-and 3D-superlattices could pave the way towards new tailored materials for plasmonic sensing, photocatalysis and manipulation of light on the nanoscale. The properties of such materials strongly depend on their geometry, and accordingly straightforward protocols to obtain precise plasmonic superlattices are highly desirable. Here, we synthesize large areas of crystalline mono-, bi-and multilayers of gold nanoparticles >20 nm with a small number of defects. The superlattices can be described as hexagonal crystals with standard deviations of the lattice parameter below 1%. The periodic arrangement within the superlattices leads to new well-defined collective plasmon-polariton modes. The general level of achieved superlattice quality will be of benefit for a broad range of applications, ranging from fundamental studies of light-matter interaction to optical metamaterials and substrates for surface-enhanced spectroscopies.

Plasmonic Supercrystals with a Layered Structure Studied by a Combined TEM‐SAXS‐XCCA Approach

“…Plasmonic supercrystals were synthesized by self‐assembly of polystyrene‐coated AuNP (AuNP@PSSH) at a toluene‐diethylene glycol (DEG) liquid‐liquid interface as described recently. [ 18 ] The synthesis protocol (see Section 5.) yields well‐defined supercrystals with crystallite sizes > 1000 µm 2 , few defects and a layered structure ( Figure ).…”

“…The closest packing of the “hard‐spheres” (AuNP + polymer shell) results in a non‐closed packing of the AuNP‐cores, that can be tuned via the thickness of the polymer shell (i.e., molecular mass of the ligand), a major advantage of polymers compared to small molecular ligands. [ 18,21,22,26,27 ] The particle‐particle interactions in such systems are dominated by the polymer shell. Because the system is nonpolar, electrostatic contributions can be neglected, leaving Van‐der‐Waals attractive forces between the AuNP‐cores and repulsive forces upon compression of the polymer shells at decreasing interparticle distances.…”

“…In the final formed superlattices, no toluene is present, and ligand‐ligand interactions are favored over interactions with air or the polar liquid subphase, resulting in coherent films (thin films would also form from bare polystyrene‐ligand solutions without particles). [ 18 ] Because the attractive ligand‐ligand interactions are rather weak (no hydrogen‐bridges, chemical cross‐linking etc. ), the resulting superlattice films are also fragile and brittle.…”

“…Supercrystals were synthesized with Polystyrene‐thiol (PSSH) functionalized AuNP ( d core = 23.4 nm, M n (PSSH) = 11 400 g mol −1 ) by self‐assembly at a toluene‐diethylene glycol (DEG) liquid‐liquid interface as described recently. [ 18 ] By adjusting the volume of the AuNP@PSSH solution (7.3 n m ) in toluene that was evaporated on the liquid subphase DEG, one sample with mostly monolayers (300 µL) and one sample with mostly bi‐ and multilayers (500 µL) was prepared.…”

Ambient microdroplet annealing of nanoparticles

“…The positively charged microdroplets convert polydispersed Ag@PET NPs to an ordered 2D superlattice structure of uniform NPs. [21][22][23][24][25][26][27][28] A superlattice in the current context refers to a localized periodic assembly of uniform NPs which possess inherent periodicity of the element. Such structures are possible only with uniform particles and the Ag@PET NPs Fig.…”