bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric Lead Zirconate Titanate and Barium Titanate Nanoshell Tubes
Authors: Luo Yun , Szafraniak Izabela , Nagarajan Valanoor , Wehrspohn Ralf B. , Steinhart Martin , Wendorff Joachim H. , Zakharov Nicolai D. , Ramesh Ramamoorthy , Alexe Marin
Published: April 2011

Wetting of the pore walls of porous templates is a simple and convenient method to prepare nanoshell tubes. Wafer-scale fabrication of ferroelectric lead zirconate titanate and barium titanate nanoshell tubes was accomplished by wetting porous silicon templates with polymeric precursors. The ferro- and piezoelectric properties of an individual ferroelectric nanoshell tube either of PZT or of BaTiO3 were electrically characterized by measuring the local piezoelectric hysteresis. A sharp switching at the coercive voltage of about 2 V was shown from the hysteresis loop. The corresponding effective remnant piezoelectric coefficient is about 90 pm/V. We have also prepared highly ordered arrays of free-standing ferroelectric nanoshell tubes obtained by partial etching of the silicon template. Such materials might be used as building blocks of miniaturized devices and could have a significant impact in the field of nano-electromechanical systems.
Nanostructured Oxide Films for High-Speed Humidity Sensors
Authors: Steele John J. , Harris Kenneth D. , Brett Michael J.
Published: April 2011

Miniaturized thin film humidity sensors were fabricated using nanostructured materials deposited by an advanced technique known as glancing angle deposition (GLAD). These sensors exhibited extremely fast desorption response times of less than 40 ms to steplike changes in humidity. Multiple response time measurements for various initial humidities have shown that the sensors maintain their rapid response at all levels of humidity.
Anomalous Magnetoresistance Behavior of Bismuth Antidot Arrays
Authors: Rabin Oded , Dresselhaus Mildred S.
Published: April 2011

Antidot arrays were formed in thin films of bismuth by the e-beam evaporation of the metal on the porous surface of porous anodic alumina templates. The magnetoresistance of the antidot array films was measured and compared to that of films deposited on glass slides. A significant difference in magnetoresistance behavior was observed, and this difference was attributed to the enhancement of the two dimensional weak antilocalization effect in the antidot arrays. Scattering rates were obtained by fitting the experimental results to the theoretical expression. The results indicate that the antidot morphology enhances the elastic scattering rate over the inelastic scattering rate.
Percolation in Multi-Wall Carbon Nanotube-Epoxy Composites Influence of processing parameters, nanotube aspect ratio and electric fields on the bulk conductivity
Authors: Sandler Jan K.W. , Windle Alan H. , Martin Christian A. , Schwarz Matthias-Klaus , Bauhofer Wolfgang , Schulte Karl , Shaffer Milo S.P.
Published: April 2011

A simple mechanical stirring process leads to charge-stabilised dispersions of aligned, substrate-grown, CVD-grown multi-wall carbon nanotubes in an epoxy resin. Subsequent sample processing, after the addition of the hardener, can be used to induce the nanotube agglomeration necessary to achieve electrically conductive bulk composites at low loading fractions. Both the nanotube percolation threshold and the resulting bulk conductivity can be adjusted by selection of suitable processing parameters and nanotube aspect ratio. This behaviour of aligned CVD-grown multi-wall carbon nanotubes allows lower electrical percolation thresholds than are possible with entangled multi-wall carbon nanotubes, single-wall carbon nanotube bundles, or carbon black in an epoxy matrix. Furthermore, the application of electric fields during composite processing induces the formation of aligned multi-wall carbon nanotube networks between electrodes dipped into the dispersion. Such composites show an electrical conductivity above the anti-static level and retain a degree of optical transmissivity.
Atom Probe Tomography Characterization of Thin Film Multilayers
Authors: Thompson G. B. , Miller M. K. , Banerjee R. , Fraser H. L.
Published: April 2011

As the individual layer of Ti is reduced in thickness in a Ti/Nb multilayered thin film structure, the Ti layer can undergo a change in phase stability fromhcptobcc. Due to its high spatial resolution, atom probe tomography (APT) is ideally suited to characterize the compositional variations in such thin film structures. A series ofhcpTi /bccNb andbccTi /bccNb multilayers have been sputtered deposited and prepared as APT specimens using a Focus Ion Beam (FIB) milling procedure. The APT results have shown a substantial interdiffusion of Nb into thebccTi layers to a pseudo-equilibrium concentration of approximately Ti-20at%Nb while maintaining a compositionally modulated interface. In contrast, thehcpTi layers indicated little Nb interdiffusion within the layers. Thermodynamic volumetric free energy modeling has indicated that this unexpected Nb interdiffusion facilitated thebccphase stability. The coupling of APT results to the pseudomorphicbccTi phase demonstrates the capability APT has in quantifying the compositional characteristics in these types of multilayered nanocomposite systems.
Structuring of Silicon Wafer Surfaces on the Sub-100 nm Scale by Hydrogen Plasma Treatments
Authors: Job R. , Ma Y. , Ulyashin A. G.
Published: April 2011

Hydrogen plasma treatments applied on standard Czochralski silicon (Cz Si) wafers cause a structuring of the surface regions on the sub-100 nm scale, i.e. a thin ‘nano-structured’ Si layer is created up to a depth of ∼ 150 nm. The formation of the ‘nano-structures’ and their evolution in dependence on the process conditions was studied. The impact of post-hydrogenation annealing on the morphology of the structural defects was studied up to 1200 °C. The H-plasma treated and annealed samples were analyzed at surface and sub-surface regions by scanning electron microscopy (SEM), atomic force microscopy (AFM), and μ-Raman spectroscopy.
TEM and DOE Optimization Studies of Electrospun Polycarbonate Nanofibers
Authors: Kattamuri Nirupama , Sung Changmo
Published: April 2011

Electrospinning of polycarbonate with solvent mixtures of THF (Tetrahydrofuran) and DMF (Dimethylformamide) has been performed. The effect of various process parameters like voltage, concentration, flow rate and distance has been investigated to yield uniform polycarbonate nanofibers with minimal bead densities. The temperature and humidity have also been carefully monitored for all the runs. The Design of Experiment (DOE) has been conducted with the help of Minitab software to find the most significant parameter for obtaining uniform beadless nanofibers. These uniform nanofibers can then be used in future work to produce TiO2 nanotubes.
Preparation of Fe-Pt Nanowires through Anodic Oxidation of Sputtered Aluminum on Glass Surface
Authors: Inoue Satoru , Chu Song-Zhu , Wada Kenji , Kanke Yasushi
Published: April 2011

New process for the preparation of Fe-Pt nanowires has been developed through anodic oxidation and electro deposition technique. Aluminum thin film sputtered on ITO thin film on a glass surface was decomposed into alumina by anodic oxidation technique. The anodic alumina layer possessed nanometer size pore array standing on the glass surface. The barrier layer at the bottom of nanopores was removed by acid etching to attain DC field smooth electro deposition. Fe-Pt components were introduced into nanopores of anodic alumina by electro deposition. The magnetization of Fe-Pt nanowires was investigated. The magnetization perpendicular to the glass surface was very strong and the in-plane magnetization was very small, indicating that the magnetic Fe-Pt nanowires could be potentially applied to ultra high density magnetic recording. The density of the nanowires was estimated to be about 1T bits /inch2.
Flame Retardancy of Laponite- and Montmorillonite-Based Nylon 6 Nanocomposites
Authors: Inan Gunes , Patra Prabir K. , Kim Yong K. , Warner Steven B.
Published: April 2011

The flame retardancy of nylon 6/laponite and nylon 6/montmorillonite nanocomposites was investigated. The pronounced effect of layered silicates on heat release and mass loss rates of nylon 6 was examined. We found that nylon 6/laponite has 46 % and nylon 6/montmorillonite has 52.5 % lower peak heat release rates than that of neat nylon 6. The 6.5 % difference between the peak heat release rates of laponite- and montmorillonite-based nanocomposites was attributed to differences in aspect ratio and surface charge density of the nanoparticles.

The barrier properties of nanocomposite chars was evaluated by examining the peak heat release and mass loss rate reductions of stacks of layers, with the bottom layer being neat nylon 6 polymer and the top layers being nanocomposites that formed chars during the experiments. We observed that the peak heat release rate of a 10×10×0.3 cm neat nylon 6 slab was reduced by about 45 % when protected with a char-forming nylon 6/montmorillonite slab of same dimensions. The dramatic reduction of the peak heat release rate of neat nylon 6 when covered with a nanocomposite char was consistent with the notion that the flame retardancy of polymer/clay nanocomposites is affected by the (thermal and/or mass) barrier properties of the char. In order to test the thermal insulation of the char, temperature profiles of the layered samples were measured during cone calorimeter experiments. We observed that the nanocomposite char that brought about a 44.5 % reduction in peak heat release and mass loss rates reduced the heating rate of the same neat nylon 6 by about 31.2 %. The reduction in the heating rate increased with the amount of nanocomposite char formed.
Topology matters: Some aspects of DNA physics
Authors: Metzler Ralf
Published: April 2011

Biological cells, in some sense, are all about topology: Biomembranes separating different volumes from one another, ions or even macromolecules having to cross these membranes in controlled fashion through membrane pores; or certain proteins moving along the DNA to find their target sequence instead of searching for this site in the full 3-dimensional cell volume. Even on the single biopolymer level, topology is an essential ingredient: Intriguingly, in bacteria DNA occurs knotted, i.e., in a state topologically different from a simply connected ring. It is a key question to understand the statistical behaviour of such knotted DNA to understand a number of physiological processes having to overcome this knottedness, or to quantify results from DNA separation techniques such as electrophoresis, in which the knottedness influences the mobility. At the same time, double-stranded DNA continuously opens up floppy single-stranded bubbles, which fluctuate in size, exposing the single Watson-Crick bases to binding proteins. Again, statistical mechanical tools can be employed to examine the bubble dynamics. Here, we introduce some recent results on DNA knots and bubble fluctuations.
Thermal Expansion and Viscosity of Confined Liquids
Authors: Xu Shuangyan , Simmons Gregory C. , Scherer George W.
Published: April 2011

The thermal expansion and viscosity of water and salt solutions in porous silica glasses have been systematically investigated, and the effect of salts on the properties of water in confined geometry has been addressed. A dilatometric method has been devised and utilized to measure the thermal expansion of confined liquids. A beam-bending method that was developed to study the permeability of porous bodies has been used to measure the relative viscosity of salt solutions to water inside the silica pores. This work has demonstrated that water when confined in nanopores shows anomalous behavior and its thermal expansion is higher than bulk water. This work has also suggested that the presence of ions in water could enhance the anomaly of water in confined space and the extent of the ion effect is dependent on the ion charge.
Collective and Molecular Dielectric Relaxation in Confined Liquid Crystals: Effect of Different Layer Thicknesses and Boundary Conditions
Authors: Aliev Fouad M. , Bengoechea Manuel Rivera
Published: April 2011

Broadband dielectric spectroscopy was used to study the influence of boundary conditions and layer thickness of liquid crystal (LC) confined to cylindrical pores on low frequency and high frequency relaxation processes. Low frequency measurements provided information on the relaxation of surface polarization that arose at LC – pore wall interface. The dynamics of molecular reorientations were investigated in high frequency experiments. In samples with axial orientation of molecules, the dielectric mode due to reorientation of molecules around their short axis was investigated. The homeotropic alignment of molecules facilitated the investigation of the librational mode. The behavior of this mode was different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. Broadening of the dielectric spectra was observed in confined LC. The broadening increases with decreasing liquid crystal layer thickness.
Mechanical Properties and Filler Distribution as a Function of Filler Content in Silica Filled PDMS Samples
Authors: Hawley M. E. , Wrobleski D. A. , Orler E. B. , Houlton R. , Chitanvis K. E. , Brown G. W. , Hanson D. E.
Published: April 2011

Atomic force microscopy (AFM) phase imaging and tensile stress-strain measurements are used to study a series of model compression molded fumed silica filled polydimethysiloxane (PDMS) samples with filler content of zero, 20, 35, and 50 parts per hundred (phr) to determine the relationship between filler content and stress-strain properties. AFM phase imaging was used to determine filler size, degree of aggregation, and distribution within the soft PDMS matrix. A small tensile stage was used to measure mechanical properties. Samples were not pulled to break in order to study Mullins and aging effects. Several identical 35 phr samples were subjected to an initial stress, and then one each was reevaluated over intervals up to 26 weeks to determine the degree to which these samples recovered their initial stress-strain behavior as a function of time. One sample was tested before and after heat treatment to determine if heating accelerated recovery of the stress-strain behavior. The effect of filler surface treatment on mechanical properties was examined for two samples containing 35 phr filler treated or untreated with hexamethyldisilazane (HMDZ), respectively. Fiduciary marks were used on several samples to determine permanent set. 35 phr filler samples were found to give the optimum mechanical properties. A clear Mullins effect was seen. Within experimental error, no change was seen in mechanical behavior as a function of time or heat-treatment. The mechanical properties of the sample containing the HDMZ treated silica were adversely affected. AFM phase images revealed aggregation and nonuniform distribution of the filler for all samples. Finally, a permanent set of about 3 to 6 percent was observed for the 35 phr samples.
Vacancies in electron irradiated 6H silicon carbide studied by positron annihilation spectroscopy
Authors: Lam C. H. , Ling C. C. , Beling C. D. , Fung S. , Weng H. M. , Hang D. S.
Published: April 2011

Positron lifetime spectroscopy was employed to study the as-electron-irradiated (10 MeV, 1×1018 cm-2) n-type 6H silicon carbide sample in the measuring temperature range of 15 K to 294 K. Isochronal annealing studies were also performed up to the temperature of 1373 K by carrying out the room temperature positron lifetime measurement. Negatively charged carbon vacancies and VCVSi divacancy were identified as the major vacancy type defects induced by the electron irradiation process. The concentration of the VCVSi divacancy was found to decrease dramatically after the 1973 K annealing.
Irradiated cubic single crystal SiC as a high temperature sensor
Authors: Volinsky Alex A. , Ginzbursky Lev
Published: April 2011

Radiation is known to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation flux on the order of 2·1020 neutrons/cm2 at 0.18 MeV causes over 3% volume lattice expansion. Radiation-induced strain (measurable by X-Ray diffraction) can be relieved when the annealing temperature exceeds the temperature of irradiation. Based on this effect the original technology of maximum temperature measurement was developed a while ago. Single crystal SiC sensor small size (200–500 microns), wide temperature range (150–1450 °C), “no-lead” installation, and exceptional accuracy make it very attractive for use in small, rotating and “hard-to-access” parts, including, but not limited to gas turbine blades, space shuttle ceramic tiles, automobile engines, etc. With the advances in X-Ray diffraction measurements, crystal and thin film growth techniques, it is the time to revise and update this technology. Modeling radiation damage, as well as annealing effects are also beneficial.
Properties of Ordered Nanoporous Alumina as a Template for Pattern Transfer by MeV Ion Irradiation
Authors: Razpet Alenka , Possnert Göran , Johansson Anders , Abid Mohamed , Hallén Anders
Published: April 2011

Ordered nanoporous alumina has recently been considered as a template for pattern transfer by MeV ion irradiation. Porous alumina of thickness 500 nm has already been used as a mask for low energy heavy ion implantation. However, in order to apply this material as a template for production of structures with higher aspect ratios, lighter ions with MeV energies and larger penetration depth should be used. The aim of this contribution is to examine the transmission of such ions through alumina templates with sufficient thickness to mask ions that are not passing the pores. A careful orientation of the pores in the direction of the incident beam is therefore needed since the acceptance angle for ions passing through the pores decreases with increasing thickness.

Typical size of pores in the investigated alumina foils was 70 nm with a repetition frequency of 100 nm. Transmission through the foil and the energy of transmitted MeV ions were measured for aligned alumina foils by standard backscattering technique. It was shown that the sample transmission is a characteristic of each sample, but for some investigated samples the proportion of transmitted ions was the same as the relative area covered by pores. The energy spectra of transmitted ions were used to further evaluate the quality of foil templates for pattern transfer. It was shown that 2 μm thick alumina films can mask 3 MeV O+ ions, which can be used for ion lithography in polymer materials.
Optical and Mechanical Properties of Photoassisted, Self-assembled Nanoparticle Films
Authors: Gaddy G. A. , Miner G. A. , Stoakley Diane M. , Locke Edward P. , Moore Rick L. , Schultz John , Creyts Don , Knotts Michael
Published: April 2011

This paper presents research funded under the Defense Advanced Research Projects Agency (DARPA) MetaMaterials program for design and development of nanoparticle based, mesoscale electromagnetic and optical materials. Specifically, we present results of formulation and near infrared measurement-model validation for photoassisted, self-assembled multilayer metallic nanoparticle films. The multilayer films may be used as optical filters and absorbers. We demonstrate that nanoparticles can be formed in advanced polymer films that exhibit new electromagnetic constitutive properties. Metal nanoparticle films are produced from a single homogeneous resin containing a soluble precursor. Films cast from doped resins are exposed to UV radiation followed by a controlled thermal cure. The combination of UV exposure and thermal curing creates a multiphase material composed of low volume fractions of dispersed metallic Pd clusters (10–20 nm in size) and high concentrations of Pd nanoparticles which form surface and embedded metallic layers in the films. The layer separation is a function of UV exposure. These materials show significant absorption in the optical and near IR region of the spectrum. Furthermore, these films exhibit mechanical properties similar to bi-metallic layers, specifically, the films display reversible bending with exposure to light and an accompanying rapid temperature increase. This paper presents formulation processes, optical-mechanical measurements and measurement model comparison.
Explosive Crystallization in Eutectic Materials of Phase Change Optical Memory
Authors: Okuda Masahiro , Inaba Hirokazu , Usuda Shouji
Published: April 2011

The excess Sb effect for the dynamics of rapid crystallization in eutectic amorphous films are discussed. This crystallization mechanism describe the propagation with high velocity in the interface separating the crystalline and amorphous phase for InSb and AgInSbTe materials. From these analysis, it is clear that the crystallization is grown up in the boundary of crystalline-amorphous region of eutectic materials, which is different from the stoichiometric GeSbTe media. Also, the quantum effect on the melting, crystallization and solidification of phase change media has been discussed.
Structure analysis of amorphous thin films of GeSbTe compounds by grazing incidence X-ray scattering
Authors: Sato Masugu , Matsunaga Toshiyuki , Kouzaki Takashi , Yamada Noboru
Published: April 2011

We have investigated the structures of amorphous thin films of GeSbTe compounds – the materials used for the recording layer of phase-change optical memory – through grazing incidence X-ray scattering (GIXS) measurements. Thin films with compositions of GeSb2Te4 and Ge2Sb2Te5 were deposited on Si substrates. Electron radial distribution functions (RDFs) derived from the data clearly showed evidence of the medium-range order with three peaks of the atomic pair distribution. The RDFs of both samples were very similar to those of amorphous bulk GeTe compounds reported from previous X-ray scattering experiments. The positions of the first peaks of these RDFs were consistent with the distances of the first nearest neighbor pairs reported from previous EXAFS experiments. A comparison of the RDF of the amorphous phase with that of the crystalline phase suggested that the phase change caused no significant change in the number of atoms included inside or the radius of the second nearest neighbor atomic shell, although it changed the coordination number and the distance of the first nearest neighbor atomic pairs. This may shorten the moving distance of atoms in the phase change and enable high-speed phase change.
Chemical Durability Studies of Waste-Simulant Doped Borosilicate Glasses
Authors: Duddridge Adam , Islam Moinul , Holland Diane , Scales Charlie R.
Published: April 2011

A mixed-alkali modified borosilicate base glass used in the vitrification of high-level nuclear waste (HLW) has been doped with a number of waste simulants to between 2 and 12 mol%. The simulants have been chosen to give two distinct series of glasses: one consisting of trivalent ions having the form M2O3

(where M is La, Bi, Al or Fe) and the other consisting of divalent simulants of the form MO (where M is Pb, Zn or Ba). An international standard Soxhlet leach test procedure was performed on each glass to study the effect of prolonged, moderate-temperature, dynamic water corrosion. Results of these studies show that, except for BaO, as the amount of simulant is increased, the amount of Na and Li leached decreases showing them to become more chemically resistant. These corrosion tests have been correlated to ionic (D.C.) conductivity measurements, which show a decrease in the conductivity of the glass as the amount of waste simulant is increased, and 11B magic-angle spinning nuclear magnetic resonance (MAS-NMR) studies, which have shown that, as more waste-simulant is loaded into the glasses the rate of conversion of [BO4] to [BO3] units increases. All of the data from these studies reflect the different network forming abilities of the divalent and trivalent cations.
Structural Characterisations of Rare Earth-Rich Glasses for Nuclear Waste Immobilisation
Authors: Bardez I. , Caurant D. , Ribot F. , Loiseau P. , Dussossoy J. L. , Villain F. , Baffier N. , Fillet C.
Published: April 2011

New glassy matrices, able to incorporate new highly concentrated radioactive liquid wastes (HLW), are being studied. Investigations were performed on rare earth-rich glasses, known as very durable matrices. The selected basic glass composition was (wt. %): 51.0 SiO2 – 8.5 B2O3–12.2 Na2O – 4.3 Al2O3 – 4.8 CaO – 3.2 ZrO2 – 16.0 Nd2O3. To determine both the environment around the rare earth in this glass and its evolution according to its concentration (1.3 – 30 wt. % Nd2O3), EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the LIII-edge of neodymium and optical absorption spectroscopy were used. By coupling these two characterisation methods, several hypotheses are proposed about the nature of the rare earth neighbouring in the glass.
Vapour Phase Hydration of Blended Oxide - Magnox Waste Glasses
Authors: Hyatt Neil C. , Lee William E. , Hand Russell J. , Abraitis Paul K. , Scales Charlie R.
Published: April 2011

Vapour phase hydration studies of a blended Oxide / Magnox simulant high level waste glass were undertaken at 200°C, over a period of 5 – 25 days. The alteration of this simulant waste glass is characterised by a short incubation time of less than 5 days, leading to the formation of an alteration layer several microns thick. Following the incubation period, the alteration proceeds at a constant rate of 0.15(1)μmd−1. The distribution of key glass matrix (Si, Na) and waste (Cs, Zr, Nd, Mo) elements was found to vary significantly across the alteration layer. Vapour phase hydration leads to formation of surface alteration products, identified as smectite, zirconium silicate and alkaline-earth molybdate phases.
Synthesis of Actinide-Doped Ceramics: from Laboratory Experiments to Industrial Scale Technology
Authors: Kitsay Alexander A. , Garbuzov Vladimir M. , Burakov Boris E.
Published: April 2011

The experience of the Laboratory of Applied Mineralogy and Radiogeochemistry of the V.G.Khlopin Radium Institute on synthesis of Pu-Am-doped ceramics is summarized. During the last 5 years, dozens of actinide doped polycrystalline samples and single crystals have been successfully synthesized such as zircon, hafnon, cubic zirconia, monazite, Ti-pyrochlore, perovskite and garnet. Actinide loading has been varied as follows:

-239Pu - from 5–6 wt.% in zircon (polycrystalline and single crystals), hafnon, garnet and perovskite to 10 wt.% in Ti-pyrochlore and up to 37 wt.% in zirconia;

- 238Pu - from 2.5 wt.% in zircon single crystals to 5 wt. % in polycrystalline zircon and 10 wt.% in monazite and cubic zirconia;

- 243Am - 20–23 wt.% in cubic zirconia and monazite.

The weight of each single ceramic pellet varied from 0.2 to 2.0 grams. Special furnaces developed in KRI for ceramic synthesis allowed obtaining up to 7 ceramic pellets simultaneously during the same experiment. The highest amounts of actinides used under glove-box conditions in the same experiment were: 1.5–2.0 g for 239Pu, 0.6 g for 238Pu and 0.3 g for 243Am. Most experiments on synthesis of ceramics and single crystals doped with 239Pu, 238Pu and 243Am carried out at the KRI did not lead to contamination of internal walls of glove boxes. No release of Pu-Am-aerosols was observed as a result of sintering or melting at 1300–1600°C. These results allowed us to conclude that at the present the KRI has developed the experimental basis for transferring laboratory innovations to the industry of actinide immobilization. It is important that adopting ceramic synthesis methods at industrial scale does not require development of new special equipment.
Modelling of Water Uptake and Salt Leaching in Bituminized Radioactive Waste: Comparison Between Numerical, Analytical and Experimental Results
Authors: Sercombe J. , Adenot F. , Tiffreau C. , Gwinner B. , Felines I.
Published: April 2011

In this paper, a simplified model which allows the derivation of analytical relations aiming at describing the diffusion-dissolution-swelling processes taking place in bituminized waste exposed to water or salt solutions is presented. The analytical solutions render the comparison with experimental data and tendencies straightforward. The validity of the simplified approach is demonstrated by comparing analytical and numerical solutions with experimental data.
Static Dissolution of α-doped UO2 in Boom Clay Conditions: Preliminary Results
Authors: Cachoir C. , Lemmens K.
Published: April 2011

To support the performance assessment (PA) calculations for the possible final disposal of spent fuel in the Boom Clay, leach experiments are performed with α-doped UO2 in clay media, simulating various near field ages. The experiments allow to measure the dissolution rate of the UO2 and to determine the assumed relationship between dissolution rate and α-activity. Tests are performed at six different α-activities, simulating various fuel ages, at 25–30°C, for durations ranging from 90 to 720 days, in a glove box with Ar/0.4%CO2 atmosphere. The solutions and solids are analyzed for U isotopes and 238Pu by radiochemical measurement and by ICP-MS. The dissolution rates of the α-doped UO2 are presented for different durations. The resulting corrosion rate is around 300 μgU.m−2.d−1. This is up to 100 times higher than found for similar conditions in the literature. In the presence of clay, there appears to be no correlation between the α-activity and the corrosion rate of the α-doped UO2.
The Effect of Cellulose Degradation Products on the Solubility and Sorption of Pu and Am in Alkaline-Plume-Affected and in Unaffected Boom Clay
Authors: Rorif F. , Valcke E. , Glaus M. A.
Published: April 2011

The potential effect of water-soluble degradation products (DPs) formed from cellulose-containing cemented radioactive waste on the behaviour of Pu(IV) and Am(III) in Alkaline-Plume-Affected (APA) and in unaffected Boom clay was assessed. After solubility measurements in APA Real Clay Water, sorption experiments of Pu(IV) and Am(III) onto APA Boom clay were performed in the presence or not of DPs or pure α-isosaccharinic acid (α-ISA). Moreover, the sorption of α-ISA onto the unaffected clay was studied.
Modelling of Pu Sorption onto the Surface of Goethite and Magnetite as Steel Corrosion Products
Authors: Duro Lara , Missana Tiziana , Ripoll Sonia , Grivé Mireia , Bruno Jordi
Published: April 2011

We have studied the surface interaction between tetravalent plutonium and two different steel corrosion products: magnetite, which is the final product of the anoxic corrosion of steel, and goethite, which exemplifies a further oxidation of the steel surface due to the presence of active oxidants in the system. The pH of the experiments has been varied from 2 to 10 and the ionic strength from 0.001 to 0.1 M NaClO4. All the sorption experiments were carried out under N2 atmosphere. No significant effect of ionic strength was observed under the conditions studied.

The pHpcz of the solids (7.78 for goethite and 6.95 for magnetite) was determined by modelling potentiometric titration data.

The results of the experiments show that the sorption edge of plutonium occurs between pH 3 and 4 when using goethite as a sorbing surface and between pH 4 and 5 when magnetite is used.

We have modelled the sorption data by using a simple surface complexation approach with no electrostatic term. The model used involves a reduction process of Pu(IV) to Pu(III) in the presence of magnetite, which can be explained by the interaction of the actinide with the ferrous iron present in the solid. In the case of the experiments conducted with goethite, this reduction process is not possible and, therefore, in the model we have included the sorption of tetravalent Pu.
The Second Safety Assessment and Feasibility Interim Report (SAFIR 2 Report) on HLW Disposal in Boom Clay: Overview of the Belgian Programme
Authors: Gens Robert , Lalieux Philippe , Preter Peter De , Dierckx Ann , Bel Johan , Boyazis Jean-Paul , Cool Wim
Published: April 2011

ONDRAF/NIRAS – the Belgian radioactive waste management agency – has published in 2001 the SAFIR 2 report on request of the authorities. The SAFIR 2 report is to be considered as a state-of-the art report and not as a complete safety case. This report gives an overview of the Belgian R&D program related to the geological disposal of HLW and ILW for the period 1990–2000 in the Boom Clay (reference host rock). The three main outcomes of the SAFIR 2 report on which this paper will be more specifically focusing, are the following (including results reported after 2000): long-term safety functions, confirmation of the role of the Boom Clay formation as the main barrier and identification of practical difficulties with respect to technical feasibility (repository design).
Study of 3-MeV electron irradiation damage in amorphous silicon with TRMC
Authors: Klaver A. , Warman J.M. , Haas M.P. de , Metselaar J.W. , Swaaij R.A.C.M.M. van
Published: April 2011

The effects of 3-MeV electron irradiation on a-Si:H have been studied using Time-Resolved Microwave Conductivity (TRMC). A Van der Graaff electron accelerator is used to generate the probe-beam pulses for the TRMC experiment as well as for the in-situ irradiation of the samples for the degradation of the material. Using several probe-beam pulse doses, TRMC transients were obtained on samples that have been subjected to various radiation fluences. These transients were later analyzed using a simple model based on the Shockley-Read-Hall capture and emission processes. Using these simulations we deduce a relationship between the radiation fluence and the defect density in the material.
Evolution of D0 and non-D0 Light Induced Defect States in a-Si:H Materials and Their Respective Contribution to Carrier Recombination
Authors: Pearce J. M. , Deng J. , Vlahos V. , Collins R. W. , Wronski C. R. , Whitaker J. , Taylor P. C.
Published: April 2011

A study has been carried out on the evolution of light induced defects in protocrystalline (diluted) a-Si:H films under 1 sun illumination. A room temperature reversal is observed in the photocurrents at 25°C, which is consistent with the relaxation in the recombination currents on corresponding p-i-n solar cells. It is also consistent with the pressure of “fast” states such as have been observed after high intensity illumination. Even with the limitations imposed by the relaxation in the light induced changes on the subgap absorption measurements, the evolution of distinctly different gap states centered around 0.9 and 1.15eV from the conduction band was identified. The kinetics of the electron occupied states, kN(E), at these two energies is compared with that of the neutral dangling bond (D0) densities as measured with electron spin resonance. Because of the similarity between the preliminary results of these kinetics it has not been possible to identify which states correspond to the D0 nor to draw any reliable conclusions about the nature of the different states.
Amorphous Si1-YGeY:H, F films obtained by Low Frequency PECVD for uncooled microbolometers
Authors: Ambrosio R. , Torres A. , Kosarev A. , Abramov A. S. , Heredia A. , Landa M. , Garcia M.
Published: April 2011

In this work, we report the composition, optical, and electrical properties of a- Si1-YGeY: H, F films to be used as sensing layer in uncooled microbolometers. The a-Si1-YGeY films where Y is Ge content in solid phase were deposited by low frequency PECVD from SiH4 and GeF4 feed gases, and H2 and Ar were used for dilution. The film composition, IR transmission and temperature dependence of conductivity were measured. The reduction of conductivity activation energy from 0.86 eV to 0.39 eV and the increase of room temperature conductivity from 1x10−9 to 2.1×10−3 Ohm−1cm−1 were observed with the change of Y from 0 (Si) to 1(Ge). These results demonstrate this material to be a good candidate as a sensing material in uncooled micro-bolometers, due to its high absorption in the range of λ = 10-13 μm, its relatively high activation energy, Ea=0.4 eV, consequently, a high temperature coefficient of resistance (TCR), and moderate resistivity at room temperature.
High Current Density in m c-Si PECVD Diodes for Low Temperature Applications
Authors: Beck Patricia A. , Nickel Janice H. , Hartwell Peter G.
Published: April 2011

The development of microcrystalline diodes grown at low temperature by PECVD techniques is reported. Current densities near 200 A/cm2 at + 2 V, and rectification ratios on the order of 105 at +/- 1V and 107at +/- 2V were obtained. The reverse currents were in the nano-ampere range. Correlations between deposition conditions and film quality are presented. The effects of mesa formation and subsequent treatments designed to reduce process damage are discussed: annealing conditions yield an increase in forward current, and a decrease in reverse current. Fabrication conditions are compatible with applications requiring low temperature processes (e. g., multi-layer structures, molecular layers, or plastic substrates and coatings).
Interpretation of Transient Photocurrents in Coplanar and Sandwich PIN Microcrystalline Silicon Structures
Authors: Reynolds Steve , Smirnov Vladimir , Main Charlie , Finger Friedhelm , Carius Reinhard
Published: April 2011

We report on the use of coplanar transient photoconductivity and post-transit time-of-flight spectroscopy techniques in the study of carrier transport in microcrystalline silicon films prepared over a range of crystallinities. Coplanar samples are susceptible to post-deposition oxidation and reversible adsorption of atmospheric gases, which may alter the apparent density of states. Coplanar measurements suggest lower deep defect densities in more highly crystalline films, but this is due at least in part to an increased occupancy of these states. A comparison of results obtained using both techniques suggests anisotropic transport, with reduced band tailing (greater structural order) along the direction of film growth, a larger defect concentration around the column boundaries, and a higher defect density within the amorphous tissue than in optimised single-component amorphous silicon films.
Metastability in Undoped Microcrystalline Silicon Thin Films Deposited by HWCVD
Authors: Persheyev S.K. , O'Neill K.A. , Anthony S. , Rose M.J. , Smirnov V. , Reynolds S.
Published: April 2011

Films deposited by the Hot Wire CVD method were studied by means of dark conductivity, FTIR, Hydrogen Evolution, SEM and AFM surface characterization. Three types of metastability were observed: a) long term irreversible degradation due to oxidization processes on the film surface, b) reversible degradation determined by uncontrolled water adsorption, c) fast field switching effect in the film bulk.

Oxygen and hydrogen content and its bonding configurations have been analyzed by hydrogen evolution and infrared spectroscopy methods on the films deposited on glass substrates and silicon wafers subsequently. It has been found that metastable processes close to the film surface are stronger than in the bulk. The switching effect is the fast increase of charge carrier density observed on bottom chromium contacts under a condition of air admittance. We propose this effect is associated with morphology changes during film growth and electrical field induced by adsorbed atmospheric components on the film surface.
External rf substrate biasing during a-Si:H film growth using the expanding thermal plasma technique
Authors: Smets A.H.M. , Kessels W.M.M. , Sanden M.C.M. van de
Published: April 2011

The interchangeability of ion bombardment and deposition temperature during a-Si:H film growth at high deposition rates (10-42 Å/s) by means of the expanding thermal plasma has been studied. The ion bombardment is generated by applying an external rf bias voltage on the substrate. It is shown that the opto-electronic performance of the a-Si:H films improves considerably when a moderate rf substrate bias voltage (∼20-60 V) is applied, i.e. the photo response increases two orders of magnitude up to 106. Furthermore, it is also revealed that the additional energy supplied to the growth surface by the ion bombardment, makes a reduction of the deposition temperature by ∼100 °C possible, while preserving good material properties. On the basis of the results obtained, three effects caused by the rf substrate bias can be distinguished: creation of an additional growth flux, a reduction of the void incorporation, and an increase in the vacancy density.
Growth and Characterization of Poly-SiGe Prepared by Reactive Thermal CVD
Authors: Zhang Jianjun , Shimizu Kousaku , Hanna Jun-ichi
Published: April 2011

We have prepared poly-Si1-xGex thin films with different germanium contents (Ge=5%∼40%) by reactive thermal CVD. In this study, the Ge content was controlled by varying the source gases GeF4 flow rate at a fixed Si2H6 flow rate. The effects of GeF4 flow rate on growth rate, film crystallinity, and electrical properties were investigated. The films were always polycrystalline when GeF4 was introduced even in a small amount, while only amorphous film deposited without GeF4. With an increase in GeF4 flow rate, Ge content and conductivity of the films increased and its activation energy decreased. When GeF4 flow rate over a certain value, the growth rate decrease and finally no film could be deposited. These behaviors are discussed in relation with a role of GeF4 for the crystal growth at a low temperature.
Solid Phase Epitaxy process integration on 50-nm PMOS devices: Effects of defects on chemical and electrical characteristics of ultra shallow junctions
Authors: Farhane R. El , Laviron C. , Cristiano F. , Cherkashin N. , Morin P. , Juhel M. , Stolk P. , Arnaud F. , Pouydebasque A. , Wacquant F. , Lenoble D. , Halimaoui A.
Published: April 2011

We demonstrate in this paper the viability of an ultra-low thermal budget CMOS process enabling the formation of ultra shallow junctions with competitive transistor characteristics. In particular, we demonstrate in this work the influence of defects on chemical and electrical results. It is shown that the use of self-amorphizing implantation with BF2for Source/Drain, reduces the junction leakage by two decades.
Applications of Ni-based silicides to 45 nm CMOS and Beyond
Authors: Kittl Jorge A. , Lauwers Anne , Chamirian Oxana , Pawlak Malgorzata A. , Van Dal Mark , Akheyar Amal , Potter Muriel De , Kottantharayil Anil , Pourtois Geoffrey , Lindsay Richard , Maex Karen
Published: April 2011

This paper presents an overview of Ni-alloy (Ni, Ni-Pt and Ni-Ta) silicide development for the 45 nm node and beyond, including applications to self-aligned silicide (SALICIDE) processes, reaction with SiGe and strained Si on SiGe, and applications to fully silicided (FUSI) gates. Key SALICIDE issues addressed include the use of spike or low temperature rapid thermal processes (RTP) to control silicidation and junction leakage on small features, factors affecting the formation of epitaxial pyramidal NiSi2 grains, and NiSi thermal stability and agglomeration kinetics. Alloying with Pt or Ta is shown to improve thermal stability of NiSi films, although with quite different behaviors. While Pt is incorporated predominantly in solution in NiSi, Ta segregates to the surface of the films. Ni-Pt alloy silicides were also found to achieve low sheet resistance on narrow gates, low contact resistivity and low junction leakage, making them attractive for CMOS applications. For the Ni/SiGe reaction, a narrower RTP process window for low sheet resistance and a lower activation energy for agglomeration were observed when compared to the Ni/Si reaction. The lower thermal stability was correlated to Ge segregation from the Ni(SiGe) films. The Ni/doped poly-Si reaction was studied for FUSI gate applications, showing a retardation of the silicidation kinetics for high B doses and a large pile- up of dopants (for As, B or P) at the NiSi/SiO2 interface due to dopant snowplow during silicidation. The work function (WF) of NiSi was observed to shift with the addition of dopants, effect attributed to modifications of the interface dipole by the pile-up of dopants. No significant degradation was observed when comparing gate oxide breakdown statistics for Ni FUSI to conventional poly-Si gates. The process window for a FUSI gate-last process (performed after S/D Ni silicidation) was evaluated showing a potential integration problem due to possible degradation of the S/D silicide during the FUSI gate reaction.
Vibrational Spectra of Nitrogen-Oxygen Defects in Nitrogen Doped Silicon using Density Functional Theory
Authors: Karoui F. Sahtout , Karoui A. , Inoue N. , Rozgonyi G. A.
Published: April 2011

The vibrational spectra of N-pairs and nitrogen-vacancy-oxygen defects in nitrogen doped Czochralski silicon have been investigated using density functional theory calculations. We found that 771 cm−1 and 967 cm−1 lines measured by FTIR are fingerprints for N-pairs in interstitial position. These confirm that nitrogen atoms are paired and bonded to Si atoms. Calculated local vibration modes of N2On complexes provide the best matching with observed FTIR frequency of N-O complexes. Nonetheless, VmN2On (m,n =1,2) can develop during crystal cooling or wafer processing, as revealed by local vibrational modes falling around, 806 and 815 cm−1 FTIR frequencies.
Processing damage and electrical performance of porous dielectrics in narrow spaced interconnects
Authors: Iacopi F. , Travaly Y. , Stucchi M. , Struyf H. , Peeters S. , Jonckheere R. , Leunissen L.H.A. , Tökei Zs. , Sutcliffe V. , Richard O. , Hove M.Van , Maex K.
Published: April 2011

The damage induced in the low-k material upon exposure to dry etch and ash plasmas is a point of major concern in terms of preservation of the dielectric properties. There is urgent need to assess, classify and quantify the extent of such damage to allow the optimization of patterning processes and conditions. Meander-fork structures with spacings between 250nm and 70nm are used in this study as vehicle to compare trends in electrical performance for different dielectrics: SiO2 and two SiOC:H low-k materials with pristine k values of 3.0 and 2.6. Here we demonstrate that the ‘electrical equivalent damage’ model is a valid and precise methodology for assessing dielectric damage upon processing from interline capacitance evaluation. This analysis allows to distinguish between bulk and sidewall modification and to quantify the extent of damage. Moreover, it provides an interpretation for the degradation of leakage current and breakdown field of the interline dielectric, revealing different trends whether due to only sidewall or total damage.
Novel Epoxy Siloxane Polymer as Low-K Dielectric
Authors: Wang Pei-I , Juneja Jasbir S. , Murarka Shyam , Lu Toh –Ming , Ghoshal Ram , Ghoshal Rajat
Published: April 2011

This paper introduces a low-k dielectric material, a novel epoxy siloxane polymer, made by Polyset Co. Inc, which has promising properties. The polymer was spin-deposited, and thickness and optical properties were measured using variable-angle spectroscopic ellipsometry (VASE). Fourier transform infrared (FTIR) spectra of as deposited and cured polymers showed that the polymer is fully cured at 165 °C. The low curing temperature of the polymer lowers stress in back-end-of-line (BEOL) stack and thus improves the reliability. The polymer is thermally stable up to 400 °C. The polymer has Young's modulus of ∼5 GPa and hardness of greater than 0.4 GPa. After multiple stress cycles up to 300 °C, the residual stress in the polymer at room temperature is less than 60 Mpa. The polymer has good adhesion with semiconductor and dielectrics such as Si, SiC, and SiO2, metals such as Al, Cu, Co, and W, and barrier materials such as TaN. The bulk dielectric constant of the polymer is 2.4 - 2.7. The leakage current density in the polymer at the applied electrical field of 1 MV/cm is in 10−9 A/cm2 range and the breakdown field of the polymer is ranging from 5 to 7 MV/cm. The polymer when subjected to bias-temperature stress (BTS) conditions of 150 °C and 0.5 MV/cm shows no C-V shift for up to 100 min indicating that the polymer resists Copper diffusion. The current density under stress conditions of 150 °C and 0.5 MV/cm was less than 10−9 A/cm2 for up to 7 hrs.