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Nicolò Maccaferri

Publications and source records attributed to Nicolò Maccaferri.

At least 19 recordsLinked to original sources
arXiv2026

Modifying Electrochemical Doping in Light-Emitting Electrochemical Cells with Gold Nanoparticles

Electrochemical doping offers dynamic control of the electronic properties of organic semiconductors, and it is the enabling feature of a range of technologies, including electrochemical transistors, energy-storage devices, light-emitting electrochemical cells (LECs), and bioelectronics. Electrochemical doping is commonly controlled by the selection of the constituents in the active material of the device or the applied voltage bias, but herein we report that the incorporation of Au nanoparticles (Au-NPs) at an electrode interface can constitute an alternative control parameter. The LEC features balanced p- and n-type electrochemical doping that forms a p-n junction doping structure in its active material, and we find that it is possible to reshape this doping profile by incorporating Au-NPs at an electrode interface. Specifically, we establish that the inclusion of neat non-capped Au-NPs at the anodic interface shifts the p-n junction (i.e., the emission zone) away from the anode. In contrast, the inclusion of Au-NPs capped with sodium citrate is found to reverse this behavior, so that the emission zone is instead moved towards the anode. We utilize this control parameter to shift the emission zone towards a position of constructive (destructive) interference, as manifested in a strong increase (decrease) of the LEC emission efficiency. Our findings establish an interfacial strategy for modulating the spatial profile of electrochemical doping and tuning device performance without altering the chemistry of the active material, relying instead on the surface modification of one electrode. This approach is important because it provides a versatile and minimally invasive route to optimize electrochemical devices while preserving the intrinsic properties and formulation of the active material.

cond-mat.mtrl-sci↗
arXiv2026

Round-Robin Test of a Light-Emitting Electrochemical Cell: Establishing a Reference Protocol for Quality Research

Emerging technologies benefit from a jointly established reference protocol, which can lower the bar of entry for new researchers while serving as a calibration standard for established actors. The light-emitting electrochemical cell (LEC) combines electrochemistry and optoelectronics in an intricate manner, and it can by that enable sustainable and commercially relevant printing fabrication of emissive thin-film devices. However, LEC performance is sensitive to a range of material and processing parameters, which frequently results in inadequate, or even erroneous, device evaluation. With this in mind, we present herein a LEC reference protocol, which details the sourcing of materials and the procedures and parameters for robust device fabrication and operation. The protocol has been tested across nine international research groups, and the collected results from this interlaboratory round-robin test confirm that good LEC performance can be reproducibly obtained following our protocol. We also identify common pitfalls that can arise during LEC development, and present practical steps for attaining optimum LEC performance. We hope this reference protocol will improve the quality of future LEC research and serve as a guide for future researchers entering this vibrant field.

cond-mat.soft↗
arXiv2026

Ultrafast excitation of Bloch plasmon polaritons in hyperbolic metamaterials with an extreme ultra-violet transient grating

Manipulating materials properties with light drives advances in materials science and photonics. Hyperbolic metamaterials are promising candidates as next-generation quantum optical media. They support Bloch plasmon polaritons, which are characterized by potentially infinite wave-vectors and long lifetimes, but cannot be excited through direct light illumination due to momentum mismatch. Here, we experimentally show that a transient grating, formed via interference of fully coherent seeded free-electron laser pulses in a thin insulator film, enables the excitation of Bloch plasmon polaritons in an underlying hyperbolic metamaterial. Finite element simulations confirm the role of the transient grating in facilitating phase-matching and mode excitation. Our findings demonstrate a route to spatiotemporally excite Bloch plasmon polaritons modes, offering an alternative to permanently nanostructured gratings and potentially enabling ultrafast control of optical modes excitation.

physics.optics↗
arXiv2026

Reconfigurable Magnetic Nanopore Platform for Selective Trapping

Solid-state nanopores offer a powerful platform for nanoscale analysis of individual analytes, including biomolecules and functionalized nanoparticles, by confining them within a precisely defined sensing region. However, their inherently passive operation restricts practical applications, as they cannot precisely control particle position or dynamics inside the pore. Here, we introduce magnetic nanopore architectures that integrate a ferromagnetic layer into the nanopore system. Acting as a magnetic discontinuity within an otherwise uniformly magnetized film, the nanopore generates localized stray magnetic fields that enable magnetic tweezing of magnetic nanoparticles, which can be functionalized with fluorescent biomolecules. Importantly, the nanopore geometry is designed to reversibly switch between a nearly uniform magnetization state and a magnetic flux-closure state through the application of short magnetic field pulses of controlled amplitude. This capability allows the magnetic tweezing effect to be selectively activated or deactivated, enabling controlled capture and release of tagged biomolecules on demand. As a proof of concept, we demonstrate the selective magnetic trapping of fluorescent magnetic particles. These findings pave the way for reconfigurable, on-chip magnetic nanopore platforms capable of selective trapping and high-throughput single-particle detection. KEYWORDS: Nanopores, magnetic tweezers, fluorescence microscopy, vortex state, active control, magnetic nanoparticles

physics.optics↗
arXiv2026

Strong light-matter interactions in hybrid polaritonic systems

Strong light-matter coupling gives rise to polaritons - hybrid excitations whose mixed photonic and matter character enables control over optical, electronic and chemical properties. This Feature Article surveys the main architectures supporting polariton formation, including photonic microcavities, plasmonic nanostructures, open cavities and metasurfaces, and outlines how inorganic semiconductors, organic aggregates and hybrid systems access strong and ultrastrong coupling. Key phenomena such as coherent dynamics, vibronic interactions, dark-state reservoirs and polariton-mediated energy and electron transport are discussed, together with the experimental and theoretical tools used to study them. We highlight examples where strong coupling modifies charge transport, energy flow and chemical reactivity, and we summarize emerging regimes, including intermediate and dark-strong coupling, that broaden the landscape of hybrid light-matter physics.

physics.optics↗
arXiv2026

Beyond the Quantum Picture: The Electrodynamic Origin of Chiral Nanoplasmonics

Chiral plasmonic nanostructures are rapidly emerging as ideal substrates for enantioselective sensing, chiral near-field engineering, and plasmon-assisted catalysis, owing to their exceptional sensitivity to structural handedness. However, the physical origin of plasmonic chirality, whether intrinsically quantum or primarily governed by collective electrodynamics, remains an open question, limiting the development of predictive theoretical methods for the design of novel chiral plasmonic architectures. Here, we show that a fully atomistic classical electrodynamic model, coupling intraband charge transport and interband polarization, quantitatively reproduces state-of-the-art \textit{ab initio} and experimental chiroptical spectra across the quantum-to-classical regime, from atomistically defined chiral Ag and Au nanostructures to DNA-origami-assembled Au nanorods containing up to $\sim 10^5$ atoms. Our results support a unified electrodynamic origin of plasmonic chirality, providing the missing foundation to connect local structural motifs to chiroptical response and local chiral near fields, and paving the way for the atomistically defined, rational design of chiral plasmonic nanostructures optimized for targeted applications.

cond-mat.mes-hall↗
arXiv2025

In-operando dipole orientation for bipolar injection from air-stable electrodes into organic semiconductors

Efficient charge-carrier injection from air-stable electrodes into organic semiconductors (OSCs) is essential for fabricating solution-processed organic optoelectronic devices under ambient conditions. Today, this is typically achieved by incorporating doped OSC interlayers, introducing self-assembled dipole monolayers, or adding mobile ions to the active material (AM). Here, we demonstrate an alternative approach that eliminates the need for additional injection layers or ionic additives. We achieve this by blending the dipolar compound TMPE-OH into the electroluminescent polymer Super Yellow (SY) and depositing this sole AM between two air-stable electrodes, forming a single-layer, dipole-doped OLED (D-OLED). By tracking its transient voltage-luminance response, performing impedance spectroscopy, and comparing these characteristics with two other single-layer device concepts, i.e. a neat-SY OLED without a dipolar compound and a light-emitting electrochemical cell (LEC) containing mobile ions, we can establish that the auxiliary dipoles in the D-OLED reorient under the applied driving voltage, enabling immediate luminance turn-on and lowering the injection barriers at both electrodes. Finally, we demonstrate that the D-OLED achieves current efficacies comparable to those of SY OLEDs incorporating dedicated injection layers or LECs. Our study establishes dipolar doping as a practical strategy for efficient bipolar charge injection from air-stable electrodes in solution-processed organic semiconductor devices.

cond-mat.mtrl-sci↗
arXiv2025

Improving conditional generative adversarial networks for inverse design of plasmonic structures

Deep learning has emerged as a key tool for designing nanophotonic structures that manipulate light at sub-wavelength scales. We investigate how to inversely design plasmonic nanostructures using conditional generative adversarial networks. Although a conventional approach of measuring the optical properties of a given nanostructure is conceptually straightforward, inverse design remains difficult because the existence and uniqueness of an acceptable design cannot be guaranteed. Furthermore, the dimensionality of the design space is often large, and simulation-based methods become quickly intractable. Deep learning methods are well-suited to tackle this problem because they can handle effectively high-dimensional input data. We train a conditional generative adversarial network model and use it for inverse design of plasmonic nanostructures based on their extinction cross section spectra. Our main result shows that adding label projection and a novel embedding network to the conditional generative adversarial network model, improves performance in terms of error estimates and convergence speed for the training algorithm. The mean absolute error is reduced by an order of magnitude in the best case, and the training algorithm converges more than three times faster on average. This is shown for two network architectures, a simpler one using a fully connected neural network architecture, and a more complex one using convolutional layers. We pre-train a convolutional neural network and use it as surrogate model to evaluate the performance of our inverse design model. The surrogate model evaluates the extinction cross sections of the design predictions, and we show that our modifications lead to equally good or better predictions of the original design compared to a baseline model. This provides an important step towards more efficient and precise inverse design methods for optical elements.

physics.optics↗
arXiv2025

Polarization conversion using hybrid near-zero and high-index metamaterials

Near-zero-refractive index materials display unique optical properties such as perfect transmission through distorted waveguides, cloaking, and inhibited diffraction. Compared to conventional media, they can fundamentally behave differently to light impinging from air, owing to the phenomenon of total external reflection. This makes them attractive for evanescent wave phenomena without prism coupling or sub-wavelength air gaps. Here, we introduce a strategy for linear-to-circular polarization conversion based on this effect. Practically realizable device designs are presented using hybrid structures of near-zero index and high index materials in a simple planar geometry. Our results predict polarization conversion in both reflection and transmission configurations based on naturally available epsilon-near-zero materials and illustrate the role of loss in limiting performance. Although the operation wavelength is limited to the epsilon-near-zero region, the concept can be implemented from the terahertz to optical domains using tunable epsilon-near-zero materials.

physics.optics↗
arXiv2025

UV-SERS monitoring of plasmons photodegradation of biomolecules on Aluminum platforms decorated with Rhodium nanoparticles

In the search for novel nanostructured materials for UV plasmonics a limited number of choices can be done. Materials such as aluminum, rhodium, gallium and few others can be used. One of the most interesting application for UV plasmonics is Surface Enhanced Raman Spectroscopy. It can be extended to this spectral range to explore spectral properties of biomolecules that have only a small cross section in the visible spectral range. We have recently reported on a functional substrates based on nanoporous aluminum decorated with rhodium nanoparticles. This system showed an interesting behavior for UV excitation at 266 nm, with an unexpected decreasing Raman intensity for increasing rhodium nanoparticles concentrations. We proposed that this effect can be due to the difficult access to the hot spots for the molecules deposited via thermal evaporation. Here we extend this study exploring the performance of the system at another UV excitation wavelengths (325 nm) reporting on experimental results obtained using a deposition process that can bring the molecules at the hot-spots in a more efficient way. Extensive spectroscopic acquisitions, combined with 3D maps, allow to shade a more clear view on the performance of this plasmonic platform. In particular, the photodegration and the potential oxidation of biomolecules driven by the hot-electron/hot-holes produced by the rhodium nanoparticles will be reported.

physics.app-ph↗
arXiv2025

Multipolar Decomposition of Magnetic Circular Dichroism in Arbitrarily Shaped Magneto-Dielectric Scatterers

Multipole expansion methods have been primarily used for analyzing the electromagnetic scattering from non-magnetic isotropic dielectric scatterers, and studies about the scattering from magnetic objects seem to be lacking. In this work, we used the multipolar expansion framework for decomposing the electromagnetic scattering by dielectric particles with magnetic properties. Magnetization current contributions were explicitly accounted for by using the vector spherical harmonics to compute the electric and magnetic multipole contributions of arbitrary order. The exact analytical expressions for the corresponding spherical multipole coefficients were employed, with the scattering efficiencies being used to distinguish the dielectric and magnetic contributions of each multipole. This enables the analysis of scattering from arbitrarily shaped, anisotropic, and inhomogeneous magnetic scatterers. It also provides a tool for studying non-reciprocal devices that exploit magnetic resonances in magnetic-dielectric materials. Calculations were made for an experimentally feasible system, namely for ferrite-based scatterers operating in the microwave regime. These materials are of interest in radio frequency (RF) applications due to their magnetic activity. We demonstrated analytically that the magnetic circular dichroism in a magnetic-dielectric scatterer in the Faraday geometry can be decomposed into individual multipole contributions. The analytical results indicate that multipole resonances associated with magnetization currents can be even stronger than multipole contributions from conventional dielectric currents. It is worth noting that these analytical results were verified through comparison with numerical results from finite element method (FEM) simulations in COMSOL Multiphysics.

physics.optics↗
arXiv2025

Layered Bimetal Nanoporous Platforms for SERS Sensing

Nanoporous metals are extensively investigated as platforms for applications in plasmonics. They present high surface areas and strong local electric fields that can be tuned at different energies, playing with the choice of the metals and the morphology of the porous layers. Until recently, research in the field of plasmonics has primarily focused on porous metals composed of a single element, with limited attention given to the impact of alloy composition. The investigation of bi-metallic systems has only just begun to emerge in the literature. In particular, combining two or more different plasmonic metals, it could be possible to explore the interactions between two metals excited at specific energies. This involves plasmonic coupling, electron transfer, band hybridization at the interface, electromagnetic field interactions, and possibly thermal and electronic energy transfer depending on separation, size, and materials involved. The analysis of bi-metal systems can also be interesting in biomolecule detection, such as in the case of Surface Enhanced Raman Scattering (SERS). Here we report, for the first time, a detailed study (comprising morphological analyses, numerical modelling, and optical spectroscopies) on bi-metal nanoporous platforms prepared with a dry-synthesis method enabling the easy and controllable fabrication of bilayers combining different metals such as Au, Ag, and Cu.

physics.app-ph↗
arXiv2025

Anomalous frequency scaling of acoustic phonon damping in nickel cavities fabricated by ps-laser delamination

Single-shot picosecond (ps) laser induced delamination allows for the direct generation of suspended membranes from a continuous metallic film, offering a promising platform for control of ultrafast magnetization dynamics driven by acoustic waves. Using the picosecond-ultrasonics method, we demonstrate that long-lived low-frequency acoustic waves can be optically-excited in the delaminated cavities. At the same time, higher-frequency modes >60GHz exhibit a surprisingly fast damping, following a scaling law incompatible with the expected attenuation mediated by phonon-phonon scattering. Comparing measurements between delaminated cavities and a benchmark nickel film in contact with the substrate, we link our findings with structural modifications of the nickel crystal induced by the delamination process.

cond-mat.mtrl-sci↗
arXiv2025

Ultrafast interband transitions in nanoporous gold metamaterial

Nanoporous metals have emerged as promising functional architectures due to their tunable optical and electronic properties, high surface areas, and versatile use in real-life applications such as sensing, catalysis, and biomedicine. While the optical and morphological properties of nanoporous metals have been extensively studied, their electronic properties at ultrafast timescales remain largely unexplored. Here, we study the transient response of a nanoporous gold metamaterial and compare it with the ultrafast dynamics of a continuous gold film. We unravel that the nanoporous sample supports lower energy interband transitions, due to a much higher electron temperature in the nanoporous material, which causes an enhanced redistribution of electron density around the Fermi level. The experimental results are consistent with the two-temperature model, which highlights the role of nanoscale porosity in enabling the more efficient generation of hot carriers, thus allowing lower energy photons to induce interband transitions. Our findings demonstrate that nanoporosity affects fundamental ultrafast electronic processes and introduces this platform as temporal metamaterial allowing the emergence of tunable electronic properties not supported by the bulk counterpart. Furthermore, we present new insights into ultrafast electronic properties of nanoporous metals, which can impact several areas, from photochemistry and catalysis to energy harvesting and opto-electronics.

cond-mat.mes-hall↗
arXiv2024

Intervalence Plasmons in Boron-Doped Diamond

Doped semiconductors can exhibit metallic-like properties ranging from superconductivity to tunable localized surface plasmon resonances. Diamond is a wide-bandgap semiconductor that is rendered electronically active by incorporating a hole dopant, boron. While the effects of boron doping on the electronic band structure of diamond are well-studied, any link between charge carriers and plasmons, has never been shown. Here, we report intervalence plasmons in boron-doped diamond, defined as collective electronic excitations between the valence subbands, opened up by the presence of holes. Evidence for these low-energy excitations is provided by valence electron energy loss spectroscopy and near-field infrared spectroscopy. The measured spectra are subsequently reproduced by first-principles calculations based on the contribution of intervalence band transitions to the dielectric function. Our calculations also reveal that the real part of the dielectric function exhibits a crossover characteristic of metallicity. These results suggest a new mechanism for inducing plasmon-like behavior in doped semiconductors, and the possibility of attaining such properties in diamond, a key emerging material for quantum information technologies.

cond-mat.mtrl-sci↗
arXiv2024

Light-matter interactions in layered materials and heterostructures: from moiré physics and magneto-optical effects to ultrafast dynamics and hybrid meta-photonics

Layered two-dimensional (2D) materials have revolutionized how we approach light-matter interactions, offering unprecedented optical and electronic properties with the potential for vertical heterostructures and manipulation of spin-valley degrees of freedom. The discovery of moiré physics in twisted heterostructures has further unlocked new possibilities for controlling the band structure of tailored semiconductor heterostructures. In parallel, the integration of 2D materials with hybrid photonic structures and ultrafast studies on their optical and spin-valley properties has revealed a wealth of novel physical phenomena. This perspective highlights the recent advances in our understanding of light-matter interactions in moiré and 2D systems, with a particular emphasis on ultrafast processes and the integration of these materials into photonic platforms. We explore the implications for optoelectronics and emerging photonic technologies, positioning 2D materials as a transformative tool for next-generation devices.

cond-mat.mtrl-sci↗
arXiv2024

Probing macroscopic temperature changes with non-radiative processes in hyperbolic meta-antennas

Multilayered metal-dielectric nanostructures display both strong plasmonic behavior and hyperbolic optical dispersion. The latter is responsible for the appearance of two separated radiative and non-radiative channels in the extinction spectrum of these structures. This unique property can open a wealth of opportunities towards the development of multifunctional systems that simultaneously can behave as optimal scatterers and absorbers at different wavelengths, an important feature to achieve multiscale control light-matter interactions in different spectral regions for different types of applications, such as optical computing or detection of thermal radiation. Nevertheless, the temperature dependence of the optical properties of these multilayered systems has never been investigated. In this work we study how radiative and non-radiative processes in hyperbolic meta-antennas can probe temperature changes of the surrounding medium. We show that, while radiative processes are essentially not affected by a change in the external temperature, the non-radiative ones are strongly affected by a temperature variation. By combining experiments and temperature dependent effective medium theory, we find that this behavior is connected to enhanced damping effects due to electron-phonon scattering. Contrary to standard plasmonic systems, a red-shift of the non-radiative mode occurs for small variations of the environment temperature. Our study shows that to probe temperature changes it is essential to exploit non-radiative processes in systems supporting plasmonic excitations, which can be used as very sensitive thermometers via linear absorption spectroscopy.

physics.optics↗
arXiv2024

Structural and optical characterization of NiO polycrystalline thin films fabricated by spray-pyrolysis

Nickel (II) oxide, NiO, a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displaying antiferromagnetic order at room temperature, has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the synthesis of polycrystalline NiO fabricated using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. We then characterized the composition and structure of our NiO thin films using X-ray diffraction, and atomic force and scanning electron microscopies, respectively. We completed our study by looking at the phononic and magnonic properties of our NiO thin films via Raman spectroscopy, and at the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that our NiO samples display the same phononic and magnonic dispersion expected for single crystal NiO at room temperature, and that electron dynamics in our system is similar to those of previously reported NiO mono- and poli-crystalline systems synthesized with different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthetize strongly correlated materials for a large set of applications.

cond-mat.mtrl-sci↗