Chapter 4 Properties of nanomaterials

3- Dielectric environment
The op;cal proper;es of metal nanopar;cles are strongly sensi;ve to the surrounding dielectric environment,
which is useful for tuning their op;cal proper;es or for biosensing.
In general, an increase of refrac;ve index of medium surrounding a nanopar;cle results in a red-shiv of the LSP
peak.
McFarland and VanDuyne studied the scatering spectra of single Ag nanopar;cles as a func;on of the
surrounding refrac;ve index . A linear fit between peak posi4on and refrac4ve index of a surrounding solvent
was demonstrated (Fig. 2.22).
A thin oxide layer forms on the surfaces of Ag, Cu and Al form when these metals are exposed to air.
Langhammer et al. considered the case of the self-limi4ng oxide that forms on Al, which was es4mated to be 3
nm thick [136]. This oxide growth has two effects on Al nanopar4cles: (1) the core Al par4cle is reduced in size
during the oxide growth, (2) the local dielectric environment is changed by the outer alumina shell. SVM
simula4ons showed that the change in dielectric environment has the strongest effect on the op4cal proper4es of
the nanopar4cle, and gives rise to a moderate red-shiQ for large par4cles, and a strong red-shiQ for small
par4cles.