Tailoring the Optical Plasmonic Resonances by the Shape of Antenna Dipole-Walls

Petr Dvořák Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Institute of physical engineering, Brno university of technology, Brno, Czech Republic Filip Ligmajer Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Martin Hrtoň Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Jiří Babocký Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Tomáš Šamořil Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Institute of physical engineering, Brno university of technology, Brno, Czech Republic Tomáš Šikola Advanced Nanotechnologies and Microtechnologies, BUT CEITEC, Brno, Czech Republic Institute of physical engineering, Brno university of technology, Brno, Czech Republic

Optical antennas are promising devices for enhancement of optical fields surrounding them. These effects are often utilized in photovoltaics, where this enhancement increases the efficiency of energy conversion process. Biosensing is another promising application as the resonant properties are influenced by refraction index of surrounding environment.

One of the key prerequisites for successful applications is possibility to precisely tune the resonant frequencies of antennas. This can be quite complicated at frequencies of the visible part of electromagnetic spectrum as the size of plasmonic antennas must be very small. In our work we present a new approach of fabrication of plasmonic resonant structures by fabrication of „walls“ surrounding the conventional antennas which exhibits additional vertical resonances. As these resonances are related to vertical dimensions, we can simply tune them by changing various technological parameters of electron beam lithography (EBL) and subsequent ion beam deposition (IBD).

We have used a dark-field spectroscopy setup enabling us to excite and measure these vertical resonances in our structures. Our measurements are supported by a numerical model based on the boundary-element method. This model predicts the strong dependence of position and strength of this vertical resonance mode on the height and sharpness of these walls, which can be easily tuned by the parameters of the fabrication process.

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