SURFACE-PLASMON SPECTROSCOPY OF NANOSIZED METAL PARTICLES

The use of optical measurements to monitor electrochemical changes on the surface of nanosized metal particles is discussed within the Drude model. The absorption spectrum of a metal sol in water is shown to be strongly affected by cathodic or anodic polarization, chemisorption, metal adatom deposition, and alloying. Anion adsorption leads to stron g damping of the free electron absorption. Cathodic polarization leads to anion desorption. Underpotential deposition (upd) of electropositi ve metal layers results in dramatic blue-shifts of the surface plasmon band of the substrate. The deposition of just 0.1 monolayer can be re adily detected by eye. In some cases alloying occurs spontaneously dur ing upd. Alloy formation can be ascertained from the optical absorptio n spectrum in the case of gold deposition onto silver sole. The underp otential deposition of silver adatoms onto palladium leads to the form ation of a homogeneous silver shell, but the mean free path is less th an predicted, due to lattice strain in the shell.