Inelastic electron tunneling (IET) driven optical antennas for ultra-fast optoelectronic signal conversion Michel Rebmann, Dr. Kai Braun Prof. Dr. Monika Fleischer, Prof. Dr. Alfred Meixner Universität Tübingen, Germany Converting an electronic signal to an optical signal and vice versa is a fundamental interest for optoelectronics. There are a variety of devices designed for this task. Maximizing the switching speed of them is a major aim for communication technology, where optoelectronics often finds application. However, fundamental limits to switching speeds, and therefore data transmission rates, exist. One of them is the wavelength of the radiation and the associated oscillation frequency of the electromagnetic field. Another limiting factor results from excitation lifetimes in emitter and detector. With their resonance wavelength in the visible regime and plasmon decay times in the femtosecond range 1 , metallic nanoparticles (MNP) utilized as optical antennas promise ultra-fast optoelectronic signal conversion. Unfortunately, there is no way to drive an optical antenna directly electronically. In our work we use inelastic electron tunneling (IET) to electronically excite plasmon oscillations in optical antennas and therefore convert an electrical signal to an optical signal 2-6 . Our group has demonstrated an on-chip device designed for optoelectronic signal conversion, based on a h-BN tunneling junction, isolating a gold electrode from a gold-nanorod-array fabricated on ITO by electron beam lithography. Predominant emission of light in the range of the plasmon resonance of the MNP was observed, rendering the device architecture applicable for data transmission. Directive antennas like Yagi-Uda antennas 7 are more suitable for data transmission experiments than rod antennas. Therefore, our current work aims to gain control over the emitting particle in more complex antenna architectures. To achieve this, we utilize a scanning tunneling microscope-tip as a flexible contact lead in the tunneling contact. The tip is placed directly above the feed antenna and the emitted light can be collected and spectroscopically analyzed by a confocal microscope setup or in widefield configuration. We also included the possibility to operate multiple tips on the same sample at the same time. Thus, getting access to data- transmission experiments, where one tip is used for excitation and the other tunneling contact on another antenna is used for receiving the signal. Additionally, we implemented a 70ps pulse generator to investigate lifetimes and switching speeds and explore the speed limits of the on-chip fabricable device. References
1. S. Link et. al., Chem. Phys. Lett. , 2002, 356 , 240-246. 2. K. Braun et. al., Nanophotonics , 2018, 7 , 1503-1516. 3. J. Kern et. al., Nature Photonics , 2015, 9 , 582-586. 4. J. Lambe and S. L. McCarthy, Physical Review Letters , 1976, 37 , 923-925. 5. M. Parzefall et. al., Nat Nanotechnol , 2015, 10 , 1058-1063.
6. M. Parzefall et. al., Nat Commun , 2019, 10 , 292. 7. R. Kullock et. al., Nat Commun , 2020, 11 , 115.
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