Far-Ultraviolet Plexciton Formation in Water-Covered Indium Clusters

In this work, we study the plexciton in the far-ultraviolet region formed between indium nanoclusters and water molecules. The indium clusters are fabricated on graphene under ultrahigh vacuum conditions and show a strong localized surface plasmon polariton (LSP) absorption band at 6-7 eV. Adsorption of water molecules onto the clusters at 115 K induces a band splitting larger than 1 eV, indicating a strong coupling between the LSP and water 4a₁ ← 1b₁ transition. The spectral evolution as a function of the water coverage is revealed, enabling the determination of the decay length of the plexciton collective effect to be ∼8 nm.