Nanogaps between metal nanostructures are useful in localizing optical energy in plasmonic antennas, but can be challenging to directly pattern. Patterning with the positive-tone polymethyl methacrylate (PMMA) resist causes an undesirable spread in nanogap dimensions. On the other hand, the negative-tone hydrogen silsesquioxane (HSQ) resist possesses the high resolution suited for the definition of nanogaps. However, it requires a hydrofluoric acid solution for lift-off, making it incompatible with the quartz or glass substrates used in optical devices.

To address this, scientists from the Institute of Materials Research and Engineering, A*STAR and Nanyang Technological University, both in Singapore, have created free-standing nanostencils in HSQ with sub-10 nm dimensions onto PMMA supports. The approach allows lift-off in organic solvents, thus extending the technique to a broad range of substrate materials.

Sensing applications

The group demonstrated the utility of these plasmonic antennas with nanogaps in a Raman scattering experiment. These antennas showed greatly enhanced Raman scattering signals, making this technique promising for single-molecule detection.

Full details can be found in the journal Nanotechnology.