The age of nuclear power originated with the gas-cooled, graphite-moderated reactor in the 1940s. Although this reactor design had intrinsic safety features and enjoyed initial widespread use, gas-cooled reactor technology was supplanted by higher power density water-cooled systems in the 1960s. However, the next-generation reactors seek enhanced power conversion efficiency and the ability to produce hydrogen, best accomplished with high-temperature gas-cooled systems. Thus, international interest in gas-cooled reactor systems is reemerging. Although the materials systems of these reactors are fairly simple, the reactor environment, particularly its high temperatures and intense irradiation, present extreme challenges in terms of material selection and survivability. This article provides a brief review of materials issues and recent progress related to graphite and ceramic materials for application in gas-cooled nuclear reactor environments. Of particular interest are the drastic, irradiation-induced microstructural evolution and thermophysical property changes occurring as a result of energetic neutron irradiation, which significantly impact the performance and lifetime of much of the reactor core. For “nuclear” graphite, the performance and lifetime not only are closely related to the irradiation environment but also are dramatically affected by the specifics of the particular graphite: manufacturing process, graphitization temperature, composition (amount of coke, filler, etc., depending on where it was mined), and so on. Moreover, the extreme environmental challenges set down by this next generation of fission nuclear plants have driven the development and application of ceramic composites for critical components, pushing beyond upper temperature limits set by metallic alloys used in previous generations of nuclear reactors. The composite material systems of particular interest are continuous carbon-fiber composites and newly developed radiation-resistant silicon carbide fiber composites.

Single phase delafossite p-type CuFeO2 (CFO) semiconductor was synthesized in bulk by modified solid state reaction technique. X-ray diffraction (XRD) and X-ray photo spectroscopy (XPS) studies suggest single phase CFO at room temperature. The energy dispersive X-ray spectroscopy (EDX) revealed that the atomic ratio of Cu and Fe is 1:1. The XPS spectra showed two intense Cu 2p3/2 and 2p1/2 peaks at 932.5 eV and 952 eV suggesting Cu is in +1 state. The temperature dependent Raman spectra of CFO displayed two intense modes at 349 cm-1 and 690 cm-1 at room temperature that matched with other delaffosite structures. The temperature dependent Raman spectra showed significant shift in both Raman active modes to lower frequency side. We observed the disappearance of pure CFO Raman active modes above 750 K and the appearance of new peaks related to CuO compounds, indicating disintegration of CFO starting above 750 K which almost completed above 1100 K. The temperature dependent thermo-gravimetric analysis indicates change in CFO mass above 750 K with wide range of differential thermo-gravimetric slope suggests disintegration started above 750 K and completed at 1100 K. Raman spectra, XPS, and XRD of disintegrated CFO matched well with the Raman spectra, XPS and XRD of CuO and CuFe2O4 confirmed its disintegration above 750 K in air.

A concept of nanoscale bearing structures utilizing nanocarbon materials is presented based on the prediction via molecular dynamics simulations. The proposed mechanism consists of a graphene layer, intercalated single walled carbon nanotubes (SWNTs), and substrate graphenes. It is found that the friction against the movement of the uppermost graphene is smallest for the 1 SWNT model.

Data retention is one of the major device reliabilities of NAND Flash memory. We found that the lower Refractive Index (RI) of the Passivation Silicon Oxynitride (SiON) layer deposited by PECVD, the better data retention behavior was achieved. The hydrogen content and the stress analysis of the films are analyzed to find out which is more important in this case. Generally, when the RI of SiON decreases, both parameters also decrease, so it is impossible to find out which parameter is major factor of data retention. To analyze the effects of two parameters separately, we applied two conditions which had the same H contents but quite different stress values. The final data retention levels are same in both conditions. In addition, even if the layer has the same H content, the retention characteristic is changed by how hydrogen is bonded in the film. In conclusion, the data retention characteristic can be explained by mobile ions generated by the hydrogen weakly bonded in PECVD SiON films in our experiment.

Ultrafine-grained samples were produced from a Ni nanopowder by hot isostatic pressing (HIP) and spark plasma sintering (SPS). The microstructure and mechanical behavior of the two specimens were compared. The grain coarsening observed during the SPS procedure was moderated due to a reduced temperature and time of consolidation compared with HIP processing. The smaller grain-size and higher nickel-oxide content in the SPS-processed sample resulted in a higher yield strength. Compression experiments showed that the specimen produced by SPS reached a maximal flow stress at a small strain, which was followed by a long steady-state softening while the HIP-processed sample hardened until failure. It was revealed that the softening of the SPS-processed sample resulted from microcracking along the grain boundaries.

We report investigation of effect of conduction band edge on the dye injection and transport by preparation of (Ti,Sn)O2 solid mixtures in ratios of 80:20 and 90:10 as possible applications in dye sensitized solar cells. SEM micrographs showed highly porous with nanometer sized particles of around 6 - 10μm diameter. X-ray diffraction patterns showed strong TiO2 anatase peaks with crystal orientation directions (101) being the strongest in both the solid mixtures and in pure TiO2. XPS studies have shown an apparent chemical shift for Ti 2p and O1s core level spectra with an energy difference between the unmodified and the solid mixture being 0.65eV. Initial I-V studies have shown high Voc but low short circuit photocurrent, showing a possible unfavorable band edge shift between the semiconductor and the dye LUMO level.

Pure and Al2O3(2%, 5%, 8%) doped sintered ZnO (n-type) and pure sintered Ca3Co4O9 (p-type) pellets were prepared by conventional solid state synthesis starting from the oxides. The sintered pellets were cut by a diamond saw in a pillar shape (15 mm×5 mm×5 mm) for experimental checks. The best doped sample was 2 % Al2O3 ZnO showing Seebeck coefficient S = -180 mV/K and electrical conductivity σ = 8 S/cm at 400°C, while thermal conductivity κ = 1.8 W/m×K at 600°C. Typical values for Ca3Co4O9 were S = 82.5 mV/K and σ = 125 S/cm at 800°C, while κ = 1.01 W/m×K at 600°C.Several modules fabricated by elements cut from sintered pellets were tested and the best performance was obtained in the module formed by six 2 % Al2O3ZnO/ Ca3Co4O9 couples, that generated an output power P = 300 mV at 500°C (when ΔT = 260°C).

This paper reviews the reliability results for the gallium nitride on silicon (GaN-on-Si) technologies for commercial and military communications markets. Two technology platforms have been qualified for volume production: one consisting of discrete heterostructure field effect transistors (HFETs) and the other consisting of HFETs integrated with passive components to form monolithic microwave integrated circuits (MMICs). The technology platform qualifications for volume production have been achieved through intrinsic reliability tests on the active and passive device elements as well as extrinsic reliability tests at the product level. This paper presents reliability results on accelerated life test (ALT), high temperature operating life under DC and RF stress (DC/RF-HTOL), electrostatic discharge (ESD), ramped voltage breakdown, electromigration, temperature cycling, robustness under voltage standing wave ratio (VSWR) mismatch conditions, and diode stability. Degradation and breakdown mechanisms are discussed in relation to material properties reliability. The results show that the HFET and MMIC technology platforms display reliable performance for 20 year product lifetime at worst case operating conditions.

Photonic crystal based back-reflectors are an attractive solution for light management and enhancing optical absorption in thin film solar cells, without undesirable losses. We have fabricated prototype photonic crystal back-reflectors using photolithographic methods and reactive-ion etching. The photonic crystal back-reflector has a triangular lattice symmetry, a thickness of 250 nm, and a pitch of 765 nm. Scanning electron microscopy images demonstrate high quality long range periodicity. An a-Si:H solar cell device was grown on this back-reflector using standard PECVD techniques. Measurements demonstrate strong diffraction of light and high diffuse reflectance by the photonic crystal back-reflector. The photonic crystal back-reflector increases the average photon collection by ˜9% in terms of normalized external quantum efficiency, relative to a reference device on a stainless steel substrate with an Ag coated back surface.

We report the dynamic control of plasmon-exciton coupling in Au nanodisk arrays adsorbed with J-aggregate molecules by incident angle of light. The angle-resolved spectra of an array of bare Au nanodisks exhibit continuous shifting of localized surface plasmon resonances. This characteristic enables the production of real-time, controllable spectral overlaps between molecular and plasmonic resonances, and the efficient measurement of plasmon-exciton coupling as a function of wavelength with one or fewer nanodisk arrays. Experimental observations of varying plasmon-exciton coupling match with coupled dipole approximation calculations.

Delafossite CuYO2 and Ca doped CuYO2 were prepared by thermal decomposition of a metal-citric acid complex. The starting solution consisted of Cu acetate, Y acetate and Ca acetate as the raw materials. Citric acid was used as the chelating agent, and acetic acid and distilled water were mixed as a solvent. The starting solutions were heated at 723 K for 5 h after drying at 353 K. The obtained powders were amorphous and single phase of orthorhombic Cu2Y2O5 was obtained by heat-treated the amorphous powder at a temperature range between 1073 and 1373 K for 3 h in air. Furthermore, Heat-treating the obtained orthorhombic Cu2Y2O5 at above 1373 K in air caused it to decompose into Y2O3, CuO and Cu2O. On the other hand, the sample powder prepared from a starting solution without citric acid, i.e., single phase of orthorhombic Cu2Y2O5 could not be obtained under the same synthesis conditions as that for a solution with citric acid. We were able to obtain delafossite CuYO2 and Ca doped CuYO2 from orthorhombic Cu2Y2O5 under a low O2 pressure atmosphere at above 1223 K. The obtained delafossite CuYO2 composed hexagonal and rhombohedral phases. The color of the CuYO2 powder was light brown and that of Ca-doped CuYO2 was light green. Diffraction peaks in the XRD pattern were slightly shifted by doping Ca for CuYO2, and these peaks shifted toward to a high diffraction angle with an increasing amount of doped Ca. From these results, we concluded that Ca doped delafossite CuYO2 could be obtained by thermal decomposition of a metal-citric acid complex.

Reliability testing often manifests device weaknesses and failure mechanisms. As new materials and structures are developed, creative and different testing is often necessary to determine reliability. We are developing an in-house reliability test system that will provide the necessary testing flexibility of HEMT devices so researchers can pinpoint defects and vulnerabilities. Using commercial off-the-shelf (COTS) power supplies and data acquisition equipment, a custom control system allows for many different tests: DC and RF, temperature, step/stress/recovery, high-speed pulse, and optical pumping, as well as combinations and automated sequencing of these tests. This flexibility allows for the creation of new test types as failure mechanisms are understood. The initial station will provide for the simultaneous, independent testing of 16 devices. This paper outlines the system design and capabilities, the motivation for the system, and some results from different tests.

Polycrystalline and mono-crystalline CVD diamonds have been investigated in relation to radiation dosimetry applications. In this work we report results on the thermoluminescence (TL), afterglow (AG) and dosimetric performance on two mono-crystalline CVD diamonds containing boron and silicon as doping materials. The samples were exposed to beta (Sr90/Y90) in the dose range of 0.07-8.26 Gy and UV light in the range of 200-400 nm, followed in both cases, by TL and AG read-outs. The boron doped sample exhibited one main TL peak at 130 °C and some overlapped peaks around 250 °C and the silicon doped samples exhibited two TL peaks around 148 and 286 °C after the crystals were subjected to beta radiation. UV radiation exposed samples showed two main TL peaks around 139 oC for boron doped, with overlapped components in the high temperature side, and at 220 and 355 oC for silicon doped samples. The integrated TL and AG intensities reached saturation around to 3.0 and 1.0 Gy in boron and silicon doped samples, respectively. The AG signal from boron doped samples reached saturation for around 60 s of 230 nm UV light irradiation and the silicon doped sample showed a linear response up to 10 minutes of 300 nm UV exposure with no apparent saturation for higher irradiation times. The TL/AG behavior of the present CVD diamond indicates the promising applications of these materials as TL/AG dosimeter for ionizing and UV radiation.

Electrophoretic deposition (EPD) coating of medical grade Ti-6Al-4V substrate with a novel silica-calcium phosphate nano-composite (SCPC) in the particle size range 50 nm-5 μm has been described. The influence of EPD parameters and thermal treatment on the coating homogeneity, thickness and adhesion strength has been studied. SEM analyses showed that EPD carried out in 5% (w/v) SCPC/ethanol suspension at 50 V produced a homogeneous coating on passivated Ti alloy discs. Tensile tests carried out to evaluate the adhesion strength at the ceramic/metal interface showed that the SCPC coating layer developed adhesion strength of 47 ± 4 MPa with Ti alloy after thermal treatment at 800 °C for 1 hr. SEM – EDX analyses of the fracture surface revealed that the presence of SCPC layer on the surface of the Ti alloy indicating high interfacial stability. Upon immersion of the SCPC-coated Ti alloy substrate in PBS, a surface biological hydroxyapatite layer was deposited suggesting bone bonding ability. The successful coating of SCPC on the Ti-6Al-4V has the potential to stimulate rapid fixation and lower stress shielding by enhancing the bone bonding ability of the implant.

This contribution presents the results obtained by a Mexican laboratory in the Asia-Pacific Economy Cooperation Interlaboratory Comparison (IC) on mechanical properties by nanoindentation from 2008 using fused silica and polycarbonate as samples. Reduced modulus and indentation hardness are the parameters asked to be measured and compared. The aim for this paper is to show and to discuss the so called “indentation size effect” (ISE) on the indentation hardness of fused silica. Using the spherical formulation of the ISE model for crystalline materials, the macroscopic hardness and material length scale of fused silica are determined as (7.34 ± 0.085) GPa and (166.36 ± 14) nm, respectively.

The galvanomagnetic and magnetic properties of novel diluted magnetic semiconductors Pb1-x-yCaxCryTe (x=0.06-0.20, y=0.003-0.045) have been investigated. Temperature dependencies of the resistivity and the Hall coefficient have a metallic character indicating the pinning of Fermi level by the chromium impurity level on the background of the conduction band states. Magnetization curves display a clear hysteresis loop over the whole temperature range investigated. The Curie temperature, determined from the temperature dependencies of magnetization, achieves 345 K. Possible mechanisms of ferromagnetic ordering were discussed.

In this study, we can successfully synthesize nano-perovskites, including nano-CaTiO3, nano-SrTiO3, and nano-BaTiO3, by a co-precipitation method. The band gap of the nano-perovskites are 3.65 eV, 3.44 eV, and 3.35 eV, for nano-CaTiO3, nano-SrTiO3, and nano- BaTiO3, respectively. The ability of photocatalysis for nano-BaTiO3 is a little bit better than other nano-perovskites. It is also observed the photocatalytic activity increases with the increasing amount of photocatalysts. Moreover, the ability of photocatalysis using a higher energy UV-light is not promoted with the low energy UV-light.

Highly monodisperse ZnO:Eu3+ nanocrystals have been synthesized by modified sol-gel method from ethanolic solutions. The effect of Eu3+ ions (x=0.05-0.30) concentration on the structural, optical and luminescent properties has been evaluated. No other than the ZnO-wurtzite phase was observed at all dopant levels, which was confirmed by FT-IR and Raman spectroscopy techniques. A blue shift of the exciton peak and the increase on the corresponding band gap were observed at increasing Europium contents, which would indicate an interaction between Eu3+ ions and the development of the ZnO host structure. The luminescence properties were also dependent on Europium contents; a systematic blue shift and enhancement of the intensity of visible luminescence peak, attributed to an increment of surface defects, was observed by a rising Europium concentration. The red luminescence band, representing the 5D0→7F0 transition, was clearly observed in nanocrystals after annealing at 300OC for one hour. The presence of this band could be considered as an evidence of the effective energy transfer from ZnO to Eu3+ ions.

A quantitative risk assessment methodology is outlined for the source term for the proposed geologic repository for high-level nuclear waste at Yucca Mountain, Nevada. The methodology involves construction of a logical event tree to identify scenarios for the success or failure of the waste isolation system. Uncertainties in the intervening events between initial conditions and consequences can be quantified using probability distributions for steps along each scenario path. Likelihood is quantified according to the frequencies for each split fraction in the event tree. The result is a calculated probability of frequency curve for the release rate(s) of the modeled radionuclide(s).

We report on the chemical deposition and electronic properties of CuInS2/Zn(S,O) interfaces. The Zn(S,O) buffer was grown by a new chemical bath deposition (CBD) process that allows the tailoring of the S/O ratio in the films. Resulting Zn(S,O) films exhibit transparencies above 80% (for λ>390 nm) and an optical energy band gap of 3.9 eV which decreases to 3.6 eV after annealing in air at 200°C. Production line CuInS2 (CIS) absorbers provided by Sulfurcell Solartechnik GmbH are used as substrates for the investigation of the CIS/Zn(S,O) interface and the chemical composition of Zn(S,O). A ZnS/(ZnS+ZnO) ratio of 0.5 is found by X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy (XPS and XAES). The valence band offset between the heterojunction partners (ΔEV = 1.8 ± 0.2 eV) has been determined by means of XPS and ultraviolet photoelectron spectroscopy (UPS). Considering the energy band gap of the CIS absorber and the measured band gap of Zn(S,O), the conduction band offset (ΔEC) is calculated as: resulting in a spike of 0.5±0.3 eV in the conduction band at the heterojunction before annealing. After the heat treatment, the valence band offset is reduced to 1.5±0.2 eV and the calculated conduction band offset remains at 0.5±0.3 eV.