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1Femtosecond laser-printed gold nanoantennas for electrically driven nanoscale light sources
D. Lebedev12*, N. Solomonov1, A. Mozharov1, D. Pavlov3, A. Kuchmizhak34, I. Mukhin15
1- Saint Petersburg Academic University, St. Petersburg, 194021 Russia 2- Institute for analytical instrumentation RAS, St. Petersburg, 190103 Russia
3- Institute for Automation and Control Processes, FEB RAS, Vladivostok, 690041, Russia
4- Pacific Quantum Center, Far Eastern Federal University, Vladivostok, 690922, Russia
5- Peter the Great Saint Petersburg Polytechnic University, St. Petersburg 195251, Russia
Recent advances in nanofabrication and plasmonic have led to renewed interest in the study of tunneling processes in sub-nanometer insulator gap in metal-insulator-metal (MIM) structures, specifically the light emission resulting from inelastic electron tunneling (LEIT). Visible and near-infrared (NIR) light sources based on the LEIT principle possess exceptional characteristics, such as sub-nanometer dimensions, radiation wavelength electrically tuned by gap bias voltage, and ultrafast response times of several femtoseconds limited only by the RC constant of the supply circuit. However, practical implementation of nanosized LEIT photon sources had long been hampered by insufficient quantum efficiency traditionally shown by such devices. This drawback primarily originated from relatively low local density of optical states (LDOS) in a flat tunnel gap, which led to the predominance of the elastic channel in the electron tunneling process providing no contribution to optical excitation. The incorporation of nanoantennas in the contact region had greatly enhanced the capabilities of LEIT devices [1].
Femtosecond (fs) laser pulses are known to drive local ultrafast liquid-to-solid phase transitions in the irradiated matter providing a simple and inexpensive way for fabrication of various plasmonic nanostructures that can be used in various applications, for example, for surface functionalization, SERS, microfluidic sensing, etc. [2].
The presented work justify facile and scalable direct fs-laser printing as a promising method for fabrication of nanoscale electrically driven light sources utilizing the effect of LEIT [3]. An important advantage of the direct laser printing method is its potential compatibility with modern photolithographic techniques employed in the manufacture of integrated circuits. Using this method, we formed on the surface of Au film an array of hemispherical nanobumps with a diameter of 520 nm, possessing the properties of optical nanoantennas. The performed study demonstrated that the nanobumps increase the LDOS in the visible (550 and 850 nm) spectral range. Therefore, such a nanobump can really act as a single nanoscale source of LEIT radiation. Moreover, the fabricated arrays of nanobumps showed collective resonances in the NIR spectral region (1.65 and 1.87 ^m), due to the coupling and destructive interference of the propagating surface plasmons. The possibility of excitation of such collective oscillatory mode driven by inelastic electron tunneling was investigated for the first time. It confirmed that this opens the way to use the LEIT phenomenon in STMs not only for LDOS studies, but for investigation of collective modes associated with nanostructures at optical and IR frequencies.
Thus, the arrays of nanobumps studied in this work possess optical resonances in a broad spectral range (visible and NIR), which allows them to be employed in nanoscale electrically driven and bias-tuned sources of optical radiation with tunable wavelength.
[1] D. Lebedev, V. Shkoldin, A. Mozharov, et al, Scanning Tunneling Microscopy-Induced Light Emission and I/V (dI/dV) Study of Optical Near-Field Properties of Single Plasmonic Nanoantennas. The Journal of Physical Chemistry Letters, 12, pp.501-507, (2021).
[2] D. Pavlov, S. Syubaev, A. Kuchmizhak, et al, Direct laser printing of tunable IR resonant nanoantenna arrays. Applied Surface Science, 469, pp.514-520, (2019).
[3] D. Lebedev, N. Solomonov, L. Dvoretckaia, et al, Femtosecond Laser-Printed Gold Nanoantennas for Electrically Driven and Bias-Tuned Nanoscale Light Sources Operating in Visible and Infrared Spectral Ranges, The Journal of Physical Chemistry Letters, 14(22), pp. 51345140, (2023).
