Optical Nanoantennas

    This research combines the knowledge of nano-optics and nano-fabrication for the development of optical antennas. In a three-step approach, our structures are first modeled, designed and simulated using Microwave Studio, Finite Difference Time Domain (FDTD), and Discrete Dipole Approximation (DDA). Extensive studies of field distribution, extinction efficiency and their dependence on geometry are carried out prior to physical design.
    The nanostructures are fabricated using electron-beam lithography and a novel nanofabrication technique developed by our group called Solid-state superionic stamping (Hsu et al., Nano Lett. 7 (2), 446). We focus on improving the capabilities of current fabrication capabilities beyond 20 nm feature size with added advantages of low cost, high throughput, ambient conditions, and large area patterning.
Antenna characterization involves several different approaches
•    Optical measurements for extinction and scattering analysis
•   High-resolution cathodoluminescence imaging and spectroscopy for analyzing various antenna modes with sub-20 nm resolution
•    Second-harmonic generation and metal-enhanced fluorescence utilizing the high fields in bowtie antenna gaps
    Additionally, thin films of noble metals are explored to reduce scattering losses in plasmonic devices due to film roughness. In these studies, a different approach based on buffer layer of various materials, e.g., Ge, MgO, NiO is first grown below the metal film that helps improve the growth process (Logeeswaran, Nano Lett., 2009).
We apply our understanding of plasmonics and antenna theory to optical wavelengths and explore ways to utilize these sub-wavelength resonant structures for molecular imaging, nanolithography, solar cell efficiency improvement, data storage and optical communication.

Figure. AFM image of a bowtie antenna (left) and a high-resolution cathodoluminescence image (right) showing the out-of-plane plasmonic mode of the nanostructures.