Study on the fabrication of plasmonic nanopot structure by directional photofluidization lithography

Abstract

Plasmonic nanostructures have high technological importance due to its numerical applications in spectroscopic sensing and nanofocusing. These various applications stem from its abilities to localize the electromagnetic field into nanoscale hot spots that exceeds the diffraction limit. Therefore, there have been a lot of attempts to fabricate plasmonic nanostructures which are comprised of both sharp tips and small gaps, as they provide much higher electromagnetic field enhancement. However, no existing nanostructures satisfy stringent requirements for the efficient electromagnetic field enhancement including vertically oriented sharp tips, uniformity over a large area, and optical tunability, which are essential for efficient plasmonic light enhancement and practical applications. Herein, we fabricated plasmonic nanopot arrays, which satisfy all the stringent requirements, by directional photofluidization lithography. Vertically aligned tips within plasmonic nanopot structures, which expanded to circular ring, enable effective light coupling and hence to high local field enhancement. Furthermore, regularly patterned large area tips of nanopot array result in uniform optical signal. Finally, the structural features of nanogaps could be precisely con-trolled in a scalable and deterministic manner, so that we can control the resonance frequency over visible range. The suggested nanopot arrays can effectively localize the electromagnetic field; therefore this structure will be of practical importance in spectroscopic and sensing application.