arXiv subjects

Rostislav Řepa

Publications and source records attributed to Rostislav Řepa.

5 recordsLinked to original sources

arXiv2026

Reconfigurable plasmonic hot spots enabled by composite VO2-gold plasmonic antennas

We theoretically investigate the formation of electric and magnetic hot spots with reconfigurable plasmonic antennas. We consider three material systems offering different levels of reconfigurability: gold with the static response, vanadium dioxide which allows for ON/OFF switching, and composite gold-vanadium dioxide material platform which offers a possibility to switch between the electric and magnetic hot spot within a single antenna. Using bowtie and diabolo antennas as a case study, we evaluate optical response functions (scattering and absorption cross-sections, electric and magnetic field enhancement). We demonstrate that the composite material system brings, in addition to enhanced reconfigurability, also novel features of plasmonic antennas, such as strong optical absorption and a joint electric-magnetic hotspot.

physics.optics↗

arXiv2026

Tuning of Localized Surface Plasmons in Vanadium Dioxide Nanoparticles via Size and Insulator-Metal Transition

Vanadium dioxide has been identified as a promising phase-changing material for use in tunable plasmonic devices. In this study, we present a comprehensive modal analysis of single-phase and multi-phase vanadium dioxide nanoparticles. In-situ high-resolution electron energy loss spectroscopy was utilized to experimentally resolve the dipole plasmon peak, higher-order and breathing plasmonic modes, and bulk losses as a function of nanoparticle size. Furthermore, the focus is directed toward capturing the dynamic nanoscale optical response throughout the metal-insulator transition in a vanadium dioxide nanoparticle. This system possesses the ability to be gradually switched on and off in terms of the emergence of near-infrared plasmonic absorption. The switching is accompanied by a gradual spectral shift of the absorption peak, amounting to 0.18 eV for a 120 nm nanoparticle. It is envisioned that this phenomenon can be generalized to larger nanostructures with a higher aspect ratio, thereby introducing a wider tunability of the system, which is essential for functional nanodevices based on vanadium dioxide.

physics.optics↗

arXiv2025

Charge reservoir as a design concept for plasmonic antennas

Plasmonic antennas exploit localized surface plasmons to shape, confine, and enhance electromagnetic fields with subwavelength resolution. The field enhancement is contributed to by various effects, such as the inherent surface localization of plasmons or the plasmonic lightning-rod effect. Inspired by nanofocusing observed for propagating plasmons, we test the hypothesis that plasmonic antennas with a large cross-section represent a large charge reservoir, enabling large induced charge and field enhancement. Our study reveals that a large charge reservoir is accompanied by large radiative losses, which are the dominant factor, resulting in a low field enhancement.

physics.optics↗

arXiv2024

Plasmonic lightning-rod effect

The plasmonic lightning-rod effect refers to the formation of a strong electric near field of localized surface plasmons at the sharp features of plasmonic antennas. While this effect is intuitively utilized in the design and optimization of plasmonic antennas, the relation between the magnitude of the electric field and the local curvature of the plasmonic antenna has not been yet rigorously established. Here, we provide such a study. We design sets of plasmonic antennas that allow to isolate the role of the local curvature from other effects influencing the field. The near electric field is inspected by electron energy loss spectroscopy and electrodynamic simulations. We demonstrate the existence of the plasmonic lightning-rod effect and establish its quantitative description, showing that its strength is comparable to the electrostatic lightning-rod effect. We also provide a simple phenomenological formula for the spatial dependence of the field. Finally, we introduce the effective radius of curvature related to the spatial distribution of induced charge in plasmonic antennas, significantly smaller than their geometrical radius.

physics.optics↗

arXiv2024

Influence of deposition parameters on the plasmonic properties of gold nanoantennas fabricated by focused ion beam lithography

The behavior of plasmonic antennas is influenced by a variety of factors, including their size, shape, and material. Even minor changes in the deposition parameters during the thin film preparation process may have a significant impact on the dielectric function of the film, and thus on the plasmonic properties of the resulting antenna. In this work, we deposited gold thin films with thicknesses of 20 nm, 30 nm, and 40 nm at various deposition rates using an ion-beam-assisted deposition. We evaluate their morphology and crystallography by atomic force microscopy, X ray diffraction, and transmission electron microscopy. Next, we examined the ease of fabricating plasmonic antennas using focused-ion-beam lithography. Finally, we evaluate their plasmonic properties by electron energy loss spectroscopy measurements of individual antennas. Our results show that the optimal gold thin film for plasmonic antenna fabrication of a thickness of 20 and 30 nm should be deposited at the deposition rate of around 0.1 nm/s. The thicker 40 nm film should be deposited at a higher deposition rate like 0.3 nm/s.

cond-mat.mtrl-sci↗