High-Performance Nanosensors Based on Plasmonic Fano-like Interference: Probing Refractive Index with Individual Nanorice and Nanobelts

We propose two different configurations for which the Fano-like interference of longitudinal plasmon resonances occurring at individual metallic nanoparticles can be easily employed in refractive index sensing: a colloidal suspension of nanospheroids (nanorice) and a single nanowire with rectangular cross section (nanobelt) on top of a dielectric substrate. We numerically study the performance of the two in terms of their figures of merit, which are calculated under realistic conditions. For the case of nanorice, we explicitly incorporate the effect of size dispersity into the simulations. Our obtained results show that the application of the proposed configurations seems to be not only feasible but also very promising

Surface Plasmon Polaritons on Rough Metal Surfaces: Role in the Formation of Laser-Induced Periodic Surface Structures

The formation of self-organized laser-induced periodic surface structures (LIPSS) in metals, semiconductors, and dielectrics upon pulsed laser irradiation is a well-known phenomenon, receiving increased attention because of their huge technological potential. For the case of metals, a major role in this process is played by surface plasmon polaritons (SPPs) propagating at the interface of the metal with the medium of incidence. Yet, simple and advanced models based on SPP propagation sometimes fail to explain experimental results, even of basic features such as the LIPSS period. We experimentally demonstrate, for the particular case of LIPSS on Cu, that significant deviations of the structure period from the predictions of the simple plasmonic model are observed, which are very pronounced for elevated angles of laser incidence. In order to explain this deviation, we introduce a model based on the propagation of SPPs on a rough surface that takes into account the influence of the specific roughness properties on the SPP wave vector. Good agreement of the modeling results with the experimental data is observed, which highlights the potential of this model for the general understanding of LIPSS in other metals

Surface Plasmon Polaritons on Rough Metal Surfaces: Role in the Formation of Laser-Induced Periodic Surface Structures

The formation of self-organized laser-induced periodic surface structures (LIPSS) in metals, semiconductors, and dielectrics upon pulsed laser irradiation is a well-known phenomenon, receiving increased attention because of their huge technological potential. For the case of metals, a major role in this process is played by surface plasmon polaritons (SPPs) propagating at the interface of the metal with the medium of incidence. Yet, simple and advanced models based on SPP propagation sometimes fail to explain experimental results, even of basic features such as the LIPSS period. We experimentally demonstrate, for the particular case of LIPSS on Cu, that significant deviations of the structure period from the predictions of the simple plasmonic model are observed, which are very pronounced for elevated angles of laser incidence. In order to explain this deviation, we introduce a model based on the propagation of SPPs on a rough surface that takes into account the influence of the specific roughness properties on the SPP wave vector. Good agreement of the modeling results with the experimental data is observed, which highlights the potential of this model for the general understanding of LIPSS in other metals

High-Contrast Fano Resonances in Single Semiconductor Nanorods

Fano resonances in plasmonics have received widespread attention for their distinctly narrow asymmetric line shapes. A variety of configurations have been considered, either requiring complex metallic nanostructures or being extremely faint if originated in simple single nanoparticles. Here we report on the emergence of high-contrast, strongly asymmetric Fano line shapes in the light scattered from semiconductor nanorods. Numerical calculations are carried out for the scattering cross sections of finite semiconducting nanorods, with dimensions such that the lowest-order (transverse) Mie resonances coexist with the lowest-order guided modes. Such intense narrow Fano resonances are strongly/weakly asymmetric in TE/TM polarization and overlap with the Mie-like background. A physical interpretation is presented stemming from the (strong or weak) interference of the far-field angular patterns of Mie resonances (indeed, of both magnetic and dielectric dipole character) with narrow Fabry–Perot (guided mode) resonances, the latter calculated through a 1D line current model. A quasi-analytical expression is developed for the scattering cross sections that reproduce fairly well the Fano numerical line shapes, along with a generalized Fano formula, with fitting factors confirming their high asymmetry and contrast. These high-contrast, strongly asymmetric Fano resonances herein obtained could be potentially exploited in nanophotonics and sensing in the visible and near-IR, eased by simplified fabrication requirements of shape (nanorod) and material (semiconductor)

Structural, Optical, and Electrical Characterization of Yttrium-Substituted BiFeO₃ Ceramics Prepared by Mechanical Activation

Ceramics of Bi_1–<i>x</i>Y_<i>x</i>FeO₃ solid solutions (<i>x</i> = 0.02, 0.07, and 0.10) have been prepared by mechanical activation followed by sintering. The effect of yttrium content on the structural, electrical, and optical properties of the materials has been studied. Thus, single-phase solid solutions with rhombohedral <i>R</i>3<i>c</i> structure have been achieved for <i>x</i> = 0.02 and 0.07, while for <i>x</i> = 0.10 the main <i>R</i>3<i>c</i> phase has been detected together with a small amount of the orthorhombic <i>Pbnm</i> phase. Multiferroic properties of the samples, studied by differential scanning calorimetry (DSC), showed that both <i>T</i>_N and <i>T</i>_C (temperatures of the antiferromagnetic–paramagnetic and ferroelectric–paraelectric transitions, respectively) decrease with increasing yttrium content. The nature of the ferroelectric–paraelectric transition has been studied by temperature-dependent X-ray diffraction (XRD), which revealed rhombohedral <i>R</i>3<i>c</i> to orthorhombic <i>Pbnm</i> phase transitions for <i>x</i> = 0.07 and 0.10. On the other hand, for <i>x</i> = 0.02 the high-temperature phase was indexed as <i>Pnma</i>. Optical properties of the samples, as studied by diffuse reflectance spectroscopy, showed low optical band gap that decreases with increasing yttrium content. Prepared ceramics were highly insulating at room temperature and electrically homogeneous, as assayed by impedance spectroscopy, and the conductivity increased with <i>x</i>

The evolving Interreligious Vision of Raimon Panikkar

Conferència a càrrec de Gerard Hall de l'Australian Catholic University sobre l'evolució del pensament interreligiós de Raimon Panikka

Nanowire Antenna Emission

We experimentally demonstrate the directional emission of polarized light from single semiconductor nanowires. The directionality of this emission has been directly determined with Fourier microphotoluminescence measurements of vertically oriented InP nanowires. Nanowires behave as efficient optical nanoantennas, with emission characteristics that are not only given by the material but also by their geometry and dimensions. By means of finite element simulations, we show that the radiated power can be enhanced for frequencies and diameters at which leaky modes in the structure are present. These leaky modes can be associated to Mie resonances in the cylindrical structure. The radiated power can be also inhibited at other frequencies or when the coupling of the emission to the resonances is not favored. We anticipate the relevance of these results for the development of nanowire photon sources with optimized efficiency and/or controlled emission by the geometry

Crystallization Kinetics of Nanocrystalline Materials by Combined X‑ray Diffraction and Differential Scanning Calorimetry Experiments

Crystallization is one key aspect in the resulting properties of nanocrystalline functional materials, and much effort has been devoted to understanding the physical mechanisms involved in these processes as a function of temperature. The main problems associated with crystallization kinetic studies come from the limitations of the employed techniques, and the obtained results may vary significantly depending on the choice of the measurement method. In this work, a complete description of the thermal crystallization event of nanocrystalline BiFeO₃ has been performed by combining the information obtained from three different experimental techniques: in situ high-temperature X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Interestingly, the kinetic analysis of the X-ray diffraction and differential scanning calorimetry data yields almost identical results, although the physical properties measured by both techniques are different. This allows the unambiguous determination of the kinetic parameters. The importance of a proper definition of the conversion degree, which is limited by the employed measurement technique, is also highlighted

Optical Mie Scattering by DNA-Assembled Three-Dimensional Gold Nanoparticle Superlattice Crystals

Programmable assemblies of gold nanoparticles engineered with DNA have intriguing optical properties such as Coulomb-interaction-driven strong coupling, polaritonic response in the visible range, and ultralow dispersion dielectric response in the infrared spectral range. In this work, we demonstrate the optical Mie resonances of individual microcrystals of DNA–gold nanoparticle superlattices. Broadband hyperspectral mapping of both transmission and dark-field scattering reveal a polarization-insensitive optical response with distinct spectral features in the visible and near-infrared ranges. Experimental observations are supported by numerical simulations of the microcrystals under a resonant effective medium approximation in the regime of capacitively coupled nanoparticles. The study identifies a universal characteristic optical response which is defined by a band of multipolar Mie resonances, which only weakly depend on the crystal size and light polarization. The use of gold superlattice microcrystals as scattering materials is of interest for fields such as complex nanophotonics, thermoplasmonics, photocatalysis, sensing, and nonlinear optics