High Q Resonant Graphene Absorber with Lossless Phase Change Material Sb2S3

Graphene absorbers have attracted lots of interest in recent years. They provide huge potential for applications such as photodetectors, modulators, and thermal emitters. In this letter, we design a high-quality (Q) factor resonant graphene absorber based on the phase change material Sb2S3. In the proposed structure, a refractive index grating is formed at the subwavelength scale due to the periodical distributions of amorphous and crystalline states, and the structure is intrinsically flat. The numerical simulation shows that nearly 100% absorption can be achieved at the wavelength of 1550 nm, and the Q factor is more than hundreds due to the loss-less value of Sb2S3 in the near-infrared region. The absorption spectra can be engineered by changing the crystallization fraction of the Sb2S3 as well as by varying the duty cycle of the grating, which can be employed not only to switch the resonant wavelength but also to achieve resonances with higher Q factors. This provides a promising method for realizing integrated graphene optoelectronic devices with the desired functionalities.

Tunable Thermal Camouflage Based on GST Plasmonic Metamaterial

Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge2Sb2Te5 (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3–5 μm.

Effect of Gradual Substitution of CaO by SrO in Glass-Ceramic Materials of the System SiO2 - Al2O3 - CaF2 - RO (R = Ca, Mg, Sr)

ABSTRACTThe density, Vickers microhardness and crystallization fraction of glass-ceramic materials synthesized from parent glasses are determined in which CaO is gradually substituted by SrO. The chemical composition (in mol.%) of the parent glasses is 54SiO2-(23-X)CaO-12MgO-5Al2O3-6CaF2-XSrO, where X is the employed CaO substitution level (X = 0, 3, 6 and 9 mol.%, with X = 0 corresponding to the reference material). In order to determine the type of crystallization occurring in the glass-ceramic samples, as well as the crystalline phases formed in them, these are characterized by both Scanning Electron Microscopy (SEM/EDS) and X-Ray Diffraction (XRD). Independently of the CaO substitution level employed, the glass-ceramics show the formation of a solid solution corresponding to diopside-type pyroxene, with chemical formula Ca(Mg,Al)(Al,Si)2O6, as a single crystalline phase. The synthesized glass-ceramic materials with the reference composition show the highest Vickers microhardness and crystallization fraction, as well as the lowest density.

Effect of Nano-Crystallization on the Mechanical Properties of the (Zr53Cu30Ni9Al8)99.5Si0.5 Bulk Metallic Glass

The (Zr53Cu30Ni9Al8)99.5Si0.5 bulk metallic glass (BMG) rods, 3 mm in diameter, with different crystallization fraction for compression test were prepared by isothermal annealing the as-cast BMG rods at the temperature in the middle of supercooled temperature region for different time period in vacuum, respectively. The result of compression test revealed that the fracture strength of these samples increases with the crystallization ratio at the beginning, then decreases rapidly at 40 vol.% crystallization fraction. In addition, the best mechanical performance with 1970MPa yield strength and 3 % plastic strain occurs at the sample with 30 vol.% nanocrystalline phase (with an average size about 50 nm). This was suggested these homogeneous distributed nanocrystals which embedded in the matrix may act as obstacles to branch the primary shear band into multiple shear band and result in improving the ductility.

Pressure-induced nanocrystallization of Zr55Al10Ni5Cu30 bulk metallic glass

The effect of pressure on the crystallization behavior of Zr55Al10Ni5Cu30 bulk metallic glass was investigated by differential scanning calorimetry, x-ray diffraction, and transmission electron microscopy. Although the crystallization products under high pressure were about the same as those under ambient pressure, the evident changes in the relative crystallization fraction of each phase were observed. The applied pressure enhanced the crystallization temperature. Pressure annealing of the bulk metallic glass produced a composite with dispersion of very fine nanocrystallites in the amorphous matrix. A full nanocrystallization was obtained for the sample annealed under 5 GPa at 793 K. The mechanism for the pressure-induced nanocrystallization is discussed.

Quantitative Crystallization and Nano-Grain Size Distribution Studies of a Fecunbsib Nanocrystalline Alloy

ABSTRACTSuperior soft magnetic properties of nanocrystalline two-phase FeCuNbSiB alloy can only be attainable from a suitably nano-crystallized structure in the amorphous matrix. In this study a thermal-cycling-annealing process was adopted to anneal the amorphous specimens. The crystallization fraction of Fe73.5Cu1Nb3Si13 5B9 ribbons after different annealing was quantitatively measured by a DTA method through the integrated crystallization enthalpy from annealed samples versus that of as-cast amorphous specimen. The crystallization fraction was estimated to be 70 % as the specimen was annealed for 550°C×7.63 ks, the optimal annealing condition. Using this method, the crystallization quantity of the crystallized FeCuNbSiB amorphous alloy was accurately estimated and controlled during nano-crystallization processes.Abstact:The nanostructure of the annealed flake were investigated by high resolution TEM. The population of grain size is dominant in the range of 3-9 and 3-11 nm, corresponding to isothermal annealing at 520 and 550 °C, respectively, for 910 s. The average grain size associated with the above two annealing conditions is estimated to be 7 and 8.5 nm, respectively. The portion of nanocrystals with grain size smaller than 10 nm is about 80 % for the annealing at 520°C×910 s and 72 % for the annealing at 550°C×910 s, respectively. However, there is only one α-Fe(Si) phase evidenced in the TEM diffraction patterns.