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

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.