Ag Nanocrystals with Nearly Ideal Optical Quality: Synthesis, Growth Mechanism, and Characterizations

Abstract

Though Ag nanocrystals are predicted to be the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirements: i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative etching by H + ions has been established. With a trace amount of Cl − ions as catalysts, H + ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely "self-focusing of size/crystallinity distribution". H + ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all related structural parameters, the full width at half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (∼20) of LSPR predicted by theory is realized. The Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned nanocrystals with the same size.

Controlled Synthesis of Ag2Te@Ag2S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near‐Infrared Window

“…The peak intensity at 34° was enlarged in Ag 2 Te@Ag 2 S QDs, indicating the formation of Ag 2 S. In the case of Ag 2 Te QDs with emission peak at 1524 nm as the core, the photoluminescence peak of Ag 2 Te@Ag 2 S QDs got a slight red‐shift to 1560 nm (Figure 4e). This was derived from the extra Ag precursor in the reaction which would be readily adsorbed onto the surface of Ag 2 Te in the nonpolar solvent, [ 42 ] resulting the increase of Ag 2 Te core to give the red‐shift of the photoluminescence. Meanwhile, the adsorbed Ag ions also induced new traps on the surface, leading to the reduction of its photoluminescence intensity (Figure S10, Supporting Information).…”

Partitioning surface ligands on nanocrystals for maximal solubility

“…Recently, conceptually new entropic ligands were introduced 8,13 , which can boost the solubility of nanocrystal-ligand complexes and enables the large-scale printing of electronics and optoelectronics 14 . Importantly, entropic ligands are identified as a general solution for achieving excellent solubility of nanocrystals with diverse inorganic composition 14,15 , which plays a decisive role in both synthesis and processing 16,17 . For instance, by simply mixing two common n -alkanoate ligands with distinguishable hydrocarbon-chain lengths, solubility of the resulting nanocrystal-ligands complexes could increase up to ~6 orders of magnitude in comparison with either of pure-ligand counterparts.…”

Rational Component and Structure Design of Noble‐Metal Composites for Optical and Catalytic Applications

“…Notably, this work suggested that it is possible to construct a plasmonic absorber that absorbs light uniformly throughout the solar spectrum by designing an appropriate Au and/or Ag architecture (mixture or tandem). Due to the good plasmonic properties of composites, many strategies have been applied to synthesize well‐defined plasmonic nanostructures such as spheres, [ 223 ] rods, [ 224 ] cubes, [ 225 ] disks, [ 226 ] dimers/trimers, [ 227 ] stars, [ 228 ] plates, [ 229 ] and dodecahedrons. [ 230 ] Lee and co‐workers vacuum deposited Au onto a polymer template and released it from the substrate to form a monodisperse 2D nanodisk.…”

“…On the other hand, the excitation of the SPR of noble‐metal composites results in the amplification of local electromagnetic fields, a process also known through the observation of surface‐enhanced Raman scattering (SERS). [ 48,223,231,232 ] The sensitivity of SERS primarily depends on electromagnetic “hotspots” where the local electric field is extremely intense, and thus, the Raman signals from molecules at these sites are particularly strong and contribute to the main fraction of the overall intensity. [ 233,234 ] Because the metal nanostructures can support surface plasmons, [ 235 ] most SERS‐active substrates are based on Ag or Au.…”