Metallic Nanostrips Research Articles

Improved near field lithography with the assistance of a metallic nanostrip array

A way of improving near field lithography is proposed, using metallic nanostrips arrangedright above the lithographic channels, between which a dielectric film is used,designed to support the strips and modulate the surface plasmon resonance at themetal/dielectric interface. The dependence of the light transmission in the channels onthe properties of the strip array and dielectric film are studied numerically. Theresults show that the transmission is associated with the width of the strip, thepermittivity of the film and the thicknesses of both. With the optimized structure, notonly is transmission efficiency promoted, but also a uniform field distribution ofgood contrast at the channel exports can be obtained, which is beneficial to thelithography.

Compact Bragg grating with embedded metallic nano-structures

A compact Bragg grating with embedded gapped metallic nano-structures is proposed and investigated theoretically. The Bragg grating consists of periodic planar metallic strips embedded in a dielectric waveguide. The grating exhibits distinct polarization characteristics due to its underlying working mechanisms of the metallic nano-strips. The grating can be considered as insulator-metal-insulator surface plasmonic polariton waveguide grating with improved light confinement for TM polarized waves. For the TE waves, significant field mismatch between metal and non-metal sections of the grating results in strong reflection. Comparison with the conventional deeply-etched grating on the same waveguide structures reveals interesting characteristics. It is concluded that the two types of grating structures share similar guidance, reflection and loss mechanisms for the TE modes. The spectral characteristics and their dependences on grating duty cycle are drastically different for the TM modes, mainly due to the SPP effect for the metal. Although the proposed grating performs slightly worse comparing to the deeply-etched grating for TE waves, its fabrication process should be easier since there will be no narrow trench (in sub-microns) deep-etching process (up to a few microns in depth) involved.

Plasmon-Assisted Optical Curtains

We predict an optical curtain effect, i.e., formation of a spatially invariant light field as light emerges from a set of periodic metallic nano-objects. The underlying physical mechanism of generation of this unique optical curtain can be explained in both the spatial domain and the wave-vector domain. In particular, in each period, we use one metallic nanostrip to equate the amplitudes of lights impinging on the openings of two metallic nanoslits and also shift their phases by π difference. We elaborate the influence on the output effect from some geometrical parameters like the periodicity, the slit height, and so on. By controlling the light illuminated on metallic subwavelength apertures, it is practical to generate optical curtains of arbitrary forms, which may open new routes of plasmonic nanolithography.

Near-Field-Resonance-Enhanced Plasmonic Light Beaming

In this paper, we have investigated the enhancement of the plasmonic light beaming efficiency by near-field resonance in different subwavelength metallic slit-groove beaming structures. We show that by selecting the suitable film thickness and separation distance of beaming gratings, the intensity of the near field can be greatly enhanced by resonance, which leads to the increase of the beaming efficiency in the far field. Moreover, we obtain a nanocavity above the nanoslit by integrating a metal nanostrip with a conventional beaming structure. The resonance of this nanocavity can further enhance the near-field intensity and improve the beaming efficiency.

Tunable magnetic response of metamaterials

We demonstrate a thermally tunable optical metamaterial with negative permeability working in the visible range. By covering coupled metallic nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response wavelength of the metamaterial is effectively tuned through control of the ambient temperature, changing the refractive index of LC via phase transitions. By increasing the ambient temperature from 20 to 50 °C, the magnetic response wavelength shifts from 650 to 632 nm. Numerical simulations confirm our tests and match the experimental observations well.

A designer approach to plasmonic nanostructures: tuning their resonance from visible to near-infrared

Using Green's matrix method and resonance capacity concept, surface plasmon resonances of metallic nanostrips are investigated. We first show how the resonance wavelength is determined by the geometric parameters. Then, resonances from visible to near-infrared, depending on the strip size, are obtained. For a specific nanostrip-type, a linear tunability of resonance wavelength is demonstrated from λR = 900 nm to λR = 1800 nm by merely changing the dimensions and keeping the aspect ratio fixed. It is also found that the near field is more enhanced around the thin and long nanostrip. These results can act as a guide in practical design work.

Gap plasmon-polariton nanoresonators: Scattering enhancement and launching of surface plasmon polaritons

Gap plasmon-polariton (GPP) nanoresonators based on a metal nanostrip separated with a small gap from a metal surface or metal block are considered. Scattering resonances and field enhancements are studied for two-dimensional structures using the Green's-function surface integral equation method (GFSIEM). For small gaps, we show that the scattering resonances occur due to the constructive interference of counterpropagating GPPs, forming standing waves. By varying the gap size we find that the resonance wavelength can be tuned over a wide range of wavelengths, which makes the resonators interesting for spectroscopic and sensing applications, and observe the transition between GPP-based resonators (for narrow gaps) and slow surface plasmon-polariton (SPP) strip resonators (for wide gaps). Considering the resonant field distributions, we find that, for an insulator thickness of 10 nm, the maximum field enhancement (with respect to the incident field) can reach values close to 50 along the line passing through the gap center. For the case of a strip placed close to a metal surface, two scattering channels, viz., the out-of-plane scattering and the scattering into SPPs (propagating along the surface) are evaluated separately using a generalized version of the GFSIEM. We find that, even though the out-of-plane scattering is in general dominating in the considered range of parameters, scattering into SPPs can be very efficient for smaller gaps featuring a cross section that at resonance even exceeds the strip width. The considered properties of GPP nanoresonators, i.e., resonant scattering and local-field enhancements along with efficient scattering into SPPs, hold promises for their useful applications within plasmonic sensing devices.

Enhancing extraordinary transmission of light through a metallic nanoslit with a nanocavity antenna

The extraordinary transmission of light through a vertical nanoslit in a metal film is enhanced by introducing a nanocavity antenna formed by a nearby metallic nanostrip over the slit opening. For a fixed wavelength, the width of the metallic nanostrip should be chosen to make the horizontal metal-insulator-metal waveguide of finite length resonant as a Fabry-Perot cavity. When such a cavity antenna is used to enhance the transmission through a nonresonant nanoslit, the slit should be opened at a position with a maximal magnetic field in the horizontal resonant cavity. It is shown that an optimized cavity antenna can enhance greatly the transmission of light through a nonresonant nanoslit (by about 20 times) or a resonant nanoslit (by 124%). Such a transmission enhancement with a nanocavity antenna is studied for the first time, and the physical mechanism is explained.

Theoretical analysis and experimental demonstration of resonant light scattering from metal nanostrips on quartz

Using the Green's tensor area integral equation method and reflection spectroscopy, resonant light scattering from rectangular gold nanostrips on quartz substrates fabricated with electron-beam lithography is analyzed theoretically and demonstrated experimentally. Theory and experiments are compared and found in a good agreement. Design curves presenting the scattering resonance wavelength as a function of the nanostrip width allow one, by carefully choosing the strip width and thickness, to realize the resonance at a given wavelength in a broad wavelength spectrum ranging from the visible (~600 nm) to the near infrared including telecommunication wavelengths (~1600 nm).

Electronically patterning through one-dimensional nanostripes with high density of states on single-crystalline Al2O3 domain

Self-assembled one-dimensional nanostripes on the single-crystalline Al2O3 domains are found to be the nucleation sites of nanoparticles through an enhanced density of states observed by the scanning tunneling microscopy and spectroscopy. Bias-dependent topographic images and the conductivity spectra indicate that these nanostripes have both enhanced occupied and unoccupied states within the oxide bandgap. These more metallic nanostripes have stronger electronically trapping ability than the oxide domain, which can be used as a one-dimensional electronically self-patterned template for the guided growth of nanostructures.

Spectral properties of plasmonic resonator antennas

A theoretical study of the optical properties of metallic nano-strip antennas is presented. Such strips exhibit retardation-based resonances resulting from the constructive interference of counter propagating short-range surface plasmon-polaritons (SR-SPPs) that reflect from the antenna terminations. A Fabry-P erot model was formulated that successfully predicts both the peak position and spectral shape of their optical resonances. This model requires knowledge of the SR-SPP reflection amplitude and phase pickup upon reflection from the structure terminations. These quantities were first estimated using an intuitive Fresnel reflection model and then calculated exactly using full-field simulations based on the finite-difference frequency-domain (FDFD) method. With only three dimensionless scaling parameters, the Fabry-P erot model provides simple design rules for engineering resonant properties of such plasmonic resonator antennas.

Negative Index Made Easy

MATERIALS SCIENCE The realization of designer materials, or metamaterials, in which the electrical permittivity and magnetic permeability can be made negative simultaneously has generated much interest, primarily due to theoretical proposals for remarkable applications such as perfect lenses and, most recently, the ability to hide, or cloak, objects from electromagnetic radiation. After the initial demonstration in the microwave regime, much of the experimental effort in metamaterial design has focused on pushing the response of these materials toward shorter wavelengths. However, the design of choice, a split ring resonator coupled to a metal wire, is somewhat limited when it comes to size reduction, and other approaches are being pursued. Chettiar et al. propose the use of a simpler structure to achieve negative refraction: a pair of metallic nanostrips separated by a thin dielectric layer, easily fabricated with existing deposition and lithographic technology down to feature sizes in the 10- to 100-nm range. Their simulations show that coupling such pairs of nanostrips to continuous metal films should provide a negative refractive index in the optical and infrared regimes. — ISO Opt. Express 14 , 7872 (2006).

Light-wave guidance through stratified photonic crystal metamaterials synthesized by superinductive layers of metallic nanostrips

The electrodynamic properties of a novel class of photonic-crystal metamaterial platform entirely synthesized by ultralow-refractive-index suspended nanostrips embedded in a dielectric matrix are described and investigated. The optical properties of the homogeneous metamaterial platform can be understood on the basis of equivalent distributed circuit extraction from an electromagnetic model that has negatively distributed superinductive properties. Low propagation loss, temperature-insensitive characteristics, and ultracompact size are the main advantages of the proposed technology, making this new type of metamaterial an excellent candidate for use in compact multilayer nanophotonic integrated systems.