Chien Yie Tsay

Microwave absorbing properties of iron nanowire at x-band frequencies

Iron nanowires and nanoparticles are fabricated via the reduction of iron salts (FeCl3•6H2O) with or without a parallel magnetic field, respectively. Polyvinyl pyrrolidone was added during the reduction process and formed a thin passive layer to minimize the oxidation. The as-obtained iron nanomaterials were then used as magnetic fillers, added to an epoxy resin, and iron nanoparticle or nanowire composites were prepared. The complex permittivity (ɛu2009–u2009jɛ) and permeability (μu2009–u2009jμ) of these composites are measured by a cavity perturbation method from 7 to 14 GHz. The iron nanowire composites exhibited superior microwaving absorbing properties compared to iron nanoparticle composites. The optimal absorption peak of iron nanowire composites reached −10.5 dB (>90% power absorption) and −15.5 dB (>97% power absorption) with a thickness of 2 and 3 mm, respectively.

Magnetoelectric behavior of carbonyl iron mixed Mn oxide-coated ferrite nanoparticles

The dielectric and magnetic properties of manganese oxide-coated Fe3O4 nanoparticles (NPs) were measured by the cavity perturbation method at x-band microwave frequencies ranging from 7–12.5 GHz with controlled external magnetic field up to 2.2 kOe at room temperature. Different ratios (5%, 10%, and 20% by weight) of coated NPs were prepared by sol-gel method then mixed with carbonyl iron powder in epoxy matrix. The saturation magnetization is inversely proportional to the NPs ratio in the mixture between 150 and 180 emu/g. The real part of the permittivity decreased with increasing NPs concentration, but the permittivity change by magnetic field increased. The tunability behavior is explained by insulator-ferromagnetic interface magnetoelectricity and the large surface volume ratio for the NPs.

Performance of low resistivity electrode prepared by electroless plated for amorphous silicon thin-film transistors

The TFTs array fabrication process for large-area TFT-LCD has been continuously developed for simplifying processing steps, improving performance and reducing cost in the process of mass production. In this study, the hydrogenated amorphous silicon (a-Si:H) TFTs with low resistivity electrodes , silver thin films, were prepared by using the selective deposition method that combined lift-off and electroless plated processes. This developed process can direct pattern the electrode of transistor devices without the etching process and provide ease processing steps. The as-deposited Ag films were annealed at 200 oC for 10 minutes under N2 atmosphere. The results shows that the adhesion properties can be enhanced and the resistivity has been improved from 6.0 μ,-cm, significantly decrease by 35%, of as-deposited Ag films by annealed. The thickness of Ag thin film is about 100 nm and the r. m. s roughness value is 1.54 nm. The a-Si:H TFT with Ag thin films as source and drain electrodes had a field effect mobility of 0.18 cm2/Vs, a threshold voltage of 2.65 V, and an on/off ratio of 3×104.

Preparation of Spray Pyrolyzed Bismuth Oxide and its Application in Inhibition of Ultraviolet from Light-Emitting Diode (LED)

In the present study, bismuth oxide (Bi2O3) powders were prepared from bismuth nitrate at various temperatures by spray pyrolysis (SP). The Bi2O3 powder can convert from a monoclinic α phase to a tetragonal β phase at a pyrolysis temperature of > 600° C. The crystallinity of the SP powder increased with the increase of pyrolysis temperature. The resulting SP powders were then mixed with organics and screen-printed onto the surface of LED for the evaluation of ultraviolet (UV) inhibition. The β-type bismuth oxide powder pyrolyzed at 700°C exhibited a fine crystal structure. This caused the efficiency of UV inhibition to be 97.71% when the powder concentration was as low as 9.04 wt%.

Electromagnetic Characteristics of Iron-Based Microwave Absorbing Materials

Nowadays human are exposed to an environment filling with electromagnetic waves over a wide frequency range. The electromagnetic properties of microwave absorbing materials plays an important role in the performance of civilian electromagnetic interference (EMI) shielding at low frequency range and military stealth technology at high frequency one. The electromagnetic properties include complex permittivity and permeability and its combination determines the electromagnetic wave absorption ability of a material. Complex permittivity and permeability can be measured by three different methods, i.e., free-space method, coaxial/waveguide method, and resonant cavity perturbation method. The first one requires a large space, expensive equipment, and not suitable for academic usage. In the present study, using coaxial/waveguide and resonant cavity perturbation methods, electromagnetic characteristics of iron-based microwave absorbing materials will be obtained and its microwave absorption performance will be investigated. In addition, a comparison between the measurements by these two methods will be addressed.

Characterization and Modification of Nanocrystalline Iron Oxide Powders Prepared by an Inert Gas Condensation Technique

Nanocrystalline iron oxide powders were prepared by an inert gas condensation technique under various oxygen partial pressures. The as-prepared nanocrystalline iron oxide powders were further modified by electroless nickel plating. The as-prepared and modified nanocrystalline powders were characterized by X-ray diffraction, transmission electron microscopy, and synchrotron X-ray absorption techniques. In addition, magnetic properties of the iron oxide nanoparticles before and after electroless nickel plating were evaluated by vibrating sample magnetometer. The experimental results show that the as-prepared nanocrystalline iron oxide powders exhibited a mixture of iron and γ-Fe2O3 phases. TEM observations revealed that oxidation started from the surface of the gas-condensed iron nanoparticles. The amount of iron oxide increased with increasing oxygen partial pressure and was confirmed by synchrotron x-ray absorption examination. A decrease in saturated magnetization and coercivity of the nanocrystalline iron oxide powders was observed after electroless nickel plating.