Open Access
Giant photodegradation rate enabled by vertically grown 1T/2H MoS2 catalyst on top of silver nanoparticles
(Wiley, 2024-08-27) Mouloua, Driss; Rajput, Nitul S.; Lejeune, Michael; Beruete Díaz, Miguel; El Marssi, Mimoun; El Khakani, My Ali; Jouiad, Mustapha; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
The exaltation of the photodegradation performance of dichalcogenide MoS2 grown on top of silver nanoparticles (Ag-NPs) is reported on. The fabricated MoS2 nanosheets nucleate vertically from Ag-NPs seeds, enabling the growth of both metallic and semiconductor phases 1T/2H-MoS2. Findings reveal remarkable enhancement of the Raman scattering and an exceptional broadband optical absorption attributed to plasmonic effects induced by the presence of both metallic 1T-MoS2 and Ag-NPS at 2H-MoS2 interfaces. To leverage this effect, photodegradation tests are conducted to remove methyl orange pollutant. Notably, results reveal a significant increase in photodegradation efficiency and rate constant, reaching up to 120% and 550% over pristine 2H-MoS2, respectively. This finding underscores the role of Ag-NPs and 1T-MoS2 tandem to unlock the superior photodegradation properties of vertically aligned 2H-MoS2 toward methyl orange, paving the way for the development of dichalcogenide-based hybrid photocatalyst for wastewater treatment and environmental remediation.
Open Access
A slow light fishnet-like absorber in the millimeter-wave range
(EMW Publishing, 2011) Navarro Cía, Miguel; Torres Landívar, Víctor; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A novel route to achieve a narrowband free-space electromagnetic absorber in any range of the spectrum based on stacked subwavelength hole arrays is proposed. The absorption is obtained by means of a slow light mode inside a fishnet-like engineered structure and exploiting the unavoidable misalignments and bucklings of the free-standing stack. An incoming pulse becomes permanently trapped in the structure due to the near zero group velocity which causes an enhancement of the radiation-structure interaction that leads to a huge increment of losses arising from the finite conductivity of the metal as well as arrangement tolerances. This approach is studied not only by simulation but also experimentally under normal incidence at millimeter wavelengths. Moreover, a basic grasp about the angular dependence of the structure is given by analyzing the 2D dispersion diagram. It shows that this scheme may also display high absorption under oblique incidence for s-polarization (or TE-polarization), whereas p-polarization (TM-polarization) would degrade its performance.
Open Access
Circuit approach to the minimal configuration of terahertz anomalous extraordinary transmission
(American Institute of Physics, 2011) Beruete Díaz, Miguel; Navarro Cía, Miguel; Kuznetsov, Sergei A.; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this letter we present an in-depth circuit analysis of anomalous extraordinary transmission ET through subwavelength slit and hole arrrays loaded by a dielectric slab. We show the key role played by the thickness of the dielectric slab in order to enhance the transmission for TE-polarized waves incident electric field parallel to the slits or to the short in-plane period in hole arrays arranged in rectangular lattice within the cut-off regime of the apertures and to suppress Wood’s anomaly. Analytical and numerical results together with experimental data are presented, showing good agreement among them. This work provides physical insight of the underlying mechanism governing anomalous ET and offers further independent control over orthogonal polarized waves impinging into subwavelength aperture arrays.
Open Access
Labyrinth metasurface for biosensing applications: numerical study on the new paradigm of metageometries
(MDPI, 2019) Jáuregui López, Irati; Rodríguez Ulibarri, Pablo; Kuznetsov, Sergei A.; Quemada Mayoral, Carlos; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
The use of metasurfaces operating in the terahertz regime as biosensor devices has attracted increased interest in recent years due to their enhanced sensitivity and more accurate detection capability. Typical designs are based on the replica of relatively simple unit cells, usually called metaatoms. In a previous paper, we proposed a new paradigm for ultrasensitive thin-film sensors based on complex unit cells, called generically metageometries or labyrinth metasurfaces. Here, we extend this concept towards biosensing, evaluating the performance of the labyrinth as a fungi detector. The sensing capabilities are numerically evaluated and a comparison with previous works in this field is performed, showing that metageometries improve the performance compared to metaatoms both in sensitivity and figure of merit, by a factor of more than four. In particular, we find that it is able to detect five fungi elements scattered on the unit cell, equivalent to a concentration of only 0.004/µm2.
Open Access
Experimental demonstration of a millimeter-wave metallic ENZ lens based on the energy squeezing principle
(IEEE, 2015) Torres Landívar, Víctor; Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Teniente Vallinas, Jorge; Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The performance of an epsilon-near zero (ENZ) plano-concave lens is experimentally demonstrated and verified at the D-band of the millimeter-waves. The lens is comprised of an array of narrow metallic waveguides near cut-off frequency, which effectively behaves as an epsilon-near-zero medium at 144 GHz. A good matching with free space is achieved by exploiting the phenomenon of energy squeezing and a clear focus with a transmission enhancement of 15.9 dB is measured. The lens shows good radiation properties with a directivity of 17.6 dBi and low cross-polar components of -34 dB. All results are supported by numerical simulations.
Open Access
Tunable beam steering enabled by graphene metamaterials
(Optical Society of America, 2016) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Khromova, Irina; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.
Open Access
Experimental realization of an epsilon-near-zero graded-index metalens at terahertz frequencies
(American Physical Society, 2017) Pacheco-Peña, Víctor; Engheta, Nader; Kuznetsov, Sergei A.; Gentselev, Alexandr; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
The terahertz band has been historically hindered by the lack of efficient generators and detectors, but a series of recent breakthroughs have helped to effectively close the “terahertz gap.” A rapid development of terahertz technology has been possible thanks to the translation of revolutionary concepts from other regions of the electromagnetic spectrum. Among them, metamaterials stand out for their unprecedented ability to control wave propagation and manipulate electromagnetic response of matter. They have become a workhorse in the development of terahertz devices such as lenses, polarizers, etc., with fascinating features. In particular, epsilon-near-zero (ENZ) metamaterials have attracted much attention in the past several years due to their unusual properties such as squeezing, tunneling, and supercoupling where a wave traveling inside an electrically small channel filled with an ENZ medium can be tunneled through it, reducing reflections and coupling most of its energy. Here, we design and experimentally demonstrate an ENZ graded-index (GRIN) metamaterial lens operating at terahertz with a power enhancement of 16.2 dB, using an array of narrow hollow rectangular waveguides working near their cutoff frequencies. This is a demonstration of an ENZ GRIN device at terahertz and can open the path towards other realizations of similar devices enabling full quasioptical processing of terahertz signals.
Open Access
Analysis of surface-plasmon-like modes under an engineering perspective
(2011) Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this communication we show how one can exploit equivalent circuits to analyze surface-plasmon-like modes (slit and hole arrays, Sievenpiper mushrooms and coaxial hole arrays) and to propose new designs with outstanding features.
Open Access
Diffusive-light invisibility cloak for transient illumination
(American Physical Society, 2016) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Martínez, Alejandro; García Meca, Carlos; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Invisibility in a diffusive-light-scattering medium has been recently demonstrated by employing a scattering-cancellation core-shell cloak. Unlike nondiffusive cloaks, such a device can be simultaneously macroscopic, broadband, passive, polarization independent, and omnidirectional. Unfortunately, it has been verified that this cloak, as well as more sophisticated ones based on transformation optics, fail under pulsed illumination, invalidating their use for a variety of applications. Here, we introduce a different approach based on unimodular transformations that enables the construction of unidirectional diffusive-light cloaks exhibiting a perfect invisibility effect, even under transient conditions. Moreover, we demonstrate that a polygonal cloak can extend this functionality to multiple directions with a nearly ideal behavior, while preserving all other features. We propose and numerically verify a simple cloak realization based on a layered stack of two isotropic materials. The studied devices have several applications not addressable by any of the other cloaks proposed to date, including shielding from pulse-based detection techniques, cloaking undesired scattering elements in time-of-flight imaging or high-speed communication systems for diffusive environments, and building extreme optical security features. The discussed cloaking strategy could also be applied to simplify the implementation of thermal cloaks.
Open Access
Multiple absorption regimes in simple lithography-free structures leading to ultrathin slabs
(2024-07-08) Lezaun Capdevila, Carlos; Navajas Hernández, David; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Electromagnetic absorbers serve as fundamental components for a wide range of applications, encompassing energy and heat management, sensing, and communications. In this study, we explore several complex permittivity combinations for lithography-free material-reflector and material-spacer-reflector configurations that lead to perfect absorption peaks across distinct permittivity regimes and varying thicknesses. We provide an extensive analysis of angle and polarization dependencies, specifically using silicon carbide as an illustrative example. Our findings reveal the potential for harnessing different absorption regimes within a single device, thus enabling the realization of multiband absorption capabilities. Furthermore, we demonstrate perfect absorption linked with extreme values of permittivity, and we find the conditions to get perfect absorption in ultrathin slabs. In addition, we carry out an analysis about the response at oblique incidence, and we identify a particular mode in the negative permittivity region and its hybridization with epsilon-near-zero modes at oblique incidence. This investigation serves as a valuable standardization of absorber design, offering insights to develop perfect absorbers for infrared applications such as thermal emission, communications, and sensing.