Optical responses of plasmonic gold nanoantennas through numerical simulation

Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. Gold nanoparticles are the material that is mostly used experimentally, since it combines a favorable dielectric function in the red and near-IR with excellent chemical stability. So, the gold material is used to build nanoantennas in this research. The optical properties of plasmonic dimer nanoantennas are investigated in detail using the finite integration technique. The validity of this technique is verified by comparison to the exact solution generalized Mie method (GMM). The influence of the geometrical parameters (antenna length, gap dimension, and shapes) on the antenna field enhancement and spectral response is discussed. Localized surface plasmon resonances of Au (gold) dimers nanospheres, bowtie and aperture bowtie nanoantennas are modeled. The enhanced field is equivalent to a strong light spot which can lead to the resolution improvement of the microscopy and optical lithography, thus increasing the optical data storage capacity. Furthermore, the sensitivity of the antennas to index changes of the environment and substrate is investigated in detail for biosensing applications. We confirm that our approach yields an exact correspondence with GMM theory, for Au dimers nanospheres at gap dimension 5 and 10 nm but gives an approximation error of less than 1.37 % for gap dimension 1 and 2 nm with diameters approaching 80 nm. In addition, the far-field characteristics of the aperture bowtie nanoantenna such as directivity and gain are studied. The promising results of this study may have useful potential applications in near-field sample detection, optical microscopy, etc.