We present the potential of ultrathin bilayer metallic nanofilms for use as broadband antireflection coatings in the terahertz frequency range. The metallic layers are modeled using a wave-impedance matching approach. The experimental and theoretical results are in good agreement. Further, a novel method using our broadband antireflection coatings is proposed to eliminate unwanted reflections that interfere with the important reflection from the sample in terahertz reflection measurement. The proposed method significantly improves the calculation of the optical properties of liquid and biological samples.
Single-phase La2(1−x)Co2xO3−δ polycrystalline samples with x=0%–8% were synthesized by the conventional ceramic method, and the effect of Co content on the magnetic behaviors has been systemically investigated. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate no Co metal clusters or secondary magnetic phases in any samples in this study. It is found that the undoped or slightly doped samples show no ferromagnetic signal, while samples with x in the range of 0.5%–2% exhibit an exponential increase of saturation magnetization (Ms) as a function of Co concentration. When x increases beyond 2%, an inverse correlation between the magnetization and Co content was observed. We reported an Ms as large as 0.05emu∕g and a Curie temperature above RT in our samples, rendering Co:La2O3 a candidate diluted magnetic oxide for RT applications. Our results also strongly support the oxygen vacancy (F-center) mediated mechanism for RT ferromagnetism in transition-metal doped high-k oxides
Diluted magnetically doped CeO2 films is an attractive dilute magnetic oxide which would facilitate the practical realization of spintronic devices and may also be used to explore novel magneto-optical applications. In this experiments, 3 at% cobalt-doped CeO2 films with the stoichiometry of Ce0.97Co0.03O2-δ (CCO) were deposited by magnetron sputtering methods on Al2O3 (0001) substrates. The structural, magnetic, and magneto-optical properties were investigated. The results indicate that CCO films with CeO2 (100) orientation can readily be obtained via magnetron sputtering on Al2O3 (0001) substrates. Films are ferromagnetic at room temperature, which is anisotropic with an out-of-plane magnetization easy axis. Magneto-optical measurements exhibit a giant Faraday rotation of about 4800 deg/cm at 650 nm wavelength in out-of-plane direction. The excellent room-temperature ferromagnetism and the giant Faraday rotation in CCO films show highly potential applications in novel magneto-optical devices as well as in spintronics.
M-type barium hexaferrite (BaM) is a promising gyromagnetic material for self-biased microwave\millimeter wave devices because of its large uniaxial magnetocrystalline anisotropy and low microwave loss in high frequency. Due to the limitation of growth conditions, it is difficult to deposit BaM films with enough thickness by PLD, MBE and Magnetron Sputtering for practical application. However, it is demonstrated in present experiment that large area polycrystalline BaM thick films (500μm) with self-biasing (high remanence) and low microwave loss can be successfully fabricated by tape casting. X-ray diffraction and Scanning electron microscopy results indicate that these BaM thick films have highly c-axis oriented crystallographic texture with hexagonal morphology. Magnetic hysteresis loops reveal that samples exhibit excellent properties with a saturate magnetization (4πMs) of 3606G, a high squareness ratio (Mr/Ms) of 0.82. In addition, ferromagnetic resonance (FMR) measurement shows that the FMR linewidth is as small as 431Oe at 48GHz. These parameters ensure these BaM thick films are potentially useful for self-biased microwave\millimeter wave devices such as circulator, phase shifter and filter.
The ferrites (Ni0.2Cu0.2Zn0.6)1.02(Fe2O4)0.98 were prepared by standard solid state method and sintered at different temperatures. The effects of different Bi2O3 additives (0<x<5 wt%) on the phase formation, crystal structure and properties were investigated. The results of thermal analysis (DSC) showed that Bi2O3 played an important role in the process of sintering. The magnetization and the permeability were measured at room temperature, with increasing of Bi2O3 amount, the saturation magnetization had no obvious change and the initial permeability decreased from 291.2 to 197.6. SEM micrographs showed that the average grain size decreased with increasing Bi2O3 contents, but more Bi2O3 (x≥4wt %) additives may resulted in the abnormal grain growth.
CaCu3Ti4O12presents colossal dielectric permittivity within a large temperature and frequency range, which makes it to be a suitable material for technological applications, such as components of capacitive memories and mobile phones. In this investigation, SrTiO3-doped CaCu3Ti4O12ceramics were prepared by solid-state reaction. The influence of doping on the structures, compositions and dielectric properties of the materials were investigated by X-ray diffraction, scanning electron microscopy and dielectric measurements between 40 Hz and 110 MHz. The material presents colossal response (εr~104−105) and the dielectric loss tangent decreased with doping level increase at high frequency. The microstructure analysis showed that the second-phase particles segregated in the doped CaCu3Ti4O12grain edges. Cole-Cole modeling correlated well the effects of this segregation with the relaxation parameters obtained. The extrinsic contributions for the dielectric response were discussed together with the structural and compositional evolution of SrTiO3-doped CaCu3Ti4O12material. The experimental results indicated that SrTiO3doping is a suitable method to optimize the dielectric response and electrical properties of CaCu3Ti4O12for the applications in microelectronic devices.
Phase transitions in stacked GeTe/SnTe and Ge2Se3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using an area detector system and by scanning electron microscopy. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, GeTe phase disappears, followed by the formation of rocksalt-structured GexSn1-xTe solid solution. In Ge2Se3/SnTe stack, the phase transition starts with the separation of SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. The migration of Sn ions and the formation of SnSe are believed to facilitate the crystallization of Ge2Se3 solid solution at ~360°C, which is much lower than the crystallization temperature of Ge2Se3, therefore consuming less power during the phase transition.
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