High Resolution Nanoimprint for Nanophotonics

Nanophotonics have drawn huge attention in recent years in various applications. Surface sensing technique, including surface-enhanced Raman spectroscopy (SERS), is an important topic of nanophotonics and has been widely investigated. The capability of SERS-active device depends on two main factors: good reproducibility and high enhancement factor. Ordered metallic nanostructures with high resolution are usually preferred for SERS application. Nanoimprint lithography can provide a low-cost and high resolution fabrication technique for SERS-active devices.

The objective of this research is to explore the application of nanoimprint lithography in SERS-active devices. This work begins with two issues of nanoimprint lithography: mold fabrication and throughput improvement. The potential of nanoimprint lithography depends on reliable mold fabrication. Two techniques are investigated, which are polyelectrolyte electrostatic self-assembly and controlled polymer reflow. Based on the observation of exceptional thermal stability of entangled polymer, step-and-repeat thermal nanoimprint lithography is developed. This technique significantly improves the throughput and enables the large scale application of thermal nanoimprint.

Ordered metallic nanostructures have been widely used as SERS-active substrates. In order to achieve high enhancement, extremely high resolution is needed, which can be limited by lithography technique. In this work, SERS-active devices based on gap surface plasmon polaritons are fabricated by nanoimprint lithography. 17 times more enhancement is achieved compared with conventional SERS-active devices on the same structure dimensions. This technique opens up possibilities of single molecule detection in the future.