Abstract
The optical properties of plasmonic dipole and bowtie nanoantennas are investigated in detail using the Green's tensor technique. The influence of the geometrical parameters (antenna length, gap dimension and bow angle) on the antenna field enhancement and spectral response is discussed. Dipole and bowtie antennas confine the field in a volume well below the diffraction limit, defined by the gap dimensions. The dipole antenna produces a stronger field enhancement than the bowtie antenna for all investigated antenna geometries. This enhancement can reach three orders of magnitude for the smallest examined gap. Whereas the dipole antenna is monomode in the considered spectral range, the bowtie antenna exhibits multiple resonances. Furthermore, the sensitivity of the antennas to index changes of the environment and of the substrate is investigated in detail for biosensing applications; the bowtie antennas show slightly higher sensitivity than the dipole antenna.
Highlights
Over the last 10 years there has been a surge of research in the optical properties of metallic nanoparticles [1,2,3,4,5,6,7,8,9,10]
The geometry of the antenna strongly influences its optical properties as indicated in Figure 2, which shows the calculated intensity spectra in the antenna gap for the dipole antenna and for the bowtie antennas with the bow angles α1 - α4
We have investigated numerically the optical properties of plasmonic dipole and bowtie nanoantennas with different bow angles as a function of the antenna length, gap, substrate and background indexes
Summary
Over the last 10 years there has been a surge of research in the optical properties of metallic nanoparticles [1,2,3,4,5,6,7,8,9,10]. The plasmonic resonances observed in such structures open the possibility to build antennas operating in the visible [11,12]. Their hot spots can be used to trigger nonlinear effects and to couple electromagnetic radiation efficiently between the antennas and dipole emitters. Experimental techniques such as tip enhanced Raman spectroscopy or surface enhanced Raman spectroscopy demonstrate the potential of such hot spots to detect radiative emitters with sensitivity down to a single molecule [13,14,15,16,17,18,19]. The enhancement of the fluorescence of molecules placed near a plasmonic nanostructure has been observed recently, tuning the plasmon resonance either to the excitation or the emission of the molecules [20,21,22,23]
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