Probing the Ultimate Limits of Plasmonic Enhancement Ciracì, C.; Hill, R. T.; Mock, J. J. ...
Science (American Association for the Advancement of Science),
08/2012, Letnik:
337, Številka:
6098
Journal Article
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Metals support surface plasmons at optical wavelengths and have the ability to localize light to subwavelength regions. The field enhancements that occur in these regions set the ultimate limitations ...on a wide range of nonlinear and quantum optical phenomena. We found that the dominant limiting factor is not the resistive loss of the metal, but rather the intrinsic nonlocality of its dielectric response. A semiclassical model of the electronic response of a metal places strict bounds on the ultimate field enhancement. To demonstrate the accuracy of this model, we studied optical scattering from gold nanoparticles spaced a few angstroms from a gold film. The bounds derived from the models and experiments impose limitations on all nanophotonic systems.
We analyze the impact of nonlocality on the waveguide modes of metallodielectric multilayers and optical patch antennas, the latter formed from metal strips closely spaced above a metallic plane. We ...model both the nonlocal effects associated with the conduction electrons of the metal and the previously overlooked response of bound electrons. We show that the fundamental mode of a metal-dielectric-metal waveguide, sometimes called the gap plasmon, is very sensitive to nonlocality when the insulating, dielectric layers are thinner than 5 nm. We suggest that optical patch antennas, which can easily be fabricated with controlled dielectric spacer layers and can be interrogated using far-field scattering, can enable the measurement of nonlocality in metals with good accuracy.
We develop a nested hybridizable discontinuous Galerkin (HDG) method to numerically solve the Maxwell's equations coupled with a hydrodynamic model for the conduction-band electrons in metals. The ...HDG method leverages static condensation to eliminate the degrees of freedom of the approximate solution defined in the elements, yielding a linear system in terms of the degrees of freedom of the approximate trace defined on the element boundaries. This article presents a computational method that relies on a degree-of-freedom reordering such that the HDG linear system accommodates an additional static condensation step to eliminate a large portion of the degrees of freedom of the approximate trace, thereby yielding a much smaller linear system. For the particular metallic structures considered in this article, the resulting linear system obtained by means of nested static condensations is a block tridiagonal system, which can be solved efficiently. We apply the nested HDG method to compute second harmonic generation on a triangular coaxial periodic nanogap structure. This nonlinear optics phenomenon features rapid field variations and extreme boundary-layer structures that span a wide range of length scales. Numerical results show that the ability to identify structures which exhibit resonances at ω and 2ω is essential to excite the second harmonic response.
•A nested HDG method to economize the solution of traditional HDG systems.•A computational framework combining nested HDG with the structure of the problem for additional computational savings.•Model order reduction strategy to identify geometries that lead to resonances at ω, 2ω.•Ability to simulate nonlocal second harmonic generation plasmonic phenomena on realistic 3-D nanostructures.
We study the effect of electron spill-out and of nonlocality on the propagation of light inside a gap between two semi-infinite metallic regions. We compare the predictions of a local response model ...taking into account only the spill-out, to the predictions of a quantum hydrodynamic model able to take both phenomena into account. We show that only the latter is able to correctly retrieve the correct limit when the gap closes, while the local model suffers from undesirable features (divergence of the fields, overestimation of the losses). Finally, we show that, to a certain extent, the correct results can be retrieved using a simple local approach without spill-out or a conventional Thomas-Fermi approximation, but considering an effective gap width.
An accurate modeling of the optical interactions in metallic nanostructures with subnanometer features requires an accurate description of quantum effects at the scale of billions of atoms. At such ...scale, first-principle methods are not computationally viable. Quantum hydrodynamic theory (QHT) has emerged as a powerful method that includes nonlocal contributions of the kinetic energy and the spatial dependence of the electron density, and it can predict both plasmon energy and spill-out effects in large metal nanoparticles. In this paper, we introduce a hybridizable discontinuous Galerkin method for solving Maxwell's equations coupled with a QHT model in order to account for quantum effects in three-dimensional metallic nanostructures. The coupled system of Maxwell's equations and QHT model is not only nonlinear but also multi-scale due to the interaction between the micrometer electromagnetic waves and the nanometer cavities of metallic nanostructures. We present extensive numerical experiments to validate the QHT model and demonstrate the capability of the HDG method to provide accurate solutions in the presence of strong nonlinearities and multiple length scales. These results offer a possibility to enhance nonlinear optical effects or to harness quantum mechanical electron tunneling by engineering metallic nanostructures at the quantum level.
•An HDG method to simulate the equilibrium equation of quantum hydrodynamic theory.•An HDG method to simulate the first-order linear system of quantum hydrodynamic theory coupled with Maxwell's equations.•2D simulation of metal nanowire and full 3D simulation of a periodic nanocoax array accounting for quantum effects.•Comparison of the optical response using quantum effects to that of local and nonlocal electron models for both applications.
A label-free localized surface plasmon resonance (LSPR)-based biosensor exploiting gold nanorods (GNRs) is proposed and demonstrated. For this aim, 35 ± 5 nm long and 20 ± 4 thick GNRs spaced by a ...few nanometers thick polyelectrolytes (PE) from a gold thin film was analyzed and synthesized. The morphology of the GNRs, the plasmon properties of GNRs, swelling of PE layers and the wettability of the surfaces were characterized by transmission and scanning electron microscopy, spectroscopic reflectivity and contact angle measurements, respectively. Indeed, when immersed in a phosphate buffer saline solution, the GNRs-PE-gold system shows an optical shift of the LSPR wavelength. This shift was found to correspond to a vertical swelling of about 2 nm, demonstrating the extreme sensitivity of the biosensor. Finally, we show that LSPR measurements can be used to detect dynamic resonance changes in response to both thickness and buffer solution, while the hydrophobic behavior of the surface can be exploited for reducing the number of liquid analytes in clinical biosensing application.
ABSTRACT
Vitamin E modulates the immune response, in part by reducing inflammation. The bacterial component lipopolysaccharide (LPS) can induce an inflammatory response in chickens. The objective of ...this study was to evaluate immunomodulatory effects of dietary type and level of vitamin E on response of broilers to LPS. One-day-old broiler males (n = 96) were placed in a vitamin E-type (synthetic, natural) × vitamin E level (22, 220 IU/kg) × LPS (LPS, saline) block design. At 22 d, LPS (or saline) was injected subcutaneously. Spleens were harvested for RNA isolation at 3 and 24 h postinjection. Relative levels of RNA expression were measured for the immune-related genes: avian β defensin 10 (AvBD10), interleukin 6 (IL6), interferon-γ (IFN-γ), inducible nitric oxide synthase (iNOS), interleukin 10 and transforming growth factor- β1 (TGF-β1). Avian β defensin 10 and iNOS are innate antimicrobial proteins. Interleukin 6 and IFN-γ are pro-inflammatory cytokines, whereas interleukin 10 and transforming growth factor-β1 are anti-inflammatory cytokines. There were significantly higher splenic levels of IL6, IFN-γ, iNOS, and IL10 RNA expression at 3 h postinjection in chickens receiving LPS than in chickens 24 h post-LPS injection or saline-injected birds at either time. These data suggest that LPS induced an immune response that was regulated by both pro- and anti-inflammatory cytokines. Birds fed natural-type (versus synthetic) vitamin E had a significantly lower LPS-induced inflammatory response, as indicated by lower IL6 RNA expression levels, suggesting a protective effect from natural-type vitamin E when a chicken encounters a bacterial component.
Vaccines, antibiotics, and other therapeutic agents used to combat disease in poultry generate recurring costs and the potential of residues in poultry products. Enhancing the immune response using ...alternative approaches such as selection for increased disease resistance or dietary immunomodulation may be effective additions to the portfolio of strategies the industry applies in poultry health management. The objective of this study was to characterize the effects of dietary supplementation with 3 immunomodulators ascorbic acid, 1,3-1,6 β-glucans from baker's yeast, and corticosterone on cytokine gene expression in the spleen of 3 distinct genetic lines of chickens. Relative mRNA expression levels were determined using quantitative reverse transcriptase PCR for IL-1β, IL-2, inducible nitric oxide synthase, and toll-like receptors 4 and 15, all of which play important roles in chicken immune function. Expression data were analyzed by mixed model analysis. The only significant effect detected was sex effect (P < 0.04) on expression of IL-1β. The present findings suggest the need for further investigations into the effects of dietary immunomodulators on cytokine gene expression in chickens so as to generate a better understanding of the immunomodulation process.
Free electron cascaded third-harmonic generation De Luca, F.; Ortolani, M.; Ciraci, C.
2021 Fifteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials),
2021-Sept.-20
Conference Proceeding
We study free electron nonlinearities in heavily doped semiconductors, which have recently emerged as low-loss and tunable materials for plasmonics at mid-infrared frequencies. We develop a ...hydrodynamic description that takes into account contributions up to the third order, usually negligible for noble metals. Our model predicts that nonlinear optical phenomena caused by free electron dynamics could overcome intrinsic semiconductor nonlinearities by two orders of magnitude. In this context, we demonstrate that, despite showing zero second-harmonic generation efficiency, a semiconductor slab can generate a cascaded third-harmonic signal (due to second-harmonic filed interactions) comparable to direct third-harmonic generation. Moreover, we suggest a possible experiment to observe such effect.
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