Apr 11, 2013
Nanostencils define sub-10 nm gaps in plasmonic antennas
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.
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.
About the author
This study was conducted by a research team in Singapore. The lead author, Dr Huigao Duan, proposed using sub-10 nm HSQ nanostencils for defining tiny gaps in plasmonic antennas. His research focuses on sub-10 nm patterning and its applications. He did this work at the Institute of Materials Research and Engineering, A*STAR, Singapore, where he was a staff scientist. Currently, he is a professor and a principle investigator at Hunan University, China. Dr Hailong Hu performed the dark-field scattering and surface-enhanced Raman scattering measurements at Nanyang Technological University (NTU) when he was pursuing his PhD degree. Now he is an engineer at Witec. Hui Kim Hui is a specialist on focused ion beam and she prepared the cross-sectional sample for the TEM to clearly see the fabricated sub-10 nm gaps. Prof. Zexiang Shen is a professor in NTU and his research field focuses on Raman spectroscopy. Dr Joel K W Yang is the principal investigator for this work. His group focuses on high-resolution patterning in nanoplasmonics and its applications.