Silicon-based plasmonic nanoantennas

In this work, silicon-based plasmonic nanoantennas was realized. Using silicon instead of metals as the material of choice in building such nanoantennas is advantageous as it enables the integration of nanoantennas-based structures into integrated-optoelectronics circuits built using the standard fabrication techniques in the electronic industry. It also allows for low cost mass production of the proposed devices. Upon light incidence on an array of nanoantennas, Localized Surface Plasmon Resonance (LSPR) is generated which causes an enhancement in the localized field inside the structure and in the near field zone. The enhanced localized field is manifested as an enhancement in the absorbed as well as the scattered field. Varying the surrounding material causes variations in the wavelength of the enhancement peak as well as the enhancement level itself. Hence, sensors can be built to facilitate sensing molecules with its characteristic vibrational transitions. In this paper, dipole and bowtie silicon nanoantennas are investigated. It is found that when using silicon with high excess carrier concentrations as the material of choice, the enhancement occur in the mid-IR spectral range which is red shifted compared to the enhancement produced when using metal such as gold or silver. Working in mid-IR is advantageous for sensing applications as the characteristic vibrational transitions of the majority of bio-chemical molecules happens in the mid-IR.