bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of Ge-Sb-Te Phase Change Materials At and Above Melting Temperatures and Set to Reset Transition of Memory Devices
Authors: Savransky Semyon D , Wicker Guy
Published: August 2010

The results of calorimetric and electrical studies of bulk Ge2Sb2Te5 and GeSb2Te4 alloys around melting temperature Tm are presented together with characteristics of phase-change memory devices from such alloys. The endothermic melting region is wider in Ge2Sb2Te5 than GeSb2Te4. Electrical resistivities of the alloys in this region have semiconductor characteristics. The width of the melting region correlates with breadth of set to reset transition in devices. This empirical correlation is probably important for alloy selection for multi-level memory cells.
Ce Doped-GeSbTe Thin Films Applied to Phase-change Random Access Memory Devices
Authors: Huang Yu-Jen , Tsai Min-Chuan , Wang Chiung-Hsin , Hsieh Tsung-Eong
Published: August 2010

A study on microstructure and electrical property of cerium (Ce)-doped Ge2Sb2Te5 (GST) layers for phase-change memory (PCM) application were presented. Ce doping does not suppress the resistivity of amorphous GST and the resistivity ratio of amorphous and crystalline GST remains at about 105. Further, Ce-doping escalates the recrystallization temperature (Tx) of GST from 159 to 236°C. Such a unique behavior would greatly benefit the preservation of signal contrast as well as the high-density signal storage and will not cause the increase of device writing current. X-ray diffraction (XRD) indicated that Ce doping stabilizes amorphous GST and suppresses the formation of hexagonal phase. Transmission electron microscopy (TEM) revealed Ce doping refines the grain size of GST. Kissinger's analysis found that Tx and activation energy (Ea) of phase transition for doped-GST both increase with the increase of Ce content. Isothermal experiment found the Ce doping increases temperature for 10-yr data retention from 76 and 170°C. This is attributed to the presence of Ce solutes in GST matrix that inhibits the grain growth during recrystallization.

Static-mode electrical test on PCM device containing doped GST as the programming layer found that Ce incorporation indeed increases the switching threshold voltage (Vth). This confirmed that Ce doping effectively retards the crystallization of GST and improves the stability of amorphous GST.
Study of crystalline structure N-doped GeSb Phase Change Material for PCRAM applications
Authors: Bastard Audrey , Lhostis Sandrine , Bonafos Caroline , Schamm-Chardon Sylvie , Coulon Pierre-Eugène , Fillot Frederic , Ghezzi Giada , Fantini Andrea , Perniola Luca , Loubriat Sebastien , Roule Anne , Gourvest Emmanuel , Arbaoui Edrisse , Fargeix Alain , Armand Marilyn , Hyot Berangere , Maitrejean Sylvain , Sousa Véronique
Published: August 2010

100 nm-thick GeSbN films with high Sb content were investigated by XRD and TEM in order to investigate crystalline phases. We observe the crystallization of the two phases separatly. First, Sb rhomboedral crystallizes at 250°C and then cubic Ge appears at 340°C according to Reflectivity and X-Ray Diffraction measurements. With the incorporation of nitrogen in the thick films, a delay to crystallization of the two phases is observed. Grain size measurements with Scherrer formula support the decrease of grain crystallization with N content. Moreover, TEM observations show clearly the separation of the two phases in the layer and the reduction in size of the grains with nitrogen content. This allows a better re-amorphization than films without nitrogen.
Electrical Resistance Change with Crystallization in Si-Te Amorphous Thin Films
Authors: Saito Yuta , Sutou Yuji , Koike Junichi
Published: August 2010

The electrical resistance change of amorphous SixTe100-x (x: 10-23) films during heating was investigated by a two-point probe method. The SixTe100-x films showed two-stage crystallization processes. The film was firstly crystallized to Te and subsequently crystallized to Si2Te3 with an electrical resistance drop. The first crystallization temperature Tx1st slightly increased with increasing Si content, while the second crystallization temperature Tx2nd was independent on the composition and was a constant temperature of 310 °C. In all films, the electrical resistance once increased in the temperature range from 250 to 295 °C before the crystallization of the Si2Te3. This temporal resistance increase could be explained by considering a formation of high-resistivity Si-rich amorphous phase.
Giant ac electrical response of La0.7Sr0.3MnO3in sub-kilogauss magnetic fields
Authors: Rebello Alwyn , Naik Vinayak Bharat , Barik Sujit Kumar , Lam Mark Choong , Ramanathan Mahendiran
Published: August 2010

We report ac electrical transport in the metallic ferromagnet La0.7Sr0.3MnO3. Both ac resistance (R) and reactance (X) were measured as a function of temperature (T= 400-100 K), frequency of the ac current (f= 100 kHz – 20 MHZ) and external dc magnetic field (H= 0-100 mT) applied parallel to the current direction. It is shown that, whileR(H= 0 T) decreases smoothly around the Curie temperature (TC) forf= 100 kHz, an abrupt increase followed by a peak close toTCoccurs forf≥ 500 kHz. The peak decreases in magnitude, broadens and shifts down in temperature with increasing values ofH. The peak inRis completely suppressed underH= 100 mT resulting in a huge low-field ac magnetoresistance (R/R= -53 % forf= 2MHz) whereas the dc magnetoresistance only -31 % even at H = 7 T. While the reactanceX(H= 0 T) also shows an abrupt increase atTCforf< 10 MHz, it decreases abruptly atTCforf≥ 12 MHz. The magnetoreactance is largest (X/X= -47 %) atf= 100 kHz and it changes sign from negative to positive with increasing frequency. It is suggested that the observed huge ac magnetoresistance arises from decrease of magnetic permeability which enhances skin depth under a magnetic field. Our results indicate that the extraordinary sensitivity of the ac magnetoresistance to low dc magnetic fields can be exploited for device applications.
Phenomena And Mechanism On Phase Transformation Twinning In Nanocrystalline BaTiO3
Authors: Mazumder Sujata , Ghosh Jiten
Published: August 2010

The detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.
Fabrication of Transparent, Conductive Phase-segregated ITO/PC Composites
Authors: Mason Celeste , Gerhardt Rosario
Published: August 2010

Fabrication of transparent, conductive phase-segregated ITO/PC composites was accomplished by compression molding of dry mixed constituents. Mixtures of 50nm indium tin oxide particles in a polycarbonate matrix of compositions ranging from phr = 1.0 to 0.001 were measured by optical and electrical methods. Measured transmittance ranged from 5% to 68% at 400nm, 15% to 80% at 700nm, and averaged 10% to 75% across the visible spectrum. Resistance was measured by impedance spectroscopy. Resistivities of the different composites spanned 10 orders of magnitude. Electrical percolation was found to occur near phr = 0.15.
Electron Microscopy (TEM) and X-ray Spectromicroscopy (STXM) of PP/MMT/PP-g-MA and PP/MMT/SEBS Nanocomposites
Authors: Martin Zulima , Gomez M. Angeles , Jimenez Ignacio
Published: August 2010

Here we present a study on the polypropylene/montmorillonite interaction based on x-ray diffraction, transmission electron microscopy (TEM) and scanning transmission x-ray microscopy (STXM) measurements, which provides a complete picture of the intercalation and exfoliation processes taking place.
Highly Controllable Nano-texturing of Silicon Using Hydrogen-assisted Reactive Ion Etching
Authors: Mehran Mahdieh , Sanaee Zeinab , Mohajerzadeh Shamsoddin
Published: August 2010

We propose a hydrogen assisted reactive ion etching method for generating nano-grass and nano-texturing of silicon substrates in desirable shapes and locations. The etching technique is based on sequential etching and passivation steps where a combination of three gases of H2, O2 and SF6 in the presence of RF plasma is exploited. Using this method it has been possible to realize high aspect ratio features on silicon substrates whereas by adjusting the etching parameters, it is possible to form texturing of silicon in desired places. This technique is highly programmable where the pressure, gas flows, plasma power and duration of each cycle can be preset to achieve desired features. The formation of nano-grass on the silicon surface improves its wetability both to water and oil spills.
Electrodeposition of Group III Doped PbTe Nanowires
Authors: Hillman Peter , Stacy Angelica M
Published: August 2010

Nanowire arrays of PbTe were electrodeposited into porous alumina templates with 40nm pores. Citric acid was used as a complexing agent for HTeO2+ shifting the reduction potential of HTeO2+/Te closer to that of Pb2+/Pb. Compositional analysis of the wires grown with the complexing agent show a 1:1 ratio of Pb:Te without any excess tellurium. Group III elements (In3+ and Tl+) can be added to the deposition solution and incorporated into the nanowires. It is proposed that indium incorporates into the PbTe lattice in a high energy interstitial site causing the lattice parameter to increase linearly with increasing indium incorporation. The addition of thallium to the deposition solution leads to a mixture of PbTe and TlTe nanowires. Upon annealing, the TlTe melts incongruently to Tl5Te3, which then alloys with PbTe, thereby increasing the lattice parameter.
Influence of Structural Defects on the Electronic Properties of Carbon Nanotubes Examined by Scanning Tunnelling Microscopy
Authors: Giusca Cristina E. , Silva Ravi
Published: August 2010

The electronic properties of carbon nanotubes are quite often drastically affected by the presence of defects that can develop during nanotube growth, processing or characterization too. Some of these defects such as pentagon-heptagon rings, substitutional impurities, vacancies and dislocations are of topological nature, and can sometimes create on-tube intramolecular junctions, as found by previous scanning tunnelling microscopy studies.

Our recent STM experiments reveal for the first time a much more complicated junction structure, a hybrid single-walled carbon nanotube consisting of a distinct coiled structure located between two straight segments, each of different helicity. We characterise the hybrid junction at the atomic level and describe its electronic behaviour that has important implications in the practical design of functional components for nanoelectronic applications.
Tunability of Carbon NanoTubes Resistance Deposited by Inkjet Printing at Low Temperature
Authors: Pacchini Sebastien , Conédéra Véronique , Mesnilgrente Fabien , Fabre Norbert , Flahaut Emmanuel , Coccetti Fabio , Dragoman Mircea , Plana Robert
Published: August 2010

A deposition method based on inkjet printing technology and conductive double-wall carbon nanotubes (DWNT) suspension is, hereby, presented. The approach exploits the selective transfer capabilities offered by the inkjet printing process and the excellent conductive characteristics of the available DWNTs, in order to realize microelectronic interconnects of arbitrary patter and given electrical properties. The DWNTs are prepared by CCVD process, oxidized and dispersed in ethylene-glycol (EG) and in water solution. The DWNTs lines are fabricated on tests structures and then characterized through impedance and current-voltage measurements. 400 μm long and 90 μm wide transmission lines have been printed by varying the number of overwrites for given DWNT density. The results confirm that the DC resistance of DWNTs lines can be changed according to the number of overwrites and that the lines preserve ohmic characteristics up to 100 MHz.
Stable and Responsive Fluorescent Carbon Nanotube Silica Gels
Authors: Gupta Gautam , Duque Juan G. , Doorn Stephen , Dattelbaum Andrew M.
Published: August 2010

Here we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous suspension of surfactant-wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes. The vapor phase silica process is performed at room temperature and is simple, reproducible, relatively quick, and requires no dilution of SWNT dispersions. However, exposure of aqueous SWNT suspensions to TMOS vapors resulted in an acidification of the suspension prior to gelation that caused a decrease in the emission signal from sodium dodecylsulfate (SDS) wrapped SWNT. We also show that although the SWNT are encapsulated in silica the emission signal from the encapsulated SWNT may be attenuated by exposing the nanocomposites to small aromatic molecules known to mitigate SWNT emission. These results demonstrate a new route for the preparation of highly luminescent SWNT/silica composite materials that are potentially useful for future sensing applications.
In situ TEM Straining of Nanograined Al Films Strengthened with Al2O3 Nanoparticles
Authors: Hattar Khalid , Clark Blythe G. , Knapp James A , Follstaedt David M , Robertson I. M.
Published: August 2010

Growing interest in nanomaterials has raised many questions regarding the operating mechanisms active during the deformation and failure of nanoscale materials. To address this, a simple, effective in situ TEM straining technique was developed that provides direct detailed observations of the active deformation mechanisms at a length scale relevant to most nanomaterials. The capabilities of this new straining structure are highlighted with initial results in pulsed laser deposited (PLD) Al-Al2O3 thin films of uniform thickness. The Al-Al2O3 system was chosen for investigation, as the grain size can be tailored via deposition and annealing conditions and the active mechanisms in the binary system can be compared to previous studies in PLD Ni and evaporated Al films. PLD Al-Al2O3 free-standing films of various oxide concentrations and different thermal histories were produced and characterized in terms of average grain and particle sizes. Preliminary in situ TEM straining experiments show intergranular failure for films with 5 vol% Al2O3. Further work is in progress to explore and understand the active deformation and failure mechanisms, as well as the dependence of mechanisms on processing routes.
Three-dimensional Structure of Twinned and Zigzagged One-dimensional Nanostructures Using Electron Tomography
Authors: Kim Han Sung , Myung Yoon , Cho Yong Jae , Jang Dong Myung , Jung Chan Soo , Ahn Jae-Pyoung , Park Jeunghee
Published: August 2010

Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique 3-dimensional (3D) structures of twinned Zn3P2 (tetragonal) and InAs (zinc blende) nanowires synthesized by the vapor transport method. The Zn3P2 nanowires adopt a unique superlattice structure that consists of twinned octahedral slice segments having alternating orientations along the axial [111] direction of a pseudocubic unit cell. The apices of the octahedral slice segment are indexed as six equivalent <112> directions at the [111] zone axis. At each 30 degrees turn, the straight and zigzagged morphologies appear repeatedly at the <112> and <011> zone axes, respectively. The 3D structure of the twinned Zn3P2 nanowires is virtually the same as that of the twinned InAs nanowires. In addition, we analyzed the 3D structure of zigzagged CdO (rock salt) nanowires and found that they include hexahedral segments, whose six apices are matched to the <011> directions, linked along the [111] axial direction. We also analyzed the unique 3D structure of rutile TiO2 (tetragonal) nanobelts; at each 90 degree turn, the straight morphology appears repeatedly, while the in-between twisted form appears at the [011] zone axis. We suggest that the TiO2 nanobelts consist of twinned octahedral slices whose six apices are indexed by the <011>/<001> directions with the axial [010] direction.
Neutron Diffraction Study of NiO/LiCoO2Electrodes for Innovative Fuel Cell Development
Authors: Coppola Roberto , Henry Paul , Moreno Angelo , Rodríguez-Carvajal Juan , Simonetti Elisabetta
Published: August 2010

Ni-NiO 30% electrodes coated with LiMg0.05Co0.95O2cobaltite deposited on the substrate by complex sol-gel process were investigated by neutron diffraction. The measurements were carried out at the D20 diffractometer at the High Flux Reactor of the Institut Max von Laue – Paul Langevin. As the catalytic layer is only a few microns thick, the diffracting volume of the cobaltite phase was optimised by stacking small rectangular pieces cut from the original electrode and assuming that the catalytic layer on the electrodes was homogenous. A pure cobaltite sample was used as a reference for identifying in the complete electrode the diffraction peaks of the catalytic layer. Both an as-received sample and an electrode tested for 100 h at 650 °C in a cell were measured. Despite the small diffracting volume, due to the high flux available at D20, it was possible to detect the hexagonal phase of the catalytic layer and estimate its volume fraction in the as-received sample; in the tested electrode the original crystallographic structure is completely modified but information on the phases present can be obtained.
X-ray Detection on Fe-H Vibrations
Authors: Wang Hongxin , Guo Yisong , Kamali Saeed , Cramer Stephen P
Published: August 2010

X-ray detection on hydrogen related events is difficult due to its extremely small scattering factor. In this report, we have used nuclear resonance vibrational spectroscopy (NRVS) to examine the nature of the Fe–H vibrational modes in several FeH model complexes, which shines light on the possible measurements on the Fe-H vibrations inside real biological systems in the future.
Mesoscale Simulations of Microstructure Evolution in a Temperature Gradient
Authors: Radhakrishnan Bala , Sarma Gorti
Published: August 2010

The evolution of pore and grain structure in a nuclear fuel environment is strongly influenced by the local temperature, and the temperature gradient. The evolution of pore and grain structure in an externally imposed temperature gradient is simulated for a hypothetical material using a Potts model approach that allows for porosity migration by mechanisms similar to surface, grain boundary and volume diffusion, as well as the interaction of migrating pores with stationary grain boundaries. First, the migration of a single pore in a single crystal in the presence of the temperature gradient is simulated. Next, the interaction of a pore moving in a temperature gradient with a grain boundary that is perpendicular to the pore migration direction is simulated in order to capture the force exerted by the pore on the grain boundary. The simulations reproduce the expected variation of pore velocity with pore size as well as the variation of the grain boundary force with pore size.
Direct Energy Conversion From Gamma Ray to Electricity Using Silicon Semiconductor Cells
Authors: Hashizume Kenichi , Kimura Hiroki , Otsuka Teppei , Tanabe Tetsuo , Okai Tomio
Published: August 2010

Spent fuels and high level radioactive wastes which emit high doze of gamma rays could be a promising and long-lasting power source, if the gamma ray energy was effectively converted other forms of energy. In the present study, we have tried to convert gamma ray to electricity directly, with using silicon semiconductor cells made of p-type Si single crystal wafers with various specific resistivities ranging from 0.01 to 1000 Ohm∙cm. On both surfaces of the cell (20×20×0.5mm3), Al and Sb were deposited in vacuum to make electrodes at room temperature. The voltage-current measurement of the cells showed a rectification effect, and Al side was found to work a cathode. This suggests a Schottky junction was formed at the interface between the deposited Al and Si wafer. The cell irradiated by gamma ray in Co-60 irradiation facility in Kyushu Univ. with an absorbed dose of about 200Gy/h, and output voltage and current generated by the irradiation with external resistances varying from 200 to 100,000 Ohm were measured. The maximum electric power obtained for each cell ranged from 0.002 to 200 micro-W/m2, and clearly increased with increasing the specific resistivity of Si wafers. For comparison, a single crystal Si solar cell (2400mm2×0.5m, 0.5V×450mA in AM1.5 condition) was also exposed to the gamma ray, and its maximum electric power was 2 micro-W/m2. The output power of the present cell with high resistivity was two orders of magnitude higher than that of the Si solar cell.

Energy deposition in the Si cell during gamma irradiation was evaluated with the Monte Carlo Simulation for N Particles (MCNP) code. For Si with 0.5 mm thickness, the deposited energy was calculated to be 17000 micro-W/m2 for 200Gy/h. Comparing the output energy by the gamma irradiation, the energy conversion efficiency of the present Si cells reached about 1%. Unfortunately, the present cells were unstable even in ambient atmosphere, the conversion ratio of which decreased to less than one tenth in six months. Further development of the cells with higher conversion ratio and improvement of its stability will be discussed.
MARS, A New Facility for X-ray Diffraction and X-ray Absorption for Radioactive Matter Studies
Authors: Schlutig Sandrine , Solari Pier Lorenzo , Hermange Hervé , Sitaud Bruno
Published: August 2010

The MARS (Multi-Analyses on Radioactive Samples) beamline, at Synchrotron Soleil (France) is fully dedicated to advanced structural and chemical characterizations of radioactive matter (solid or liquid), coupling analytical tools such as X-ray absorption spectroscopy, X-ray diffraction, X-ray fluorescence and associated micro-beam techniques. This beamline is now partially operational and has completed its first year of working with samples below exemption limits. This paper describes the beamline design and its technical specifications as well as the standard equipment of the experimental stations and the first obtained results.
Thermochemistry of Elementary Actinide Sulfide Molecules: A Gas-Phase Study of Curium Sulfide
Authors: Pereira Cláudia C. L. , Marçalo Joaquim , Gibson John K.
Published: August 2010

Experiments to explore the reactivity and thermochemistry of elementary transuranium sulfide molecules have been initiated to expand the basis for a fundamental understanding of actinide bonding, and to enable the development of advanced theoretical methodologies which will be of general applicability to more complex molecular systems. Bimolecular gas-phase reactions between transuranium actinide ions and neutral reagents are employed to obtain thermochemical information. The initial actinide sulfide studies have focused on obtaining the 298 K bond dissociation energy for the CmS+ ion, D[Cm+-S] = 475±37 kJ mol-1; from this result and an estimate of IE[CmS] ≈ IE[CmO] + 0.5 eV, we obtain D[Cm-S] = 563±64 kJ mol-1. The bond dissociation energies, D[Cm+-S] and D[Cm-S] are approximately 200 kJ mol-1 and 150 kJ mol-1 lower than for the corresponding oxides, CmO+ and CmO. The nature of the bonding in the CmS+ ion appears to be generally similar to that in other oxophilic metal sulfides. Comparisons with previous bond dissociation energies reported for ThS and US may suggest a difference in the An-S bonds for these early actinide sulfides as compared with CmS.
Electronic structure theory of Pu-Am and Pu-Ce alloys, and thin δ-Pu films
Authors: Kolorenc Jindrich , Shick Alexander , Havela Ladislav , Lichtenstein Alexander
Published: August 2010

We study effects of electron correlations on the electronic structure and spectra of Pu, Am and their alloys. We make use of the LDA + Hubbard-I approximation being implemented in the full-potential LAPW basis and including self-consistency over the charge density. We demonstrate that this approximation correctly captures trends observed in the experimental photoemission spectra of plutonium and its compounds: insensitivity of the f electron spectral features to alloying with another element and enhancement of f electron localization in thin films compared to the bulk material.
Photoelectron Spectroscopy of U Oxide at LLNL
Authors: Tobin James G , Yu Sung Woo , Chung Brandon W , Waddill G. Dan
Published: August 2010

X-ray photoelectron spectroscopy has been used to characterize a sample of UO2 grown on an underlying substrate of Uranium. Both AlKα (1487 eV) and MgKα (1254 eV) emission were utilized as the excitation.
Anisotropy of antiferromagnetic spin fluctuations in the heavy fermion superconductors of CeMIn5 and PuMGa5 (M=Co, Rh)
Authors: Sakai Hironori , Kambe Shinsaku , Tokunaga Yo , Haga Yoshinori , Baek Seung -H. , Ronning Filip , Bauer Eric , Thompson Joe D
Published: August 2010

The anisotropy of antiferromagnetic spin fluctuations has been investigated microscopically in the heavy fermion systems of CeMIn5 and PuMGa5 (M=Co, Rh) by means of nuclear magnetic resonance (NMR). Both systems are known to be relatively high-Tc superconductors among the heavy fermion systems, especially PuCoGa5, which has a Tc=18.5 K almost one order of magnitude larger than for CeCoIn5 ( Tc=2.3 K). Analysis of the Knight shift and spin-lattice relaxation rates suggests XY-type anisotropy in the antiferromagnetic spin fluctuations in the normal states of these unconventional superconductors. Moreover, the 115 superconductors with larger XY-type fluctuations have a higher Tc, compared to the anisotropy of spin fluctuations in the related paramagnetic system UFeGa5 and antiferromagnets UPtGa5, NpCoGa5, NpFeGa5.
Establishment of Uncertainty Ranges and Probability Distributions of Actinide Solubilities for Performance Assessment in the Waste Isolation Pilot Plant
Authors: Xiong Yongliang , Nowak Jim , Brush Laurence H. , Ismail Ahmed E. , Long Jennifer
Published: August 2010

The Fracture-Matrix Transport (FMT) code developed at Sandia National Laboratories solves chemical equilibrium problems using the Pitzer activity coefficient model with a database containing actinide species. The code is capable of predicting actinide solubilities at 25 °C in various ionic-strength solutions from dilute groundwaters to high-ionic-strength brines. The code uses oxidation state analogies, i.e., Am(III) is used to predict solubilities of actinides in the +III oxidation state; Th(IV) is used to predict solubilities of actinides in the +IV state; Np(V) is utilized to predict solubilities of actinides in the +V state. This code has been qualified for predicting actinide solubilities for the Waste Isolation Pilot Plant (WIPP) Compliance Certification Application in 1996, and Compliance Re-Certification Applications in 2004 and 2009.

We have established revised actinide-solubility uncertainty ranges and probability distributions for Performance Assessment (PA) by comparing actinide solubilities predicted by the FMT code with solubility data in various solutions from the open literature. The literature data used in this study include solubilities in simple solutions (NaCl, NaHCO3, Na2CO3, NaClO4, KCl, K2CO3, etc.), binary mixing solutions (NaCl+NaHCO3, NaCl+Na2CO3, KCl+K2CO3, etc.), ternary mixing solutions (NaCl+Na2CO3+KCl, NaHCO3+Na2CO3+NaClO4, etc.), and multi-component synthetic brines relevant to the WIPP.
Uranium (VI) Solubility in Carbonate-Free ERDA-6 Brine
Authors: Lucchini Jean-Francois , Khaing Hnin , Reed Donald T.
Published: August 2010

When present, uranium is usually an element of importance in a nuclear waste repository. In the Waste Isolation Pilot Plant (WIPP), uranium is present in significant quantities, with about 647 metric tons to be placed in the repository [1]. Therefore, the chemistry of uranium, and especially its solubility, needs to be determined under WIPP-relevant conditions.

Long-term experiments were performed to measure the solubility of uranium (VI) in carbonate-free ERDA-6 brine, a simulated WIPP brine, at pCH+ values between 8 and 12.5. These data, obtained from the over-saturation approach, were the first WIPP repository-relevant data for the VI actinide oxidation state. The solubility trends observed pointed towards low uranium solubility in WIPP brine and a lack of amphotericity. At the expected pCH+ in the WIPP (˜ 9.5), measured uranium solubility approached 10-7 M. The objective of these experiments was to establish a baseline solubility to further investigate the effects of carbonate complexation on uranium solubility in WIPP brines, during the ongoing research program in actinide solubility under WIPP-relevant conditions.
The Role of the Actinides in a Performance Assessment of a Nuclear Waste Repository. SKB's Supporting Actinide Research
Authors: Werme Lars , Butorin Sergei , Oppeneer Peter M
Published: August 2010

After a few hundred years, the actinides will dominate the radiotoxicity of spent nuclear fuel. This does not necessarily mean that the actinides will dominate the dose to organisms at the surface above a geologic repository. Quite the contrary, in most performance assessments this dose is dominated by long-lived fission products, activation products and, in the very long perspective, actinide daughters.

This makes the far-field migration properties of the actinides less interesting for further research. There are, however, other aspects of the presence of actinides in spent nuclear fuel and some of these and SKB's research in these fields is presented and discussed here.
Selective Radionuclide (Cs+, Sr2+, and Ni2+) Ion-exchange by K2xMgxSn3-xS6(x=0.5-0.95) (KMS-2)
Authors: Mertz Joshua Leighton , Manos Emmanouil J. , Kanatzidis Mercouri
Published: August 2010

137Cs and90Sr, both byproducts of the fission process, make up the majority of high-level waste from nuclear power plants.63Ni is a byproduct of the erosion-corrosion process of the reactor components in nuclear energy plants. The concentrations of these ions in solution determine the Waste Class (A,B, or C) and thus selective removal of these ions over large excesses of other ions is necessary to reduce waste and cut costs. Herein we report the use of the Inorganic Ion Specific Media (ISM) K2xMgxSn3-xS6(x=0.5-0.9) (KMS-2) for the ion exchange of Cs+, Sr2+, and Ni2+in several different conditions. We will also report the stability of this new material in the general conditions found at nuclear power plants (pH ˜6-8) and DOE sites (pH>10). Measurements at low concentrations were conducted with inductively coupled plasma mass spectrometry and Kd values are reported for each of the ions in a variety of conditions.
Assessment of Concrete Cracking at Nuclear Waste Disposal Facilities via Fiber Optic Sensors
Authors: Lair Sanaan Cherie , Walton John C. , Woocay Arturo , Motta Antonio
Published: August 2010

Fiber optic sensors offer a novel approach to monitoring of fractures in concrete waste disposal vaults and offer the possibility of determining the quantity, width and location of the cracks as they form. Fiber optics can directly detect cracks if they form within the path of a fiber optic as well as monitor secondary indicators of cracking such as temperature changes and strain. When cracks form in concrete waste disposal vaults they can fill with water which has a high heat capacity, this enables cracks to be observed by monitoring temperature variations near the crack. An analytical solution for heat transfer is applied to estimate the propagation of temperature waves around cracks. It is demonstrated that discharge rates through the concrete which are less than 10-5 m3/m-s do not produce a meaningful temperature wave through the concrete. Fractures in the concrete must be larger than 0.07 cm to produce a measurable result and temperature sensors must be located within 0.5 meters of a crack to detect a change in temperature produced by seasonal groundwater flow through a crack. A distributed system of fiber optic sensors may be embedded in the concrete vault and used to monitor crack formation, temperature variations and strain.
Seismic Tomography Investigation in 140m Gallery in the Horonobe URL Project
Authors: Sugita Yutaka , Nakamura Takahiro , Sanada Hiroyuki , Aizawa Takao , Ito Shunichiro
Published: August 2010

The Japan Atomic Energy Agency (JAEA) established the Horonobe Underground Research Laboratory (URL) Project at Horonobe, in Hokkaido, Japan to enhance reliability of nuclear waste disposal technologies to be developed in deep sedimentary environments. JAEA has undertaken a number of in-situ experiments to determine changes in the properties of the host rock and the extent of the excavation disturbed zone (EDZ) created by the excavation of underground galleries for the disposal of radioactive waste. This paper reports a seismic tomography survey (using a hammer seismic source) of the “140m Gallery” at a depth of 140m below the surface of the Horonobe URL. The observation area was 3m square on the horizontal plane along the sidewall of the 140m Gallery. The measurement was repeated with the progress of excavation of a tunnel. In this experiment, the distribution of seismic velocity in the rock around the new tunnel and its decrease as the tunnel was dug, were observed using a simple small-scale seismic tomography system. The data collected show that this system can be used to capture the EDZ around tunnels.
Performance Indicators Quantifying the Contribution of Safety Functions to the Confinement of Radionuclides in a Geological Repository System
Authors: Weetjens Eef , Marivoet Jan , Seetharam Suresh C.
Published: August 2010

The main indicators for the evaluation of the safety of a geological repository are the dose or the risk that are estimated for a sufficiently representative set of possible evolution scenarios. In recent years complementary sets of safety and performance indicators have been developed within national geological disposal programmes and international projects. Whereas safety indicators aim at giving an indication on the level of safety provided by the repository system, performance indicators aim at illustrating how the repository system works. Most sets of performance indicators that have been introduced hitherto in safety cases of geological repositories are related to the multi-barrier concept; they quantify or illustrate the contribution of the main engineered and natural barriers to the confinement of the radionuclides within the repository system. However, the application of the defence-in-depth principle to geological disposal has led to the introduction of safety functions in safety cases. Because of the paramount role played by the multi-safety-functions concept in recent safety cases, we have derived performance indicators that quantify the contribution of the main safety functions to the confinement of radionuclides in the geological repository system. The considered safety functions are containment, limitation of release and retardation. The proposed performance indicators are based on time-integrated activity or radiotoxicity fluxes released from the main successive compartments of the repository system. The proposed indicators can be applied to individual radionuclides as well as to a weighted sum of all radionuclides.
Thermoelectric Performance of Nanostructured ZrNiSn Compounds Synthesized by Mechanical Alloying
Authors: Germond Jeffrey D , Schilling Paul J , Takas Nathan J. , Poudeu Pierre F. P.
Published: August 2010

Samples with a composition ZrNiSn were synthesized by a combination of mechanical alloying (MA) and consolidation by either Spark Plasma Sintering (SPS) or hot pressing (HP). Appropriate stoichiometric ratios of the starting materials were milled under an inert atmosphere in a high energy ball mill for 6 hours, achieving a half-Heusler phase. X-Ray diffraction patterns of as milled powders and consolidated samples were compared and analyzed for phase purity. Thermal conductivity, electrical conductivity and Seebeck coefficient were measured as a function of temperature in the range 300 K to 800 K and compared with measurements reported for high temperature solid state reaction synthesis of this compound. HP samples, compared to SPS samples, demonstrate increased grain growth due to longer heating times. Reduced grain size achieved by MA and SPS causes increased phonon scattering due to the increased number of grain boundaries, which lowers the thermal conductivity without doping the base system with addition phonon scattering centers.
High thermoelectric efficiency in co-doped degenerate p-type PbTe
Authors: Androulakis Ioannis , Todorov Ilyia , Chung Duck Young , Ballikaya Sedat , Wang Guoyu , Uher Ctirad , Kanatzidis Mercouri
Published: August 2010

We explored the effect of K and K-Na substitution for Pb atoms in the lattice of PbTe, in an effort to test a hypothesis for the development of a resonant state that may enhance the thermoelectric power. At 300K the data can adequately be explained by a combination of a single and two-band model for the valence band of PbTe depending on hole density that varies in the range 1-15 × 1019 cm-3. A change in scattering mechanism was observed in the temperature dependence of the electrical conductivity, σ, for samples concurrently doped with K and Na which results in significantly enhanced σ at elevated temperatures and hence power factors. Thermal conductivity data provide evidence of a strong interaction between the light- and the heavy-hole valence bands at least up to 500K. Figure of merits as high as 1.3 at 700K were measured as a result of the enhanced power factors.
NMR and Computational Studies of Ba8Ga16Sn30 Clathrates
Authors: Rodriguez Sergio Yanuen , Zheng Xiang , Saribaev Laziz , Ross Joseph H
Published: August 2010

We have synthesized type-VIII and type-I Ba8Ga16Sn30 clathrates by using different annealing treatments, confirmed with XRD and electron microprobe measurements. NMR lineshape measurements identified a broad resonance corresponding to first-order-shifted satellites. Simulations for the type I structure based on first principles calculations provided an excellent fit to the data, with the best agreement provided by the calculated lowest-energy configuration, having no Ga-Ga bonds. These results allow us to address local configurations within the random type-I alloy, as well as atomic displacements and bond-length distributions, which we compare to experiment.
Reduction of the Lattice Thermal Conductivity in Immiscible PbS-PbTe Systems
Authors: Johnsen Simon , Girard Steven N , Todorov Ilyia , Chung Duck Young , Kanatzidis Mercouri
Published: August 2010

The synthesis and properties characterization of several PbS1-xTexx = 0-0.16 samples are presented. Notably it is shown how a local minimum occurs in the thermal diffusivity for the PbS1-xTex samples at x ≈ 0.03. The thermoelectric properties of doped PbS1-xTex with x = 0.03 are reported and the properties are compared to the pure PbS and PbTe end members. The electronic contribution to the total thermal conductivity is analyzed for PbS1-xTexx = 0.03 and it is shown how the lattice thermal conductivity is significantly lowered compared to single crystalline PbS.
Metal Nanoinclusions (Bi and Ag) in Bi2Te3 for Enhanced Thermoelectric Applications
Authors: Santhanam Sumithra , Takas Nathan J. , Henderson Natheniel L , Nolting Westly M , Misra Dinesh , Poudeu Pierre F. P. , Stokes Kevin L.
Published: August 2010

Metal nanoinclusions inside the bulk thermoelectric matrix have the potential to increase the power factor and reduce the lattice thermal conductivity. We have synthesized Bi2-xTe3+x (x=0, 0.05)compositions, to achieve better tenability in Seebeck and electrical conductivity. In this matrix phase, different volume fractions of Bi metal nanoinclusions were incorporated and its effect on thermoelectric properties is discussed. Ag metal nanoinclusions were incorporated into Bi2Te3(2:3) composition, and its effect on power factor is discussed here.
The Effect of Cross-sectional Geometry on ZT Enhancement in Rough Silicon Nanostructures
Authors: Sadhu Jyothi Swaroop , Ghossoub Marc G , Sinha Sanjiv
Published: August 2010

The dramatic reduction in the thermal conductivity of rough silicon nanowires is due to phonon localization in the wire resulting from multiple scattering of phonons from the rough walls. We report the dependence of thermal conductivity of the nanowires as a function of the surface roughness and the diameter of the wire by modeling the nanowire as a waveguide. In addition, we estimate the impact of boundary condition, dimensionality and cross section of rough wire on the thermal conductivity. This theoretical model gives insights for tailoring thermal conductivity and enhancing the ZT of silicon to 1 for its use in thermoelectrics
Synthesis of sodium cobalt oxide submicron tubules using citric acid-based sol-gel route assisted by porous aluminum oxide membrane
Authors: Liu Chia-Jyi , Shih Long-Jiann , Huang Hsueh-Jung
Published: August 2010

We report synthesis of the sodium cobalt oxide γ-NaxCoO2 submicron tubules using the citric acid-based sol-gel route with the assistance of commercial porous anodized aluminium oxide (AAO) membrane with a nominal pore size of 200nm as supporting templates. The γ-NaxCoO2 submicron tubules can be obtained at 500°C using a rapid-heat-up procedure and held for 30 min. The submicron tubules have a diameter of 200-250 nm. The products are investigated using various techniques including powder x-ray diffraction, field emission scanning electron microscope and transmission electron microscope. The atomic ratio of Na/Co of theγ-NaxCoO2 submicron tubules is determined using energy dispersive x-ray spectra. The atomic ratio of Na/Co tends to be less than 0.5 due to the tendency of Na+ de-intercalating from its parent structure during the tubules collecting process.
In-plane Thermal Conductivity Determination in Silicon on Insulator (SOI) Structures Through Thermoreflectance Measurements
Authors: Aubain Max S , Bandaru Prabhakar
Published: August 2010

Heat dissipation in Silicon-On-Insulator (SOI) based microdevices is hindered in the silicon device layer by the low thermal conductivity of the neighboring oxide and reduced in-plane thermal conductivity in very thin layers. This work shows that the in-plane thermal conductivity of a 260 nm thick device layers in SOI substrates can be characterized by measuring the temperature distributions induced by AC joule heating through microfabricated heaters by a scanning thermoreflectance technique. These data were fitted to numerical solutions of the heat conduction equation calculated using COMSOL® Multiphysics modeling software, suggesting the in-plane thermal conductivity of the device layer is reduced to 90±10 W/(m.K), which is consistent with phonon boundary scattering theory predictions.
Quasi-single Crystal Semiconductors on Glass Substrates Through Biaxially Oriented Buffer Layers
Authors: Lu Toh-Ming , Li Huafang , Gaire Churamani , LiCausi Nicholas , Chan Tzu Liang , Bhat Ishwara , Zhang Shengbai , Wang Gwo Ching
Published: August 2010

High efficiency photovoltaic devices are normally fabricated on single crystalline substrates. These single crystalline substrates are expensive and volume production for widespread usage has not been realistic. To date, large volume production of solar cells is on less expensive non-crystalline substrates such as glass. Typically the films grown on glass are polycrystalline with less than ideal efficiency. It was proposed that a dramatic gain in the efficiency may be achieved if one uses a biaxially oriented buffer layer on glass to grow biaxial semiconductor films to fabricate solar devices compared to that of films grown directly on glass. Biaxial films are not exactly single crystal but have strongly preferred crystallographic orientations in both the out-of-plane and in-plane directions. Typically the misorientation between grains can be small (within a few degrees) and may possess low carrier recombination rate. In this paper we shall discuss growth techniques that would allow one to produce biaxial buffer layers on glass. A specific strategy using an atomic shadowing mechanism in an oblique angle deposition configuration that allows one to grow biaxial buffer layers such as CaF2on glass substrate will be discussed in detail. Results of heteroepitaxy of semiconductor materials such as CdTe and Ge on these biaxial buffer/glass substrates characterized by x-ray pole figure, reflection high energy electron diffraction (RHEED) pole figure and transmission electron microscopy (TEM) will be presented.
Mechanisms of Ionic Transport in Membranes for Batteries and Fuel Cells
Authors: Halley J. Woods , Jia Lingling , Bowman Sean
Published: August 2010

Ionic transport in electrolyte membranes limits performance in both battery and fuel cell membranes. The problems have been well known for years, sometimes decades, but empirical progress in solving them has been slow. The focus here is on studies to improve understanding of transport mechanisms, which despite extensive study, remain in dispute in several important cases. For lithium transport in polymer membranes, I will review simulation work by ourselves and others, and contend that the original qualitative picture by Ratner and coworkers is confirmed in many respects by recent work. It means, however, that the fundamental difficulty is that the transport is controlled by torsion forces in the hydrocarbon backbone which are extremely difficult to manipulate experimentally. Turning to possibly promising additives, I review recent work on proton and lithium transport in ionic liquids, on which promising experimental results have been reported. The data, both from simulation and experiment, indicate nontrivial collective effects in the transport properties which need to be sorted out to control these systems. In the case of proton transport, we report results suggesting that high mobilities occur in acid-ionic mixtures with a common anion in mixtures near phase separation.
Scratch Damage and Recovery of Controlled Epoxy Networks
Authors: Lakrout Hamed , Forster Aaron M. , Sung Lipiin , Michaels Chris A. , Wang Deborah
Published: August 2010

Surface scratches in a series of controlled epoxy networks (CEN) were measured using a combination of instrumented indentation protocols and laser scanning confocal microscopy. Identical epoxy chemistry with increasing molecular weight between crosslinks provided different viscoelastic relaxation behaviors with the same modulus at ambient conditions. The glass transition temperatures (Tg)ranged between 70°C and 117°C. The high Tg CEN exhibited the lowest penetration depth and the highest elastic recovery. The results are analyzed with respect to the macroscale bulk properties and underlying molecular architecture of the CEN materials.