Anomalous phonon relaxation in Au ₃₃₃ (SR) ₇₉ nanoparticles with nascent plasmons

Abstract

Research on plasmons of gold nanoparticles has gained broad interest in nanoscience. However, ultrasmall sizes near the metal-to-nonmetal transition regime have not been explored until recently due to major synthetic difficulties. Herein, intriguing electron dynamics in this size regime is observed in atomically precise Au333(SR)79 nanoparticles. Femtosecond transient-absorption spectroscopy reveals an unprecedented relaxation process of 4–5 ps—a fast phonon–phonon relaxation process, together with electron–phonon coupling (∼1 ps) and normal phonon–phonon coupling (>100 ps) processes. Three types of –R capped Au333(SR)79 all exhibit two plasmon-bleaching signals independent of the –R group as well as solvent, indicating plasmon splitting and quantum effect in the ultrasmall core of Au333(SR)79. This work is expected to stimulate future work on the transition-size regime of nanometals and discovery of behavior of nascent plasmons.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100O167} Cluster

“…There are 28 body Ce atoms in the core, the rest are on the surface. Hence 4 is of a similar size to large nanoclusters of Mo, [29] Ag [30] and Au [31–33] that have been reported. Ce oxidation states and O protonation levels were determined by bond valence sum (BVS) calculations, revealing a Ce 3+ 8 Ce 4+ 92 situation and 18 surface OH − ions. All three low‐index facets of CNPs, namely (111), (110) and (100), are present in 4 . Only the Ce 40 ( 3 ) has previously exhibited all three types. All eight Ce 3+ ions are on the surface and all are in (100) facets, as also found in almost all the smaller MNPs, the exception being Ce 19 where a Ce 3+ is located on a Ce 2 edge joining two (111) hexagons. The capping ligands on (111) facets are H 2 O or PhCO 2 H. Most of the PhCO 2 − /PhCO 2 H binding modes are the same as seen previously in the smaller MNPs, except for two new μ 2 ‐PhCO 2 H and μ 4 ‐PhCO 2 − bridging modes (Figure S4).…”

“…There are 28 body Ce atoms in the core, the rest are on the surface. Hence 4 is of a similar size to large nanoclusters of Mo, [29] Ag [30] and Au [31–33] that have been reported.…”

Sub‐3 nm Aluminum Nanocrystals Exhibiting Cluster‐Like Optical Properties

“…Subwavelength metal nanoparticles often show surface plasmon resonances (SPRs) caused by coherent oscillation of free electrons in response to incident light. [ 7 ] Since the real parts of dielectric functions (ε r ) of gold and silver are positive in ultraviolet (UV) range with wavelength less than 200 nm, [ 8 ] it is difficult for nanoclusters made by them to show PL in short UV range. [ 7b ] On the contrary, an earth‐abundant light metal, aluminum, exhibits strong free electron behavior and negative ε r from near infrared to short UV range.…”

“…[ 7 ] Since the real parts of dielectric functions (ε r ) of gold and silver are positive in ultraviolet (UV) range with wavelength less than 200 nm, [ 8 ] it is difficult for nanoclusters made by them to show PL in short UV range. [ 7b ] On the contrary, an earth‐abundant light metal, aluminum, exhibits strong free electron behavior and negative ε r from near infrared to short UV range. [ 8 ] For this reason, aluminum has attracted increasing attention as an emerging plasmonic material, with profound applications in UV.…”

“…[ 11a ] Tetraoctylammonia bromide (TOAB) was used as the surfactant for its demonstrated success in the preparation of nanoparticles of comparable size, such as gold nanoclusters and silicon quantum dots. [ 7a,14 ] The resulting bare AlNCs were surface modified by PAs. PAs were known to form well‐organized, high‐quality SAMs on the surface of metal oxides, with molecular degree of control and packing density close to alkane thiols on gold.…”