bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Situ Diagnostics at High Pressures: Ellipsometric and Rheed Studies of the Growth of Yba2Cu3O7
Authors: Blank Dave H. A. , Rogalla Horst
Published: April 2011

Pulsed Laser and Sputter Deposition are used for the fabrication of complex oxide thin films at relatively high oxygen pressures (up to 0.5 mBar). This high pressure hampers the application of a number of in-situ diagnostic tools. One of the exceptions is ellipsometry. Using this technique we studied in-situ the growth of off-axis sputtered Yba2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Furthermore, the oxidation process from O(6) to O(7) has been studied by performing spectroscopic ellipsometry during isobaric cooling procedures.

Another suitable in-situ monitoring technique for the growth of thin films is Reflection High Energy Electron Diffraction (RHEED). In general this is a (high) vacuum technique. Here, we present an RHEED-system in which we can observe clear diffraction patterns up to a deposition pressure of 0.5 mBar. The system has been used for in-situ monitoring of the heteroepitaxial growth of YBa2Cu3 06+x on SrTiO3 by pulsed laser deposition.
In Situ Initial Growth Studies of (Sr, Ca)CuO2 ON SrTiO3 by High Pressure Rheed
Authors: Koster Gertjan , Runders Guus J. H. M. , Blank Dave H. A. , Rogalla Horst
Published: April 2011

The initial growth of pulsed laser deposited SrCuO2 (SCO) and CaCuO2 (CCO) on SrTiO3 has been studied using high pressure Reflection High Energy Electron Diffraction (RHEED) and Atomic Force Microscopy (AFM). For this, we developed a Pulsed Laser Deposition (PLD)- RHEED system, with the possibility to study the growth and to monitor the growth rates, in situ, at typical PLD pressures (10–50 Pa). In case of depositing oxide materials, high oxygen pressures are desired. Moreover, crystallinity can be improved using higher oxygen pressures and therefore higher temperatures. With this technique we are able to obtain atomically flat films, a first step towards multi-layer structures.

In this paper we present the initial growth studies of SCO and first results incorporating CCO layers in a SCO matrix.
Real-time Monitoring of semiconductor growth by Spectroscopic ellipsometry
Authors: Johs B. , Hale J. , Herzinger C. , Doctor D. , Elliott K. , Olson G. , Chow D. , Roth J. , Ferguson I. , Pelczynski M. , Kuo C. H. , Johnson S.
Published: April 2011

in situ Spectroscopic Ellipsometry (SE) is an optical technique which is well suited for the monitoring of epitaxial semiconductor growth, due to its high surface sensitivity and non-invasive nature. In this work, SE systems were installed on both MBE and MOCVD deposition systems to monitor the epitaxial growth of InxGa1−xAs and InxAl1−xAs compounds on InP substrates. The structures grown include thick lattice matched In0.53Ga0.47As buffer layers (for HBT collectors), and strained RTD structures. SE was used to monitor in real-time layer composition and thickness during growth. To enhance the precision and accuracy of the SE determined growth parameters, it was necessary to optimize the SE data analysis strategies. A methodology to determine the best spectral region for the SE data analysis in the presence of noise and systematic effects (such as angle of incidence uncertainty, detector wavelength shifts, surface roughness, uncertainty in surface temperature, non-ideal growth modes, etc.) is presented. Using the optimized data analysis strategies, long term SE-determined InxGa1−�As composition accuracy (as verified by ex situ x-ray measurements) of ±0.002 in ‘x’ was achieved. SE thickness measurements of ultra-thin (<30Å) strained AlAs barrier layers were also in excellent agreement (±0.5Å) with real-time photo-emission oscillation measurements.
Material Balance Modeling of End-Point Uniformity in Silicon Dioxide Plasma Etching
Authors: Chamberst J. J. , Min K. , Hauser J. R. , Parsonst G. N.
Published: April 2011

As wafer diameters increase, monitor wafers become more costly for process characterization and real-time sensors become more attractive. Process-state sensors are generally easier to implement than direct wafer-state sensors, but process-state sensors are usually not thought to provide wafer-state analysis. Utilizing a process-state sensor, such as a mass spectrometer, for wafer-state information will result in new approaches for sensing, optimizing, and controlling integrated circuit fabrication processes. We used a two stage differentially pumped mass spectrometer system sampling directly from an electron cyclotron resonance (ECR) chamber to sense the process-state and monitor end-point during silicon dioxide etch. The end-point uniformity is characterized using mass spectroscopy and material balance modeling. Specifically, using CF4 and D2 etch gases, the partial pressure of CO-containing etch products decays near the endpoint, and the average initial slope is directly correlated with the uniformity determined from optical interferometry thickness measurements. Changing the ECR magnet geometry defines the etch uniformity, and the resulting CO+ end-point signal is sensed with the mass spectrometer. By analyzing the initial slope of the CO+ signal near the end-point, a correlation exists between uniformity and the mass spectrometry signal. A COF2 etch product material balance provides a concentration versus time end-point model which substantiates the correlation between the mass spectrometer signal and the etch uniformity. This model is valid for any sensor that detects a change in the COF2 concentration at the end-point.
Simulations of Electromigration At A Tungsten/Aluminum Junction
Authors: Enver A. , Povirk G. L.
Published: April 2011

Finite element solutions to problems of electromigration and stress-driven diffusion are presented. The numerical procedures are based on a formulation that assumes bulk diffusion, so that diffusion along grain boundaries and interfaces is not explicitly taken into account. Two cases are considered: (1) a tungsten via/aluminum line junction, and; (2) a one-dimensional case with a blocking boundary at one end of the line. The results show that line geometry can significantly affect the magnitude of the stresses that develop, although in each case the maximum hydrostatic stress in the line was proportional to the square root of time.
Under Bump Metallization Development For High Sn Solders
Authors: Korhonen T. M. , Hong S. J. , Su P. , Zhou C. , Korhonen M. A. , Li C.-Y.
Published: April 2011

Several under bump metallisation (UBM) schemes using Ni or CuNi alloys as the solderable layer were investigated. Cr or Ti was used as the adhesion layer. The UBM pads of different compositions were sputter deposited on silicon wafers and patterned using standard photolithographic processes. Eutectic Sn-Pb solder balls were reflowed on top of the pads. The resulting interfacial microstructures were examined by SEMIEDX analysis of cross-sectioned samples. The integrity of the UBMIsolder interface was characterized by micromechanical shear testing of flip chip test samples. Growth of intermetallic layers was found to be significantly slower in Ni and CuNi schemes compared to pure Cu. The joints on Ni and CuNi had also a better adhesion at the UBM/solder interface, and in the shear tests the fracture occurred through the solder
Observation of Dislocation DisAppearance in Aluminum Thin Films and Consequences for Thin Film Properties
Authors: Müllner P. , Arzt E.
Published: April 2011

Dislocation structures in Al-Cu thin films have been studied by transmission electron microscopy (TEM). We have observed that the contrast of interface dislocations disappears in the electron beam. We assume that the contrast dissolution is due to the spreading of the dislocation core at the crystalline/amorphous interface or due to a diffusive movement of the dislocation through the oxide. In any case, the relaxation is assumed to be controled by irradiation induced diffusion. As a consequence, the short range stresses and at least partly also the long range stresses of the dislocations relax. This relaxation changes the interaction force between dislocations and may thus significantly affect the mechanical properties of thin films. It is concluded that interaction between interface dislocations may not be responsible for the high temperature strength of aluminum films.
Theoretical Analysis of Electromigration-Induced Failure of Metallic Thin Films
Authors: Maroudas Dimitrios , Gungor M. Rauf , Ho Henry S. , Enmark Matthew N.
Published: April 2011

A comprehensive theoretical analysis is presented of the failure of metallic thin films due to electromigration-induced morphological evolution of transgranular voids. Fully self-consistent dynamical simulations emphasize the important effects on void dynamics of the surface diffusivity anisotropy, together with the strength of the applied electric field and the void size. The simulation results are discussed in the context of an approximate linear stability theory. Our simulations predict formation of wedge-shaped voids, as well as failure due to propagation of slit-like features emanating from void surfaces, in excellent agreement with recent experimental observations.
Tensile Strength and Fracture Toughness of Surface Micromachined Polycrystalline Silicon Thin Films Prepared Under Various Conditions
Authors: Tsuchiya Toshiyuki , Sakata Jiro , Taga Yasunori
Published: April 2011

A new tensile tester for thin films was developed to evaluate the reliability of the microelectro- mechanical devices. This tester uses the grip that fixes a thin film specimen to a probe by electrostatic force. We applied this tester for polycrystalline silicon (poly-Si) thin films prepared under various conditions. The microstructure of the film is controlled by the crystallizing temperature. The process conditions and the microstructures that contribute to the strength of poly-Si film are identified by the tensile strength and the fracture toughness. The mean tensile strength of each specimen size ranges from 1.8 to 3.7 GPa, and the fracture toughness calculated from the strength of the notched specimen ranges from 1.9 to 4.5 MN/m3/2. The 1000°C annealed film has higher strength and toughness than the other films because of the high annealing temperature and the small grain size. The contributions to the strength are evaluated by the additional annealing at 1000°C for the low temperature annealed films.
The Relationship Between Near-Surface Mechanical Properties, Loading Rate And Surface Chemistry
Authors: Mann A. B. , Searson P. C. , Pethica J. B. , Weihs T. P.
Published: April 2011

The presence of thin surface films and adsorbate layers on both metals and ceramics can cause dramatic changes in the mechanical response of the material. A similar, related, variation in tribological properties has also been observed. Though the importance of surface effects is well known and widely documented, the exact physical and chemical mechanisms that are operating remain poorly understood. The development of point probe techniques now permits the examination of mechanical and tribological properties on the same length scale as the surface films. Recently, the utilization of these testing techniques has provided a clear insight into the mechanical processes which are operating on the atomic scale. The nanoindentation results presented here show that the mechanical deformation of an individual nano-contact is a highly dynamic phenomena in which the tip-momentum on contact, as well as the loading rate during the indentation, dictate the observed mechanical properties of the material. These results indicate that the initiation of plastic deformation is dependent on the stability of atomic-size surface asperities which can be deformed irreversibly by the high stresses generated during the initial contact. Additionally, the generation of dislocations and the presence of discontinuities in the loading curve are shown to depend upon the loading rate. More significantly, it has been found that modifying the surface chemistry can cause dramatic changes in both the mode of deformation and the time-dependence of nano-scale mechanical properties. The principal conclusion that can be drawn is that the high stresses which operate over short distances make time and temperature dependent phenomena, such as diffusion and the dissipation of energy via phonons, of vital importance in determining the near-surface mechanical properties of a material. Such effects are further magnified in tribological processes where normal and tangential loading of the surface leads to the repeated making and breaking of nano-asperity contacts.
Thermal Cycling Fatigue In Aluminum-Alloy Thin Films On Silicon Substrate
Authors: Koike J. , Utsunomiya S. , Maruyama K.
Published: April 2011

Thermal cycling was performed in Al-lmo%Si thin films deposited on Si wafers. After a given number of cycling between room temperature and 723 K, residual stress was measured at room temperure. Residual stress was found to increase with increasing the cycling number up to the 4th cycle, followed by further a continuous decrease by further cycling. The intial increase was found to be related to the increase of lattice dislcocations and their tangling. The following decrease was caused by crack formation along grain boundaties or by film delamination in some cases.
Mechanical Characterization Of Ultra-Thin, Hard-Disk Overcoats Using Scratch Testing And Depth-Sensing Indentation
Authors: Hay J. L. , White R. L. , Lucas B. N. , Oliver W. C.
Published: April 2011

Two series of five diamond-like carbon (DLC) coatings were sputtered under nominally identical conditions, but to different film thicknesses of 20 nm and 105 nm. First, the hardness of each sample was determined by depth-sensing indentation. Hardness measurements were substrate-affected to some extent for all samples but especially so for the 20 nm coatings. Two types of scratch tests were performed in an attempt to isolate and characterize the top coatings. The first was a wear test, which consisted of moving the sample back and forth repeatedly under a small constant load. The residual damage was inconsistent, but appeared to be a function of the composite, or substrate-affected hardness. The second test was a single-pass scratch in which the normal load was ramped linearly. For all samples, the friction coefficient was approximately constant as a function of load. Furthermore, samples with the same top coats yielded similar friction coefficients, regardless of the coating thicknesses. Friction coefficient decreased with hydrogen content and to some extent, increased with hardness, as measured on the 105 nm samples. The friction coefficient measured during a ramp-load scratch offers an alternative for characterizing ultra-thin films, when indentation alone yields measurements that are significantly affected by the substrate.
A Method for Independent Measurement of Elastic Modulus and Poisson's Ratio of Diamond-Like Carbon Films
Authors: Cho Sung-Jin , Lee Kwang-Ryeol , Eun Kwang Yong , HAN Jun Hee , Ko Dae-Hong
Published: April 2011

A simple method to measure the elastic modulus and Poisson's ratio of diamond-like carbon (DLC) films deposited on Si wafer was suggested. This method involved etching a side of Si substrate using the DLC film as an etching mask. The edge of DLC overhang free from constraint of Si substrate exhibited periodic sinusoidal shape. By measuring the amplitude and the wavelength of the sinusoidal edge, we can determine the strain of the film required to adhere to the substrate. Combined with independent stress measurement by laser reflection method, this method allows calculation of the biaxial elastic modulus, E/(1 − v), where E is the elastic modulus and v Poisson's ratio of the DLC films. By comparing the biaxial elastic modulus with plane-strain modulus, E/(1 −v2), measured by nano-indentation, we could further determine the elastic modulus and Poisson's ratio, independently. This method was employed to measure the mechanical properties of DLC films deposited by C6H6 r.f. glow discharge at the deposition pressure 1.33 Pa. The elastic modulus, E, increased from 94 to 128 GPa as the negative bias voltage increased from 400 to 550 V. Poisson's ratio was estimated to be about 0.22 in this bias voltage range. For the negative bias voltages less than 400 V, however, the present method resulted in negative Poisson's ratio. The limitation of the present method was discussed.
Microstructure And Wear Resistance Of Doped Diamondlike Carbon Prepared By Pulsed Laser Deposition
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Oktyabrsky S. , Sankar J. , Narayan J.
Published: April 2011

We have investigated the microstructure and tribological properties (wear resistance) of diamondlike carbon (DLC), DLC doped with Cu and DLC doped with Ti deposited by a sequential pulsed laser ablation of two targets onto Si(100) substrates. The composition of these films was determined by Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy(XPS). Raman spectroscopy and detailed analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dominated by sp3 bonded carbon. Wear resistance measurements made on these samples by means of the “crater grinding method” showed that DLC + 2.75%Ti has the highest wear resistance, while that of undoped DLC has the lowest among the samples. The improvement of wear behavior of the doped films was attributed to the reduction of internal compressive stress due to the presence of more compliant atoms, as indicated by the G-peak position shift to smaller Raman shift. The XPS studies showed the evidence for the formation of Ti- C bonding in the Ti doped films. Thus we expect metal-doped DLC coatings can have better tribological properties than the undoped, highly stressed DLC coatings.
Development of Mechanical Stress in Cuni(mn) Films During Temperature Ramping: Related Mechanisms
Authors: Brückner W. , Baunack St. , Pitschke W. , Thomas J.
Published: April 2011

This paper focusses on the development of biaxial stress in Cu0.57Nio.42Mno.ol thin films during annealing in Ar and, for comparison, in vacuum. Besides stress-temperature measurements also resistance-temperature investigations as well as chemical and microstructural characterization by Auger electron spectroscopy, scanning and transmission electron microscopy, and X-ray diffraction were carried out. To explain the stress evolution, atomic rearrangement (excessvacancy annihilation, grain-boundary relaxation, and shrinkage of grain-boundary voids) and oxidation were considered. Up to 250 - 300 °C grain-boundary relaxation was found to be the dominating process. A sharp transition from compressive to tensile stress between 300 °C and 380 °C is explained by the formation of a NiO surface layer
Stress Characterization of Sputtered PZT Films
Authors: Mescher M. J. , Reed M. L. , Schlesinger T. E.
Published: April 2011

In this work we show that stress in sputter deposited lead zirconate titanate (PZT) films can be controlled by variation of both deposition and annealing temperatures. These films were deposited via reactive rf magnetron sputtering using a Pb1.25Zr. 52Ti. 48 03 composite target and 02 as a reactive gas in an Ar ambient. Variation of stress as a function of deposition and annealing temperature was characterized. The deposited film composition was determined from x-ray fluorescence measurements. There is a strong correlation between film stress, composition, and crystallographic orientation. Stress was determined from the deflection of released SiO 2/Pt cantilever beams. We show that films with a wide range of intrinsic stress can be deposited which still exhibit good piezoelectric properties, making the fabrication of reliable thin film piezoelectric actuators possible.
Influence of Target Structure on Film Stress in WTI Sputtering
Authors: Lo Chi-Fung , Wang Hong , Gilman Paul
Published: April 2011

In this report, the effect of sputtering target microstructure on the deposited film stress was investigated. By controlling the metallurgical process, two types of W-10wt%Ti target constituents, namely single-phase and multiple-phase WTi, were prepared. The former one was composed of W-rich (βTi,W) phase only, the latter one was with W, W-rich (βTi,W) and Ti-rich (βTi,W) phases. The stress of the films deposited on 12.7 cm diameter silicon oxide wafers from the single-phase target tends to be more compressive than that from the multiple-phase target. By increasing wafer temperature, the compressive stress was linearly decreased. In addition, the level of film stress was also affected by the film thickness and other sputtering parameters. To understand the causes for the differences in film stress between the multiple-phase and singlephase derived films, an evaluation of the film structure using a field-emission scanning electron microscope (FE-SEM) and mechanical testing using a nano-indentation instrument were performed. Finer domains with denser laminar structure were observed on the films deposited from the single-phase target. However, no significant difference in mechanical properties was found between these two from the nano-indentation measurements. It is envisioned that the more uniform solid solution between the W and Ti in the films obtained by sputtering the single-phase targets generates a higher compressive stress when deposited on the silicon oxide wafers resulting in a higher compressive stress.
Interfacial Strain Reliefs in Epitaxial YBa2Cu3O7–δ Thin Films Grown on SrTiO3 Buffered MGO Substrates
Authors: Cui Xingtian , Chen Q. Y , Guo Yongxiang , Chu W. K.
Published: April 2011

High quality YBa2Cu3O7–δ, (YBCO) epitaxial thin films grown on MgO substrate with a strainrelieved SrTiO3 (STO) buffer layer have been investigated by Rutherford backscattering spectrometry (RBS), ion channeling and high resolution cross sectional transmission electron microscopy (XTEM). The in-situ growth of STO buffer layer along with the YBCO films was carried out by pulsed laser ablation. In this work, minimum yield of channeling measurements have shown that a very thin STO buffer layer is sufficient to grow highly crystalline YBCO thin films on MgO substrates. TEM studies showed that the STO layers were strain-relieved by an array of periodic edge dislocations. The YBCO films on STO buffer, as in those grown directly on an STO substrate, evolved from a strained layer to a largely dislocation free area.
Measurement of Residual Stress in Thin Films Using the Optical Microprobe
Authors: Atkinson A. , Clarke D. R. , Jain S. C. , Pinardi K. , Webb S.
Published: April 2011

The laser optical microprobe is a powerful tool for studying the spatial variation of residual stress exploiting the sensitivity of Raman and luminescence spectra to the local stress. Here, using two different examples, we consider some issues determining the depth and lateral resolution of these techniques and their use in stress mapping in thin films. The first example involves Raman microprobe studies of a strained GeSi alloy quantum wire structure. The second example involves stress mapping using chromium ion luminescence in alumina films grown by high temperature thermal oxidation of NiAl single crystals.
Microstructures and Mechanical Properties of Sputtered Cu/Cr Multilayers
Authors: Misra A. , Kung H. , Mitchell T. E. , Jervis T. R. , Nastasi M.
Published: April 2011

The microstructures and mechanical properties of Cu/Cr multilayers prepared by sputtering onto {100} Si substrates at room temperature are presented. The films exhibit columnar grain microstructures with nanoscale grain sizes. The interfaces are planar and abrupt with no intermixing, as expected from the phase diagram. The multilayers tend to adopt a Kurdjumov- Sachs (KS) orientation relationship: {110}Cr //{111}Cu, <111>Cr //<110>Cu. The hardness of the multilayered structures, as measured by nanoindentation, increase with decreasing layer thickness for layer thicknesses ranging from 200 nm to 50 nm, whereas for lower thicknesses the hardness of the multilayers is independent of the layer thickness. Dislocation-based models are used to interpret the variation of hardness with layer periodicity. The possible effects of factors such as grain size within the layers, density and composition of films and residual stress in the multilayers are highlighted. Comparisons are made to the mechanical properties of sputtered polycrystalline Cu/Nb multilayers which, like Cu/Cr, exhibit sharp fcc/bcc interfaces with no intermixing and a KS orientation relationship, but have a small shear modulus mismatch.
Mechanical Characterization of Sub-Micron Polytetrafluoroethylene (PTFE) Thin Films
Authors: Lucas B. N. , Rosenmayer C. T. , Oliver W. C.
Published: April 2011

This study reports the results of an investigation of the mechanical properties of polytetrafluoroethylene (PTFE) thin films on silicon substrates in the 0.5 to 15 μm thickness regime using frequency specific depth-sensing indentation. All measurements were conducted at an excitation frequency of 45 Hz using a constant (1/P dP/dt) load ramp of 0.1 s−1. The modulus of the PTFE at a depth of 5% of the film thickness was measured to be approximately 1 GPa (v = 0.46) independent of film thickness. These values are somewhat higher than the values obtained from free-standing 15 μm film measurements of 0.4 GPa for the tensile modulus and 0.49 GPa for the storage modulus @ 1.1 Hz. The film hardness at these depths was observed to range between 30 and 55 MPa with no correlation observed between the hardness and respective film thickness. While reliability modeling for interconnects currently uses interlayer dielectric mechanical properties data determined from free-standing films with thicknesses of several microns, these insitu results should more closely mimic the constrained deformation that occurs during service and perhaps lead to a better understanding of the electromigration resistance of PTFE.
Transport and Retention Within the Fracturing Network of an Indurated Argillaceous Formation (Tournemire Site, France)
Authors: Windt L. De , Cabrera J. , Boisson J.-Y.
Published: April 2011

The characteristics of indurated argillaceous formations, considered as potential host media for high level radioactive waste disposal, differ in many aspects from plastic clays or crystalline rocks. In order to develop generic research on the containment properties of such formations, the French Institute for Protection and Nuclear Safety (IPSN) selected the Tournemire site ]1]: a sub-horizontal claystone layer (250 m thick, argilites and marls from Toarcian and Domerian formations) located between two limestone aquifers. Water circulations seem to be of very minor importance in the claystones, with a main diffusive component for transport ]1]. However, since a few weak water inflows occur in fracturing networks induced by tectonics, one of the key issues in the site characterisation is to adequately identify the water flows and the related transport and retention features within these specific water-conducting features. It is the purpose of the authors to present some insights in such a complex topic, using informations acquired in the framework of the Tournemire Project.
Simulation of Steady-State Groundwater Flow in the Gorleben Area
Authors: Genteri M. , Klemenz W. , Ludwig R. , Wollrath J.
Published: April 2011

The Gorleben salt dome, near the river Elbe at the border between Lower Saxony and Brandenburg in Germany, is under investigation as a candidate site for the final disposal of radioactive waste. The diapir is crossed by an Elsterian subglacial erosion channel, which forms the lowest aquifer in the salt dome area and contains saturated brines. The salt dome is bounded in the North and the South by pronounced structural depression zones, with deepening of the Tertiary and Quaternary layers. At the bottom the aquifer system is bounded by a thick clay layer (Rupelton). Saltwater is also present in the lowermost part of the aquifer system outside of the salt dome area. The area between the infiltration zone in the South (Gartower Tannen) and the exfiltration zone in the North, West and South-West covers approximately 350 km2 (see figure 1). The field investigations in the Southern part are completed, whereas the area North of the Elbe river is currently under investigation.
The Assessment of Radionuclide Retardation in Fractured Crystalline Rocks
Authors: Alexander W. Russell , Ota Kunio , Frieg Bernhard , Mckinley Ian G.
Published: April 2011

The joint Nagra/PNC Radionuclide Migration Programme has been running for over ten years in Nagra‘s Grimsel Test Site in the central Swiss Alps. The programme is specifically aimed at the further development of conceptual models of radionuclide transport in the geosphere, rigorously testing the applicability of current transport codes to quantify radionuclide migration in situ and assessing how successfully laboratory sorption data (specifically, Kd values) may be extrapolated to in situ conditions to predict radionuclide retardation in the geosphere [1]. A large series of field tracer migration experiments was carried out in a hydrologically well characterised water-bearing, complex fracture (or shear zone), increasing in complexity from simple, nonsorbing fluoresceine (a fluorescent dye), 3H, 3,4He, 82Br and 123I through weakly sorbing 22.24Na,85Sr and 86Rb to a final, long-term experiment with moderately sorbing 134,137Cs. The radionuclides were injected into a dipole flow field where the flowpath length, dipole width or shape and groundwater flow velocity were all varied. After a considerable learning period, generally good fits could be obtained between transport code predictions and subsequent field tracer breakthrough curves, suggesting that the transport codes tested were a reasonable representation of in situ conditions.
Thermal Alteration of Uranium Mobility in Clay Minerals
Authors: Ritherdon B. , Hughes C. R. , Livens F. R. , Richardson S. , Braithwaite A.
Published: April 2011

Clay minerals are well known to be capable of retarding the movement of many potential pollutants, such as uranium, with their relatively high sorption capacities2. It has been suggested that high temperature thermal treatment processes are a potential method for the in situ immobilization of radionuclides or other contaminants2. The effect of progressive heating on the leaching behaviour of uraniferous clay material has therefore been investigated.
Nd-Sr Isotope and REE Evidence for the Long-Term Stability of HLW Glass Products and Trace Metal Migration in a Salt Repository: Corroding Basaltic Dykes in Evaporites as Natural Analogues
Authors: Steinmann M. , Stille P. , Mengel K. , Siemann M. , Bernotat W.
Published: April 2011

Basaltic dykes in salt rocks can be used in two different ways as natural analogues for high level radioactive waste (HLW) in a salt repository: In the first approach the basalts serve as analogues for the corrosion behavior of HiLW glass products during millions of years because of many similarities in their physical and chemical properties.
Kinetics of Reduction and Precipitation of U(VI) in the Dissolution of UO2(s) Under Anoxic Conditions in NaCl 5 mol kg−1. Influence of Metallic Iron
Authors: Giménez J. , Molera M. , Casas I. , Torrero M.E. , de Pablo J.
Published: April 2011

Experiments of spent fuel dissolution performed in presence of iron show, for uranium as well as for some radionuclides, lower final concentrations than measured in similar experiments but in absence of iron. So far, only the final concentrations obtained in these experiments have been published. In this work, we have focused our study on the reduction of uranium (VI) due to the presence of iron and the subsequent precipitation of Uranium (IV) due to its lower solubility. This behavior has been confirmed using a Scanning Electron Microscope by observing an uranium phase precipitated on the iron surface and assuming, under the experimental conditions, that it most likely corresponds to U02(s). We have modeled this process assuming a first-order kinetic.
Corrosion Mechanisms of Spent Fuel Under Oxidizing Conditions
Authors: Finn P. A. , Finch R. , Buck E. , Bates J.
Published: April 2011

The release of99Tc can be used as a reliable marker for the extent of spent oxide fuel reaction under unsaturated high-drip-rate conditions at 90°C. Evidence from leachate data and from scanning and transmission electron microscopy (SEM and TEM) examination of reacted fuel samples is presented for radionuclide release, potential reaction pathways, and the formation of alteration products. In the ATM-103 fuel, 0.03 of the total inventory of99Tc is released in 3.7 years under unsaturated and oxidizing conditions. Two reaction pathways that have been identified from SEM are 1) through-grain dissolution with subsequent formation of uranyl alteration products, and 2) grain-boundary dissolution. The major alteration product identified by X-ray diffraction (XRD) and SEM, is Na-boltwoodite, Na[(UO2)(SiO3OH)]H20, which is formed from sodium and silicon in the water leachant.
Study of Uranium Incorporation Into Zircon: Solubility Limits and Durability of Fixation
Authors: Ioudintsev S.V. , Omelianenko B.I. , Lapina M.I.
Published: April 2011

Research on synthetic zircons fabricated in system ZrO2-UO2-SiO2 at T = 400 - 750° C, PH20 = 100-200 MPa, and Ni-NiO oxygen buffer was made in order to estimate the limits of uranium incorporation into the phase's structure. It was shown that up to 27 wt.% of uranium may locally enter into the synthetic zircons. SEM/EDS study of the samples has showed that the element is uniformly distributed within the zircon crystals. Incorporation of U into zircon increases its unit-cell dimensions up to α = 6.70 A and c = 6.00 A relative to 6.60 and 5.98 A for a pure phase without impurities.

After thermal high temperature treatment of the samples under 1400° C, in air, for 6 hours inhomogeneous distribution of uranium within the zircon grains was revealed. Very small uranium rich spots probably corresponding to a newly formed phase were observed in the zircon crystals. Contents of the element throughout the grains decreased to about 10 wt.%. It is probably caused by destruction of zircon-coffinite solid solution formed at hydrothermal conditions in the course of its re-heating.

Study of interaction of natural zircons with alkaline carbonate solution at 100° C shows that U release from the phase can reach up to 6 % of total uranium in the samples even under relatively short term interaction. Loss of uranium rises with the element content (or amorphisation degree) and run duration, as well as with grain size reduction. Research on uranium distribution in natural zircons picked up from altered and weathered rocks is characterised by strong depletion of U at grain margins relative to the centre of the crystals. These results indicate that zircon may lose some uranium and, probably, the other actinides with time due to its lattice destruction under radioactive decay followed by hot water attack.
Leaching of Spent Fuel and Simulated Fuel in the Presence of Environmental Materials: Integral Experiments
Authors: Le Lous K. , Constantin S. , Paul J.L. , Sambugaro D. , Vernaz E.
Published: April 2011

We have designed an apparatus which simulates the conditions of a deep geological repository in order to study the behaviour of spent fuel under leaching. A spent fuel and a Simfuel have thus been leached by synthesized clayey or granitic groundwater in sandy clay (90 % sand) or granite, in reducing conditions, at 90°C and 40 bars.

The apparent leach rate for spent fuel in clayey water is 3.33 µg.m−2.dr−1in the presence of clay and 3.37 µg.m-−2.d−1in the presence of granite. The apparent leach rate in granitic water is slower, being 0.37 µg.m−2d−1in the presence of clay and 0.74 µg.m−2d−1in the presence of granite.

For Simfuel, the apparent leach rate in clayey water is 7.4 µg.m−2.d−1in the presence of clay and 1. 1 µg.m−2.d−1in the presence of granite, which is the same order of magnitude as that for spent fuel. In granitic water, the apparent leach rate is 20 to 40 times greater than that for spent fuel. It is 14.8 µg.m−2.d−1in the presence of clay and 18.5 µg.m−2.d−1in the presence of granite.
Scientific Studies on the Immobilization of Pu by ISV in Field Trials at Maralinga, Australia
Authors: McGlinn P.J. , Hart K.P. , Day R.A. , Harries J.R. , Weir J.A. , Thompson L.E.
Published: April 2011

ANSTO has studied material resulting from an In Situ Vitrification (ISV) trial on contaminated soil from the Maralinga nuclear weapons test range in Australia. The investigations included determining the distribution of Pu and α-activity in the intermediate scale melt, leach testing of sub-samples from the melt, and physical characterisation of the ISV material, prior to and after leaching. The results show that Pu is well mixed though the whole vitrified/ceramic block from the ISV trials at Maralinga and the durability of the vitrified/ceramic product ensures that the Pu is satisfactorily encapsulated.
Synthesis of Ce-Doped Zircon by a Sol-Gel Process
Authors: Ushakov S.V. , Burakov B.E. , Garbuzov V.M. , Anderson E.B. , Strykanova E.E. , Yagovkina M.M. , Helean K.B. , Guo Y.X. , Ewing R.C. , Lutze W.
Published: April 2011

Zircon, ZrSiO4, is a prospective durable host material for the immobilization of excess weapons plutonium. Using cerium as a chemical analogue for plutonium, the experiments on the synthesis of Ce-doped zircon were conducted by sintering of sol-gel precursors in air and vacuum. The results showed that cerium substantially promotes zircon formation from sol-gel precursors and sintering in air is preferable for cerium incorporation in zircon structure. Based on measured lattice constants, solid solution compositions (Zr0.96Ce0.04)SiO4 and (Zr0.98Ce0.02)SiO4 were formed in samples sintered in air at 1400°C and 1600°C, respectively. The solubility limits of cerium and actinides in zircon and mechanism of zircon formation are discussed.
R&D in Support of Repository Implementation Do We Need Any More?
Authors: Mccombie Charles
Published: April 2011

Is there any need for further scientific and technical development work in the field of waste management? Radically different views on this provocative question have been put forward by opposing sides in the nuclear debate. P. Slovik [1] quotes various leaders on the nuclear community who for years have been claiming that waste management has no unsolved technical problems. At the recent public hearing in England [2], on the other hand, Greenpeace and others convinced the Inspector that, despite a GBP 200 million site characterisation programme with many deep boreholes, UK-Nirex still knew too little about the deep hydrogeology to justify even the sinking of an exploratory shaft at Sellafield. Where does the truth lie?
Diffusion of Cs and Sr in Compacted Bentonites Under Reducing Conditions and in the Presence of Corrosion Products of Iron
Authors: Idemitsu K. , Tachi Y , Furuya H. , Inagaki Y. , Arima T.
Published: April 2011

In high-level waste repositories, a carbon steel overpack will be corroded by consuming oxygen trapped in the repository after closure. Iron corrosion products are expected to interfere with migration of radionuclides by filling the pore in bentonite and sorbing radionuclides. In this study the apparent diffusion coefficients of cesium and strontium were measured in compacted Na-bentonites (Kunigel VI® and Kunipia F®, JAPAN) contacted with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients of cesium with and without corrosion product were 2.2 to 13 × 10−12m2/s. The apparent diffusion coefficients of strontium with and without corrosion product were 3.1 to 25 × 10−12m2/s. There were significant effects of dry density (0.8 to 2.0 g/cm3) and montmorillonite contents (50% for Kunigel V1 or 100% for Kunipia F). The presence of corrosion product decreased the apparent diffusion coefficients of Cs in both bentonites and that of Sr in Kunigel V1, especially at low dry density. This may be due to corrosion product filling the pore in the bentonite, decreasing the free pore size and density for diffusion.
Influence of Hydromechanical Couplings on the Resaturation of Engineered Barriers
Authors: Lassabatere T.
Published: April 2011

This paper presents a fully coupled model for unsaturated deformable materials like swelling clays of engineered barriers. A thermodynamic framework is adopted which allows to take into account the influence of the mechanical variables (stress and strain tensors) upon the hydraulic part of the state equations (suction - water content relation). So, a fully coupled behaviour formulation is stated which, when combined with « classical » phenomenological relations, makes it possible to study the influence of the mechanical state of the barrier on the kinetics of its resaturation.
Alteration of Repository Structural Materials Within the First Few Years
Authors: West J. M. , Cave M. , Coombs P. , Milodowski A. E. , Rochelle C. A.
Published: April 2011

A series of batch laboratory experiments were set up to study the gross effects of microbial activity on repository geochemistry, radionuclide sorption and integrity of repository and host rock materials. The experiments were fully monitored for 550 days and some were continued, under apparently aerobic conditions, for 1700 days. Geochemical modelling of the experiments reproduced many of their features, but showed that the contents were not in chemical equilibrium after 1700 days with redox disequilibrium a likely feature. The models could not predict localised reactions such as enhanced pitting of steel which appeared to be microbially mediated.
The Leaching Behavior of Bituminized Radioactive Waste in the Geologic Disposal Conditions of the Boom Clay Formation
Authors: Sneyers A. , Iseghem P. Van
Published: April 2011

As part of the evaluation of the safety of geologic disposal, the leaching behaviour of two types of bituminized radioactive waste (Eurobitum and CEA bitumen) has been studied as a function of temperature, pressure, leachant composition and bitumen matrix type. Inactive and active bitumen samples were brought into contact with two test media, simulating the geologic disposal environment of the Boom clay formation. At contact with these media, the samples swelled and soluble salts and radionucides were leached. It was found that the leach rate is influenced by temperature, the leachant composition, and the physical characteristics of the bitumen matrix. The release of nitrate is interpreted as a diffusion controlled process, which can however be disturbed by crack formation. The leaching of 60Co, 90Sr, and total β is diffusion controlled. Low leach rates were measured for Pu and Am: the release of Pu and Am is limited by their solubility in the leachant. Pu and Am are preferentially sorbed to the Boom clay, the test container or the bitumen. The leached mobile Pu and Am concentrations are of the order of 10−10 to 1013 M at 23°C. The results of this study suggest that the integrity of bituminized waste packages is seriously affected due to the leaching of soluble salts: a full-size 220 litre Eurobitum drum is predicted to be depleted in NaNO3 in less than 20,000 years.
Comparative Structural Study and Dissolution of Simplified Glasses: A Radioactive Waste Glass (R7T7) and a Basaltic Glass
Authors: Angeli F. , Faucon P. , Charpentier T. , Petit J.C. , Virlet J.
Published: April 2011

The local cation environments in a borosilicate glass (containing the main components of the French nuclear waste glass, R7T7) and of basaltic-like glass are presented on the basis of17A1 and23Na Multi-Quanta Magic-Angle Spinning Nuclear Magnetic Resonance (MQ-MAS NMR) spectroscopies. The chemical and geometrical environment of each nucleus is characterized. Moreover, qualitative information about the distribution of these parameters, characteristic of the disorder level in the structure, is obtained. These results are presented with the characteristics of the Al and Na dissolution in water at 100°C. The relation between the local environments of these cations and their mass loss in solution is discussed.
Sorption Kinetics of Uranium-238, Neptunium-237, Caesium-134, and Strontium-85 on a Glacial Deposit
Authors: Moyes L.N. , Bunker D.J. , Smith J.T. , Livens F.R. , Hughes C.R. , Hilton J. , Braithwaite A. , Richardson S.
Published: April 2011

Batch sorption experiments have been used to assess the sorption behaviour of four radionuclides, important in the context of low-level waste disposal, on a glacial substrate. Data for sorption of 238U, 237Np, 134Cs and 85Sr are compared and agree well with independent studies. A series of well-established kinetic models have been used to describe the individual uptake mechanisms and rate parameters reported. Sorption occurs via both equilibrium and kinetically controlled pathways, with neptunium sorption being under kinetic control to the greatest extent.
A Comprehensive Hydrodynamic Modeling Approach for the Hydrogeological Site Characterization and for Deriving Input to Performance Assessment
Authors: Vinard P. , Vomvoris S. , Marschall P.
Published: April 2011

This paper gives an overview of the numerical models employed for the simulation of ground-water flow at the Wellenberg site, the runs carried out and the kind of products which were specified as results of the modelling calculations. With respect to more conventional modelling approaches, based mainly on fully deterministic and steady-state schemes, this new approach integrates both deterministic and stochastic aspects (hydraulic conductivity distribution, geometry of the fracture network, etc.) in three different groundwater models, accounting for different scale levels. Moreover, this new approach is as close as possible to a realistic representation of the in situ conditions, since it is based on plausible distributions of transmissivity and hydraulic conductivity at all scales and takes the transient nature of flow fully into account. This latter aspect is fundamental since, at Wellenberg, both the underground facilities and a natural head anomaly in the host rock cause pressure disturbance in the flow field. Finally, and because boundary conditions (especially topographic surface and overburden) vary over time, model predictions based on current topography and climatic conditions are of limited duration and hence a validity duration has to be defined.
The Adsorption of Humic Acids and Europium-Humate Colloids Onto Repository Components: Boom Clay, Bentonite, and Fe2O3
Authors: Wei Jiang
Published: April 2011

Batch sorption experiments were carried out to investigate the adsorption of humic acids (HA) and Eu-humate colloids onto repository components: Boom clay, bentonite and Fe2O3as a function of pH. The concentration of humic acids is 150 mg/l and the bulk concentration of Eu is 10−6M. Radioactive152Eu was used as a tracer. The adsorption of humic acids onto bentonite and Fe2O3decreased with increasing pH. Humic acids were probably complexed to Al/Fe sites on the adsorbents through COOH and phenolic OH groups. It is difficult to interpret the adsorption of humic acids onto Boom clay because Boom clay itself contains high content of organic matters. The adsorption of Eu-humate colloids onto repository components were performed near neutral pH conditions. Eu was strongly adsorbed by three adsorbents, and pH had little effect on the adsorption in the neutral pH range. The strong complexation of Eu with humic acids did not prevent Eu from being adsorbed. Eu is likely bound to solid surfaces via humic acids. The adsorption of Eu-humate colloids onto mixed adsorbents (Boom clay + bentonite, Boom clay + Fe2O3, bentonite + Fe2O3, and Boom clay + bentonite + Fe2O3) was investigated. Most of Eu-humate colloids was adsorbed by the mixed adsorbents. The desorption of humic acids and Eu from repository components was also examined.