Search Results (80)

Magneto-plasmonic structures have been a subject of tremendous attention of researchers in recent decades as they provide unique approaches regarding the efficient control of optical, magneto-optical, and nonlinear-optical effects. Among others, magneto-plasmonic crystals (MPCs) have become one of the most studied structures, known for their high-quality tunable resonant optical properties. Here, we present the results of experimental and numerical studies on the functional magneto-optical (MO) response of planar 1D plasmonic crystals composed of Co/Au stripes of submicron period on the surface of a 3 μm thick rare-earth garnet layer. The experimental and numerical studies confirm that the wavelength–angular spectra of such structures contain a set of tunable resonant features in their optical and magneto-optical response, associated with the excitation of (i) surface plasmon polaritons at the Co/Au grating–garnet interface, as well as (ii) waveguide (WG) modes propagating in the garnet slab. A comparison of the MO effects in the transversal and longitudinal magnetization of the plasmonic structures is presented. We show that the most efficient Fano-type MPC magneto-optical response is realized for the WG modes of the first order for the longitudinal magnetization of the structure. Further perspectives regarding the optimization of this type of plasmonic crystal are discussed. Full article

Nickel (Ni) ultrathin films exhibit phase-dependent electrical, magnetic, and optical characteristics that are significantly influenced by deposition methods. However, these films are inherently prone to rapid oxidation, with the oxidation rate dependent on substrate, temperature, and deposition parameters. The focus of this research is to investigate the temporal oxidation of RF-sputtered Ni ultrathin films on Corning glass under ambient atmospheric conditions and its impact on their structural, surface, and optical characteristics. Controlled film thicknesses were achieved through precise manipulation of deposition parameters, enabling the analysis of oxidation-induced modifications. Atomic force microscopy (AFM) revealed that films with high structural integrity and surface uniformity are exhibiting roughness values (Rq) from 0.679 to 4.379 nm of corresponding thicknesses ranging from 4 to 85 nm. Scanning electron microscopy (SEM) validated the formation of Ni grains interspersed with NiO phases, facilitating SPR-like effects. UV-visible spectroscopy is demonstrating thickness-dependent spectral (plasmonic peak) shifts. Finite Difference Time Domain (FDTD) simulations corroborate the observed thickness-dependent optical absorbance and the resultant shifts in the absorbance-induced plasmonic peak position and bandgap. Increased NiO presence primarily drives the enhancement of electromagnetic (EM) field localization and the direct impact on power absorption efficiency, which are modulated by the tunability of the plasmonic peak position. Our work demonstrates that controlled fabrication conditions and optimal film thickness selection allow for accurate manipulation of the Ni oxidation process, significantly altering their optical properties. This enables the tailoring of these Ni films for applications in transparent conductive electrodes (TCEs), magneto-optic (MO) devices, spintronics, wear-resistant coatings, microelectronics, and photonics. Full article

A kind of magnetoplasmonic resonators is numerically designed with hexagonally arrayed Au/bismuth iron garnet (BIG) bilayer nanodiscks on Au thin film layers. Multi-physics coupling calculation on their magnetoplasmonic resonance features suggest that there exists a strong resonant coupling between the surface plasmon excited by the hexagonal grating and the waveguide modes induced by Au-BIG-Au, which can significantly enhance the transverse magneto-optical Kerr effect. Interestingly, a new type of circular oscillating can be induced in the optical-transparent BIG layers as the thickness of BIG layers is between 2 nm and 22 nm. This circular oscillating exhibits a distinct thickness-dependent feature, which can be attributed to the near field interference of the excited localized plasmon resonance between the two interfaces formed by the middle BIG nanodiscs in the top Au nanodisks and the bottom Au thin film layers according to the simulation. These unique magnetoplasmonic features endow this kind of magnetoplasmonic resonators with a greatly enhanced refractive index sensing property, with a calculated figure of merit (FOM) value of up to 7527 RIU⁻¹. Full article

Magneto-optic surface plasmon resonances (MOSPRs) rely on the interaction of magnetic fields with surface plasmon polaritons (SPP) to modulate plasmonic bands with magnetic fields and enhance magneto-optical activity. In the present work, a study on the magnetoplasmonic behavior of Ag/Fe bilayers is carried out by VIS-NIR spectroscopy and backed with SQUID measurements, determining the thickness-dependent magnetization of thin-film samples. The MOSPR sensing properties of Ag/Fe planar bilayers are simulated using Berreman’s matrix formalism, from which an optimized structure composed of 15 nm of Ag and 12.5 nm of Fe is obtained. The selected structure is fabricated and characterized for refractive index (RI) sensitivity, reaching 4946 RIU⁻¹ and returning an effective enhancement of refractometric sensitivity after magneto-optical modulation. A new optimized and cobalt-free magnetoplasmonic Ag/Fe bilayer structure is studied, fabricated, and characterized for the first time towards refractometric sensing, to the best of our knowledge. This configuration exhibits potential for enhancing refractometric sensitivity via magneto-optical modulation, thus paving the way towards a simpler, more accessible, and safe type of RI sensor with potential applications in chemical sensors and biosensors. Full article

The study focuses on the synthesis of Fe₃O₄@SiO₂-NH₂-Au heterostructures with magneto-plasmonic properties composed of well-defined cubic Fe₃O₄ cores (79 nm) covered with 10 nm silica shell and gold nanoparticles (8 nm) fabricated on silica shell. The surface-anchored MHDA (16-mercaptohexadecanoic acid) linker facilitated cellulase bioconjugation, which was confirmed through Raman spectroscopy. The presence of gold nanoparticle islands on the heterostructure enabled surface-enhanced Raman scattering (SERS), demonstrating the potential for bioactive substance identification. Immobilization of cellulase allowed for pH enhancement and enzyme thermal stability. The optimal pH shifted from 4.0 (free enzyme) to 6.0 while thermal stability increased by 20 °C. The immobilized cellulase kept its 49% activity after five hydrolysis cycles, compared to significantly lower activity for free cellulase. The proposed heterostructures for cellulase immobilization demonstrate potential for practical applications. Full article

In this paper, we demonstrate the magnetic field-adjustable group delay of the reflected beam in the terahertz frequency range, using a multilayer architecture incorporating three layers of antisymmetric graphene. The observed enhancement in group delay results from localized field amplification, which occurs due to the excitation of surface plasmon polaritons on the graphene at the interface between two dielectric layers. By considering the quantum mechanical response of graphene, the polarity of the group delay can be reversed by exploiting the antisymmetric conductivity characteristics of graphene. Furthermore, the group delay can be dynamically modulated either by varying the external magnetic field or by adjusting the structural parameters. The achieved enhancement and tunability of the group delay offer significant potential for the development of graphene-based terahertz modulation devices and other optical delay applications. Full article

AuCo alloys are promising materials due to their magnetic, magneto-optical and magneto-plasmonic properties. These two metals are characterized by having zero mutual solubility at room temperature, significant differences in their physical and mechanical parameters and positive enthalpy of mixing. In the form of bulk samples, AuCo alloys can be synthesized by high-pressure torsion. In this study, the influence of the thermal conditions of high-pressure torsion synthesis and subsequent annealing procedures on the phase composition, magnetic domain structure and bulk magnetic properties of non-equilibrium AuCo alloys are investigated. Magnetic atomic force microscopy revealed the presence of a different magnetic domain structure in the AuCo alloys after high-pressure torsion synthesis at −193 and 23 °C. Specifically, in the AuCo alloy synthesized after 10 revolutions at 23 °C, a stripe domain structure was formed, whereas, after cryo-deformation, blurred low-contrast domain walls prevailed in the allow. The regularities of the magnetic domain structure were compared with the magnetic response of the bulk sample obtained by vibrating sample magnetometry. It was found that the saturation magnetization was slightly higher for the alloy synthesized at 23 °C, while the coercive force was higher for the AuCo alloy synthesized at −193 °C. Thermal treatment of these alloys leads to an increase in coercivity which doubles and reaches a plateau after annealing at 310 °C after cryo-deformation. Full article

Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences. Full article

This study examined applications of polarized evanescent guided wave surface-enhanced Raman spectroscopy to determine the binding and orientation of small molecules and ligand-modified nanoparticles, and the relevance of this technique to lab-on-a-chip, surface plasmon polariton and other types of field enhancement techniques relevant to Raman biosensing. A simplified tutorial on guided-wave Raman spectroscopy is provided that introduces the notion of plasmonic nanoparticle field enhancements to magnify the otherwise weak TE- and TM-polarized evanescent fields for Raman scattering on a simple plasmonic nanoparticle slab waveguide substrate. The waveguide construct is called an optical chemical bench (OCB) to emphasize its adaptability to different kinds of surface chemistries that can be envisaged to prepare optical biosensors. The OCB forms a complete spectroscopy platform when integrated into a custom-built Raman spectrograph. Plasmonic enhancement of the evanescent field is achieved by attaching porous carpets of Au@Ag core shell nanoparticles to the surface of a multi-mode glass waveguide substrate. We calibrated the OCB by establishing the dependence of SER spectra of adsorbed 4-mercaptopyridine and 4-aminobenzoic acid on the TE/TM polarization state of the evanescent field. We contrasted the OCB construct with more elaborate photonic chip devices that also benefit from enhanced evanescent fields, but without the use of plasmonics. We assemble hierarchies of matter to show that the OCB can resolve the binding of Fe²⁺ ions from water at the nanoscale interface of the OCB by following the changes in the SER spectra of 4MPy as it coordinates the cation. A brief introduction to magnetoplasmonics sets the stage for a study that resolves the 4ABA ligand interface between guest magnetite nanoparticles adsorbed onto host plasmonic Au@Ag nanoparticles bound to the OCB. In some cases, the evanescent wave TM polarization was strongly attenuated, most likely due to damping by inertial charge carriers that favor optical loss for this polarization state in the presence of dense assemblies of plasmonic nanoparticles. The OCB offers an approach that provides vibrational and orientational information for (bio)sensing at interfaces that may supplement the information content of evanescent wave methods that rely on perturbations in the refractive index in the region of the evanescent wave. Full article

Organic–inorganic nanocomposites have the potential to be used in photovoltaic materials due to their eco-friendliness, suitable band gaps, and high stability. In this work, we integrated gold and Fe₃O₄ magnetic nanoparticles with poly-m-amino benzene sulfonic (m-ABS) to synthesize Fe₃O₄@Au@poly-(m-aminobenzenesulfonic acid) (Fe₃O₄@Au@m-ABS) magneto-plasmonic nanoparticles (MPNPs) to enhance the performance of the organic photovoltaic (OPV). These MPNPs exhibit broad UV-Vis absorption and a low band gap of 2.878 eV, enhancing their suitability for photovoltaic applications. The MPNPs were introduced into the ZnO electron transporting layer (ETL) and active layer to investigate the influence of MPNPs on the power conversion efficiency (PCE) of the OPVs. When 0.1 vol% MPNPs were incorporated in the ETL, the OPVs achieved a PCE of 14.24% and a fill factor (FF) of 69.10%. On the other hand, when 0.1 vol% MPNPs were incorporated in the active layer, the OPVs showed a PCE of 14.11% and an FF of 68.83%. However, the OPVs without MPNPs only possessed a PCE of 13.15% and an FF of 63.69%. The incorporation of MPNPs increased the PCE by 8.3% in the OPV device. These findings suggest that Fe₃O₄@Au@m-ABS MPNPs are promising nanocomposite materials for enhancing the performance of OPVs. Full article

This work reports on the design, development, and characterization of novel magneto-plasmonic elastic liposomes (MPELs) of DPPC:SP80 (85:15) containing Mg_0.75Ca_0.25Fe₂O₄ nanoparticles coupled with gold nanorods, for topical application of photothermal therapy (PTT). Both magnetic and plasmonic components were characterized regarding their structural, morphological, magnetic and photothermal properties. The magnetic nanoparticles display a cubic shape and a size (major axis) of 37 ± 3 nm, while the longitudinal and transverse sizes of the nanorods are 46 ± 7 nm and 12 ± 1.6 nm, respectively. A new methodology was employed to couple the magnetic and plasmonic nanostructures, using cysteine as bridge. The potential for photothermia was evaluated for the magnetic nanoparticles, gold nanorods and the coupled magnetic/plasmonic nanoparticles, which demonstrated a maximum temperature variation of 28.9 °C, 33.6 °C and 37.2 °C, respectively, during a 30 min NIR-laser irradiation of 1 mg/mL dispersions. Using fluorescence anisotropy studies, a phase transition temperature (T_m) of 35 °C was estimated for MPELs, which ensures an enhanced fluidity crucial for effective crossing of the skin layers. The photothermal potential of this novel nanostructure corresponds to a specific absorption rate (SAR) of 616.9 W/g and a maximum temperature increase of 33.5 °C. These findings point to the development of thermoelastic nanocarriers with suitable features to act as photothermal hyperthermia agents. Full article

In this review, the state of research over the past fifteen years in the field of the applications of metal phthalocyanines and porphyrin derivatives as well as their hybrid materials with carbon nanotubes, metal oxides, and polymers in optical sensors based on the phenomenon of surface plasmon resonance (SPR) is analyzed. The first chapter of the review presents an analysis of works on the use of porphyrins and phthalocyanines in classical SPR sensors for the detection of gases and volatile organic vapors, as well as their improved modifications, such as total internal reflection ellipsometry (TIRE) and magneto-optical SPR (MOSPR) methods, while the second chapter is devoted to their application for the detection of various analytes in solutions. The third chapter of the review summarizes publications describing recent advances in the use of porous materials based on hybrids of carbon nanotubes and oxides with metal phthalocyanines. The fourth chapter describes two-dimensional metal-organic frameworks (MOFs) based on metal porphyrin derivatives as SPR sensitizers. Full article

The development of integrated, compact, and multifunctional photonic circuits is crucial in increasing the capacity of all-optical signal processing for communications, data management, and microsystems. Plasmonics brings compactness to numerous photonic functions, but its integration into circuits is not straightforward due to insertion losses and poor mode matching. The purpose of this article is to detail the integration strategies of plasmonic structures on dielectric waveguides, and to show through some examples the variety and the application prospect of integrated plasmonic functions. Full article

In this paper, the magnetically tunable Goos–Hänchen (GH) shift of a reflected beam at terahertz frequencies is achieved by using a multilayer structure where three layers of anisotropic graphene are inserted. The enhanced GH shift phenomenon results from the local field enhancement owing to the excitation of graphene surface plasmon polaritons at the interface between two dielectric materials. By considering the quantum response of graphene, the GH shift can be switched from negative to positive by harnessing the anisotropic conductivity of graphene, and the GH shift can be actively tuned through the external magnetic field or by controlling the structural parameters. By setting appropriate magnetic field and structural parameters, we can obtain GH values of −140 microns to 220 microns in the terahertz band. This enhanced and tunable GH shift is promising for fabricating graphene-based terahertz shift devices and other applications in nanophotonics. Full article

Magneto-plasmonic nanoparticles were fabricated using a 1064 nm picosecond-pulsed laser for ablation of Fe/Au and Fe/Au/Fe composite thin films in acetone. Nanoparticles were characterized by electron microscopy, ultraviolet-visible (UV-VIS) absorption, and Raman spectroscopy. Hybrid nanoparticles were arranged on an aluminum substrate by a magnetic field for application in surface-enhanced Raman spectroscopy (SERS). Transmission electron microscopy and energy dispersive spectroscopy analysis revealed the spherical core-shell (Au-Fe) structure of nanoparticles. Raman spectroscopy of bare magneto-plasmonic nanoparticles confirmed the presence of magnetite (Fe₃O₄) without any impurities from maghemite or hematite. In addition, resonantly enhanced carbon-based bands were detected in Raman spectra. Plasmonic properties of hybrid nanoparticles were probed by SERS using the adsorbed biomolecule adenine. Based on analysis of experimental spectra and density functional theory modeling, the difference in SERS spectra of adsorbed adenine on laser-ablated Au and magneto-plasmonic nanoparticles was explained by the binding of adenine to the Fe₃O₄ structure at hybrid nanoparticles. The hybrid nanoparticles are free from organic stabilizers, and because of the biocompatibility of the magnetic shell and SERS activity of the plasmonic gold core, they can be widely applied in the construction of biosensors and biomedicine applications. Full article