Structure analysis and magnetic properties of nano-sized Nb(x)Ni(y)Zn1-x-yFe2O4 powders formed by combustion synthesis and mechanical milling

Nano-sized Nb(x)Ni(y)Zn1-x-yFe2O4 ferrites with average particle size of less than 100 nm were prepared by using self-propagating high-temperature synthesis and mechanical ball milling. Average ferrites size of the SHS products were less than about 100 nm after 20 minutes mechanical milling. The average combustion temperatures and the combustion propagating rates were in the ranges of 1145 to 1543 K and 4.1 to 7.2 mm/s, respectively. Rietveld refinement of the pattern converged to good agreement (chi2 = 4.87). Final product of SHS was Nb0.13Ni0.41Zn0.46Fe2O4 with Fd3m structure and the lattice parameter of 0.83623 nm. Maximum magnetization (Ms), residual magnetization (Mr), coercive force (iHc) and susceptibility of the Nb0.013Ni0.41Zn0.46Fe2O4 ferrites formed at the oxygen pressure of 0.25 MPa were 12.30 Wb/m2 Kg, 1.57 Wb/m2 Kg, 6321 A/m, and 0.02 m3/Kg, respectively. Niobium addition to nickel-zinc ferrites resulted in increasing Ms, Mr and iMc about 59%, 78% and 387%, respectively. Neutron diffractometry revealed that the variation of magnetic properties was related to non-stoichiometric number and oxygen position of the niobium-nickel-zinc ferrites due to the competitive reduction reaction among niobium, nickel and zinc oxides.     

Restoring electrical conductivity of dielectrophoretically assembled graphite oxide sheets by thermal and chemical reduction techniques

Thin layers of graphite oxide sheets were dispersed in dimethylformamide and dielectrophoretically assembled onto predefined and opposing metal electrodes. The dielectrophoretic method resulted in the deposition of multiple layers of graphite oxide. After drying, the deposits were then reduced by thermal or chemical methods. Raman spectroscopy and electrical transport measurements revealed that the thermal reduction technique was more effective in restoring electrical conductivity than the chemical reduction method.     

Effects of working pressure on morphology,structural, electrical and optical properties of a-InGaZnO thin films

Amorphous In–Ga–Zn–O (a-IGZO) thin films (～200 nm thickness) were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates at various working pressures (0.67–2.67 Pa) and a fixed oxygen-to-argon gas-flow ratio (O₂/Ar = 5%). The transparency of all of the films was more than 85% in the visible range. With increased working pressure, the surface morphology of the films, as observed under atomic force microscopy (AFM), became rough; the optical band gap, estimated by Tauc plot, increased, and the mobility and carrier concentrations, according to Hall measurement, decreased and increased, respectively. The resistivity of the films initially decreased (up to 2.00 Pa working pressure) and then increased (at 2.67 Pa). It is suggested that the electrical property changes were affected by the role of the oxygen vacancies, whether as effective donors or as scattering centers.     

Information-based connection algorithm for supporting QoS in nested mobility network

A multihop mobile wireless network can be a collection of wireless mobile nodes forming a temporary network without the aid of any established infrastructure or centralized administration. Mobile nodes communicate with each other using multihop wireless links. Each mobile node in the network also acts as a router, which forwards data packets to other nodes. A main challenge in the design of this mobile network is the development of dynamic routing protocols that can efficiently find routes between two communicating nodes that often change the network topology drastically and unpredictably. All communications between the nodes inside the mobile network and the global Internet must be maintained, although the mobile router (MR) connecting the other mobile network to the global Internet must change their address; and mobile nodes suffer from end-to-end delay and handoff delay. That is to say, hereafter the packets sailing for the mobile node would not be routed directly for the destination, but will always make a detour by way of HA to the target node. In this paper, we suggest Information-based Connection Algorithm that adds keyword management method in order to resolve such a problem, simulations are carried out with NS-2 for performance evaluation. The results of the simulations show an improvement on throughput and handoff delay, and consequently the QoS improvement.

Biogenic formation and growth of uraninite (UO₂)

Biogenic UO? (uraninite) nanocrystals may be formed as a product of a microbial reduction process in uranium-enriched environments near the Earth's surface. We investigated the size, nanometer-scale structure, and aggregation state of UO? formed by iron-reducing bacterium, Shewanella putrefaciens CN32, from a uranium-rich solution. Characterization of biogenic UO? precipitates by high-resolution transmission electron microscopy (HRTEM) revealed that the UO? nanoparticles formed were highly aggregated by organic polymers. Nearly all of the nanocrystals were networked in more or less 100 nm diameter spherical aggregates that displayed some concentric UO? accumulation with heterogeneity. Interestingly, pure UO? nanocrystals were piled on one another at several positions via UO?-UO? interactions, which seem to be intimately related to a specific step in the process of growing large single crystals. In the process, calcium that was easily complexed with aqueous uranium(VI) appeared not to be combined with bioreduced uranium(IV), probably due to its lower binding energy. However, when phosphate was added to the system, calcium was found to be easily associated with uranium(IV), forming a new uranium phase, ningyoite. These results will extend the limited knowledge of microbial uraniferous mineralization and may provide new insights into the fate of aqueous uranium complexes.     

Broad-band light source using mutually injected Fabry-Pe/spl acute/rot laser diodes for WDM-PON

We propose and demonstrate a new broad-band light source (BLS) for a wavelength division multiplexing-passive optical network (WDM-PON) based on the wavelength locked Fabry-Pe/spl acute/rot laser diodes (F-P LDs). By mutual injection between two antireflection-coated F-P LDs, we realized a broad-band light with a low relative intensity noise. By using the proposed BLS for wavelength locking of the F-P LD, we achieve color-free operation of the optical network termination with Manchester coded data. We also demonstrate a WDM-PON based on the proposed BLS.     

Effects of catalytic surface layer on Zr-based alloy getters for hydrogen absorption

Hydrogen sorption characteristics of Zr-based alloy getters fabricated in the forms of bulk were investigated. Non-evaporable getters (NEGs) have been widely used in vacuum devices, but thermal activation process at high temperature and high vacuum environment is inevitably required for efficient sorption rate. In order to solve this problem and improve sorption kinetics, we developed and characterized Ni-coated NEGs. Ni-coated NEGs show good gettering performance and fast sorption kinetics without any activation process, compared to conventional Zr-based NEGs. It is mainly caused by the catalytic effect of surface Ni layer. Surface Ni plays an important role as a catalyst that enables hydrogen to dissociate on surface more easily and also as a protection layer against oxidation. Consequently, Ni-coated NEGs can be easily applicable to vacuum devices because those need not go through the activation process and show fast hydrogen sorption kinetics.     

Effects of centerline macrosegregation on necking of P-added extra low carbon steel sheet

Effects of centerline macrosegregation on necking was examined by the stretching experiment for cold rolled P-added extra low carbon steel sheets. The centerline macrosegregated zone containing high concentration of Mn and P was elongated in the rolling process. The elongated macrosegregated zone induced instability in the strain state when the sheet was stretched, thus resulted in the waved sheet surface. The formability of cold rolled steel sheet was deteriorated due to the wave formed by the macrosegregation. The waved surface was thought to be caused by the higher hardness in the macrosegregated zone compared to the segregation free zone. The experiments on the stretching of sheet including macrosegregation showed that the macrosegregation was the important source of instability in that of the cold rolled steel sheets. A 3D FEM analysis was carried out for the quantitative evaluation of waved surface. It was confirmed that the main source of the waved surface was the macrosegregation. Stretching in the transverse direction under the plane strain condition made the cold rolled steel sheet more inhomogeneous than stretching in any other strain condition. The thickness difference in the stretched sheet was linearly increased when the ratio of hardness in the macrosegregated zone to that of the segregation free zone was increased. The macrosegregation formed in the internal crack close to the surface was more harmful to the formability in the cold rolled steel sheet than the centerline macrosegregation.     

Alteration for a diffusion barrier design concept in future high-density dynamic and ferroelectric random access memory devices

The barrier properties and failure mechanisms for many diffusion barriers in high-density volatile and non-volatile capacitors were reviewed. Based on failure mechanisms of these barriers reported by others, we suggested the new design concept for a diffusion barrier and developed the new Ta+CeO₂ and Ta+RuO₂ barriers. Although both barriers were shown to exhibit good diffusion barrier properties, however, oxide-incorporated barriers result in the surface oxidation of the under-layer during deposition and/or post-thermal budgets, resulting in the degradation of capacitor performance. The design concept for a diffusion barrier should be changed to sacrificial oxygen diffusion barrier concept, and both the RuTiN and the RuTiO films, as new sacrificial oxygen diffusion barriers, were proposed. New RuTiN and RuTiO barriers showed the higher oxidation resistance and cell capacitance and the lower contact resistance up to high temperatures. Therefore, the design concept of a sacrificial diffusion barrier should be emphasized to achieve high-density dynamic and ferroelectric random access memory devices.     

Plasmon Enhanced Direct Bandgap Emissions in Cu7S4@Au2S@Au Nanorings

Nanostructured copper sulfides, promising earth‐abundant p‐type semiconductors, have found applications in a wide range of fields due to their versatility, tunable low bandgap, and environmental sustainability. The synthesis of hexagonal Cu₇S₄@Au₂S@Au nanorings exhibiting plasmon enhanced emissions at the direct bandgap is reported. The synthesized Cu₇S₄@Au₂S@Au nanorings show greatly enhanced absorption and emission by local plasmons compared to pure copper sulfide nanoparticles.