bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Ge Nanocrystals in High-k Dielectric Layers for Memory Applications
Authors: Dimitrakis Panagiotis , Ioannou-Sougleridis Vassilios , Normand Pascal , Bonafos Caroline , Schamm Sylvie , Mouti A , Schmidt Bernd , Becker Jill
Published: August 2010

In this paper, the fabrication of Ge-NCs embedded in Al2O3 and HfO2 layers by ion-beam-synthesis for memory applications is investigated. Structural properties of the high-k layers before and after implantation and annealing were studied by TEM observation and EELs analysis. Spherical Ge-NCs 5nm in diameter were observed in Al2O3 implanted layers after furnace annealing at 800°C in nitrogen. Annealing studies in the range 700-1050°C in nitrogen revealed the evolution of the charge storage properties of these structures utilizing MIS capacitors test structures. No NCs were observed in HfO2 implanted layers. However, significant negative-differential-resistance regions were observed in I-V characteristics of the related MIS structures. These may be attributed to the formation of conductive paths made of hafnium germanide (HfGe2) or hafnium germanate (HfGeO) regions.
Overview and Technical Trend of Chain FeRAM
Authors: Takashima Daisaburo
Published: August 2010

A chain FeRAMTMis the best solution to realize high-speed and high-bandwidth nonvolatile RAM with low power dissipation. In this paper, the overview of chain FeRAM, the technical trend for FeRAM scaling and the marketing strategy are presented. First of all, the concept and performance of chain FeRAM are described. Secondly, the status and history of chain FeRAM development are presented. Thirdly, four kinds of scaling strategies for chain FeRAM are presented; (1) A shrink trend of chain cell including a capacitor plug shared with twin cells, and process techniques including Ir/TiAlN-barrier metal and MOCVD-PZT with SrRuO3electrode, which are installed in 16Kb, 8Mb, 32Mb, 64Mb and 128Mb chain FeRAMs, (2) Capacitor damage suppression processes to reinforce step coverage and protect H2damage even in 0.1μm2capacitor of 128Mb, (3) A scalable array architecture such as an octal / quad bitline architecture to reduce bitline capacitance and ensure enough cell signal in scaled ferroelectric capacitor, and (4) A ferroelectric capacitor overdrive technique by driving shield-bitlines to enlarge tail-to-tail cell signal in low voltage operation of 1.3V. Fourthly, future direction of chain FeRAM is discussed. The vertical capacitor is one of candidates for gigabit-scale chain FeRAMs, and solves signal problem and achieves small 4F2cell without contact formation. Finally, the marketing strategy to take full advantage of chain FeRAM is presented. A nonvolatile FeRAM cache is the promising candidate to achieve high bandwidth memory systems. Applications of chain FeRAM to solid-state drive (SSD) and hard-disk drive (HDD) and their system performance improvements are demonstrated.
Characteristics of ZnO Thin Film for the Resistive Random Access Memory
Authors: Seo Jung Won , Baik Seung Jae , Kang Sang Jung , Lim Koseng Su
Published: August 2010

We report resistive switching characteristics in Pt/ZnO/Pt devices where ZnO thin film is fabricated at various oxygen conditions. With the increase of oxygen contents in ZnO thin film, the forming voltage is gradually increased while reset and set voltages are almost unchanged. We also investigated the effect of top electrodes on resistive switching of top electrode/ZnO/Pt device. For a Pt/ZnO/Pt device, it exhibits the excellent resistive switching behavior due to high electrical field of the well-defined Schottky barrier. For Al/ZnO/Pt device, little resistive switching phenomena were occurred due to leakage current of the weak Schottky (or Ohmic) contact.
Effect of W Substitution in Strontium Bismuth Tantalate Ferroelectric Ceramics: Enhanced Ferroelectric Properties
Authors: Coondoo Indrani , Panwar Neearj , Biradar Ashok , Jha Arun
Published: August 2010

Tungsten (W)-substituted SBT ceramics [SrBi2(Ta1-xWx)2O9; 0.0 ≤ x ≤ 0.20] were synthesized by solid state reaction method using different sintering temperatures (1100 οC, 1150 οC, 1200 οC and 1250 οC). W substitution is found to significantly affect the electrical properties of SBT, including dielectric permittivity, Curie temperature, and ferroelectricity. Dielectric constant (εr) and the Curie temperature (Tc) increase with increasing W content. The dielectric loss reduces significantly with increase in W concentration. The maximum Tc of ~ 390 οC is observed in the sample with x = 0.20 as compared to ~ 320 οC for the pure sample when sintered at 1200 οC. The peak ε increases from ~ 270 in the sample with x = 0.0 to ~ 700 for the composition with x = 0.20, when sintered at 1200 οC. All the tungsten-substituted ceramics have higher 2Pr than that in the pristine sample. The maximum 2Pr (~25 μC/cm2) is obtained in composition with x = 0.05 sintered at 1200 οC. These effects have been interpreted based on the model of the recovery of oxygen vacancies upon W substitution. Such compositions with low loss and high Pr values should be excellent materials for highly stable ferroelectric memory devices.
Crystallization of ion amorphized Ge2Sb2Te5 in nano-structured thin films
Authors: Mio Antonio Massimiliano , Carria Egidio , De Bastiani Riccardo , Miritello Maria , Bongiorno Corrado , D'Arrigo Giuseppe , Spinella Corrado , Grimaldi MariaGrazia , Rimini Emanuele
Published: August 2010

The crystallization kinetics of nano-structured amorphous Ge2Sb2Te5 (GST) regions (20-100 nm in diameter) obtained by Electron Beam Lithography (EBL) and 40 KeV Ge+ 1014/cm2 ion irradiation of crystalline 20 nm thick films was investigated. The amorphous regions, surrounded by crystalline cubic (fcc) or hexagonal (hcp) phase, were recrystallized by isothermal annealing in the temperature range 80°C - 120°C and by focused electron beam irradiation. The process was followed in situ by transmission electron microscope (TEM). The recrystallization is governed by the growth of the surrounding f.c.c. crystalline interface with a velocity of 2×10-2 nm/s at 110°C. The interface velocity is higher in the h.c.p. substrate less than a factor ten. Local focused electron beam irradiation induces instead crystalline nucleation inside the nano amorphous regions. Similar experiments have been performed on planar ion amorphized thin films lying on both GST crystalline phases. In both cases the recrystallization is mainly associated to the movement of the amorphous-crystalline interface. These results indicate that the stability of the amorphous region, generated by ion irradiation, is severely affected by the adjacent crystalline structure and by the size of the amorphous area, critically involved in the scaling of the PCM-based devices.
Phase Transition Behaviors of AgInSbTe-SiO2 Nanocomposite Thin Films for Phase-change Memory Applications
Authors: Huang Yu-Jen , Chung Tzu-Chin , Wang Chiung-Hsin , Hsieh Tsung-Eong
Published: August 2010

Phase-change kinetics, structure evolution and feasibility to phase-change memory (PCM) of Ag2In7Sb64Te27 (AIST) and its nanocomposite comprised of 85 wt.% AIST and 15 wt.% SiO2 were presented. In-situ heating x-ray diffraction (XRD) indicated nanocomposite transforms from amorphous to HCP structure during heating and incorporation of SiO2 increases the recrystallization temperature (Tx) of samples (189°C for AIST and 223°C for nanocomposite). XRD and transmission electron microscopy (TEM) analyses both revealed the grain refinement in nanocomposite. Kissinger's analysis found the increase of activation energy (Ea) of phase transition in nanocomposite, denoting the SiO2 embedment restrains the grain growth of AIST during recrystallization. Johnson-Mehl-Avrami (JMA) theory revealed the decrease of Avrami exponent (n), indicating that the phase transition is prone to be heterogeneous since the dispersed SiO2 particles may provide additional nucleation sites.

Static I–V measurement indicated that the switching threshold voltage (Vth) of nanocomposite device (1.65 V) is higher than that of the AIST device (1.10 V). Increase of dynamic resistance in nanocomposite device leads to the reduction of writing current. I–V analysis also confirmed the retardation of recrystallization in AIST due to the incorporation of SiO2 and the rise of Ea is able to enhance the thermal stability of amorphous state in PCM devices.
Activated Pulsed Metalorganic Chemical Vapor Deposition of Ge2Sb2Te5 Thin Films Using Alkyl Precursors
Authors: Reso Denis , Silinskas Mindaugas , Kalkofen Bodo , Lisker Marco , Burte Edmund P.
Published: August 2010

Ge-Sb-Te (GST) thin films were deposited by chemical vapor deposition (CVD) and hot-wire chemical vapor deposition (HW CVD). Several precursor sets (tetraethylgermanium - trimethylantimony - dimethyltellurium (TEGe-TMSb-DMTe), tetraisopropylgermanium - triisopropylantimony - di-tertiarybutyltellurium (TiPGe-TiPSb-DtBTe) and tetraallylgermanium - triisopropylantimony - diisopropyltellurium (TAGe-TiPSb-DiPTe)) were tested for CVD. For the TEGe-TMSb-DMTe precursor set tellurium and germanium could be detected in the films for all deposition temperatures investigated, while Sb was found only in the films deposited at elevated temperature higher than 550 °C. The deposition temperature could be reduced by using two other precursor sets (TiPGe-TiPSb-DtBTe and TAGe-TiPSb-DiPTe). The Ge content, however, could not be sufficiently increased to obtain stoichiometric Ge2Sb2Te5 films. Therefore, the hot wire or catalytic method was applied to improve the decomposition of the precursors. In this case, the desired composition (e.g. Ge2Sb2Te5) was obtained at each investigated temperature by adjusting dosing and deposition parameters. Additionally, film roughness (as low as 2 nm) and deposition rates could be optimized by adjusting deposition temperature and pressure.
Ab Initio Calculations of Crystalline and Amorphous In2Se3 Compounds for Chalcogenide Phase Change Memory
Authors: Chen Renyu , Dunham Scott T
Published: August 2010

Ab Initio calculations of various configurations of In2Se3 compounds are used to gain insight into the transition from crystalline to amorphous phase. The structures considered are based on wurzite structures with 1/3 of indium sites vacant as observed experimentally. From extensive calculations for possible vacancy configurations in In2Se3 compounds, predictions based on the local coordination of In/Se atoms are made for the energetically favorable vacancy ordering structures. Results indicate that in the most stable In vacancy configurations, Se atoms have coordination of either 2 or 3 (In atoms have coordination of 4). Other coordinations lead to significantly higher formation energies. Results from analyzing the total energy and electronic structure of a range of off-stoichiometry, including vacancies, interstitials and anti-site, configurations, suggest that the energetically most favorable way to form In-rich material is via incorporation of Se vacancies, while Se occupying a vacant site is the most favorable for formation of Se-rich phase. Based on these calculations, predictions are made on how stoichiometry deviations impact structural evolution during phase change.
Evidence for Magnetic Polarons in Hole-Doped Cobalt Perovskites
Authors: Podlesnyak Andrey , Furrer Albert , Straessle Thierry , Pomjakushina Ekaterina , Conder Kazimierz , Khomskii Daniel
Published: August 2010

A substitution of La3+ by Sr2+ in LaCoO3 induces holes in the low-spin ground state of the Co ions, which behave like magnetic impurities with a very high spin value (13 μB per hole). In this work, using single-crystal neutron spectroscopy, we prove that the charges introduced by strontium doping do not remain localized at the cobalt sites. Instead, each hole not only creates Co4+ in low-spin state, but it also transforms the six nearest neighboring Co3+ ions to the intermediate-spin state thereby forming a magnetic seven-site (heptamer) polaron. Spin-state polarons behave like magnetic nanoparticles embedded in an insulating nonmagnetic matrix. Therefore, lightly doped La1-xSrxCoO3 is a natural analog to artificial structures composed of ferromagnetic particles in insulating matrices.
Silver/Gold Heterometallic Nanostructures and Their Surface Plasmon-related Behaviors
Authors: Song Hyunjoon
Published: August 2010

A combination of silver and gold is demonstrated in nanoscale objects. Silver and gold have similar but distinct chemical and physical properties. We employed three main chemistry related to silver and gold – underpotential deposition, epitaxial growth, and Galvanic replacement. Selective underpotential deposition of silver guided the growth direction of gold and generated gold octahedrons, cuboctahedrons, cubes, and rods. Epitaxial growth of silver on gold decahedral seeds formed silver-gold-silver heterometallic nanorods and wires. Galvanic replacement of silver for gold yielded asymmetric single hollow and symmetric double hollow structures. All silver/gold nanostructures exhibited characteristic optical features in the UV-vis-NIR ranges. Such structural variation and corresponding optical properties are useful for diverse applications in electronics, photonics, biology, and catalysis.
High transversal relaxivities of silica coated multicore iron oxide nanoparticles suitable for magnetic resonance imaging
Authors: Roig Anna , Taboada Elena , Rodríguez Elisenda
Published: August 2010

We report on high transversal relaxivity values of composite iron oxide-silica nanoparticles. To obtain the material, pre-formed maghemite nanoparticles were coated with silica by sol-gel chemistry, using supercritical fluids as the reaction media. The composite particles were monodisperse and consisted of a core of several maghemite nanoparticles, surrounded by a thick silica shell. The high pressure and high temperature process did not affect the iron oxide particle size but induced an increase on their saturation magnetization values, possibly due to an improvement of the particle crystallinity. These iron oxide-based materials present very high transversal relaxivity values which can be correlated to the magnetic moment and to the silica shell width of the composite particles. Moreover, composite particles are not cytotoxic and they are dispersable in polar solvents.
Active Nanostructures at Interfaces for Photocatalytic Reactors and Low-power Consumption Sensors
Authors: Gole James L , Ozdemir Serdar , Prokes Sharka M , Dixon David M
Published: August 2010

Active nanostructures which provide unique transformations are being introduced to phase matched porous silicon (PS) nano/micropores to form a platform for low power consumption highly selective sensors and microreactors. TiO2-xNx photocatalysts have been formed in seconds at room temperature at the nanoscale via the direct nitration of anatase TiO2 nanocolloids. Tunability throughout the visible depends upon the degree of agglomeration and the ability to seed these nanoparticles with metal ions. Co metal ion seeding leads to the efficient room temperature phase transformation, of anatase to rutile TiO2, where normally much higher temperatures are required. Seeding of a properly nitridated TiO2 nanocolloid with transition metal ions (Co, Ni) allows for the enhancement of the infrared spectra of the TiO2-xNx nitridated titania surface in excess of 10-fold, providing a means to analyze for minor contaminants and intermediates. Evidence for nitrogen fixation is found in Fe treated systems. The TiO2-xNx systems act as visible light absorbing photocatalyts. These photocatalysts and additional nanostructured metal oxides can be placed on the surface of PS-based sensor and microreactor configurations to greatly improve the interface response.
Optoelectronic and Interfacial Properties of CNT and ITO on Borosilicate Glass and PET Substrates with Nano- and Hetero-structural Aspects
Authors: Park Joung-Man , Wang Zuo-Jia , Kwon Dong-Jun , DeVries Lawrence K
Published: August 2010

Nano- and hetero-structures of carbon nanotube (CNT) and indium tin oxide (ITO) can control significantly piezoelectric and optoelectronic properties in Microelectromechanical Systems (MEMS) as sensing and actuators under cyclic loading. Optimized preparation conditions were obtained for multi-functional purpose of the specimens by obtaining the best dispersion and turbidity in the solution. Optical transmittance and electrical properties were investigated for CNT and ITO dipping and spraying coating on boro-silicate glass and polyethylene terephthalate (PET) substrates by electrical resistance measurement under cyclic loading and wettability test. Uniform dipping coating was performed using Wilhelmy plate method due to it simple and convenience. Specimen was applied with spraying coating additionally. The change in the electrical and optical properties of coated layer is mainly dependent upon the number of dip-coating, the concentration of CNT and ITO solutions, and the surface treatment condition. Electric properties of coating layers were measured using four-point probe method, and surface resistance was calculated using a dual configuration method. Optical transmittance of CNT and ITO coated PET film was also evaluated using UV spectrum. Surface energy and their hydrophilic and hydrophobic properties of CNT and ITO coated substrates were investigated by wettability test via static and dynamic contact angle measurements. As the elapsing time of cyclic loading passed, the stability of surface resistance and thus comparative interfacial adhesion between coated layer and substrates was evaluated to compare the thermodynamic work of adhesion, Wa. As dip-coating number increased, surface resistance of CNT coating decreased, whereas the transmittance decreased step-by-step due to the thicker CNT and ITO networking layer. Nano- and hetero-structural effects of CNT and ITO solution on the optical and electrical effects have been studied continuously.
WO3 Doping Effects on the Photoelectrocatalytic Activity of TiO2 Nanotube Film Prepared by an Anodization Process
Authors: Tsai Hei Lok , Leung Micheal K.H. , Li Gui Sheng , Leung Dennis C.Y.
Published: August 2010

WO3 doped TiO2 nanotube(WO3-doped TNT) thin film was fabricated by anodizing the TiO2 nanotube (TNT) film in an NH4F electrolyte containing WO4- ions. The sample was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectroscopy (DRS). The results show that WO3 was successfully doped into TiO2 nanotubes and the absorption edge of WO3 doped TNT appeared to be red shifted. The photoelectrocatalytic (PEC) activity of WO3 doped TNT electrode was evaluated through the PEC degradation of aqueous Acid Blue 80. The experimental results demonstrated that the PEC degradation rate of WO3 doped TNT is increased by 48% and by 167% over that of non-doped TNT under UVA light irradiation and visible-light irradiation, respectively, at an applied potential of 1.54V. The degradation rates of WO3 doped TNT under photocatalytic (PC), electrochemical (EC), and PEC processes were compared. The results reveal the synergetic effect of PC and EC processes.
Nanoporous Anodic Alumina as Template and Mask for Functional Nanostructures Fabrication
Authors: Hernández-Vélez Manuel , Sanz R , Manso Miguel , Sanchez O , de Melo O , Asenjo Agustina , Minguez-Bacho I. , Vázquez Manuel
Published: August 2010

Nanoporous Anodic Alumina Films (NAAF) have been used for growing a lot of nanostructure functional materials. Of particular interest is the NAAF conversion into membranes (NAAM) with different highly controlled pore diameter and distribution to be used as templates and masks to grow a wide variety of nanomaterials. This work constitutes an approach to a review of our latest results regarding the use of NAAF and NAAM as templates in which II-VI semiconductor, functional oxides, hard materials and magnetic nanowires have been grown. The growth techniques and methods used include Isothermal Close Space Sublimation (ICSS), Magnetron Sputtering, electroplating and sol-gel. Ion Beam Irradiation (IBI) combined with different NAAM as masks has been also used for Titania substrates functionalization.
Magnetism in Cylindrical NiFe Nanotubes
Authors: liew hwifen , Goolaup Sarjoosing , Wang Xinghua , Lew Wensiang
Published: August 2010

We report the fabrication of ferromagnetic NiFe nanotubes with a wall thickness of 80 nm by electrodeposition in nanoporous templates. The structure and wall thickness of the nanotubes are controlled by the thickness of the conductive layer at the back of the templates. The NiFe nanotubes have shown soft magnetic material properties with high magnetic saturation and low coercivity. The NiFe nanotube arrays are preferentially magnetized in the perpendicular direction to the nanotubes. Micromagnetic simulation results show that a curling mode is perceived with the formation of opposite magnetic vortex states on the end of the nanotube surface during the magnetization process.
Material Properties in Codimension > 0: Graphene Edge Properties
Authors: Branicio Paulo Sergio , Srolovitz David J
Published: August 2010

When materials are very thin in one or more dimensions, their equilibrium shapes are often curved/bent. Such shapes commonly represent a compromise between elastic strain energy and other thermodynamic forces (e.g. related to surface stresses, electrostatic interactions, or adsorption). Examples include ZnO and SnO2nanobelts, silica/carbonate helicoids, and graphene sheets and nanoribbons. Here, we demonstrate that when the equilibrium shape of a nanomaterial is not flat/straight, important fundamental material properties may be orders of magnitude different from their bulk counterparts. We focus here primarily on the graphene edges. Graphene in three dimensions is a codimensionc= 1 material; the codimension isc = D – d= 3 – 2 = 1, whereDis the dimensionality of the space in which the material is embedded anddis the dimensionality of the object. By contrast, a flat graphene sheet hasc= 2 – 2 = 0. We use the REBO-II interatomic potential to calculate the edge orientation dependence of the edge energy and edge stresses of graphene withc= 0 andc= 1. The edge stress for all edge orientations is compressive withc= 0. Both edge energy and stresses are in reasonable agreement with DFT calculations. The compressive edge stresses inc= 0 lead to edge buckling (out-of-the-plane of the graphene sheet) for all edge orientations (c= 1). The edge buckling inc= 1 reduces all edge energies and dramatically reduces all edge stresses to near zero (more than an order of magnitude drop). We also report the effect of codimension on the free energy and entropy of a graphene sheet and the elastic properties of ZnO nanohelices.
Simulations of Pressurized Water Flow through Carbon Nanotubes
Authors: Shaw Samantha , Faux David
Published: August 2010

Molecular dynamics simulations of the flow of pressurised water through carbon nanotubes of chirality (9,0), (12,0), (15,0) and (18,0) have been undertaken at 298K with a water density of approximately 1240kg/m3. Results show that the rate of filling is least in the smallest diameter nanotube, but that there is less variation in the time taken to reach maximum occupancy. The water molecules are found to undergo restructuring due to their confinement, with detailed molecular arrangement dependent on CNT diameter. Enhanced rates of flow are shown for the (15,0) nanotube, highlighting the effect of nanotube diameter on confinement and thus on flow.
Electrical Properties of Pd-contacted Single-walled Carbon Nanotubes: A Scanning Probe Microscopy Study
Authors: Kononenko Oleg , Bozhko S I , Matveev V N , Volkov V T , Knyazev M A , Il'in A I , Matveev D V , Kasumov Yu A , Khodos I I
Published: August 2010

Pd is widely used in producing electrodes to single-walled carbon nanotubes (SWNT). However up to now its ability to form ohmic contacts to SWNTs was not employed in scanning probe microscopy (SPM). Here we present a study of SWNTs with Pd electrodes by SPM using Pd-coated tips. SWNTs were selectively grown on oxidized silicon substrates by low pressure CVD method. Pd electrodes were prepared to SWNTs to fabricate two terminal structures for SWNTs resistance measurements. It is shown that SPM Kelvin mode is a reliable technique for SWNT detection on insulating substrate. Contact potential difference between Pd electrode and SWNT is measured using the Kelvin mode.
Layer-by-layer CdTe Nanoparticle Absorbers for ZnO Nanorod Solar Cells - The Influence of Annealing on Cell Performance
Authors: Briscoe Joe , Gallardo Diego E. , Dunn Steve
Published: August 2010

The conformal coating of ZnO nanorods with CdTe nanoparticles using layer-by-layer (LbL) processing produces a quantum dot-sensitised solar cell. As the number of CdTe layers increases the absorption of incident light increases below the absorption onset of the nanoparticles (650 nm). Photoluminescence investigations of the CdTe-ZnO composite structure suggest a transfer of photoexcited electrons from the CdTe nanoparticles the ZnO nanorods. Filling of the semiconductor composite structure with CuSCN provides the solar cell with a p-type semiconductor to collect the photogenerated holes from the system. Annealing the CdTe-polymer coated nanorods lowers the series resistance of the cell by removing the polymer component of the film. A cell annealed at 350 °C has aJscof 0.12 mAcm-2, and aVocof 49 mV under 0.25 mW/cm2illumination.
Photovoltaic Devices from Silicon Nanoparticles
Authors: Rier Christoph , Schierning Gabi , Wiggers Hartmut , Schmechel Roland , Jäger Dieter
Published: August 2010

In this paper, results of designing, fabricating and characterizing photovoltaic devices made from tailored silicon nanoparticles are shown as proof-of-principle to adopt this material into the photovoltaic sector. The silicon nanoparticles are used as active material for direct separation of the light induced charge carriers. Homo pn-junctions were constructed by silicon wafers and silicon nanocrystals, the latter doped with the opposite carrier type than the wafers. Nanocrystals were sintered on top of the wafer by a spark plasma sintering process, maintaining the nanocrystalline character. This way, the nanoparticle layers are a combined absorbing and charge separating medium. Electrical characterization measurements of the devices show a reproducible short-circuit current of up to 20 μA under illumination. A maximum short-circuit current density of 6.25 μA/cm2 was realized.
Electronic Structure of La(Fe0.88Si0.12)13
Authors: Kamakura Nozomu , Okane Tetsuo , Takeda Yukiharu , Fujimori Shin-ichi , Saitoh Yuji , Yamagami Hiroshi , Fujimori Atsushi , Fujita Asaya , Fujieda Shun , Fukamichi Kazuaki
Published: August 2010

La(Fe0.88Si0.12)13 shows peculiar magnetic properties such as the first order paramagnetic-ferromagnetic transition and magnetic-field induced metamagnetic transition accompanied by the lattice expansion. The practical application using the magnetic transition temperature controlled by hydrogen absorption is expected in this compound. Here, the electronic structure of La(Fe0.88Si0.12)13 has been investigated by photoemission spectroscopy using synchrotron soft x-rays. The Fe 3s core-level photoemission spectra below and above the Curie temperature TC exhibit a satellite structure at ~ 4.3 eV higher binding energy than the main peak, which is attributed to the exchange splitting due to the local moment of Fe. The exchange splitting of the Fe 3s photoemission spectrum with the asymmetric line shape shows that the magnetization of La(Fe0.88Si0.12)13 is derived by the exchange split Fe 3d bands like the itinerant ferromagnetism in Fe metal, while the magnetic transition of La(Fe0.88Si0.12)13 is the first order. The valence band photoemission spectrum shows temperature dependence across the TC. The temperature dependence of the photoemission spectra is discussed based on the difference between the electronic structure in the ferromagnetic phase and that in the paramagnetic phase.
Kinetic Monte Carlo Simulation of the Aging of Nanoporous Metals
Authors: Wagner Gregory J. , Seif Dariush , Ong Markus D.
Published: August 2010

A kinetic Monte Carlo (kMC) model for the simulation of the coarsening of nanoporous metals is developed and demonstrated. The model treats surface evolution through the mechanism of surface diffusion by following atoms hopping between sites on an FCC lattice. Using a generic model for event energy barriers, we are able to demonstrate trends in the simulation and show that at high temperatures, coarsening follows approximately the scaling law predicted by continuum surface diffusion theory; the behavior is less clear at low temperatures. By selecting event energies to model palladium we show that we are able to reach temperatures and time scales that have relevance to experiments and applications.
Atom Probe Tomography characterization of the microstructural evolution of a low copper reactor pressure vessel steel under neutron irradiation
Authors: Huang Hefei , Radiguet Bertrand , Todeschini Patrick , Chas Guillaume , Pareige Philippe
Published: August 2010

A low copper reactor pressure vessel steel was characterised by atom probe tomography after neutron irradiation at different fluences. The specimens were irradiated within the frame of the Surveillance Program of a production reactor. Roughly spherical clusters enriched in nickel, manganese, silicon and, in a lesser extent, phosphorus and copper were observed at all fluences. The chemical composition of these clusters shows no evolution with fluence, as well as their diameter, close to 3 nm. Their number density increases linearly with the neutron fluence. A continuous segregation of the elements found in the clusters is also observed along dislocation lines, with similar enrichments.
Multiscale Modeling of Irradiation Induced Hardening in a-Fe, Fe-Cr and Fe-Ni Systems
Authors: Mastorakos Ioannis , Le Ngoc , Zeine Melody , Zbib Hussein M , Khaleel Moe
Published: August 2010

Structural materials in the new Generation IV reactors will operate in harsh radiation conditions coupled with high levels of hydrogen and helium production, thus experiencing severe degradation of mechanical properties. The development of structural materials for use in such a hostile environment is predicated on understanding the underlying physical mechanisms responsible for microstructural evolution along with corresponding dimensional instabilities and mechanical property changes. As the phenomena involved are very complex and span in several length scales, a multiscale approach is necessary in order to fully understand the degradation of materials in irradiated environments. The purpose of this work is to study the behavior of Fe systems (namely a-Fe, Fe-Cr and Fe-Ni) under irradiation using both Molecular Dynamics (MD) and Dislocation Dynamics (DD) simulations. Critical information is passed from the atomistic (MD) to the microscopic scale (DD) in order to study the degradation of the material under examination. In particular, information pertaining to the dislocation-defects (such as voids, helium bubbles and prismatic loops) interactions is obtained from MD simulations. Then this information is used by DD to simulate large systems with high dislocation and defect densities.
Actinide Science with a Soft X-ray Scanning Transmission X-ray Microscope (STXM)
Authors: Glans Per-Anders , Szigethy Geza , Demoin Dustin , Tyliszczak Tolek , Xu Jide , Guo Jinghua , Raymond Kenneth N. , Shuh David K.
Published: August 2010

Soft x-ray scanning transmission x-ray microscope (STXM) spectromicroscopy has been developed and employed to investigate several aspects of actinide chemistry and materials science at the Advanced Light Source Molecular Environmental Science (ALS-MES) Beamline 11.0.2 STXM end station. The basic approach and fundamentals of STXM experiments for radioactive materials systems is discussed. Representative results from STXM spectromicroscopy investigations of a mixed phase uranium nitride, single crystals of Eu(III)[TREN(Me-3,2-HOPO)]32H2O and hydrated Pu2(III)(C2O4)3(6H2O) 3H2O complexes are presented. The STXM images and soft x-ray absorption spectra illustrate the capabilities and utility of soft x-ray STXM for providing information about actinide materials, especially the light element constituents. Lastly, new and future opportunities for actinide science utilizing soft x-ray STXM are discussed in light of the planned upgrades for the STXM end stations at the ALS.
Nuclear Fuels – Present and Future
Authors: Olander Donald
Published: August 2010

The important developments in new nuclear fuels are reviewed and compared with the status of present light-water reactor fuels. The limitations of LWR fuels are reviewed with respect to important recent concerns, namely provision of outlet coolant temperatures high enough for use in H2 production, destruction of plutonium to eliminate proliferation concerns, and burning of the minor actinides to reduce the waste repository heat load and long-term radiation hazard. In addition to current oxide-based fuel-rod designs, the hydride fuel with liquid metal thermal bonding of the fuel-cladding gap is covered. Finally, two of the most promising Generation IV reactor concepts, the Very High Temperature Reactor(VHTR) and the Sodium Fast Reactor (SFR) , and the accompanying reprocessing technologies, aqueous-based UREX+1a for the VHTR and pyrometallurgical for the SFR, are summarized.
Electronic Properties of ζ-U-Pu Alloys
Authors: Havela Ladislav , Adamska Anna , Eloirdi Rachel , Colineau Eric , Griveau Jean-Christophe , Gouder Thomas , Huber Frank , Bouexière Daniel , Shick Alexander
Published: August 2010

The ζ-phase, existing between 35 and 70% U in Pu, belongs to the high density phases seen from the point of view of systematics of allotropic modifications of Pu metal. Despite the volume per actinide atom only slightly higher than for α-Pu, it magnetic susceptibility is much higher than for α-Pu and exceeds even the δ-Pu value. Similarly, the Sommerfeld coefficient γ > 40 mJ/mol Pu K2 exceeds the experimental δ-Pu value. The data confirm that the volume is not the primary control parameter affecting the situation around the Fermi level of common Pu phases and they point against the traditional belief that they are essentially narrow 5f band systems.
Capture and Sequestration of Radioactive Iodine
Authors: Westphal Brian , Cummings Daniel G. , Giglio Jeff J. , Wahlquist Dennis L. , Bateman Ken J. , McCartin William M. , Park Jang J. , Shin Jin M. , Begg Bruce D.
Published: August 2010

Trapping experiments have been performed at the Idaho National Laboratory to assess the performance of AgX sorbent media in capturing volatile iodine during the oxidation of irradiated oxide fuel. The demonstration of iodine release and capture from the used fuel has been accomplished with laboratory-scale equipment in a hot cell environment. Iodine loadings as high as 6 ug/g media have been achieved via chemical adsorption with filter efficiencies in excess of 90%. In addition to iodine, significant quantities of tritium have also been collected on the AgX filter media. Filter media loaded with radioactive iodine has been sequestered in a tin matrix by hot isostatic pressing at 200°C. The placement and encapsulation of the sorbent media was examined by neutron radiography, thus confirming the sequestration of radioactive iodine.
Characterization of the Penetration Mechanisms of Water into Polycrystalline UO2
Authors: Marchetti Ilaria , Belloni Fabio , Himbert Jerome , Carbol Paul , Fanghänel Thomas
Published: August 2010

Following containment failure in the scenario of geological disposal of spent nuclear fuel, the penetration rate of groundwater into the UO2 matrix could cause a rapid increase of the fraction of inventory becoming available for prompt dissolution. In this respect, oxygen and water diffusion mechanisms are key issues to investigate. In this work, secondary-ion-mass-spectrometry (SIMS) depth profiling has been applied to characterize a polycrystalline UO2 pellet exposed to 18O-labelled water at room temperature. 18O depth profiling up to 25 μm beneath the pellet surface clearly indicates a combination of oxygen diffusion into the UO2 lattice and water diffusion along grain boundaries, behaving as high diffusivity paths. The lattice diffusion coefficient of oxygen, DL, and the quantity δDB – product of the grain boundary width, δ, and the grain boundary diffusion coefficient of water, DB – have been measured, resulting in DL = (2.5 ± 0.1) × 10-24 m2 s-1 and δDB = (7.5 ± 0.3) × 10-24 m3 s-1.
Structure and alteration kinetics of rare-earth rich borosilicate glasses with (64 – 2x) SiO2 / 18 B2O3 / 18 Na2O / x RE2O3 composition (RE = Y or Eu+ La)
Authors: Majerus Odile , Caurant Daniel , Li Ning , Baudouin Jean-Baptiste , Manolescu Gabriela , Barboux Philippe , Charpentier Thibault , de Ligny Dominique
Published: August 2010

The high level nuclear waste load is likely to increase in the future containment glasses, rising new questions about their long-term chemical durability. In this study sodium borosilicate compositions with Si substituted for RE (RE = rare earth) are altered under static conditions at fixed pH (8.5). The Na and B leached fractions reached just after the rate drop increase with the RE2O3 content. Part of the RE ions remain in the altered layer which is significantly de-polymerised (IR-ATR and NMR results). Their environment is reorganized and adopts a more centrosymetrical character. The higher leached fractions are attributed to rapid hydrolysis of Si/B-O-RE bonds with respect to Si-O-Si bonds.
Nanocrystalline silicon compacted by spark-plasma sintering: Microstructure and thermoelectric properties
Authors: Schierning Gabi , Claudio Tania , Theissmann Ralf , Stein Niklas , Petermann Nils , Becker Andre , Denker Joachim , Wiggers Hartmut , Hermann Raphael T. , Schmechel Roland
Published: August 2010

Nanocrystalline bulk silicon samples were fabricated using silicon nanoparticles from the gas phase, applying a spark-plasma sintering process. The mean diameter of the crystalline grains after sintering was 30 nm and smaller, the density above 97 % of that of crystalline silicon. Transmission electron microscopy showed a homogenous nanostructure. The thermal conductivity of such an n-type sample with a nominal doping level of 5×1020 cm-3 was around 11 Wm-1K-1 at room temperature. With Seebeck-coefficient α = -150 μV/K and specific conductivity σ = 290 S cm-1, the resulting efficiency ZT is approximately 0.02.
Performance Optimization of a TE Generator Element With Linear Material Profiles in a 1D Scheme
Authors: Zabrocki Knud , Seifert Wolfgang , Mueller Eckhard
Published: August 2010

Thermoelectric (TE) effects as a coupling between heat and charge transfer can be described on a classical level in the framework of the Onsager theory. Under isotropic and steady state conditions the conservation equations can be combined to obtain a thermal energy balance containing the temperature distribution as target function. Besides the temperature the balance equation contains material properties represented by the Seebeck coefficient S, the electrical and thermal conductivities σ and κ, respectively. For the sake of simplicity, a 1D scheme has been chosen for the analytical and numerical treatment. Performance investigations are often done within the framework of the Constant Properties Model (CPM) or based on temperature dependent material properties. In the 1D steady state, there is an alternative approach available based on spatial material profiles. Following the approach by Müller and co-workers, the temperature profile T(x) is calculated numerically within a model-free setup directly from the 1D thermal energy balance, e.g., based on continuous monotonous gradient functions for all material profiles, and independent and free variability of the material parameters S(x), σ(x), and κ(x) is assumed initially. Doing so, the optimum electrical current density can be determined from the maximum of the global performance parameter (power output P or efficiency η). We present analytical results for the performance optimization calculating P and η with linear material profiles for S(x), a constant electrical and thermal conductivity, fixed TE element length L and fixed boundary temperatures.
Thermoelectric Properties of Non-equilibrium Synthesized Ce0.9Fe3CoSb12 Filled Skutterudites
Authors: Jie Qing , Zhou Juan , Dimitrov Ivo K. , Li Chang-Peng , Uher Ctirad , Wang Hsin , Porter Wallace D. , Li Qiang
Published: August 2010

We report on the thermoelectric properties of the filled skutterudite Ce0.9Fe3CoSb12 prepared via non-equilibrium synthesis method. Melt-spun ribbons were directly converting into single phase polycrystalline pellets under pressure. For comparison, pellets with the same composition were also prepared using the conventional solid-state reaction followed by long term annealing. It was found that the non-equilibrium synthesized samples have higher power factors and lower thermal conductivity, leading to substantially higher figure of merit.
Synthesis and Thermoelectric Properties of Doped Yb14MnSb11-xBix Zintls
Authors: Star Kurt , Zevalkink Alex , Huang Chen-Kuo , Dunn Bruce , Fleurial Jean-Pierre
Published: August 2010

Yb14MnSb11 is a very promising thermoelectric material for high temperature applications. This compound is a member of a large family of Zintl phases with a “14-1-11” A14MPn11 stoichiometry (Pn = P, As, Sb, Bi; A = Ca, Ba, La, Sr, Yb, Eu; M = Mn, Al, Cd, Ga, In, Nb, Zn). Yb14MnSb11 exhibits low lattice thermal conductivity values and a p-type semimetallic behavior with values of the non-dimensional figure of merit zT peaking at 1.4 above 1200 K. There is significant interest in investigating how substitutions on any of the atomic sites impact the charge carrier concentration and mobility, band gap and lattice thermal conductivity. Recent reports have studied substitutions on the Yb and Mn sites with the goal of reducing hole carrier concentration and improving carrier mobility values.

High energy ball milling has been shown to be a convenient method of synthesis to prepare Yb14MnSb11 and it has been used here to explore the solid solution systems derived from this compound by substituting Sb with Bi. High energy ball milling is a non-equilibrium process and not all of the 14-1-11 compounds are easily formed with this method. Characterization of the synthesized compositions was done by X-ray diffraction, electron microprobe, and high temperature measurements of the electrical and thermal transport properties up to 1275 K. The experimental results on undoped and doped solid solution samples are compared to that of pure Yb14MnSb11 samples prepared by the same high energy ball milling technique.
Effects of MeV Si Ions Modification on the Thermoelectric Properties of SiO2/SiO2+Cu Multilayer Thin Films
Authors: Chacha John , Budak S. , Smith Cydale , Pugh Marcus , Ogbara Kudus , Heidary Kaveh , Johnson R. B. , Muntele Claudiu , ILA D.
Published: August 2010

The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. We have prepared 100 alternating multi-nano layer of SiO2/SiO2+Cu superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed at the different fluences using the AAMU Pelletron ion beam accelerator to make quantum clusters in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric thin films before and after Si ion bombardments we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.
The Role of Nanoparticle Inclusions on High-performance half-Heusler Thermoelectric Materials
Authors: Yaqub Rumana , Sahoo Paranti Sahoo , Makongo Julien Pierre , Notling Westly M , Poudeu Pierre F. P. , Stokes Kevin L.
Published: August 2010

We report the effect of adding NiO nanoparticles on the transport properties of the half-Heusler alloys Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01 (x=0, and 0.2). The half-Heusler matrix materials are prepared by traditional powder metallurgy methods. The resulting bulk matrix is mixed with different volume fractions of nanometer-sized NiO particles, previously synthesized by solution-phase chemical methods. The resulting mixture is densified under uniaxial pressure to form a composite. The resulting material is found to contain both half-Heusler and full-Heusler phases. The corresponding compounds have higher thermal conductivity and electron mobility.
Improvements of Thermoelectric Performances in AgSbTe2 System With in-situ Ag2Te Nano-Precipitations
Authors: Zhang Shengnan , Yang Shenghui , Jiang Guangyu , Shen Junjie , Zhu Tiejun , Zhao Xinbing
Published: August 2010

AgSbTe2 is the critical component in both LAST-m and TAGS-x system, which are two state-of-the-art mid-temperature thermoelectric bulk nanocomposites. By adjusting the Ag2Te/Sb2Te3 ratio, Sb2Te3 and Ag2Te precipitated samples were obtained with x = 0.68 to 0.74 and x = 0.84 to 0.90 (x as in (Ag2Te)x/2(Sb2Te3)1-x/2), respectively. The single phased AgSbTe2 was obtained with the x value of 0.78 and 0.81, which is consistent of the previous results on the phase diagram of (Ag2Te)x(Sb2Te3)1-x system. Comparing the effect of the two different precipitates, Ag2Te are much effective for the improvements of thermoelectric properties in AgSbTe2 nanocomposites. Utilizing the high-resolution transmission electron microscopy, Ag2Te was observed as nanodots and nano-lamellae embedded in the AgSbTe2 matrix, which can be related to the energy filtering effect for the increase of Seebeck coefficient. The relationship among the composition, microstructure and thermoelectric properties was systematically studied. It can be noticed that the thermoelectric properties of AgSbTe2 system are very sensitive to the composition, especially at low temperature. The maximum figure of merit ZT value of 1.53 was obtained at 500 K for Ag0.84Sb1.16Te2.16 with 40% increase comparing with the single phased sample.
Spinodal Decomposition in Off-stoichiometric Zr0.5Hf0.5Co1-yIrySb1-zSnz half-Heusler Phases
Authors: Takas Nathan J. , Misra Dinesh , Gabrisch Heike , Poudeu Pierre F. P.
Published: August 2010

The formation of nanostructures within the matrix of half-Heusler thermoelectric materials can be produced by spinodal decomposition of off-stoichiometric compositions. CoSb is insoluble at high temperatures in Zr0.5Hf0.5Co1-yIrySb1-zSnz half-Heusler phases. This phase can be solubilized into the half-Heusler matrix by the use of high energy ball milling at room temperature as the synthetic method of choice. The metastable half-Heusler material decomposes in-situ while hot-pressing the powder sample into a compact pellet. Despite the fact that the thermal conductivity of the inclusion material, CoSb, is very large, (>35W/m•K), we observed reduction in the lattice thermal conductivity of the composite material. Furthermore, the electrical resistivity of the specimen was also reduced due to the metallic nature of the CoSb inclusion phase. Addition of a large fraction of the metallic inclusion leads to a percolation network of the metallic phase, thus reducing the Seebeck coefficient of the composites. Electron microscopy is carried out in order to examine boundaries between the two. Changes in the thermoelectric properties of Zr0.5Hf0.5Co1-yIrySb1-zSnz half-Heusler matrix with increasing mass percent of CoSb inclusion will be discussed.