Magnetic Plasmon Research Articles

Size- and Shape-Controlled Synthesis and Properties of Magnetic-Plasmonic Core-Shell Nanoparticles.

Magnetic-plasmonic core-shell nanomaterials offer a wide range of applications across science, engineering and biomedical disciplines. However, the ability to synthesize and understand magnetic-plasmonic core-shell nanoparticles with tunable sizes and shapes remains very limited. This work reports experimental and computational studies on the synthesis and properties of iron oxide-gold core-shell nanoparticles of three different shapes (sphere, popcorn and star) with controllable sizes (70 to 250 nm). The nanoparticles were synthesized via a seed-mediated growth method in which newly formed gold atoms were added onto gold-seeded iron oxide octahedrons to form gold shell. The evolution of the shell into different shapes was found to occur after the coalescence of gold seeds, which was achieved by controlling the amount of additive (silver nitrate) and reducing agent (ascorbic acid) in the growth solution. First principles calculation, together with experimental results, elucidated the intimate roles of thermodynamic and kinetic parameters in the shape-controlled synthesis. Both discrete dipole approximation calculation and experimental results showed that the nanopopcorns and nanostars exhibited red-shifted plasmon resonance compared with the nanospheres, with the nanostars giving multispectral feature. This research has made a great step further in manipulating and understanding magnetic-plasmonic hybrid nanostructures and will make important impact in many different fields.

Millimeter-Wave Sources at 60 and 140 GHz by Magnetic-Plasmon-Waveguide-Based In-Phase Coupled Oscillator Network in 65-nm CMOS

High output power density millimeter-wave (mm-wave) signal sources are demonstrated at 60 and 140 GHz by a magnetic plasmon waveguide (MPW) based in-phase coupled oscillator network (CON) in 65-nm CMOS. Each oscillator unit-cell is designed by an MPW-based low-loss inter-digital zero-phase coupler (ZPC). With multiple in-phase coupled ZPC unit-cells, a high output power mm-wave signal is generated at the center of the CON by an in-phase power combination. A 60-GHz CON-based signal source is implemented with four in-phase CON unit-cells at 60 GHz in a compact core chip area of ${\text {0.11 mm}}^{2}$ . It is measured with 2-mW peak differential output power, 2.2% power efficiency, ${\text {18.2-mW/mm}}^{2}$ output power density, $-{\text {113.9-dBc/Hz}}$ phase noise at 10-MHz offset, and 15.8% frequency tuning range (FTR) centered at 63.1 GHz. Moreover, a 140-GHz signal source is implemented by the combination of second-order harmonics of four in-phase coupled ZPC unit-cells at 70 GHz in a compact core chip area of ${\text {0.13 mm}}^{2}$ . It is measured with 3.5-mW peak output power, 2.4% power efficiency, ${\text {26.9-mW/mm}}^{2}$ output power density, $-{\text {104.9-dBc/Hz}}$ phase noise at 25-MHz offset, and 9.7% FTR centered at 133.5 GHz.

Tunnel Light Through a Continuous Optically Thick Metal Film Utilizing Higher Order Magnetic Plasmon Resonance

In this letter, we investigate the extraordinary optical transmission behavior of a flat continuous metal film sandwiched by magnetic plasmonic structures. A new mechanism by utilizing higher order magnetic plasmon resonance is proposed to enhance the transmission. Numerical simulation results show that 80 % electromagnetic energy can be transmitted through the middle 50-nm-thick continuous gold film in near-infrared regime. The excitation of the second-order magnetic plasmons and the propagating surface plasmons, as well as the interaction between them accounts for such a high transmission. The interaction of magnetic plasmons and surface plasmons leads to new hybrid modes, and the coupled oscillator model is introduced to analyze this hybridization. This work extends the application range of higher order magnetic plasmons and may have potential in transparent electrode and electromagnetic energy transfer applications.

Self‐Assembly/Disassembly of Nanostructures Confers “Off/On” Signal for Molecular Imaging

AbstractMolecular imaging (MI) plays an important role in both clinical diagnosis and laboratorial research. Developing a “smart” strategy with higher sensitivity for more precise imaging is of great significance but remains challenging. If employed for MI, the self‐assembly/disassembly of nanostructures carries five characteristic superiorities in its specific response to a physiological environment: lower toxicity, longer circulating time, higher imaging efficiency, higher signal‐to‐noise ratio, and ease of functionalization. This review focuses on recent approaches involving the self‐assembly/disassembly of nanostructures for the MI of biological events by using different modalities (e.g., magnetic resonance imaging, optical imaging, plasmonic and photoacoustic imaging). We envision that by incorporating multiple imaging modes to the monomer/nanostructures for self‐assembly/disassembly, researchers should be able to use this “smart” system for more precise MI in the near future.

Surface-Plasmon-Polaritons-Assisted Enhanced Magnetic Response at Optical Frequencies in Metamaterials

We theoretically study the coupling of magnetic plasmon polaritons (MPPs) with propagating surface plasmon polaritons (SPPs) in a system composed of an array of metal nanowires close to a metal film with a dielectric spacer. Strong coupling between MPPs and SPPs is observed, manifested by the anticrossing behavior of the resonant positions in the reflection spectra. It creates narrow-band hybridized MPPs with Rabi-type splitting as large as 250 meV. Moreover, we also found that the coupling between the MPPs and the SPPs can be tailored by the period of the metal nanowire array to affect the magnetic response of the plasmonic structure. Above the resonant wavelength of the MPPs, coupling between two kinds of resonance modes can lead to a 20-fold enhancement of the magnetic fields in the dielectric spacer, as compared with the pure magnetic resonance upon the excitation of the hybridized MPPs, whereas below it, coupling cannot lead to a magnetic field enhancement. We suggest that this feature could offer a feasible way to achieve huge magnetic field enhancement at optical frequencies and hold promising potential applications in magnetic nonlinearity and sensors.

Correction: Beyond "turn-on" readout: from zero background to signal amplification by combination of magnetic separation and plasmon enhanced fluorescence.

Correction for 'Beyond "turn-on" readout: from zero background to signal amplification by combination of magnetic separation and plasmon enhanced fluorescence' by Suqin Gong and Yunsheng Xia, Chem. Commun., 2016, 52, 9660-9663.

Beyond "turn-on" readout: from zero background to signal amplification by combination of magnetic separation and plasmon enhanced fluorescence.

By magnetic separation and subsequent plasmon enhanced fluorescence, an assay platform with a signal output from completely "zero" background to fluorescence amplification is achieved, using quantum dots as reporters. So, it well breaks through the conventional "turn-on" strategy in both lower and upper limits. The sensitivity for hyaluronidase sensing is enhanced 10(4)-10(6) times as compared with previous fluorescence methods.

Electrochemiluminescent Spin-Polarized Modulation by Magnetic Ions and Surface Plasmon Coupling.

Electrochemiluminescent modulation: Electrochemiluminescence (ECL) of CdS nanocrystal (NC) film-Au nanoparticle (NP) integrated system is controllably quenched by magnetic Co(2+) ions without external magnetic field owing to spin-polarized modulation of the electron-hole recombination caused by ferromagnetic alignment of Co(2+) in close proximity to Au NPs.

Electrochemiluminescent Spin‐Polarized Modulation by Magnetic Ions and Surface Plasmon Coupling

Electrochemiluminescent Spin‐Polarized Modulation by Magnetic Ions and Surface Plasmon Coupling

Shaping the fluorescence emission by cavity plasmons in dielectric-metal core-shell resonators

We observe experimentally the spectral and spatial reshaping of fluorescence emission in dye-doped dielectric-metal core-shell resonators that support multipolar electric and magnetic-based cavity plasmon resonances. By comparing the experimental fluorescence spectra with analytical calculations based on Mie theory, we are able to demonstrate that the strong reshaping effects are the results of the coupling of dye molecules to those narrow-band cavity plasmon resonances. In addition, we show that the polarization of the fluorescence emission can also be modified by selectively coupling the molecules to the magnetic or electric based cavity plasmons.

Graphene Based Surface Plasmon Polariton Modulator Controlled by Ferroelectric Domains in Lithium Niobate.

We proposed a ferroelectric domain controlled graphene based surface plasmon polariton modulator. Ferroelectricity-induced electronic and optical property tuning of graphene by domain in lithium niobate was theoretically investigated considering both interband and intraband contributions of surface conductivity. With the corrected Sellmeier equation of lithium niobate, the propagation of transverse magnetic mode surface plasmon polaritons in an air/graphene/lithium niobate structure was studied when monolayer graphene was tuned by down polarization direction ferroelectric domain with different polarization levels. The length of the ferroelectric domain was optimized to be 90 nm for a wavelength of 5.0 μm with signal extinction per unit 14.7 dB/μm, modulation depth 474.1 dB/μm and figure of merit 32.5. This work may promote the study of highly efficient modulators and other ultra-compact nonvolatile electronic and photonic devices in which two-dimensional materials and ferroelectric materials are combined.

Atomically thin spherical shell-shaped superscatterers based on a Bohr model

Graphene monolayers can be used for atomically thin three-dimensional shell-shaped superscatterer designs. Due to the excitation of the first-order resonance of transverse magnetic (TM) graphene plasmons, the scattering cross section of the bare subwavelength dielectric particle is enhanced significantly by five orders of magnitude. The superscattering phenomenon can be intuitively understood and interpreted with a Bohr model. In addition, based on the analysis of the Bohr model, it is shown that contrary to the TM case, superscattering is hard to achieve by exciting the resonance of transverse electric (TE) graphene plasmons due to their poor field confinements.

Complementary structure for designer localized surface plasmons

Magnetic localized surface plasmons (LSPs) supported on metallic structures corrugated by very long and curved grooves have been recently proposed and demonstrated on an extremely thin metallic spiral structure (MSS) in the microwave regime. However, the mode profile for the magnetic LSPs was demonstrated by measuring only the electric field, not the magnetic field. Here, based on Babinet's principle, we propose a Babinet-inverted, or complementary MSS whose electric/magnetic mode profiles match the magnetic/electric mode profiles of MSS. This complementarity of mode profiles allows mapping the magnetic field distribution of magnetic LSP mode profile on MSS by measuring the electric field distribution of the corresponding mode on complementary MSS. Experiment at microwave frequencies also demonstrate the use of complementary MSS in sensing refractive-index change in the environment.

Surface magneto plasmons and their applications in the infrared frequencies

Abstract Due to their promising properties, surface magneto plasmons have attracted great interests in the field of plasmonics recently. Apart from flexible modulation of the plasmonic properties by an external magnetic field, surface magneto plasmons also promise nonreciprocal effect and multi-bands of propagation, which can be applied into the design of integrated plasmonic devices for biosensing and telecommunication applications. In the visible frequencies, because it demands extremely strong magnetic fields for the manipulation of metallic plasmonic materials, nano-devices consisting of metals and magnetic materials based on surface magneto plasmon are difficult to be realized due to the challenges in device fabrication and high losses. In the infrared frequencies, highly-doped semiconductors can replace metals, owning to the lower incident wave frequencies and lower plasma frequencies. The required magnetic field is also low, which makes the tunable devices based on surface magneto plasmons more practically to be realized. Furthermore, a promising 2D material-graphene shows great potential in infrared magnetic plasmonics. In this paper, we review the magneto plasmonics in the infrared frequencies with a focus on device designs and applications. We investigate surface magneto plasmons propagating in different structures, including plane surface structures and slot waveguides. Based on the fundamental investigation and theoretical studies, we illustrate various magneto plasmonic micro/nano devices in the infrared, such as tunable waveguides, filters, and beam-splitters. Novel plasmonic devices such as one-way waveguides and broad-band waveguides are also introduced.

Magnetically manipulable unidirectional self-collimated propagation in two-dimensional ferromagnetic material

We present microwave self-collimated properties in two-dimensional ferromagnetic photonic crystals (FPCs) made of an array of ferrite rods. Through utilizing the time reversal symmetry-breaking nature of the FPCs, a technique, i.e., unidirectional self-collimation transmission, can be exhibited near the magnetic surface plasmon resonance and the spin wave resonance by designing the appropriate structure. An incident self-collimated beam can be absorbed completely at a particular bending channel, while an obvious transmission is observed at the symmetrically opposite direction. The working frequency of the unidirectionality can be controlled as well by tuning the external static magnetic field.

Experimental observation of sharp cavity plasmon resonances in dielectric-metal core-shell resonators

We report on the experimental realization of dielectric-metal core-shell resonators with a nearly perfect metal shell layer by physically depositing metal onto the self-supporting dielectric colloids. Sharp electric and magnetic-based cavity plasmon resonances are experimentally observed, whereas increasing the metal shell thickness increases their Q-factors while narrowing their linewidths. In particular, a high Q-factor up to ∼100 with a correspondingly narrow linewidth down to ∼12 nm is experimentally obtained at a dipolar magnetic cavity plasmon resonance. Simulations and analytical Mie calculations show excellent agreements with the experimental results and demonstrate strong optical field confinement of such three-dimensional resonators.

Manipulation of Magnetic Fano Resonances in Double Split-Hole Disk

The plasmon resonances and magnetic field enhancement in double split-hole disk are investigated by using finite element method. The multipolar modes and the magnetic Fano resonances of the double split-hole disk can be tuned by modifying the structure parameters. The oscillate direction of the closed current in the right and the left split hole can be tuned, achieving the bright and dark magnetic modes of this system. These new emergent phenomena in this nanostructure have potential applications in the propagation of low-loss magnetic plasmons and advanced devices based on magnetic Fano resonances.

Experimental demonstration of high-order magnetic localized spoof surface plasmons

We experimentally demonstrate that an ultrathin metallic spiral structure is able to support multiple high-order magnetic localized spoof surface plasmons (LSSPs), which were absent in previously reported magnetic LSSPs. Near-field response spectra and near-field mapping are performed in the microwave regime to confirm this phenomenon. We also show that the high-order magnetic LSSPs are more sensitive to the surrounding refractive index change than the previously reported magnetic dipole mode. Our study may be useful in electromagnetic near-field sensing from microwave to infrared frequencies.

Magneto-optical response of two-dimensional magnetic plasmon structures based on gold nanodisks embedded in a ferrite garnet layer

Resonance optical effects in ordered two-dimensional arrays of gold nanodisks embedded in an insulating magnetic film are investigated. The angle-resolved transmission spectra exhibit features related to the excitation of local surface plasmons and lattice plasmon polaritons in the gold nanoparticles and waveguide modes in the magnetic insulator layer. Resonance enhancement of the linear magneto-optical intensity effect in transmission configuration is found in the vicinity of the lattice plasmon resonance and the waveguide mode in the structures under study.

New Regime of Plasmonically Induced Transparency

Electromagnetically induced transparency is a phenomenon that drastically alters light-matter interactions such that an optically opaque medium becomes transparent. To date, it is widely accepted that broken symmetry is a necessary and sufficient condition for the realization of electromagnetically induced transparency (EIT) in nano-plasmonic structures. We have confirmed that even without broken symmetry, the plasmonically induced transparency (PIT) effect based on excitation of magnetic plasmon resonance can be created. We also demonstrated that in general, in the system allowing for higher-order mode excitation, broken symmetry may not be a sufficient condition for the realization of the EIT, in that the EIT may disappear even if the symmetry is broken.