bluuebunny/crossref_metadata_2025 huggingface dataset:
Dislocation Confinement and Ultimate Strength in Nanoscale Polycrystals
Authors: Li Qizhen , Anderson Peter M. , Mills Michael , Hazzledine Peter
Published: April 2011

Nanoscale polycrystalline metals typically exhibit increasing hardness with decreasing grain size down to a critical value on the order of 5 to 30 nm. Below this, a plateau or decrease is often observed. Similar observations are made for nanoscale multilayer thin films. There, TEM observations and modeling suggest that the hardness peak may be associated with the inability of interfaces to contain dislocations within individual nanoscale layers. This manuscript pursues the same concept for nanoscale polycrystalline metals via an analytic study of dislocation nucleation and motion within a regular 2D hexagonal array of grains. The model predicts a hardness peak and loss of dislocation confinement in the 5 to 30 nm grain size regime, but only if the nature of dislocation interaction with grain boundaries changes in the nanoscale regime.
Numerical Derivative Analysis of Load-Displacement Curves in Depth-Sensing Indentation
Authors: Juliano Tom , Domnich Vladislav , Buchheit Tom , Gogotsi Yury
Published: April 2011

The use of load-displacement derivative behavior and power-law curve fitting is applied to find the location of events for a number of different materials during depth-sensing indentation. Load-displacement curves for Berkovich indentations on fused silica, fullerene thin film on sapphire, CdTe thin film on silicon, single crystal silicon, carbide derived carbon, and a polymethylmethacrylate/hydroxyapatite (PMMA/HA) particle composite are examined. The analysis is applied to quantify the location of different events that occur during material loading and unloading.
Vibrational Frequency of MgO Nanoparticles in a polymer matrix
Authors: Jha Prafulla K. , Talati Mina
Published: April 2011

By using elastic continuum model for a spherical body along with the appropriate boundary conditions at the surface of the body, vibrational frequencies of MgO nanoparticles are calculated in the present paper. It is found that the vibrational frequencies corresponding to these eigen values depend strongly on the size of the nano particles and the peaks in the Raman spectra shift to the higher frequencies side as size of the nano particles decreases. We have also investigated the effect of a polymer matrix on the frequencies and Raman shift of MgO nanoparticles. The damping constant is found to vary linearly with the size of nano particles which shows that the mechanical damping is the prominent mechanism in the damping of the acoustic phonon modes.
Mechanical Properties of Chemically Functionalized Clay Vinyl Ester Nanocomposites
Authors: Balakrishnan S. , Raghavan D.
Published: April 2011

This study focuses on the role of chemistry of onium salt(s) used in functionalizing clay and the processing conditions in achieving exfoliated clay vinyl ester nanocomposites. Two different clay treatments were added to vinyl ester resin and three different processing conditions were examined in the formulation of nanocomposite. Through this study, we demonstrate that the degree of exfoliation and dispersion of layered silicate nanocomposite is affected by both processing and the clay chemical treatment. At an organoclay loading of only 3.5wt%, the modulus improved by 20% in partially reactive organoclay system, while the modulus improved by 10% in nonreactive organoclay system compared to that of pristine vinyl ester resin.
Structural and Mechanical Properties of Boron Nanotubes
Authors: Evans Matthew H. , Joannopoulos John D. , Pantelides Sokrates T.
Published: April 2011

We report the results of first-principles calculations showing that boron can form a wide variety of metastable planar and tubular forms with unusual electronic and mechanical properties. The preferred planar structure is a buckled triangular lattice that breaks the threefold ground state degeneracy of the flat triangular plane. When the plane is rolled into a tube, the ground state degeneracy leads to a strong chirality dependence of the binding energy and elastic response, an unusual property that is not found in carbon nanotubes. The achiral (n, 0) tubes derive their structure from the flat triangular plane. The achiral (n,n) boron nanotubes arise from the buckled plane, and have large cohesive energies and novel structures as a result.
In situ TEM study of irradiation-induced transformation in TiNi shape memory alloys
Authors: Zu X. T. , Wan F.R. , Zhu S. , Wang L. M.
Published: April 2011

TiNi shape memory alloy (SMA) has potential applications for nuclear reactors and its phase stability under irradiation is becoming an important topic. Some irradiation-induced diffusion-dependent phase transformations, such as amorphization, have been reported before. In the present work, the behavior of diffusion-independent phase transformation in TiNi SMA was studied by electron irradiation at room temperature. The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by Transmission Electron Microscopy (TEM) with in-situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltage of 200 kV, 300 kV, 400 kV and 1000 kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 320 kV, but never appeared at 300 kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of Electron-irradiation-induced the martensitic transformation due to displacements of atoms from their lattice sites produced by the accelerated electrons.
Can we trust TEM images of silicate glasses?
Authors: Jiang Nan
Published: April 2011

Electron irradiation-induced modifications in two glasses, K2O – SiO2 and Au doped Na2O – B2O3 – SiO2, were observed in electron microscope. The products of modifications were “nano-particle” like contrasts in transmission electron microscopy (TEM) images, which can be easily confused with real nano-particles and phase separation. The driving force for the modifications in the glasses is the tendency of elimination of non-bridging oxygen (NBO) through the removal of cations. The phase separation into cation rich and poor region is their nature under electron irradiation. Therefore, it is absolutely essential to record in situ frames when the TEM images are used to provide microstructure information of glasses. Additionally, charging effects in glasses have also been discussed.
Damage Evolution and Annealing of Au-Irradiated Samarium Titanate Pyrochlore
Authors: Zhang Y. , Shutthanandan V. , Thevuthasan S. , McCready D. E. , Young J. , Devanathan R. , Andreasen J. , Balakrishnan G. , Paul D. M. , Weber W. J.
Published: April 2011

Damage evolution and thermal recovery of 1 MeV Au2+ irradiated samarium titanate pyrochlore (Sm2Ti2O7) single crystals were studied by Rutherford backscattering spectroscopy and nuclear reaction analysis. The damage accumulation follows a nonlinear dependence on dose that is well described by a disorder accumulation model, which indicates a predominant role of defect-stimulated amorphization processes. The critical dose for amorphization at 170 and 300 K is ∼0.14 dpa, and a higher dose of ∼ 0.22 dpa is observed for irradiation at 700 K, which agrees with previous in-situ transmission electron microscopy (TEM) data for polycrystalline Sm2Ti2O7. Annealing in an 18O environment reveals a damage recovery stage at ∼ 850 K that coincides with a significant increase in 18O exchange due to oxygen vacancy mobility. This thermal recovery stage is also consistent with the critical temperature for amorphization measured by in-situ TEM in polycrystalline samples.
Mössbauer study of 50MeV Li3+ion irradiated Mg0.9Mn0.1InxFe2-xO4ferrite
Authors: Singh M. , Dogra Anjana , Kumar Ravi
Published: April 2011

A series of samples of Mg0.9Mn0.1InxFe2-xO4for x=0, 0.3, 0.5 were prepared by conventional solid-state technique. The spinel structure of this ferrite was confirmed by X-ray diffraction technique. The samples were irradiated with 50 MeV Li3+ions with fluence 5×1013ions/cm2. The Mössbauer studies were performed on unirradiated as well as on irradiated samples. Mössbauer study for unirradiated samples show insignificant variation of isomer shifts at both the tetrahedral and octahedral sites. On irradiation isomer shift changes from negative to positive values. This anomalous character of isomer shift after irradiation is due to a change in the electronic configuration of Fe3+ions. The quadrupole splitting of unirradiated samples are negligibly small, indicates the presence of cubic symmetry at both the sites. On irradiation appreciable changes are observed in quadrupole splitting due to the presence of lattice strain. On irradiation super-exchange interaction energy is weakened which decrease the hyperfine field. PACS: 61.80, 76.80, 61.72
γ-Ray Irradiation Practical Conditions for Low Molecular Weight Chitosan Material Production
Authors: Yoksan Rangrong , Akashi Mitsuru , Miyata Mikiji , Biramontri Siriratana , Chirachanchai Suwabun
Published: April 2011

The present work focuses on the γ-ray irradiation doses and conditions (dry solid state, solid state dispersing in 0.5–2 % aqueous H2O2 solution, solid state dispersing in 1% aqueous acetic acid, and 2% aqueous K2S2O8) to determine the level that the molecular weight of chitosan is lowered significantly without changing its primary structure. Molecular weight of chitosan (105-106 Dalton) is reduced approximately 50% under the γ-ray dose of 20 kGy in the dry solid state. The decrease in molecular weight is enhanced up to 80% when chitosan is suspended in 0.5–2 % aqueous H2O2 solution during γ-ray irradiation. In either condition, the backbone structure of the irradiated product is maintained with little change in the terminal chain. In the cases of (i) chitosan suspended in 2% aqueous K2S2O8 and (ii) chitosan in 1% aqueous acetic acid, chitosans lose their primary structures and physical properties.
Comparative Study of Defect Properties in GaN: Ab Initio and Empirical Potential Calculations
Authors: Gao Fei , Bylaska Eric J. , El-Azab Anter , Weber William J.
Published: April 2011

Density functional theory (DFT) is used to study the formation, properties and atomic configurations of monovacancies, antisite defects and possible interstitials in GaN. The relaxation around a vacancy is generally small, but the relaxation around antisite defects is large, particularly for a Ga antisite defect, which is not stable and converts to an N-N<0001> split interstitial. All N interstitials, starting from any possible site, eventually transfer into the N-N split interstitials, forming N2 molecules with one N-N bond, but also some covalent bonds to the surrounding atoms. In the case of Ga interstitials, the most favorable configuration is the Ga octahedral interstitial. However, it is found that the Ga-Ga<1120> split interstitial can bridge the gap between non-bonded Ga atoms along the <1120> direction, which leads to the formation of Ga atomic wires in GaN, with bond distance (2.3Å) close to those noted in bulk Ga. In addition, two representative potentials, namely Stillinger-Weber and Tersoff-Brenner potentials, have been employed to determine the formation of defects using molecular dynamics (MD) method in GaN. The MD results are discussed and compared to DFT calculations. The present DFT and MD results provide guidelines for evaluating the quality and fit of empirical potentials for large-scale simulations of ion-solid interaction and thermal annealing of defects in GaN.
Microstructure and He Bubble Effects on Al-Cu Thin Films
Authors: Camacho C.S. , Fichtner P.F.P. , Zawislak F.C. , Feldmann G.
Published: April 2011

The effects of film morphology (mosaic- or bamboo-like grain structures) and of He bubbles on the redistribution of Cu, as well as on the formation of Al-Cu precipitates in 200 nm thick Al/SiO2 films similar to microelectronic device interconnects, are investigated using Rutherford backscattering spectrometry, elastic recoil detection analysis and transmission electron microscopy. As-deposited and pre-annealed Al films were implanted with Cu and/or He ions forming concentration profiles located 100 nm below the surface and with peak concentrations of about 3 at.%. It is shown that grain boundaries and/or He bubbles can affect the vacancy fluxes inside the grains and reduce or even inhibit the Cu redistribution as well as the nucleation and growth of θ and θ′ Al-Cu precipitates during post-implantation annealings at temperatures from 473 to 553 K. It is also shown that mosaic-like grain structures allow the control of grain size distribution within the 25 to 1500 nm size range, thus providing an additional microstructure engineering tool to improve device reliability against electromigration failures.
Ion Beam Manipulation to Fabricate Ordered Layered Structures and Amorphous Alloys in Some highly Immiscible Binary Metal Systems
Authors: Li X. Y. , Zhang R. F. , Liu B. X.
Published: April 2011

We developed a new scheme, namely ion beam manipulation, i.e. interface-assisted ion beam mixing, for fabricating amorphous alloys and artificial solid-state microstructures in metal-metal multilayers, in which the individual layer thickness is down to about 2 nm, differing significantly from the typical thickness of 5–8 nm in conventional ion beam mixing. Employing the scheme, some interesting results were obtained in three highly immiscible systems. In the Ag-W system, which has the largest positive heat of formation among the transition metal alloys, amorphous alloys were obtained, for the first time, through a two-step structural transition, i.e. the initial polycrystalline Ag and W transformed into an intermediate bcc phase, which later transformed into an amorphous state. In the Ru-Pd system, the initial polycrystalline Pd and Ru first transformed into a single crystalline FCC phase, and then turned into a well-ordered structure, which showed an apparent tendency to transform back to the FCC phase upon over-irradiation. In the Ag-Co system, an ordered layered structure was observed and identified to consist of two overlapped FCC lattices, corresponding to a new magnetic state of Co atom with an average magnetic moment measured to be 2.84 μB, which was about twice the equilibrium datum and was the largest value ever observed. We present, in this paper, a brief review concerning the scheme of ion beam manipulation in fabricating the metastable alloys, the structural evolution upon ion irradiation and the associated magnetic properties of some ordered structures obtained by the scheme.
Trapping of argon in ion beam deposited thin films of CNx Hy
Authors: Kayani Asghar N. , Ingram David C.
Published: April 2011

Unbalanced magnetron sputtering deposition of CNx Hy films has been performed with various levels of negative substrate bias and with different flow rates of nitrogen and hydrogen. Argon was used as a sputtering gas and formed the majority of the gas in the plasma. The elemental concentrations of the films were measured in samples deposited on glassy carbon with a 2.2 MeV of He beam used to perform simultaneous RBS and ERS. Argon was found to be trapped in the non-hydrogenated films to a level of up to ∼ 4.6 %. The concentration of argon increased for the films deposited under higher negative bias. With the introduction of hydrogen, argon trapping was first minimized and later completely eliminated, even at higher bias conditions, suggesting that the softness of the films brought on by hydrogenation also caused the films to be unable to trap argon during growth and thus showing that argon stability is dependent on burial below a surface of particular structural properties.
High rate etching of GaAs and GaP by gas cluster ion beams
Authors: Nagano Masahiro , Houzumi Shingo , Toyoda Noriaki , Yamada Susumu , Akita Shirabe , Yamada Isao
Published: April 2011

Gas cluster ion beam (GCIB) techniques have recently been proposed as new processing methods. We have been investigating the characteristics of GCIB techniques through sputtering GaAs and GaP by Ar gas cluster ion beams as a function of cluster size and acceleration energy. The Ar cluster size was selected by a magnetic spectrometer, and was obtained from the mass spectra measured by a time of flight mass spectrometer. The average sputtering yields of GaAs and GaP were 0–47 and 0–66 atoms/ion for 5–30 k V, respectively. The sputtering yields of GaAs and GaP were higher than those of an Ar monomer ion.
Fabrication of two-dimensional Si/Ge nanowires and nanorings
Authors: Kawamura Midori , Voigtländer Bert , Paul Neelima , Cherepanov Vasily
Published: April 2011

We show that two-dimensional Si/Ge nanostructures with a thickness of a single atomic layer can be imaged with chemical sensitivity using a scanning tunneling microscope (STM). An atomic layer of Bi terminating the surface is used to distinguish between Si and Ge. This distinction between Si and Ge enabled us to fabricate two-dimensional Si/Ge nanostructures in a controlled way by self-organized growth. Si/Ge nanoring structures consisting of alternating Si and Ge rings having a width of ∼5 nm were grown around a Si core on a Si(111) substrate by molecular beam epitaxy (MBE). The thickness of the Si and Ge rings is only one atomic layer (0.3 nm). Alternating Si/Ge nanowires with a width of ∼3.5 nm and a thickness of 0.3 nm were also fabricated using alternating Si/Ge deposition in the step flow growth mode.
Epitaxial Metallic Islands: Charge Confinement And Templates For Atomic Wires
Authors: Mazzone A.M. , Savini G.L.
Published: April 2011

Hartree-Fock calculations at semiempirical level, using the Extended Debey-Hückel Approximation, and LDA with pseudopotentials are used to investigate the properties of homoepitaxial islands formed by Cu and Ag. The islands have a three-dimensional shape and the dimensions of their height and basis are in the range of the bulk Fermi wavelength. Linear chains of Ag and Cu atoms are deposited on the island steps. The calculations describe the binding action of the island on the chain as well as the allowed energies and the density of states of the complete system. The results indicate that, due to the corrugation of the potential at the island-substrate interface, the more stable chain configurations are the ones near the island top rather than at its basis. Furthermore at these small sizes the island steps act as weak and permeable barriers. In fact, the electronic charge retains bulk-like features, though traces of quantum confinement can be identified.
Microscopic theory of electromagnetic energy transport in nanostructured media
Authors: Xue Yongqiang , Ratner Mark A.
Published: April 2011

We present a microscopic theory of electromagnetic energy transport in nanostructured media based on the Lagrangian formulation of semiclassical electrodynamics. We show the importance of the interplay between transverse and longitudinal local fields in determining the light-matter interaction in nanostructured media. We derive rigorously the coupled-dipole equation of the local fields and apply the theory to analyze energy transport in metal nanoparticle chain waveguide.
In-situ TEM Study of the Crystallization of Thin Films composed of Sb3.6Te with Ge
Authors: Kooi Bart J. , Groot Willemijn M.G. , De Hosson Jeff Th.M.
Published: April 2011

This paper addresses the crystallization of amorphous Sb3.6Te films (40 nm thick) and 5 at.% Ge containing Sb3.6Te films (10, 20 and 40 nm thick) as studied using in-situ annealing in a Transmission Electron Microscope (TEM). These materials show growth-dominated crystallization, in contrast to Ge2Sb2Te5 that shows nucleation-dominated crystallization. Particularly the crystal-growth velocity in these systems is measured as a function of temperature from which the activation energy for growth can be derived. The strong effect of the 5 at.% Ge addition on the total crystallization behavior is revealed: Ge increases the crystallization temperature (from 95 to 150 °C), increases the activation energy for growth (from 1.58 to 2.37 eV), increases the nucleation rate and decreases the growth anisotropy.
Modeling InSe Phase-change Materials
Authors: Kohary K. , Burlakov V. M. , Nguyen-Manh D. , Pettifor D. G.
Published: April 2011

The amorphous structure of InxSey has been studied by a first principles tight-binding molecular dynamics technique using the program package PLATO (Package for Linear-combination of Atomic Type Orbitals). The three-dimensional amorphous structures with different densities were prepared by quick quenching from the liquid phase. The characteristics of short-range order such as coordination numbers, radial and bond angle distributions, and ring statistics have been analyzed.
Thermodynamic Properties of Pu-O-H Compounds and Alloys from Density Functional Theory
Authors: Korzhavyi P. A. , Vitos L. , Johansson B.
Published: April 2011

A theoretical approach has been developed that allows one to obtain thermodynamic properties of plutonium-based alloys and compounds from first-principles electronic structure calculations based on density functional theory. The approach is applied to study the defect structure in non-stoichiometric PuO2±δ.
Iron – Phosphate Glass (IPG) Waste Forms Produced using Induction Melter with Cold Crucible
Authors: Aloy A.S , Soshnikov R. A. , Trofimenko A. V. , Gombert D. , Day D. , Kim C. W.
Published: April 2011

A simulated sodium bearing waste (SBW), which represented a type of high sodium and sulfate waste, was successfully vitrified in iron phosphate glasses (IPG), at a maximum waste loading of 40 wt%, using a cold crucible induction melter (CCIM). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that all of the IPG waste forms did not contain sulfate salt segregation or crystalline phases. The calculated composition and the average analytical composition obtained by Electron Probe Microanalysis (EPMA) were in good agreement. The major elements were uniformly distributed throughout the samples. The chemical durability of the IPG waste forms containing 40wt% SBW was evaluated by the product consistency test (PCT) and met current DOE requirements. IPG waste forms were melted at a relatively low temperature and for short times compared to borosilicate glasses. These advantages, combined with those of a significantly higher waste loading and the feasibility for CCIM melting, offer a considerable savings in time, energy, and cost for vitrifying this high sodium and sulfate waste.
Development Of A Glass-Encapsulated Ceramic Wasteform For The Immobilization Of Chloride-Containing ILW
Authors: Metcalfe Brian L. , Fong Shirley K. , Donald Ian W.
Published: April 2011

Pyrochemical reprocessing of plutonium generates several ILW waste-streams and a simple process has been developed at AWE to immobilize the chloride and actinide ions present in one of these waste-streams (Type 1) by calcining the waste with calcium phosphate. We have now investigated the possibility of using this process as the basis for treating a more complex waste-stream (Type 2) and have determined that with some minor modification the original process can effectively immobilize the greater range of cations present in Type 2 waste to again produce a free-flowing non-hygroscopic powder. Weight for weight replacement of the Type 1 waste by Type 2 produced a powder which was approximately 20% deficient in PO43- when compared with stoichiometric powder. Addition of phosphorus pentoxide to the simulant waste/calcium phosphate powder mixture prior to calcination to produce stoichiometric powder significantly improved the chloride ion uptake. In order to comply with safety requirements it is necessary to convert the free-flowing powder into a monolithic wasteform suitable for long term storage. Conversion of the powder to a monolithic wasteform by sintering using a sodium aluminophosphate glass as a binder has been investigated and has proved successful, but to achieve high densities it has been necessary to cold press the samples prior to sintering.
Structural Studies of Hollandite-Based Radioactive Waste Forms
Authors: Whittle K. R. , Ashbrook S. E. , Redfern S.A.T. , Lumpkin G. R. , Attfield J. P. , Dove M. , Farnan I.
Published: April 2011

Hollandites with compositions Ba1.2-xCsxMg1.2-x/2Ti6.8+x/2 O16, and Ba1.2-xCsxAl2.4-xTi5.6+xO16 (x=0, 0.1, 0.25) have been synthesised using a modified alkoxide/acetate precursor route. The samples have been sintered using two procedures; hot isostatic pressing and sintering at ambient pressure. X-ray powder diffraction has shown samples from both systems to form tetragonal hollandites, with little change when pressed by both methods. Cs-133 MAS NMR spectra have been recorded showing the chemical shift in Al containing samples to be ∼250ppm, and in Mg hollandites ∼175ppm and 200ppm, with little change when prepared by both methods.
Zeolite - Salt Occlusion: A Potential Route for the Immobilisation of Iodine-129?
Authors: Hyatt Neil C. , Hriljac Joseph A. , Choudhry Alia , Malpass Laura , Sheppard Gareth P. , Maddrell Ewan R.
Published: April 2011

Reactions of zeolite Na-A with AgI, and the sodium, copper and lead forms of zeolites A, LTA, X and Y with NaI, have been examined as possible starting routes to the long term immobilisation of iodine-129. Heating the salts in air, at 500°C, with the sodium forms of the zeolites leads to the formation of occlusion products, where the iodide salt migrates into the zeolite pores. Detailed studies of the Na-A / 5AgI complex indicate it has a uniform distribution of Na, Si, Al, Ag and I, and is thermally stable to ca. 750°C, where there is a substantial weight loss as iodine is released. In situ powder X-ray diffraction studies have been used to monitor the occlusion reaction at 400°C, and show that the occlusion product decomposes to produce a single crystalline phase at 800°C prior to further decomposition at 850°C to a mixture of nepheline and elemental silver.
Thermodynamic Modeling and Sensitivity Analysis of Kd Values for Radionuclide Migration in Sedimentary Host Rocks
Authors: Talerico Caterina , Ochs Michael , Ueta Shinzo , Sasaki Noriyuki
Published: April 2011

The effects of key geochemical parameters on Kd values for radionuclides in the host rock (pumice, sandstone) of a LLW repository were elucidated through a sensitivity analysis, using a thermodynamic speciation/sorption model for the elements Sr and Ni. The complex mineral assemblage of the rock was approximated by a component-additivity approach. Using published ion exchange and surface complexation parameters, Kd for both Sr and Ni could be well explained by the same model mineralogy and surface chemistry. Model results suggest that pCO2 can have a significant effect on Kd, and that a correct approximation of groundwater chemistry is a critical component of sorption modeling.
Smectite Dissolution Kinetics in High-Alkaline Conditions
Authors: Ohmoto Hiroshi , Spangler Kathryn R. , Watanabe Yumiko , Kamei Gento
Published: April 2011

To determine the initial rates and effects of silica in solution on the dissolution kinetics of smectite, short- and long-term batch experiments (0.5 hour to 30 days) were completed at three temperatures (T = 25, 50, and 75°C) using stock solutions pH adjusted by NaOH (pH = 12, 13, and 13.5) with varying initial silica concentrations (0, 30, 60, and 100 ppm). The following important characteristics were observed at pH = 12: (1) The concentrations of Al, Si, Mg, Fe, and Ti in solutions increase rapidly during the first ∼2 hours and reach steady state (equilibrium) within ∼5 days. (2) The concentration ratios of Al, Si, Fe, Mg, and Ti in solutions during the early (<2 hours) reaction phase differ significantly from those of smectite, indicating initial dissolution proceeds non-stoichiometrically; Al dissolves much faster than Si, Mg, Fe, and Ti. (3) Further dissolution of smectite proceeds nearly stoichiometrically, including Fe and Ti. (4) The high solubility of Ti in highly alkaline solutions may be due to the formation of aqueous complexes, such as TiO(OH)3− and TiO2(OH)22−, similar to aqueous silica species. (5) The initial rate of smectite dissolution increases with increasing pH, T, and initial silica content of solution. (6) The silica in solution acts as a promoter and a catalyst, rather than an inhibitor, of smectite dissolution in high-alkaline solutions. This role is easily recognizable when the solubility of smectite and amorphous silica are very high, i.e., at pH >∼9.
Reactive Transport Modeling of Radionuclide Source-Terms in an Underground Spent Fuel Disposal
Authors: De Windt L. , Catalette H. , Gras J. M.
Published: April 2011

The reactive transport model HYTEC was used to simulate the migration over 100,000 years of cesium, americium and uranium released from spent fuel packages in the near-field components of an underground stiff clay disposal site. A global equilibrium thermodynamic approach including kinetic control of the spent fuel pellets was used with instantaneous release fractions and congruent dissolutions of the rim and the core zones. A failure scenario of the waste package after 10,000 years was considered with magnetite as the main corrosion product. The retention properties of magnetite and the different effects of bentonite and cementitious backfill materials were specifically analysed.
Geochemical Indicators of Groundwater Stability
Authors: Bath Adrian , Strömberg Bo
Published: April 2011

The interpretation of geochemical and isotopic data as indicators of past hydrodynamic stability of groundwaters in fractured rock is discussed. Knowledge of the conditions and timing of past groundwater stability supports scenarios for safety assessments. Stratification of water masses according to densities is an important factor affecting stability. Chloride variations and concentration gradients are therefore diagnostic of mixing and the duration of stable conditions. Further evidence of timescales is provided by carbon-14 and tritium data although sampling difficulties and other uncertainties may allow only qualitative interpretations. Data from Äspö and other Swedish sites, Sellafield (UK) and Olkiluoto (Finland) are used to illustrate the approach. The palaeohydrogeology of such sites has been strongly influenced by distributions of saline waters. Scenarios for groundwater stability should consider these as well as glacial melt waters.
Local- and Repository-Scale Hydrodynamic Modeling for Geoscientific Characterization of a Candidate ILW/HLW Repository Site in Northern Switzerland
Authors: Kuhlmann Ulrich , Marschall Paul
Published: April 2011

Hydrodynamic modelling on the site- and repository scale was aimed at testing the performance of both, geological and engineered barriers as part of the Swiss program for disposal of high- and intermediate-level radioactive waste. Conceptual and parameter uncertainties were addressed by sensitivity studies to explore the robustness of the overall disposal concept. Consistency was demonstrated between modelling results and hydrogeological and geochemical evidence from the Benken borehole, increasing confidence in the comprehension of the key hydrogeological features of the candidate repository site. Assessment of a wide spectrum of repository closure conditions highlighted the function of the waste confinement concept. Visualisation and animation of the modelling results has proven to be of great help in communicating the level of comprehension of groundwater movement in the vicinity of a potential repository in the Zürcher Weinland.
Study on Unearthed Bronzes Relics of Xizhou Dynasty, China
Authors: Zhangru Chen , Zhijian Wen , Guang Fan , Yuemiao Liu
Published: April 2011

Engineered barrier for HLW repository is composed of the waste form, the canister and the buffer/backfill material. Assessment of the applicability of metal as candidate materials of canister for HLW has been conducted in some countries. Many bronze relics from the XiZhou Dynasty, China, dated from more than 3,000 years ago, have been preserved perfectly. The study on the corrosion of the bronze relics could contribute to the material selection and design of canisters for HLW. The corrosion products of ancient bronzes consist of copper carbonate hydrate, lead carbonate, copper oxides etc. The corrosion mechanism of the substrate was mainly characterized by electrochemical corrosion, whereas the corrosion mechanism of surface layers was characterized by direct chemical corrosion and electrochemical corrosion.
Granite Recrystallization - The Key to an Alternative Strategy for HLW Disposal?
Authors: Gibb Fergus G. F.
Published: April 2011

An alternative strategy is proposed for the disposal of spent nuclear fuel (SNF) and other forms of high-level waste (HLW) whereby the integrity of a mined and engineered repository for the bulk of the waste need be preserved for only a few thousand years. This is achieved by separating the particularly problematic components, notably heat generating radionuclides (HGRs) and very long lived radionuclides (VLLRs) from the waste prior to disposal. Such a solution requires a satisfactory means of disposing of the relatively minor amounts of HGRs and VLLRs removed from the waste. This could be by high-temperature very deep disposal (HTVDD) in boreholes in the continental crust [1,2]. However, the viability of HTVDD, and hence the key to the entire strategy, depends on whether sufficient melting of granite host rock can occur at suitable temperatures and whether the melt can be completely recrystallized. The high-temperature, high-pressure experiments reported here demonstrate that granite can be partially melted and completely recrystallized on a time scale of years, as opposed to millennia as widely believed. Furthermore, both can be achieved at temperatures and on a time scale appropriate to the disposal of packages of heat generating HLW. It is therefore concluded that the proposed strategy, which offers, environmental, safety and economic benefits, could be a viable option for a substantial proportion of HLWs.
Vertically Integrated Amorphous Silicon Particle Sensors
Authors: Wyrsch N. , Miazza C. , Dunand S. , Shah A. , Moraes D. , Anelli G. , Despeisse M. , Jarron P. , Dissertori G. , Viertel G.
Published: April 2011

Vertically integrated particle sensors have been developed using thin-film on ASIC technology. Hydrogenated amorphous silicon n-i-p diodes have been optimized for particle detection. These devices were first deposited on glass substrates to optimize the material properties and the dark current of very thick diodes (with thickness up to 50 m). Corresponding diodes were later directly deposited on two types of CMOS readout chips. These vertically integrated particle sensors were tested in beta particle beam from 63Ni and 90Sr sources. Detection of single low- and high- energy beta particle was achieved.
Solar Cells on Foreign Substrates Using Poly-Si Thin Films by Metal Induced Growth
Authors: Ji Chunhai , Anderson Wayne A.
Published: April 2011

The poly-Si film was deposited by using the metal-induced growth (MIG) method on tungsten substrates. By making Au/n-Si Schottky photo-diodes, doping density effect was studied by using three different doping level Si sputtering targets. Increasing the Si target resistivities from 0.02Ω-cm to 50Ω-cm, open-circuit-voltage (Voc) decreased from 0.22V to 0.14V while short-circuit-current density (Jsc) increased from 1.55mA/cm2 to 2.42mA/cm2. C-V results revealed a high charge density in the device, which may be due to the oxygen thermal donor effects. Using an oxygen filter for the sputtering gas effectively reduced the charge densities and increased the Jsc value. The p/n junction solar cells were fabricated by using ion implantation at 1013∼1014cm−2 dose and 100∼200keV. The cells with wider emitter layer by double-ion implantation gave higher Jsc and Voc values. Passivation of the Si film by using hydrogenation improved the Jsc, Voc and spectral response of the solar cells.
Development of a Porous Silicon Product for Small Molecule Mass Spectrometry
Authors: Credo Grace , Hewitson Hillary , Benevides Christopher , Bouvier Edouard S. P.
Published: April 2011

Previous work has demonstrated the utility of desorption/ionization on silicon (DIOS) time-of-flight mass spectrometry (TOFMS) in drug molecule and peptide detection[1-7]. In this work, the utility of DIOS for small molecule detection is established using commercially available porous silicon (por Si)-based target plates for MS. Since the morphology and handling of the substrates can have dramatic effects on the MS characteristics, the development of consistent manufacturing methods and characterization protocols has been central to the production of reproducible target plates[7]. Using sample substrates manufactured in-house, we show that 1) small molecules and protein digests were detected without matrix-related peaks, 2) por Si morphology was optimized for small molecule detection, 3) reproducible DIOS plates were produced, 4) although the target plates were shown to be sensitive to contamination, a consistent cleaning procedure was developed to remove contaminants, and 5) stability and shelf life were characterized as a function of surface derivatization. Dynamic range, sensitivity, quantitation, speed of analysis, solution composition, and automated deposition have also been evaluated and are described in related work[7-9]. Potential applications include high-throughput small molecule assays for drug discovery[10a] and high sensitivity (sub-femtomole) peptide identification for proteomics[10b].
Excimer-Laser Growth of Si Large-Grain Arrays
Authors: Matsumura Masakiyo
Published: April 2011

Amorphous silicon (a-Si) Thin Film Transistors (TFT) will continue to play an important role in large-area liquid crystal displays (LCD), however, there is also a strong demand for ultra-high performance TFTs aimed at intelligent small (or medium) size displays. For this reason, “Crystal Si on glass” has become an increasingly attractive solution. This paper reviews recent work performed at ALTEDEC (Advanced LCD Technologies Development Center Co., Ltd, with regard to growing an array of large Si grains at low temperature. The results obtained so far indicate that satisfactory progress has been made towards the achievement of this goal.
Electronic Properties of RF Glow Discharge Intrinsic Microcrystalline Silicon near the Amorphous Silicon Phase Boundary
Authors: Gutierrez James J. , Halverson Adam F. , Tweeten Eric D. , Cohen J. David , Yan Baojie , Yang Jeffrey C. , Guha Subhendu
Published: April 2011

The electronic properties of microcrystalline silicon have been characterized for the first time using transient photocapacitance spectroscopy (TPC) and drive-level capacitance profiling (DLCP). These methods were applied to microcrystalline films deposited by the RF glow discharge method at United Solar. The DLCP method allowed the shallow doping density to be profiled and the deep defect densities to be estimated. The TPC spectra were found to reveal that both a microcrystalline as well as an amorphous component are present in these samples. By varying the measurement temperature for these TPC spectra we were also able to directly monitor the degree of minority carrier collection in these films. Significant effects due to light soaking on the TPC spectral properties were also observed.
Surface Potential and Surface Photovoltage of Oxide and Nitride coated multicrystalline Silicon Solar Cells using a Scanning Kelvin Probe
Authors: Baikie Iain D.
Published: April 2011

We have applied a high resolution scanning Kelvin probe to perform dark surface potential topographies of multicrystalline silicon solar cells having thin coatings of Si3N4 and SiO2. We clearly observe the electrical characteristics of the screen printed bus-bar and associated fingers, grain boundaries, together with characteristic structures on the oxide and nitride, coupled to significant surface potential variations across larger sections of the wafer. Associated surface photovoltage measurements can be unambiguously decoded to show coating and bulk contributions. The nitride coating exhibits carrier trapping lifetimes in excess of 13 minutes at 300K.
New ultrahigh vacuum setup and advanced diagnostic techniques for studying a-Si:H film growth by radical beams
Authors: Hoefnagels J.P.M. , Langereis E. , Sanden M.C.M. van de , Kessels W.M.M.
Published: April 2011

A new ultrahigh vacuum setup is presented which is designed for studying the surface science aspects of a-Si:H film growth using various advanced optical diagnostic techniques. The setup is equipped with plasma and radical sources which produce well-defined radicals beams such that the a-Si:H deposition process can be mimicked. In this paper the initial experiments with respect to deposition of a-Si:H using a hot wire source and etching of a-Si:H by atomic hydrogen are presented. These processes are monitored by real time spectroscopic ellipsometry and the etch yield of Si by atomic hydrogen is quantified to be 0.005±0.002 Si atoms per incoming H atom.
Growth of hydrogenated microcrystalline silicon (μc-Si:H) films by HWCVD using a Graphite catalyzer
Authors: Bhusari D.M. , Kumar P. , Kupich M. , Schroeder B.
Published: April 2011

A graphite catalyzer has been used to grow μc-Si:H films using the thermo-catalytic (HW) chemical vapor deposition (CVD) technique. The films grown in the amorphous-microcrystalline ‘transition regime’ have been found to exhibit a high photosensitivity of the order of 102-103 at a crystalline volume fraction of 0.2-0.4. The effects of deposition parameters such as silane concentration, pressure and substrate temperature on the microstructure and electrical properties of the films have been studied. It has been found that the graphite catalyzer offers a wider window of the deposition parameters for the growth of the ‘transition regime’ films as compared to the conventional W and Ta catalyzers. In addition, the graphite wires also exhibit significantly greater chemical as well as mechanical stability than the W and Ta wires, which results in improvement of the reproducibility of the technique. However, at the same filament temperature and other conditions, the deposition rates are about 10 times lower than for W or Ta filament. Increasing of the filament temperature, on the contrary, lead to radiative heating and carbon contamination of the growing film.
Devices Fabrication with Narrow-Bandgap a-SiGe:H Alloys Deposited by HWCVD
Authors: Xu Yueqin , Yan Baojie , Nelson Brent P. , Iwaniczko Eugene , Reedy Robert C. , Mahan A.H. , Branz Howard
Published: April 2011

We incorporate narrow-gap amorphous silicon germanium (a-SiGe:H) alloys grown by hot-wire chemical vapor deposition (HWCVD) into single-junction n-i-p solar cells, and improve both fill factor (FF) and open-circuit voltage (Voc) by bandgap grading. The Tauc bandgap (ET) of the a-SiGe:H is as low as about 1.25 eV. Previously [1], we obtained a short-circuit current density (Jsc) up to 20 mA/cm2 in an n-i-p device incorporating an ungraded 120-nm i-layer of 1.25-eV a-SiGe:H. However, without buffer layers or bandgap profiling, the fill factor was only 38%, likely due to an abrupt bandgap transition and poor hole collection. To overcome these problems, we have used composition bandgap profiling throughout the i-layer and improved both Voc and FF significantly without any Jsc loss. The solar cell efficiency is improved from 3.55% to 5.85% and Voc rises from 0.475 to 0.550 eV. This improved single-junction a-SiGe:H solar cell has a quantum efficiency of about 48% at l=800 nm and about 15% at l=900 nm. We present details of the bandgap profiling and its effect on device performance.
Channel engineering and junction overlap issues for ultra-shallow junctions formed by SPER in the 45 nm CMOS technology node
Authors: Severi Simone , Henson Kirklen , Lindsay Richard , Lauwers Anne , Pawlak Bartek J. , Surdeanu Radu , Meyer K. De
Published: April 2011

The feasibility of the SPER junction process as a reasonable alternative to the spike anneal junction is proved in this work. Good control of the SCE and performance competitive results as compared to the spike junction are obtained. An analysis of the interaction between the halo dopant and the SPER junctions has been carried out; it is shown that the performance degrades with increasing halo dose as a consequence of an overlap resistance problem.
Simulation and Electron Energy-Loss Spectroscopy of Electron Beam Induced Point Defect Agglomerations in Silicon
Authors: Stoddard Nathan G. , Duscher Gerd , Windl Wolfgang , Rozgonyi George A.
Published: April 2011

Nitrogen doped silicon samples were irradiated with 200 kV electrons in a transmission electron microscope (TEM). The resulting room temperature point defect creation, bonding and segregation were studied by in situ conventional and Z Contrast TEM imaging and electron energy loss spectroscopy (EELS). Energy loss spectra from areas attributed to be rich in vacancies or silicon self-interstitials are found to be significantly different from the bulk in the near-edge structure of their Si-L2,3 edges. The experimental results are compared with ab initio density of states calculations for electronically excited atoms near relaxed point defect structures and plans are outlined to extend this technique to individual point defect characterization.
Study of Ni(Pt) germanosilicides formation on fully-strained Si0.9Ge0.1 and Si0.899Ge0.1C0.001 by Raman Spectroscopy
Authors: Chaw J. Y. Y. , Pey K. L. , Lee P. S. , Chi D. Z. , Liu J. P.
Published: April 2011

In this work, Raman spectroscopy was used to study the reaction of pure Ni and Ni(Pt 5 at. %) with fully-strained Si0.9Ge0.1 and Si0.899Ge0.1C0.001. With pure Ni, it was found that the incorporation of 0.1% C in the substrate resulted in out-diffusion of Ge from the germanosilicide film at a lower rapid thermal annealing (RTA) temperature compared to that of pure Ni on Si0.9Ge0.1. This Ge out-diffusion phenomenon is evident from the gradual shift in the NiSi1-wGew (w ≤ x) Raman peak from ∼213 cm−1 to higher wavenumbers, closer to 217 cm−1 as reported for pure Ni/Si, indicating that Ge is being depleted from the film with increasing RTA temperatures. In addition, it was found that severe agglomeration of the germanosilicide film occurred at a lower RTA temperature for the Ni/Si0.899Ge0.1C0.001 system. This corresponds to the observations from the Raman spectra, where a sharp increase in the Si substrate peak at 520 cm−1 was observed, coupled with the appearance of the transverse acoustic (TA)-phonon peak of Si at 301 cm−1. When Pt was introduced into the Ni film, significant improvements were observed for the germanosilicide films on Si0.9Ge0.1 and Si0.899Ge0.1C0.001 substrates, both in terms of Ge out- diffusion and agglomeration. Initial findings show that the addition of Pt promotes the formation of the low resistivity mono-germanosilicide phase at temperatures as low as 300°C.
Millisecond Microwave Annealing: Reaching the 32 Nm Node
Authors: Thompson Keith , Booske John H. , Ives R.L. , Lohr John , Gorelov Yurii A. , Kajiwara Ken
Published: April 2011

The next generation of Si devices requires thermal treatments of 1200°C – 1300°C but can only withstand temperatures above 800°C for a few milliseconds. Current rapid thermal processing techniques cannot meet these requirements. We have designed, constructed, and tested a microwave reactor that heats Si to 1300°C in only a few milliseconds and cools the wafer at a rate that exceeds a million degrees per second. Applying millisecond microwave annealing to ultra-shallow junction formation in advanced Si devices shows that this technique meets or exceeds the thermal processing requirements for the next several generations of Si devices.