Nickel Gratings Research Articles

Quantitative Ultrafast Magnetoacoustics at Magnetic Metasurfaces.

Femtosecond (fs) time-resolved magneto-optics is applied to investigate laser-excited ultrafast dynamics of one-dimensional nickel gratings on fused silica and silicon substrates for a wide range of periodicities Λ = 400-1500 nm. Multiple surface acoustic modes with frequencies up to a few tens of GHz are generated. Nanoscale acoustic wavelengths Λ/n have been identified as nth-spatial harmonics of Rayleigh surface acoustic wave (SAW) and surface skimming longitudinal wave (SSLW), with acoustic frequencies and lifetimes being in agreement with theoretical calculations. Resonant magnetoelastic excitation of the ferromagnetic resonance (FMR) by SAW's third spatial harmonic, and, most interestingly fingerprints of the parametric resonance at 1/2 SAW frequency have been observed. Numerical solutions of Landau-Lifshitz-Gilbert (LLG) equation magnetoelastically driven by complex polychromatic acoustic fields quantitatively reproduce all resonances at once. Thus, our results provide a solid experimental and theoretical base for a quantitative understanding of ultrafast fs-laser-driven magnetoacoustics and tailoring the magnetic-grating-based metasurfaces at the nanoscale.

Solar thermal absorber based on dielectric filled two-dimensional nickel grating

In this paper, a solar thermal absorber based on a dielectric filled two-dimensional nickel grating is designed and numerically investigated for wide-angle and polarization-independent broadband absorption. The absorption of the proposed two-dimensional meta-surface absorber reaches nearly 100% in the whole visible region (400-800 nm). The physical mechanisms responsible for the high absorption including the impedance matching with the free space, the cavity resonances and the surface plasmonic resonances have been elucidated in detail. The strong resonances effectively trap the incident light in the nano-cavities and then dissipate it by the ohmic losses of the metal, giving rise to the high absorption of the proposed absorber. The meta-surface absorber may find applications in solar cells, photovoltaics, thermos-photovoltaics, thermal emitters, plasmonic sensors, and solar-energy harvesting.

Analysis of Absorptive Nickel Grating with a Dielectric Layer

Background: Nickel grating absorber has been studied and shows good absorption property in the visible band. In order to further improve the absorption performance, reflection should be reduced, and anti-reflection layer should be added upon or under the gratings. Method: In this paper, the dielectric layer is added between and upon the nickel gratings. Equivalent medium theory is used to analyze the role of dielectric layer on absorption mechanism of nickel gratings. photoresist is used to illustrate the possible practical usage of the proposed method. Results: Absorption efficiency of TM (transverse magnetic) and TE (transverse electric) polarization show growing trend with the increase of refractive index of the dielectric material. PMMA and TU7 are chosen as the dielectric material. The simulation results show that TM absorption reduced slightly in visible band, and improved by up to 86% in the near infrared region. TE absorption shows up to 79% improvement in the whole visible to near infrared waveband. Conclusion: Nickel grating based broadband absorber is analyzed in this paper. Dielectric layer is added upon the gratings, and act as the anti-reflection layer. The refractive index and layer thickness is analyzed by using equivalent medium theory. Dielectric material that has high refractive index is more desired. The designed nickel grating shows high absorption property from 450nm to 800nm for both TM and TE polarization.

Design of One-dimensional Nickel Grating Based Broadband Absorber

Background: Electromagnetic wave absorbers that has near perfect performance have been studied since 2008, various one dimensional and two dimensional structures have been optimized. High absorption at certain frequency can be easily realized. However, high absorption that covers broad band is relatively hard to realized. Method: In this paper, a nickel nanograting is designed by using rigorous coupled wave analysis theory. The effect of grating height and grating width on absorption performance is analyzed physically by using equivalent medium theory and Fabry-Pérot resonate theory. Results: Because of the intrinsic absorption character and the influence of F-P resonance, TM absorption shows periodically increase with the increasing of metal thickness. Absorption of the TE polarization slightly increases with the increasing of grating height. Peak absorption of TM polarization light can be gotten when DC of 0.52 is chosen, however, absorption performance of TE polarization light degrades seriously. In this paper, DC of 0.19 is chosen. Conclusion: A one dimensional nickel grating based broadband absorber is analyzed in this paper. The proposed absorber has good absorption performance over the visible band, and shows no clear degradation over a wide incident angle (-40° to 40°).

Wavelength-Selective Solar Thermal Absorber With Two-Dimensional Nickel Gratings

The direct utilization of solar radiation has been considered a promising energy source because of its abundance, sustainability, and cleanness. The conversion of solar radiation into usable heat largely depends on the absorption characteristics of a solar thermal collector. In the present study, we conducted design analysis of a wavelength-selective absorber composed of a two-dimensional Nickel grating, a thin SiO2 film, and a Nickel substrate. Dimensions of the two-dimensional grating were determined with the Taguchi method, which optimized the spectral absorptance for both polarizations. The spectral absorptance demonstrated a broad-band plateau within the visible and the near-infrared spectral region, but it was significantly suppressed at longer wavelengths. Moreover, the absorptance plateau was nearly insensitive to the incident orientation of solar radiation. Physical mechanisms of the absorption enhancement were elucidated with the local magnetic field distribution.

Study of moiré grating fabrication on metal samples using nanoimprint lithography

A moiré grating is a basic optical component used in various moiré methods for deformation measurement. In this study, nanoimprint lithography (NIL) was proposed to produce high frequency moiré gratings on metal samples. A new type of NIL mold and a hot embossing system were developed to overcome the poor flatness and roughness of metal samples. This three-layer mold based on nickel grating was unbreakable, and the self-developed hot embossing system used a bellows cylinder to satisfy the parallelism requirement of grating fabrication on metal samples. In order to generate high quality moiré patterns, the grating profile of the mold was optimized. Then, 1200-3000 lines/mm frequency gratings were successfully fabricated on the different materials such as SiO2, aluminum and stainless steel. In order to evaluate the quality of the replication, the distortion in the fabricated SiO2 grating was analyzed by an inverse moiré method. As an application, the replicated grating on the aluminum sample in combination with the moiré interferometry was used to measure the tensile deformation of the sample. The successful experimental results demonstrate the feasibility and reliability of nanoimprint lithography to produce gratings on metal samples.

Polarized thermal radiation by layer-by-layer metallic emitters with sub-wavelength grating

Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 mum, as well as high emissivity up to 0.65 at a wavelength of 3.7 microm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by the gratings and the intensified electric-field is only observed for the polarizations perpendicular to the top sub-wavelength grating. This result suggests how the emissivity of a metal can be selectively enhanced at a certain range of wavelengths for a given polarization.

Shear horizontal wave transduction in plates by magnetostrictive gratings

Shear horizontal waves are very useful in nondestructive evaluation applications because of their non-dispersive property. The objective of this research is to investigate frequency-tuned shear horizontal wave transduction in plates by using magnetostrictive nickel gratings. Since wireless energy conversion between magnetic energy and acoustic energy in magnetostrictive material can take place, the generation and measurement of waves by the magnetostrictive principle have recently received much attention. In this work, a grating-type magnetostrictive transducer was considered for SH wave transduction; waves can be effectively tuned at desired frequencies by changing grating size and distance. The present experiments showed that the bias field strength and grating width should be selected appropriately to avoid generating unwanted wave modes such as the S0-Lamb wave modes. It is also confirmed from experiments that the grating distance controls the center (or tuning) frequency of the grating transducer.

SU-8 plating mold for high-aspect-ratio nickel zone plates

Nickel zone plates are fabricated by electrodeposition into a mold with high aspect ratio and narrow line width. This process requires high-mechanical stability of the mold to avoid pattern collapse in the plating bath. In the present paper we demonstrate how SU-8 can be used as plating mold material in a tri-layer resist to fabricate 35-nm half-pitch nickel gratings with an aspect ratio exceeding 11:1. To attain sufficient stability of the mold the SU-8 was cured by e-beam exposure with a dose of 25 mC/cm 2 at 5-keV electron energy.

Wireless frequency-tuned generation and measurement of torsional waves using magnetostrictive nickel gratings in cylinders

The objective of this work is to experimentally investigate the possibility of using a magnetostrictive nickel grating for frequency-tuned wireless generation/measurement of elastic torsional waves in a non-ferromagnetic aluminum cylinder. In doing so, the effects of the grating size and distance on the frequency-tuning characteristics are studied. Although the employed transduction principle is the magnetostrictive principle used in the existing surface acoustic wave devices which are magnetostrictively transduced, the magnetostrictive nickel grating in our transducer configuration served not as electrical conductors but as deforming elements. The transduction frequency was controlled by the grating distance and the wireless wave generation/measurement was carried out employing solenoid coils encircling a nickel-grated cylinder. In addition, two small permanent magnets were installed to adjust the wave propagation direction.

Plasmon emission studies on nano-scale particulate recording materials

The optical field emitted by radiatively decaying plasmons is studied for the case when the surface supporting the plasma excitations is that of a ferromagnetic metal rather than that of one of the commonly studied noble metals. Comparison is made between the phenomenon observed for plasmons travelling freely on a continuous conducting surface and those localized around nano-scale particles on an insulating substrate or embedded in a dielectric host. In the first case, structure mediated optical excitation on a nickel grating produces plasmons that travel away from their source becoming subject to a variety of decay mechanisms including radiative emission. Similarly, localized plasmons created in a cobalt longitudinal recording medium composed of particles having near mono-disperse magnetic volumes ≈7 × 10−25 m3 are likewise observed to re-emit optical radiation in a narrow beam at high non-specular angles consistent with radiative plasmon decay. Moreover, the plasmon mode structure supported by the particles, and which is reflected in the angular structure of the emitted radiation, appears indicative of the physical shape of the particles. The possible significance of plasmon behaviour in the development of ultra-high density recording media is highlighted.