Nanosecond Shape-driven Localized Surface Plasmon Resonance Switching in Silver Nanoparticles

The ability to tune the localized surface plasmon resonance (LSPR) in a fast and repeatable manner could form the basis for a hypothetical optical switch. Here we demonstrate a reversible change in the LSPR wavelength of Ag nanoparticles based on nanosecond melting induced shape effects. When Ag nanoparticles are melted by nanosecond laser pulses, the resulting contact angle is determined by the fluid environment during melting. For instance, Ag nanoparticles on quartz substrates melted in air are near hemispherical in shape (with contact angle ~ 96^o), while those melted under water and glycerol have larger contact angles of ~127^o and ~172^o respectively. This shape or contact angle change significantly modifies the intensity and wavelength of the dipolar and quadrupolar plasmonic signals. We have utilized this shape change to switch the plasmonic signals over multiple cycles of irradiation and determined the fatigue limit of LSPR switching between air and glycerol environments. Such shape control and repeatable modification of the plasmonic wavelength could serve as a useful system for biological sensing and optical tuning applications.