bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Remote Hydrogen Plasma Treatment on ZnO Single Crystal Surfaces
Authors: Strzhemechny Yuri M. , Nemergut John , Bae Junjik , Look David C. , Brillson Leonard J.
Published: April 2011

We have studied the effects of hydrogen plasma treatment on the defect characteristics in single crystal ZnO grown at Eagle-Picher by chemical vapor transport. Depth-dependent cathodoluminescence (CL) spectra, temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence (PL) spectra reveal significant changes resulting from unannealed exposure of n-type ZnO to a remote hydrogen plasma. Low temperature PL spectra show that this hydrogen exposure effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a new peak feature at 3.366 eV possibly related to a neutral donor bound exciton. A simple thermal analysis of the activation energy for the 3.366 eV line yields 5–10 meV. Hydrogenation also produces a violet 100 meV-wide peak centered at 3.16 eV. Remote plasma hydrogenation produces similar changes in room-temperature CL spectra: near-band edge emission intensity increases with hydrogenation. Furthermore, this new emission increases with proximity to the free ZnO surfaces, i.e., with decreasing the energy of the incident electron beam from 3.0 down to 0.5 keV. Subsequent annealing at 450 °C completely restores both the PL and CL spectra in the sub-band gap range. The appearance of a new bound-exciton feature at 3.366 eV with H plasma exposure, the near-surface nature of the spectral changes, and the reversibility of spectral features with annealing indicate a direct link between H indiffusion and appearance of a shallow donor.
Far-infrared magnetooptical generalized ellipsometry determination of free-carrier parameters in semiconductor thin film structures
Authors: Hofmann Tino , Grundmann Marius , Herzinger Craig M. , Schubert Mathias , Grill Wolfgang
Published: April 2011

In accord with the Drude model, the free-carrier contribution to the dielectric function at infrared wavelengths is proportional to the ratio of the free-carrier concentration N and the effective mass m*, and the product of the optical mobility μ and m*. Typical infrared optical experiments are therefore sensitive to the free-carrier mass, but determination of m* from the measured dielectric function requires an independent experiment, such as an electrical Hall-effect measurement, which provides either N or μ. Highly-doped zincblende III-V-semiconductors exposed to a strong external magnetic field exhibit non-symmetric magnetooptical birefringence, which is inversely proportional to m*. If the spectral dependence of the magnetooptical dielectric function tensor is known, the parameters N, m* and μ can be determined independently from optical measurements alone. Generalized ellipsometry measures three complex-valued ratios of normalized Jones matrix elements, from which the individual tensor elements of the dielectric function of arbitrarily anisotropic materials in layered samples can be reconstructed. We present the application of generalized ellipsometry to semiconductor layer structures at far-infrared wavelengths, and determine the magnetooptical dielectric function for n-GaAs and n-AlGaInP for wavelengths from 100 μm to 15 μm. We obtain the effective electron mass and mobility results of GaAs in excellent agreement with results obtained from Hall-effect and Shubnikov-de-Haas experiments. The effective electron mass in disordered n-AlGaInP obtained here is in very good agreement with previous k·p calculations. (Far)-infrared magnetooptic generalized ellipsometry may open up new avenues for non-destructive characterization of free-carrier properties in complex semiconductor heterostructures.
MOCVD Growth and Characterization of InNAs/GaAs Quantum Wells
Authors: El-Emawy Abdel-Rahman A. , Nuntawong Noppadon , Cao Hongjun , Liu Chiyu , Xu Huifang , Osiński Marek
Published: April 2011

InNAs/GaAs multiple-quantum-wells were grown by MOCVD on (100) SI-GaAs substrates using trimethylindium, tertiarybutylarsine, and 95–97.5% of dimethylhydrazine (DMHy) in the vapor phase. The crystalline quality and solid phase composition were evaluated using highresolution x-ray diffraction analysis. Nitrogen content in InNAs wells was determined to be 28%. Electron energy loss spectroscopy was used to confirm the presence of nitrogen in quantum wells. Surface morphology was investigated by atomic force microscopy (AFM) and field emission microscopy (FEM).
Photoluminescence of Ge Nanoclusters in Ion Implanted SiO2
Authors: Lopes J.M.J. , Zawislak F.C. , Behar M. , Fichtner P.F.P. , Rebohle L. , Skorupa W.
Published: April 2011

180 nm thick SiO2 films produced by wet oxidation of (100) Si wafers were implanted at room temperature with 120 keV Ge+ ions at a fluence of 1.2×10 cm-2 in order to allow the formation of Ge nanoparticles upon post implantation thermal annealings within the interval 400°C ≤ T ≤ 900°C. The size and depth distribution of the Ge nanoparticles were characterized by Transmission Electron Microscopy and Rutherford Backscattering Spectrometry. In addition, the room temperature photoluminescence (PL) bands of the nanoparticles system were studied in the regions of the blue-violet and ultra-violet emissions. The mean diameter of the nanoclusters increases from 2.2 nm at 400°C to 5.6 nm at 900°C. Concomitantly, the blue-violet PL intensity increases by a factor of 12 within the same temperature interval. The results are discussed in terms of possible atomic mechanisms involved in the coarsening behavior and leading to the formation of luminescent centers.
Half-Integer Spin Molecular Nanomagnets
Authors: Hendrickson David N. , Christou George , Wernsdorfer Wolfgang , Hill Stephen O. , Aliaga-Alcade Núria , Bhaduri Sumit , Edwards Rachel S. , Aubin Sheila M. J. , Sun Ziming
Published: April 2011

Single-molecule magnets (SMM) are molecules that function as single-domain nanomagnets. SMMs have been characterized with a ground-state spin ranging from S = 4 to S = 13. A few SMMs have been identified that have half-integer spin ground states. [Cation][Mn12O12(O2CR)16(H2O)4] complexes, where R is some substituent, are SMMs that have either a S = 19/2 or 21/2 ground state. Quantum tunneling of magnetization (QTM) is observed for these half-integer-spin Kramers [Mn12]- degenerate SMMs in zero external magnetic field, as well as for a class of S = 9/2 Mn4 SMMs. The presence of QTM in zero external field is attributed to a transverse component of a nuclear spin field, dipolar interactions and intermolecular exchange interactions. The Landau-Zener method is used to measure the tunnel splitting as a function of transverse magnetic field for a single crystal of the S = 9/2 SMM [Mn4O3(OSiMe3)(OAc)3(dbm)3]. Spin parity dependent QTM is established. The effect of a magnetic exchange interaction between two S = 9/2 Mn4 SMMs upon QTM was studied for another compound. The hydrogen bonding and Cl…Cl contacts within a supramolecularly linked [Mn4]2 dimer lead to a weak antiferromagnetic exchange interaction between the two S = 9/2 SMMs. This interaction causes a shift (exchange bias) from zero field for the magnetic field at which QTM occurs.
Bistable memory effect in chromium oxide junctions
Authors: Sokolov A. , Yang C.-S. , Ovtchenkov E. , Yuan L. , Liou S.-H. , Doudin B.
Published: April 2011

Magnetotransport properties of granular CrO2 /Cr2O3 films made of CrO2 crystals covered by 1– 2 nm native insulating Cr2O3 are presented. Electrical properties of a limited number of grains measured in series and parallel (10 to 15 grains) reveal intergrain tunneling characteristics. At lowest temperatures, a well pronounced zero bias anomaly indicates that impurities in the junctions block the electronic flow.

Hysteresis in the IV curves are observed at intermediate temperatures on zero-field cooled samples. Changing the polarity of a short excitation pulse (100ns) of amplitude smaller than 1 V triggers a change in the zero-bias resistance by 10–50%. These states are stable and well reproducible in the temperature interval ranging from 100K to 250K. Applying an external magnetic field cancels the IV hysteresis. The resistance of the devices in the kΩ range, the potential high-speed for writing and reading the resistance sate, make these systems interesting candidates for magnetic non-volatile memories.
Ab-initio theory of CPP transport
Authors: Weinberger P.
Published: April 2011

The phenomenon of electric transport perpendicular to the planes of atoms is discussed in terms of an ab-initio approach based on the Kubo-Greenwood equation. Since level of decription is fully relativistic “artifacts” due to spin resolution are avoided. Besides a formal discussion of the applied methods and an illustration of the numerical procedures, in particular the dependence of the magnetoresistance on the quality of interfaces, and issues concerning “tunneling” in metal/non-metal heterojunctions are discussed.
Magnetic Properties of Ni Nanoparticles Embedded in Amorphous SiO2
Authors: Fonseca Fabio C. , Goya Gerardo F. , Jardim Renato F. , Muccillo Reginaldo , Carreño Neftalí L. V. , Longo Elson , Leite Edson R.
Published: April 2011

A modified sol-gel technique was used to synthesize nanocomposites of Ni:SiO2 which resulted in Ni nanoparticles embedded in a SiO2 amorphous matrix. Transmission electron microscopy TEM analysis were performed to study the structure and morphology of the magnetic powders. The Ni particles were found to have a good dispersion and a controlled particle size distribution, with average particle radius of ∼ 3 nm. A detailed characterization of the magnetic properties was done through magnetization measurements M(T,H) in applied magnetic fields up to ± 7 T and for temperatures ranging from 2 to 300 K. The superparamagnetic (SPM) behavior of these metallic nanoparticles was inferred from the temperature dependence of the magnetization. The blocking temperature TB, as low as 20 K, was found to be dependent on Ni concentration, increasing with increasing Ni content. The SPM behavior above the blocking temperature TB was confirmed by the collapse of M/MS vs. H/T data in universal curves. These curves were fitted to a log-normal weighted Langevin function allowing us to determine the distribution of magnetic moments. Using the fitted magnetic moments and the Ni saturation magnetization, the radii of spherical particles were determined to be close to ∼ 3 nm, in excellent agreement with TEM analysis. Also, magnetic hysteresis loops were found to be symmetric along the field axis with no shift via exchange bias, suggesting that Ni particles are free from an oxide layer. In addition, for the most diluted samples, the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles. This was confirmed by the temperature dependence of the coercivity field that obeys the relation HC(T) = HC0 [1-(T/TB)1/2] below TB with HC0 ∼ 780 Oe.
Dynamic growth mechanism and interface structure of crystalline zirconia on silicon
Authors: Wang S J , Huan A C H , Ong C K
Published: April 2011

In present report, we have studied the initial stage of the growth of crystalline yttria-stabilized zirconia (YSZ) films on the natively oxidized Si (100) wafer by pulsed-laser deposition. X-ray photoelectron spectroscopy (XPS) and high-resoluti on transmission electron microscopy (HRTEM) show that, for the first few monolayers of crystalline YSZ deposited on Si (100), the dynamic processes appear to be the decomposition of SiO2 to SiO, the formation of ZrO2, and the desorption of SiO. The native amorphous silicon oxide layer is removed completely with the continued deposition of YSZ and the oxygen in this layer is used as oxygen source for forming stable crystalline oxide film. XPS depth profile and HRTEM investigation showed that the interface of crystalline YSZ film in contact with silicon was found to be atomically sharp and commensurately crystallized without an amorphous layer. The interface structure is suggested to have a sequence of-Si-O-Zr-O-. For the film with electrical equivalent oxide thickness 1.46 nm, the leakage current is about 1.1×10- A/cm2 at 1 V bias voltage. The hysteresis and interface state density in this film are measured to be less than 10 mV and 2.0×1011eV-1cm-2.
X-ray Amorphous P-type Conductive Oxide; ZnRh2O4
Authors: Narushima Satoru , Mizoguchi Hiroshi , Ohta Hiromichi , Hirano Masahiro , Shimizu Ken-ichi , Ueda Kazushige , Kamiya Toshio , Hosono Hideo
Published: April 2011

An amorphous p-type conductive oxide semiconductor was created based on a mother crystalline material, a p-type conductive ZnRh2O4 spinel. The amorphous film of ZnRh2O4 was deposited by an rf sputtering method. Seebeck coefficient was positive, +78 μVK-1, indicating that major carrier is a positive hole. A moderate electrical conductivity (2 S cm-1 at room temperature) for a p-type semiconductor was observed. Optical band gap was estimated to be 2.1 eV. P-n junction diodes with a structure of Au / a-ZnRh2O4 / a-InGaZnO4 / ITO fabricated on glass substrates, operated with a good rectifying characteristics, a rectification current ratio at ± 5V of ∼103. The threshold voltage was 2.1 eV, which corresponds to the band gap energy of the amorphous ZnRh2O4. This is the first discovery of a p-type amorphous oxide and the demonstration of p-n junction all composed of amorphous oxide semiconductors.
Photoemission Study of Interfacial Oxidation in ZrO2/subnanometer SiONx/Si(100) Stacked Structures
Authors: Miyazaki Seiichi , Yamashita Hiroki , Nakagawa Hiroshi , Yamaoka Masanori
Published: April 2011

For staked structures consisting of evaporated ZrO2 and ∼0.6nm-thick silicon oxynitride formed on Si(100), the blocking capability of the silicon oxynitride against oxidation in dry-O2 anneal at 500°C has been studied as a function of nitrogen content in the barrier layer in the range within ∼11at.%. With increasing nitrogen content, the interfacial oxide thickness is decreased linearly and, to suppress the growth of the interfacial oxide layer within two monolayers, a nitrogen content of ∼10at.% is necessary. Observed efficient blocking against oxidation, even for the case with a nitrogen content as small as ∼6at.%, is attributable to the improved homogeneity in the Si-O-Si bonding features at the interface by nitrogen incorporation of a few at.%, which is suggested from the experimental fact that the bandwidth of LO phonons near the interface due to the nitrogen incorporation is decreased as obtained by FT-IR-ATR measurements.
Stability of Indium Tin Oxide/Polymer Interfaces
Authors: Crispin X. , Crispin A. , de M. P. , Marciniak S. , Osikowicz W. , Jönsson S. , Fahlman M. , Kugler Th. , van IJzendoorn L. J. , de M. J. A. , Salaneck W. R.
Published: April 2011

Interfacial chemistry at indium tin oxide/polymer interfaces is of fundamental importance for the performance of polymer-based light emitting diodes. X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry are used to investigate the stability of the interface formed between indium tin oxide and (i) the light emitting polymer poly(p-phenylenevinylene), and (ii) the hole injecting layer poly(3,4-ethylenedioxythiophene) polystyrenesulfonate. The formed interfaces are not stable and indium-containing species diffuse from the metal oxide surface into the polymer layers.
Role of Ambience on the Diffusion of Charge Carriers in the Tio2 Layers Investigated by the Photovoltage Technique
Authors: Duzhko V. , Rappich J. , Dittrich Th.
Published: April 2011

The transition from anatase to rutile crystalline phase and from continuous to porous morphology was observed by Raman spectroscopy and scanning electron microscopy, respectively, in anodic TiO2 layers as the time of anodization was increased. The mechanism of the PV formation changes from trap- limited PV in thin continuous layers to diffusion PV in thick porous layers. The generation of excess charge carriers and their subsequent separation in space are strongly dependent on the ambience (air, vacuum, water) in porous layers. The importance of polar water molecules for screening of surface ions of porous TiO2 and excess charge carriers separated in space is discussed.
“Novel Mechanisms on the Growth Morphology of Films“
Authors: Lu T.-M. , Zhao Y.-P. , Drotar J.T. , Karabacak T. , Wang G.-C.
Published: April 2011

Random surface roughness very often can occur during the growth or etching of films under non-equilibrium conditions. Several competing mechanisms such as noise, surface diffusion, and shadowing all play a role in the evolution of surface roughness. However, recent results obtained in many growth and etching processes exhibit an unusual tendency: the morphology is very rough where it is expected to be smooth and vice versa. The origin, we believe, is due to the fact that during the deposition and etching processes the atoms very often do not stick to the surface upon their first strikes. Atoms actually bounce around before all settle on surface sites. This non-unity sticking probability can lead to a very rough surface during etching and a very smooth surface during sputter or chemical vapor deposition that cannot be explained by the conventional mechanisms.
Kinetic Modeling Of Dopant And Impurity Surface Segregation During Vapor Phase Growth: Multiple Mechanism Approach
Authors: Arnold Craig B. , Aziz Michael J.
Published: April 2011

We propose a new kinetic model for surface segregation during vapor phase growth that accounts for multiple segregation mechanisms, including mechanisms for terrace mediated exchange and step edge mediated exchange. The major result of the model is an analytic expression for the experimentally measured segregation length and profile broadening that can be readily calculated without the need for numerical simulations. We compare the model to experimental measurements for the temperature dependence of segregation of Sb in Si(001). The model is able to accurately describe both the anomalous segregation at low temperature and the transition between equilibrium and kinetically limited segregation at high temperature. An excellent agreement is obtained using realistic energies and pre-exponential factors for the kinetic rate constants. The model can be applied to other segregating systems in planar geometries, including metallic and III-V semiconducting thin films.
Threshold Energy for Generating Damage with Cluster Ion Irradiation
Authors: Seki Toshio , Aoki Takaaki , Nakai Atsuko , Matsuo Jiro , Takaoka Gikan H.
Published: April 2011

In order to understand the damage formation by cluster ion irradiation, Si substrates were irradiated with Ar cluster ions at the acceleration energy of 1–20keV. The mean size of cluster was about 3000 atoms. The amount of damage after Ar cluster ion irradiation was measured with Rutherford backscattering spectrometry (RBS). The amount of damage was decreased with decrease of the energy and no damage formed at less than 2keV. This energy of 2keV represents the threshold energy to generate damage with the cluster size of 3000. According to Molecular dynamics (MD) simulation, the damage formation with cluster ion irradiation also depends on cluster size. The size dependence of amount of damage has been investigated experimentally. The cluster size distribution could be changed with the ionization condition and could be measured using Time-of-Flight (TOF) method. The threshold energy was increased with cluster size. These results indicate that undamaged films can be created by using large size of cluster ion with low acceleration energy.
The surfactant effects of antimony on the formation of InAsSb nanostructures on GaAs by metal-organic chemical vapor deposition
Authors: Cederberg J.G. , Biefeld R.M.
Published: April 2011

We have investigated InAsSb nanostructures formed on GaAs during MOCVD. The transition thickness from 2D growth to 3D growth is reduced by the addition of TMSb/Sb4. This is consistent with both an increase in the adatom diffusion length and a reduction in the epilayer/vapor surface energy attributed TMSb/Sb4.
Biomedical Potential of a Zirconium-Based Bulk Metallic Glass
Authors: Horton J. A. , Parsell D. E.
Published: April 2011

Due to their unique mechanical properties, bulk metallic glasses (BMG) have potential for biomedical applications. Biocompatibility and corrosion tests of a zirconium-based BMG showed comparable behavior to current implant alloys. Mechanical properties, such as an elastic limit of 2% and a yield strength of 1700 MPa, are significantly higher than current implant alloys. In addition, it was found that medical MRI images of BMG, possibly due to the amorphous structure, are significantly better than other alloys even though the reference alloy contains 14.6 at.% Ni. Nickel-free compositions also retained similar glass forming characteristics and showed even better MRI images. Edge holding for cutting tool applications was demonstrated. Fatigue tests were performed in simulated body conditions and directly compared to Ti-6 Al-4 V. While one specimen failed at more than 3,000,000 cycles at 500 MPa, there was much scatter in the data. Further concentration on processing issues to produce pore free material is needed to produce reliable materialfor prototype development. Potential uses, especially associated with an interventional MRI for MRI guided surgeries, will be discussed.
Thermal Tempering of Bulk Metallic Glasses
Authors: Aydiner Cahit C. , Üstündag Ersan
Published: April 2011

The recent development of multi-component alloys with exceptional glass forming ability has allowed the processing of large amorphous metal samples. The possibility of formation of thermal tempering stresses during the processing of these bulk metallic glass (BMG) specimens was investigated using the (1) instant freezing, and (2) viscoelastic models. Both models yielded similar results although from vastly different approaches. It was shown that fast convective cooling of Zr41.2Ti13.8Cu12.5Ni10Be22.5 plates could generate significant compressive stresses on the surfaces balanced with mid-plane tension. The crack compliance method was then employed to measure the stress profiles in a BMG plate that was cast in a copper mold. These profiles were roughly parabolic suggesting that thermal tempering was indeed the dominant residual stress generation mechanism. However, the magnitude of the measured stresses (with peak values of only about 1.5% of the yield strength) was significantly lower than the modeling predictions. Possible reasons for this discrepancy are described in relation to the actual casting process and material properties.
Effects of Annealing and Annealing with Pressure on Devitrification of Al87Ni7Gd6
Authors: Wesseling Paul , Ko B.C. , Vatamanu L.O. , Caris J. , Lewandowski J.J.
Published: April 2011

The effects of annealing for 30 minutes at temperatures ranging from 123–232°C on the structure evolution, resulting hardness, and tensile properties were determined for amorphous ribbons of Al87Ni7Gd6. Structure evolution was determined using a combination of XRD, DSC, and TEM, while micro-hardness and tensile testing of ribbon specimens was used to evaluate the mechanical properties. Significant effects of annealing on the evolution of structure and properties were obtained, while the superposition of 940 MPa pressure during annealing further enhanced the structure evolution with corresponding changes to the resulting properties.
Ductile Dendritic Phase Reinforced Ti-Base Bulk Metallic Glass-Forming Alloys
Authors: He G. , Eckert J. , Löser W. , Schultz L.
Published: April 2011

Bulk metallic glasses (BMG) exhibit high strength but limited ductility due to their inhomogeneous deformation behavior under load, which seriously limits their application. To prevent the inhomogeneous deformation, attempts have been made by introducing in situ formed ductile dendritic phases in present study. Ti-base BMG-forming alloys were selected and modified by adding refractory metals Nb, Ta, Mo and Zr. Ductile dendrites / nanostructured matrix composites were synthesized which exhibit a plastic strain larger than 14% together with high strength (ultimate strength higher than 2400 MPa). The experimental results show evidence that shear banding is the main deformation mode in nanostructured matrix. The localized shear bands are limited in the inter-dendrite regions by micrometer-sized dendrites. The dendrites act as obstacles to limit the excessive deformation in the localized shear bands and contribute to the plasticity by dislocations.
Glass Formation and Reddish Coloring Properties in Zinc Phosphotellurite Glass.
Authors: Konishi Tomoya , Hondo Takaharu , Araki Tetsuo , Nishio Keishi , Tsuchiya Toshio , Matsumoto Takehisa , Suehara Shigeru , Todoroki Shin-ichi , Inoue Satoru
Published: April 2011

Various compositions of P2O5-TeO2-ZnO glasses were prepared by using a combinatorial glass preparation system including a batch-preparing apparatus and a multi-sample casting machine, and the compositional dependence of glass forming tendency and thermal properties were intensively investigated. The samples exhibited a variety of colors, such as transparent, yellow, wine red and brown depending on its composition. Analyses with scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the reddish coloration is responsible for colloidal suspension of nanometer sized elemental Te particles.
Computer-Aided Development of Multicomponent Metallic Glasses
Authors: Takeuchi Akira , Inoue Akihisa
Published: April 2011

Asynthesized calculation model for developing metallic glasses has been created by taking into account criteria for the achievement of high glass-forming ability (GFA) and viscosity. The model deals with amorphous-forming composition region (AFCR), crystallization temperature (Tx) and three GFA factors: critical cooling rate (Rc), reduced glass-transition temperature (Tg/Tm) and supercooled liquid region (ΔTx=Tx-Tg) where Tg and Tm are glass transition and melting temperature, respectively. The principle of the model is based on thermodynamic functions for multicomponent systems, i.e., mismatch entropy and mixing enthalpy which express the criteria in terms of the number of elements, atomic size differences and the heat of mixing. By combining these thermodynamic quantities with the Miedema's semi-empirical model, AFCR was calculated, and was compared with the experimental results. The GFA factors were also analyzed from viscosity. The Rc was derived from transformation diagram of metallic glasses for crystallization while ΔTx was calculated by solving a differential equation expressing the change in free volume with temperature. As a result of these analyses, Rc-Tg/Tm and R-ΔTx diagrams were found to fit with the experimental results qualitatively. Furthermore, crystallization temperature (Tx) was also calculated for multicomponent metallic glasses by the modification of the Miedema's binary model for the calculation of Tx. The reduced crystallization temperature (Tx/Tl), where Tl is liquidus temperature, was calculated for evaluating GFA of metallic glasses instead of Tg/Tm. Some of the calculation methods used in the present study have theadvantage giving results as a function of composition; thus, there exists possibility to lead to the prediction of glassy alloys compositions. In this sense, the present calculation methods are completely different to the current method for the development of new metallic glasses relying on the empirical criteria which suggest only appropriate systems and/or elements of the alloysfor the achievement of high GFA. In near future, this kind of calculation technique can be used for the prediction of optimal compositions of the metallic glasses with high GFA.
In-plane Anisotropy in Hetero-Amorphous (CoFeB)-SiO2 Thin Films
Authors: Johnsson P. , Aoqui I. , Nötzold K. , Allebert J. , Munakata M. , Grishin A. M.
Published: April 2011

In order to engineer materials suitable for micromagnetic inductor cores we have fabricated and investigated the properties of granular (CoFeB)-SiO2 amorphous thin films. The deposition method, synchronous triple-rf magnetron sputtering onto rotating substrates, induces anisotropy in the film plane. Here we present magnetic hysteresis loops, resistivity and magnetoresistance measurements of two of these films, with different amount of metallic content. Both films have anisotropic resistivity, which is higher for the film with less metallic content. The low-metallic-content film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher metallic content shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples. The behaviour of the resistivity versus temperature ρ (T) indicates that the sample with lower metallic content consists of isolated grains while the high-metallic-content sample consists of a percolated network. Experimental ρ (T) data for the low-metallic-content sample fit: to the variable-range hopping model at temperatures lower than 221 K and can be described by excitation of the carriers to the mobility edge at higher temperatures.
The Intermediate Phase in Ternary GexAsxSe1–2x Glasses
Authors: Qu Tao , Georgiev D.G. , Boolchand P. , Micoulaut M.
Published: April 2011

Melt-quenched AsxGexSe1–2x glasses over the composition range, 0 < x < 0.26, are examined in Raman scattering, T-modulated Differential Scanning Calorimetry (MDSC), and 119Sn Mossbauer spectroscopy measurements. The non-reversing enthalpy near Tg, ΔHnr(x), accessed from MDSC shows a global minimum (∼ 0) in the xc(1) = 0.09 < x < xc(2) = 0.16 range, and increases by an order of magnitude both at x < xc(1) and at x > xc(2). Raman mode frequency of corner-sharing Ge(Se1/2)4 tetrahedra studied as a function of x, also shows three distinct regimes (or power-laws, p) that coincide with ΔHnr(x) trends. These regimes are identified with mechanically floppy (x < xc(1)), intermediate (xc(1) < x < xc(2)), and stressed-rigid (x > xc(2)) phases. The Raman elasticity power-law in the intermediate phase, p1 = 1.04(3), and in the stressed rigid phase, p2= 1.52(5), suggest effective dimensionalities of d = 2 and 3 respectively.
Intermediate Range Order in Silicate Melts and Glasses: Computer Simulation Studies
Authors: Horbach Jürgen , Winkler Anke , Kob Walter , Binder Kurt
Published: April 2011

We present the results of large scale computer simulations to discuss the structural and dynamic properties of silicate melts with the compositions (Na2O)(2·SiO2), (Na2O)(20·SiO2) and (Al2O3)(2·SiO2). We show that these systems exhibit additional intermediate range order as compared to silica (SiO2) where the characteristic intermediate length scales stem from the tetrahedral network structure. Furthermore we show that the sodium dynamics in the sodium silicate systems exhibits a very peculiar feature: the long–time decay of the incoherent intermediate scattering function can be described by a Kohlrausch law with a constant exponentβforq > qthwherebyqthis smaller than the location of the main peak in the static structure factor for the Na–Na correlations.
Actinide Migration in Granite Fractures: Comparison between In-Situ and Laboratory Results
Authors: Kienzler Bernhard , Römer Jürgen , Vejmelka Peter , Jansson Mats , Eriksen Trygve E. , Spahiu Kastriot
Published: April 2011

Results of migration experiments with fractured drill cores performed in laboratory and in the CHEMLAB 2 probe under in-situ conditions at Äspö HRL are presented. Drill cores for both experiments are prepared by the same method and provide similar hydraulic properties. As tracers, actinides Am(III), Pu(IV) and Np(V) are applied. Breakthrough of Np is found to be unre-tarded in comparison to inert HTO tracer. Recovery of Np amounts to less than 40%. Am and Pu are not eluted from the cores. Lower limits of the retardation factor of 135 are calculated for both Am and Pu. Post mortem investigations of the fractured cores are performed by cutting perpendicular to the cylinder axis and subsequent chemical and radiochemical analysis of abraded material and slices. Imaging of the slices reveals the geometry of the flow path. α-radiography of the slices shows similar distribution patterns of Np and Am. It is shown by TTA extraction that Np bound onto the slices is in the tetravalent state. Hence, Np(V) undergoes reduction during migration. Retention of Am and Np is attributed to different processes.
Results from burial experiments with simulated medieval glasses
Authors: Roemich Hannelore , Gerlach Sandra , Mottner Peter , Mees Florias , Jacobs Patric , Dyck Dirk van , Doménech Carbó Teresa
Published: April 2011

During several hundred years of burial in the soil, glasses, especially those with medieval compositions, develop heavily corroded surfaces, showing phenomena such as local pitting, laminated layers and browning effects. For this study the damage phenomena have been characterised for three original glasses, using conventional methods (light microscopy and SEM of the surface and cross sections) and microfocus X-ray computed tomography (mCT), a new non-destructive analytical technique.

The degradation of glass in the soil depends on a variety of parameters, concerned with the glass itself and with the burial environment. Since synergetic effects may complicate any mechanistic studies, laboratory experiments have been carried out under controlled conditions.

Humid soil environments with a pH of 6.5 to 7.5 lead to the development of local microcracks on the surface, whereas more alkaline soil conditions (pH 8.0 to 9.0) favour the formation of laminated structures. The conclusions of the paper focus on the effect of glass composition (model glasses and archaeological glasses), soil conditions (variation of pH) and exposure time (23 months versus several centuries).
Dynamic Behavior of Colloidal Silica in the Presence of Solid Phase
Authors: Chida Taiji , Niibori Yuichi , Tochiyama Osamu , Tanaka Koichi
Published: April 2011

Since silica undergoes polymerization, precipitation, and dissolution depending on the change in pH or temperature, the chemical behavior of silica would be much complicated when cement for the construction of geological disposal system greatly changes the pH (8 to 13) of groundwater. To clarify the dynamic behavior of silica in such an alkaline solution, the concentrations of silica in both soluble and colloidal form in the supersaturated solution in the presence of solid phase have been traced over a 40-day period. In the experiment, the concentration of silica in a soluble form was determined by the silicomolybdenum-yellow method, and the concentration of silica in soluble plus colloidal forms was determined by adjusting the pH of the solution to 13, where all the silica changes into a soluble form (mainly monomeric). In order to examine the dynamic behavior of colloidal silica with solid phase of silica, this study has used natural quartz and pure commercial amorphous silica, both in a size fraction of 74–149 μm, whose specific surface-area (BET, N2 gas) were respectively 1.0 m2/g and 400 m2/g. The Na2SiO3 solution (250 ml, pH>10, 298 K) was poured into a polyethylene vessel containing quartz or amorphous silica (0.1 g or 0.5 g), HNO3 and a buffer solution. The pH of the solution was set to 8. The silica initially in a soluble form at pH>10 (6.8×10-3 M or 1.2×10-2 M) became supersaturated and either deposited on the solid surface or changed into the colloidal form. The ratio of silica in those form depended both on the initial concentration of soluble-silica and the surface area of the solid. The concentration of colloidal-silica gradually decreased, where the logarithm of its concentration decreased linearly against time after the concentration of soluble-silica decreased to a metastable concentration slightly higher than the solubility of soluble-silica.
Incorporation of Radioactive Metals and Trace Metals into Phosphate “Anhydrous” Autunite: Thermodynamic Evaluation
Authors: Xu Huifang , Wang Yifeng
Published: April 2011

The prediction of heavy metal solubility in the presence of phosphate is the key for designing a successful environmental remediation strategy or for the performance assessment of a nuclear waste repository. In order to evaluate the possibility for solubilities and incorporation of U and its fission products, such as Cs, Np, Pu, it is important to have the Gibbs free energies of formation of possible end-member phases. In this paper, we use a linear free energy relationship to calculate the Gibbs free energies of formation of divalent cation “anhydrous” autunite phases [M2+(UO2)2(PO4)2] and monovalent cation “anhydrous” autunite phases [M+2(UO2)2(PO4)2]. Based on predicted Gibbs free energies of formation for autunite phases, an equilibrium calculation indicates that it is feasible to incorporate NpO2+ into the autunite phases. If concentration of Cs+ is high, Cs+ will be incorporated into the autunite phases. However, it is not feasible to incorporate low concentration Cs+ released from spent fuel into the uranyl phosphate phases with layered structure and interlayer water (such as autunite phases, boltwoodite phases, and uranophane phases) as previously proposed. The predicted data can be considered as a first order approximation.
Characterization of α-Isosaccharinic acid: pKa-determination
Authors: Ekberg S. , Ekberg C. , Albinsson Y.
Published: April 2011

The stability constant for isosaccharinic acid dissociation is of importance in complexation studies involving species present in radioactive waste. As there are very few stability constants reported in the literature, this study has determined stability constants at 22.8, 34.5 and 44.2° C, using potentiometric titrations in a 1 M NaClO4 solution. The stability constants were linear functions of the inverted temperature, thus allowing for a simple determination of the entropy and enthalpy of the reaction.
Dissolution of a Multiphase Waste Form
Authors: Lewis Michele A. , Dietz Nancy L. , Fanning Thomas H.
Published: April 2011

The dissolution behavior of the ceramic waste form (CWF) is being investigated to support its qualification for disposal in the proposed repository at Yucca Mountain. The CWF consists of sodalite and glass phases and has been consolidated either by hot isostatic pressuring (HIP) or by pressureless consolidation (PC). In this paper we compare the dissolution behavior of the two materials using in MCC-1 type tests at 90°C in a simulated silicate groundwater. The test solutions were periodically exchanged limit feedback effects. The solid surface area to volume ratio was 10 m-1. Five types of samples were tested: (1) HIP CWF, (2) binder glass vitrified by HIP, (3) PC CWF, (4) binder glass vitrified by PC, and HIP sodalite. Boron releases were used to monitor glass dissolution; these were similar in tests with HIP CWF, HIP glass, and PC CWF, but about 3X higher in tests with PC glass. At the end of the tests, the surfaces of the reacted materials were examined with scanning electron microscopy for signs of preferential dissolution. Differences in the dissolution behaviors of the materials are described and the implications of the test results regarding the performance of the CWF in the disposal system are discussed.
Mobilization/Retention of Radionuclides during Corrosion of High Burnup Spent Fuel and Backfill Materials in Salt Brines
Authors: Loida Andreas , Kienzler Bernhard , Geckeis Horst
Published: April 2011

With respect to the assessment of the long-term behavior of the waste form spent fuel it is of high importance to study the fuel alteration in contact with groundwater and near field materials. The aim of this work is to evaluate the impact of candidate backfill materials hydroxylapatite and magnetite on the overall corrosion behavior of this waste form in salt brine; both materials are used in corrosion tests together with spent fuel. The instant releases and the matrix dissolution rates appear to be similar in presence and in absence of any backfill material under study. However, Am,Np,Pu,U and Sr are retained at different ratios on the hydroxylapatite, on the magnetite and on the fuel sample, indicating possibly the formation of different radionuclide containing new solid phases.
Maintaining Chemically Reducing Waste-Package Conditions
Authors: Forsberg Charles W. , Dole Leslie R.
Published: April 2011

Most fission products and actinides in spent nuclear fuel (SNF) are trapped in the uranium dioxide (UO2) crystal structure and cannot escape until the UO2 is oxidized. Oxidation destroys the crystal structure, exposes the radionuclides to groundwater, and creates the potential for dissolution. For a repository in an oxidizing geochemical environment, the potential exists to delay the release of radionuclides for hundreds of thousands to millions of years by using a combination of excess depleted uranium dioxide and iron in the waste package (WP) to locally maintain chemically reducing conditions. This approach limits the rate of oxygen transport to the SNF after WP failure. Alternative methods of oxygen transport to the SNF were investigated, including transport by groundwater, diffusion through air, and diffusion through water.
Novel Functionalized Ceramic Getter Materials for Adsorption of Radioiodine.
Authors: Mattigod Shas V. , Fryxell Glen , Parker Kent , Kaplan Dan
Published: April 2011

A new class of getter materials has been synthesized for immobilization of long-lived radionuclides such as129I. These novel materials consist of nanoporous ceramic substrates with tailored pore sizes ranging from 2 – 20 nm. These high surface area (∼1000 m2/g) ceramic substrates have been functionalized with self-assembled monolayers consisting of soft cation-capped thiol-functionality. The resulting getter materials exhibit highly dense binding sites, and excellent selectivity for iodide. The effectiveness of these novel getter materials was evaluated using radioiodide-spiked samples of surface water and concrete leachate and adsorption performance was compared with natural sulfide mineral getter materials. The data indicated that the novel getter materials have very high affinity for radioiodide (Kd: 4 × 104– 3 × 105ml/g and 6 × 105ml/g in surface and concrete leachate respectively). Comparatively, the radioiodide Kdvalues for natural mineral getters were typically two to three orders magnitude less than the novel getters. The results indicated that the synthetic getter materials have the potential to immobilize and therefore retard the migration of129I in the subsurface environment. Additional studies are being conducted to evaluate thelong-term stability of these materials in waste disposal environments.
Cold Gas Dynamic Manufacturing – A new approach to Near-Net Shape Metal Component Fabrication
Authors: Morgan R. H. , Sutcliffe C. J. , Pattison J. , Murphy M. , Gallagher C. , Papworth A. , Fox P. , O'Neill W.
Published: April 2011

Cold Gas Dynamic Manufacturing (CGDM) is a high-rate, direct deposition process capable of combining many dissimilar materials in the production of a single component. The process is based on Cold Gas Dynamic Spraying (CGDS) – a surface coating technology in which small, un-heated particles are accelerated to high velocities (typically above 500 m/s) in a supersonic gas jet and directed towards a substrate material. The process does not use a heat source (as with similar plasma and HVOF spray technologies), but rather employs the high kinetic energy of the particles to effect bonding through plastic deformation upon impact with the substrate or previously deposited layer. As a consequence it lends itself to the processing of temperature sensitive material systems such as oxidising, phase-sensitive or nano-structured materials. To achieve metallic bonding incident particles require velocities greater than a certain material-specific threshold value, such that thin surface films are ruptured, generating a direct interface. This bonding mechanism has been compared to explosive welding.

This paper discusses the further development of the CGDS technique from surface coating technology into the basis for a novel Additive Fabrication process. The description of the apparatus is presented in addition to the basic processing conditions for the deposition of aluminium material. Particular attention is paid to the morphology of the deposited material, the microstructure and the interfacial boundary between splats.
Monolithic Three-Dimensional Integration of Micro-Fluidic Channels and Optical Waveguides in Fused Silica
Authors: Bellouard Yves , Said Ali , Dugan Mark , Bado Philippe
Published: April 2011

This paper presents dramatic improvements in the micro-fabrication of three-dimensional microfluidic channels and high-aspect ratio tunnels within the bulk of a fused silica substrate. We also report the fabrication of optical waveguides within the same substrate, which is a major step towards the integration of sensing capabilities within microfluidic networks.

This integrated device, which combines both fluidic channels and optical waveguides, opens new opportunities in bio- and chemical sensing. The flexibility of the improved manufacturing process offers substantial new design capabilities, especially for single channel probing and massively parallel processing and sensing.
Microwave Molecular Sieves Synthesis and Capillary Crystal Growth by Geometric Confinement.
Authors: Ogunwumi Steven B. , Wight John F. , Fajardo James C.
Published: April 2011

Microwave heating is an alternate means for material processing. The technique is promising for the accelerated synthesis of new materials. Microwave molecular sieves synthesis is combined with capillary confinement as a novel synthetic method. It is successfully demonstrated in the preparation of small ZSM-5 crystals by microwave hydrothermal synthesis within 1–1.7 μm channels of a capillary bundle. The geometric and spatial confinement offered by the capillary is expected to define and control the resulting crystal size distribution and orientation.

MCM-41, a mesoporous molecular sieve with a uni-dimensional regular array of hexagonal channels is investigated as a candidate for capillary confinement. The large porous channels of MCM-41(>35 å ) is attractive as a host for promoting inclusions of guest molecules or templates. The successful confinement of MCM-41 represents an important step towards the alignment of molecular sieves in a defined orientation within thin capillaries bundled (less than 5 μm channels). Ultimately, such an approach may be useful for the fabrication of new molecular sieve devices.
Dissipation Mechanisms in Thin-Film Silicon Microresonators on Glass Substrates
Authors: Gaspar J. , Chu V. , Conde J. P.
Published: April 2011

The fabrication and characterization of thin-film silicon resonators processed at temperatures below 110°C on glass substrates is described. The microelectromechanical structures consist of surface micromachined bridges of phosphorus-doped hydrogenated amorphous silicon (n+-a-Si:H) deposited by plasma-enhanced chemical vapor deposition (PECVD) suspended over a metallic gate counterelectrode. The structures are electrostatically actuated. Resonance frequencies in the MHz range and quality factors as high as 5000 are observed in vacuum. The effect of the geometrical dimensions of the bridges and of the measurement pressure on the resonance amplitude and frequency is studied. The elementary energy dissipation processes in a-Si:H-based resonators are discussed. At atmospheric pressure, air damping dominates the energy dissipation. In vacuum, intrinsic mechanisms, such as clamping losses and surface losses, control the energy dissipation.