Engineering and Characterization of Resonant Optical Antennas
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1248-D08-04
Engineering and Characterization of Resonant Optical Antennas Matthias D. Wissert1, Andreas W. Schell1, Konstantin S. Ilin², M. Siegel², U. Lemmer³, and Hans-Juergen Eisler1 1
Lichttechnisches Institut (LTI), DFG Heisenberg Group ‘Nanoscale Science’, Karlsruher Institut fuer Technologie, Karlsruhe, Germany
2
Institut für Mikro- und Nanoelektronische Systeme (IMS), Karlsruher Institut fuer Technologie, Karlsruhe, Germany ³ Lichttechnisches Institut (LTI), Karlsruher Institut fuer Technologie, Karlsruhe, Germany ABSTRACT Resonant optical dipole antennas, consisting either of two arms coupled by a small gap or of a single, uncoupled arm only, are fabricated by the application of electron beam lithography and gold evaporation. Using dark-field microscopy, scattering spectra of structures with varied antenna arm length and varied gap size are obtained. The results show not only a spectral redshift for coupled structures compared to single arm structures, but also that the far-field scattering intensity is significantly higher for two arm structures with gap. In addition to the dipole structures, first fabrication results on quadrupole antennas and split-ring antennas are presented, offering novel pathways for an enhancement of the optical response function. INTRODUCTION Optical antennas [1,2,3] have recently been investigated in several ways, including linear spectroscopy [4,5], two-photon induced luminescence intensity mapping [6,7], and near-field microscopy [8,9]. They are of high interest as they can provide efficient coupling from the farfield to the near-field (and vice versa) [10], thereby enabling potential for offering extremely high electromagnetic field densities at very small volumes. It is thus very important to exactly know the resonances offered by such structures to gain an insight into applicable wavelength and structure size regions [11]. Such insight can lead to significant advances in areas such as optical characterization and sensing [12], manipulation of nano-objects [13], or the creation of single photon light sources and detectors [14]. In the following, we present optical antennas we have fabricated so far, and give details of our engineering protocol. In addition, optical dark-field microscopy characterization of dipole antennas is presented. EXPERIMENT Optical Antenna Fabrication Various optical antennas were fabricated using electron beam lithography. In preparation, a glass cover slip was baked out for several hours at 510°C (to avoid glass auto-fluorescence and minimize sample surface defects), and cleaned using acetone and isopropanol. To achieve the
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sample DC conductivity required for electron beam lithography, a 30 nm layer of indium tin oxide (ITO) was sputtered onto the glass surface. A 45 nm layer of PMMA 950k was used as res
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