Background: The performance of plasmonic nanostructures is based on
optical properties and the intensity of the electric field. The nature of the nearfields
around coinage metal nanoparticles has been well-studied. However, how to
project the enhanced electric field to several hundred nanometers distance might
be more convenient for the real applications.
Methods: In this paper, we examine whether an array of gold nano-stars may be
used as enhancement of the electric field to the several hundred nanometers distance.
Electron beam lithography was used to fabricate gold nano-star arrays.
Near-field optical properties of these arrays were then obtained using near-field
scanning optical microscopy (NSOM). The near-field optical properties were also
explored with finite-difference time-domain (FDTD) simulations.
Results: In the model, a scanning electron microscope image of actual nano-stars was used to build
the FDTD targets of 40 nm thickness. The incident wavelength was 532 nm in both simulation and
experiment. In the simulations the near-field optical intensity distribution was studied with monitors
positioned at various distances (0, 1 and 2 μm above the top surface of a nano-star). The FDTD results
were found to be consistent with the experimental NSOM results.
Conclusion: We found that the field enhancement is not only localized to the individual nanostars
but also projected several hundred nanometers into the space. Such an array could be potential used
to probe the intracellular environment of an adjacent cell or near-field imaging.