Aloe vera plant-extracted solution hydrothermal synthesis and magnetic properties of magnetite (Fe3O4) nanoparticles

Magnetite (Fe₃O₄) nanoparticles have been successfully synthesized by a novel hydrothermal method using ferric acetylacetonate (Fe(C₅H₈O₂)₃) and aloe vera plant-extracted solution. The influences of different reaction temperatures and times on the structure and magnetic properties of the synthesized Fe₃O₄ nanoparticles were investigated. The synthesized nanoparticles are crystalline and have particle sizes of ～6–30 nm, as revealed by transmission electron microscopy (TEM). The results of X-ray diffraction (XRD), High resolution TEM (HRTEM) and selected area electron diffraction (SAED) indicate that the synthesized Fe₃O₄ nanoparticles have the inverse cubic spinel structure without the presence of any other phase impurities. The hysteresis loops of the Fe₃O₄ nanoparticles at room temperature show superparamagnetic behavior and the saturation magnetization of the Fe₃O₄ samples increases with increasing reaction temperature and time.     

Synthesis and optical properties of nanocrystalline ZnO powders prepared by a direct thermal decomposition route

This paper reports the synthesis and optical properties of nanocrystalline ZnO powders with crystallite sizes of 32.5 (±1.4)–43.4 (±0.4) nm prepared by a direct thermal decomposition of zinc acetate at the temperatures of 400, 500, 600, and 700°C for 4 h. The structure of the prepared samples was studied by XRD and FTIR spectroscopy, confirming the formation of wurtzite structure. The morphology of the samples revealed by SEM was affected by the thermal decomposition temperature, causing the formations of both nanoparticles and nanorods with different size and shape in the samples. The synthesized powders exhibited the UV absorption below 400 nm (3.10 eV) with a well defined absorption peak at around 285 nm (4.35 eV). The estimated direct bandgaps were obtained to be 3.19, 3.16, 3.14, and 3.13 eV for the ZnO samples thermally decomposed at 400, 500, 600, and 700°C, respectively. All the samples exhibited room-temperature photoluminescence (PL) showing a strong UV emission band at ∼395 nm (3.14 eV), a weak blue band at ∼420 nm (2.95 eV), a blue–green band at ∼485 nm (2.56 eV), and a very weak green band at ∼529 nm (2.35 eV). The mechanisms responsible for photoluminescence of the samples are discussed.     

Mu-near-zero metasurface for microstrip-fed slot antennas

A mu-near-zero metasurface as a superstrate consisting of a periodically square closed ring is proposed for gain and bandwidth enhancement of microstrip-fed slot antennas (MFSAs). The metasurface exhibits near-zero permeability (0<μ<1) and negative reflection phase. For a unidirectional radiation pattern, the metasurface above the MFSA is employed to reduce the back-lobe radiation (180^°) and enhance the gain at 0^° without a metallic reflector. Interestingly, if additional metasurfaces are placed on both sides of the MFSA, a low-profile, high-gain and wide-band bidirectional antenna can be obtained. The results indicate that the metasurface can also enhance the radiation characteristics, impedance bandwidth and efficiency. Both simulation and measurement of the proposed antennas with metasurface show a fractional bandwidth of 25 % and the overall thicknesses of λ ₀/12 and λ ₀/6 of uni- and bidirectional antennas, respectively.