Localized surface plasmon resonances of size-selected large silver nanoclusters (n = 70-100) soft-landed on a C₆₀ organic substrate

Silver nanoclusters (Ag_n NCs) exhibit a remarkable optical property known as localized surface plasmon resonance (LSPR) in the visible to ultraviolet wavelengths. In this study, we address the size gap in LSPR responses between small NCs and nano-islands by synthesizing large Ag_n NCs with a countable number of atoms (n = 70-100) using a magnetron sputtering method, which were precisely size-selected and soft-landed onto substrates. The monodispersed Ag_n NCs were immobilized on a pre-decorated substrate with fullerene (C₆₀) molecules, and their LSPR behaviors were characterized using two-photon photoemission (2PPE) spectroscopy. Due to the distinct polarization selectivity of incident light associated with LSPR, the intensity ratio between p- and s-polarized lights (I_p/I_s) in 2PPE spectroscopy serves as a reliable indicator of LSPR and its structural correlations. From n = 70 to 100, the I_p/I_s value gradually decreases as the cluster size increases. This decrease is attributed to the enhancement of s-polarized light (I_s), indicating that large Ag_n NCs on a C₆₀ substrate undergo a deformation from spherical to flattened geometries, particularly above approximately n = 55.