  The key component of nanoplasmonics is metals. For a long time, gold and
silver have been the metals of choice for constructing plasmonic nanodevices
because of their excellent optical properties. However, these metals possess a
common characteristic, i.e., their optical responses are static. The past
decade has been witnessed tremendous interest in dynamic control of the optical
properties of plasmonic nanostructures. To enable dynamic functionality,
several approaches have been proposed and implemented. For instance, plasmonic
nanostructures can be fabricated on stretchable substrates or on programmable
templates so that the interactions between the constituent metal nanoparticles
and therefore the optical responses of the plasmonic systems can be dynamically
changed. Also, plasmonic nanostructures can be embedded in tunable dielectric
materials, taking advantage of the sensitive dependence of the localized
surface plasmon resonances on the neighboring environment. Another approach,
which is probably the most intriguing one, is to directly regulate the carrier
densities and dielectric functions of the metals themselves.
