Patterned Plasmonic Surface on MEMS
Sponsored by: DARPA Young Faculty Award.
We focus on developing optical “surface coating” technologies that can be applied universally to enhance near-field nanoscale imaging and molecular sensing. Through nanofabrication, the technology can be applied to both flat and curved surfaces ranging from commercial MEMS canning probes-based imaging devices to emerging lab-on-chip biosensors. The advancements in tunability, efficiency, and affordability will enable a wide range of applications from early cancer detection to tracking of biological and military threats.
As one example, we present a novel concept to design apertureless plasmonic probes for near-field scanning optical microscopy (NSOM) with enhanced optical power throughput and near-field enhancement. Specifically, we combine unidirectional surface plasmon polariton (SPP) generation along the tip lateral walls with nanofocusing of SPPs through adiabatic propagation towards an apertureless tip. Three key design parameters are considered: the nanoslit width, the pitch period of nanogrooves for unidirectional plasmonic excitation and the pyramidal geometry of the NSOM probe for SPP focusing. Optimal design parameters are obtained with 2D analysis and two realistic probe geometries with patterned plasmonic surfaces are proposed using the optimized designs. The electromagnetic properties of the designed probes are characterized in the near-field and compared to those of a conventional single-aperture probe with same pyramidal shape. The optimized probes feature FWHM around 150nm, comparable with conventional NSOM designs, but over 3 orders of magnitude larger field enhancement, without degrading its spatial resolution. Our ideas effectively combine the resolution of apertureless probes with throughput levels much larger than those available even in aperture-based devices.