bluuebunny/crossref_metadata_2025 huggingface dataset:
Tapping-mode AFM - Force Measurement Capabilities on Compliant Surfaces
Authors: Nnebe Ijeoma M. , Schneider James W.
Published: April 2011

We investigate the feasibility of tapping-mode atomic force microscopy (TM-AFM) as a force measurement tool for compliant surfaces. For quantitative extraction of the tip-sample interactions, numerical modeling of the cantilever dynamics is required using a defined form for the interaction, with the results compared to experiment. Through TM force measurements on silicon, we illustrate that a forced damped harmonic oscillator model sufficiently represents the motion of the cantilever. Particularly for liquid operation, distance-dependent dissipation must be included in the model for accurate quantification of the tip-sample interactions and for successful reproduction of experimental force curves. This dissipation is not due to damping from the bulk viscous medium, but is likely frictional in origin. This investigation shows that TM force measurement in liquid is feasible and could be particularly advantageous for the measurement of intermolecular interactions from soft and easily deformed molecular layers.
Carbon Nanotube and Nanofibre Reinforced Polyamide-12 Fibres
Authors: Shaffer M. S. P. , Sandler J. K. W. , Pegel S. , Windle A. H. , Gojny F. , Schulte K. , Cadek M. , Blau W. J. , Lohmar J. , van Es M.
Published: April 2011

A range of multi-wall carbon nanotubes and carbon nanofibres were mixed with a polyamide-12 matrix using a twin-screw microextruder, and the resulting blends used to produce a series of reinforced polymer fibres. The aim was to compare the dispersion and mechanical properties achieved for nanofillers produced by different techniques. A high quality of dispersion was achieved for all the catalytically-grown materials and the greatest improvements in stiffness were observed using aligned, substrate-grown, carbon nanotubes. The use of entangled multi-wall carbon nanotubes led to the most pronounced increase in yield stress. The degrees of polymer and nanofiller alignment and the morphology of the polymer matrix were assessed using X-ray diffraction and calorimetry.
The Temperature Dependent Damping Behavior of Novel Nanocomposites for Structural Materials Applications
Authors: Asmatulu Ramazan , Claus Rick , Mecham Jeff , Inman Dan
Published: April 2011

Near nanoscale fine particles including vanadium dioxide (VO2) and zinc oxide (ZnO) were incorporated into matrix materials (tin and polymer adhesives). A number of mechanical damping tests were conducted on the prepared composite materials at frequency ranges of 0 − 2 kHz and over a broad temperature range. The mechanical vibration test results showed that VO2 and ZnO gave significantly higher negative-stiffness (or damping) at approximately 68 °C (155 F) and 29 °C (85 F). For example, approximately 15% and 12% damping values were achieved at first and second resonance frequencies, respectively, which can potentially prevent vibration on the materials. This significant improvement on the damping of the nanocomposite material may be because of the ferroelasticity, viscoelasticity and/or interfacial sliding at those particular temperatures. It was also observed the etching of substrate surfaces improved adhesion and contributed consistent results to vibration testing reproducibility. Thus, it is concluded that nanocomposite existing damping properties can be an important method to achieve large damping responses over a broad temperature range.
Effect of nm-Thin Inorganic Layered Fillers on the Crystallization of Polymer Nanocomposites
Authors: Nakajima H. , Wang Z. M. , Strawhecker K. , Manias E.
Published: April 2011

The crystallization behavior of polymers in nanocomposites with inorganic fillers (montmorillonite layered silicate, MMT) is reviewed. Various different polymers are comparatively discussed [poly(vinyl alcohol) (PVA), polypropylene (PP), syndiotactic-polystyrene (sPS), and poly(ethylene oxide) (PEO)] representing three types of filler/matrix interactions: strong specific interactions (PVA/MMT), weak/negligible interactions (sPS and PP/o-MMT), and “unfavorable” (PEO/MMT). In the case of PVA/MMT, crystallization of PVA is strongly promoted by MMT, also stabilizing a new crystal form not found in bulk PVA. For sPS and PP/o-MMT, crystallization is only moderately affected, exhibiting traces of simple heterogeneous nucleation and mostly bulk-like crystal structures, with very small traces on non-bulk crystals. For PEO, crystallization is impeded near the MMT surfaces, due to coordination of the surface cations to the PEO. In all cases smaller spherulite sizes develop when filler is added, independent of the size of the bulk polymer spherulites, whereas the crystallization temperature changes reflect the strength of the polymer/surface interactions.
Characterization of Strain-Tolerant Ceramic/SAM Bilayer Coatings
Authors: Yang Q. , Salami T. O. , Chitre K. , Oliver S. R. , Cho J.
Published: April 2011

Ceramic coatings can provide an ideal protection for MEMS (MicroElectroMechanical Systems) structures while imposing a great challenge in processing a prime, reliant coating due to their inherent brittleness and defects formed during processing. In an attempt to compensate for the weakness of the ceramic coating, we have developed a low-temperature solution precursor process to create strain-tolerant, protective bilayer coating consisting of an integrated ceramic-organic hybrid material. The top ceramic coating offers an inert, protective layer whereas the underlying nanometer scale self-assembled organic coating provides compliance for the overlying hard coating. Together, these bilayers minimize mechanical and thermal stresses. In addition, organic self-assembled monolayers(SAM) act as a ‘template’ by forming a proper surface functionality for the subsequent growth of hard ceramic coatings. Molecular level understanding of the microstructure and micromechanics involved in the synthesis and processing of the coating is systematically studied by a variety of characterization techniques such as XRD, AFM, SEM/EDS and nanoindentation. This work is also complemented by numerical simulation to provide a clearer understanding of the stress development in the ceramic coating and its interfacial properties.
Deformation Processes during Indentation of Mesoporous Silica Thin Films
Authors: Klotz M. , Perriot A. , Barthel E.
Published: April 2011

Nanoindentation was used to probe the mechanical response of mesoporous silica films as a function of processing treatment. A contrasted behaviour appears between low temperature processed films which retain the templating agent and are thus little compressible, and high temperature processed films, which are more condensed and also exhibit high porosity. We suggest that the behaviour of the former is dominated by shear flow, at least above a given threshold, while the latter are characterized by a yield strength in compression as is commonly found in porous materials. The response to indentation allows fast qualitative comparison of mechanical responses: in the present work, we show that a fast UV-O3 treatment results in mechanical properties which are undistinguishable from a much more cumbersome high temperature heat treatment.
Production and Mechanical Properties of Nanocrystalline Intermetallics Based on TiAl3-X
Authors: Calderon H. A. , Aguilar-Virgen J. C. , Cruz-Gandarilla F. , Umemoto M.
Published: April 2011

Production of intermetallic materials in the system TiAl3-X (X = Cr, Mn, Fe) has been achieved by means of mechanical milling and sintering techniques. Spark plasma sintering is used since it reduces time at high temperature and inhibits grain growth. The produced materials have grain sizes in the nano and microscale depending on the material and processing variables. The TiAl3-X alloys are formed mostly by the cubic L12 phase. The average grain size ranges between 30 and 50 nm in the as sintered condition. Aging at elevated temperature has been used to promote grain growth. Compression tests have been performed to evaluate mechanical properties as a function of temperature and grain size. In all cases yield stresses higher that 700 MPa are obtained together with a ductility that depends upon temperature and grain size. No ductility is found for the smallest grains sizes tested (30 nm) at room temperature. Above 673 K, these materials show ductility and additionally they present a quasi superplastic behavior at temperatures higher that 973 K. On the other hand ductility can also be developed in the TiAl3-X alloys by inducing grain growth via annealing. Alloys with grains sizes around 500 nm show high ductility and a large density of microcraks after deformation suggesting that the yield strenght becomes lower than the stress to propagate the cracks. In such materials, a considerably high strength is retained up to 873 K.
Mechanical Properties of Boron Doped Diamond Films Prepared by MPCVD
Authors: Liang Qi , Catledge Shane A. , Vohra Yogesh K.
Published: April 2011

A chemical vapor deposition hydrogen/methane/nitrogen feedgas mixture with unconventionally high methane (15% CH4 by volume) normally used to grow ultra-hard and smooth nanostructured diamond films on Ti-6Al-4V alloy substrates was modified to include diborane (10% B2H6 in hydrogen) for boron-doping. The flow rate for B2H6 was varied to investigate its effect on plasma chemistry, film structure, and mechanical properties. It was found that boron in the plasma can easily be incorporated into diamond films and change the lattice parameter and affect film structure as measured by Raman spectroscopy. Grazing angle x-ray diffraction shows a strong dependence of diamond lattice parameter with diborane flow rate and B2H6:CH4 flow rate ratio. Thermal stability of these films was evaluated by heating in an oxygen environment above 700 °C. Nanoindentation measurements show that the films have high hardness close to that of nanostructured diamond. High film hardness and toughness, combined with good thermal stability and low surface roughness indicate great potential as wear resistant coatings able to withstand high temperature oxidizing environments.
Channeling Study of the Damage Induced in Ion-Irradiated Ceramic Oxides
Authors: Thomé Lionel , Gentils Aurélie , Garrido Frédérico , Jagielski Jacek
Published: April 2011

The evaluation of the damage generated in crystalline ceramic oxides placed in a radiative environment is a major challenge in many technological domains. The use of the channeling technique is particularly well adapted to measure the depth distribution of the irradiation-induced disorder and to monitor the damage build-up. This paper describes the methodology used for the study of radiation damage with the channeling technique, presents a new method of analysis of channeling data based on Monte-Carlo simulations and provides recent results concerning the damage induced in ion-bombarded ceramic oxide single crystals in both nuclear (low-energy ion irradiation) and electronic (high-energy ion irradiation) slowing-down regimes.
Surface Modification of γ - Al2O3 nanoparticles by Electron Co-irradiation-induced Graft polymerization of MMA
Authors: Xiang X. , Zu X.T. , Wang Z.G. , Jiang B.
Published: April 2011

Electron beam co-irradiation graft polymerization has been carried out up to an absorbed dose of 30 kGy in air at room temperature between methyl methacrylate (MMA) monomer and γ- Al2O3 nanoparticles and micronparticles, respectively. The results showed that the percent graft of nano-Al2O3 and micron-Al2O3 is 6.4% and 0.9%, respectively. In the FT-IR spectra of irradiated nanoparticles, there was a new absorption peak at 1725 cm-1 that was attributed to carbonyl stretching vibration and Al-O-C bonds forming on the surface of nanoparitcle. But in the spectra of micron-Al2O3, the absorption peak at 1725 cm-1 was very weak. X-ray photoelectron spectroscopy (XPS) measurements confirmed the existence of carbonyl. The UV absorption intensities of two γ- Al2O3 powders strengthened after irradiation graft polymerization. These results showed that MMA has been successfully grafted onto nano-Al2O3 surface at the dose of 30 kGy. However, there were few new chemical bonds on micron-Al2O3 surface. It could be deduced that irradiation graft polymerization of γ- Al2O3 nanoparticles was easier than that of micronparticles.
Electron-irradiation-induced Changes of martensitic transformation characteristics in TiNi shape memory alloys
Authors: Zu X. T. , You L.P. , Zhu S. , Wang Z. G. , Wu J. H. , Wang L. M.
Published: April 2011

TiNi shape memory alloy samples were irradiated within R-phase by 1.7 MeV electrons with different doses. The martensitic transformation temperatures were measured by Differential Scanning Calorimeter (DSC). The results indicated that the temperature Ms of the onset of R-phase-to-martensite transformation decreased with increasing the dose. The electron irradiation had a slight effect on the other transformation temperatures. The second lifetime of positrons determined by Positron Annihilation Technology were lowered with an increment of the irradiated dose. Relaxation of the elastic stress fields around the Ti3Ni4 precipitates was the cause of the observed change of the transformation characteristics because of the migration and accumulation of electron irradiation-induced point defects.
Atomistic simulations of threshold displacement energies in SiO2
Authors: Mota F. , Caturla M.-J. , Perlado J.M. , Dominguez E. , Kubota A.
Published: April 2011

Silica is one of the candidate materials for final focusing mirrors in inertial fusion reactors. This material will be exposed to high neutron irradiation fluxes during operation. Radiation damage results in point defects that can lead to obscuration of this material; that is, degradation of the optical properties of silica. In this paper we present molecular dynamic simulations of defect production in silica glass. Results on the threshold displacement energies due to oxygen Primary Knock-on Atoms (PKA) are reported concluding that a range of energies (20–40 eV) exists in which the defects have a probability to be created. In addition, we determine a range of distances for a PKA to become a stable defect out of its original position. Our present analysis is focused on the formation of Oxygen Deficient Centers (ODC).
Isotope and Dose Effects in Low-Energy H/D Blistering of Silicon: Narrow Operational Window for Ion-Cutting at < 100 nm
Authors: Moutanabbir O. , Terreault B. , Shaffer E. , Ross G. G.
Published: April 2011

Hydrogen ion blistering has applications in the fabrication of silicon-on-insulator and other devices. Si (001) samples implanted with different fluences of 5 keV H or D ions were rapidly thermal annealed under vacuum. The surface morphology studied by atomic force microscopy revealed that: (1) there is not only a threshold fluence but also a maximum fluence for blistering; and (2) there is a giant isotope effect: The H and D blistering fluence “windows” are (1.5–3.5) × 1016 H cm-2 and (4–8) × 1016 D cm-2 respectively. Due to the higher fluences and higher gas pressure, D blisters are larger (80% surface coverage) than H blisters (60% coverage) and twice as voluminous. Raman spectroscopy and thermal desorption spectrometry suggest that the high fluence blister absence and the giant isotope effect are both connected with an enhancement of the Si–H/D bond stability.
Enhancement effect of photoluminescence in Si nanocrystals by phosphorus implantation
Authors: Kim Joonkon , Woo H.J. , Choi H.W. , Kim G.D. , Hong W.
Published: April 2011

Different from bulk silicon crystal, nano-sized Si crystalline embedded in dielectric medium is known as an efficient light emitting center. In nano-crystalline Si, excitonic electron-hole pairs are considered to be attributed to radiative recombination. But the defects surrounding crystalline nc-Si suppress light emitting, which works as a non-radiative decay path. Hydrogen is usually utilized in order to encapsulate the dangling bonds in the Si:SiO2 interface, dramatically enhancing luminescence yield from nc-Si embedded in dielectric medium. Unfortunately because hydrogen has higher mobility in the matrix, subsequent thermal processes may reduce the enhancement effect. Thus instead of easily reversible hydrogen, phosphorus was introduced by implantation, and was to have the same effect and to be resistive to thermal treatments. Samples were prepared by 400 keV Si implantation with dose of 1 × 1017 Si /cm2 and by multi-energy P implantation to make relatively uniform P concentration in the region where implanted Si ions are distributed. Precipitation of crystalline silicon was obtained by annealing at 1100°C for 2 hour in pure Ar environment. Experimental data such as enhancement effect of PL yield, decay time, peak shift for the phosphorus implanted nano-crystalline Si are shown, and the possible mechanisms are discussed.
Effects of Surfactants N and Br on Ordering in GaInP
Authors: Chapman D.C. , Howard A.D. , Rieth L. , Wixom R.R. , Stringfellow G.B
Published: April 2011

Formation of the CuPt ordered structure during the organometallic vapor phase epitaxial (OMVPE) growth of GaInP has significant effects on the electrical and optical properties, necessitating control of ordering. Formation of the CuPt structure is thermodynamically driven by the surface structure during growth. This has led to the study of the use of surfactants as a way of controlling ordering. To date, these studies have centered on the group V elements isoelectronic with P. Sb and Bi are both larger than P. This leads to less ordering. N, on the other hand, is smaller than P, which makes it potentially interesting. The other disordering mechanism, observed for Te as a surfactant in GaInP, is kinetic. Rapid step propagation leads to a reduction in ordering. This suggests another potentially interesting class of surfactants, the group VII elements, such as Br, that have been reported to increase the step velocity during OMVPE growth. This paper describes the results of the addition of the surfactants N and Br during the OMVPE growth of GaInP. Addition of N (DMHy) results in a clear reduction in order parameter, due to thermodynamic effects. The addition of Br (CBr4) is also observed to systematically decrease the amount of CuPt ordering and is found to correspond to a significant roughening of the surface, which is postulated to be the origin of the reduction in order parameter.
Quadruple-period ordering in MBE GaAsSb alloys
Authors: Batyrev Iskander G. , Norman Andrew G. , Zhang Shengbai , Wei Su-Huai
Published: April 2011

Experimental and theoretical studies are reported for a quadruple period ordering found in GaAsSb alloy layers grown by molecular beam epitaxy at high growth temperatures. We propose a growth model that accounts for the observed three-dimensional (3D) ordered structure. It is shown that the already-ordered material in the previously grown layer affects the reconstruction of the growth front with respect to the underlying alloy template resulting in the correct stacking of the individual 2D ordered layers into the observed 3D ordered structure.
1.5 micron InAs quantum dot lasers based on metamorphic InGaAs/GaAs heterostructures.
Authors: Ustinov V.M. , Zhukov A.E. , Kovsh A.R. , Maleev N.A. , Mikhrin S.S. , Vasil'ev A.P. , Nikitina E.V. , Semenova E.S. , Kryzhanovskaya N.V. , Musikhin Yu.G. , Shernyakov Yu.M. , Maximov M.V. , Ledentsov N.N. , Bimberg D. , Alferov Zh.I.
Published: April 2011

1.5 micron range emission has been realized using the InAs quantum dots embedded into the metamorphic InGaAs layer containing 20% of InAs grown by MBE on a GaAs substrate. Growth regimes were optimized to reduce significantly the density of dislocations propagating into the active layer from the lattice mismatched interface. 2 mm long InGaAs/InGaAlAs lasers with 10 planes of quantum dots in the active region showed threshold current density about 1.4 kA/cm2 with the external differential efficiency as high as 38%. Lasing wavelength depends on the optical loss being in the 1.44–1.49 micron range at room temperature. On increasing the temperature the wavelength reaches 1.515 micron at 85C while the threshold current characteristic temperature of 55–60K was estimated. High internal quantum efficiency (η>60%)and low internal losses (α=3–4 cm ) were realized. Maximum room temperature output power in pulsed regime as high as 5.5 W for 100 micron wide stripe was demonstrated. Using the same concept 1.3 micron InGaAs/InGaAlAs quantum well lasers were fabricated. The active region contained quantum wells with high (∼40%) indium content which was possible due to the intermediate InGaAs strain relaxation layer. 1 mm stripe lasers showed room temperature threshold current densities about 3.3 kA/cm (λ=1.29 micron) and 400 A/cm2 at 85K. Thus, the use of metamorphic InGaAs layers on GaAs substrate is a very promising approach for increasing the emission wavelength of GaAs based lasers.
Instabilities, Elasticity, and Wetting Effect in Multilayer Heteroepitaxial Growth
Authors: Huang Zhi-Feng , Desai Rashmi C.
Published: April 2011

For multilayer semiconductor films comprising various material layers, the coupling of elastic states in different layers as well as the nonequilibrium nature of the growing process are essential in understanding the surface and interface morphological instability and hence the growth mechanisms of nanostructures in the overall film. We present the theoretical work on the stress-driven instabilities during the heteroepitaxial growth of multilayers, based on the elastic analysis and the continuous nonequilibrium model. We develop a general theory which determines the morphological evolution of surface profile of the multilayer system, and then apply the results to two types of periodic structures that are being actively investigated: alternating tensile/compressive and strained/spacer multilayers. The wetting effect, which arises from the material properties changing across layer-layer interfaces, is incorporated. It exhibits a significant influence of stabilization on film morphology, particularly for the short-period superlattices. Our results are consistent with the experimental observations in AlAs/InAs/InP(001) and Ge/Si(001) multilayer structures.
Hexagonal Lattice Photonic Crystal in Active Metallic Microcavity
Authors: Tam H. L. , Huber R. , Li K. F. , Wong W. H. , Pun Y. B. , So S. K. , Xia J. B. , Cheah K. W.
Published: April 2011

A hexagonal lattice photonic crystal was fabricated inside the metallic microcavity. And a thin film of Alq3 was incorporated inside the textured cavity as an active medium. The microcavity is designed such that the modified photonic modes due to the textured structure can couple to the excited electronic states of Alq3. This leads to changes in the emission characteristics of Alq3. From the angle-resolved transmission (ARTR) results, the photonic bandgap was observed at all angles from normal incident to 60°. The presence of surface plasmon (SP) was observed in both TM and TE modes of the transmission. Compare to the bulk Alq3 photoluminescence spectrum, significant modification of the photoluminescence (PL) spectrum was observed in the angle-resolved photoluminescence (ARPL). The photoluminescence spectra showed clear suppression in luminescence intensity for the range inside the photonic bandgap. We use decouple approximation for the standing wave modes and derive the photonic waveguide characteristics for two-dimensional textured metallic microcavities. The theoretical result is in good agreement to the experimental result.
Characterization By Variable Angle Spectroscopic Ellipsometry Of Dielectric Columnar Thin Films Produced By Glancing Angle Deposition
Authors: Gospodyn James , Brett Michael J. , Sit Jeremy C.
Published: April 2011

Thin films composed of MgF2 and TiO2 were grown by glancing flux incidence, where the physical vapor flux arrives at the substrate between 80° and 90° with respect to substrate normal. The resulting films are composed of slanted columns inclined toward the incoming flux. The films were modeled using the Bruggemann effective medium approximation (EMA) and were found to be biaxial with one of the principal indices of refraction along the direction of the posts. The indices of refraction for MgF2 and TiO2 films were found to be in the range of 1.06 to 1.2 and 1.36 to 1.62, respectively, at a wavelength of 600 nm. The indices of refraction were found to decrease as the deposition angle increased. The film density was also found to be independent of the film thickness for films ranging in thickness from 500 nm to 3400 nm.
Photonic Crystal Tapers for Coupling Large Ridge Waveguides to Photonic Crystal Waveguides
Authors: Ndi Francis C. , Toulouse Jean
Published: April 2011

We present a study of various photonic crystal taper structures each characterized by the taper angle and roughness for coupling light into 2-dimensional photonic crystal waveguides from large ridge waveguides. The photonic crystal waveguide is made of a triangular lattice of holes in a dielectric. The objective is to find a taper structure that offers the best coupling efficiency over a range of widths of the ridge waveguide while leaving a small footprint. We show that such a structure indeed exists and can be further optimized as the width of the ridge waveguide gets even larger leading to more than 90% increase in coupling efficiency in some cases.
Ultrasmall Lasers Based on Photonic Crystal Line Defects
Authors: Baba Toshihiko
Published: April 2011

In this paper, we discuss unique light localization in a single line defect, which is effective for constructing photonic crystal light lasers. The localization is based on additional defect doping that breaks the symmetry of the line defect. Even though such a defect is opened to the line defect, the optical field is well confined around the defect at cutoff frequencies of the line defect. This concept expands the design flexibility of microcavities; for example, the composite of point and line defects and waveguide components such as bends and branches can be microcavities. It also allows effective mode controls such as the singlemode operation in relatively large cavities. The lasing operation of these cavities in a GaInAsP photonic crystal slab was experimentally observed by photopumping at room temperature. This paper reports lasing characteristics and the dependence on various structural details.
Interfacial Energy and Materials Selection Criteria in Composite Microstructured Optical Fiber Fabrication
Authors: Hart Shandon D. , Fink Yoel
Published: April 2011

The recently expanding field of microstructured optical fibers relies on the controlled fabrication of sub-micron features in a fiber drawn in the viscous fluid state. Microstructured fibers have generated great interest owing to their potential in areas such as photonic bandgap guidance of light in low-index media; high-energy laser transmission; and unique control over waveguide non-linearities, dispersion and modal properties [1–6]. These fibers have been made from a single material with air holes [7, 8] and as multi-material ‘composite’ fibers where air is not a part of the microstructured region [6, 9]. While single-material microstructured fibers generally rely on the established technology base of fused silica, the use of less conventional materials may enable applications not possible using silica [6]. Multi-material fibers may also present certain fabrication advantages due to their incompressible domains and simple cylindrical geometries. However, the use of more than one material raises questions about which types of materials can be combined in the drawing of a microstructured fiber. This problem can be approached by analyzing the relative importance of different materials properties such as viscosity, interfacial energy, and thermal expansion. In this study we focus on the effects of interfacial energy in composite microstructured fibers. We measure the interfacial energies at high temperature of a chalcogenide glass and an organic polymer recently employed in the fabrication of composite photonic bandgap optical fibers. We discuss the effect of interfacial energy during fiber draw, as well as the interplay between surface and viscous forces. Finally, we comment on the implications of this analysis for understanding what classes of materials can be used in composite microstructured fiber fabrication.
Visualization of electrons and holes localized in the gate thin film of metal-oxide nitride-oxide semiconductor type flash memory by using scanning nonlinear dielectric microscopy
Authors: Honda Koichiro , Cho Yasuo
Published: April 2011

We used scanning nonlinear dielectric microscopy to observe the position of electrons and holes in the gate SiO2-Si3N4-SiO2 (ONO) film of metal-oxide-nitride-oxide semiconductor type Flash memory. The electrons were detected in the Si3N4 part of the ONO film. The holes, on the other hand, were found in the Si3N4 film as well as in the bottom SiO2 film.
Local Surface Modification of ECR Sputtered Carbon Film and Its Application to Ultra High Density Data Storage
Authors: Tsuchitani S. , Isozaki M. , Kaneko R. , Tanaka I. , Hirono S.
Published: April 2011

We propose a probe storage using a carbon film deposited by electron cyclotron resonance plasma (ECR) sputtering as a recording material. Such storage has a potential to achieve an electrical data storage with small writing voltage and ultra high recording density due to super hardness and large electric conductivity of the ECR sputtered carbon (ECR-C). The ECR-C film is deposited on a silicon substrate covered by a thermal oxide. Recording experiments are performed by a conductive atomic force microscope with a gold coated tip. The electrical resistance of the film surface is decreased locally by applying voltages smaller than 2V between the film and the tip. The resistance decrease of the film by the voltage application are caused by a thermal reaction due to Joule's heat at contact portion of the film with the tip. Data bits with size of about 70nm can be formed by applying a pulse row as a writing voltage.
Media Technologies for 20 GB Single Layer and 36 GB Dual Layer Phase Change Rewritable Disc “HD DVD-ARW”
Authors: Ashida Sumio , Yusu Keiichiro , Nakai Tsukasa , Tsukamoto Takayuki , Ichihara Katsutaro , Ohmachi Noritake , Morishita Naoki , Ogawa Akihito , Nakamura Naomasa
Published: April 2011

In an effort to achieve as high a storage capacity as possible on a disc format that is similar to conventional DVD using blue-violet laser, a number of new technologies have been implemented for the phase change rewritable media. The technologies include the ways to meet challenges in obtaining larger signal amplitude for shorter bit lengths and lowering the cross erase for narrower track pitches. Technologies developed for both the single layer and the dual layer discs are discussed.
Optical Properties of Multi-layer Chalcogenide Thin Film for Optical Recording Media
Authors: Kang Myung-Jin , Park Chan-Gyung , Choi Se-Young
Published: April 2011

We present the results of optical properties of multi layer thin films as in the media of phase change optical disk data storage. Reflectance and optical contrast of multi layer thin films increased rapidly between 100 °C and 150 °C. Moreover, optical contrasts at different wavelength were also studied. The refractive index and the optical band gap decreased, while the extinction coefficient increases as the crystallization occurs. The Egopt of crystalline thin film was ∼0.6 eV lower than that of amorphous thin film. Egopt decreased as the number of stacked layer increased.
Secondary Phases on the Surface of Real Vitrified Radioactive Waste Disposed in a Loamy Soil
Authors: Ojovan Natalie V. , Sartceva Irene V. , Barinov Alexander S. , Mokhov Andrew V. , Ojovan Michael I. , Möbus Günter
Published: April 2011

This work examines secondary phases formed on the surface of radioactive borosilicate glass K-26 during 12 years of testing in the loamy soil. This glass has been produced to immobilise intermediate level operational nuclear power plant (NPP) radioactive waste. An altered layer has been formed at the glass surface that had been contacting with the repository environment. The layer is morphologically following the bulk waste glass. The layer is chemically inhomogeneous and non-uniform in thickness and structure. It contains in addition to the major vitreous phase, alpha quartz, calcite, aluminium hydrochlorides, and molybdenum compounds.
Ceramic Wasteforms for the Conditioning of Spent MOxFuel Wastes
Authors: Maddrell E. R. , Abraitis P. K.
Published: April 2011

Crystalline ceramic wasteforms have been fabricated to immobilise a combined fission product and actinide waste stream arising from spent MOx fuel. The fuel is conditioned by a UREX process, as contrasted to PUREX, to produce a waste stream containing fission products and transuranics. Zirconia rich Synroc derivatives have been formulated to minimise formation of perovskite. This ensures that the transuranics are predominantly immobilised in zirconolite. For comparison, a wasteform has also been produced in which transuranics and rare earth element fission products are immobilised in a radiation resistant cubic zirconia solid solution, whilst caesium, strontium and barium are partitioned to an alumina rich magnetoplumbite phase.
Examination of Synthetic Murataite Structure Using Data of Mossbauer Spectroscopy
Authors: Urusov Vadim S. , Rusakov Vyacheslav S. , Yudintsev Sergey V. , Stefanovsky Sergey V.
Published: April 2011

Murataite-based ceramics were recently suggested as promising matrices for immobilization of rare earths and actinides from high-level waste (HLW). Nevertheless, the crystal-chemical formula of the phase has not been accurately determined yet. We have examined structural features of murataite with Mössbauer spectroscopy. Initial batches were prepared from CaO, Al2O3, Fe2O3, MnO2, ZrO2, TiO2, ZrO2, and UO2. Mixtures were melted in platinum crucibles in a resistive furnace in air at 1450°C for 1 h followed by cooling to 1000°C at the rate of 10°C/min. and final cooling down with the furnace switched-off. Study with XRD, SEM, and TEM showed the samples are composed of two co-existing murataite-type phases with five- and eight-fold elementary fluorite cells. To investigate the valence and structural position of iron ions, Mössbauer spectroscopy on 7Fe nuclei in geometry “on absorption” was used. The data obtained let us conclude that in both murataite varieties trivalent iron is distributed almost statistically (3:1) between B octahedra and C five-vertex polyhedra, while tetrahedral sites T are probably not populated. Taking into account these suggestions, the idealized crystal chemical formula of synthetic murataites can be simplified to A3[8]B6[6]C2[5]O22-x/2. Recalculation of chemical analyses to atomic numbers results in the conclusion that average cation valence for murataites is 3.33. Then, calculation for the generalized formula M11O22-x/2 (M=A,B,C) gives a value x/2 = 3.7, i.e., the number of O atoms in the formula is 22–3.7 = 18.3. Final conclusions on the murataite formulae have to be verified by direct structural research on a single crystal.
Effects of pH and Uranium Valence State on the Aqueous Dissolution of Brannerite
Authors: Zhang Y. , Loi E. , Blackford M. , McLeod T. , Li H. , Begg B.
Published: April 2011

The dissolution of the thorium analogue of brannerite (ThTi2O6-I) and U(IV)/U(V) doped Th-brannerite (Th0.97U0.03Ti2O6-II and Th0.955U0.03Ca0.015Ti2O6-III) in aqueous media under atmospheric conditions has been studied to elucidate the effects of pH and uranium valence state on the dissolution rate.

The dissolution of I is nearly stoichiometric but slightly preferential release of U occurs for II and preferential release of Ca and U occur for III. The V-shape pH dependence previously observed for U-brannerite only occurs for U (not other matrix elements) for II, indicating that the pH dependence is related to the U oxidation state upon dissolution. The normalised U dissolution rates of III are nearly an order of magnitude higher than those of II for pH values over 3, suggesting brannerite is less durable with U(V) doping. TEM examination of specimens after leaching revealed few surface alteration products, which is consistent with the nearly stoichiometric dissolution of thorium brannerite.
Effects of the Environmental Pressure in the Corrosion Potential of the Copper that Will Be Used as Container of High Level Radioactive Waste
Authors: Escobar I. , Silva E , Lamas C. , Silva C. , Werme L.
Published: April 2011

The SKB project of Sweden has considered copper as the most appropriate metal to be used as container for high activity radioactive waste. However, it is still necessary to carry out some studies that can assure that their chemical, physical, mechanical properties, etc. do not loose stability in a period so long as 100.000 years.

In this work we show using anodic polarization, the corrosion potential (Ecorr) behaviour in different pressurized environment. The copper surface was characterized using optical microscopy. The electrochemical cell was mounted in a high pressure chamber that allowed to work up to 40 atm. The electrolyte solution simulates the deep groundwater, being the composition reported in literature [1].

The experimental results in solutions without bentonite show only slightly changes of the corrosion potential to cathodic values. At pressures of 40 atm, products of corrosion are observed, covering micropitting, that can be induced because of a bigger interaction metal/ ion at these pressures.

In the other case, bentonite presence produces beneficial effects in the resistance of the copper corrosion, since it is observed that the corrosion potential is displaced to more anodics values. This effects could be explained due to that this clay is able to retain ions that are aggressives for copper, such as chloride, sulphide, etc., and it liberates others that don't produce deterioration, such as sodium, that is in concordance with others authors[15].
The Effect of EDZ on the Migration of Radionuclides in a KBS-3 Type Repository
Authors: Autio Jorma , Hjerpe Thomas , Siitari-Kauppi Marja
Published: April 2011

The role of excavation damaged zone (EDZ) in a KBS-3 type repository for spent nuclear fuel depends significantly on the design of the engineered barrier systems such as tunnel backfill since one obvious function of the backfill is to prevent the growth of EDZ. Main results of EDZ studies based on using 14C-PMMA method carried out at Äspö Hard Rock Laboratory in Sweden, and at Research Tunnel at Olkiluoto in Finland by Posiva and SKB in co-operation are presented. The significance of the results is evaluated quantitatively and qualitatively. The EDZ around the deposition hole on migration of radionuclides diffusing out of a waste canister was found unlikely to be a significant migration route in the absence of large hydraulic gradients. According to the study the EDZ caused by state-of-the-art drill and blast excavation adjacent to walls and roof of deposition tunnels was found negligible, however the EDZ adjacent to deposition tunnel floor is evidently more extensive and more significant.
Effects of Cement Additives on Radionuclide Mobility
Authors: Dario Mårten , Molera Mireia , Allard Bert
Published: April 2011

The effects of organic cement additives (totally 7) on the sorption of Eu on cement and TiO2 were measured with variation of the concentration of the additive (0.001–10% of the water phase) and reaction time (up to 420 d). There was a significant reduction of the sorption of Eu on cement as well as on TiO2 after 24 h of exposure time in the presence of additives at levels that would be obtained in a cement/water system if the total load of the additive in the cement (up to 3%) would be released into the water phase. Sorption increased with time and would be expected to reach constant levels after 100–200 d. Storage of the additives at 60 and 120 °C, pH 12.5, for up to 110 d (in order to degrade them) did not lead to significantly altered sorption behaviour.
Sorption of Actinides onto Granite and Altered Material from Äspö HRL
Authors: Kienzler Bernhard , Römer Jürgen , Schild Dieter , Bernotat Walter
Published: April 2011

Within the scope of a bilateral cooperation between Svensk Kärnbränslehantering AB (SKB) and Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung (FZK-INE), actinide migration experiments with Pu, Am, and Np are conducted at the Äspö Hard Rock Laboratory. Migration experiments are complemented by batch experiments providing detailed information on the relevant retention processes for actinides onto granite and altered fracture material. The same kinds of experiments are performed with well defined minerals. α-autoradiography and XPS were used to quantify local sorption properties of the rock samples. It is shown that Np is retained by reduction to Np(IV) in the presence of Fe(II) minerals. The sorption coefficient for Pu is significantly higher compared to Np or U. Pu retention takes place on a multitude of minerals. Sorption of U is also strongly correlated with the occurrence of Fe oxide phases.
Surface Site Densities of Uranium Oxides: UO2, U3O8
Authors: Clarens F. , Pablo J. de , Casas I. , Giménez J. , Rovira M.
Published: April 2011

The estimation of the surface site density for UO2 (main component of the SF matrix) is an important aspect to take into account in the development of radiolytical models for the dissolution of the spent nuclear fuel (SF). Also, other oxides can be formed on the SF surface due to the effect of radiolytically-formed oxidizing species. Due to the lack or reliable data in literature we have studied the surface site densities of two uranium oxides: UO2 and U3O8.

For this determination, the knowledge of both the reactive surface area and the surface charge of the solid are necessary. In this work the reactive surface area of the two solids was determined by the BET method while the surface charge was determined by potentiometric acid-base titrations of suspensions of the solids at different ionic strengths (0.001, 0.01, and 0.1 mol·dm−3) under N2 atmosphere.

The amount of adsorbed protons was calculated by subtracting blank titration from thesolid suspension titration. The single-site nonelectrostatic model (NEM) was used to describe titration data. Uranium speciation in solution was included in the model as well.

The surface area values obtained were 0.15 ± 0.01 m2·g−1 for UO2 and 0.77 ± 0.02 m2·g−1 for U3O8, while the surface acidic site densities were determined to be 165 ± 10 sites·nm−2 and 48 ± 3 sites·nm−2 for UO2 and U3O8, respectively.
The Oxidative Dissolution Mechanism of Uranium Dioxide. The Effect of pH and Oxygen Partial Pressure
Authors: Pablo Joan de , Casas Ignasi , Giménez Javier , Clarens Frederic , Duro Lara , Bruno Jordi
Published: April 2011

The dissolution of the unirradiated uranium dioxide, UO2, is largely affected by chemical variables like pe, pH and carbonate concentration in solution. In a previous paper [1], we studied the kinetics of the dissolution of UO2as a function of pH and oxygen partial pressure and the experimental dissolution rates obtained showed a fractional dependence on both parameters. These fractional orders indicate a dissolution occurring via a surface mediated mechanism.

In this work we have developed a mechanism accounting for the oxidative dissolution of UO2, which depends on the oxygen concentration in solution and on the pH and a general rate equation has been deduced. This mechanism has been used to explain the results obtained by different authors and to explain and predict the dissolution of the spent nuclear fuel matrix.
Spent Fuel Leaching under Anoxic Conditions and the Effect of Canister Materials
Authors: Cui Daqing , Low Jeanett , Lundström Max , Spahiu Kastriot
Published: April 2011

The results of a spent fuel leaching experiment in which a fuel pin (17.7 g) was contacted with 380 mL of a 10 mM NaCl, 2 mM NaHCO3 solution by taking special care to minimize atmospheric oxygen contamination are presented. During the first 287 days, the fractions of inventory in the aqueous phase per day (f/d) increased nearly constantly for all nuclides (except for 100Mo), but were higher for fission products f/d(137Cs)=1.210−6, f/d(99Tc)=1.1·10−6 and f/d(90Sr)= 6.7 · 10−7 than for actinides: f/d (238U) =1.0 · 10−7, f/d(237Np)= 2.6 · 10−7 and f/d(239Pu) = 5.1 ·10−9. After adding iron, cast iron and copper foils (of ∼30 mm2 size), the concentrations of 238U, 237Np and 99Tc decreased by 80%, 97% and 88% to relatively stable levels (500ppb, 0.2 ppb and 0.6 ppb respectively). 239Pu concentrations increased from a level around 0.05 ppb to PuO2 solubility level, 0.5 ppb, and stabilized. The leaching process for 137Cs, 100Mo and 90Sr seems not to be influenced by the addition of metal foils. The observations in the present work contribute to an improved understanding of the behavior of spent fuel under near field repository conditions.
Evolution of the Cavern-Extended Storage (CES) Concept for Flexible Management of HLW
Authors: McKinley Ian G. , Neall Fiona B. , Smith Paul A. , West Julia M. , Kawamura Hideki
Published: April 2011

The search for greater public acceptance for radioactive waste disposal has meant that repository planning increasingly includes monitoring, institutional control and flexibility with respect to retrieval and reversability. However, the fundamental repository designs are generally unchanged. This paper describes an alternative – the Cavern Extended Storage concept – which aims to incorporate requirements for flexibility and choice for future generations into a deep geological disposal concept that provides a much safer option than extended surface storage.
Absence of enhanced stability in deuterated amorphous silicon thin film transistors
Authors: Lin Shufan , Flewitt Andrew J. , Milne William I. , Wehrspohn Ralf B. , Powell Martin J.
Published: April 2011

A comparison of the threshold voltage shift after gate-bias stress in hydrogenated and fully deuterated amorphous silicon thin film transistors (TFTs) is presented. A series of fully deuterated bottom gate TFTs consisting of a deuterated n+ contact layer, deuterated intrinsic amorphous silicon (deposited at a range of pressures) and deuterated silicon nitride gate insulator have been produced. A similar series of fully hydrogenated bottom gate TFTs have also been produced, and the stability of the two sets of devices compared. Deuterated and hydrogenated amorphous silicon deposited under the same process conditions do not have the same material properties due to the difference in the ion energy of H and D in the plasma. However, deuterated and hydrogenated material deposited at the same growth rate have almost identical structural properties. Hydrogenated and deuterated TFTs are found to exhibit the same variation in stability as a function of growth rate. In particular, there is no evidence for increased stability in deuterated TFTs. Previous reports of more stable deuterated TFTs, by other groups, can be explained by a change in the Si network properties due to the higher ion energy of deuterium in comparison with hydrogen, when using similar deposition conditions. The implication of our experimental results is that, for the same amorphous network and hydrogen/deuterium concentration, the stability is identical for hydrogenated and deuterated TFTs. Therefore, there is no giant isotopic effect in amorphous silicon TFTs. The study also further supports the idea that Si-Si bond breaking is the rate-limiting step for Si dangling bond defect creation, rather than Si-H bond breaking.