Nestor J. Zaluzec

Multimetallic Au/FePt3 Nanoparticles as Highly Durable Electrocatalyst

We report the design and synthesis of multimetallic Au/Pt-bimetallic nanoparticles as a highly durable electrocatalyst for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. This system was first studied on well-defined Pt and FePt thin films deposited on a Au(111) surface, which has guided the development of novel synthetic routes toward shape-controlled Au nanoparticles coated with a Pt-bimetallic alloy. It has been demonstrated that these multimetallic Au/FePt(3) nanoparticles possess both the high catalytic activity of Pt-bimetallic alloys and the superior durability of the tailored morphology and composition profile, with mass-activity enhancement of more than 1 order of magnitude over Pt catalysts. The reported synergy between well-defined surfaces and nanoparticle synthesis offers a persuasive approach toward advanced functional nanomaterials.

Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y1Ba2Cu3Ox

Measurements of the transport critical‐current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak‐link regions between high Jc regions. The weak‐link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 A). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.

GridAnt: a client-controllable grid workflow system

Process management is an extremely important concept in both business and scientific communities. Several workflow management tools have been proposed in recent years offering advanced functionality in various domains. In the business world, workflow vendors offer commercial and customized solutions targeting specific users. In the scientific world, several open-source workflow management tools are freely available. However they are directed toward service aggregation rather than distributed process management. Little consideration is given to the needs of the client in terms of mapping the process flow of the client. In the grid community it is essential that the grid users have such a tool available enabling them to orchestrate complex work-flows on the fly without substantial help from the service providers. At the same time it is important that the grid user not be burdened with the intricacies of the workflow system. With the perspective of the grid user in mind, an extensible client-side workflow management system, called GridAnt, has been developed. This paper discusses the design principles, functionality, and application of the proposed GridAnt workflow manager.

Analysis and Provision of QoS for Distributed Grid Applications

Abstract Grid computing provides the infrastructure necessary to access and use distributed resources as part of virtual organizations. When used in this way, Grid computing makes it possible for users to participate in collaborative and distributed applications such as tele-immersion, visualization, and computational simulation. Some of these applications operate in a collaborative mode, requiring data to be stored and delivered in a timely manner. This class of applications must adhere to stringent real-time constraints and Quality-of-Service (QoS) requirements. A QoS management approach is therefore required to orchestrate and guarantee the timely interaction between such applications and services. We discuss the design and a prototype implementation of a QoS system, and demonstrate how we enable Grid applications to become QoS compliant. We validate this approach through a case study of an image processing task derived from a nanoscale structures application.

Single Particle Plasmon Spectroscopy of Silver Nanowires and Gold Nanorods

The excitation of surface plasmons in individual silver nanowires and gold nanorods is investigated by means of high-resolution electron energy loss spectroscopy in a transmission electron microscope. The transverse and longitudinal modes of these nanostructures are resolved, and the size variation of the plasmon peaks is studied. The effect of electromagnetic coupling between closely spaced nanoparticles is also observed. Finally, the relation between energy-loss measurements and optical spectroscopy of nanoparticle plasmon modes is discussed.

Fabrication and characterization of solid-state nanopores using a field emission scanning electron microscope

The fabrication of solid-state nanopores using the electron beam of a transmission electron microscope (TEM) has been reported in the past. Here, we report a similar method to fabricate solid-state nanopores using the electron source of a conventional field-emission scanning electron microscope (FESEM) instead. Micromachining was used to create initial pore diameters between 50nm and 200nm, and controlled pore shrinking to sub 10nm diameters was performed subsequently during in situ processing in the FESEM. Noticeably, different shrinking behavior was observed when using irradiation from the electron source of the FESEM than the TEM. Unlike previous reports of TEM mediated pore shrinkage, the mechanism of pore shrinkage when using the FESEM could be a result of surface defects generated by radiolysis and subsequent motion of silicon atoms to the pore periphery.

In situ studies of ion irradiated zirconolite, pyrochlore and perovskite

The relative radiation resistance of the structures of zirconolite, pyrochlore and perovksite were investigated by in situ transmission electron microscopy using 1.5 MeV Kr+ ions in the HVEM-Tandem User Facility, at Argonne National Laboratory. A suite of six fabricated zirconolites, one fabricated pyrochlore and one natural perovskite was used. Damage accumulation essentially occurs in the same way in all three phases and is revealed by the following changes in SAD patterns: weakening of superlattice Bragg diffraction maxima, appearance of diffuse rings which increase in intensity with dose, disappearance of superlattice or other specific classes of maxima, and disappearance of remaining sublattice maxima leaving only diffuse rings. The average critical doses for amorphisation (Dc) for all the zirconolites (undoped, Nd-doped, U-doped and Th-doped) and the pyrochlore in this study varied by a factor of ∼ 2 (from 3.5 to 6.1 × 1018 ions m−2). No correlations were observed between Dc and the atomic weight of dopants in zirconolite or the mean atomic weight of the sample. The Dc value at room temperature of perovksite was found to be 1.8 × 1019 ions m−2, 3–5 times the Dc values for zirconolite. This observation is in line with what one expects from the topologic and chemical complexity of the two phases and is compared with the results of previous authors. Preliminary assessment was made of EELS as a tool for monitoring radiation damage.

Temperature dependence of ion irradiation damage in the pyrochlores La2Zr2O7 and La2Hf2O7

Synthetic samples of the pyrochlores La2Zr2O7 and La2Hf2O7 were irradiated in situ in the intermediate voltage electron microscope (IVEM-Tandem Facility) at Argonne National Laboratory using 1.0 MeV Kr2+. Results of this study demonstrate that both pyrochlores pass through the crystalline–amorphous transformation albeit with significantly different critical amorphization dose curves. The critical dose values extrapolated to 0 K (Dc0) are 11 ± 3 × 1014 ions cm−2 ( dpa) for La2Zr2O7 and 5.5 ± 0.7 × 1014 ions cm−2 ( dpa) for La2Hf2O7. Non-linear least squares analysis of the dose–temperature curves gave values of the critical temperature (Tc) of 339 ± 49 K for La2Zr2O7 and 563 ± 10 K for La2Hf2O7. This analysis also gave values of the activation energy (Ea) for thermal recovery of damage of 0.02 ± 0.01 and 0.05 ± 0.01 eV for the zirconium pyrochlore and the hafnium pyrochlore, respectively. These results demonstrate that there is a major difference in the dose–temperature response dependent upon the nature of the B-site cation of these two pyrochlores. Results are discussed in terms of the pyrochlore structural parameters rA/rB and x(48f) as well as the stopping powers, displacement energies, and defect energies of the materials.

Measurement of low-order structure factors for silicon from zone-axis CBED patterns

Abstract The ability to acquire digitally collected, energy-filtered electron diffraction patterns has permitted the development of fully quantitative methods of pattern analysis based on fitting theoretical calculations to experimental intensities. We have developed a method of extracting accurate low-order structure factor information from zone-axis CBED patterns using an automated pattern matching technique. The feasibility of such an approach has already been established by fitting to simulated data-sets. Results are now presented from pattern matching calculations using energy-filtered Si [110] zone-axis patterns obtained with a serial EFLS detector attached to a Philips EM420 TEM. Fits to patterns at two different sample thicknesses (measured to be 2761 and 4092 A) are discussed. The results show good agreement with the most accurate Si structure factors obtained from X-ray measurements.

Magnetoresistance of single magnetic vortices

The magnetoresistance in a 1μm Permalloy disk, that develops a vortex state during reversal, has been experimentally measured and modeled. The agreement between measurements and numerical simulations shows that the conventional anisotropic magnetoresistance effect is the main source of magnetoresistance. The results demonstrate that magnetoresistance can be used to determine the chirality of the vortex thereby improving the chances that patterned dot arrays could be used in data storage technology.