Open Access
Exploring surface roughness in epsilon-near-zero materials
(IEEE, 2024-10-08) Navajas Hernández, David; Pérez Escudero, José Manuel; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
The practical application of materials with epsilon-near-zero (ENZ) characteristics heavily depends on the quality of real-world ENZ materials, considering factors like material losses and surface roughness. These materials have drawn interest due to their strong nonlinear responses and unique behavior. In this study, an experimental examination of how surface roughness affects ENZ substrates is presented. We employed silicon carbide (SiC) substrates deliberately engineered to exhibit different levels of roughness, enabling us to analyze samples spanning from a few to hundreds of nanometers in size scales. Substrates with nanoscale roughness experience adverse effects due to longitudinal phonon coupling and strong ENZ fields, while at larger roughness scales, the ENZ band demonstrates to be more robust compared to dielectric and surface phonon polariton (SPhP) bands.
Open Access
Surface roughness effects on ENZ media IR spectra
(IEEE, 2023-09-04) Navajas Hernández, David; Pérez Escudero, José Manuel; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
The development of high-performance nanophotonic technologies faces challenges like material losses and surface roughness. While surface roughness has been studied in the plasmonic regime, its effect on epsilon-near-zero (ENZ) media has been less explored. Two theoretical scenarios arise regarding roughness in ENZ media: one predicts the excitation of a strong longitudinal electric field, while the other suggests minimal changes in reflection due to the large effective wavelength. This study investigates silicon carbide (SiC) as an ENZ substrate, using deep reactive ion etching (DRIE) to create significant surface roughness. The findings show that surface roughness affects the reflection spectra, induces polaritonic effects, and highlights the robustness of SiC against surface roughness. Numerical simulations and experimental measurements confirm these results, revealing that ENZ substrates maintain their reflective properties even with surface roughness on the scale of hundreds of nanometers.
Open Access
Addressing the impact of surface roughness on epsilon-near-zero silicon carbide substrates
(American Chemical Society, 2023) Navajas Hernández, David; Pérez Escudero, José Manuel; Martínez Hernández, María Elena; Goicoechea Fernández, Javier; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Epsilon-near-zero (ENZ) media have been very actively investigated due to their unconventional wave phenomena and strengthened nonlinear response. However, the technological impact of ENZ media will be determined by the quality of realistic ENZ materials, including material loss and surface roughness. Here, we provide a comprehensive experimental study of the impact of surface roughness on ENZ substrates. Using silicon carbide (SiC) substrates with artificially induced roughness, we analyze samples whose roughness ranges from a few to hundreds of nanometer size scales. It is concluded that ENZ substrates with roughness in the few nanometer scale are negatively affected by coupling to longitudinal phonons and strong ENZ fields normal to the surface. On the other hand, when the roughness is in the hundreds of nanometers scale, the ENZ band is found to be more robust than dielectric and surface phonon polariton (SPhP) bands.
Open Access
Spectrally stable thermal emitters enabled by material-based high-impedance surfaces
(Royal Society of Chemistry, 2023) Navajas Hernández, David; Pérez Escudero, José Manuel; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Radiative thermal engineering with subwavelength metallic bodies is a key element for heat and energy management applications, communication and sensing. Here, we numerically and experimentally demonstrate metallic thermal emitters with narrowband but extremely stable emission spectra, whose resonant frequency does not shift with changes on the nanofilm thickness, the angle of observation and/or polarization. Our devices are based on epsilon-near-zero (ENZ) substrates acting as material-based high-impedance substrates. They do not require from complex nanofabrication processes, thus being compatible with large-area and low-cost applications.
Open Access
Narrowband and spectrally robust thermal emission from metallic thin films on top of epsilon-near-zero substrates
(IEEE, 2022) Navajas Hernández, David; Pérez Escudero, José Manuel; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The absorption and emission of infrared radiation by ultra-thin metallic films is a key element in several thermal engineering applications such as heat and energy management, and thermal camouflage. However, ultra-thin metallic films are broadband and low-efficiency emitters. Here, we demonstrate numerically and experimentally that metallic films placed on top of epsilon-near-zero (ENZ) substrates become narrowband and efficient thermal emitters. Our experiments show that ENZ-based emitters feature a narrow linewidth whose frequency positioning is robust against variations in the geometry of the system and the observation angle. Moreover, since ENZ emitters are based on the material properties of the substrate, no nanofabrication processes are needed, opening the pathway towards widefield and large-scale applications.