bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of Cluster Size Effect with Size-selected Cluster Ion Beam System
Authors: Toyoda Noriaki , Houzumi Shingo , Aoki Takaaki , Yamada Isao
Published: April 2011

A size-selected gas cluster ion beam (GCIB) system has been developed to study the size effects of energetic large cluster ion bombardments on a solid surface for the first time. This system equipped a permanent magnet with a magnetic flux density of 1.2 T. There is a sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. By locating a sample at a certain position, particular size of cluster ion can be irradiated continuously with affordable ion current density. When the total acceleration energy of Ar-GCIB was 5keV, both amorphous and oxide thickness on Si substrate increased with decreasing cluster size. This result showed good agreement with that obtained from molecular dynamics simulations.
Structure of Cu Ions in (Cu + Halogen or Chalcogen)-Ion Implanted Silica Glasses
Authors: Fukumi Kohei , Chayahara Akiyoshi , Kageyama Hiroyuki , Kitamura Naoyuki , Kadono Kohei , Kinomura Atsushi , Mokuno Yoshiyuki , Horino Yuji , Nishii Junji
Published: April 2011

Structure of Cu ions in (Cl+Cu)-, (Br+Cu)-, (I+Cu)-, (S+Cu)- and (Se+Cu)-ion implanted silica glasses has been studied by x-ray absorption and optical absorption spectroscopies. Cu ions formed Cu-O bonds in the as-implanted glasses, due to the homogeneous distribution of Cu ions and the low local concentration of halogen and chalcogen ions in silica glass. Heat treatment at about 600°C caused the formation of bonds between Cu ions and halogen/chalcogen ions without forming Cu halide or chalcogenide crystals. It was deduced that the formation of these bonds was controlled by the diffusion of Cu ions in silica glass. On the other hands, it was inferred that the formation of Cu halide and chalcogenide crystals was controlled not only by the diffusion of halogen/chalcogen ions but also by the diffusion of matrix ions.
Damage Mechanisms of Ion Implanted Bulk (0001) ZnO Single Crystals.
Authors: Adekore B.T. , Usov I. , Patnaik B. , Parikh N. , Davis R.F
Published: April 2011

Crystalline damage created by ion-implantation of dopant impurities in ZnO (0001) substrates was characterized as a function of atomic mass of implanted species using triple-axis (2θ-ω/ω) x-ray diffraction and Rutherford backscattering (RBS). The former revealed the presence of implantation-induced strain through the broadening of the isometric and asymmetric 2θ-ω reflections. However, RBS indicated that the damage introduced during implantation of these ions was insufficient to transform the crystalline lattice into a completely amorphous state. Additional XRD characterization as a function of annealing temperature of the implanted materials showed a reduction in the broadening of the isometric reflections, indicating that structural recovery of implanted ZnO crystals can be achieved.
Diffraction Contrast Image Analysis on the Facet Defects of the Laser Diodes Caused by ECR Cleaning Process
Authors: Cheng S.C. , Ouyang M.X.
Published: April 2011

Cross-sectional and plan-view TEM techniques were used to study the ion beam passivation of 980 nm laser pump diodes. It is found that under certain operation conditions, the ECR cleaning process produces crystal defects in the facets region of the diodes. By TEM diffraction contrast image analysis, the crystal defects are determined as Frank dislocation loops at the {111} planes of the GaAs crystal. The details of the TEM analysis procedures are described in the paper. In order to obtain high quality passivation of the diodes, the parameters of the ECR cleaning process have to be optimized to eliminate the induced defects.
MAS NMR Study on the Microstructural Changes of Zeolite-NaY under Neutron Irradiation
Authors: Chen J. , Beck L. W. , Wang L. M. , Gu B. X. , Ewing R. C.
Published: April 2011

The results of high-resolution solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) indicate the bond angles of Al-O-Si decrease with the increase of neutronirradiation dose, but there are only minor changes for Si-O-Si bond angles in the current dose range studied. This suggests that zeolite with higher Si/Al ratio is more resistant to neutron irradiation damage. It is also found that [AlO6] formed at higher dose range. The ratio of Si/Al changed from 2.57 before neutron irradiation to 2.76 when the dose reached 2.25×1019 n/cm2, which shows that mild dealumination occurred during neutron irradiation. The strontium ion exchange experiments have been conducted for neutron irradiated, thermally treated and original zeolite samples, respectively. It is found that the ion-exchange ability of neutron-irradiated zeolite-NaY is between those of original and heat-treated zeolite samples. The distortion of the framework under neutron irradiation by the decrease of Al-O-Si bond angles and the formation of [AlO6] is partially responsible for the ion-exchange variability variation of zeolite-NaY.
Ion Beam Irradiation Effects on Polymers
Authors: Chipara Mircea
Published: April 2011

The main effects of the interaction of accelerated ions with polymeric targets are critically reviewed. The possibility of a relatively reduced heating of polymer during ion beam bombardment is analyzed. Experimental data pointing towards various radiation-induced modifications in polycarbonate (free radicals production, modifications of the energy gap) are discussed.
γ - Ray Detectors Based on Composite A1B5C6 Semiconductors
Authors: Khlyap Galina , Andrukhiv Mikhail , Panchenko Ludmila
Published: April 2011

Metal-semiconductor structures based on composite semiconductors A1B5C6 are investigated as possible γ-ray detectors. Electric measurements carried out on the samples before the irradiation have exhibited no special peculiarities. After irradiation the analogous investigations have shown dramatic changes of charge carriers transport. Numerical analysis showed the field-current characteristics similar to the p-n-homo-junction: the forward current is described by the power law I∼(Fa)3/2, where Fa stands for applied electric field. Under reverse bias two clear modes of the carriers transport are observed: under the so-called threshold field FTR ∼ 300 V/m the experimental current is governed by quasi-ohmic law I∼(Fa)0.8; as the applied field exceeds the threshold value, the field-current dependence points out the strong trap-assistant tunneling processes: I∼(Fa)5.
Simulations of Electron Diffraction Contrast Images of Nanometer-sized Dislocation Loops
Authors: Zhou Zhongfu , Dudarev Sergei L , Jenkins Michael L , Sutton Adrian P , Kirk Marquis A
Published: April 2011

A computer code has been developed to solve numerically the Howie-Basinski equations of electron diffraction theory, and has been applied to simulate diffraction contrast images of small dislocation loops under weak-beam diffraction conditions. In this paper we describe the basis of the code, and apply it to simulate weak-beam images of small loops under a variety of imaging conditions.
Multi-Dot Floating-Gates in MOSFETs for Nonvolatile Memories – Their Ion Beam Synthesis and Morphology
Authors: Müller T. , Heinig K.-H. , Bonafos C. , Coffin H. , Cherkashin N. , Ben Assayag G. , Schamm S. , Zanchi G. , Claverie A. , Tencé M. , Colliex C.
Published: April 2011

Scalability and performance of current flash memories can be improved substantially by novel devices based on Multi-Dot Floating Gate MOSFETs. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS). Here, we present both experimental and theoretical studies on IBS of multi-dot layers consisting of Si nanocrystals (NCs). The NCs are produced by ultra low energy Si+ ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this supersaturation leads to phase separation of the excess Si from the SiO2. Till now, the study of this phase separation suffered from the weak z contrast between Si and SiO2 phases in Transmission Electron Microscopy (TEM). Here, this imaging problem is solved by Energy Filtered Scanning Transmission Electron Microscopy (EFSTEM). Additionally, kinetic lattice Monte Carlo simulations of Si phase separation have been performed and compared with EFSTEM images. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These patterns agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental one. Because oxidants of the ambient atmosphere penetrate into the as-implanted SiO2, a substantial fraction of the implanted Si is lost due to oxidation.
Fast Neutral Ar Penetration during Gas Cluster Ion Beam Irradiation into Magnetic Thin Films
Authors: Kakuta Shigeru , Seki Toshio , Sasaki Shinji , Furusawa Kenji , Aoki Takaaki , Matsuo Jiro
Published: April 2011

Ar penetration during gas cluster ion beam (GCIB) irradiation has been investigated using secondary ion mass spectroscopy (SIMS). The concentration of Ar rose to a maximum and then decreased gradually with increasing depth. The depth of the Ar penetration peak increased in proportion to the cube root of the acceleration voltage of GCIB and was independent of ion dose. Ar penetration was attributed to fast neutrals in the GCIB and was successfully suppressed by decreasing the pressure of the space downstream of the GCIB or decreasing the monomer ion density in order to suppress charge transfer collisions.
Controlled Fabrication by LPCVD of Luminescent SiGe/SiO2 (LTO) Very Thin Multilayers
Authors: Rodríguez A. , Sangrador J. , Rodríguez T. , Avella M. , Prieto A. C. , Jiménez J. , Ortiz M. I. , Ballesteros C.
Published: April 2011

Amorphous SiGe/SiO2 multilayers with controlled thickness in the range of nanometers have been deposited by LPCVD at low temperature in a single multistep run. Continuous and discontinuous layers have been deposited. No intermixing between the SiGe and SiO2 layers has been observed. As-deposited and crystallized multilayers have been characterized by Raman spectroscopy, Cathodoluminescence and TEM. The luminescence emission is more intense in the discontinuous layers than in the continuous ones.
Laterally Graded Rugate Filters in Porous Silicon
Authors: Foss Sean E. , Finstad Terje G.
Published: April 2011

Rugate optical reflectance filters with position dependent reflectance peaks in the visible to near infrared spectrum were realized in porous silicon (PS). Filters with strong reflection peaks, near 100%, no detectable higher order harmonics and suppressed sidebands compared to discrete layer filters were obtained by varying the current density continuously and periodically during etching. An in-plane voltage up to 1.5 V was used to obtain refractive index and periodicity change along the filter surface resulting in reflectance peak shifts of up to 100 nm/mm in the direction of the voltage drop. The effect of the lateral change in optical parameters on the filter characteristics is studied by varying the gradient and comparing measurements at different positions with measurements on a non-graded filter. We have observed extra features in the reflectance spectrum of these graded filters compared with reflectance from a non-graded filter which is likely caused by the gradient.
Fabrication of Two-dimensional Nonlinear Photonic Crystal by Electron Beam Lithography
Authors: Kang Chiang Huen , Shen Ze Xiang , Tang Sing Hai
Published: April 2011

In this paper, we present a study on quasi-phase matched (QPM) two-dimensional χ(2) lithium niobate (LN) nonlinear photonic crystal (NPC) for frequency doubling at λ = 1064nm. The NPCs were fabricated by electron beam lithography (EBL) through periodic polarization inversion of the ferroelectric domains and characterized with electrostatic force microscopy (EFM), atomic force microscopy and optical microscopy. Domain inversion occurred through the entire wafer thickness of 0.5mm as EFM images on the +c face of the z-cut wafer showed uniform domain structures throughout the corresponding electron beam irradiated regions of the -c face. In addition, the intended periodicity was observed. Moreover, domain inversion was also seen to have taken place in bulk from the optical images of the chemically etched samples. The EBL technique offers great flexibility in superlattice design and relative ease of fabrication as compared to the conventional poling techniques as pattern transfer is direct without the need for a mask and/or a coating of resist. Besides, micro- or sub-micro scale superlattices corresponding to wavelengths in the visible and into the ultraviolet are highly feasible, restricted only by the transparency of the crystals.
Photonic Quasiperiodic Multilayers of Porous Silicon
Authors: Nava R. , del Río J. A. , Alonso J. C. , Wang C.
Published: April 2011

Porous silicon is an efficient photo- and electro-luminescence material and represents a promising candidate for opto-electronic applications. In the last years, porous silicon multilayers with a high enough refractive index contrast have been obtained. In this work, we study the light transmission in Fibonacci multilayers made of porous silicon. The theoretical reflectance spectra are compared with experimental data, observing a good agreement, even though they are extremely fragile when the number of quasiperiodic layers increases. The photoluminescence spectra show evidences of the quasiperiodic structure and in particular, the observed enhancement in comparison with that of single porous silicon layer could be due to the quasiperiodicity.
Effect of as-deposited residual stress on transition temperature of VO2 films
Authors: Tsai Kuang Yue , Chin Tsung-Shune , Shieh Han-Ping D. , Ma Cheng Hsin
Published: April 2011

VO2 is a material with reversible thermo-chromic properties. The reversible phase transition of a strain-free single-crystalline VO2, at a transition temperature (Tt) 68°C, is accompanied with changes in crystal structure, optical and electrical properties. With different processing conditions during thin film deposition, different transmittance loops will be resulted upon thermal cycling. The residual stress of the thin films with poor crystallinity, as determined from X-ray diffractometry, is found to be an important factor responsible for the Tt that increases with increasing residual stress. Residual stress affects the hysteresis span of the transmittance loop. The relationship between residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen under the residual stress are also delineated.
Effect of Gamma and Alpha Irradiation on the Corrosion of the French Borosilicate Glass SON 68
Authors: Abdelouas Abdesselam , Ferrand Karine , Grambow Bernd , Mennecart Thierry , Fattahi Massoud , Blondiaux Gilbert , Houée-Lévin Chantal
Published: April 2011

Corrosion experiments with the French borosilicate glass SON 68 were conducted under gamma (60Co source) and alpha (cyclotron) irradiation conditions. Static tests with glass powder were conducted at 90°C under saturation conditions with synthetic solutions rich in Si, B and Na. The initial pH was 9.8 and the SA/V was 3970 m−1. For gamma irradiation tests with the highest dose (∼ 58000 Gy) the pH decreased by almost a unit, which lasted for two weeks. The ion-exchange between glass and solution was enhanced as evidenced by the increase of the Li-normalized mass loss within 93 days. The measured H2O2 concentration in the experiment with the glass was as high as 1.51 10−5. The alpha irradiation tests with a total dose of 1800 Gy did not affect the solution pH and therefore the leaching rate of the glass remained similar to that in the blank experiment after 59 days. However, the measured H2O2 concentration was as high as 2.32 10−5. This work indicates that high irradiation doses may enhance the ion-exchange process due to the pH decrease.
Titanate Ceramic Matrices for Alumina-Rich Wastes
Authors: Begg Bruce D. , Vance Eric R. , Li Huijun , McLeod Terry , Scales Nicholas , Bhati Mugdha
Published: April 2011

In the early 1980s a synroc variant, SYNROC-D, was developed for immobilisation of high-level defence waste stored at the Savannah River Plant, USA. A key phase in the immobilisation matrix was spinel, used to immobilise the large proportion of iron and alumina in the waste. Here we examine the feasibility of this approach for other alumina-rich wastes, not necessarily containing iron, derived from the dissolution of aluminium fuel cladding. The advantages of using a magnesia spinel, as opposed to hercynite (FeAl2O4), as the primary alumina-bearing phase are discussed in terms of an increase in waste loading and process flexibility. Two options for sodium incorporation, glass and the titanate phase freudenbergite, are considered.
Application of an On-line Corrosion Probe and a Reference Electrode for Copper Corrosion Studies in Repository Conditions
Authors: Betova Iva , Heinonen Jussi , Kinnunen Petri , Lilja Christina , Ruokola Esko , Saario Timo
Published: April 2011

Two sensors, an on-line corrosion sensor based on the wire-resistance probe design and a reference electrode which are applicable in repository conditions are introduced. Both sensors have been tested in simulated repository conditions in bentonite saturated with highly saline groundwater at 80 °C temperature and 14 MPa pressure up to 150 h exposure. In addition, it has been demonstrated that after an initial transient period of ca. 5–8 h, Cu corrosion in highly saline groundwater filled with bentonite becomes undetectably low probably because of the anoxic conditions reached in the free groundwater. At the same time, the measured corrosion potential of Cu is still in the active corrosion region. Furthermore, redox potentials in the wetted bentonite remain significantly higher than in the free groundwater. This may mean that the decomposition of oxygen contained in the pores of the bentonite is a process occurring in a time scale larger than that of the present experiments.
Investigations of Resistance Variations in Electrically Heated Canisters for Deep Repository
Authors: Zhu Baohua , Hermansson Hans-Peter , Sjöblom Rolf , Ramqvist Gunnar
Published: April 2011

At the end of 2001, measurements indicated that the resistance between the conductors had fallen in SKB's (Svensk Kärnbränslehantering AB) electrically heated test canisters. Electrochemical impedance spectroscopy (EIS) was employed together with chemical analysis of gas compositions and corrosion products to investigate the causes of the resistance decrease inside the canister. The measured system is complicated and the evaluation not straightforward. However, it seems that the plug connecting the external electrical power supply to the heaters in the canister is a critical component and that a moisture film around the electrical contacts of the plug may explain the resistance decrease. It is suggested to continue to monitor the EIS spectra with time to gain more information about the cause of the resistance drop.
Analysis of Uranium Diffusion Coefficients in Compacted FEBEX Bentonite
Authors: García-Gutiérrez M. , Cormenzana J. L. , Missana T. , Mingarro M. , Alonso U.
Published: April 2011

In the Spanish concept of a high level radioactive waste (HLRW) repository, the canister with the spent fuel would be surrounded by a layer of FEBEX bentonite (Ca-Mg smectite clay) compacted to a dry density of 1.65 g/cm3. Since the permeability of the compacted bentonite is very low, the main mechanism for radionuclide transport in the clay barrier is expected to be diffusion, retarded by the sorption on the solid. Since the mayor component of the radioactive waste is uranium it is very important to study its diffusion behaviour in the compacted clay.

Generally, effective (De) and apparent (Da) diffusion coefficients are obtained from "through-diffusion" and "in-diffusion" experiments, respectively. The obtention of both parameters in the same sample is a very interesting issue because the former includes the information on the porous medium structure (connectivity, constrictivity, tortuosity) and the latter takes into account the sorption on the solid phase. In this work, through-diffusion experiments were carried out for studying uranium diffusion and both effective and apparent diffusion coefficients were estimated, from the same experiment, by using different theoretical approaches.
Colloid Transport of Radionuclides: Yucca Mountain Performance Assessment
Authors: Traexler Kathy A. , Utsunomiy Satoshi , Kersting Annie B. , Ewing Rodney C.
Published: April 2011

Colloids have the potential to enhance transport of contaminants in the subsurface. Kersting et. al.,[1] have shown that plutonium, as well as europium, cobalt and cesium, were associated with groundwater colloids at the Nevada Test Site.240Pu/239Pu isotopic evidence confirmed that the plutonium was from the Benham nuclear test located 1.3 km away. This observation has lead to an increased concern that colloids may be potential vectors for radionuclide transport from an underground geologic repository [1].

The Anaylsis/Model Reports (AMRs) describe the characteristics of colloids for sparingly soluble radionuclides. The types of colloids formed, stability of the colloids as a function of pH and ionic strength, and the attachment of radionuclides to the colloids are modeled by the AMRs. The AMRs attempt to present bounding and conservative estimates for key parameters; however, waste form corrosion data, natural system studies, and experimental data do not always support the assumptions made in the AMRs. Most specifically, all colloids at Yucca Mountain, whether generated by the dissolution of waste glass or spent nuclear fuel or occurring naturally in groundwater, are assumed to be either smectite or iron-oxy-hydroxides. Data from waste form corrosion experiments do not support this assumption: numerous other phases have been identified including weeksite, clay particles with brockite inclusions, schoepite, soddyite, uranophane, boltwoodite, calcite, dolomite, Na-silicates, Al-oxides, absolone, birnessite, analcime, hydrated silicates, and apatite. Furthermore, the response of many of these phases to changes in pH or ionic strength is not known. If fundamental data for these phases, such as the point of zero charge (PZC), is different than that of either smectite or iron oxy-hydroxides, the TSPA may not accurately predict colloid transport of radionuclides.

We have analyzed colloid samples from groundwater at the Nevada Test Site using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive spectroscopic (EDS) elemental mapping, and found that light rare-earth elements (LREE) and Th are associated with monazite. Cesium and uranium are associated with an unidentified phase that is rich in Si and Fe. In addition, Co-60, a fissiogenic element, is associated with a complex metal colloid that includes Fe, Ni, Mo, and Cr. None of these phases are accounted for in the AMRs and their response to changing geochemical conditions is unknown. In addition, the PZC of several Mn-oxide phases was determined and was found to extend beyond the range of PZCs accounted for in the AMRs by smectite and iron oxy-hydroxides. Pu has been shown to preferentially adsorb onto Mn-oxides in the presence of Fe-oxides [2, 3], and the AMRs may not accurately predict Mn-oxide colloid stability and subsequent transport of radionuclides of interest.
The Compilation of Geochemical Data Bases for Performance Assessment of a Planned Repository in the Opalinus Clay in Northern Switzerland
Authors: Schwyn Bernhard , Wersin Paul
Published: April 2011

Chemical retention of radionuclides in the near field and in the host rock is an important safety pillar within the Swiss concept for a radioactive waste repository. Geochemical databases for solubility limits in cement and bentonite porewater and sorption / diffusion in cement, compacted bentonite and Opalinus Clay were compiled for use in safety assessment calculations. The databases are presented for selected safety-relevant radioelements. In contrast to earlier safety assessment studies Kdvalues were not truncated at 5 m3kg−1and values well above 10 m3kg−1(e.g. for actinides) are reported.
Dissolution of UO2 by One- and Two-Electron Oxidants
Authors: Jonsson Mats , Ekeroth Ella , Roth Olivia
Published: April 2011

In this work, the efficiency of one- and two-electron oxidants in oxidative dissolution of UO2 has been investigated. This was accomplished by measuring the U(VI)-concentration in solution after exposing UO2-powder to controlled amounts of oxidants in aqueous solution. The oxidants used in this study are H2O2, IrCl62−, CO3• and OH•. H2O2 acts as a two-electron oxidant while the remaining three oxidants are one-electron oxidants. CO3 and OH• were generated using γ-radiolysis. The results clearly show that the dissolution yields for one-electron oxidants (per electron pair) are lower than the yields for two-electron oxidants. Furthermore, the yields for one-electron oxidants increase with increasing amount of oxidant (especially at low amounts of oxidant). The rationale for this is that U(VI) is the main soluble species which is formed directly upon two-electron oxidation. For one-electron oxidants the primary oxidation product is U(V) which can form U(VI) upon reaction with a second oxidant. The probability for a second oxidation is however low at low concentrations of oxidant.
Solute Transport in Fractured Rock. Testing a New and Simple Aapproach
Authors: Moreno Luis , Crawford James , Neretnieks Ivars
Published: April 2011

A new and simple approach for modelling solute transport in fractured rock is presented, based on our previously used Channel Network Model (CNM). In our underlying concept, solute transport in fractured rocks takes place through undulating flat channels in the rock fractures. The channels form a 3-dimensional network. For non-interacting solutes the volume of the channels determines the residence time of a stream of water. For sorbing radionuclides the residence time is mainly determined by the ratio between the Flow Wetted Surface (FWS) and the flow rate in the channel (Q), in addition to the parameters that determine the interaction between the rock and the radionuclides. The main question explored in this paper is whether it is necessary to solve the flow problem for each studied case. From previous investigations, we have found that the flow rates in the channels where the solutes travel are closely related to the transmissivities of the channels. Simulations are presented in which streams of water are allowed to randomly select channels and trace out the paths where the path volume and its FWS can be assessed. The results obtained in this manner for the RTD (Residence Time Distribution) show rather good agreement with those obtained by solving the full flow problem and tracing particles in the network.
Microbial Sulphide Production in Compacted Bentonite at the Commencement of Long-Term Disposal of High-Level Radioactive Waste
Authors: Masurat Peter , Pedersen Karsten
Published: April 2011

The use of nuclear reactors produces electrical power but also high-level radioactive waste (HLW). In Sweden it has been decided that the HLW shall be disposed of in a deep geological repository 500 meters underground. The HLW will be encapsulated in copper canisters, surrounded by bentonite and then the access tunnel will be backfilled with a bentonite and crushed rock mixture.

We have investigated activity of sulphate reducing bacteria (SRB) in compacted bentonite with densities of 1.5, 1.8 and 2.0 g·cm−3 using stainless steel oedometers with 35SO42- as the main sulphur source for the SRB. The investigations were performed under in situ conditions at a depth of 450 m at the Äspö Hard Rock Laboratory. Canister type copper plates were placed in the oedometers, with the top either in contact with the added groundwater or with 3–4 mm bentonite between the plate and the added groundwater. Radioactive hydrogen sulphide formed by the SRB reacted with the copper and formed radioactive copper sulphide, which was measured by electronic radiography using an Instant Image Micro autoradiography instrument (Packard). A similar set-up with filter-sterilized groundwater (0.2 μm) was used as control. A second experiment was set up as the first experiment but using only filtered groundwater and adding heat treatment of the bentonite in the control. Here, we show that SRB were active and produced hydrogen sulphide during the initial phase of bentonite swelling. The activity of the SRB was inversely correlated with the final density of the bentonite as the highest density had the lowest overall SRB activity. We also found that SRB were present in a dormant state in the commercial MX-80 bentonite. By addition of water, these dormant SRB became active and started to produce hydrogen sulphide.
Mobilisation of Radionuclides by Ligands Produced by Bacteria from the Deep Subsurface
Authors: Arlinger Johanna , Oskarsson Anna , Albinsson Yngve , Andlid Thomas , Pedersen Karsten
Published: April 2011

Microbial processes can influence retention of radionuclides directly or indirectly in several different ways. Many microorganisms produce various kinds of ligands or chelating compounds to increase the bioavailability of essential elements needed for metabolism. These ligands are not always highly specific, and several of them will also mobilise other elements such as heavy metals and radionuclides. Three bacterial species (Shewanella putrefaciens, Pseudomonas fluorescensandPseudomonas stutzerii), isolated from the deep subsurface, and four radionuclides,59Fe(III),147Pm(III),234Th(IV) and241Am(III), were selected for this study. The microbes were cultured in the laboratory, separated from their exudates by centrifugation, and the supernatants were collected. The supernatants were mixed with radionuclide and solid phase (TiO2or SiO2). The pH ranged from 7.5–9.0. All three bacterial species produced ligands that were able to complex up to 90% of the radionuclides in competition with the solid phases. High performance liquid chromatography analysis detected four Fe-complexing substances in the supernatant from P. fluorescens and two peaks and one peak, respectively, fromP. stutzeriiandS. putrefaciens. All substances eluted from the column varied in retention times, indicating that the microbes studied produced several metabolites that have different chelating abilities.
Modelling Biochemical Processes in Rocks: Analysis and exploratory simulations of competition of different processes important for ferrous mineral oxidation and oxygen depletion
Authors: Sidborn Magnus , Neretnieks Ivars
Published: April 2011

There are several oxygen consuming processes occurring in deep subsurface fractured rocks. The importance of each process depends on the prevailing conditions and what function it has in the overall oxygen scavenging process. In the present work, some of these processes are studied. The aim is to build a frame of maximum rates for each parallel process. Therefore, several rate-limiting factors are not included. Rate expressions were obtained from the literature and compared for different cases to address under which conditions each process is important. Some of the processes may be considered parallel and independent while others occur in series. The main reactions accounted for are abiotic and biotic pyrite and ferrous iron oxidation and the non-oxidative dissolution of matrix ferrous minerals. In addition, transport processes of oxygen and other substrates within the rock matrix are considered. The main conclusions are that initially, when the diffusion resistance in the matrix is nonexistent or small, reaction kinetics are important. However, in a longer time perspective, diffusion processes limit the oxygen scavenging process.
Palaeohydrogeological Evidences from Fracture Filling Minerals - Results from the Äspö/Laxemar Area
Authors: Tullborg Eva-Lena
Published: April 2011

Two different EU projects: the EQUIP project (Evidences from Quaternary Infills from Palaeohydrogeology) running from 1997 to 2000 and the ongoing PADAMOT-project (Palaeohydrogeological Data Analysis and Model Testing) have addressed the possibility of using fracture minerals as recorders of past hydrochemical and hydrogeological environments. The Swedish contribution in these two projects has concentrated on studies of fracture filling calcites from the Äspö/Laxemar area, southeast Sweden.

The analyses applied in the two projects comprise stable isotope ratios of carbon and oxygen and strontium together with trace element contents and textural studies. The results obtained so far (mainly from the EQUIP project) show that several generations of calcite can be identified, chemical zoning is common, and the influence on calcite precipitation of fresh and marine water decreases with depth. It can be concluded that fine scale zoning, possible dissolution/redistribution of calcite, and the disturbances caused by drilling (where loose material which may contain young calcite precipitates were lost), introduce uncertainties in the recognition of different calcite generations. However, despite these problems it is indicated that calcite fracture fillings in Precambrian bedrock environments can add information e.g. concerning changes in groundwater chemistry and redox conditions in the past. The possibilities and problems with palaeohydrogeological interpretations are discussed based on the available data.
Project Opalinus Clay – Geoscientific Basis for the Demonstration of Feasibility of Disposal (Entsorgungsnachweis) for SF, Vitrified HLW and Long-Lived ILW in Switzerland
Authors: Gautschi A. , Lambert A. , Zuidema P.
Published: April 2011

Nagra - the Swiss National Cooperative for the Disposal of Radioactive Waste - has completed a study to determine the suitability of Opalinus Clay as a host rock for a SF/HLW/ILW repository in a potential siting area (reference repository site) in the Zürcher Weinland in northeastern Switzerland. Geoscientific information has been used to a wide extent for the demonstration of siting and engineering feasibility, and for the demonstration of long-term safety. It is shown that the selected area in the Zürcher Weinland fulfils the fundamental requirements placed on a siting area for a deep geological repository and that, in terms of the Opalinus Clay host rock option, the geological environment is advantageous.
Project Opalinus Clay (Entsorgungsnachweis) - Illustrating the Safety and Robustness of the Proposed Disposal System for SF, HLW and Long-lived ILW
Authors: Johnson L. H. , Schneider J. W. , Zuidema Piet , Gribi P. , Mayer G. , Smith P. A.
Published: April 2011

Nagra (the Swiss National Cooperative for the Disposal of Radioactive Waste) has completed a study to determine the suitability of Opalinus Clay as a host rock for a repository for spent fuel (SF), high-level waste from reprocessing (HLW) and long-livedintermediate-level waste (ILW). The proposed siting area is in the Zürcher Weinland region of Northern Switzerland. A repository at this site is shown to provide sufficient safety for a spectrum of assessment cases that is broad enough to cover all reasonable possibilities for the evolution of the system. Furthermore, the system is robust; i.e. remaining uncertainties do not put safety in question.
Scientific Arguments for New – Deterministic Approach to HLLLW Management
Authors: Ninkovic Marko M. , Raicevic Jagos J.
Published: April 2011

One of the greatest challenges in the use of nuclear energy is the high radioactive long-lived waste which is generated during production. It must be dealt with safely and effectively. While technical solutions exist, including deep geological repositories, progress in the disposal of radioactive waste has been influenced, and in many cases delayed, by public perceptions about the safety of the technology. One of the primary reasons for this is the long life of many of radionuclides, actinides and fission products, with half-lives on the order of a hundred thousand to a millions years. Problems of perceptions could be reduced significantly, according to our and many others author's opinion, if there were a way to burn or destroy the most toxic long-lived radioactive wastes. As there are no industrial methods for waste destroying today, in this paper it was suggested a new hybrid, deterministic approach: instead of final waste disposal, long-termed but yet temporal storage only, striving towards final destruction once the appropriate conditions are maintained. This new or modified old approach could affect current HLLLW management and related activities in: changes of processing technology; prolonging the time period of waste storage at temporal depositories; increasing the investment into research regarding the methods and technologies for destructions of these materials, and slowing down the investments into the very expensive final disposal repositories. It is authors' opinion that such deterministic, conceptual approach would contribute the reviving interest in nuclear energy, all over the world and especially in small and developing countries.
In Situ Sintering of Waste Forms in an Underground Disposal Environment
Authors: Ojovan Michael I. , Gibb Fergus G. F. , Lee William E.
Published: April 2011

A waste management scheme is described, which aims to utilise the ambient pressure of a disposal environment, its radiation shielding and extended time of storage to ensure reliable immobilisation of radioactive waste in a glass composite or polycrystalline matrix form. The conditions required for natural sintering of the waste form in the repository are assessed for viscous flow and grain boundary diffusion mechanisms. In situ sintering of materials in the repository creates geochemically stable materials in equilibrium with the disposal environment ensuring a higher degree of safety compared to existing approaches.
Leaching Behavior of Unirradiated High Temperature Reactor (HTR) UO2-ThO2 Mixed Oxides Fuel Particles
Authors: Landesman Catherine , Delaunay Sandra , Grambow Bernd
Published: April 2011

The dissolution rate of small UO2, ThO2 and mixed UO2–ThO2 particles, representative of unirradiated HTR fuel, are investigated in the pH range 1.7 to 5.5 under oxic conditions. For UO2 particles, the dissolution is kinetically control while for ThO2 particles, a solubility control mechanism seems to prevail for pH > 2. In the mixed oxides UO2–ThO2 particles, a selective release of uranium is observed, which could be either the result of a dissolution/precipitation mechanism in which thorium reprecipitate as oxide or hydroxide phase, or a result of a higher accessible surface area. Under oxic conditions, uranium may be considered as a tracer for the other soluble elements. So, assuming constant conditions with time, one can estimate from these preliminary results that unirradiated thorium based fuel kernels seem to present intrinsic confinement properties for 15000 years relative to soluble elements.
Evaluation of an alternative technique for the fabrication of direct detector X-ray imagers: spray pyrolysis of lead iodide and mercury iodide
Authors: Condeles J. F. , Ugucioni J. C. , Mulato M.
Published: April 2011

This work discusses the new use of an old deposition technique: spray pyrolysis. The objective is the deposition of thin films of lead iodide and mercury iodide and their future use as photoconductors in medical X-ray digital imagers. We discuss the main advantages and limitations of the deposition process comparing both materials. The final thin films are structurally investigated using X-ray diffraction and microscopy. The deposition technique seems to be very promising for the future development of large area radiation detectors.
A Phase Diagram for Morphology and Properties of Low Temperature Deposited Polycrystalline Silicon Grown by Hot-wire Chemical Vapor Deposition
Authors: Richardson Christine E. , Mason Maribeth S. , Atwater Harry A.
Published: April 2011

The fabrication of low temperature polycrystalline silicon with lifetimes close to single crystalline silicon, but with internal surface passivation similar to that observed in deposited microcrystalline silicon, is a promising direction for thin film polycrystalline silicon photovoltaics. To achieve this, large grains with passivated grain boundaries and intragranular defects are required. We investigate the low-temperature (250-550°C) epitaxial growth of thin silicon films by hot-wire chemical vapor deposition (HWCVD) on Si(100) substrates and large-grained polycrystalline silicon template layers formed by selective nucleation and solid phase epitaxy (SNSPE). Using reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have observed epitaxial, twinned epitaxial, mixed epitaxial/polycrystalline and polycrystalline phases in the 50 nm–15 μm thickness regime. HWCVD growth on Si(100) was performed using a mixture of diluted silane (4% in He) and hydrogen at a H2/SiH4 ratio of 50:1 at substrate temperatures from 300–475°C. We will discuss the relationship between the microstructure and photoconductive decay lifetimes of these undoped layers on Si(100) and SNSPE templates as well as their suitability for use in thin-film photovoltaic applications.
Effects of Facet Growth and Nucleation on Microcrystalline Silicon by Numerical Model
Authors: Kobayashi Yasuyuki , Satake Koji
Published: April 2011

We have presented a model of microcrystalline silicon (μc-Si) growth based on the Van der Drift model. The model needs growth velocities of the facets (100) and (111), an amorphous silicon growth velocity and a grain nucleation rate. The growth velocity ratio of the facets, (100) and (111), determines the preferred orientation and the morphology of the μc-Si film, especially oriented to (110). As the grain nucleation rate increases, the ratio of the living grain number to the total grain number decreases and the crystallinity increases, so the grain nucleation rate governs the trade-off relation of the μc-Si cells between decreasing the open circuit voltage and increasing the short circuit current as the crystallinity increases.
Evaluation of Ar-Diluted Silane PECVD for Thin Film Si:H Based Solar Cells
Authors: Selvan J. A. Anna , Li Yuan-Min , Li Liwei , Delahoy Alan E.
Published: April 2011

Dilution by Ar of silane plasma has been reported to increase the stability of a-Si:H films. A critical question is whether Ar diluted i-layers offer higher stabilized solar cell efficiencies than the conventional hydrogen dilution method. We have fabricated a-Si:H p-i-n solar cells with RF-PECVD i-layers by Ar dilution of silane. Ar dilution ratio (ADR, Ar/SiH4), RF power,pressure, and i-layer thickness were varied. At low ADR < 20, such solar cells show comparable initial efficiencies and stability as those devices having H2-diluted i-layers of similar thickness. For cells made with ADR > 20, the initial efficiency decreases dramatically with further increase in Ar dilution, and light soaking causes only mild changes in efficiencies. The stabilized efficiencies of cells made with high ADR are inferior to the cells produced with low ADR or cells prepared by H2 dilution. Further, Voc of solar cells made with high ADR (> 50) decreases substantially in ambient, indicating a porous microstructure susceptible to oxidation. While thermal annealing improves the Voc, a full recovery of Voc is made by accelerated light soaking.

The combination of high power and high ADR can lead to nanocrystalline silicon (nc-Si:H) growth, although nucleation is much more difficult to attain by the Ar dilution method compared to hydrogen dilution. We have succeeded in fabricating p-i-n solar cells with nc-Si:H i-layers prepared by the Ar dilution approach. The double dilution by Ar and hydrogen of silane (Ar+H2+SiH4) can result in nc-Si:H i-layers with enhanced long wavelength spectral response compared to devices incorporating nc-Si:H i-layers grown by H2 dilution only. The nc-Si:H solar cells with Ar+H2 diluted i-layers exhibit no light-induced degradation.

Using energetic Ar-rich plasma, in a process much simpler than the traditional nc-Si:H technique, doped a-Si:H thin layers can be prepared to form excellent tunnel junctions for multi-junction solar cells. We demonstrate such a novel, non-contaminating tunnel junction in tandem a-Si/a-Si and a-Si/nc-Si solar cells entirely fabricated in a single-chamber RF-PECVD system.
Atomistic Modeling of Ion Beam Induced Defects in Si: From Point Defects to Continuous Amorphous Layers.
Authors: Pelaz Lourdes , Marqués Luis A. , López Pedro , Santos Iván , Aboy María
Published: April 2011

We present an atomistic model that describes the evolution of ion induced damage ranging from individual defects to continuous amorphous layers. The elementary units used to reproduce the defective zones are Si interstitials, vacancies and the IV pair, which is a local distortion of the Si lattice without any excess or deficit of atoms. More complex defect structures can be formed as these elementary units cluster. The amorphous pockets are treated as agglomerates of IV pairs, whose recrystallization rate depends on the local density of these defects. The local excess or deficit of atoms in the amorphous regions experiences some rearrangement as recrystallization takes place. In sub-amorphizing implants amorphous pockets are disconnected and when they recombine, they leave behind the local excess of Si interstitials and vacancies. When a continuous amorphous layer initially extends to the surface, the excess or deficit atoms within the amorphous layer are swept towards the surface where they are annihilated and only the defects beyond the amorphous-crystalline interface remain.
Measurements of Ultra-Shallow Junction (USJ) Sheet Resistance with a Non-Penetrating Four Point Probe
Authors: Hillard Robert J. , Mazur Robert G. , Alexander William J. , Ye C. Win , Benjamin Mark C. , Borland John O.
Published: April 2011

An accurate method to measure the four point probe (4PP) sheet resistance (Rs) of USJ Source-Drain structures is described. The new method utilizes Elastic Material probes (EM- probe) to form non-penetrating contacts to the silicon surface. The probe design is kinematic and the force is controlled to ensure elastic deformation of the probe material. The probe material is selected so that large direct tunneling currents can flow through the native oxide thereby forming a low impedance contact. Sheet resistance measurements on USJ implanted P+/N structures with SIMS junction depths as shallow as 15 nm have been measured. The sheet resistance values obtained with the new EM-probe 4PP method were found to be consistent with expectations. In this paper, the method will be demonstrated on a variety of implanted USJ structures.
Erbium-Silicided Source/Drain Junction Formation by Rapid Thermal Annealing Technique for Decananometer-Scale Schottky Barrier Metal-Oxide-Semiconductor Field- Effect Transistors
Authors: Jang Moongyu , Kim Yarkyeon , Shin Jaeheon , Park Kyoungwan , Lee Seongjae
Published: April 2011

The stable growth conditions of erbium-silicide on silicon-on-insulator (SOI) are investigated considering annealing temperature, SOI and sputtered erbium thickness. From the sheet resistance measurement, X-ray diffraction and Auger electron spectroscopy analysis, the optimum annealing temperature is determined as 500°C. Also, for the stable growth of erbium- silicide on SOI, the sputtered erbium thickness should be less than 1.5 times of SOI thickness. As the SOI thickness decreases below this critical thickness, erbium-rich region is formed at the erbium-silicide and buried-oxide interface. By applying the optimized erbium-silicide growth conditions, 50-nm-gate-length n-type SB-MOSFET is manufactured, which shows the possible usage of erbium-silicide as the source and drain material in the n-type Schottky barrier MOSFETs for decananometer regime applications.