Author: Author

Congratulations for our new paper in Optik Journal

Red and Blue color production by flexible all-dielectric structure

N. Roostaei, N. S. Shnan, S. M. Hamidi

Color production by using plasmonic structures has been extensively studied. Due to the inherent damping of plasmons, such plasmonic structures are challenging to produce high-resolution color. Recently, color production by using all-dielectric metasurfaces has attracted much attention. Here, all-dielectric structure with different dimensions were fabricated by a nanoimprint lithography method. Color production in both reflection and transmission modes and imaging using metasurfaces were performed. The refractive index of our fabricated metasurface was calculated, and the effect of refractive index changes onto the loss, transparency, and also resolution of image and color production has been investigated. By considering the low cost and high resolution, this research will be useful for the structural color production in industrial applications.

News On Magnetic Metasurface

In this days, the Journal of Nature communications publishes a new paper entitled as “All-dielectric magnetic metasurface for advanced light control in dual polarizations combined with high-Q resonances”

Nanostructured magnetic materials provide an efficient tool for light manipulation on subnanosecond and sub-micron scales, and allow for the observation of the novel effects which are fundamentally impossible in smooth films. For many cases of practical importance, it is vital to observe the magneto-optical intensity modulation in a dual-polarization regime. However, the nanostructures reported on up to date usually utilize a transverse Kerr effect and thus provide light modulation only for p polarized light. We present a concept of a transparent magnetic metasurface to solve this problem, and demonstrate a novel mechanism for magneto-optical modulation. A 2D array of bismuth-substituted iron-garnet nanopillars on an ultrathin iron-garnet slab forms a metasurface supporting quasi-waveguide mode excitation. In contrast to plasmonic structures, the all-dielectric magnetic metasurface is shown to exhibit much higher transparency and superior quality-factor resonances, followed by a multifold increase in light intensity modulation. The existence of a wide variety of excited mode types allows for advanced light control: transmittance of both p- and spolarized illumination becomes sensitive to the medium magnetization, something that is fundamentally impossible in smooth magnetic films. The proposed metasurface is very promising for sensing, magnetometry and light modulation applications.

Congratulations for our new paper in Journal of Physica Scripta

Plasmonic wideband and tunable absorber based on semi etalon nano structure in the visible region

Neda Roostaei1, Hossein Mbarak2, Sekineh Almasi Monfared2 and Seyedeh Mehri Hamidi3

In this study, a plasmonic meta-surface absorber by semi-etalon structure is introduced due to the importance of wideband absorbers in the visible region as solar absorber. For this purpose, soft nanolithography method was adopted to construct semi-etalon absorber based on poly-dimethyl-siloxane flexible membrane and gold grating structure onto its top and down side. In parallel, the structure was simulated by the aid of finite difference time domain method, and obtained good agreement between the measured and simulated results. The results indicated the etalon-based absorber achieved light absorption from 500 to 700 nm compared to one face gold grating which works in the wavelength range 500 to 600 nm with half of absorbed power. In addition, color production was evaluated via the proposed structure, and tunable colors were produced by changing the polarization and incidence angle. Thus, the proposed structure as a good wide-band absorber, and can be used for producing tunable colors under different polarization and incidence angles. The absorber can offer new insight in larger area solar absorber based on soft nano-lithography method because of the low cost and flexibility.

News On Magneto-plasmonics

In this days, the Journal of Physics: Photonics publishes a new paper entitled as “Observation of strong magneto plasmonic nonlinearity in bilayer graphene discs” Graphene patterned into plasmonic structures like ribbons or discs strongly increases the linear and nonlinear optical interaction at resonance. The nonlinear optical response is governed by hot carriers, leading to a red-shift of the plasmon frequency. In magnetic fields, the plasmon hybridizes with the cyclotron resonance, resulting in a splitting of the plasmonic absorption into two branches. Here we present how this splitting can be exploited to tune the nonlinear optical response of graphene discs. In the absence of a magnetic field, a strong pump-induced increase in on-resonant transmission can be observed, but fields in the range of 3 T can change the characteristics completely, leading to an inverted nonlinearity. A two temperature model is provided that describes the observed behavior well.

News On Nonlinear Plasmonics

In this days, the Journal of Sensors publishes a new paper entitled as “Few Percent Efficient Polarization-Sensitive Conversion in Nonlinear Plasmonic Interactions Inside Oligomeric Gold Structures”

Abstract: The backscattering spectra of a 500 nm thick gold film, which was excited near the 525 nm transverse localized plasmon resonance of its constituent, self-organized, vertically-aligned nanorods by normally incident 515 nm, 300 fs laser pulses with linear, radial, azimuthal and circular polarizations, revealed a few-percent conversion into Stokes and anti-Stokes side-band peaks. The investigation of these spectral features based on the nanoscale characterization of the oligomeric structure and numerical simulations of its backscattering response indicated nonlinear Fano-like plasmonic interactions, particularly the partially degenerate four-wave mixing comprised by the visible-range transverse plasmon resonance of the individual nanorods and an IR-range collective mode of the oligomeric structure. Such oligomeric structures in plasmonic films may greatly enhance inner nonlinear electromagnetic interactions and inner near-IR hotspots, paving the way for their engineered IR tunability for broad applications in chemosensing and biosensing.

News

In This days the Journal of Scientific Reports publishes a new paper entitled as “Influence of plasmon excitations on atomic‑resolution quantitative 4D scanning transmission electron microscopy”

Scanning transmission electron microscopy (STEM) allows to gain quantitative information on the atomic‑scale structure and composition of materials, satisfying one of todays major needs in the development of novel nanoscale devices. The aim of this study is to quantify the impact of inelastic, i.e. plasmon excitations (PE), on the angular dependence of STEM intensities and answer the question whether these excitations are responsible for a drastic mismatch between experiments and contemporary image simulations observed at scattering angles below∼ 40 mrad. For the two materials silicon and platinum, the angular dependencies of elastic and inelastic scattering are investigated. We utilize energy filtering in two complementary microscopes, which are representative for the systems used for quantitative STEM, to form position‑averaged diffraction patterns as well as atomically resolved 4D STEM data sets for different energy ranges. The resulting five‑dimensional data are used to elucidate the distinct features in real and momentum space for different energy losses. We find different angular distributions for the elastic and inelastic scattering, resulting in an increased low‑angle intensity (∼ 10–40 mrad). The ratio of inelastic/elastic scattering increases with rising sample thickness, while the general shape of the angular dependency is maintained. Moreover, the ratio increases with the distance to an atomic column in the low‑angle regime. Since PE are usually neglected in image simulations, consequently the experimental intensity is underestimated at these angles, which especially affects bright field or low‑angle annular dark field imaging. The high‑angle regime, however, is unaffected. In addition, we find negligible impact of inelastic scattering on first‑ moment imaging in momentum‑resolved STEM, which is important for STEM techniques to measure internal electric fields in functional nanostructures. To resolve the discrepancies between experiment and simulation, we present an adopted simulation scheme including PE. This study highlights the necessity to take into account PE to achieve quantitative agreement between simulation and experiment. Besides solving the fundamental question of missing physics in established simulations, this finally allows for the quantitative evaluation of low‑angle scattering, which contains valuable information about the material investigated.

News On Plasmonic

In this days, the Journal of ACS Nano publishes a new paper entitled as “Long-Lived Hot Electron in a Metallic Particle for Plasmonics and Catalysis: Ab Initio Nonadiabatic Molecular Dynamics with Machine Learning”

ABSTRACT: Multiple experiments provide evidence for photovoltaic, catalytic, optoelectronic, and plasmonic processes involving hot, i.e., high energy, electrons in nanoscale materials. However, the mechanisms of such processes remain elusive, because electrons rapidly lose energy by relaxation through dense manifolds of states. We demonstrate a long-lived hot electron state in a Pt nanocluster adsorbed on the MoS2 substrate. For this purpose, we develop a simulation technique, combining classical molecular dynamics based on machine learning potentials with ab initio nonadiabatic molecular dynamics and real-time time-dependent density functional theory. Choosing Pt20/MoS2 as a prototypical system, we find frequent shifting of a top atom in the Pt particle occurring on a 50 ps time scale. The distortion breaks particle symmetry and creates unsaturated chemical bonds. The lifetime of the localized state associated with the broken bonds is enhanced by a factor of 3. Hot electrons aggregate near the shifted atom and form a catalytic reaction center. Our findings prove that distortion of even a single atom can have important implications for nanoscale catalysis and plasmonics and provide insights for utilizing machine learning potentials to accelerate ab initio investigations of excited state dynamics in condensed matter systems.

News

In this days, the Journal of ACS Nano publishes a new paper entitled as “Long-Lived Hot Electron in a Metallic Particle for Plasmonics and Catalysis: Ab Initio Nonadiabatic Molecular Dynamics with Machine Learning”

Abstract- Multiple experiments provide evidence for photovoltaic, catalytic, optoelectronic, and plasmonic processes involving hot, i.e., high energy, electrons in nanoscale materials. However, the mechanisms of such processes remain elusive, because electrons rapidly lose energy by relaxation through dense manifolds of states. We demonstrate a long-lived hot electron state in a Pt nanocluster adsorbed on the MoS2 substrate. For this purpose, we develop a simulation technique, combining classical molecular dynamics based on machine learning potentials with ab initio nonadiabatic molecular dynamics and real-time time-dependent density functional theory. Choosing Pt20/MoS2 as a prototypical system, we find frequent shifting of a top atom in the Pt particle occurring on a 50 ps time scale. The distortion breaks particle symmetry and creates unsaturated chemical bonds. The lifetime of the localized state associated with the broken bonds is enhanced by a factor of 3. Hot electrons aggregate near the shifted atom and form a catalytic reaction center. Our findings prove that distortion of even a single atom can have important implications for nanoscale catalysis and plasmonics and provide insights for utilizing machine learning potentials to accelerate ab initio investigations of excited state dynamics in condensed matter systems.

News On plasmonic biosensing

The Journal of Light: Science & Applications published a paper entitled as “Handheld high-throughput plasmonic biosensor using
computational on-chip imaging”

We demonstrate a handheld on-chip biosensing technology that employs plasmonic microarrays coupled with a lens-free computational imaging system towards multiplexed and high-throughput screening of biomolecular interactions for point-of-care applications and resource-limited settings. This lightweight and field-portable biosensing device, weighing 60 g and 7.5 cm tall, utilizes a compact optoelectronic sensor array to record the diffraction patterns of plasmonic nanostructures under uniform illumination by a single-light emitting diode tuned to the plasmonic mode of the nanoapertures. Employing a sensitive plasmonic array design that is combined with lens-free computational imaging, we demonstrate label-free and quantitative detection of biomolecules with a protein layer thickness down to 3 nm. Integrating large-scale plasmonic microarrays, our on-chip imaging platform enables simultaneous detection of protein mono- and bilayers on the same platform over a wide range of biomolecule concentrations. In this handheld device, we also employ an iterative phase retrieval-based image reconstruction method, which offers the ability to digitally image a highly multiplexed array of sensors on the same plasmonic chip, making this approach especially suitable for high-throughput diagnostic applications in field settings.

News On Plexcitonics

In this days, Journal of Physical Chemistry publishes a new paper entitled as “Plasmon-Induced Suppression of Exciton Self-Trapping in Polymer-Bound Pseudoisocyanine J-aggregates”

Features of plasmon-enhanced fluorescence in pseudoisocyanine (PIC) J-aggregates formed in polyelectrolyte films at liquid nitrogen temperature have been studied. Due to efficient exciton selftrapping in polymer-bound PIC J-aggregates, their fluorescence spectra consist of two well-separated bands: a narrow near-resonant band belonging to free excitons and a wide red-shifted band assigned to self-trapped excitons. It has been found that in hybrid complexes composed of polymer-bound Jaggregates and gold nanoparticles placed on some optimal distance from J-aggregates, the interaction with plasmon resonance of gold nanoparticles leads to the increase of free excitons fluorescence, whereas self-trapped excitons emission slightly decreases. Suppression of exciton self-trapping due to plasmon-induced enhancement of the exciton coherence length has been supposed and confirmed by the two-fold decrease of the exciton-phonon coupling constant.