The formation of uranyl peroxide phases was identified as a corrosion product of spent fuel by Hanson et al [1]. The subsequent analysis of this phase showed that metastudtite retained 241Am, 237Np and 239Pu [2]. In this study, the retention of radionuclide Pu4+ and An3+, released from the spent fuel matrix into studtite structure, has been evaluated by the precipitation of studtite from uranyl dissolution with variable concentrations of REE (Th, Nd, Sm and Eu). Three different precipitation conditions parameters were studied: media of synthesis, time of synthesis and REE concentration. Synthesized phases were characterized by XRD and the cell parameter was calculated. The REE incorporation was determined by ICP-MS analysis. The results showed that studtite could incorporate 63% of Th in solution during its precipitation. Changes in the “a” cell parameter were identified. The results suggest that studtite coprecipitated with REE could play a role as a limiting for the REE mobility.

III-V compound multi-junction solar cells have high efficiency potential of more than 50% due to wide photo response, while limiting efficiencies of single-junction solar cells are 31-32%. In order to realize high efficiency III-V compound multi-junction solar cells, understanding and controlling imperfections (defects) are very important. This paper reviews fundamentals of defects and defect management for III-V compound materials, single-junction, multi-junction, space and concentrator solar cells.

Colloids with anisotropic shape and properties can enable the assembly of advanced materials otherwise not attainable by microfabrication. In this study, we present a convenient method using common microfabrication tools to generate a diverse array of non-spherical microparticles with well-defined shapes, sizes, electromagnetic properties for self-assembly applications. Projection photolithography onto SU-8 photoresist enabled the production of large aspect ratio microparticles such as cubes, cuboids, cylinders, hexagonal prisms, and parallelepipeds. We characterized these particles to confirm their anisotropic shape and size monodispersity. Fluorescent stains (e.g., Nile red) were mixed into the photoresist prepolymer to enhance the visualization of particle orientation. Particles designed for passive self-assembly were prepared by conventional photolithographic techniques. Particles designed for active assembly were then decorated with metallic patches in precise locations along the surface (e.g., top, side or multiple sides) using electron beam metal evaporation. This metal deposition process can enable orientational control of particles during their assembly in directed fields. After fabrication, large particles (e.g., 1,000 µm3) were released from the substrate via gentle sheer forces, whereas small particles (e.g., 10 µm3) were released by the dissolution of a sacrificial layer underneath the SU-8. Suspending the particles in water with surfactant (or other suitable solvents) provided amenable conditions for their assembly in static or dynamic systems. These conventional methods have the potential to catalyze new research in the fabrication and assembly of anisotropic patchy particles with controllable properties for the hierarchical development of self-assembled micromirrors, biosensors, and photonic crystals as examples.

Carbon nanotube field effect transistors (CNT FETs) have many possible applications in future nano-electronics due to their excellent electrical properties. However, one of the major challenges regarding their performance is the noticeable gate hysteresis which is often displayed in their transfer characteristics. The hysteresis phenomenon is often attributed to water-mediated charge transfer between the CNT and the dielectric layer or the CNT and the water layer itself. In this study, we implement three different experimental techniques and provide evidence that the hysteresis phenomenon of suspended CNT FETs, as well as of on-surface CNT FETs which operate at low gate voltage regimes (| Vg | < 3V), is based on gate-induced, water-assisted redistribution of mobile charge on the SiO2 surface, and it is not related to charge injection from the CNT itself. Two techniques are based on the current measurements through the CNT and the third utilizes electrostatic force microscopy (EFM) setup. In addition, the applied external gate voltage affect the relaxation time of the current. This change arises from the modification of the amount of water layers which adsorb onto the dielectric surface, which caused by dielectrophoresis attraction between the water molecules and the substrate. It is found that the relaxation time, and hence the surface conductivity, are very sensitive for the first few layers, and saturates above three monolayers of water molecules.

The US Department of Energy’s (DOE) Fuel Cell Technologies Office has made significant progress in fuel cell technology advancement and cost reduction. Encouragingly, rollouts of fuel-cell vehicles by major automotive manufacturers are scheduled over the next several years. With these rollouts, enabling technologies for the widespread production of affordable renewable hydrogen becomes increasingly important. Near-term utilization of current reforming and electrolytic processes is necessary for early hydrogen markets, but transitioning to industrial-scale renewable hydrogen production remains essential to the longer term. Central to the long term vision is a portfolio of renewable hydrogen conversion processes, including, for example, the direct photoelectrochemical and thermochemical routes, as well as photo-assisted electrochemical routes. DOE utilizes technoeconomic analyses to assess the long-term viability of these emerging hydrogen production pathways and to help identify key materials- and system-level cost drivers. Sensitivity analysis from the technoeconomic studies will be discussed in connection with the metrics and fundamental materials properties that have direct impact on hydrogen cost. It is clear that innovations in macro-, meso- and nano-scale materials are all needed for pushing forward the state-of-the-art. These innovations, along with specific research and development pathways for advancing materials systems for the renewable hydrogen conversion technologies are discussed.

Preparation and characterization of a Simulated Spent Nuclear Fuel (SIMFuel), which replicates the chemical state and microstructure of Spent Nuclear Fuel (SNF) discharged from UK Advanced Gas-cooled Reactor (AGR) after a cooling time of 100 years is described. Thirteen stable elements were added to depleted UO2 and sintered to simulate the composition of fuel pellets after burn-ups of 25 and 43 GWd/tU and, as a reference, pure UO2 pellets were also investigated. The fission product distribution was calculated using the Fispin code provided by NNL. SIMFuel pellets exhibit a microstructure up to 92% TD. During the sintering process in H2 atmosphere Mo-Ru-Rh-Pd metallic precipitates and grey-phase ((Ba, Sr)(Zr, RE)O3 oxide precipitates) formed within the UO2 matrix. These secondary phases are present in real PWR and AGR SNF, although they are smaller in size than those examined in this study. The grain size of the produced SIMFuel is in good agreement with literature references.

We use Raman scattering to study the spatially-resolved strain and stress in a complex zinc blende GaAs/GaP heterostructured nanowire which contains both axial and radial interfaces. The nanowires are grown by metal-organic chemical vapor deposition in the [111] direction with Au nano particles as catalysts, High spatial resolution Raman scans along the nanowires show the GaAs/GaP interface is clearly identifiable. We interpret the phonon energy shifts in each material as one approaches the interface.

The integrated sorption and diffusion (ISD) model has been developed to quantify radionuclide transport in compacted bentonite. The current ISD model, based on averaged pore aperture and the Gouy-Chapman electric double layer (EDL) theory can quantitatively account for diffusion of monovalent cations and anions under a wide range of conditions (e.g., salinity, bentonite density). To improve the applicability of the current ISD model for multivalent ions and complex species, the excluded volume effect and the dielectric saturation effect were incorporated into the current model, and the modified Poisson-Boltzmann equations were numerically solved. These modified models had little effect on the calculation of effective diffusivity of Sr2+/Cs+/I−. On the other hand, the model, modified considering the effective electric charge of hydrated ions, calculated using the Gibbs free energy of hydration, agreed well with the diffusion data including those of Sr2+.

Two adjacent fuel rod segments were irradiated in a pressurized water reactor achieving an average burn-up of 50.4 GWd/tHM. A physico-chemical characterisation of the high burn-up fuel rod segments was performed, to determine properties relevant to the stability of the spent nuclear fuel under final disposal conditions. No damage of the cladding was observed by means of visual examination and γ-scanning. The maximal oxide layer thickness was 45 µm. The relative fission gas release was determined to be (8.35 ± 0.66) %. Finally, a rim thickness of 83.7 µm and a rim porosity of about 20% were derived from characterisation of the cladded pellets.

Developing advanced ionic electroactive devices such as ionic actuators and supercapacitors requires the understanding of charge drifting and diffusion processes, which depends on the distances over which the ions travel. The charge dynamics of Aquivion membrane actuators with EMI-Tf ionic liquid are investigated over a broad film thickness (d) range. A time domain charge dynamic method based on Poisson-Nernst-Planck relation is employed to evaluate the charge transport behaviors in the actuators. It is found that for the initial charging process the double layer time τDL is linearly proportional to the film thickness (d). However, for the later charging process under a high applied voltage (>0.5V ) where the substantial electromechanical reaction occurs, the charge transport behavior does not follow the d2 dependence as predicted by the random walk diffusion model. For comparison the charge dynamics of BMI-PF6 ionic liquid films without polymer was also investigated.

Lightweight porous foams have been of particular interest in recent years, since they have a very unique set of properties which can be significantly different from their solid parent materials. These properties arise from their random porous structure which is generated through specialized processing techniques. Their unique structure gives these materials interesting properties which allow them to be used in diverse applications. In particular, highly porous Al foams have been used in aircraft components and sound insulation; however due to the difficulty in processing and the random nature of the foams, they are not well understood and thus have not yet been utilized to their full potential. The objective of this study was to integrate experiments and simulations to determine whether a relationship exists between the relative density (porous density/bulk density) and the mechanical properties of open-cell Al foams. Compression experiments were performed using an Instron Universal Testing Machine (IUTM) on ERG Duocel open-cell Al foams with 5.8% relative density, with compressive loads ranging from 0-6 MPa. Foam models were generated using a combination of an open source code, Voro++, and MATLAB. A Finite Element Method (FEM)-based software, COMSOL Multiphysics 4.3, was used to simulate the mechanical behavior of Al foam structures under compressive loads ranging from 0-2 MPa. From these simulated structures, the maximum von Mises stress, volumetric strain, and other properties were calculated. These simulation results were compared against data from compression experiments. CES EduPack software, a materials design program, was also used to estimate the mechanical properties of open-cell foams for values not available experimentally, and for comparison purposes. This program allowed for accurate prediction of the mechanical properties for a given percent density foam, and also provided a baseline for the Al foam samples tested via the IUTM method. Predicted results from CES EduPack indicate that a 5.8% relative density foam will have a Young’s Modulus of 0.02-0.92 GPa while its compressive strength will be 0.34-3.37 MPa. Overall results revealed a relationship between pores per inch and selected mechanical properties of Al foams. The methods developed in this study can be used to efficiently generate open-cell foam models, and to combine experiments and simulations to calculate structure-property relationships and predict yielding and failure, which may help in the pursuit of simulation-based design of metallic foams. This study can help to improve the current methods of characterizing foams and porous materials, and enhance knowledge about theirproperties for novel applications.

Stress Corrosion Cracking (SCC) has been detected in Boiling Water Reactors (BWRs) on core shrouds and primary water re-circulation piping made of low carbon stainless steels. Material hardening strongly affects SCC propagation behavior, and SCC growth rates increase with increasing hardness of austenitic stainless steels caused by cold work or neutron irradiation.

Research work has been conducted in the authors’ laboratories with the aim of improving SCC resistance using chemical composition control of stainless steels. It has been previously reported that high stacking fault energy (SFE) materials showed better SCC resistance than low SFE materials due to hardening being suppressed in high SFE materials. In the present study, SCC growth rate (CGR) tests were performed using 15% cold worked Types 316L and 25Cr-20Ni stainless steels in a simulated BWR water environment. The 25Cr-20Ni stainless steel used has high SFE value due to chemical composition control and measured SCC growth rates were lower than those of low SFE stainless steels.

However, oxidation behavior is one of the more important factors influencing SCC of austenitic stainless steels in addition to material hardening behavior, and the influence of the chemical composition control necessary to increase SFE on oxidation behavior in BWR primary coolants is still unclear. In this study, therefore, immersion tests using Types 316L and 25Cr-20Ni stainless steel specimens were also conducted in the simulated BWR water environment. The surface oxide films on the specimens were then analyzed with micro-Raman spectroscopy and glow discharge optical emission spectroscopy in order to help clarify the oxidation behavior.

The results of these tests and analyses showed that the NiFe2O4 content of the outer oxide layers on the high SFE stainless steels was higher than that on the low SFE stainless steels. The inner oxide film on the 25Cr-20Ni stainless steel also had a high chromium content.

Based on the above results, SCC resistance and oxidation behavior of high SFE austenitic stainless steels in a simulated BWR water environment will be discussed.

Experiments on the dissolution kinetics of natural pyrrhotite (FeS1-x-) and pyrite (FeS2) under imposed redox conditions to evaluate the oxygen uptake capacity of both minerals were carried out at 25°C and 1 bar. Experimental data indicate that in both cases, Fe(II) released from dissolution of these Fe-bearing sulphides is kinetically oxidized to Fe(III) to precipitate as Fe(III)-oxyhydroxides. While the system is pH controlled by the extent of the sulphide oxidation, Eh is controlled by the redox pair Fe2+/Fe(III)-oxyhydroxides. Pyrrhotite dissolution is faster than that of pyrite but generates less acidity. Consequently, the achieved redox value is more reducing. Experimental data show that the oxidation rates of both minerals (in mol·g-1·s-1) are equivalent under the studied conditions. This fact gives a new opportunity to quantify the reductive buffering capacity of pyrrhotite, for which no kinetic rate law has been still established.

Mesoporous Fe3O4 nanoparticles coated with ZnO nanocrystals were successfully synthesized by a simple solution method at low temperature. The transmission electron microscopy analysis indicates that the mesoporous Fe3O4 nanoparticles are monodispersed with a mean diameter of 160 nm and the thickness of ZnO layer is 15 nm approximately. The porosity of the products was further substantiated by the nitrogen (N2) sorption measurement. The N2 adsorption-desorption isotherm curve can be identified as type IV, which is a characteristic of mesopores. Electromagnetic (EM) wave absorption properties of the as-prepared Fe3O4@ZnO mesoporous spheres-wax composites were investigated at a room temperature in the frequency range of 0.5∼18 GHz. Interestingly, the Fe3O4@ZnO mesoporous spheres exhibit an enhanced EM wave absorption due to the mesoporous structure. The multiple absorbing mechanisms result from the interface polarization induced by the special core/shell and mesoporous structures as well as dipole polarization of both Fe3O4 and ZnO. The results demonstrate that the Fe3O4@ZnO mesoporous spheres are attractive candidates for a new kind of EM wave absorption materials with wide absorption frequency band.

A charge-injection GeTe/Sb2Te3 superlattice phase change memory (PCM or PRAM) has been developed as a candidate for a non-volatile memory that replaces NAND flash memory. It differs from PRAM with the conventional material of GeSbTe, and is therefore named “TRAM (topological switching random access memory)”. First principle calculations showed a resistance change in the GeTe/Sb2Te3 superlattice was enhanced by charge injection. The fabrication and analyses of a one-resistor TEG revealed that the superlattice structure was maintained after 1M endurance, which proved the occurrence of non-melting resistance change in TRAM. The reset current of TRAM was found to be less than 1/5 of that of conventional PRAM. Furthermore, TRAM enables a set -speed of 10 ns and reset -operation by DC-sweep to be achieved, which experimentally proved the atomic movement in TRAM can be enhanced by charge injection.

We successfully fabricated semiconductor microspheres of ZnO, ZnSe, etc., by laser ablation in superfluid helium and investigated their morphology and optical properties. Time-resolved photoluminescence spectroscopy in ultraviolet region of single ZnO microspheres shows luminescence spectra with mode structures and remarkable reduction of the luminescence decay time compared to that of polycrystals or non-spherical microparticles. This indicates strong light-matter interaction due to efficient light-confinement in the ZnO microspheres. In addition, the fabricated ZnSe microspheres also show the photoluminescence spectra with typical mode structures indicating their high sphericity.

The semiconductor cuprous oxide crystallizes in a simple cubic structure and reveals outstanding characteristics: Independent of the method and conditions of the synthesis of crystalline Cu2O its Raman spectra are dominated by infrared active, silent, and defect modes rather than by Raman allowed phonon modes only. A detailed group theoretical analysis demonstrates that point defects reduce the local symmetry, lift the Raman selection rules, and thus diminish the distinction between Raman allowed and Raman forbidden lattice vibrations. Of all intrinsic defects only the presence of the copper vacancy in the so called split configuration introduces possible Raman activity for all Cu2O extended phonon modes observed in experiment.

Using first-principles full-field electromagnetic simulations, we demonstrate that near-perfect above-band-gap solar absorption can be achieved in nanostructured, ultra-thin-film iron oxide photoanodes for photoelectrochemical (PEC) water splitting. In our designed core-shell nanocone structures, all regions of hematite (α-iron oxide) are away from the interface between hematite and water by a minimum distance of less than the hole diffusion length in hematite, which is assumed to be no greater than 20nm. The optical absorption in our structure corresponds to a photocurrent density of 12.5mA/cm2 if one assumes an air mass 1.5 solar spectrum and a unity absorbed photon-to-current efficiency (APCE) for all wavelengths in that spectrum. Our photon management strategy eliminates the trade-off between optical absorption and carrier collection as commonly found in conventional designs of PEC cells, and variants of the strategy are generally applicable to other material systems.

The influence of annealing ambient conditions and deposited passivation materials on indium-gallium-zinc-oxide (IGZO) thin-film transistor (TFT) performance is investigated. Results from annealing experiments confirm that a nominal exposure to oxidizing ambient conditions is required, which is a function of temperature, time and gas environment. Nitrogen anneal with a controlled air ramp-down provided the best performance devices with a mobility (µsat) of 11-13 cm2/V·s and subthreshold slope (SS) of 135-200 mV/dec, with some hysteresis. Plasma-deposited passivation materials including sputtered quartz and PECVD SiO2 demonstrated a significant increase in material conductivity, which was not significantly reversible by an oxidizing ambient anneal. E-beam evaporated Al2O3 passivated devices that were annealed in air at 400 °C demonstrated improved stability over time and suppressed hysteresis in comparison to unpassivated devices. Devices which were passivated with B-staged bisbenzocyclobutene-based (BCB) resins and annealed in air at 250 °C also exhibited suppressed hysteresis.