Emergence of metallicity in silver clusters in the 150 atom regime: a study of differently sized silver clusters

Abstract

We report the systematic appearance of a plasmon-like optical absorption feature in silver clusters protected with 2-phenylethanethiol (PET), 4-flurothiophenol (4-FTP) and (4-(t-butyl)benzenethiol (BBS) as a function of cluster size. A wide range of clusters, namely, Ag₄₄(4-FTP)₃₀, Ag₅₅(PET)₃₁, ∼Ag₇₅(PET)₄₀, ∼Ag₁₁₄(PET)₄₆, Ag₁₅₂(PET)₆₀, ∼Ag₂₀₂(BBS)₇₀, ∼Ag₄₂₃(PET)₁₀₅, and ∼Ag₅₃₀(PET)₁₀₀ were prepared. The UV/Vis spectra show multiple features up to ∼Ag₁₁₄; and thereafter, from Ag₁₅₂ onwards, the plasmonic feature corresponding to a single peak at ∼460 nm evolves, which points to the emergence of metallicity in clusters composed of ∼150 metal atoms. A minor blue shift in the plasmonic peak was observed as cluster sizes increased and merged with the spectrum of plasmonic nanoparticles of 4.8 nm diameter protected with PET. Clusters with different ligands, such as 4-FTP and BBS, also show this behavior, which suggests that the 'emergence of metallicity' is independent of the functionality of the thiol ligand.

Controlled synthesis and characterization of the elusive thiolated Ag55cluster

“…FWHM of silver clusters are broad in nature compared to gold clusters and we have studied them extensively. 41 Laser intensity-dependent study (Fig. S2, ESI †) shows similar observation as reported in the case of Ag 152 (PET) 60 .…”

“…Recently, we have shown the optical spectrum of the 2-phenylethanethiol protected Ag 55 cluster while exploring the appearance of plasmon excitation in silver clusters. 41 Here, we report thiolated Ag 55 clusters and their most essential characterization. The synthesis involves reaction of the metal salt (AgNO 3 ) and the thiol (BBSH) in a 1 : 4 ratio in a mortar and pestle to form the thiolate in the solid state.…”

[Ag67(SPhMe2)32(PPh3)8]3+: Synthesis, Total Structure, and Optical Properties of a Large Box-Shaped Silver Nanocluster

“…Particularly, we synthesized and fully characterized a novel NC of [Ag67(SPhMe2)32(PPh3)8] 3+ using a one-pot synthetic strategy, in which both thiol and phosphine co-ligands were judiciously chosen to produce this large stable NC of a box-like shape. While the syntheses of Ag NCs with similar or larger sizes have been reported, 40,41 they were plagued by instability issues precluding their structure elucidation and precise molecular formula determination (e.g. restricting the estimation of NCs' formulae to matrix-assisted laser desorption ionization mass spectrometry).…”

Observing Ultra-Small Gold Cluster to Plasmonic Nanoparticle Evolution in a One-Pot Aqueous Synthesis

“…Au 144 (SR) 60 was the smallest cluster reported in which a plasmon was present, though the plasmon was core‐localized instead of the surface one ,. Researchers reported the emergence of metallicity in the >150 atom regime in several metal systems ,,. Nanoclusters with >200 atoms (∼2 nm core diameter) show broad and weak plasmon peak at ∼510 nm .…”

“…Based on the studies on a number of gold nanoclusters and plasmonic nanoparticles, Dass and co‐workers reported broadly three different, size‐regime dependent optical properties . Similarly, Pradeep's group also studied thiol‐protected silver nanoclusters of various sizes and identified the size regime where the metallicity appeared . It should be noted that investigations of the emergence of the plasmon phenomenon in the metal clusters have great significance because such phenomenon is presently not understood in terms of any microscopic theory .…”