Field canalization using anisotropic 2D plasmonics

Optical devices capable of suppressing diffraction nature of light are of great technological importance to many nanophotonic applications. One important technique to achieve diffractionless optics is to exploit field canalization effect. However, current technological platforms based on metamaterial structures typically suffer from strict loss-confinement trade-off, or lack dynamic reconfigurability over device operations. Here we report an integrated canalization platform that can alleviate this performance trade-off. It is found that by leveraging material absorption of anisotropic 2D materials, the dispersion of this class of materials can flatten without increasing propagation losses and compromising confinement. The realization of such plasmon canalization can be considered using black phosphorus (BP), where topological transition from elliptic to hyperbolic curves can be induced by dynamically leveraging material absorption of BP. At the transition point, BP film can support long range, deeply subwavelength, near-diffractionless field propagation, exhibiting diffraction angle of 5.5°, propagation distance of 10λspp, and λspp < λ0/300.

Dual-Gratings Imaging Spectrometer

Common dispersive-type spectroscopic instruments include prism-type and grating-type, usually using a single dispersive element. The continuous imaging band is always limited by the dispersion angle. When it is necessary to image two wavebands with an ultra-spectral resolution that are far apart, the imaging is difficult due to the large diffraction angle. To broaden the spectral coverage of the imaging spectrometer, in this paper, we propose a dual-gratings imaging spectrometer with two independently rotating gratings. In this proposed system, two very far apart wavelength bands can be imaged in the adjacent areas by adjusting the angle of the dual gratings. This greatly expands the spectral coverage of the imaging spectrometer. Currently, the only application area considered for this instrument is solar applications. In this article, we present the optical system of the dual-gratings imaging spectrometer, illustrate several advantages of the new structure, and discuss new problems caused by the dual-gratings, which are referred to as overlap between two spectra and double image offset. We deduced the calculation process of the dual grating rotation angle, the relationship between the final acquired image and the slit, the relationship between the angle change between the dual gratings and the double image offset, and the relationship between the MTF upper limit reduction and the spatial frequency. This article also summarizes the shortcomings of this structure and studies the applicable fields under these shortcomings. At last, we simulate a dual-gratings imaging spectrometer system, compare this scheme with two traditional schemes, and conclude that this instrument has certain practical significance.

Structural Analysis of CdO2(1-X) AlX Thin Films Prepared by Pulsed-Laser Deposition

In this study, CdO2 (1-X) AlX thin films were prepared by pulsed-laser deposition. The X-ray diffraction patterns reveal that the films were polycrystalline with a cubic structure, and the composition of the material changed from CdO at the target to CdO2 in the deposited thin films. The intensity of the diffraction peak (or the texture factor) decreases with increasing hkl and has a maximum value for the (111) plane, the interplanar distance and diffraction angle has a high deviation from the standard value for the (111) plane and. This deviation is affected by doping concentration and shows its highest deviation at a doping concentration of 0.1 wt.% for the (111) and (200), and the 0.3 and 0.5 wt.% for the (210) and (220) planes, respectively. The crystalline size take a less value at plane has a high texture factor that is (111) plane and decreases with increase the doping concentration.

An investigation on thermal and chemical behavior of jute/hemp/flax fiber reinforced woven composites and its hybrids

Natural fiber has emerged as a viable alternative to synthetic fibers like glass, carbon, and Kevlar for the development of polymeric composites. Present study focused on Thermo-gravimetric analysis (TGA), Differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FTIR) of the reinforced fibers and developed composites. HR-X-Ray Diffraction of neat epoxy, jute, hemp, and flax fibers was also performed. For TGA, as the temperature increases up to 2500C, thermal degradation of all composites is higher as compared to the neat epoxy. Addition of natural fibers as reinforcement with epoxy matrix affects the transmittance peaks between 1000-1500 cm-1 and 1608-1738 cm-1 in FTIR spectra. The peaks transmittance between 1000-1500 cm-1 represents the chemical compositions of the fibers (hemicellulose, cellulose, lignin, and pectin) which are the necessary part of plant fibers. In X-ray diffraction, two sharp peaks appear at a diffraction angle of 21.40 and 14.80 for jute, hemp, and flax fibers. Peak at a diffraction angle (2Ɵ) of 26.30 represents α-cellulose and 14.260 represents non-cellulose material such as hemicellulose and lignin in fiber.

Effect of Annealing Temperature on Structural and, Morphological Properties of Zno Thins Films

In this work, thins films of zinc oxide were deposited on n-type silicon substrates by chemical electrodeposition. The effect of annealing temperature from 200 ° C to 600 ° C, with a step of 100 ° C, on the structural and morphological properties of ZnO layers has been studied. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and contact angle measurements were used to characterize the morphology and structure of ZnO without and with annealing. The XRD patterns of unannealed ZnO thins films indicate the presence of three intense peaks along (100), (002) and (101) planes, while for the annealed ZnO layers the XRD patterns show also the three major peaks but the intensity of these peaks is increased except for a temperature of 600 ° C where is decreased. The comparison of the XRD patterns of the ZnO layers without and with annealing, reveal a shift in the 2θ diffraction angle, the calculation of the crystallinity confirms the obtained results. The contact angle measurements indicate that the ZnO layers without and with annealing at 200 °C are hydrophobic, the surface of the ZnO layer becomes hydrophilic at annealing temperatures exceeding 300 ° C. Finally, SEM images show the change in structure from a sand rose shape to a granular structure, confirming the XRD and contact angle results.

All-Dielectric Huygens’ Metasurface for Wavefront Manipulation in the Visible Region

All-dielectric Huygens’ metasurfaces have been widely used in wavefront manipulation through multipole interactions. Huygens’ metasurfaces utilize the superposition between an electric dipole and a magnetic dipole resonance to realize transmission enhancement and an accumulated 2π phase change. Benefiting from this unique property, we design and numerically investigate an all-dielectric Huygens’ metasurface exhibiting high-efficiency anomalous refraction. To suppress the substrate effect, the metasurface structure is submerged in a dielectric plate. We strategically placed two elements in four short periods to form a unit cell and adjusted the spacing between the two elements to effectively inhibit the interaction between elements. At the operating wavelength of 692 nm, the obtained anomalous transmission efficiency is over 90.7% with a diffraction angle of 30.84°. The performance of the proposed structure is far superior to most of the existing phase-gradient metasurface structures in the visible region, which paves the way for designing efficient beam deflection devices.

Combining a multi-analyzer stage with a two-dimensional detector for high-resolution powder X-ray diffraction: correcting the angular scale

In a test experiment, a two-dimensional pixel detector was mounted on the nine-channel multi-analyzer stage of the high-resolution powder diffraction beamline ID22 at the ESRF. This detector replaces a bank of scintillation counters that detect the diffracted intensity passing via the analyzer crystals as the diffractometer arm is scanned. At each diffractometer detector arm angle 2Θ, a 2D image is recorded that displays nine distinct regions of interest corresponding to the diffraction signals transmitted by each of the analyzer crystals. Summing pixels from within each region of interest allows the diffracted intensity to be extracted for each channel. X-rays are diffracted from the sample at various angles, 2θ, into Debye–Scherrer cones. Depending on the azimuthal angle around the cone, diffracted photons satisfy the analyzer-crystal Bragg condition at different diffractometer 2Θ values and arrive on the detector at different horizontal (axial) positions. The more the azimuthal angle deviates from diffraction in the vertical plane, the lower the 2Θ angle at which it is transmitted by an analyzer crystal, and the greater the distance of the detecting pixel from the centerline of the detector. This paper illustrates how the axial resolution afforded by the pixel detector can be used to correct the apparent diffraction angle, 2Θ, given by the diffractometer arm to its true diffraction angle, 2θ. This allows a reduction in peak asymmetry at low angle, and even with a relatively small axial acceptance, the correction leads to narrower peaks than if no correction is applied. By varying axial acceptance with diffraction angle, it is possible to optimize angular resolution at low diffraction angles and counting statistics at high angles. In addition, there is an intrinsic peak broadening with increasing azimuthal angle, dependent on the axial beam and detector pixel sizes. This effect reduces with 2θ, as the curvature of the Debye–Scherrer cones decreases. This broadening can be estimated and used to help choose the axial range to include as a function of diffraction angle.

Pengaruh Waktu Milling Terhadap Sifat Desorpsi Material Penyimpan Hidrogen MgH2-Ni Melalui Teknik Mechanical Alloying

Hydrogen is a renewable energy source that can be used as a fuel and as an alternative to fossil fuels. Solid storage media in solid form are safer to use than liquid (-253 oC) or gaseous media (700 bar) media. To store hydrogen in a solid medium, it requires a metal able to interact with hydrogen . Magnesium is one of the metals which can form metal hybrids based on MgH2 which is capable of absorbing hydrogen up to (7.6wt%). However, the reaction kinetics for magnesium are very slow, it takes at least 60 minutes to absorb hydrogen and the operating temperature is always very high (300 oC). Several attempts have been made to add the catalytic converter and milling time. Hydrogen storage material based on MgH2 with a 10wt%Ni catalyst was successfully synthesized using a mechanical alloy technique with time variations of 2 hours, 5 hours, and 10 hours. From the results of the X-ray diffraction schema at a diffraction angle of 2θ=37.87o, it shows the presence of a MgH2 phase, Ni phase is at a diffraction angle of 61.85o, the diffraction peak also shows that there was a widening of the diffraction peak with increasing milling time, this explains that there was a reduction in the size of the crystal. When calculating with the Schereer method, the crystal size of the material reaches 10 nm. The results of the DSC test indicated a decrease in temperature of 383 oC in 41 minutes with a milling time of 10 hours.

Structural and Optical Properties of BiFeO3 via Polymer-Assisted Hydrothermal Synthesis under Different Weight of Chitosan

In this work, single phase Bismuth Ferrite, BiFeO3 was successfully synthesized by using hydrothermal method assisted with different weight (0.24 g, 0.36 g and 0.48 g) of Chitosan. Potassium hydroxide (KOH) were used as a mineralizer during the synthesis process for the precipitation. The samples were characterized for different properties such as structural and optical properties, and were then compared with previous works. The X-ray diffraction data for all the samples showed that the samples had a single phase belonging to R3c space group with perovskite rhombohedral structure at diffraction angle 32.0° to 32.5° even though the slight presence of secondary phase at diffraction angle 28° was detected. Scanning electron microscope revealed a decrement in particle size as the weight of Chitosan increased indicating effective used of Chitosan in controlling the agglomeration of the particles. All samples BiFeO3 assisted with and without Chitosan showed significant enhancement in energy gap where the obtained results showed a small energy gap values ranging from ~1.22 eV to ~1.88 eV determined from UV-vis absorbance characterization. Therefore, by the addition of Chitosan, the properties of BiFeO3 such as structural and optical have changed as well as preventing from the particle to agglomerate.

Light-Driven Pitch Tuning of Self-Assembled Hierarchical Gratings

Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning is accomplished in hierarchical gratings formed in a molecular switch doped CLC. We fabricate a checkerboard hierarchical CLC grating for a demonstration, whose pitch is optically tuned from 4.6 µm to 10.7 µm. Correspondingly, the first-order diffraction angle continuously changes from 9.4° to 4.8° and a significant polarization selectivity is also observed. In addition, hierarchical CLC gratings with triangular wave pattern, Archimedean spiral, and radial stripes are also demonstrated. This work creates new opportunities for soft-matter-based intelligent functional materials and advanced photonic devices.