Electronic structure and energetics of tetragonal SrCuO 2 and its high-pressure superstructure phase

First-principles calculations have been used to investigate the electronic structure and energetics of the simple tetragonal SrCuO 2 ( P 4/ m m m ) and its high-pressure tetragonal superstructure ( P 4/ m m m ). Based on the calculations, the high-pressure phase is metastable as compared with the low pressure tetragonal phase, with an energy difference of 0.13 eV per SrCuO 2 formula unit. The energy barrier to the transition from the superstructure to the simple tetragonal structure is 0.24 eV at 7 GPa; thus, high temperatures are required to synthesize the latter. Among the possible structural configurations resulting from the partially occupied oxygen site in the superstructure phase, the most stable structure has a space group ##IMG## [http://ej.iop.org/images/0953-8984/23/46/465503/cm401032ieqn3.gif] {$P\bar {4}m 2$} , reduced from that of the simple tetragonal structure P 4/ m m m . The detailed analysis of the electronic band structures of the simple tetragonal and superstructure phases suggests that the out-of-plane buckling of the O atoms in the superstructure leads to significant decrease in the O p–Cu d orbital overlap, allowing the energy of the system to be lowered, which is necessary for the structural stability. An understanding of the electronic structure and energetics of the high-pressure superstructure phase and its relation to the simple tetragonal phase provides a basis for exploring the physical properties of the infinite layer, high- T C superconductor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90783/1/0953-8984_23_46_465503.pd

Direct evidence of N aggregation and diffusion in Au+Au+ irradiated GaN

A surface amorphized layer and a buried disordered structure were created in gallium nitride (GaN) irradiated using 1.0 MeV1.0MeV Au+Au+ ions to fluences of 25 and 70 Au+/nm270Au+∕nm2 at room temperature. Bubbles of N2N2 gas within both the amorphized and disordered GaN are formed. A gradient profile with a lower N concentration in the amorphized region is observed, which provides direct evidence of N loss by diffusion in the Au+Au+ irradiated GaN. These results are important to understanding the amorphization processes in GaN and may have significant implications for the design and fabrication of GaN-based devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87811/2/021903_1.pd

Simultaneous formation of surface ripples and metallic nanodots induced by phase decomposition and focused ion beam patterning

We report the simultaneous formation of self-assembled surface ripples in Cd2Nb2O7Cd2Nb2O7 pyrochlore caused by focused ion beam (FIB) patterning and uniformly distributed metallic nanodots induced by phase decomposition under ion bombardment. The characteristic wavelength of the surface ripples is controllable from the nm to the sub-μmsub-μm scale. High-density Cd metallic nanoparticles, ∼ 5 nm∼5nm, formed and the distribution of nanoparticles is consistent with the morphological characteristics of the ripple pattern. This approach provides a means of fabricating surface nanostructure with various patterns and a controllable particle size and distribution by combining ion beam-induced phase decomposition with high-precision FIB patterning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87787/2/093112_1.pd

Critical success factors and risk mitigation strategy for new product development

”Success in new product development (NPD) offers a competitive and comparative advantage in the marketplace. A primary objective in an NPD project is to launch world class products with minimal risk. To deliver the superior quality and performance customers require, a company must develop the right NPD structure and framework for seamless execution by the NPD project teams throughout the product lifecycle. Companies must understand how to identify and mitigate risk to enable the success of their NPD projects. The costs to develop new products are often a considerable portion of an organization’s budget; however, studies have shown only 60 percent of new products making it to the market are commercially successful. Therefore, NPD project teams need to have a risk mitigation strategy, methodology, or framework to help with the identification and mitigation of risks in the product development process. This research conducted a systematic literature review to document the current research in the development of a risk mitigation framework tied to critical success factors (CSFs) that can be applied in the NPD process. The purpose of this research was to 1) determine the top CSFs that enable successful NPD through a worldwide multi-industry survey and 2) develop an NPD framework to mitigate risk. The survey responses were analyzed using the Kruskal-Wallis non-parametric statistical analysis to determine statistical differences in the CSFs based on rank. The top CSFs were then grouped to provide a conceptual highlevel view for managers to consider when developing or continuously improving their NPD execution structure, methods, and processes. An NPD framework was proposed based on the CSFs in order to mitigate risk”--Abstract, page iv

Materials science - Displaced by radiation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62871/1/445161a.pd

Luminescent hydroxylapatite nanoparticles by surface functionalization

Hydroxylapatite (HA) nanoparticles were functionalized by depositing rare-earth-doped Y2O3Y2O3 nanoparticles on the surface, and the structural evolutions of both HA and Y2O3Y2O3 phases at different annealing temperatures were investigated by x-ray diffraction and transmission electron microscopy. Laser spectroscopy indicated that the surface functionalized HA nanoparticles exhibited strong visible emissions. No visible emissions were observed from rare-earth-doped Y2O3Y2O3 without any substrate, suggesting a doping-induced environmental change of optically active rare-earth elements in the functionalized HA nanoparticles. The luminescent hydroxylapatite nanoparticles may find important applications as a biodegradable substrate for biomarking and drug delivery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87791/2/183106_1.pd

Chemical corrosion of highly radioactive borosilicate nuclear waste glass under simulated repository conditions

This review summarizes the results of the joint Japanese (Central Research Institute of Electric Power Industry, CRIEPI, Tokyo), Swiss (National Cooperative for the Storage of Radioactive Waste, NAGRA, Baden), Swedish (Swedish Nuclear Fuel and Waste Management Company, SKB, Stockholm) international ‘JSS' project on the determination of the chemical durability of the French nuclear waste borosilicate glass, which was completed in 1988. Radioactive and nonradioactive glass specimens were investigated. A data base was created with results from glass corrosion tests performed with different water compositions, pH values, temperatures, sample surface areas (S), solution volumes (V), and flow rates. Glass corrosion tests were performed with and without bentonite and/or steel corrosion products present. Variation of the glass composition was taken into account by including the borosilicate glass ‘MW' in the investigations, formulated by British Nuclear Fuels, plc. An understanding was achieved of the glass corrosion process in general, and of the performance of the French glass under various potential disposal conditions in particular. A special effort was made to establish a corrosion data base, using high S/V ratios in the experiments in order to understand the glass durability in the long ter

Plasma deposition of thin carbonfluorine films on aligned carbon nanotube

The thin film of carbonfluorine was deposited on the surfaces of aligned carbon nanotubes using a plasma polymerization treatment. High-resolution transmission electron microscopy images revealed that a thin film of the polymer layer (20 nm)(20nm) was uniformly deposited on the surfaces of the aligned carbon nanotubes. Time-of-flight secondary ion mass spectroscopy and Fourier transform infrared experiments identified the carbonfluorine thin films on the carbon nanotubes. The plasma deposition mechanism is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87850/2/043107_1.pd

Caesium-rich micro-particles: A window into the meltdown events at the Fukushima Daiichi Nuclear Power Plant

The nuclear disaster at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011 caused partial meltdowns of three reactors. During the meltdowns, a type of condensed particle, a caesium-rich micro-particle (CsMP), formed inside the reactors via unknown processes. Here we report the chemical and physical processes of CsMP formation inside the reactors during the meltdowns based on atomic-resolution electron microscopy of CsMPs discovered near the FDNPP. All of the CsMPs (with sizes of 2.0–3.4 μm) comprise SiO2 glass matrices and ~10-nm-sized Zn–Fe-oxide nanoparticles associated with a wide range of Cs concentrations (1.1–19 wt% Cs as Cs2O). Trace amounts of U are also associated with the Zn–Fe oxides. The nano-texture in the CsMPs records multiple reaction-process steps during meltdown in the severe FDNPP accident: Melted fuel (molten core)-concrete interactions (MCCIs), incorporating various airborne fission product nanoparticles, including CsOH and CsCl, proceeded via SiO2 condensation over aggregates of Zn-Fe oxide nanoparticles originating from the failure of the reactor pressure vessels. Still, CsMPs provide a mechanism by which volatile and low-volatility radionuclides such as U can reach the environment and should be considered in the migration model of Cs and radionuclides in the current environment surrounding the FDNPP