arXiv subjects

Maria Villanueva-Blanco

Publications and source records attributed to Maria Villanueva-Blanco.

3 recordsLinked to original sources

arXiv2026

Cd(Zn)O on SiC: epsilon-near-zero modes and plasmon-phonon coupling

Cd(Zn)O stands out as probably the best plasmonic material in the mid-IR, but it is usually grown on sapphire or other passive substrates. In this work we introduce SiC as a novel, highly polar, dopable substrate for Cd(Zn)O. The Cd(Zn)O/SiC system is analyzed as a function of the Zn concentration and thin film thickness, and the results are compared to those obtained in the Cd(Zn)O/sapphire system. XRD and reflectance measurements show that the alloy with 10 % Zn nominal concentration has the best crystalline and plasmonic quality, with optical losses as good as 13 % of the plasma frequency. The thin films show two surface polariton modes: a purely plasmonic symmetric mode at higher energies with negligible frequency dispersion and pinning at the plasma frequency for the thinnest films, characteristic of an ideal epsilon-near-zero mode; and a plasmonic-phononic hybridized antisymmetric mode at lower energies, which thanks to the large value of the higher frequency dielectric constant of SiC compared to sapphire, shows much lower frequency dispersion, indicative of the stronger epsilon-near-zero character. Hence, Cd(Zn)O/SiC offers a promising platform for the development of ENZ devices on an active substrate.

physics.optics↗

arXiv2025

GaN mid-IR plasmonics: low-loss epsilon-near-zero modes

Epsilon-near-zero (ENZ) materials, defined by $ | Re(ε) | < 1$, enable unique light propagation characteristics, including confinement within sub-wavelength regions. To reduce losses in this regime, materials with both near-zero permittivity and $n<1$ refractive index, known as near-zero-index (NZI) materials, are desired. When both conditions are satisfied, the resulting region is classified as a low-loss ENZ medium combining strong light confinement with reduced optical losses. To achieve this behavior in the mid-IR, heavily doped semiconductors are required, and those compatible with current technologies are most desirable. This work provides the first in-depth study, supported by experimental demonstrations, of the plasmonic properties of highly doped GaN thin films on Si, exhibiting low optical losses and low-loss ENZ characteristics up to $3μm$. From the extracted optical parameters, the ENZ and NZI regions are determined and compared with the existing literature. As a result of the large polar character of nitrides, a hybridization of the surface plasmon and phonon polaritons is observed, accompanied by a flat-dispersion of the high-energy mode (pinned near the plasma frequency) indicative of its ENZ character. Establishing GaN as a viable platform for mid-IR ENZ-based plasmonics paves the way for integration into future infrared photonic technologies.

physics.optics↗

arXiv2025

Near Field Enhancement via Plasmon Phonon Polariton Coupling with CdO Stripes

The mid-infrared spectral region presents significant potential for sensing and spectroscopic applications. However, traditional plasmonic materials exhibit substantial optical losses within this range, thereby constraining their effectiveness. Emerging materials such as cadmium oxide (CdO) have demonstrated promise in overcoming these limitations. In this work, we introduce a novel approach to engineer large coupling between localized surface plasmons (LSPs) in CdO and localized surface phonon polaritons (LSPhP) in sapphire. By developing a successful dry etching protocol for CdO, we fabricate stripe arrays with tunable sizes, allowing the spectral alignment between the LSP and LSPhP modes. We demonstrate both experimentally and numerically that when these polaritons become resonant, hybrid modes emerge, resulting in coupling. Finite element simulations reveal near-field enhancements exceeding a factor of 1000, spatially extended hundreds of nanometers around the etched structures. Our approach bridges the plasmonic and phononic responses of two mid-IR active materials, paving the way for scalable, high-performance infrared sensing platforms.

physics.optics↗