bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Redox Environments on the Geochemical Behaviour of Radionuclides
Authors: Bidoglio G. , Avogadro A. , Plano A. De 
Published: March 2011

AbstractStudies were carried out on the effect of redox conditions on the release from simulated vitrified HLW of Np-237, Pu-238 and Tc-99 and their migration through columns packed with site-specific porous material representative of clay and salt aquifers. Results obtained under oxic and anoxic conditions are compared. The release rates of Np, Pu and Tc were found to be lower in the absence of air than with oxygenated groundwaters. Speciation studies showed that neptunium and technetium were released in the oxidized forms Np(V) and Tc(VII) even under the investigated anoxic conditions where reduced species are thermodynamically more stable. In spite of that, a stronger interaction was observed when the leachate was passed through the column in the absence of air. A surface reduction process accounts for the observed behaviour. Under more reducing conditions, plutonium appears to be present in the tetravalent state in colloidal form.
Studies on the Radionuclide Coprecipitation-Solid Solution Formation. The UO2(S)-La(OH)3(S) Coprecipitation as an Analogue for The UO2(S)-Pu(OH)3(S) System
Authors: Bruno Jordi , Grenthe Ingmar , Muñoz Maria 
Published: March 2011

AbstractThe UO2(s)-La(OH)3(s) coprecipitation equilibria have been studied in 0.5 M NaClO4 medium, at 25°C under anoxic conditions. The data obtained in the pH range between 2 and 5, and at different initial La(III)/U(IV) ratios (10%,5%,3%,2% and 1%), is explained by applying the Doerner-Hoskins logarithmic law. The same law can also be used to describe previously collected UO2(s)-Pu(OH)3(s) coprecipitation data. A method is proposed which uses the logarithmic distribution constants and the thermodynamic quantities for the pure phases to describe the solubility of radionuclides under repository conditions.
Analysis of Colloid Transport
Authors: Travis B. J. , Nuttall H. E. 
Published: March 2011

AbstractThe population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models.The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column.Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site.
Diffusion and Permeability Based Sorption Measurements in Intact Rock Samples
Authors: Bradbury Michael H. , Stephen I. G. 
Published: March 2011

AbstractDistribution ratios have been determined for Sr, Cs and Tc (as pertechnetate) over a range of concentrations for a Darley Dale sandstone by three different methods: crushed rock batch tests, with W/R ratio and particle size range as independent variables, diffusion-sorption and permeability-sorption experiments on intact rock samples. Comparisons of Rd - values obtained from batch and diffusion-sorption experiments indicate that crushed rock tests can overestimate sorption by as much as one or two orders of magnitude.
An Analogue Validation Study of Natural Radionuclide Migration in Crystalline Rocks using Uranium-Series Disequilibrium Studies
Authors: Smellie J. A. T. , MacKenzie A. B. , Scott R. D. 
Published: March 2011

AbstractConcentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water-conducting fractures deep in the bedrock. Radioactive disequilibria resulting from rock-water interactions were observed in two of the cores. These indicated uranium migration along distances of 40 cm or more on a timescale of 106 years in conjunction with thorium immobility under the same conditions. Fracture surface minerals showed a high affinity for radionuclide retardation and a limit of about 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock. This limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels.
Nucleation of Internal Melt During Pulsed Laser Irradiation
Authors: Peercy P. S. , Thompson Michael O. , Tsao J. Y. , Poate J. M. 
Published: March 2011

ABSTRACTReal-time measurements of the molten layer thickness and simultaneous measurements of the melt duration at the surface reveal that melt nucleates internally when Si implanted with low solid-solubility impurities such as In is melted with a 30 nsec laser pulse at 694 nm. Internal nucleation of melt was observed for all energy densities examined. Furthermore, at energy densities insufficient to melt the entire amorphous layer, internal nucleation of melt is followed by an explosive-like process in which a buried molten layer propagates toward the irradiated surface.
Laser Induced Oxidation of Heavily Doped Silicon
Authors: Fogarassy E. , White C.W. , Lowndes D.H. , Narayan J. 
Published: March 2011

ABSTRACTWe have investigated the incorporation of oxygen into heavily doped silicon during UV excimer laser irradiation. For the case of repetitive laser irradiations in air, we observe that the amount of oxygen incorporated into Si depends markedly on the dopant. For As and Sb implanted silicon, there is no anomalous oxygen incorporation. By contrast, increasing amounts of 0 are incorporated into In implanted silicon as a function of number of laser shots. The incorporation of 0 is associated with degradation of the optical and structural properties of the surface, and a deep diffusion of the dopant. This behavior is believed to be partly related to specific chemical reactions between oxygen and indium present in the surface at high concentrations as the result of dopant segregation during solidification.
Cross-Sectional Tem Characterization of Structural Changes Produced In Silicon By One Micron Picosecond Pulses
Authors: Smirl Arthur L. , Boyd Ian W. , Boggess Thomas F. , Moss Steven C. , Pinizzotto R.F. 
Published: March 2011

ABSTRACTPlan and cross-sectional transmission electron microscopy (TEM) has been used to examine the various bulk and surface structural changes observed in crystalline silicon following melting caused by the absorption of 1-μm pulses that are 4 ps in duration. We show for the first time that for picosecond excitation polycrystalline Si (p-Si), rather than singlecrystal Si, is always formed when the melt resolidifies. Specifically, cross-sectional TEM analyses indicate that a thin layer of fine-grained p-Si is formed at the interface of the melted region with the bulk. When the incident fluence is more than 10% above the melting threshold, the region between the surface and the fine-grained p-Si regrows as largergrain p-Si. This is the first reported observation of a large-grain p-Si layer on a fine-grain p-Si base in crystalline material. If the incident fluence is less than 10% above threshold, the region near the surface resolidifies as amorphous Si, but the narrow layer of fine-grained p-Si remains at the interface with the single crystal material. Present models for resolidification must be modified to account for these features.
Time-Resolved Optical Studies of Picosecond Laser Interactions With Gaas Surfaces
Authors: Liu J.M. , Malvezzi A.M. , Bloembergen N. 
Published: March 2011

ABSTRACTThe interactions of picosecond laser pulses at 532 nm wavelength with GaAs surfaces have been studied with time-resolved reflectivity and transmission measurements at three probe wavelengths. At fluences below the melting threshold, the laser-generated electron-hole plasma is limited to a density below ≈1020cm−3. The high reflectivities of molten GaAs observed at fluences above the tlhreshold have a wavelength dependence inconsistent with a simple Drude model for a metallic GaAs molten layer. At high fluences, the evolution of a laser-induced vapor cloud is observed.
Dynamical Laser Desorption Process of Ionic Clusters In Group Iv Elements
Authors: Kasuya A. , Nishina Y. 
Published: March 2011

ABSTRACTEmission of ionic clusters from surfaces of group IV elements has been analyzed by means of time-of-flight measurements under nitrogep laser irradiation in its peak intensity ranging from 50 to 200 MW/cm with pulse duration of 10 ns. The measurements on Si, Ge and β-Sn with a straight flight tube show a continuous distribution of spectra in the flight time corresponding to the mass-to-charge ratio between 1 and 2 in units of the singly charged atom of respective elements. The line shape analysis indicates that emitted ions immediately after laser excitation are coagulated in the form of large clusters having nearly an equal mass-to-charge ratio between 5/4 and 3/2. They eventually decompose into monoatoms and their ions in a time scale of 10 ps as confirmed by a quadrupole mass analysis. These results are in remarkable contrast with the case of graphite which exhibits a series of sharp spectral peaks. The clear distinction between graphite and other group IV elements is attributed to the intrinsic difference in their chemical bonds under highly excited conditions.
Amorphous Gallium Produced By Pulsed Excimer Laser Irradiation
Authors: Fröhlingsdorf J. , Stritzker B. 
Published: March 2011

ABSTRACTPure crystalline Ga films (α-Ga, β-Ga) have been irradiated at low temperatures (≤ 20 K) with an Excimer laser. By measuring the superconducting transition temperature Tc and the residual resistivity ≤o, the resulting Ga phases (α-Ga, β-Ga, a-Ga) can be identified.Both crystalline Ga phases can be transformed into the amorphous phase.The threshold energy density for the β→ a transition depends on the film thickness, whereas the α →. a transition occurs always at about 225 mJ/cm2 This behavior is in agreement with earlier observations that a-Ga can grow on top of the in-phase but not on the β-phase.The results of laser quenching are compared with other non-equilibrium techniques for the production of a-Ga, such as vapor quenching and low temperature ion iradiation.
Self And Ion Beam Annealing of P,Ar, And Kr In Silicon
Authors: Cannavo S. , Ferla A. La , Campisano S.U. , Rimini E. , Ferla G. , Gandolfi L. , Liu J. , Servidori M. 
Published: March 2011

ABSTRACTThe damage produced by high current density ∿l0µA/cm2 implants of 120 keV P+ into <111> and <100> silicon wafers, 500 °m thick, has been investigated in the fluence range 1×l01 5/cm2-l×l016 /cm2 by ion channeling and by transmission electron microscopy. For both orientations the thickness of the damage layers increases with the fluence up to 2×1015 /cm2 and then decreases. The rate of regrowth is a factor two faster for the <100> with respect to the <111> oriented Si crystals. Similar ratios have been found in pre-amorphized samples and irradiated with Kr+ ions in the temperature range 350°C-430°C. The TEM analysis reveals the presence of hexagonal silicon and of twins in small amounts for both orientations. The beam induced epitaxial growth depends also on the species present in the amorphous layer. A comparison between self-annealing and beam annealing in Si <100> preamorphized with Ar+ or P+ shows a noticeable retardation of the growth rate in the presence of Ar+.
Mev Ion Induced Modification of The Native Oxide of Silicon
Authors: Headrick R.L. , Seiberling L.E. 
Published: March 2011

ABSTRACTWe have studied the native oxide of silicon (110) and the changes roduced by MeV ion bombardment using transmission ion channeling of 5.9 MeV9Be, and Elastic Recoil Detection Analysis (ERDA). Transmission channeling was used to measure interfacial nonregistered Si and adsorbed C and 0. ERDA was used to measure the surface concentration of H. MeV ions were found to cause an increase in the interfacial nonregistered silicon which saturates at approximately one monolayer. Rapid desorption of hydrogen was observed. The effect of 2 keV electrons on the silicon native oxide was also studied by Auger Electron Spectroscopy.
Nonlinear Optics And Surface Science
Authors: Shen Y. R. 
Published: March 2011

ABSTRACTThe recent status of applications of nonlinear optics to surface science is reviewed. The basic theory of wave mixing on a surface layer, and the possibility of using various nonlinear optical processes for surface probing are briefly discussed. Emphasis is on surface second harmonic generation, which is shown with many illustrations to be a rather unique and versatile tool for surface studies.
Amorphization And Recrystallization Processes In Monocrystaline Beta Silicon Carbide Thin Films
Authors: Edmond J.A. , Withrow S.P. , Kong H.S. , Davis R.F. 
Published: March 2011

ABSTRACTIndividual, as well as multiple doses of 27Al+, 31p+, 28Si+, and 28Si+ plus 12C+ were implanted into (100) oriented monocrystallne β-SiC films+. A critical energy of =16 eV/atom required for the amorphization of β-SiC via implantation of Al and P was determined using the TRIM84 computer program for calculation of damage-energy profiles coupled with results of RBS/ion channeling analyses. In order to recrystallize amorphized layers created by the individual implantation of all four ion species, thermal annealing at 1600, 1700, or 1800°C was employed. Characterization of the recrystallized layers was performed using XTEM. Examples of SPE regrown layers containing; 1) precipitates and dislocation loops, 2) highly faulted, microtwinned regions, and 3) random crystallites were observed.
Ion Implantation At Elevated Temperatures
Authors: Lam Nghi Q. , Leaf Gary K. 
Published: March 2011

ABSTRACTA kinetic model has been developed to investigate the synergistic effects of radiation-enhanced diffusion, radiation-induced segregation and preferential sputtering on the spatial redistribution of implanted solutes during implantation at elevated temperatures. Sample calculations were performed for Al+ and Si+ ions implanted into Ni. With the present model, the influence of various implantation parameters on the evolution of implant concentration profiles could be examined in detail.
Binary And Ternary Amorphous Alloys of Ion-Implanted Fe-Ti-C
Authors: Follstaedt D. M. , Knapp J. A. 
Published: March 2011

ABSTRACTThe microstructure of Fe implanted with up to 50 at.% C was found to consist of hexagonal iron carbide precipitates oriented with respect to the Fe matrix. For higher C concentrations, an amorphous phase forms. This concentration dependence is explained in terms of the lattice structure of the iron carbide. In Ti-implanted Fe, substitutional Ti was found in the bcc Fe lattice for concentrations ≤ 15 at.% Ti. The work of others suggests that amorphous phases form for ≥ 33 at.% Ti. These results are discussed in terms of concentration boundaries of the ternary Fe(Ti,C) amorphous phase.Ion beam alloying methods are currently being used to form metastable alloys [1], both for fundamental investigations of such alloys as well as for potential use to improve physical properties of components [2]. An important consideration in metal alloys is what phase will form upon implantation; one aspect of this question is to determine when amorphous phases will form. Rules are currently being advanced to predict alloy systems which will yield amorphous phases. By using ion irradiation and ion beam mixing as well as ion implantation, such rules can be evaluated over entire composition ranges.To gain insight into amorphous phase formation, we have studied Fe alloys implanted with C, Ti and Ti + C. The Fe(C) alloys exhibit compound precipitation and amorphous phase formation; the precipitation and the concentrations at which the amorphous phase appears can be accounted for by considerations of the structure of the hexagonal carbide which forms. Based on conventional uses of the Fe(C) system, such alloys may be useful for improving mechanical properties by implanting C into ferrous components. Iron implanted with Ti is examined to a limited extent here, but by including ion irradiation studies by others [3], a more complete characterization of Fe(Ti) alloys is obtained. The microstructures of Fe(C) and Fe(Ti) are examined along with the known composition limits of amorphous Fe(Ti,C) alloys, which are important for their improved mechanical properties [2]. Taken together, a more complete determination of amorphous phase formation in this ternary system is obtained.
Collision Cascades, Ionization, Spikes And Energy Transfer
Authors: Brown W. L. 
Published: March 2011

ABSTRACTThe collisions of an individual energetic ion in a solid set atoms of the solid in motion and excite electronic states. The moving atoms collide with others to form a collision cascade and the electronic excitation also forms a branched trail around the track of the ion. If the densities of the energy deposition in either of these modes is high the result is called a “spike”. The low density regimes of collision and ionization cascades and evidence for the transition to non-linear high density spikes are summarized. The understanding of the latter is still quite incomplete as is also understanding of the transfer of energy between the kinetic and the electronic modes, particularly at high energy densities.
Laser Recrystallization of Mocvd Poly-Gaas on Insulating Substrates
Authors: Bao X.M. , Huang X.F. , Han P. , Yin J.M. 
Published: March 2011

ABSTRACTPoly-GaAs films have been grown on amorphous insulating substrates by MOCVD technique. The films were analyzed using TEM, X-ray diffraction, AES and ESCA measurements. The results show that poly-GaAs films are flat, bright and close in texture and stoichiometric. The grain size is about 200Å. The film contains trace impurities such as Si,O and C. They are evenly distributed in the film. The poly-GaAs films were crystallized by CW Ar+ laser with a increase of grain size from 200Å to 40 µm. Schottky barrier diodes of good I-V characteristics were made on the laser recrystallized GaAs films.
Solid Phase Epitaxial Recrystallization of Sos, with Applications to Submicrometer Cmos and Bipolar Devices
Authors: Vasudev P.K. 
Published: March 2011

ABSTRACTCMOS/SOS devices and circuits were fabricated in 0.3-µm-thick epitaxial silicon-on-sapphire (SOS) films. Two solid phase epitaxial recrystallization techniques (DSPE* and SPEAR**) reduced the total microtwin concentrations in the Si layers more than ten- fold, while increasing electron and hole inversion layer mobilities between 30 and 45%. Leakage currents were substantially reduced in all SPEAR devices and in n-channel DSPE transistors, with some increase observed for p-channel DSPE devices. Drive currents and subthresholds slopes also showed significant improvement in both n- and p-devices. Propagation delays below 75 ps were obtained for CMOS/SOS inverters with Lef = 0.5 µm. The application of DSPE and SPEAR techniques to 0.3-µm SOS films will extend the scaling of CMOS/SOS to circuits with very large scale integration (VLSI) complexity.
High-Quality Thin Si Film By Spe Regrowth on Epitaxially Grown Spinel
Authors: Kimura Takafumi , Yamawaki Hideki , Arimoto Yoshihiro , Ikeda Kazuto , Ihara Masaru , Ozeki Masashi 
Published: March 2011

ABSTRACTA high-quality thin Si layer on epitaxial spinel(MgO·Al2O3) on Si substrate has been developed. It was obtained by the solid phase epitaxial (SPE) regrowth of amorphous Si with Si seed islands on the epitaxially grown spinel. The SPE-Si layer on the epitaxial spinel was superior to conventional Si on sapphire (SOS) in stacking-fault density, Hall mobility, and contamination from the insulating materials. The SPESi layer has low stacking-fault density of 10–50 cm-2, even for 0.4 μm thickness. This value is eight orders of magnitude less than that of Si on epitaxial spinel obtained by vapor phase epitaxial (VPE) growth with SiH4. The SPE-Si also has high electron Hall mobility of 880 cm2/V-s for n=5×l016 cm-3, for 1-μm-thick Si. This value is about 85% of that in bulk Si, and is higher than that in Si on spinel grown by VPE-growth and SOS. (100) spinel layer was grown on (100) Si substrate by a MgCI2-Al-HCI-CO2-H2 VPE growth system. After thermal oxidation, Si seed islands were grown on the spinel by the pyrolysis of SiH4. Amorphous Si was deposited on the Si seed islands by chemical vapor deposition (CVD) of SiH4. The SPE-Si layer was obtained by regrowth of the amorphous Si in a hydrogen atmosphere.
Reduction of Ca and F Segregated at the Surface of a Si/CaF2/Si(100) Structure By Solid Phase Epitaxy of Si
Authors: Sasaki Masayoshi , Onoda Hiroshi , Hirashita Norio 
Published: March 2011

ABSTRACTEpitaxial Si films have been grown on single crystalline CaF2 on (l00)Si substrates by molecular beam epitaxy(MBE) or combination of MBE and solid phase epitaxy(SPE) of deposited amorphous Si(a-Si). It has been found that Ca and F segregate at the surface of the Si grown by MBE. The high energy electron diffraction (RHEED) patterns from the Si surface show the superstructures which are caused by the existence of Ca and F at the Si surface. To reduce the segregation effect, SPE process has been successfully applied to Si epitaxy. The Si SPE performed on top of the MBE Si layer reduces the Ca concentration at the Si surface by an order of magnitude, although the segregation effect is not completely suppressed.
Silicon on Insulator Formed By O+ OR N+ Ion Implantation
Authors: Hemment P.L.F. 
Published: March 2011

ABSTRACTThe synthesis of buried layers of SiO2 and Si3N4, by ion implantation is reviewed. This process, which may be used to form device worthy silicon-on-insulator (SOI) structures, involves (i) implantation of O+ or N+ ions and (ii) high temperature processing to achieve defect annealing and chemical segregation of the implanted species.
Properties of Thin Films After Focused Beam Processing
Authors: Campbell I.H. , Fauchet P.M. 
Published: March 2011

ABSTRACTA Raman microprobe is used to detect the changes in crystallinity, stress and homogeneity on thin films of SOI irradiated by a single laser pulse. Maximum, isotropic, planar tensile stress increased from 5x109 dyn/cm2 to 12x109 dyn/cm2 in the processed area and stress of 8x109 dyn/cm2 was observed 20 μm beyond the damaged region. Crystallite sizes of 50 Å to greater than 300 Å were observed inside the processed area. Results obtained with different pulsed laser frequencies are compared and significant differences in the processing effects are observed.
Mechanical Properties of Ga1–xInxAs
Authors: Guruswamy S. , Hirth J.P. , Faber K.T. 
Published: March 2011

ABSTRACTSubstantial solid solution strengthening of GaAs by In acting as InAs4 units has recently been predicted. This strengthening could account for the reduction of dislocation density in GaAs single crystals grown from the melt. High temperature hardness measurements up to 700ºC have been carried out on (100) GaAs and Ga0.9975 In0.0025 As wafers. Results show a significant strengthening effect in In—doped GaAs even at concentration levels of about 0.2 wt%. A temperature independent flow stress region is observed for both these alloys. The In—doped GaAs shows ahigher plateau stress level compared to the undoped GaAs. The results are consistent with the solid solution strengthening model.