Nanomechanical membrane resonator as a novel platform for the detection and analysis of FEBID plasmonic nanostructures

Localized surface plasmon resonance (LSPR) in nanostructures has been extensively studied during the last decades due to its remarkable optical properties. The understanding and analysis of LSPR in various nanostructures is... [ view full abstract ]

Localized surface plasmon resonance (LSPR) in nanostructures has been extensively studied during the last decades due to its remarkable optical properties. The understanding and analysis of LSPR in various nanostructures is important for the optimizations of devices. Focused electron beam induced deposition (FEBID) is a mask-free, resist-free direct write additive nanofabrication method where noble metal plasmonic nanostructures can be deposited in-situ in a single process step with minimum limitation on geometry and with high purity. In this work, as a proof of principle, nano-ellipsoids were deposited on a 50 nm-thick rectangular silicon-rich silicon nitride membrane using 3 kV acceleration voltage and 1 nA beam current. A LEO 1530 VP SEM with home-built gas injection system was used to inject precursors inside the system. By exploiting the thermoplasmonic effect of nanostructures, we use a nanomechanical membrane resonator as a novel optical detection scheme for the experimental analysis of LSPR, as shown in figure 1. The FEBID nano-ellipsoids on membrane resonator are scanned with a 633 nm pumping laser with linear polarization to investigate the effects of aspect ratio and orientation on LSPR. During scanning, the excitation of LSPR in the nano-ellipsoids results in a heat influx into the membrane. The heating-induced detuning of the membrane resonance frequency was monitored with a laser Doppler vibrometer incorporated with a phase-locked loop. The results in figure 2 demonstrate the corresponding relative frequency detuning in the membrane resonator caused by the specific absorption cross-section of nano-ellisoids with different aspect ratio and orientation. Due to the red-shift of LSPR with increasing aspect ratio of nano-ellipsoids, the enhanced absorption at 633 nm in high aspect ratio nano-ellisoids results in larger relative frequency shift. The effect of nano-ellipsoid orientation relative to polarization is also observable. With the current setup, we are able to detect a dissipated power of 300 fW, which result in extremely high signal-to-noise ratio in plasmonic nanostructure with LSPR around VIS-NIR regime even with small pumping powers of only 300 µW. With this new plasmonic characterization technique, in combination with FEBID, LSPR with various nanostructures can easily be investigated with almost no limitation in geometry.