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Raman spectroscopy plays a pivotal role in spectroscopic investigations. The small Raman scattering cross-section of numerous analytes, however, requires enhancement of the signal through specific structuring of the electromagnetic and morphological properties of the underlying surface. This enhancement technique is known as surface-enhanced Raman spectroscopy (SERS). Despite the existence of various proposed alternatives, the approach involving Fabry–Pérot cavities, which constitutes a straightforward method to enhance the electromagnetic field around the analyte, has not been extensively utilized. This is because, for the analyte to experience the maximum electric field, it needs to be embedded within the cavity. Consequently, the top mirror of the cavity will eventually shield it from the external laser source. Recently, an open-cavity configuration has been demonstrated to exhibit properties similar to the classic Fabry–Pérot configuration, with the added advantage of maintaining direct accessibility for the laser source. This paper showcases how such a simple yet innovative configuration can be effectively utilized to achieve remarkable Raman enhancement. The simple structure, coupled with its inexpensive nature and versatility in material selection and scalability, makes it an ideal choice for various analytes and integration into diverse Raman apparatus setups. [ABSTRACT FROM AUTHOR]

We use the Toda chain model to demonstrate that numerical simulation of integrable Hamiltonian dynamics using time discretization destroys integrability and induces dynamical chaos. Specifically, we integrate this model with various symplectic integrators parametrized by the time step τ and measure the Lyapunov time T Λ (inverse of the largest Lyapunov exponent Λ). A key observation is that T Λ is finite whenever τ is finite but diverges when τ → 0. We compare the Toda chain results with the nonintegrable Fermi–Pasta–Ulam–Tsingou chain dynamics. In addition, we observe a breakdown of the simulations at times T B ≫ T Λ due to certain positions and momenta becoming extremely large ("Not a Number"). This phenomenon originates from the periodic driving introduced by symplectic integrators and we also identify the concrete mechanism of the breakdown in the case of the Toda chain. [ABSTRACT FROM AUTHOR]

Bio‐inspired and biodegradable quantum optics scenarios constitute a pathway toward environmentally friendly front‐end technologies. Such an inspiring perspective necessitates the replacement of classic gain materials with a biological counterpart like photoluminescent bacteria. It is easy to imagine that, in this case, a planar and cell‐viable substitute of classic bulk solid‐states resonators can be highly beneficial. In this paper a micro‐ and nano‐photonic structuration of both a standard and a functionalized version of a typical bacterial growth medium (Luria‐Bertani Agar – LBA) is successfully realized. Three structures belonging to the categories of photonic crystals are replicated, such as quasi‐crystals and meta‐surfaces, demonstrating how the proposed media can be used as templates for high‐end photonic applications. The optical quality of the replicated structures is confirmed by far‐field diffraction measurements. The structured growth media allow for a broad control of the surface wettability by accessing a so‐called Wenzel state, in which the original hydrophilicity of a material is increased due to the photonic structuration. Finally, the suitability of the nano‐structured LBA as a plasmonic platform is evidenced. The proposed micro‐and nano‐structured photonic growth media constitute the first, fundamental step toward quantum optical frameworks from biological media. [ABSTRACT FROM AUTHOR]

The strong coupling of optical resonators results in a mode splitting proportional to the coupling strength, which can be achieved with metal‐dielectric‐metal (MDM) cavities that have similar thickness and refractive index. However, an active control of the mode coupling is challenging. Here, an alternative configuration of an MDM cavity coupled with a Guided‐Mode‐Resonator (GMR) is explored. The GMR grating is fabricated on top of the MDM cavity, such that the coupling can be tuned by the thickness of the central metal. The typical modal anti‐crossing (with a splitting of ≈50–65 meV) detected in the angular dispersion of the GMR‐MDM is observed. Excellent agreement of the experimental reflectance with simulations allows to report the angular dispersion from −50° to 50°. The anisotropy of the GMR modes enables to switch in and out of the strong coupling by changing the polarization of the incident light. Moreover, the asymmetry of the GMR‐MDM architecture induces a side‐dependent response. The MDM cavity is only transparent at its resonances, which leads to a suppression of all modes outside the resonance bands when impinging from the MDM side. These features are highly interesting for optoelectronic applications such as optical switches and multi‐level optical multiplexing. [ABSTRACT FROM AUTHOR]

Enhancement in the output performance of triboelectric nanogenerators by using different suitable techniques is of tremendous interest among researchers. Here, we propose an easy and cost-effective technique to improve the output performance of the rarely explored poly(vinylidene fluoride) (PVDF) based piezo-tribo hybrid nanogenerators. The space charge polarization of the PVDF based composites has been tuned here by forming a PVDF/0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Ti0.8Zr0.2)O3 (BCZT)/Multi-Walled Carbon Nanotube (MWCNT) based ternary composite. Along with the improved piezoelectricity of PVDF–BCZT based binary composites, the addition of a third MWCNT phase has helped in significantly improving the space charge polarization. The ac conductivity is increased to 5.29 × 10−12 and 1.23 × 10−11 Ω−1 cm−1 for the binary and ternary composites, respectively, from a value of 7.64 × 10−13 Ω−1 cm−1 (at 1 kHz) for neat PVDF. This improved conducting pathway formed by the increased space charge polarization has supported the easy transportation of mobile charge carriers within the composite film and film to the electrode, which has augmented the overall output piezo-tribo hybrid energy harvesting performance of the device. An ultrahigh output power density of ∼150 μW/cm2 has been achieved for the said ternary system, which suppresses the value of output power density of the other similar kind of devices fabricated via a similar technique. The applicability of this device has been further demonstrated by using it in powering up small electronic devices and in different sensing and energy harvesting applications. Thus, the device, after further tuning of its dimension, may be applied as a power source in various low-power-consuming portable electronic systems and self-powered sensing devices. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMDCs) monolayers make an excellent component in optoelectronic devices such as photodetectors and phototransistors. Selenide‐based TMDCs, specifically molybdenum diselenide (MoSe2) monolayers with low defect densities, show much faster photoresponses compared to their sulfide counterpart. However, the typically low absorption of the atomically thin MoSe2 monolayer and high exciton binding energy limit the photogeneration of charge carriers. Yet, integration of light‐harvesting materials with TMDCs can produce increased photocurrents via energy transfer. In this article, it is demonstrated that the interaction of cesium lead bromide (CsPbBr3) nanocrystals with MoSe2 monolayers results into an energy transfer efficiency of over 86%, as ascertained from the quenching and decay dynamics of the CsPbBr3 nanocrystals emission. Notably, the increase in the MoSe2 monolayer emission in the heterostructure accounts only for 33% of the transferred energy. It is found that part of the excess energy generates directly free carriers in the MoSe2 monolayer, as a result of the transfer of energy into the exciton continuum. The efficiency of the heterostructure via enhanced photocurrents with respect to the single material unit is proven. These results demonstrate a viable route to overcome the high exciton binding energy typical for TMDCs, as such having an impact on optoelectronic processes that rely on efficient exciton dissociation. [ABSTRACT FROM AUTHOR]

Strong light–matter interaction is usually achieved by embedding a gain medium in a high‐quality (Q)‐factor cavity made with thick external mirrors. The high reflectivity of the mirrors poses, therefore, a trade‐off between pump radiation coupling efficiency and high Q‐factor, thus preventing the use of optical cavities in photonic contexts where the photosensitive element necessitates to be readily accessible. Here, this long‐standing problem is overcome by engineering "Pseudo‐Cavity Modes" (PCM) in a Metal/Dielectric Open Cavity (MDOC) system that has been commonly thought to be incapable to show resonances. The MDOC system lets the embedded fluorophore exposed to radiation, opening to strong light/matter interaction. To prove this: i) exciton/PCM strong coupling regime, with 160 meV Rabi splitting, ii) photoluminescence enhancement by more than 7 times, and iii) polarized and angle‐dependent spontaneous emission are experimentally and theoretically demonstrated. The proposed system holds great potential envisioning scenarios like cavity‐enhanced photovoltaics, surface‐enhanced Raman scattering, open‐cavity lasers, photoluminescence steering and polarization. [ABSTRACT FROM AUTHOR]

Here we report the effect of surface hydroxylation of BiFeO3 fillers on the dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of poly(vinylidene fluoride). Surface hydroxylation helped to improve the interfacial interaction between the filler and PVDF matrix by introducing a strong hydrogen bonding between the –OH group of the hydroxylated BiFeO3 filler surface and the –CF2 dipole of PVDF in place of electrostatic interfacial interaction between non-hydroxylated BiFeO3 and the –CH2 dipole of PVDF. The amount of polar phase increased to around 91% for a 7 wt% hydroxylated BiFeO3 loaded PVDF film (7BFOH) by this new type of interfacial interaction. The dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of the PVDF based composite films also improved by the above said technique. Upon repeated human finger tapping, the 7BFOH film delivered ∼18 V output peak to peak open circuit ac voltage (VOC). After rectification, the VOC of the 7BFOH film was able to charge a 10 μF capacitor up to ∼3 V which was able to light up some LEDs (connected in parallel) together instantaneously, which proved the real life applicability of the composite films in low power consuming self-powered electronic devices. [ABSTRACT FROM AUTHOR]

Confining near-infrared (NIR) and mid-infrared (MIR) radiation (1–10 μm) at the nanoscale is one of the main challenges in photonics. Thanks to the transparency of silicon in the NIR-MIR range, optoelectronic systems like electro-optical modulators have been broadly designed in this range. However, the trade-off between energy-per-bit consumption and speed still constitutes a significant bottleneck, preventing such a technology to express its full potentialities. Moreover, the harmless nature of NIR radiation makes it ideal for bio-photonic applications. In this work, we theoretically showcase a new kind of electro-optical modulators in the NIR-MIR range that optimize the trade-off between power consumption, switching speed, and light confinement, leveraging on the interplay between graphene and metamaterials. We investigate several configurations among which the one consisting in a SiO2/graphene hyperbolic metamaterial (HMM) outstands. The peculiar multilayered configuration of the HMM allowed one also to minimize the equivalent electrical capacitance to achieve attoJoule electro/optical modulation at about 500 MHz switching speed. This system manifests the so-called dielectric singularity, in correspondence to which an HMM lens with resolving power of λ/1660 has been designed, allowing to resolve 3 nm-wide objects placed at an interdistance of 3 nm and to overcome the diffraction limit by 3 orders of magnitude. The imaging possibilities opened by such technologies are evident especially in bio-photonic applications, where the investigation of biological entities with tailored/broadband-wavelength radiation and nanometer precision is necessary. Moreover, the modulation performances demonstrated by the graphene-based HMM configure it as a promise for ultrafast and low-power opto-electronics applications. [ABSTRACT FROM AUTHOR]

Optically controlled non-equilibrium solvation dynamics in condensed phase have been studied extensively both experimentally and theoretically. The main drawback of linear response theory (LRT) and other existing theories is that they are unable to elucidate the dependence of non-equilibrium solvation time correlation function, S(t), on the excitation wavelength, as observed in the experiment. In order to explain the experimental observation, we first develop a kinetic equation in 1D solvation coordinate (SC) space and then we propose a new perturbative method to derive an analytical expression for S(t) for an anharmonic potential in SC space. We observe from the result of S(t) that the calculated results of the same depend strongly on the innumerable optical states through excitation wavelength, when the potential is anharmonic in SC space, indicating the breakdown of LRT. We have shown that both excitation wavelength and rotational relaxation time carry the information of micro-heterogeneity. Another significant aspect of our work is that the analytical expression obtained for S(t) corresponding to the anharmonic potential decays multi-exponentially, whereas S(t) decays single exponentially for a harmonic potential. More significantly, the calculated results for S(t) are found to be in excellent agreement with the available experimental results for the heterogeneous system. [ABSTRACT FROM AUTHOR]

Highly flexible biocompatible nanocomposites comprising of Polyvinylpyrrolidone (PVP) modified Barium Calcium Zirconate Titanate (BCT-BZT) /Polyvinylidene fluoride (PVDF) were fabricated. The crystalline BCT-BZT powders were synthesized by a simple sol-gel method. Rietveld refinement analysis confirmed the coexistence of orthorhombic and tetragonal phase in the synthesized powders. The structural, dielectric and ferroelectric properties of the composites were analysed. Addition of PVP modified BCT-BZT powders was observed to enhance the polar phase in PVDF matrix. The piezoelectric output response as a function of different weight percentage of ceramic powders in the PVDF matrix was investigated. The optimal device with 60 wt% PVP modified BCT-BZT powders exhibited maximum peak to peak voltage of 23 V when tested for harnessing waste biomechanical energy (human hand palm force). The nanogenerator was easily scaled up to 4 × 4 cm and the stored power was utilized for powering fifty five LEDs. The fabricated device is flexible, light- weight and eco-friendly. Therefore, it can be explored as a potential candidate for application as self powered sensor. [ABSTRACT FROM AUTHOR]

Wehave derived here for the first time an exact dynamical equationwithin the domain of classical mechanics for the time dependent densitydistribution function of one-dimensional reaction coordinate (RC)in the condensed phase for electron transfer reaction by projectingthe dynamics of slower modes in multidimensional Liouville space startingwith a given set of coordinates of the faster modes. After the fastermodes were ensemble averaged, the dynamics of the whole system solelydepends on the slower RC. To simplify the complicated equation intoa tractable form, benchmark approximations are employed to reducethe formally exact equation into an equation similar to the Smoluchowskiequation with a delocalized sink term. As a test case, a Hamiltonianfor the solute–solvent system modeled by quadratic functionsfor fast-relaxing vibrational and slow-relaxing polarization modes,respectively, has been considered. Interestingly, our simplified kineticequation corresponding to this model Hamiltonian is transformed intothe well-known phenomenological Sumi–Marcus equation. [ABSTRACT FROM AUTHOR]

Energy transfer, excitons, free carrier generation, perovskite nanocrystals, transition metal dichalcogenides, trions Keywords: energy transfer; excitons; free carrier generation; perovskite nanocrystals; transition metal dichalcogenides; trions EN energy transfer excitons free carrier generation perovskite nanocrystals transition metal dichalcogenides trions 1 1 1 07/20/22 20220718 NES 220718 Cesium lead bromide (CsPbBr SB 3 sb ) nanocrystals with excellent absorption and emission properties when coupled to a molybdenum diselenide (MoSe SB 2 sb ) monolayer, transfer more than 86% of their photo-excited energy to MoSe SB 2 sb . [Extracted from the article]

We have derived here an exact kinetic equation for the time evolution of the probability distribution for a general reaction coordinate space, starting from a multidimensional Liouville equation based on first-principles theory. To make the equation tractable we use two standard approximations, which reduce the exact equation into a Fokker-Planck-type equation with a sink term. As illustrative examples, we consider its application to two important classes of reactions, viz., the electron transfer and diffusion-controlled reactions. The kinetic equations for the reaction coordinates corresponding to these reactions become one dimensional. We also provide a scheme to find the critical value of the reaction coordinate at which the reaction takes place, and also to obtain the initial distribution function in the same space for different experimental situations. In the case of photoinduced electron transfer, we introduce the effect of excitation frequency through the use of suitable initial distribution functions. [ABSTRACT FROM AUTHOR]

We formulate a set of conditions under which the nonstationary Schrödinger equation with a time-dependent Hamiltonian is exactly solvable analytically. The main requirement is the existence of a non-Abelian gauge field with zero curvature in the space of system parameters. Known solvable multistate Landau-Zener models satisfy these conditions. Our method provides a strategy to incorporate time dependence into various quantum integrable models while maintaining their integrability. We also validate some prior conjectures, including the solution of the driven generalized Tavis-Cummings model. [ABSTRACT FROM AUTHOR]