Metal Wire Grid Research Articles

The Effect of Nanometer Size Effect on the Optical Property of Metallic Wire Grid

We mainly investigated the effect of metallic wire grid on its optical property. At first, we give one simple model to deduce an expression which can describe the relationship of the optical property with the width of metallic wire grid. This expression could be used to calculate the reflectance of the metallic wire grid. We also give the corresponding computer simulation. Our simulation shows that the reflectance would increase when the width of metallic wire grid increase. The wider the metallic wire grid is, the higher the reflectance is. The reflectance would reach the maximum value only when the width is over the free path of electronic.

Flexible Sub-THz Metal Wire Grid Polarizer Based on an EGaIn<formula> <tex>$_{24.5}$</tex> </formula> Alloy

A flexible sub-THz polarizer based on an eutectic Gallium-Indium alloy (EGaIn $_{24.5}$ ) on a vinyl acetate substrate is fabricated and tested. The EGaIn $_{24.5}$ alloy shows low melting point, good wettability, and high conductivity, resulting in a low-cost alternative to conductive inks based on metal nanoparticles. These properties are exploited to draw metal wire grid polarizers by using a technical pen on a bendable sheet of vinyl acetate monomer. Measurements are carried out with a transmission THz-TDS setup in the frequency range from 0.1 to 0.6 THz, showing an extinction ratio up to 20 dB. This approach allows a quick low-tech and cost effective implementation of flexible polarizers in the sub-THz band.

Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarization parallel to the strips into a designed direction and transmit the orthogonal polarization component. Measured radiation patterns show reasonable deflection efficiency and high polarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.

High-resolution LA-ICP-MS trace element mapping of igneous minerals: In search of magma histories

We report experiments on optimisation of LA-ICP-MS mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals. The experimental design was refined with maps on clinopyroxene and amphibole macrocrysts (mainly antecrysts) from a porphyritic lamprophyre in NE Spain, as well as on a high precision metal wire grid. In terms of spatial resolution, we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0.4 and 0.7μm of material, depending on ablation parameters. Maps were produced with square laser beam spots of 12 and 24μm. It was found that complexities can be resolved in the sample even though they are smaller than the beam diameter (e.g., 7–10μm discontinuities using 12μm laser beam). Resolution in x and y was found to be identical, probably reflecting the fast washout of the two-volume ablation cell and the short total dwell time of the analyte menu selected. Due to the excellent stage reproducibility and the limited ablation depth, it is feasible to re-ablate the identical map area many times employing different instrument parameters or analyte menus.On the magmatic crystals, LA-ICP-MS maps define very sharp compositional zoning in trace elements, highlighting complex crystallisation histories where ‘normal’ magmatic fractionation is not the only process. Events of mafic recharge are easily recognised as zones enriched in compatible metals such as Cr, Ni or Sc. Further, trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data. These include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones. Therefore, LA-ICP-MS mapping opens a new window of opportunity for analysis of magmatic histories. The wide combination of instrumental parameters, such as laser beam size, scan speed and repetition rate, make it possible to carry out experiments at different levels of detail. We recommend a two-step approach to mapping. The initial step involves rapid maps to gain an overview of potential complexities in the sample; this enhances representativeness of the analysed materials, as a large number of crystals and trace elements can be tested in little time. Subsequently, detailed maps can be carried out on areas of interest. An additional functionality is to create 1D-profiles from 2D-maps. The potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond.

Broadband tunable liquid crystal terahertz waveplates driven with porous graphene electrodes

AbstractVersatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses.

Rapid gas-chromatographic determination of marking agents added to the industrial plastic explosives in air

Results of the study of the conditions of detection of traces of marking agents added to industrial plastic explosives in air using preconcentration and subsequent analysis on a ECHO-V-IDVS modernized gas chromatograph with a polycapillary column, an ionization detector of a varying selectivity (IDVS), and atmospheric air as a carrier gas are presented. A significant effect of air humidity on the limits of detection for 4-nitrotoluene and 2,3-dimethyl-2,3-dinitrobutane is demonstrated; the highest IDVS sensitivity was observed at the humidity of the carrier gas less than 8.5 mg/m3. For the preconcentration of marking agents, concentrators based on Tenax adsorbent or those produced as metal wire grids coated with a stationary phase are most efficient. The limits of detection for vapors of marking agents in sampling 1 L of air to a concentrator are 22 pg/cm3 for 4-nitrotoluene and 0.1 pg/cm3 for 2,3-dimethyl-2,3-dinitrobutane.

Shielding Effectiveness of Protective Metallic Wire Meshes: EM Modeling and Validation

An effective-layer model is proposed to predict the EM shielding performances of metallic wire grids typically used as protective layers in carbon fiber-reinforced composite laminates for aeronautical applications. The model is valid over a wide frequency range and it takes into account the field penetration through the grating. The shielding performance of the wire grid is estimated by means of the average shielding effectiveness, which represents the response of the material to an incident plane wave having both transverse-magnetic and transverse-electric polarizations. The proposed model is validated by comparison with experimental data, which demonstrates its validity over a wide frequency range, up to 18 GHz.

Tunable nanostructured composite with built-in metallic wire-grid electrode

In this paper, the authors report an experimental demonstration of microwave reflection tuning in carbon nanostructure-based composites by means of an external voltage supplied to the material. DC bias voltages are imparted through a metal wire-grid. The magnitude of the reflection coefficient is measured upon oblique plane-wave incidence. Increasing the bias from 13 to 700 V results in a lowering of ∼20 dB, and a “blueshift” of ∼600 MHz of the material absorption resonance. Observed phenomena are ascribed to a change of the dielectric response of the carbon material. Inherently, the physical role of tunneling between nanofillers (carbon nanotubes) is discussed. Achievements aim at the realization of a tunable absorber. There are similar studies in literature that focus on tunable metamaterials operating at either optical or THz wavelengths.

Polarisation analysing complementary metal‐oxide semiconductor image sensor in 65‐nm standard CMOS technology

In the present study, the authors demonstrate a complementary metal-oxide semiconductor (CMOS) image sensor implemented with on-chip polarisers using 65-nm standard CMOS technology. The polariser is composed of metal wire grids made of metal wires fabricated by the CMOS process. An extinction ratio of 18.8 dB was obtained for a single pixel with an on-chip polariser, where the line/space widths have the finest pitch obtainable by 65-nm technology. Electrical crosstalk between pixels is reduced by over 25% using a guard ring structure. Polarisation imaging by the sensor was also performed.

Image sensor pixel with on-chip high extinction ratio polarizer based on 65-nm standard CMOS technology

In this study, we demonstrate a polarization sensitive pixel for a complementary metal-oxide-semiconductor (CMOS) image sensor based on 65-nm standard CMOS technology. Using such a deep-submicron CMOS technology, it is possible to design fine metal patterns smaller than the wavelengths of visible light by using a metal wire layer. We designed and fabricated a metal wire grid polarizer on a 20 × 20 μm(2) pixel for image sensor. An extinction ratio of 19.7 dB was observed at a wavelength 750 nm.

Biologically Inspired CMOS Image Sensor for Fast Motion and Polarization Detection

A complementary-metal-oxide semiconductor (CMOS) image sensor replicating the perception of vision in insects is presented for machine vision applications. The sensor is equipped with in-pixel analog and digital memories that allow in-pixel binarization in real time. The binary output of the pixel tries to replicate the flickering effect of an insect's eye to detect the smallest possible motion based on the change in state of each pixel. The pixel level optical flow generation reduces the need for digital hardware and simplifies the process of motion detection. A built-in counter counts the changes in states for each row to estimate the direction of the motion. The designed image sensor can also sense polarization information in real time using a metallic wire grid micropolarizer. An extinction ratio of 7.7 is achieved. The 1-D binary optical flow is shown to vary with the polarization angle of the incoming light ray. The image sensor consists of an array of 128 × 128 pixels, occupies an area of 5 × 4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and it is designed and fabricated in a 180-nm CMOS process.

On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths

We have measured, using a custom setup, the emissivity of metallic wire-grids, suitable for polarimeters and interferometers at mm and far infrared wavelengths. We find that the effective emissivity of these devices is of the order of a few %, depending on fabrication technology and aging. We discuss their use in astronomical instruments, with special attention to Martin–Puplett Interferometers in low-background applications, like astronomical observations of the Cosmic Microwave Background.

Selective electroless plating of silver nanograting patterns with no lateral growth for the fabrication of polarizers

Metal patterning has been useful for fabricating many optical and electronic devices. Among all the patterning methods, selective electroless plating in combination with micro-contact printing (μCP) is a simple process compatible with roll-to-roll processing. However, this process suffers from the difficulty to avoid lateral growth during the electroless plating of metal. That will place a limitation on the fabrication of nanoscale patterns, such as the metal wire grid polarizer. In this study, we launch a new approach to restrict the lateral growth of metal by depositing metal selectively in the grooves of a three-dimensional template. The template was first treated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) only on the protrusion surface using μCP, and then treated in SnCl2 solution to activate the surface of the trenches for the selective electroless plating (ELP) of silver inside the trenches. A wire-grid polarizer was thus fabricated by selectively depositing 70nm-thick silver in the trenches of a nanograting template with a trench width of 100nm and a pitch of 180nm. The maximum extinction ratio of the polarizer thus obtained was about 130 in the wavelength range of 635–650nm.

Achromatic polarization splitting effect of metallic gratings with sub-50 nm wide slits

We report on a broadband polarization splitting phenomenon in an aluminum grating with its period much smaller than the wavelength of incident light. Under oblique incidence, grating is highly transparent for one polarization, but it is opaque and reflects the orthogonal polarization. By using the Fourier modal method and planar waveguide theory, we show that, comparing with the traditional metallic wire grid polarizers, the improved confinement of TM0 mode within the sub-50 nm wide grating slits is responsible for this polarization splitting effect.

Continuous phase-shift lithography with a roll-type mask and application to transparent conductor fabrication

We report the development of a near-field optical nanolithography method using a roll-type phase-shift mask. Sub-wavelength resolution is achieved using near-field exposure of photoresist through a cylindrical phase mask, allowing dynamic and high throughput continuous patterning. As an application, we present the fabrication of a transparent electrode in the form of a metallic wire grid by using the roller-based optical lithography method. To fabricate a mesh-type metal pattern, a specific phase-shift mask was designed and critical experimental parameters were also studied. As a result, a transparent conductor with suitable properties was achieved with a recently built cylindrical phase-shift lithography prototype designed to pattern on 100 mm2 of substrate area.

Facile route of flexible wire grid polarizer fabrication by angled-evaporations of aluminum on two sidewalls of an imprinted nanograting

In this study, we report a new method to fabricate a wire grid polarizer (WGP) that greatly relaxes the requirement on patterning and etching, and can be easily applied to produce flexible WGPs. The technique is to pattern a high aspect ratio and narrow linewidth grating by nanoimprint lithography followed by two angled aluminum depositions in opposite directions to produce the narrow spacing between the aluminum lines required for a visible band WGP. Anisotropic reactive ion etching is used to remove the aluminum deposited at the top of the grating but leave the aluminum layer on the grating sidewalls, thereby forming a metal wire grid with much smaller spacings than a lithographically defined grating. As a result, the fabricated WGP showed good performance in a wide range of visible wavelength.

Fabrication and characterization of bilayer metal wire-grid polarizer using nanoimprint lithography on flexible plastic substrate

In this work, we demonstrate the fabrication of bilayer metal wire-grid polarizers and the characterization of their performance. The polarizers with 200 nm period were fabricated on flexible plastic substrates by nanoimprint lithography (NIL), followed by aluminum deposition. Transmission efficiency over 0.51 and extinction ratio higher than 950 can be achieved in the visible range when the aluminum thickness of the polarizer is 100 nm. The fabrication process only involves direct imprinting on flexible plastic substrates and aluminum deposition, without any resist spin-coating, lift-off, and etching processes, which is much simpler, less costly, and applicable to large volume production.

Polarization Analyzing Image Sensor with On-Chip Metal Wire Grid Polarizer in 65-nm Standard Complementary Metal Oxide Semiconductor Process

A polarization analyzing complementary metal oxide semiconductor (CMOS) image sensor with a fine on-chip metal wire grid polarizer in the 65-nm standard process is presented. The extinction ratio is an important characteristic for a polarizer that depends largely on the feature size of the metal wire grid pitch and the fabrication CMOS process. To improve the extinction ratio, we designed and fabricated a sensor chip in the 65-nm process. The design rules of the 65-nm process realize the fine metal wire grid pitch compared with the wavelength of visible light. Improvement of extinction ratio is expected by such a fine structure. With the fabricated sensor, an extinction ratio greater than 40 was achieved. The difference between the measured value and the simulation value of the extinction ratio, and pixel crosstalk of the fabricated sensor are discussed.

Polarization Analyzing Image Sensor with On-Chip Metal Wire Grid Polarizer in 65-nm Standard Complementary Metal Oxide Semiconductor Process

A polarization analyzing complementary metal oxide semiconductor (CMOS) image sensor with a fine on-chip metal wire grid polarizer in the 65-nm standard process is presented. The extinction ratio is an important characteristic for a polarizer that depends largely on the feature size of the metal wire grid pitch and the fabrication CMOS process. To improve the extinction ratio, we designed and fabricated a sensor chip in the 65-nm process. The design rules of the 65-nm process realize the fine metal wire grid pitch compared with the wavelength of visible light. Improvement of extinction ratio is expected by such a fine structure. With the fabricated sensor, an extinction ratio greater than 40 was achieved. The difference between the measured value and the simulation value of the extinction ratio, and pixel crosstalk of the fabricated sensor are discussed.

Direct printing of silver nanoparticles by an agarose stamp on planar and patternedsubstrates

In this study, we have used an agarose stamp to conduct direct printing of silver nanoparticles,nanowires and nanoplates on both planar and structured substrates. Nanoparticle solutioncould be first coated on an agarose stamp, and then transferred to a planar substrate.Micro-patterns comprising metal nanoparticles could be printed on planar substrates withoutthe formation of residual layers. Thus a three-dimensional metal microstructure could beeasily fabricated. The patterning of electrodes by printing Ag nanowires directly onTiO2 was also demonstrated to fabricate resistive random access memory (RRAM) devices byall-solution-processing methods. By using a flat agarose stamp, the patterns printed on themicrostructured substrates were quite different from those on the nanostructuredsubstrates. On the microstructured substrates, direct printing could print silvernanoparticles onto the protrusion surface, and could print silver layers as thickas several microns, useful for high conductivity electrodes. On the substrateswith nanostructures such as photonic crystals or nano-gratings, direct printingcould transfer nanoparticles into the grooves or cavities only due to the contactof the agarose stamp with the groove or concavity surface. A new approach tofabricate metal wire grid polarizers was further demonstrated. A nanoporousagarose stamp has a good potential for printing using nanoparticle suspension.