Search

Abstract Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts, including telecommunications, biology and chemistry. The ability to control polarization at ultrafast speed would pave the way for the development of unprecedented free-space optical links and of novel techniques for probing dynamical processes in complex systems, as chiral molecules. Such high switching speeds can only be reached with an all-optical paradigm, i.e., engineering active platforms capable of controlling light polarization via ultrashort laser pulses. Here we demonstrate giant modulation of dichroism and birefringence in an all-dielectric metasurface, achieved at low fluences of the optical control beam. This performance, which leverages the many degrees of freedom offered by all-dielectric active metasurfaces, is obtained by combining a high-quality factor nonlocal resonance with the giant third-order optical nonlinearity dictated by photogenerated hot carriers at the semiconductor band edge.

In this study we will start from a suggestion taken from Kayne’s proposal (2016) about silent heads, in order to analyse the structure of some specific adverbial PPs in different languages. It will be argued that behind certain manner constructions consisting of a preposition plus an adjective may lie a full nominal phrase, whose head is generally – but not exclusively – silent. This study will show that there is a cross-linguistic tendency to create manner expressions using a nominal head meaning ‘way’ or ‘manner’, and also that this head may change diachronically, either becoming silent to form idiomatic expressions, or being reanalysed and grammaticalised into a productive adverbial suffix.

Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Recently, a dry synthesis of nanoporous films based on the plasma treatment of metal thin layers deposited by physical vapour deposition has been demonstrated, as a general route to form pure nanoporous films from a large set of metals. An interesting aspect related to this approach is the possibility to apply the same methodology to deposit the porous films as a multilayer. In this way, it is possible to explore the properties of different porous metals in close contact. As demonstrated in this paper, interesting plasmonic properties emerge in a nanoporous Au–Ag bi-layer. The versatility of the method coupled with the possibility to include many different metals, provides an opportunity to tailor their optical resonances and to exploit the chemical and mechanical properties of components, which is of great interest to applications ranging from sensing, to photochemistry and photocatalysis.

Metallic nanostructures exhibit localized surface plasmons (LSPs), which offer unprecedented opportunities for advanced photonic materials and devices. Following resonant photoexcitation, LSPs quickly dephase, giving rise to a distribution of energetic ‘hot’ electrons in the metal. These out-of-equilibrium carriers undergo ultrafast internal relaxation processes, nowadays pivotal in a variety of applications, from photodetection and sensing to the driving of photochemical reactions and ultrafast all-optical modulation of light. Despite the intense research activity, exploitation of hot carriers for real-world nanophotonic devices remains extremely challenging. This is due to the complexity inherent to hot carrier relaxation phenomena at the nanoscale, involving short-lived out-of-equilibrium electronic states over a very broad range of energies, in interaction with thermal electronic and phononic baths. These issues call for a comprehensive understanding of ultrafast hot electron dynamics in plasmonic nanostructures. This paper aims to review our contribution to the field: starting from the fundamental physics of plasmonic nanostructures, we first describe the experimental techniques used to probe hot electrons; we then introduce a numerical model of ultrafast nanoscale relaxation processes, and present examples in which experiments and modelling are combined, with the aim of designing novel optical functionalities enabled by ultrafast hot-electron dynamics.

Plasmonic metal nanomaterials are usually supported by rigid substrates, typically made of silicon or glass. Recently, there has been growing interest in developing soft plasmonic devices. Such devices are low weight, low cost, exhibit elevated flexibility and improved mechanical properties. Moreover, they maintain the features of conventional nano-optic structures, such as the ability to enhance the local electromagnetic field. On account of these characteristics, they show promise as efficient biosensors in biological, medical, and bio-engineering applications. Here, we demonstrate the fabrication of soft polydimethylsiloxane (PDMS) plasmonic devices. Using a combination of techniques, including electroless deposition, we patterned thin membranes of PDMS with arrays of gold nanoparticle clusters. Resulting devices show regular patterns of gold nanoparticles extending over several hundreds of microns and are moderately hydrophilic, with a contact angle of about 80°. At the nanoscale, scanning electron and atomic force microscopy of samples reveal an average particle size of ∼50 nm. The nanoscopic size of the particles, along with their random distribution in a cluster, promotes the enhancement of electromagnetic fields, evidenced by numerical simulations and experiments. Mechanical characterization and the stress-strain relationship indicate that the device has a stiffness of 2.8 MPa. In biological immunoassay tests, the device correctly identified and detected anti-human immunoglobulins G (IgG) in solution with a concentration of 25 μg/ml.

Solar-thermal technologies for converting chemicals using thermochemistry require extreme light concentration. Exploiting plasmonic nanostructures can dramatically increase the reaction rates by providing more efficient solar-to-heat conversion by broadband light absorption. Moreover, hot-carrier and local field enhancement effects can alter the reaction pathways. Such discoveries have boosted the field of photothermal catalysis, which aims at driving industrially-relevant chemical reactions using solar illumination rather than conventional heat sources. Nevertheless, only large arrays of plasmonic nano-units on a substrate, i.e., plasmonic metasurfaces, allow a quasi-unitary and broadband solar light absorption within a limited thickness (hundreds of nanometers) for practical applications. Through moderate light concentration (∼10 Suns), metasurfaces reach the same temperatures as conventional thermochemical reactors, or plasmonic nanoparticle bed reactors reach under ∼100 Suns. Plasmonic metasurfaces, however, have been mostly neglected so far for applications in the field of photothermal catalysis. In this Perspective, we discuss the potentialities of plasmonic metasurfaces in this emerging area of research. We present numerical simulations and experimental case studies illustrating how broadband absorption can be achieved within a limited thickness of these nanostructured materials. The approach highlights the synergy among different enhancement effects related to the ordered array of plasmonic units and the efficient heat transfer promoting faster dynamics than thicker structures (such as powdered catalysts). We foresee that plasmonic metasurfaces can play an important role in developing modular-like structures for the conversion of chemical feedstock into fuels without requiring extreme light concentrations. Customized metasurface-based systems could lead to small-scale and low-cost decentralized reactors instead of large-scale, infrastructure-intensive power plants.

The photoexcitation of plasmonic nanostructures with ultrashort laser pulses allows for elucidating the mechanisms underlying the ultrafast nonlinear optical response of such systems, gaining insight into the fundamental processes triggered by light absorption at the nanoscale. To date, the complex temporal and spectral features of the photoinduced response are not fully understood, especially when the photon energies are close to the interband transitions of the metallic medium. Herein, the effects of photoexcitation of plasmonic nanostructures are studied by resorting to a combinaion of broadband transient absorption spectroscopy and semiclassical nonlinear simulations of the energy relaxation processes following illumination. The proposed approach enables an in‐depth disentanglement of all the contributions to the ultrafast transient optical response of supported gold nanocrystals. From these methods, the apparent transient blue shift of the localized plasmon resonance observed in the pump–probe signals is rationalized as an interplay between different and spectrally dispersed permittivity modulations, instead of a simple negative permittivity change, as it could be concluded based on the Fröhlich condition. The results provide a comprehensive understanding of the thermo‐modulational nonlinearities of plasmonic nanostructures exhibiting resonances close to the interband transition threshold.

Para manutenção do ciclo biológico de Schistosoma mansoni em laboratório, é necessário que moluscos hospedeiros intermediários sejam mantidos em condições favoráveis para o seu desenvolvimento. Para a avaliação da biologia reprodutiva (fecundidade e fertilidade), do efeito dos nutrientes (alface e ração de peixe) e dos substratos (argila, mistura de sais e CaCO₃) e suas combinações, foram formados 10 grupos experimentais com 30 Biomphalaria glabrata cada: RC (Ração de peixe/CaCO₃); LC (Alface/CaCO₃); RA (Ração de peixe/Argila); LA (Alface/Argila); RS (Ração de peixe/Mistura de sais); LS (Alface/Mistura de sais); RCA (Ração de peixe/CaCO₃/Argila); LCA (Alface/CaCO₃/Argila); RSA (Ração de peixe/Mistura de Sais/Argila); LSA (Alface/Mistura de sais/Argila). Os efeitos sobre a fecundidade dos animais foram avaliados semanalmente através da contagem do número de massas ovígeras por molusco, do número de ovos por massa ovígera e da quantidade de ovos por molusco. A fertilidade foi avaliada através da taxa de eclosão dos ovos por molusco. Entre os grupos estudados, RCA e RA apresentaram maior produção de ovos e massa ovígera. A média da quantidade de ovos férteis dos grupos RCA, RSA e RA foi maior que dos grupos alimentados com alface. Pôde-se observar que a alimentação interfere na fecundidade, aumentando o número de ovos individual e por massa ovígera e o número de massa. Os moluscos alimentados com ração de peixe apresentaram maturidade sexual mais precoce em relação aos animais alimentados por alface.

The scope of this essay is to analyze some decisions of the Brazilian federal administration concerning actions to minimize the current pandemic of COVID-19 to understand to which extent such discretionary decisions could be subject to a judicial review.

Hydrogel nanocomposites have lately taken part in the biomaterials scenario for several applications in the biomedical field, e. g., drug delivery, biosensing and cancer therapy. The inclusion of a broad variety of nanomaterials inside the hydrogel matrix leads to the successful development of hybrid platforms with superior and advantageous features. In this way, finely designed nano‐systems can be obtained, which are able to overcome the intrinsic limitations of conventional hydrogels, such as weak mechanical properties, burst drug delivery, extremely high hydrophilicity and lack of multifunctionality. This review aims to outline the last advances in the manufacturing of nanocomposite systems and their novel applications to the biomedical field, providing an overview of the most used nanoparticles with a special focus on gold nanoparticles. [ABSTRACT FROM AUTHOR]

Plasmonic nanoparticles (NPs) are exploited to concentrate light, provide local heating and enhance drug release when coupled to smart polymers. However, the role of NP assembling in these processes is poorly investigated, although their superior performance as nanoheaters has been theoretically predicted since a decade. Here we report on a compound hydrogel (agarose and carbomer 974P) loaded with gold NPs of different configurations. We investigate the dynamics of light-heat conversion in these hybrid plasmonic nanomaterials via a combination of ultrafast pump-probe spectroscopy and hot-electrons dynamical modeling. The photothermal study ascertains the possibility to control the degree of assembling via surface functionalization of the NPs, thus enabling a tuning of the photothermal response of the plasmon-enhanced gel under continuous wave excitation. We exploit these assemblies to enhance photothermal release of drug mimetics with large steric hindrance loaded in the hydrogel. Using compounds with an effective hydrodynamic diameter bigger than the mesh size of the gel matrix, we find that the nanoheaters assemblies enable a two orders of magnitude faster cumulative drug release toward the surrounding environment compared to isolated NPs, under the same experimental conditions. Our results pave the way for a new paradigm of nanoplasmonic control over drug release.

The light-driven control over the properties of optical nanostructured materials has been shown to be a promising route to achieve various functionalities, possibly on sub-picosecond time scales when ultrashort pulses are employed. Here, we discuss how to induce and reveal an ultrafast dichroism in a set of plasmonic metasurfaces with increasing symmetry by using femtosecond pump-probe spectroscopy. We show that such effect is general, promoted by the photogeneration of out-of-equilibrium electrons, and it can be induced in any sufficiently large nanoresonator, provided that plasmonic modes with well-defined symmetry are excited. The intensity of the photoinduced ultrafast dichroisms depends on the geometry of the nanoresonator, and scales up when the excitation symmetry of the plasmonic mode decreases. Our comparative analysis demonstrates the possibility to exploit light-matter interaction as an effective tool to manipulate transient optical symmetry of metasurfaces.

The transient optical response of multiresonant all‐dielectric nanoantennas via a combination of broadband ultrafast reflectivity experiments and nonlinear optics nanoscale modeling is studied. Ultrafast all‐optical control of the reflectivity is demonstrated in variably sized Al.18Ga.82As nanoantennas over four distinct Mie resonances (including Fano‐like resonances), spanning a broad spectral range, from the red to the near‐infrared. A spatially inhomogeneous dynamical model, which accounts for diffusion of the photogenerated carriers inside the semiconductor, is introduced and exploited to isolate the physical phenomena leading to the overall transient response, namely, Drude plasma formation and Pauli blocking following band filling and thermo‐optical effect. The results pave the way to the development of multiwavelength all‐optically reconfigurable filters for next‐generation ultrafast add/drop multiplexing.