bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Porous Ceramics Through Directional Solidification and Freeze-Drying
Authors: Kisa Predrag , Fisher Patrick , Olszewski Al , Nettleship Ian , Eror Nicholas G.
Published: April 2011

This study investigated the microstructural characteristics of directionally solidified freeze-dried silica sols. Porous structures were formed by depositing silica sol on silicon (100) single crystals. The deposited sols were unidirectionaly solidified by placing the silicon substrate on a copper block immersed in liquid nitrogen and then subsequently freeze-dried. Freeze drying removal of ice crystals created three-dimensional pore channels ranging from 3 to10 micrometers in diameter aggregated in grain like colonies 50–100 micrometers in diameter. Pore size, spacing, colony size and microstructure were determined using optical microscopy (OM) and scanning electron microscopy (SEM) while the structure of the amorphous SiO2 was characterized by X-ray diffraction (XRD). The microstructure results are compared and contrasted with silica aerogel obtained through conventional processing using supercritical CO2.
Thermally activated phenomena observed by atomic force microscopy
Authors: Gnecco Enrico , Riedo Elisa , Bennewitz Roland , Meyer Ernst , Brune Harald
Published: April 2011

Thermal effects may affect the velocity dependence of friction on the nanoscale in different ways. In a dry environment the stick-slip motion of a nanotip sliding across a crystalline surface is modified by thermal vibrations, which leads to a logarithmic increase of friction with the sliding velocity at very low speeds (v < 10 μm/s). At higher speeds the role of thermal activation is negligible, and friction becomes velocity-independent. An analytical expression, which explains both regimes of friction vs. velocity, is introduced. In a humid environment the situation is complicated by water capillaries formed between tip and surface, which act as obstacles for thermally activated jumps. Depending on the wettability of the surface, different tendencies in the velocity dependence are observed.
Sliding-induced non-equilibrium in confined systems
Authors: Müser Martin H.
Published: April 2011

When two solids are in relative sliding motion, the intervening layer separating the two surfaces (for example the boundary lubricant) is typically far from thermal equilibrium. With the help of a generic model reflecting the boundary lubricant, it will be shown that it is often not possible to characterize a sliding contact by means of a single effective temperature. The reason is that the probability distribution (PD) of microscopic variables differs in a characteristic fashion from equilibrium PDs. Non-equilibrium velocity PDs are not Gaussian but tend to be exponential, thus favoring rare events. Leaving dynamic equilibrium by non-uniform sliding conditions leads to yet additional effects, in particular to enhanced dissipation. This is shown in a model describing rubbing polymer brushes in good solvent conditions. Shortly after returning the sliding velocity, the brush interdigitation is distinctly larger than during steady-state sliding. Based on this observation, predictions can be made at what amplitude the loss is maximum for a given driving frequency.
Exploring Reaction Pathways of Single-Molecule Interactions through the Manipulation and Tracking of a Potential-Confined Microsphere in Three Dimensions
Authors: Wong Wesley P. , Heinrich Volkmar , Evans Evan
Published: April 2011

Weak non-covalent interactions between single molecules govern many aspects of microscopic biological structure and function, e.g. cell adhesion, protein folding, molecular motors and mechanical enzymes. The dynamics of a weak biomolecular bond are suitably characterized by the kinetic transport of molecular states over an effective energy landscape defined along one or more optimal reaction pathways. Motivated by earlier developments [1,2], we present a novel method to quantify subtle features of weak chemical transitions by analyzing the 3D Brownian fluctuations of a functionalized microsphere held near a reactive substrate. A weak optical-trapping potential is used to confine motion of the bead to a nanoscale domain, and to apply a controlled bias field to the interaction. Stochastic interruptions in the monitored bead dynamics report formation and release of single molecular bonds. In addition, variations in the motion of a bead linked to the substrate via a biomolecule (a protein or nucleic acid) signal conformational changes in the molecule, such as the folding/unfolding of protein domains or the unzipping of DNA. Thus, energy landscapes of complex biomolecular interactions are mapped by identifying distinct fluctuation regimes in the 3D motion of a test microsphere, and by quantifying the rates of transition between these regimes as mediated by the applied confining potential.

The 3D motion of the bead is tracked using a reflection interference technique combined with high-speed video microscopy. The position of the bead is measured over 100 times per second with a lateral resolution of ∼3–5 nm and a vertical resolution of ∼1–2 nm. Crucial to the interpretation of results, a Brownian Dynamics simulation has been developed to relate the statistics of bead displacements to molecular-scale kinetics of chemical interactions and structural transitions. The experimental approach is designed to enlarge the scope of current techniques (e.g. dynamic force spectroscopy [3]) to encompass near-equilibrium forward/reverse transitions of weak-complex interactions with multiple binding configurations and more than one transition pathway.
Effect of Different Layer Thicknesses and Boundary Conditions of Confined Liquid Crystal on Dynamics of Director Relaxation: Dynamic Light Scattering Investigations
Authors: Basu Sarmistha , Aliev Fouad M.
Published: April 2011

Dynamic light scattering (DLS) has been used to study the influence of boundary conditions (planar-axial and homeotropic-radial) and layer thickness of liquid crystal (8CB) confined to cylindrical pores on phase transitions and relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first relaxation is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation (with relaxation time slower than the first one) is most likely due to the fluctuations in the layers nearest the wall surface. In samples with radial boundary conditions, we observed the onset of smectic-A phase order formation on the pore wall even though the rest of the liquid crystal could be in the nematic phase. The influence of pore wall-liquid crystal interactions on the properties of the confined 8CB was stronger for radial boundary conditions of confined liquid crystal, than in the case of axial orientation‥ The separation between the first and the second (slow) process was clearer for thinner layers and the amplitude of the slow process was greater for thinner layers. This suggests that the slow process was related to surface relaxation of director fluctuations.
Terahertz Radiation Spectroscopy on Chloroform Confined in Porous Silica Glasses
Authors: Yamamoto Kohji , Satoh Taku , Okuno Hiroaki , Tominaga Kiesuke , Saito Shinji , Loughnane Brain J. , Scodinu Alessandra , Fourkas John T.
Published: April 2011

Terahertz (THz) time-domain spectroscopy (TDS) has been used to study far infrared absorption spectra of chloroform confined within nanoporous glasses of various pore sizes. Intermolecular interactions and dynamics in the confined system are discussed.
Retention of Liquids Above Microporous Membranes
Authors: Charkoudian John , Thom Volkmar
Published: April 2011

The ability of membranes to retain fluids without leaking in devices such as high throughput multiwell plates was examined as a function of membrane polymer, surface modification, and liquid surface tension. Microporous membranes (200–800nm) act as arrays of millions of imperfect microcapillaries. Extrusion and leaking requires pressure plus coalescence of microdroplets. For unmodified membranes, the liquid hold up height (pressure) is critically dependent on liquid surface tension, rising rapidly when the contact angle prevents droplet spreading and coalescence. Topography, as measured by AFM, also plays a role in ease of coalescence. Surface modification has a large impact on hold up pressure and its dependence on liquid surface tension.
Comparison between Adsorption in Pores of a Simple Geometry and Realistic Models of Porous Materials
Authors: Coasne B. , Pikunic J. P. , Pellenq R. J. -M. , Gubbins K. E.
Published: April 2011

We study, by means of Grand Canonical Monte Carlo simulations, the effect of disorder in pore morphology and topology on adsorption of simple fluids at 77 K. We consider the case of microporous carbons and mesoporous silicas. For both systems, we found that morphological and topological disorder affects the adsorption isotherm. Consequently, we show that complex porous networks cannot be modeled as a collection of unconnected pores of simple geometry. In the case of microporous carbons, the isosteric heat of adsorption for disordered systems differs significantly from that obtained for an assembly of unconnected slit pores. In contrast, the isosteric heat of adsorption for the disordered mesoporous silica sample compares reasonably well with that observed for a silica material having regular cylindrical pores.
Raman-Active Nanostructured Materials for Use as Novel Stress-Sensitive Polymeric Coatings
Authors: Halary Jérôme , Stanford John L. , Lovell Peter A. , Young Robert J.
Published: April 2011

Nanocomposites and nanostructured polymers with unique opto-mechanical properties have been developed as smart coatings for use in a novel, high resolution, and non-contact strain-measuring application. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics), and determine local strains on the micron scale directly from stress/strain induced Raman band shifts.

The research is aimed at providing a novel high-resolution non-contact technique for the determination of surface stresses and strains in a wide variety of engineering components used in both laboratory and in-the-field (external) applications.
Meso-to-Nano-scopic Polycrystal/Composite Strengthening
Authors: Armstrong R. W. , Conrad H. , Nabarro F. R. N.
Published: April 2011

A great challenge associated with current investigations of the structural strength properties of nanometrically-scaled polycrystals and/or composite materials relates to quantitative description of the continuous transition in mechanical behaviors occurring when going over to such materials from those microstructural, and larger, scale material deformation properties seemingly well-understood and modeled during the research investigations of the previous century [1]. The consideration relates to whether the same dislocation generation/interaction mechanisms operating within the grain volumes of a conventional microstructured material, say, as compared in the same case for local deformations, dislocation or otherwise, at the grain boundary regions, are either additionally restricted from operation, or enhanced, for nanostructured materials. The deduced indication is that there should be a relatively smooth mechanical property transition, if any change at all, to be demonstrated here on the basis of available experimental and theoretical modeling results. The predicted smooth transition in behavior, however, may be upset, possibly, by failure to achieve the demanding quality control predictably needed for the combined considerations of: (1) structural characterization; (2) mechanical testing methods; and, (3) model computations, so as to allow quantification of the finer-scaled material behaviors. The combined property behavior is illustrated by application of effective low temperature grain boundary strengthening models at larger grain (or particle) sizes, then, transitioning to effective grain size weakening at the smallest grain sizes, with such weakening thought to occur because of otherwise normal high temperature diffusional or grain boundary weakening mechanisms being promoted somehow to become controlling in the practical “thought-to-be” low temperature regime.
Phase Mixture Models for Metallic Materials with Submicrometer Grain Size
Authors: Estrin Yuri , Kim Hyoung Seop , Bush Mark
Published: April 2011

Phase mixture models describing the mechanical properties of submicrometer grained metals are presented. In this approach, grain boundaries or cell walls are treated as a separate phase. Two cases are considered: the mechanical response of an ultrafine grained material and the process of grain refinement by equal channel angular pressing. Model predictions with regard to the evolution of the microstructure, strength and texture are verified for Cu.
Raman Investigation of Fullerene [60] Under hydrostatic Pressure
Authors: El-Ashry Mostafa , Amer Maher , Maguire John F.
Published: April 2011

We report the results of a study of adsorption of small molecules on the surface of buckminsterfullerene, C60. The pressure dependence of the Raman spectrum was investigated over the range 0–10 GPa in methanol-water mixtures that were used as the pressure transmitting fluid (PTF) in a diamond anvil cell. It is found that the spectral shift and its pressure derivative are sensitive to both the applied pressure and to the composition of the PTF. These observations are consistent with an explanation that involves preferential adsorption onto the surface of the C60. In particular, the notion of C60 collapse needs not be invoked to explain the observations.
The Irradiated Microstructure of Ferritic-Martensitic Steel T91 and 9Cr-ODS
Authors: Gan J. , Allen T. R. , Cole J. I. , Ukai S. , Shutthanandan S. , Thevuthasan S.
Published: April 2011

A ferritic steel T91 and an oxide dispersion strengthened (ODS) martensitic steel 9Cr-ODS were irradiated with 5 MeV Ni ions at 500°C at a dose rate of 1.38×10-3 dpa/s to doses of 5, 50 and 150 dpa. Both alloys are iron-based with 9Cr and have been designed for use in higher temperature energy systems. However, the radiation effects on these two alloys are not well characterized. For T91, the irradiated microstructure was dominated by tangled dislocation and precipitates, similar to the unirradiated condition except the presence of large dislocation loops of type a<100>. The microstructure of alloy 9Cr-ODS for both the unirradiated and irradiated cases was dominated by dense dislocations, precipitates and yttrium oxides particles and no dislocation loops were observed. The average size of yttrium oxides particles slightly decreased with dose from 11.8 nm for the unirradiated to 9.1 nm at 150 dpa. No voids were detected for both alloys up to a dose of 150 dpa.
Gas Cluster Ion Beam Processing of GaSb and InSb Surfaces
Authors: Krishnaswami K. , Vangala S.R. , Krejca B. , Allen L.P. , Santeufemio C. , Dauplaise H. , Liu X. , Whitten J. , Ospina M. , Sung C. , Bliss D. , Goodhue W.D.
Published: April 2011

Gas Cluster Ion Beam (GCIB) processing has recently emerged as a novel surface smoothing technique to improve the finish of chemical-mechanical polished (CMP) GaSb (100) and InSb (111) wafers. This technique is capable of improving the smoothness CMP surfaces and simultaneously producing a thin desorbable oxide layer for molecular beam epitaxial growth. By implementing recipes with specific gas mixtures, cluster energy sequences, and doses, an engineered oxide can be produced. Using GaSb wafers with a high quality CMP finish, we have demonstrated surface smoothing of GaSb by reducing the average roughness from 2.8Å to 1.7Å using a dual energy CF4/O2-GCIB process with a total charge fluence of 4×1015ions/cm2. For the first time, a GCIB grown oxide layer that is comprised of mostly gallium oxides which desorbed at 530°C in our molecular beam epitaxy system is reported, after which GaSb/AlGaSb epilayers have been successfully grown. Using InSb, we successfully demonstrated substrate smoothing by reducing the average roughness from 2.5Å to 1.6Å using a triple energy O2-GCIB process with a charge fluence 9×1015ions/cm2. In order to further demonstrate the ability of GCIB to smooth InSb surfaces, sharp ∼900nm high tips have been formed on a poorly mechanically polished InSb (111)A wafer and subsequently reduced to a height of ∼100nm, an improvement by a factor of eight, using a triple energy SF6/O2-GCIB process with a total charge fluence of 6×1016ions/cm3.
Influence of High-Fluence Proton Irradiation on the Optical Absorption and Microstructure of Rutile
Authors: Lu Tiecheng , Zhu Sha , Wang Lumin
Published: April 2011

Rutile (TiO2) single crystals of (110) or (001) orientation were irradiated by high fluence protons with the energy of 0.5, 4.9 and 18 MeV and with the fluence of 1×1018 and 1.9×1022 m-2. UV-VIS-IR, LRS and HRTEM were used to analyze the optical absorption and microstructure of samples. The UV-VIS-IR results showed that proton irradiation induces two absorption peaks centered at 760 and 1700 nm respectively, even high fluence irradiation induces absorption plateau at 600∼2500 nm. LRS results showed that the related intensity of common vibration modes is different for different planes. Proton irradiation induces the vibration frequency and related intensity change for inherent LRS modes, and several new vibration modes also appear. High fluence proton irradiation induced large defect clusters, i.e. stacking faults, which is demonstrated by HRTEM observation. The optical absorption mechanism also has been discussed.
Influence of Hydrogen Plasma Treatment on He Implantation-Induced Nanocavities in Silicon
Authors: Vengurlekar A. , Ashok S. , Liu C. L. , Ntsoenzok E. , Barthe M. F. , Desgardin P. , Ruault M. O.
Published: April 2011

He implantation followed by thermal anneal is a well-established technique for creating layers or bands of cavities in silicon. This process is a consequence of the interaction between He and ion-implant-induced vacancies. Applications of such cavity layers include gettering and localized minority carrier lifetime control, and compliant substrates for lattice-mismatched heteroepitaxy. Studies have shown that the presence of interstitial-type defects can lead to the shrinkage of He-cavities due to the interstitial capture by the cavities. However, few of them deal with the interaction of cavities with vacancies. Here we present results on the formation of He-cavities in Si in the presence of atomic hydrogen and vacancies produced by effusion of hydrogen. Following a helium implant, samples were hydrogenated with an electron cyclotron resonance (ECR) hydrogen plasma. Control samples without any hydrogenation were also used. We studied the influence of hydrogen on void morphology. While hydrogen enhances void size at higher energy implants, the enhancement effect is absent in lower energy implants. The results underscore the role of vacancies in void formation and growth.
The Origin of Radiation Resistance of Magnesium Aluminate Spinel
Authors: Gritsyna Vasyl T. , Kazarinov Yurij G. , Kobyakov Volodymyr A. , Sickafus Kurt E.
Published: April 2011

We propose here a new mechanism to explain the observed high radiation tolerance of magnesium aluminate compounds with crystal structures known as spinel. By using optical methods, we found that the kinetics of accumulation of optical absorption centers under different types of irradiation, as well as the kinetics of absorption decay after termination of irradiation, along with radio-luminescence processes, are consistent with a new model regarding defects and radiation damage in spinel. This model assumes the existence of spatially-correlated antisite defects in the form of dipoles: (Al3+tet)+-(Mg2+oct)-. These spatially-correlated point defect complexes serve as centers for annihilation of radiation-induced cation Frenkel pairs. In addition to the spatially-correlated defects, the high concentration of cation structural vacancies inherent to the spinel lattice also serves to promote high mobility of both Mg and Al interstitial species. This enhanced mobility leads to increased probability of annihilation at the dipole centers proposed in this model. Such annihilation then diminishes the probability for formation of defect clusters, dislocation loops, or amorphization of the irrradiated spinel.
Structural Disordering in Magnesium Aluminate Spinel Compounds under Ion-Beam Irradiation
Authors: Matsumura Syo , Shimada Mikio , Yasuda Kazuhiro , Kinoshita Chiken
Published: April 2011

High Angular Resolution Electron Channeling X-ray Spectroscopy (HARECXS) of analytical electron microscopy was employed in quantitative analysis of irradiation-induced structural disordering in MgO·n Al2O3 spinel compounds irradiated with 1 MeV Ne+ ions and 200 MeV Xe14+ ions. The results successfully show the disordering behavior in MgO·n Al2O3 as a function of composition and irradiation condition. It has been revealed by HARECXS that 1 MeV Ne+ irradiation at 873 K causes significant cation-disordering in the pre-peak damaged area where no indication is recognized in conventional TEM observation. Displacement of O2- ions is also recognized in heavily damaged areas. Irradiation with 200 MeV Xe14+ swift ions, on the other hand, forms structurally-disordered cylinders of 4 nm in diameter along their tracks. HARECXS profiles indicate that the disordering takes place over extended areas of about 10 nm in radius centered on the ion tracks.
Low-Energy Ne+ Ion Channeling and Implantation into Cu(100) and Cu3Au(100)
Authors: Rasulov Akbarali M. , Dzhurakhalov Abdurauf A.
Published: April 2011

By computer simulation details have been observed regarding the dynamics of the change of the character of trajectories, the range and energy losses of channeled ions, as well as the angular and energy distributions of ions transmitted through thin crystal versus the composition of single crystal, the impact parameters from the center of the channel and the initial energy. It has been established that for a paraxial part of a channeled beam the inelastic energy losses comprise the main loss of energy. The elastic energy losses of the channeling ions in the case of Cu3Au(100) crystal are larger than in the case of Cu(100). As Au atoms are heavier than Cu atoms, in the case of Cu3Au(100) the degree of the dechanneling of particles is greater and the range is smaller in comparison with the similar characteristics for Cu(100).
Pit nucleation in compound semiconductor thin films
Authors: Bouville Mathieu , Falk Michael L. , Millunchick Joanna Mirecki
Published: April 2011

Pit nucleation has been observed in a variety of semiconductor thin films. We present a model in which pit nucleation is considered to arise from a near-equilibrium nucleation process in which the adatom concentration plays an important role. Although pits relieve elastic energy more efficiently than islands, pit nucleation is prevented if the adatom concentration is too high. Inhomogeneities in the adatom density on the surface due to three-dimensional islands enhance pit nucleation. Thermodynamic considerations predict several different growth regimes in which pits may nucleate at different stages of growth depending on the materials system and growth conditions. However kinetics must be taken into account to make direct comparisons to experimental observations. These comparisons show good agreement given the uncertainties in quantifying experimental parameters such as the surface energy.
Effects of clustering and dimensionality on the magnetic properties of diluted magnetic semiconductors
Authors: Bhatt R. N. , Kennett Malcolm. P. , Kassaian Adel
Published: April 2011

The magnetic properties of films of diluted magnetic semiconductors (DMS) such as (Ga,Mn)As, as well as bulk grown crystals of similar materials, have been found to be extremely sensitive to growth conditions, both in terms of the ferromagnetic transition temperature, and the details of their magnetization curves. We study an impurity band model for carriers in Mn-doped DMS applicable in the low carrier density regime, and discuss the effects of clustering on the magnetic properties of DMS, using both numerical mean field and Monte Carlo simulations. In addition, we study the effects of dimensionality on the transition temperature and other magnetic behaviour, and compare our results with experimental data.
Aperiodic lattices for photonic bandgap engineering
Authors: Chakraborty Subhasish , Hasko David G. , Mears Robert. J.
Published: April 2011

A new method is presented, based on the discrete Fourier Transform, for the design of aperiodic lattices to be used in photonic bandgap engineering. Designing an aperiodic lattice by randomly choosing defects is unlikely to result in useful optical transmission characteristics. By contrast, this new method allows an aperiodic lattice to be designed directly from the desired optical characteristic. The use of this method is illustrated with a design for a structure to realise two transmission wavelengths in the stopband of a one-dimensional photonic lattice. This design has been fabricated in silicon-on-insulator and some optical characteristics are given.
Quantifying Field-Induced Contrast Effects in Photoelectron Emission Microscopy
Authors: Siegrist K. , Ballarotto V. W. , Williams E. D.
Published: April 2011

Samples consisting of electrically isolated titanium lines fabricated on a titanium surface were used to quantify voltage-induced contrast effects in photoelectron emission microscopy (PEEM). Induced contrast effects were observed to extend 6 μm for a -5 V bias applied to a 303 nm tall raised line. We therefore explored, via numerical calculation, the spatial extent of the perturbation to the PEEM accelerating field caused by the bias applied across the step height. The intensity full width at half minimum agreed well with the calculated width defined by the 10% level of lateral field strength. For a line 550 nm tall, a correspondence was found for a calculated width defined by a 5% lateral field strength. It was observed that neighboring structures a few μm away affected the image contrast, for sufficiently strong applied bias. This suggests that effects can easily be induced at distances of 0.5 μm for modest applied voltages, as has been previously observed for structures buried under oxide layers 0.5 μm thick [1].
Femtosecond Laser-induced Crystallization in As-deposited Ge1Sb2Te4 Films
Authors: Wang Qin F. , Shi Lu P. , Huang Su M. , Miao Xiang S. , Wong Kai P. , Chong Tow C.
Published: April 2011

Time resolved imaging has been used to investigate the whole process of the crystallization induced by intense 130 femtosecond laser pulses in as-deposited Ge1Sb2Te4 films. With an average fluence of 24mJ/cm2 a transient non-equilibrium state of the excited material is formed within 1 picosecond. The results are consistent with an electronically induced non-thermal phase transition.
Multi Layer Disk Design For Near Field Phase-Change Recording
Authors: Kishima Koichiro , Ichimura Isao , Saito Kimihiro , Yamamoto Kenji , Iida Atsushi , Osato Kiyoshi
Published: April 2011

We propose multi-layer near-field recording with using inner focus mode. The restricted conditions for multi-layer near-field recording are discussed from the viewpoint of both media structure and optical setup. One solution is presented for dual layer recording with a numerical aperture (NA) of 1.5 and a wavelength of 405 nm as a light source of GaN laser diode.

In the proposed layer structure, a Nb2O5 material has been adopted as the intermediate layer because of its high refractive index, n = 2.4, in order to prevent the decrease of beam propagation that corresponds to NA>1. Almost the same signal characteristics can be obtained from both recording layers at the air gap of 40 nm. The adjustment of focusing position and the compensation of spherical aberrations have been implemented by the combination of an expander lens unit and a liquid crystal (LC) panel in the optical setup.
Microstructure and Chemistry of an Aluminophosphate Glass Waste Form under Electron Beam Irradiation
Authors: Sun K. , Wang L. M. , Ewing R. C.
Published: April 2011

An alkali-containing (mainly sodium) aluminophosphate glass waste form was studied by analytical electron microscopy. Bright-field imaging showed that small bubbles formed under the electron irradiation even at a low electron dose (8×1022e/m2). These bubbles grew with the increase of the electron dose and were finally released at the surface of the sample. At the same time alkali elements were also lost under irradiation. At an electron dose of about 2.2×1026e/m2 (6.6×1011Gy), all the bubbles were released and no bubbles were formed with further irradiation. The glass was finally transformed to a pure aluminophosphate glass. Further irradiation resulted in the phase separation between the Al-rich and the P-rich phases. The electron irradiation damage effects on the aluminophosphate glass are compared to those observed in iron phosphate glasses.
Hollandite-rich Ceramic Melts for the Immobilisation of Cs
Authors: Carter M. L. , Vance E. R. , Li H.
Published: April 2011

Ceramic wasteforms designed to be processed by melting in air has been developed to immobilise Cs-rich wastes. Detailed characterisation electron microscopy is presented on versions of these melted materials which are rich in Cr-, Ni-, Zn or Co- substituted titanate hollandites and which have PCT-B normalised Cs leachate concentrations of < 0.2 g/L. To assist in understanding the general crystal chemistry of titanate hollandites, this study also investigates the solubility limits of Cs in single-phase hollandite BaxCsy(M3+)2x+yTi8–2x-yO16 where M = Cr and BaxCsy(M2+)x+y/2Ti8-x-y/2O16 formulations where M = Zn, Co or Ni.
Posiva's Site Investigations Programme
Authors: Ryhänen Veijo
Published: April 2011

Four nuclear power plant units have been operated in Finland over 20 years. The plants are located at two sites, Olkiluoto and Loviisa. Responsibility for nuclear waste management lies on the utilities, which have established a joint company POSIVA to take care of spent fuel disposal and other expert tasks of nuclear waste management.

Already in 1983 the Finnish Government set the objectives and the schedule for the national waste management programme. Since then, two shallow underground repositories have been constructed for low- and medium-level operating waste in crystalline rock at the power plant sites. At the end of 2002 the amount of operating waste emplaced in these two facilities was 4923 m3 (total accumulation 6724 m3).

Spent nuclear fuel is stored in interim storage pools at the nuclear power plant sites. The total accumulation was 1228 tU at the end of 2002. Today, the main activities in nuclear waste management concern spent fuel disposal deep in the Finnish bedrock. Apart from technical and scientific issues, a major challenge faced has been the creation of sufficient public acceptance, which is a must in order to obtain favourable political decisions.
The Immobilization of Cesium and Strontium in Ceramic Materials Derived from Tungstate Sorbents
Authors: Luca Vittorio , Drabarek Elizabeth , Griffith Christopher S. , Chronis Harriet , Foy James
Published: April 2011

The effective immobilization of Cs+ and/or Sr2+ sorbed on hexagonal tungsten oxide bronze (HTB) adsorbent materials can be achieved by heating in air at temperatures in the range 500 – 1000 °C. Crystalline powdered HTB materials formed by heating at 800 °C show leach characteristics comparable to Cs-containing hot-pressed hollandites in the pH range from 0 to 12. If the Cs-loaded HTB sorbents are pressed into pellets prior to calcination, ceramic monoliths can be prepared. Heating to temperatures in excess of 1250 °C results in the melting of the sorbent to form millimetre-sized crystals of bronzoid phases. Thermal analysis shows that melting of the cation-exchanged tungstate sorbents is initiated at temperatures as low as 850 °C and concludes by 1300 °C. The absence of any significant mass loss immediately after melting, as well as chemical analyses before and after melting, confirm that Cs is not volatilized to any significant extent at the temperatures required to generate durable, coarsely crystalline products. The melted bronzoid product is a multiphase ceramic in which Cs+ remains bound within, and appears to stabilize, the hexagonal bronze phase, even after complete melting at 1300 °C, while elements such as Sr2+ are present within other tungstate phases. The bronzoid chemical system appears capable of accommodating a wide range of other elements. Here we have demonstrated that modification of the sorbent properties by incorporation Mo does not impact severely on the durability of materials prepared below 1000 °C, even when exposed to strong acid (pH=1) and elevated temperature (150 °C). As an example, one-day MCC1 leach rates lower than 1×10−5g/m2/day were measured using demineralized water at 90 °C for Cs-saturated Mo-doped sorbents that had been heated in air at 900 °C, while the fraction of Cs leached from powdered samples in 0.1 M HNO3 solutions at 150 °C for 4 days is only 4×10−3 g/m2/day.
Effects of Technical Adsorbents and Cleaning Agents in a Cement Matrix – A Case Study
Authors: Dario Mårten , Molera Mireia , Allard Bert
Published: April 2011

The effects of organic cleaning agents (totally three) and degradation products from solid technical adsorbents (two) on the sorption of Eu on cement and TiO2 were measured with variation of concentration (0.001–10 % of the water phase for the cleaning agents, alkaline degradation products corresponding to 0.03–8 mM DOC for the adsorbents) and reaction time (up to 420 d). The effects of the cleaning agents Industrikombi and Prefect Citron were minor. The degradation of the ion exchanger (metaacrylic polymer) had no significant effect on the Eu-sorption. The other adsorbent (filter aid, inert fibre; acrylonitrile polymer) was rapidly degrading at high pH, and the degradation products had a significant reducing effect on the sorption of Eu at added DOC-levels in the mM-range. This category of adsorbent materials should not be incorporated in a cement waste matrix or be stored in a cementitious environment together with radionuclides.
Atmospheric Corrosion of Copper 450 Metres Underground. Results From Three Years Exposure in the Äspö HRL
Authors: Taxén Claes
Published: April 2011

Results from an atmospheric exposure of copper at the Äspö Hard Rock Laboratory (HRL) are reported. Corrosion test coupons were exposed under sheltered conditions at 450 meters depth. The exposure was performed in order to gain insight into the likely state of a copper canister surface at the time when water begins to fill a repository for nuclear waste. The conditions for the experiment were selected to be relevant for the conditions predicted for a repository during an initial dry phase. Visual observations show that copper exposed at ambient temperature remained bright and shiny whereas coupons exposed at elevated temperature had a dull greenish appearance.
Anaerobic Corrosion of Steel in Bentonite
Authors: Smart Nicholas R. , Rance Andrew P. , Werme Lars O.
Published: April 2011

In Sweden, spent nuclear fuel will be encapsulated in sealed cylindrical canisters, consisting of a ferrous insert and a copper outer container, for disposal in a geologic repository. Ferrous support structures will also be used in the repository, which will be backfilled with bentonite clay. Once any residual oxygen has been consumed, any ferrous material exposed to anoxic groundwater will undergo anaerobic corrosion, liberating hydrogen, forming a magnetite film, and releasing iron ions into the surrounding matrix. In order to characterise these processes the rate of hydrogen generation of steel in bentonite was measured using a barometric gas cell technique. The initial corrosion rates were found to be higher than measured previously in comparable aqueous solutions, but the long-term corrosion rates were similar. Analysis of the bentonite matrix showed that iron produced by corrosion had penetrated into the bentonite matrix, suggesting that ferrous ion exchange had occurred.
Development of a Used Fuel Container for Nuclear Fuel Waste
Authors: Maak Peter
Published: April 2011

The deep geologic repository (DGR) concept is one of the approaches being considered in Canada for long-term management of used CANDU fuel. The Canadian concept entails encapsulating used CANDU fuel bundles in durable used-fuel containers (UFCs) and burying the UFCs in an engineered repository at depth in the Canadian Shield. Currently, an updated concept for a DGR is being prepared by Ontario Power Generation (OPG).

This technical paper describes OPG's studies from 1999 to 2002 that have led to the development of an updated reference UFC design. The updated UFC design holds 324 used CANDU fuel bundles. It consists of an outer corrosion-resistant oxygen-free phosphorous-doped copper vessel and an inner load-bearing steel vessel. The used-fuel bundles are placed within a fuel basket for handling and loading into the UFC. This reference UFC design would be used for future safety assessment and engineering studies.
Groundwater Flow and Transport Modelling at Äspö for a Glaciation Period
Authors: Jaquet O. , Siegel P. , Klemenz W. , Selroos J. O.
Published: April 2011

This study [1] was performed for SKB (Swedish Nuclear Fuel and Waste Management Co) within the framework of the assessment of the long-term safety of a deep repository for spent nuclear fuel.

Subsequent to work performed by [5], SKB decided to carry out additional hydrogeological modelling studies related to glaciation effects at Äspö. In particular, subglacial groundwaterflow and the impact assessment on a repository required further studies. The presence of subglacial groundwater flow beneath ice sheets is due to basal melting occurring during glaciation periods.

As compared to the previous model [5], the domain geometry and processes involved remained identical but this time numerical calculations are performed with the NAMMU program. Modified assumptions corresponding to specific boundary conditions were implemented and additional variations of the base case were simulated.
Geophysical Applications for Deep Geological Repository Studies in Plutonic Rocks of Canada
Authors: Lodha Ganpat S. , Serzu Mulugeta H. , Kozak Ed T. , Everitt Richard A. , Tomsons Dzintars K. , Hayles John G.
Published: April 2011

Atomic Energy of Canada Limited (AECL) has been conducting detailed geological, geophysical and geotechnical investigations in plutonic rocks at several research areas. The main focus of the work was on developing and testing site evaluation and site characterization methods to investigate progressively smaller volumes of plutonic rocks in greater details. In this process extremely detailed airborne, surface and borehole geophysical surveys were done to identify fractures and understand groundwater flow conditions. A brief review of geophysical methods, which demonstrate the area scale, site scale and vault scale characterization techniques has been included in this paper. The boreholes in the Whiteshell Research Area (WRA) of Lac du Bonnet Batholith and at its Underground Research Laboratory (URL) excavated to 420 m depth have provided extensive opportunities to develop and test these methods. One example of geophysical surveys associated with the Moderately Fractured Rock (MFR) experiment at 240 Level is discussed in some length.
Advances in Classifications for Structural Modelling of the Olkiluoto Site
Authors: Vaittinen Tiina , Ahokas Henry , Hellä Pirjo , Saksa Pauli , Oy Fintact
Published: April 2011

The site characterization for the construction of the repository of spent nuclear fuel is carried out at Olkiluoto in Finland. The results of geological, geophysical, and hydrogeological investigations are integrated in a bedrock model to describe rock types, fractured zones and potential hydraulic connections. In modelling it is essential to determine structures important for construction of underground facilities. This question encompasses objectives and scale of the modelling. Important parameters in structural modelling are fracture frequency and hydraulic conductivity. The definitions need to be evaluated site-specific, because the geological circumstances control the properties of structures. An important issue is the possible existence of a boundary zone close to structures.
Diffusion and Migration of Ions in Sedimentary Rock Matrix: Effects of Ionic Strength and Tracer Concentration on Diffusion of Cs+ ions in Sandstone
Authors: Sato Haruo
Published: April 2011

In-diffusion experiments for Cs+ and I− in sandstone were performed as a function of ionic strength ([NaCl]=0.01, 0.51M) and tracer concentration ([CsI]=7.5E-5, 1.5E-2M) together with the measurements of the physical and chemical properties of sandstone, and apparent diffusivities (Da) for Cs+ were obtained. The obtained Da-values for Cs+ scarcely depended on [NaCl], but increased with increasing [Cs+]. This trend is consistent with that of rock capacity factors (α), indicating that distribution coefficient (Kd) onto sandstone and effective diffusivity scarcely depend on [NaCl]. The concentration profiles of I− were all in already breakthrough. Although this indicates that I− diffusion is faster than that of Cs+, the concentration profiles of I− may have been lower than those for blank samples, judging synthetically from the correlations between α-values and the concentration profiles of Cs+ and from the concentration profiles of I− in the blank samples. Finally, the effects of [Cs+] and[NaCl] on Kd/-values for Cs+ were discussed from the viewpoint of adsorption by ion exchange and electrostatic attraction. The kd-values were considered to be combined sorption by both reactions.
Sorption of Caesium on Commercial Magnetite with low Silica Content: Experimental and Modelling
Authors: Rovira Miquel , Pablo Joan de , Casas Ignasi , Giménez Javier , Clarens Frederic
Published: April 2011

Interaction of Cs on commercial magnetite has been studied under different experimental conditions at high solid/liquid ratios. At pH 8.2 the Freundlich isotherm was able to describe an important range of the experimental data and at high Cs concentration surface precipitation was found likely to occur. Special attention has been given to silica, present in the system as an impurity of magnetite, since it plays an important role on the sorption mechanism in which a ternary complex magnetite-Si-Cs is formed.
About the Luminescence Mechanisms of Composite a-Si:nc-Si System Obtained by Ion-Beam Amorphization in the Wide Dose Region
Authors: Tetelbaum David I. , Ezhevskii Alexander A. , Mikhaylov Alexey N. , Lebedev Mikhail Yu. , Mendeleva Yuliya A. , Ershov Roman G. , Morozov Sergey V.
Published: April 2011

Red/near-infrared photoluminescence (PL) of silicon irradiated by ions for wide dose range is investigated. The results are presented obtained for doses near amorphization threshold, where PL is associated with the formation of composite structure composed of nanocrystals (quantum dots) embedded into amorphized matrix and for doses that are strongly larger than amorphization threshold. The PL in this case is caused by formation of nanocrystals due to recrystallization of amorphous layer and penetration of stresses behind the border of this layer.
Fabrication and Characterization of Hydrogenated Amorphous Silicon Bipolar Thin Film Transistor (B-TFT)
Authors: Kuo Yue , Lei Yu , Nominanda Helinda
Published: April 2011

The conventional a-Si:H thin film transistor (TFT) is a field effect transistor (FET), which has disadvantages of a low operation speed and a small current driving capability. To achieve a higher speed and larger current driving capability, a potential solution is to fabricate the a-Si:H-based bipolar thin film transistor (B-TFT). In this study, a-Si:H p-i-n junctions were prepared and studied in order to determine the proper layer thickness for good junction behaviors. B-TFTs composed of a stacked structure of n+/i/p/i/n+ were then fabricated. The complete B-TFT was made using plasma enhanced chemical vapor deposition (PECVD) to deposit all doped and undoped a-Si:H layers and SiNx dielectrics at 250°C. Reactive ion etching (RIE) and wet etching methods were used to define base and emitter regions and contacts. The I-V characteristics of the complete B-TFT were investigated. The common-emitter current gain is 3∼6, which is larger than the literature report of 2∼3. In addition, a collector current larger than the literature value was obtained. A significant current noise was observed, which may be contributed to the high series resistance of the base layer and defective junction interfaces. In this paper, process and structure influences on the a-Si:H junction and B-TFT performances are discussed.
Bottom-Gate TFTs with Channel Layer Grown by Pulsed PECVD Technique
Authors: Grant David J. , Lee Czang-Ho , Nathan Arokia , Das Ujjwal K. , Madan Arun
Published: April 2011

In this paper, we report on nc-Si:H thin films deposited by the pulsed PECVD technique at a temperature of 150C and TFTs made using this material. RF power and silane flow rate were varied in order to study the effect of different levels of crystallinity on the film. Electrical conductivity, Hall mobility, optical transmittance, and Raman backscattering were measured on films of two different thicknesses. From the Raman data we see that the 50 nm films with hydrogen dilution are mostly amorphous, indicating the presence of a thick incubation layer. The values obtained for the conductivity, mobility, and optical gap varied depending on the processing conditions and these results are discussed. Bottom-gate TFTs were fabricated using a pulsed PECVD channel layer and a SiN gate dielectric. The TFTs' extracted parameters are msat μsat ≤ 0.38 cm2=(V s), Vt,sat ≥7:3 V, Ion/off >106, and S < 1 V/decade. The TFT performance and material properties are presented and discussed.
Microstructure Evolution with Thickness and Hydrogen Dilution Profile in Microcrystalline Silicon Solar Cells
Authors: Yan Baojie , Yue Guozhen , Yang Jeffrey , Guha Subhendu , Williamson D. L. , Han Daxing , Jiang Chun-Sheng
Published: April 2011

Hydrogenated microcrystalline silicon (m c-Si:H) solar cells with different thicknesses were deposited on specular stainless steel substrates and on textured Ag/ZnO back reflectors using RF and modified very high frequency glow discharge at various deposition rates. Raman spectra and X-ray diffraction patterns exhibit a significant increase of microcrystalline volume fraction and in grain size with film thickness. Atomic force microscopy reveals an increase in the size of microstructural features and the surface roughness with increasing thickness. Based on these results, we believe that the increase of the microcrystalline phase with thickness is the main reason for the deterioration of cell performance with the thickness of the intrinsic layer. To overcome this problem, we have developed a procedure of varying the hydrogen dilution ratio during deposition. Using this method, we have been successful in controlling the microstructure evolution and achieved an initial active-area efficiency of 8.4% for a c-Si:H single-junction solar cell, and 13.6% for an a-Si:H/a-SiGe:H/m c-Si:H triple-junction solar cell.