Gap plasmon resonance in electromagnetically-actuated nanomechanical silicon nitride strings

We present a new kind of electromagnetically-actuated nanoplasmomechanical string resonator. This nanomechanical resonator is made of two gold covered silicon nitride (SiN) strings separated by a 100 nm wide gap. These strings... [ view full abstract ]

We present a new kind of electromagnetically-actuated nanoplasmomechanical string resonator. This nanomechanical resonator is made of two gold covered silicon nitride (SiN) strings separated by a 100 nm wide gap. These strings were cut into a SiN membrane with focused ion beam milling, as shown in the SEM image of the resonator on Figure 1. Besides supporting the induced plasmon resonance, the gold strips additionally act as actuation elements, being electrically connected. Placed in a static magnetic field (using neodymium magnets), the nanomechanical resonators are actuated by passing an oscillating current through one of the strings (see the schematic of the experimental setup on Figure 2). The induced Lorentz force makes the string vibrate, which varies the gap size between the two SiN strings. The string vibration is detected from the modulation of a tunable probe laser polarized perpendicularly to the direction of the strings, with a maximal scattering at the mechanical resonance frequency of the electromagnetically-actuated string. This can be seen on Figure 3, where we plotted the measured optical intensity and phase of the transmitted signal as a function of the frequency of the oscillating current, for an applied voltage of 1 mV and a laser wavelength of 780 nm. This kind of structure enables the investigation of the plasmonic resonances of plasmonic structures in close proximity, by electromagnetically-controlling the distance between those structures. This is particularly interesting in order to analyze the internal optical forces between plasmonic structures or to study quantum phenomena such as tunneling effects between these structures for gaps smaller than 1 nm.