C.K. Lin

Microwave absorbing properties of La0.7Sr0.3MnO3 composites with negative magnetic susceptibility

The complex permittivity and permeability of La0.7Sr0.3MnO3 (LSMO)-epoxy composite absorbers are investigated in the microwave ranges from 2 to 18 GHz by transmission/reflection method. A negative magnetic susceptibility of perovskite oxides has been obtained in the frequency range of 4–18 GHz. By the use of the cavity perturbation technique, the negative magnetic susceptibility for 7.5–14 GHz is reconfirmed. For LSMO-epoxy composite with 80 wtu2009% fillers, the maximum reflection loss can reach 23 dB at 10.5 GHz and the absorbing bandwidth above 10 dB is 1.5 GHz with 2 mm thickness.

Electromagnetic characteristics of surface modified iron nanowires at x-band frequencies

Surface modified iron nanowire nanoparticles were prepared via reduction of iron salts (FeCl3· 6H2O) under an applied magnetic field. To minimize the surface oxidation, dextran (0.05 and 0.25 wt. %) was added during the process and formed a thin passive layer over iron nanowires with alcohol and acetone used to wash iron nanowires. The complex permittivity (ɛ′-jɛ′′) and permeability (μ′-jμ″) of absorbers are measured by a cavity perturbation method from 7 to 14 GHz. In the present study, the iron nanowire prepared with 0.25 wt. % dextran and washed by acetone (D25AC) exhibited the best microwave absorption performance. Depending on the test frequency, D25AC possessed the largest permittivity loss ranged from 0.14 to 0.17 and relatively small permeability loss (<0.05). Its high permittivity dissipation is responsible for the excellent microwave absorption performance where the reflection loss was-7.7 dB at a matching frequency of 9.0 GHz.

Investigations of mechanically alloyed Ni-Zr-Ti-Si amorphous alloys with significant supercooled regions

Abstract This study examined the amorphization behavior of Ni 57 Zr 20 Ti 23− x Si x ( x =0, 1, 3) alloy powders synthesized by mechanical alloying technique. According to the results, after 5 h of milling, the mechanically alloyed powders were amorphous at compositions of Ni 57 Zr 20 Ti 23− x Si x ( x =0, 1, 3). The amorphization behavior of Ni 57 Zr 20 Ti 20 Si 3 was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni 57 Zr 20 Ti 23− x Si x amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a large supercooled liquid region before crystallization. The supercooled liquid regions, defined by the difference between T g and T x , (i.e. Δ T = T g − T x ), are 95 K, 66 K, and 88 K, for Ni 57 Zr 20 Ti 23 , Ni 57 Zr 20 Ti 22 Si 1 , and Ni 57 Zr 20 Ti 20 Si 3 , respectively.

Self-Aligned Deposition Process for Ultrathin Electroless Barriers and Copper Films on Low-k Dielectric Films

A self-aligned, integrated plating technique based on plasma physics and colloidal-related chemistry is proposed to fabricate patterns of ultrathin (≤20 nm) Co-based barriers and copper films in a selective manner on dielectric (HOSP and SiO 2 ) films using electroless plating. High-resolution X-ray absorption spectroscopy, transmission electron microscopy, and atomic force microscopy reveal that, once properly pretreated by a gaseous plasma (O 2 or H 2 /N 2 ) and hydrogen peroxide (H 2 O 2 ) in a basic aqueous solution, the dielectric films can adsorb highly populated metallic (Ni) precipitates of sizes approximately from 2 to 4 nm to catalyze the deposition of electroless Co-based barriers. Finally, the capability of this technique to fabricate self-aligned patterns of barrier and copper is demonstrated and the importance of the plasma pretreatment and hydrogen peroxide (in SC-1 solution) is discussed.

Photocatalytic activity of TiO2 nanoparticle fluid prepared by combined ASNSS

Abstract In this article, low-pressure control methods for a combined arc submerged nanoparticle synthesis system (ASNSS) was proposed and developed for TiO 2 nanoparticle fabrication. The photocatalytic reaction is carried out in a photochemical reactor. The UV light is obtained from UV-lamps with wavelength of (253.7±0.8) nm. The UV-Vis spectrometry is used to monitor the absorbance spectra of methylene blue as a function of illumination time. Experimental results show that the rate constant of photocatalytic reaction of TiO 2 nanoparticles for methylene blue is 0.0365 min −1 . The surface adsorption plays an important role in the decomposition of methylene blue. Experimental results indicate that the TiO 2 nanoparticle fluid possesses excellent photocatalytic activity in photodegradation of methylene blue.

Phase Differentiation and Characterization of Nanostructured Composites by Synchrotron Radiation Techniques

The complexity of nanostructured materials presents challenging difficulties in characterization using conventional techniques. For example, conventional x-ray diffraction may not provide accurate information on the structure (solid solution or phase separation) of nanostructured materials. Complementary advanced characterization methods are often required in the detailed understanding of structures. In this paper we report our work on characterization of two nanostructured systems, namely, AgNi powder and NiCo films, using synchrotron radiation techniques of x-ray diffraction, anomalous x-ray scattering and x-ray absorption spectroscopy.

Synthesis and Characterization of PANI-MWCNTs Supported Nano Hybrid Electrocatalysts

Among new energy systems, fuel cells are electrochemical devices transforming chemical energy directly into electrical energy. In our previous works, MWCNTs (the multi walled carbon nanotubes) supported palladium anodic electrocatalysts for DFAFCs (direct formic acid fuel cells) have been studied. MWCNTs can be modified by appropriate oxides, for example, cerium oxide, zirconium oxide and N-doped titanium dioxide, to enhance the electrocatalytic performance of the catalysts. But the oxides and the defects of the acid oxidized MWCNTs, denoted as AO-MWCNTs, can cause the electron capture and reduce both the catalyst conductivity and the catalysts activity. In order to improve the conductive properties of the support, in the present work a conductive polymer was introduced to modify the surface of carbon nanotubes. PANI (polyaniline) has a long-chain structure and conjugated structure and exhibits good conductivity, high stability, and is non-toxic. After PANI modification, AO-MWCNTs can provide efficient electronic conduction network. In this study, PANI modified AO-MWCNTs were prepared via polymerization process. AO-MWCNTs were homogeneously coated with PANI to obtain composite with weight ratio 50:50 PANI to MWCNTs. The thickness of the PANI layer was 4-9 nm. It was shown that the photosynthesis process is a better method to reduce Pd on PANI/AO-MWCNTs than by using NaBH4. By adjusting pH value to 9, during preparation of Pd/PANI/AO-MWCNTs composites by X-ray irradiation process, smaller Pd particles were obtained and PANI deprotonation was avoided which explains better activity of this composite in formic acid electro oxidation.

Synthesis and Characterization of Nano-hybrid Noble Metals/N doped TiO 2 /MWCNTs Electrocatalysts

Novel metal catalysts are easily poisoned by CO adsorption or leaching in oxidation of formic acid that leads to decrease the performances of catalyst. To increase the catalyst activity and poison tolerance in fuel cells, novel metal nanoparticles are usually supported on modified support materials to enhance its performance. In this study, TiO2/MWCNTs are synthesized by sol-gel method. Also, ammonium is used to dope nitrogen into TiO2 to modify its electrical and chemical property. MWCNTs, TiO2/MWCNTs and N-doped TiO2/MWCNTs are three supporters using in this study to examine the effects of supporters on the electrocatalytic performance of Pd and AuPd catalysts. The synthesized metal nanoparticles are uniformly dispersed on the surfaces of MWCNTs, TiO2 and N-doped TiO2 modified MWCNTs. The electrochemical analysis illustrate that Pd/N-doped TiO2/MWCNTs (molar ratio of NH4OH:TiO2=4:1) catalyst exhibits higher activity and better stability than that of Pd/MWCNTs either/or Pd/TiO2/MWCNTs catalyst in formic acid electrooxidation. Same results are observed in AuPd series of catalyts. It indicates that suitable N-doping TiO2 improves dramatically on the performance of Pd or AuPd-based catalysts in electrochemical reaction. Thus, hybrid AuPd/N-doped TiO2/MWCNTs (molar ratio of NH4OH:TiO2=4:1) materials have potentially to be used in the direct formic acid fuel cells (DFAFCs) in the future. Keywords—Fuel cells, Formic Acid, Pd, AuPd, N-doped TiO2, catalyst, MWCNTs