Plasmonic dipole antennas on silicon

Metallic nanowires of rectangular cross-section can operate as isolated or arrayed optical monopole or dipole antennas, and when deposited on a Si substrate and covered with water, become useful as (bio)chemical sensors. The optical performance of such antennas is assessed over a broad wavelength range as a function of geometrical parameters, including wire thickness, width, length, and gap (in the case of dipoles). Effects caused by varying the pitch of two-dimensional arrays of antennas are also determined. Given a uniform broadside excitation, antennas resonate in the main mode of propagation of the corresponding asymmetric metal stripe waveguide, and antennas performance is related to its propagation characteristics. The structures considered are amenable to fabrication via metal evaporation and lift-off, with the nanowires defined by electron beam patterning