Ultrathin nanocapacitor assembled via atomic layer deposition.

We fabricated ultrathin metal - oxide - semiconductor (MOS) nanocapacitors using atomic layer deposition. The capacitors consist of a bilayer of Al2O3 and Y2O3 with a total thickness of ~10 nm, deposited on silicon substrate. The presence of the two materials, each slab being ~5 nm thick and uniform over a large area, was confirmed with Transmission Electron Microscopy and X-ray photoelectron spectroscopy (XPS). The capacitance in accumulation varied from 1.6 nF (at 1MHz) to ~2.8 nF (at 10 kHz), which is one to two orders of magnitude higher than other nanocapacitors. This high capacitance is attributed to the synergy between the dielectric properties of ultrathin Al2O3 and Y2O3 layers. The electrical properties of the nanocapacitor are stable within a wide range of temperatures, from 25 °C to 150 °C, as indicated by capacitance-voltage (C - V). Since the thickness-to-area ratio is negligible, the nanocapacitor could be simulated as a single parallel plate capacitor in COMSOL Multiphysics, with good agreement between experimental and simulation data. As a proof-of-concept we simulated a MOSFET device with the nanocapacitor gate dielectric, whose drain current is sufficiently high for micro and nanoelectronics integrated circuits, including for applications in sensing.

High-Refractive-Index Materials for Giant Enhancement of the Transverse Magneto-Optical Kerr Effect.

The ability of plasmonic structures to confine and enhance light at nanometer length scales has been traditionally exploited to boost the magneto-optical effects in magneto-plasmonic structures. These platforms allows for light control via externally applied magnetic fields, which is of prime importance for sensing, data storage, optical-isolation, and telecommunications applications. However, applications are hindered by the high-level of ohmic losses associated to metallic and ferromagnetic components. Here, we use a lossless all-dielectric platform for giant enhancement of the magneto-optical effects. Our structure consists of a high-refractive index dielectric film on top of a magnetic dielectric substrate. We numerically demonstrate an extraordinarily enhanced transverse magneto-optical Kerr effect due to the Fabry-Perot resonances supported by the high-refractive index slab. Potential applications for sensing and biosensing are also illustrated in this work.

Plasmonics for Telecommunications Applications.

Plasmonic materials, when properly illuminated with visible or near-infrared wavelengths, exhibit unique and interesting features that can be exploited for tailoring and tuning the light radiation and propagation properties at nanoscale dimensions. A variety of plasmonic heterostructures have been demonstrated for optical-signal filtering, transmission, detection, transportation, and modulation. In this review, state-of-the-art plasmonic structures used for telecommunications applications are summarized. In doing so, we discuss their distinctive roles on multiple approaches including beam steering, guiding, filtering, modulation, switching, and detection, which are all of prime importance for the development of the sixth generation (6G) cellular networks.

Cooperative Full-Duplex V2V-VLC in Rectilinear and Curved Roadway Scenarios.

We study here the vehicle-to-vehicle (V2V) visible light communication (VLC) between two cars moving along different roadway scenarios: (i) a multiple-lane rectilinear roadway and (ii) a multiple-lane curvilinear roadway. Special emphasis was given to the implementation of full-duplex (FD) cooperative communication protocols to avoid communication disruption in the absence of a line-of-sight (LOS) channel. Importantly, we found that the cooperative FD V2V-VLC is promising for avoiding communication disruptions for cars traveling in realistic curvilinear roadways. Results in this work can be easily extended to the case of vehicle-to-infrastructure (V2I), which can also be promising in cases of low-car-density environments.

Chiral Plasmonics and Their Potential for Point-of-Care Biosensing Applications.

There has been growing interest in using strong field enhancement and light localization in plasmonic nanostructures to control the polarization properties of light. Various experimental techniques are now used to fabricate twisted metallic nanoparticles and metasurfaces, where strongly enhanced chiral near-fields are used to intensify circular dichroism (CD) signals. In this review, state-of-the-art strategies to develop such chiral plasmonic nanoparticles and metasurfaces are summarized, with emphasis on the most recent trends for the design and development of functionalizable surfaces. The major objective is to perform enantiomer selection which is relevant in pharmaceutical applications and for biosensing. Enhanced sensing capabilities are key for the design and manufacture of lab-on-a-chip devices, commonly named point-of-care biosensing devices, which are promising for next-generation healthcare systems.

Surface Plasmon Resonances in Silver Nanostars.

The recent development of silver nanostars (Ag-NSs) is promising for improved surface-enhanced sensing and spectroscopy, which may be further exploited if the mechanisms behind the excitation of localized surface plasmon resonances (LSPRs) are identified. Here, we show that LSPRs in Ag-NSs can be obtained with finite-difference time-domain (FDTD) calculations by considering the nanostars as combination of crossed nanorods (Ag-NRs). In particular, we demonstrate that an apparent tail at large wavelengths ( λ ≳ 700 nm) observed in the extinction spectra of Ag-NSs is due to a strong dipolar plasmon resonance, with no need to invoke heterogeneity (different number of arms) effects as is normally done in the literature. Our description also indicates a way to tune the strongest LSPR at desired wavelengths, which is useful for sensing applications.

All-Dielectric Chiral Metasurfaces Based on Crossed-Bowtie Nanoantennas.

Circular dichroism spectroscopy is a technique used to discriminate molecular chirality, which is essential in fields like biology, chemistry, or pharmacology where different chiral agents often show different biological activities. Nevertheless, due to the inherently weak molecular-chiroptical activity, this technique is limited to high concentrations or large analyte volumes. Finding novel ways to enhance the circular dichroism would boost the performance of these techniques. So far, the enhancement of light-matter interaction mediated by plasmons is the most common way to develop chiral plasmonic structures with extraordinarily strong chiroptical responses. However, absorptive losses of metals at optical frequencies has hindered its practical use in many scenarios. In this work, we propose an all-dielectric low-loss chiral metasurface with unit cells built by high-refractive-index crossed-bowtie nanoantennas. These unit cells, built of silicon, strongly increase the chiroptical effect through the simultaneous interaction of their electric and magnetic modes, which in contrast to other recent proposals shows at the same time a high concentration of the electric field in its gap that leads to the presence of hotspots. The proposed structure exhibits a circular dichroism spectra up to 3-fold higher than that of previous proposals that use complex plasmonic or hybrid nanostructures, making it a clear alternative to develop low-loss metasurfaces with potential applications in chiral target sensing/biosensing. For completeness, single triangular shaped and symmetric (achiral) bowtie nanostructures were also studied as possible candidates for a detection up to the single-molecule level due the lack of a circular dichroism background of the nanostructures themselves.

Hybrid Superconducting-Ferromagnetic [Bi2Sr2(Ca,Y)2Cu3O10]0.99(La2/3Ba1/3MnO3)0.01 Composite Thick Films.

We report here on the development of composite thick films exhibiting hybrid superconducting and ferromagnetic properties, produced through a low-cost, fast, and versatile process. These films were made of high Tc cuprate superconductor Bi2Sr2(Ca,Y)2Cu3O10 (with Y:Ca ratio of 5%) and ferromagnetic perovskite La2/3Ba1/3MnO3, synthesized by melting-quenching annealing process on a MgO substrate. Curie temperature for La2/3Ba1/3MnO3 was determined (~336 K ) by magnetic field assisted thermogravimetric analysis (TGA), while superconducting behavior of Bi2Sr2(Ca,Y)2Cu3O10/MgO films was observed through temperature-dependent resistance measurements. Superconducting features in our hybrid compound were corroborated by temperature-dependent resistivity and magnetic susceptibility.

Giant Second-Harmonic Generation in Cantor-like Metamaterial Photonic Superlattices.

We present a nonlinear transfer matrix method for studying the second-harmonic generation (SHG) in nonperiodic metamaterial photonic superlattices. A large enhancement of up to 5 orders of magnitude in SHG efficiency was observed for superlattices made with a Cantor-like quasiperiodic assembly of a nonlinear material and a metamaterial. The enhancement was found to depend much more on the electric field amplitude along the structure because of self-similarity effects than on the amount of nonlinear material, which opens the way to design superlattices for tailored applications in broad-band tunable lasers.