Tunable Localized Surface Plasmon Resonances in a New Graphene-Like Si2BN’s Nanostructures

The optical response of a new graphene-like material Si₂BN’s nanostructures and some kinds of hybrid structures formed by Si₂BN and metal nanoparticles was studied by using time-dependent density functional theory (TDDFT). We found that the periodic structures of Si₂BN have wider absorption ranges than graphene. When the impulse excitation polarizes in different directions (armchair-edge direction and zigzag-edge direction), the absorption spectra of Si₂BN nanostructures would be different (optical anisotropy). And in the hybrid structures, the increase of metal nanoparticles’ number brings the absorption intensity strengthening and red shift, which means a stronger ability of localized surface plasmon tuning. Also, the different metal nanoparticles were used to form the hybrid structures; they show an obviously different property as well. In addition, in the kinds of situations mentioned above, the plasmons were produced in visible region. This investigation provides an improved understanding of the plasmon enhancement effect in graphene-like photoelectric devices.

     

Resonant Broadband Field Enhancement in Cylindrical Plasmonic Structure Surrounded by Perovskite Environment

We demonstrate the optical response of metal nanoparticles and their interaction with organic-inorganic perovskite (methyl ammonia lead halide (CH₃NH₃PbI₃)) environment using discrete dipole approximation (DDA) simulation technique. Important optical properties like absorption, scattering, and electric field calculations for metal nanoparticle using different geometry have been analyzed. The metal nanoparticles embedded in the perovskite media strongly support surface plasmon resonances (SPRs). The plasmonic interaction of metal nanoparticles with perovskite matrix is a strong function of MNP’s shape, size, and surrounding environment that can manipulate the optical properties considerably. The cylindrical shape of MNPs embedded in perovskite environment supports the SPR which is highly tunable to subwavelength range of 400–800 nm. Wide range of particle sizes has been selected for Ag, Au, and Al spherical and cylindrical nanostructures surrounded by perovskite matrix for simulation. The chosen hybrid material and anisotropy of structure together make a complex function for resonance shape and width. Among all MNPs, 70-nm spherical silver nanoparticle (NP) and cylindrical Ag NP having diameter of 50 nm and length of 70 nm (aspect ratio 1.4) generate strong electric field intensity that facilitates increased photon absorption. The plasmonic perovskite interaction plays an important role to improve the absorption of photon inside the thin film perovskite environment that may be applicable to photovoltaics and photonics.

     

Observation of Optical Bistability in a Polaritonic Material Doped with Nanoparticles

We study the optical bistability and multistability in a defect structure doped with polaritonic materials and three-level nanoparticles. It is realized that the threshold of optical bistability can be manipulated by some controllable parameters such as Rabi frequency, line width of upper level, and thickness of defect structure. Due to dense doping of three-level nanoparticles, the dipole-dipole interactions (DDI) between nanoparticles become important. Therefore, the DDI has been considered as an interesting mechanism for transition from optical bistability to multistability. The line width effect of upper level and thickness of defect structure on threshold of optical multistability has also been investigated. We hope that our proposed model may be useful for developing the future all-optical devices in nanoscales.

     

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species,organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Furthermore, the emphasis of this review is on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺, Cu²⁺, Hg²⁺, F⁻, peptides), and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in the tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.     

Single-Particle Spectroscopy of Supported Silver Clusters on Silicon: Substrate Effects on Localized Surface Plasmons

The presence of a surrounding medium strongly affects the spectral properties of localized surface plasmons at metallic nanoparticles. Vice versa, plasmonic resonances have large impact on the electric polarization in a surrounding or supporting material. For applications, e.g., in light-converting devices, the coupling of localized surface plasmons with polarizations in semiconducting substrates is of particular importance. Using photoemission electron microscopy with tunable laser excitation, we perform single-particle spectroscopy of silver nanoclusters directly grown on Si(100). Two distinct localized surface plasmon modes are observed as resonances in the two-photon photoemission signals from individual silver clusters. The strengths of these resonances strongly depend on the polarization of the exciting electric field, which allows us to assign them to plasmon modes with polarizations parallel and perpendicular, respectively, to the supporting silicon substrate. Our mode assignment is supported by simulations which provide insight into the mutual interaction of charge oscillations at the particle surface with electric polarizations at the silver/silicon interface.

     

Angular Optical Transparency Induced by Photonic Topological Transition in Hexagonal Boron Nitride

The transmission property of hexagonal boron nitride at its four photonic topological transitions has been studied. An interesting result is revealed that the angular optical transparency can be achieved at wavelength 12.0494 μm. The numerical results indicate that the transparency window has an angular full width at half maximum of 4° with an optical transmission higher than 0.9 at normal incidence. Besides, corresponding to an angular full width at half maximum narrower than 20°, the wavelength span is about 230 nm. These features may make the hexagonal boron nitride holds promise for applications in private screens and optical detectors.

     

Magnetic Field Effect on Fresnel Coefficients of the Thin Slab of Graphite Nanocomposite

In this theoretical study, optical properties of a thin slab including graphite nanoparticles doped in a host medium such as silica and silicon have been investigated. A constant magnetic field is used for controlling Fresnel coefficients of the slab. Depending on the direction of the normal vector of the basal plane of the graphite structure with respect to the electric field of the incident electromagnetic wave (perpendicular or parallel), optical behavior of graphite is different. Electric permittivity of an individual magnetized graphite nanoparticle is calculated by a semi-empirical Drude-like model for both kinds of the normal vector of the basal plane orientation. By means of well-known Maxwell-Garnett theory, effective permittivity of the magnetized nanocomposite slab is obtained. It is shown that at the mid-IR frequency range, exerting a magnetic field of few hundred Tesla can lead to the substantial variations of Fresnel coefficients. Effect of the magnetic field on the optical properties of the slab is more evident when the population of the graphite nanoparticles with the parallel orientation of the basal plane is increased.

     

Conformational and phase transitions in DNA—photosensitive surfactant solutions: Experiment and modeling

DNA binding to trans‐ and cis‐isomers of azobenzene containing cationic surfactant in 5 mM NaCl solution was investigated by the methods of dynamic light scattering (DLS), low‐gradient viscometry (LGV), atomic force microscopy (AFM), circular dichroism (CD), gel electrophoresis (GE), flow birefringence (FB), UV–Vis spectrophotometry. Light‐responsive conformational transitions of DNA in complex with photosensitive surfactant, changes in DNA optical anisotropy and persistent length, phase transition of DNA into nanoparticles induced by high surfactant concentration, as well as transformation of surfactant conformation under its binding to macromolecule were studied. Computer simulations of micelles formation for cis‐ and trans‐isomers of azobenzene containing surfactant, as well as DNA‐surfactant interaction, were carried out. Phase diagram for DNA‐surfactant solutions was designed. The possibility to reverse the DNA packaging induced by surfactant binding with the dilution and light irradiation was shown. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 109–122, 2015.     

Studies on Freezing Injury of Plant Cells: I. Relation between Thermotropic Properties of Isolated Plasma Membrane Vesicles and Freezing Injury

The thermotropic transition of plasma membrane of Dactylis glomerata was studied by using fluorescence polarization of embedded fluorophore, 1,6-diphenyl-1,3,5-hexatriene. Under the presence of 35% ethylene glycol, reversible thermotropic transitions were observed in isolated plasma membrane vesicles in nearly the same temperature range as the temperature of freezing injury to cells. In liposomes prepared from isolated plasma membranes, however, the thermotropic transitions occurred at much lower temperatures in comparison with those of intact membrane vesicles. Following treatment with pronase, the thermotropic transition also shifted downward.

Thus, the thermotropic properties of plasma membranes appeared to be dependent on the membrane proteins. In vitro freezing of the isolated plasma membrane vesicles without addition of any cryoprotectant, such as sorbitol, resulted in an irreversible alteration both in the fluorescence anisotropy values and the temperatures for the thermotropic transition, suggesting an irreversible alteration in the membrane structure, presumably changes in lipid-protein interactions and protein conformation.

     

Study on the Effect of Poly(Styrene 4-Sulfonic Acid-co-Maleic Acid) Toward Metallization and Plasmonic Tuning of Silver Nanoparticle Thin Films

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

     

The chromatin fiber: structure and conformational transitions as revealed by optical anisotropy studies

Structure and conformational transitions of the chromatin fiber as revealed by optical anisotropy studies are reviewed. The data in the literature do not allow a definite interpretation; in fact some of them are contradictory. The major findings are reported here and an attempt is made to analyse them with respect to the internal dynamics and the various models suggested for the organization of the chromatin fiber.     

Surface Plasmon Resonance Enhanced Faraday Rotation in Fe3O4/Ag Nanoparticles Doped Diamagnetic Glass

Diamagnetic TeO₂-PbO-B₂O₃ glasses were melt-quenching fabricated and characterized for Fe₃O₄/Ag nanoparticles doping through radio-frequency sputtering and thermal treatment techniques. The surface plasmon resonance influenced structure, composition, optical, and magneto optical properties of Fe₃O₄/Ag doped glasses were investigated through XRD, SEM, XPS analysis, and Faraday rotation measurement. The optimized sputtering and thermal conditions Fe₃O₄ and Ag nanoparticles were obtained. Under the optimized conditions, a great enhancement of Faraday rotation, thermal property, and big UV cutoff red-shift due to the excited surface plasma’s resonance effect was achieved in diamagnetic glass.

     

Anisotropy of Bullet-Shaped Magnetite Nanoparticles in the Magnetotactic Bacteria Desulfovibrio magneticus sp. Strain RS-1

Magnetotactic bacteria (MTB) build magnetic nanoparticles in chain configuration to generate a permanent dipole in their cells as a tool to sense the Earth’s magnetic field for navigation toward favorable habitats. The majority of known MTB align their nanoparticles along the magnetic easy axes so that the directions of the uniaxial symmetry and of the magnetocrystalline anisotropy coincide. Desulfovibrio magneticus sp. strain RS-1 forms bullet-shaped magnetite nanoparticles aligned along their (100) magnetocrystalline hard axis, a configuration energetically unfavorable for formation of strong dipoles. We used ferromagnetic resonance spectroscopy to quantitatively determine the magnetocrystalline and uniaxial anisotropy fields of the magnetic assemblies as indicators for a cellular dipole with stable direction in strain RS-1. Experimental and simulated ferromagnetic resonance spectral data indicate that the negative effect of the configuration is balanced by the bullet-shaped morphology of the nanoparticles, which generates a pronounced uniaxial anisotropy field in each magnetosome. The quantitative comparison with anisotropy fields of Magnetospirillum gryphiswaldense, a model MTB with equidimensional magnetite particles aligned along their (111) magnetic easy axes in well-organized chain assemblies, shows that the effectiveness of the dipole is similar to that in RS-1. From a physical perspective, this could be a reason for the persistency of bullet-shaped magnetosomes during the evolutionary development of magnetotaxis in MTB.     

Near-field enhancement of infrared intensities for <Emphasis Type="Italic">f-f</Emphasis> transitions in Er<Superscript>3+</Superscript> ions close to the surface of silicon nanoparticles

Erbium doped waveguide amplifiers can be used in optical integrated circuits to compensate for signal losses. Such amplifiers use stimulated emission from the first excited state (⁴ I _13/2) to the ground state (⁴ I _15/2) of Er³⁺ at 1.53 μm, the standard wavelength for optical communication. Since the intra-f transitions are parity forbidden for free Er³⁺ ions, the absorption and the emission cross sections are quite small for such doped amplifiers. To enhance the absorption, Si nanoclusters can be embedded in silica matrix. Here we investigate the effect of the Si nanocluster on the Er³⁺ emission using ab initio theory for the first time. We combine multi-reference configuration interaction with one-electron spin-orbit Hamiltonian and relativistic effective core potentials. Our calculations show that the presence of a polarizable Be atom at 5Ǻ from the Er³⁺ ion in a crystalline environment can lead to an enhancement in the emission by a factor of three. The implications of this effect in designing more efficient optical gain materials are discussed.     

Plasmonic Effects of Dual-Metal Nanoparticle Layers for High-Performance Quantum Dot Solar Cells

To improve quantum dot solar cell performance, it is crucial to make efficient use of the available incident sunlight to ensure that the absorption is maximized. The ability of metal nanoparticles to concentrate incident sunlight via plasmon resonance can enhance the overall absorption of photovoltaic cells due to the strong confinement that results from near-field coupling or far-field scattering plasmonic effects. Therefore, to simultaneously and synergistically utilize both plasmonic effects, the placement of different plasmonic nanostructures at the appropriate locations in the device structure is also critical. Here, we introduce two different plasmonic nanoparticles, Au and Ag, to a colloidal PbS quantum dot heterojunction at the top and bottom interface of the electrodes for further improvement of the absorption in the visible and near-infrared spectral regions. The Ag nanoparticles exhibit strong scattering whereas the Au nanoparticles exhibit an intense optical effect in the wavelength region where the absorption of light of the PbS quantum dot is strongest. It is found that these dual-plasmon layers provide significantly improved short-circuit current and power conversion efficiency without any form of trade-off in terms of the fill factor and open-circuit voltage, which may result from the indirect contact between the plasmonic nanoparticles and colloidal quantum dot films.

     

Manipulation of Microscale Fluid Using Laser-Irradiated Nanoparticle Arrays

The manipulation of microscale fluid has been widely used in biology, medicine, and chemistry. However, the traditional control systems are relatively large, complex, and costly. Optical driving micro- and nanofluid is a new trend of microfluidics, which combines the advantages of both optics and microfluidics in the micro-nano scale. In the present work, we investigated a method to drive microfluid by taking advantage of the localized surface plasmon resonance effect of gold nanoparticles, which can convert optical energy to fluid motion. First, numerical simulation was carried out to calculate the electromagnetic, temperature, and flow field around laser-irradiated gold nanoparticles. Then, the simplified heat source condition was verified. The nanoparticle array was regarded as heat source to induce convection flow. The influence of the spacing and number of nanoparticles in array was investigated. On this basis, the structural parameters of nanoparticle array that can be used to regulate the velocity of microfluidic were obtained.

     

Fano Resonances in Compositional Clusters of Aluminum Nanodisks at the UV Spectrum: a Route to Design Efficient and Precise Biochemical Sensors

In this study, we have investigated the plasmon resonance coupling between proximal compositional Al nanoparticles that are organized in a closely spaced molecular orientation as nanoclusters. Plasmon hybridization model is employed as a theoretical model to study the spectral response of the proposed nanostructures. The optical properties of trimer, heptamer, and octamer clusters based on Al/Al₂O₃ nanodisks are evaluated using finite-difference time-domain (FDTD) model numerically. We have proved that a constructive and weak interference between subradiant dark and superradiant bright modes as the plasmon resonance modes causes the appearance of strong Fano resonances at the spectral response of the heptamer and octamer clusters at the UV spectrum. The effects and results of the structural and chemical modifications in the proposed nanoclusters have been discussed and determined. Finally, illuminating an octamer cluster composed of Al/Al₂O₃ nanoparticles and simultaneous modifications in the refractive index of the dielectric environment lead to dramatic changes in the position and quality of the Fano dip. Plotting a linear figure of merit (FoM) for the proposed octamer and quantifying this parameter for the structure as 7.72, we have verified that the structure has a strong potential to be used in designing precise localized surface plasmon resonance (LSPR) sensors that are able to sense minor environmental perturbations with high accuracy. Proposed clusters composed of Al/Al₂O₃ provide an opportunity to design and fabricate low-cost, high responsivity, tunable, and CMOS-compatible devices and efficient biochemical sensors.     

Investigating the Effect of Ag and Au Nanostructures with Spherical and Rod Shapes on the Emission Wavelength of OLED

Noble metals, especially Ag and Au nanostructures, have unique and adjustable optical attributes in terms of surface plasmon resonance. In this research, the effect of Ag and Au nanoparticles with spherical and rod shapes on the light extraction efficiency and the FWHM of OLED structures was investigated using the finite difference time domain (FDTD) method. The simulation results displayed that by changing the shape and size of Ag and Au nanostructures, the emission wavelength can be adjusted, and the FWHM can be reduced. The presence of Ag and Au nanoparticles in the OLEDs showed a blue and red shift of the emission wavelength, respectively. Also, the Ag and Au nanorods caused a significant reduction in the FWHM and a shift to the longer wavelengths in the structures. The structures containing Ag nanorods showed the narrowest FWHM and longer emission wavelength than the other structures.