bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of inxGa1-xAs Crystals Grown by Lpee on Patterned GaAs Substrates
Authors: Bryskiewicz T. , Jiran E. , Bryskiewicz B. , Buchanan M.
Published: April 2011

InxGa1-xAs crystals, 0 < x < 0.2, have been successfully grown by LPEE on the GaAs substrates which, prior to growth, were coated with SiO2 layer and patterned by photolithography. The ternary seeds originated in the oxide free seeding windows, 2 – 20 μm wide and 100 μm apart, extended over SiO2 coating and merged to result in a continuous, monocrystalline layer with no apparent trace of boundaries of the merging islands. A considerable improvement in structural perfection of the ternary crystals has been achieved: the FWHMs of the rocking curves and dislocation density was in the 30 –40 arc seconds and low 105cm−2 range, respectively. Structural perfection of InxGa1-xAs crystals grown on patterned GaAs substrates is far superior to that of the ternary buffer layers grown by MBE or MOCVD.
Plasma Effects on Thin Film Microstructure
Authors: Naeem Munir D. , Rossnagel Stephen M. , Rajan Krishna
Published: April 2011

We have studied the effects of low energy ion bombardment on thin copper films. Evaporated, sputtered and CVD copper films (∼50 nm) were exposed to Magnetically Enhanced (ME) Ar plasmas. The microstructural changes (grain size) in the films were studied using Transmission Electron Microscopy (TEM).

Grain growth is observed in thin Cu films when the films are exposed to low energy (87 eV) Ar plasmas. The microstructural changes in sputtered and evaporated films are quite significant whereas the plasma bombardment has less effect on CVD films. These changes occur very rapidly and cannot be attributed solely to the thermal effects, especially at low RF power levels (500 W). The initial microstructure of the film has a significant effect on grain growth during plasma exposure.
Chemical Stability of Reactively Sputtered AlN with Plasma Enhanced Chemical Vapor Deposited SiO2 and SiNx
Authors: Cho Jaeshin , Saha Naresh C.
Published: April 2011

We have studied the chemical stability of reactively sputtered aluminum nitride film with plasma-enhanced chemical vapor deposited SiO2 and SiNx films. It was found that the PECVD SiO2 film reacted with A1N to form aluminosilicate (3Al2O3·2SiO2) at the SiO2/A1N interface after annealing above 550°C. The presence of Al-0 bonds at the SiO2/AlN interface was verified with x-ray photoelectron spectroscopy and x-ray induced Auger electron spectroscopy. The formation of aluminosilicate resulted in significant decrease in the wet etch rate of A1N layer. For SiNx/AlN/Si layered structure, no interfacial reactions were detected at the SiNx/AlN interface after annealing up to 850°C. These results confirm the thermodynamic predictions on the mutual stability of SiNx/AlN and SiO2/AlN.
Microstructure and Chemical Ordering in UHV-Deposited, Polycrystalline Coxpt1−x Alloy Films for Magneto-Optical Recording
Authors: Farrow R. F. C. , Weller D. , Toney M. F. , Rabedeau T. A. , Hurst J. E. , Harp G. R. , Marks R. F. , Geiss R. H. , Notarys H.
Published: April 2011

We report magneto-optical recording with 62 dB CNR (carrier-to-noise ratio) at 488 nm for quadrilayer structures comprising polycrystalline CoxPt1-x (x = 0.28) alloy films deposited on ungrooved, silicon nitride -coated glass discs, held at 300°C, by UHV evaporation. The key parameter controlling magnetic anisotropy of the films is substrate temperature during deposition. Polycrystalline films grown on amorphous silicon nitride have a large coercivity and full perpendicular remanance when grown at 300°C. Synchrotron X-ray diffraction data for polycrystalline films grown at 300 and 600°C confirm the presence of short-range compositional order, to the CoPt3-L12 phase in both cases. Such ordering can introduce an anisotropy in the distribution of Co-Co pairs in the alloy and is a possible source of the magnetic anisotropy.
Magnetic and Magneto-Optical Properties of Sputter-Deposited and Annealed Co-Pt Alloys
Authors: Park Sung-Eon , Jung Pu-Young , Kim Ki-Bum , Lee Seh-Kwang , Kim Soon-Gwang
Published: April 2011

We have produced Co1-xPtX (X = 0.53 and 0.75) alloy films using DC magnetron sputtering and investigated their magnetic properties using vibrating sample magnetometry(VSM) and Kerr hysteresis loop tracer. The as-deposited Co-Pt alloy films show a strong in-plane magnetization. By annealing the alloy samples, we have identified that the magnetic properties are drastically changed. While the magnetic properties of the Co0 25Pt0 75 alloy films show no noticeable changes, the coercivity and the squareness of the Co0.47Pt0.53 alloy films are drastically increased after annealing. Transmission electron microscopy(TEM) and x-ray diffractometry(XRD) analysis showed that CoPt(L10) and Co-Pt3 (L12) ordered phases, respectively, are formed in each case with a strong (11) texture. We suggest that the perpendicular magnetic anisotropy in the Co-Pt system does not depend on the mere textureness of the layer but strongly depends on the arrangement of Co and Pt at an atomic scale.
The Effect of Incident Kinetic Energy on Stress in Sputter-Deposited Refractory-Metal Thin Films
Authors: Vink T.J. , van Zon J.B.A.D. , Kools J.C.S. , Walrave W.
Published: April 2011

In magnetron sputter deposition the intrinsic stress in refractory-metal films changes from compressive to tensile on increasing the working-gas pressure. This pressure dependence is linked to the particle transport process from target to substrate during deposition. In this work we apply a Monte Carlo (MC) technique to simulate the transport of sputtered atoms and reflected neutrals in a background gas. Specific examples of Cr, Mo and W thin film growth in Ar and Ne gas ambients are presented. Trends in thermalization of the depositing atoms coincided with the observed trends in the compressive-to-tensile stress curves, for the different target and working-gas combinations studied. Furthermore, a quantitative correlation between the stress transition pressures and the incident kinetic energy of both sputtered atoms and reflected neutrals during film growth was found. In this case the contribution of the latter species was weighted with a relatively low factor.
Polycrystalline Silicon Layers for Shallow Junction Formation: Phosphorus Diffusion from In Situ Spike-Doped Chemical Vapor Deposited Amorphous Silicon
Authors: Krüger D. , Schlote J. , Röpke W. , Kurps R. , Quick Ch.
Published: April 2011

Shallow and lateral homogeneous delineated n+p-junctions were formed utilizing solid source diffusion from a deposited amorphous silicon layer with an in situ imbedded ultrathin phosphorus-rich zone. SIMS, AES, and TEM investigations were carried out to analyze the dopant behavior in correlation to morphological and structural changes during subsequent heat treatments. After heat treatments up to 950°C the layer remained flat, surface roughness was found to be less than 3 nm. Dopant pile up at the Si-layer/Si-substrate interface was observed and interpreted on the basis of segregation phenomena. From the time dependence the P segregation-pile-up was found to be diffusion limited except for a small starting period. The dopant concentration in the Si-substrate drops down over more than 2 orders of magnitude in a thickness range less than 20 nm.
Silicon Nitride Optimisation for a-Si:H TFTs Used in Projection LC-TVs
Authors: French I. D. , Curling C. J. , Goodyear A. L.
Published: April 2011

Multi-layer devices based on thin films in Large Area Electronics have different intrinsic and extrinsic properties that must be optimised to produce the correct physical shape of the device, in addition to having acceptable electrical characteristics. For instance it is quite easyto produce individual layers optimised for electrical performance that will physically “pull off” underlying films, or result in poor step coverage. The factors that must be considered include mechanical stress, etching rates and profiles, thickness and stoichiometry uniformity, and thermal budgets, as well as electrical characteristics. This paper gives an example of silicon nitride optimisation for use in a-Si:H TFT projection displays. Three different silicon nitride layers were included to give a storage capacitor, together with controlled etch profiles for step coverage. The layers were optimised with respect to several different parameters in the minimum number of depositions by the use of experimental design techniques.
Rapid Thermal Crystallization Of LPCVD Amorphous Silicon Films
Authors: Voutsas A. T. , Hatalis M. K. , Olasupo K. R. , Nanda A. K. , Alugbin D.
Published: April 2011

The crystallization of LPCVD a-Si by Rapid Thermal Anneal was investigated. RTA polysilicon films can find application in the fabrication of TFTs for AMLCDs, due to the lower thermal budget associated with fast crystallization at high temperatures. It was found that the grain size of the crystallized films decreases with the temperature, in the range of 700°C to 1100°C, while for higher temperatures the opposite trend is observed. The latter observation was attributed to the high thermal vibration of subcritical clusters, that was assumed responsible for the decline in the nuclei population at high annealing temperatures, combined with the faster crystalline growth rate at high temperatures. RTA silicon films were found to have lower intra-grain defect density, that may result in the improvement of the electrical characteristics of the polysilicon films.
Non-Invasive Measurement of Subcutaneous Fat Thickness in Beef Cattle
Authors: Taylor Leonard S. , Buck Nelson L.
Published: April 2011

The object of this project was the evaluation of microwaves as a non-invasive tool for determining the thicknesses of the fat layers directly beneath the hides of beef cattle. The motive for the project is the elimination of the cost of feeding cattle beyond the point at which the muscle is optimally marbled. The nature of the animals and the conditions for operation require a simple, rugged, non-invasive system. Modified open-ended microwave S-band coaxial cavities were applied as contact radiators to the surface of a three-layer sample composed of lean meat and fat tissue, which simulated the configuration of hide, fat and muscle on the outside of an animal. The lean and fat layers loaded the cavity, affecting the resonance frequency, bandwidth, and center-frequency reflection coefficient. Measurements were made with a network analyzer. An exact analysis of the microwave circuit has not been possible, but the in vitro laboratory tests show that a system based on this device can be used to measure subcutaneous fat layer thicknesses up to 16 mm beneath hides up to 16 mm thick.
Microwave Characterization of Materials Using a Vector Network Analyzer
Authors: Blackham David , Pollard Roger
Published: April 2011

The vector network analyzer provides a versatile tool for use in the microwave characterization of material permittivity and/or permeability. An understanding of network analyzer error sources can be leveraged into better measurement results. Vector error correction not only reduces the systematic errors but can also be used to remove the effects of dielectric dams in broadband transmission/reflection measurements.
High Temperature Dielectric Property Measurements - An Insight into Microwave Loss Mechanisms in Engineering Ceramics
Authors: Binnen J. G. P. , Cross T. E. , Greenacre N. R. , Naser-Moghadasi M.
Published: April 2011

It is now possible, in a number of laboratories worldwide, to make microwave dielectric property measurements at temperatures up to about 1500°C. These measurements have shown that the loss tangent, tanδ, of a wide range of engineering ceramics increases dramatically at elevated temperatures. The interaction between the ceramic material and the impurities present during processing can have a dramatic effect on both the ease with which the material is able to extract energy from the microwave field and on the properties of the final ceramic. While the effect of impurities on the ceramic properties is relatively well understood the effect of impurities on the microwave loss mechanisms at elevated temperatures is not. This paper will review some of the recent work on the high temperature microwave dielectric property measurements performed at Nottingham.
Numerical Models for the Sintering of Ceramics in a Multi-Mode Cavity
Authors: Dibben David C. , Fu Wai B. , Axas Ricky A.C. Met
Published: April 2011

We present two distinct approaches to the numerical determination of electromagnetic field intensities which must be known before the sintering of ceramics can be modelled in a multi-mode microwave cavity. In the first, a Finite Element Method, we employ edge elements to discretise Maxwell's Equations and apply the conjugate gradient algorithm to solve the resulting system of linear algebraic equations at each time step. The second, which is based on the Method of Lines, is a variant of the Finite Difference Time Domain technique and is used to transform Maxwell's Equations into a set of time-dependent ordinary differential equations. These methods are compared with the help of three examples: a small tray of mashed potatoes placed inside a cavity, a standard waveguide partially filled with a ceramic, and a cavity inhomogeneously loaded with the same material. The good agreements which we have found give us confidence in the soundness of either approach for use in numerical simulation work.
Calculation of Heating Patterns in Microwave Sintering using a 3D Finite-Difference Code
Authors: Tucker James , Iskander Magdy F. , Huang Zhenlong
Published: April 2011

Analysis of heating patterns in microwave sintering experiments provide information on the contributions of the various heat transfer components to the overall temperature pattern. Measured temperature patterns provide limited information on overall effects. Numerical simulations provide a cost effective way from which the effect of geometry, material properties and the presence of stimulus such as SiC rods or sheets on the heating pattern can be studied separately. Parametric studies allow us to identify the most significant properties and provide guidelines for the routine successful utilization of microwave sintering experiments. These guidelines may also facilitate the scale up and commercialization of microwave sintering.

In this paper we describe a thermal model that calculates the temperature distribution in ceramic samples and insulation under realistic microwave sintering conditions. The calculation process involves a two-step procedure. The first step is to calculate the microwave power deposition in the sample and surrounding insulation. 3D FDTD calculations, described in a companion paper[1,2], are used for this purpose. The other step involves calculation of the temperature distribution using a 3D finite-difference heat-transfer program developed in our Departments[3]. Results illustrating the effect of thickness of insulation and the placement of SiC rod susceptors in picket-fence arrangement are presented.
First Results on Large Cerium Fluoride Crystals in A Test Beam
Authors: Auffray E. , Beckers T. , Chipaux R. , Dafinei I. , Depasse P. , El Mamouni H. , Faure J.L. , Fay J. , Hillemanns H. , Ille B. , Lebrun P. , Lecoq P. , Nelissen J. , Nikl M. , Raghavan R. , Rosowsky A. , Schneegans M.
Published: April 2011

Cerium Fluoride, a new, dense, fast and radiation hard scintillator, is at present the favored candidate for high-resolution calorimetry at future colliders. This crystal has been extensively studied – in particular by the Crystal Clear Collaboration – and the conditions for production of large, high-quality crystals are now being optimized in seven firms all over the world. Recently the collaboration has received several CeF3 crystals, up to 17cm long, from three companies. A small assembly of such crystals with silicon photodiode readout was exposed to high energy electrons and muons in the H2-beam of the SPS at CERN. The results of these tests with longitudinally segmented towers are presented and discussed, in particular in terms of light yield and energy resolution.
Overview of the Major Phosphor Technologies
Authors: Yocom P. Niel
Published: April 2011

Phosphors are ubiquitously present in our everyday environment. The most common uses are in fluorescent lamps and display devices; e.g., TV tubes and computer displays. In addition, phosphors are used in medical radiology to transform the x-ray energy to light that is recorded on film for diagnostic purposes. The types of phosphors, mechanisms of operation, and future needs for these major phosphor technologies will be surveyed. In addition, brief mention will be made of some of the minor uses of phosphor materials.
Microstructural Characterization of Creep Tested Cryomilled NiAl-13vol. % AlN
Authors: Garg A. , Whittenberger J. D. , Aikin B. J. M.
Published: April 2011

Cryomilling of prealloyed NiAl powders, followed by extrusion, has been used to produce a particulate strengthened NiAl-13vol.% AlN material. At 1300 K, the compressive strain rate-flow stress diagram has two distinct deformation regimes, with the transition occurring near 150 MPa. The low and the high stress regimes have power law creep exponents of ∼ 6.1 and 14.2, respectively. Microstructural characterization of the as-extruded and tested samples has been performed to develop an understanding of the superior mechanical properties of the material. The microstructure of the as-extruded material was inhomogeneous and consisted of mantle regions containing a mixture of small NiAl grains (diameter ∼ 50–150 nm) and fine AlN particles (size ∼ 5–50 nm) that surround larger NiAl grains (diameter ∼ 0.3–8.0 μm) which were mostly particle free. In the low-stress regime, samples tested to steady state exhibited a structure composed of subgrain boundaries in the particle-free NiAl grains. In addition, some of the subgrains had developed a well defined dislocation network. AlN patricles occasionally found within large NiAl grains acted as pinning centers for dislocations. Small NiAl grains and the AlN particles constituting the mantle coarsened during these tests. In the high-stress regime, samples tested to steady state exhibited a high density of dislocations in most of the particle-free NiAl grains. Subgrain boundaries were found occasionally but dislocation networks were rare. The AlN particles had not significantly coarsened due to the shorter times at temperature.
Vapor Phase Synthesis of Ti Aluminides and the Interfacial Bonding Effect on the Mechanical Property of Micro-Composites Reinforced by Pyrolized SiC Fibers
Authors: Suzuki T. , Umehara H. , Hayashi R.
Published: April 2011

Vapor phase processings for manufacturing near-net-shaped composites, continuous fiber reinforced composites or lamellar composite will be hopeful methods. The method for synthesis of TiAl by a magnetron sputtering using a multiple target has been successfully established, and the tensile property of the microcomposite with SiC fibers has been studied. The TiAl produced by a vapor phase processing was evaluated by Auger electron spectroscopy and the x-ray analysis. The tensile strength properties of the SiC/TiAl microcompositesof which the interface bonding was controlled with the powers of sputtering were estimated. The properties of SiC/TiAl microcomposites are decreasing with increasing the sputtering power. The irradiation-cured SiC fiber has better compatibility with TiAl than the oxidation-cured SiC fiber. The strength of the microcomposite has been improved with using a thin C-coated irradiation-cured SiC fiber.
The EL Berrocal Project: Geological Characterisation and Radionuclide Migration Studies in a Fractured Granitic Environment
Authors: Miller W. M. , Pérez Villar L. , Gómez P. , Ivanovich M. , de la Cruz B. , Rivas P. , Hernán P. , Carrera J. , Guimerà J. , Holmes D. , Avogadro S. , Fernández J.-M. , Bruno J.
Published: April 2011

El Berrocal is an abandoned uranium mine in a mineralised quartz vein hosted by a Hercynian granite in central Spain. This mine is the focus of an international project to characterise and model natural elemental migration in a fractured-rock environment as an aid to understanding and predicting processes that may occur in a geological repository for radioactive wastes.

Uranium in the mineralised quartz vein has been shown to have originated from the orthomagmatic uraninite in the granite with the elemental removal and migration occurring predominately by hydrothermal fluids. Mobilisation of uranium from the mineralised quartz vein and from granite adjacent to hydraulically-active fractures away from the vein occurred over the geologically-recent past and in the present-day. The most recent mobilisation is evidenced by dissolution features seen in SEM photomicrographs; mineral growth and sorption signatures identified by enhanced uranium concentrations on the surfaces of preexisting minerals; and measured disequilibrium in the uranium series for whole rock close to fracture walls.

Present-day groundwaters in the studied area are young meteoric waters. They are generally calcium-sulphate enriched, oxidising and mildly acidic near the surface, becoming more bicarbonate-rich with near neutral pH in the deeper zones, except around the mineralised vein where the waters are acid (pH around 3) due to oxidisation of the sulphide minerals. No deep, chemically-reducing groundwaters have yet been identified in the El Berrocal boreholes.
Development of a Conceptual Flow-Path Model of Nuclide Migration in Crystalline Rock - A Case Study at the Kamaishi in-Situ Test Site, Japan -
Authors: Osawa H. , Sasamoto H. , Nohara T. , Ota K. , Yoshida H.
Published: April 2011

The objective of this study is to develop a conceptual flow-path model for nuclide migration in fractured crystalline rock at the Kamaishi In-Situ Test Site because improvement of existing models of matrix diffusion |e.g. 1,2|, based on realistic geological data, is necessary for a better understanding of nuclide migration into rock matrix. Data from field observations indicate that fractures at the Kamaishi In-Situ Test Site can be classified into three types; type A with a zone of fracture fillings, type B with a zone of fracture fillings and an altered zone, type C consisting of several fractures with a zone of fracture fillings and an altered zone. Fracture type B was studied in detail by laboratory experiments because type B is predominant in the studied area with more than 60 % of a total of 400 fractures observed in the fracture mapping. Data from laboratory experiments on core, crosscutting a water-bearing fracture and the surrounding rock, indicate that the zone of fracture fillings and the altered zone in the vicinity of the fracture contain flow-paths in which nuclides can migrate and be trapped. The fracture fillings contain more interconnected and permeable flow-paths than the altered and unaltered zones. This implies that migrating nuclides can access flow-paths in the altered zone. The altered zone adjacent to the zone of the fracture fillings contains flow-paths such as microfractures, cracks within quartz, and grain boundaries between altered minerals, through which nuclides will migrate from the fracture fillings into the altered zone and be trapped. The fracture fillings and the specimen of the altered zone have higher sorption capacity than the specimen of the unaltered zone. These data suggest that retention of nuclides can be expected in the vicinity of the fracture. In conclusion, a conceptual flow-path model consisting of a zone of fracture fillings, an altered zone, and an unaltered zone has been developed for a better understanding of nuclide migration in fracture type B.
Radionuclide Release from the Kbs-3 Repository-Sensitivity to the Variability of Materials and Other Properties
Authors: Romero L. , Andersson Å. , Moreno L. , Neretnieks I.
Published: April 2011

Radionuclides leaking from a canister spread into the backfill material surrounding the canister and then migrate through different pathways into the mobile water in the rock fractures. In order to quantify uncertainties regarding the release to the far field, a sensitive analysis is performed for the uncertainties in the parameters governing the release.

For nuclides escaping through a damaged canister in a repository of the type KBS-3 [1], most nuclides migrate through the pathways appointing to the fracture intersecting the deposition hole and the disturbed zone below the tunnel.

The sensitivity analysis showed that the grade of impact on the release of uncertainties in the parameters cannot be generalized for all nuclides, however, some patterns of the influence can be given. Uncertainties in the hole size and uranium solubility for nuclides embedded in the matrix have a strong influence on the release. The adsorption capacity of the bentonite surrounding the canister and the hydraulic properties of the fractured rock in the short pathways to the mobile water have to be accurately known to reduce uncertainties in the release to the far field. For nuclides with a high diffusion coefficient in the bentonite, e.g. cesium and strontium, the hydraulic properties of the fractured rock nearest to the canister have to be well known. For the iodide, on the other hand, with a very low diffusion coefficient, uncertainties in the hydraulic properties have a very small effect on the release. The uranium release with a very high inventory is not affected by uncertainties in the hydraulic properties of the rock.

The released nuclide fraction through each pathway is not largely influenced by uncertainties in the transport properties of the backfill materials whereas uncertainties in the water flow rates in the zones in the rock where the water flows, have a strong influence on the nuclide release distribution.
Non-Conservative Assumptions in the 1992 Performance Assessment for the Waste Isolation Pilot Plant
Authors: Neill R. H. , Lee W. W.-L.
Published: April 2011

Performance/safety assessments have been conducted for the Waste Isolation Pilot Plant, a repository for transuranic waste in salt. We challenge two key assumptions in the 1992 Performance Assessment that led to non-conservative results. The predicted release rate of radionuclides appears underestimated due to the use of expert elicited solubilities. The overall release has been underestimated due to the use of improperly elicited human intrusion probabilities.
A New Approach to the Selection of Materials for Engineered Barriers and Appropriate Host Rocks for High Level Waste Disposal
Authors: Omelianenko B.I. , Nikonov B.S. , Ryzhov B.I. , Shikina N.D. , Yudintsev S.V.
Published: April 2011

Sorptive properties of weathered dunites, gabbro-diabases and basic volcanic rocks for Sr and Cs were studied. The results show that the sorptive capacities of these rocks are equivalent to or, in some cases, superior to industrial sorptive materials. Results of a uranium distribution study by fission-track radiography suggest that material from weathered basic rocks is characterized by high sorptive properties for uranium also. One can assume that other radionuclides of the transuranic group will be intensely sor-bed by the residuum of weathered basic rocks. Low-temperature hyd-rothermal transformation leads to sealing fissures of the basic rocks with highly sorptive minerals, for example, smectite, chlorite, serpentine, talc, zeolite, hydroxides of Fe, Ti, Mn. The process results in contemporaneous decreasing hydraulic conductivity and increasing sorptive capacity of the rocks. HLW disposal at the radiochemical plant “Mayak” is expected to be produced in deep wells situated in basaltic rocks. The safety of disposal is based on high sorptive properties of the crust of weathering and protective capacities of volcanic rocks. This method is not expensive and may allow the disposal of HLW in the near future.
The Long-Term Stability of Becquerelite
Authors: Finch R.J. , Suksi J. , Rasilainen K. , Ewing R.C.
Published: April 2011

Uranium-series disequilibria data, in conjunction with petrographic analyses, indicate that the uranyl oxide hydrate becquerelite can persist for hundreds of thousands of years, possibly longer. Becquerelite probably forms continuously as ground water compositions permit and is resistant to U leaching by ground water. On the time scale of interest for the geologic disposal of spent UO2nuclear fuel, becquerelite is a long-lived sink for uranium in oxidizing, U and Ca-bearing ground waters. Such long-term stability also supports recent solubility experiments that indicate natural becquerelite has a lower solubility product than that determined for synthetic becquerelites.
Performance Analysis of Copper Canister Corrosion Under Oxidizing or Reducing Conditions
Authors: Worgan Karen , Apted Michael , Sjöblom Rolf
Published: April 2011

The finite-difference CAMEO code for modeling general corrosion of copper canisters is described. CAMEO represents the engineered barrier system and surrounding fractured host rock in 3-dimensional cylindrical coordinates. The time of containment failure is evaluated using CAMEO, as constrained by transport rates of corrodants to the canister or by transport rates of corrodant products away from the canister. Additional chemical processes explicitly modeled in CAMEO include 1) copper corrosion, and 2) kinetics of Cu(I) oxidation to Cu(II), both as a function of near-field pore water chemistry, specifically pH, Eh, and chloride concentration. The diffusional transport and sorption behavior of Cu(I) and Cu(II) are also separately incorporated.
Canister Filling Materials - Design Requirements and Evaluation of Candidate Materials
Authors: Oversby V. M. , Werme L. O.
Published: April 2011

SKB has been evaluating a copper/steel canister for use in the disposal of spent nuclear reactor fuel. The canister consists of an outer layer of about 50 mm thickness of copper to provide corrosion resistance and an inner layer of similar size to provide structural strength. Once the canister is breached by corrosion, it is possible that the void volume inside the canister might fill with water. Water inside the canister would moderate the energy of the neutrons emitted by spontaneous fission in the fuel. If the space in the canister between and around the fuel pins is occupied by canister filling materials, the potential for criticality is avoided. We have developed a set of design requirements for canister filling material for the case where it is to be used alone, with no credit for burnup of the fuel or other measures, such as the use of neutron absorbers. Requirements were divided into three classes: essential requirements, desirable features, and undesirable features. The essential requirements are that the material fill at least 60% of the original void space, that the solubility of the filling material be less than 100 mg/l in pure water or expected repository waters at 50°C, and that the material not compact under its own weight by more than 10%. In this paper we review the reasons for these requirements, the desirable and undesirable features, and evaluate 11 candidate materials with respect to the design requirements and features. The candidate materials are glass beads, lead shot, copper spheres, sand, olivine, hematite, magnetite, crushed rock, bentonite, other clays, and concrete. Emphasis is placed on the determination of whether further work is needed to eliminate uncertainties in the evaluation of the ability of a particular filling material to be successfully used under actual conditions, and on the ability to predict the long-term performance of the material under the repository conditions.
Interactions Between Np-Doped Synroc and Boom Clay
Authors: Hart K. P. , Robinson B. J. , Payne T. E. , Van Iseghem P. , Lemmens K.
Published: April 2011

Leaching experiments with deionised water at 70°C have been carried out to ascertain the effect of oxidising and anaerobic conditions and the presence of Boom clay on Np release from Synroc.

The normalised solution leach rates of Np measured in these experiments are about a factor of 10 lower under reducing conditions than oxidising conditions and the presence of Boom clay was found not to enhance the leaching of Np from Synroc. Neptunium was found to be predominantly in the mobile fraction and was not removed from the leaching solutions significantly by filtration or ultrafiltration.
Synthesis and Characterization of A Metastable (SiC)aN4 Phase
Authors: Uslu C. , Park B. , Poker D. B.
Published: April 2011

A metastable C-Si-N compound has been synthesized by high dose N+ implantation into polycrystalline /8-SiC (cubic phase). The thin films formed upon 100 keV implantations were characterized with respect to various ion doses and target temperatures. X-ray diffraction with a position-sensitive detector and cross-sectional transmission electron microscopy revealed that the as-implanted surfaces contained ∼0.15 jttm thick continuously-buried amorphous layers. Rutherford backscattering spectroscopy showed that the peak concentration of nitrogen saturated up to approximately 54 at. % with increasing doses, suggesting a new phase formation.
Ion irradiated polystyrene: transport and hardness Measurements
Authors: Folk II Robert H. , Luzzi David E. , Composto Russell J. , Rothmant J. Bruce
Published: April 2011

Thin films of polystyrene (PS) were modified using oxygen (0+) and helium (He+) ions and analyzed via diffusion and hardness measurements. One micron thick films were modified with 400 keV 0+ and He+ ions. The fluence was varied from 1.7 to 34.0 x 1013 ions/cm2 for both incident ions. Following irradiation, some samples were covered with a probe layer of deuterated PS, and annealed at 170°C. Using forward recoil spectrometry, the diffusion of d-PS and the PS hydrogen loss were measured as a function of incident ion species and dose. For all modified samples, d-PS diffusion was significantly retarded compared to the unmodified case. Atomic force microscopy measurements on the as-cast and irradiated PS samples suggest that the relative hardness of the 0+ modified PS was greater than that of the as-cast PS. The force-displacement curves of the modified PS displayed no hysteresis whereas the as-cast PS had a large hysteresis due to tip penetration and tip-polymer adhesion. These results indicate that ion irradiation decreases transport in PS and increases PS hardness.
UV Laser Deposition of Thin Films at 248 NM for Phase Shifting Mask Repair
Authors: Farkas Janos , Comita Paul B. , Novotny Vlad , Miller Dolores , yeng Baurui , Cohen Martin
Published: April 2011

Laser-induced deposition of controlled quality silicon dioxide and thin metallic films was investigated at 248 nm for phase shifting mask (PSM) repair. SiOx (x-1.5-2) films were deposited from single precursors, such as triethoxyvinylsilane (TEVS), tetraallyloxysilane (TAOS), di-t-butoxy-diacetooxysilane (TBSA) with no oxidizing coreactant. A deposition rate of 0.25 A/pulse was possible at room temperature, with excellent optical properties (n-1.47, k-0.05). Metallic films were deposited from tungsten, gold, molybdenum and chromium compounds. The results showed that the optical transmission and phase-shifting properties of the deposits can be matched well to the films commonly used in phase shifting masks.
Temperature Dependent Growth of LaAIO3 Films on YBa2Cu3O7 C-Axis Films for Multilayer Structures
Authors: Hawley M.E. , Houlton R.J. , Raistrick I. A. , Garzon F.H.
Published: April 2011

Fabrication of ultra smooth films, free of micro-shorts, is essential to the development of High Temperature Superconducting (HTS) thin film devices. One such example is a SNS junction consisting of two HTS layers separated by a uniformly smooth continuous barrier material. Other schemes under consideration require multilayer structures of up to 5 - 7 epitaxially grown layers of complex oxide material. Successful fabrication of such devices necessitates understanding the epitaxial growth of polycrystalline oxide films on polycrystalline film templates. Toward this end we have developed a set of deposition parameters that produce high quality epitaxial insulating layers suitable for HTS device applications. All films in this study were grown by off-axis RF magnetron sputter deposition. LaAlO3 films were deposited over MgO grown YBa2Cu3O7 (YBCO) c-axis thin films at temperatures ranging from 200 to 700C and on virgin substrates at 600C. Atomic Force Microscopy, eddy current measurements, and x-ray diffraction techniques were used to monitor the effect of growth conditions on the resulting film crystallinity, nanostructure, and electrical properties.

Ex-situ interrupted growth characterization of these materials has yielded new insight into the processes that control the growth mechanism and resulting microstructure. All films were polycrystalline. Below 600C, LaAlO3 films were not epitaxial while films grown at 650C showed some <200> orientation. The shape of the underlying YBCO film is most clearly evident for the film grown at 400C. Surface roughness depended on the appearance of crystals on the film surface. The superconducting properties of the underlying YBCO film required O2 annealing prior to deposition of the LaAlO3 layer.
Structure of Oxides Grown on Zr-20Nb Alloy
Authors: Woo O.T. , Lockwood D.J. , Lin Y.P. , Urbanic V.F.
Published: April 2011

Oxides grown on Zr-20Nb were characterized by Raman Spectroscopy (RS), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). These oxides were steamformed at 400°C, water-formed at 360 °C and at 300 °C, and air-grown at 400°C. For the oxides grown after relatively short exposures at 360°C and at 400°C, Raman spectra revealed broad peaks at 260 and 660 cm− indicating a crystal structure with high symmetry. Comparison with reference Raman spectra of cubic (c), tetragonal (t), and monoclinic (m) ZrO2 suggested that the oxide was predominantly nearly-cubic (tetragonal with c/a ratio ≈ 1), with minor amounts of moxide. The tetragonality is found to be consistent with TEM analyses and XRD results which showed the presence of a doublet near 2θ ° 74°. The crystal structure in the short-term exposed oxides is interpreted in terms of a tetragonal distortion arising from the displacement of oxygen atoms within the cubic ZrO2 crystal structure. For oxides grown after longer periods of exposure at 300°C and at 400°C, RS and XRD indicate increased amounts of m-oxide.
Composition Dependence of The Electrical Conductivity of n-p Ceramic Composite
Authors: Jun Seok-Taek , Choi Gyeong-Man
Published: April 2011

Electrical properties of ZnO-CuO ceramic composites with varying composition were investigated. The electrical conductivity increased with increasing CuO volume fraction between 1 mol% to 95 mol%. Impedance response showed three semicircles, indicating three resistive elements contributing to the total resistance of the composite. A new model based on the equivalent circuits was developed to explain the contribution of grain boundaries to the resistance of the composite. The change of electrical conductivity was explained by the probability change of two equivalent circuits.
Rare-Earth Doped Silicon-Rich Silica: Evidence for Energy Transfer between Silicon Microclusters and Rare-Earth Ions
Authors: Kenyon A.J. , Trwoga P.F. , Federighi M. , Pitt C.W.
Published: April 2011

We report the fabrication of rare-earth doped silicon-rich silica thin films by PECVD. The films exhibit absorption edges in the visible region of the optical spectrum consistent with the presence of silicon microclusters. Weak visible photoluminescence due to silicon microclusters is observed. In addition, strong luminescence from the rare-earth ion is obtained even when excited away from characteristic absorption bands; indeed, the luminescence intensity is largely independent of excitation wavelength below 514 nm. We ascribe this to excitation of silicon microclusters followed by an efficient transfer of energy to the rare-earth ions.

The very broad absorption of this material opens up the possibility for flashlamp-pumped optoelectronic devices. In addition, we report the fabrication of silicon-rich silica films by PECVD. We show that the optical properties of these films are consistent with the presence of silicon microclusters and show absorption spectra similar to those of the rare-earth doped silicon-rich silica samples. This supports the hypothesis that the principal absorbing species in the rare-earth doped films is microclustered silicon
Generation and Structural Analysis of Silicon Nanoparticles
Authors: Li Ping , Sattler Klaus
Published: April 2011

We have generated 20 to 100 nm sized silicon nanoparticles and analyzed their morphologies using an atomic force microscope (AFM). The particles are formed by deposition of silicon vapor onto silicon wafers and highly oriented pyrolytic graphite (HOPG). On silicon substrates, the particles are close to spherical with relatively narrow size distributions and they are randomly located. On graphite substrates the particles are arranged in chains. Within the chains they show strong deformations in the contact areas. We relate this to covalent inter-particle interactions.
Some Natural Three-and Lower-Dimensional Semiconductor Systems with Metal-Halide Units
Authors: Papavassiliou George C. , Koutselas I.B. , Terzis A. , Raptopoulou C.P.
Published: April 2011

The structural, optical and related properties (i.e. photoluminescence, photoconductivity etc.) of some natural three- and lower-dimensional semiconductor systems based on metal halides are briefly reviewed and some new results are reported. A blue shift of the excitonic bands was observed by decreasing the dimensionality or the size of the materials active part. The results are similar to those obtained from conventional semiconductor systems (e.g. GaAs, CdS, PbI2) by decreasing artificially the dimensionality or decreasing the size.
Photoluminescence Excitation Spectroscopy Of Porous Silicon
Authors: Kux A. , Ben Chorin M.
Published: April 2011

We combine photoluminescence excitation spectroscopy and photoconductivity to extract information about the bandgap and particle size distribution of porous silicon. This allows us to specify the influence of size dispersion and to show that different methods to determine absorption probe different parts of the size distribution.
Structural and Electrical Properties of Undoped Microcrystalline Silicon Grown by 70 MHz and 13.56 MHz PECVD
Authors: Flückiger R. , Meier J. , Crovini G. , Demichelis F. , Giorgis F. , Pirri C.F. , Tresso E. , Pohl J. , Rigato V. , Zandolin S. , Caccavale F.
Published: April 2011

Microcrystalline silicon films deposited by plasma methods have an optical absorption for photon energies above 2.0 eV lower than a-Si:H films and can be efficiently doped with boron or phosphorus. The most widely used deposition technique is the 13.56 MHz PECVD. However quite recently µc-Si:H films were grown at high deposition rates by the 70 MHz PECVD. In this work the authors report on a comparison between µc-Si:H films deposited by both 70 MHz and 13.56 MHz techniques. Particular attention has been devoted to differences and similarities between structural, compositional and electrical properties of the films deposited with the two systems.
Study of Onion-Like Carbon (OLC) Formation from Ultra Disperse Diamond (UDD)
Authors: Kuznetsov Vladimir L. , Chuvilin Andrey L. , Butenko Yurii V. , Mal'kov Igor Yu. , Gutakovskii Anton K. , Stankus Sergey V. , Khairulin Raschid A.
Published: April 2011

Measurements of diamond bulk density change of carbon powder in the annealing of UDD to OLC (293-2400 K) was performed by irradiating the samples with a narrow beam of gamma quanta (137Cs gamma-ray source). The intermediates of UDD to OLC transformation were registered by high resolution TEM. The annealing products were also characterized by true density and specific area adsorption measurements. The structural rearrangement of UDD begins from the surface towards a crystal bulk. UDD annealing proceeds via particles composed of semi-spherical shells enclosed one-to-one with the rest of diamond core and quasispiral carbon shells. The influence of particle size on the temperature of UDD to OLC transformation was found.
Electronic Angular Momentum Effects in the Photophysical Behavior of Fullerenes
Authors: Argentine S. M. , Francis A. H.
Published: April 2011

The intensity of the electronic origin in the emission spectrum of C70 exhibits a strong solvent sensitivity. The intensity of this peak increases relative to the vibronic features as the dielectric constant of the solvent increases. This solvent dependence is explained by an extension of Platt's Perimeter Free Electron Orbital model. The fullerenes, in particular C60 and C70, possess a nearly spherical symmetry that gives rise to the presence of significant electronic orbital angular momentum. The unexpected spectral sensitivity is shown to arise from quenching of the electronic angular momentum by the solvent environment.
Hrem Lattice Image Simulations of Circular Cross-Sectional Multishell Carbon Nanotubes
Authors: Cullen S. L. , Morgan C.J. , Boothroyd C.B. , Humphreys C.J.
Published: April 2011

In recent years there has been much interest in a newly found member of the fullerene family, carbon nanotubes. As a result of the small dimensions of these structures much of the structural investigation has involved the use of HREM images of the tubes1−3. From these images it has been proposed that the idealised structure of a carbon nanotube comprises closed cylindrical coaxial shells of graphite in which each shell may have its own unique helical pitch due to the numerous ways in which a sheet of graphite may be rolled to form a cylinder. We have previously discussed HREM image simulations of the {100} fringes at the centre of nanotubes which assumed that the top and bottom faces of the tube were parallel4. In this paper attention is focused on image simulations for complete ideal tubes of circular cross-section in order to elucidate further the structure of the tubes. However, due to the complexity and large range of possible configurations and orientations of the tubes, we have not attempted to match the simulations to a particular tube. Instead we have chosen one representative structure and have varied the parameters of the tube in order to observe the effects on the image of the stacking of the shells relative to each other, tilt of the tube along the long axis and helical pitch of the shells. Features which occur in the simulations are compared qualitatively to experimental images.
Fluorescence of Cyclic Adducts of Fullerene
Authors: Lin Tsung-I , Lin Syh-Kun , Shiu Lung-Lin , Chien Kuo-Ming , Luh Tien-Yau
Published: April 2011

Five cyclic adducts C60C4H6, C60C5H6, C60NHCO2, C60NCO2Et, and C60CHCO2Et have been synthesized and their absorption and fluorescence spectral properties investigated and compared with those of the parent. Breaking the structural symmetry of C60 apparently resulted in enhancing the quantum yield two to three-folds in some adducts and thus made fluorescence much easier to be measured at room temperature. New absorption bands and altered fluorescence spectra were observed in the adducts. The Stokes' shifts of the adducts were small, about 4-5 nrm, compared to 68 nm for the parent compound. All the adducts exhibited a single fluorescence lifetime about the same as C60 (ca. 1.3 ns). Aliphatic solvents had little influence on the absorption or fluorescence spectral profile except on the molar absorptivity whereas aromatic and polar solvents strongly interacted with the adducts causing a peak broadening effect.