bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaporative Evolution of Brines from Synthetic Topopah Spring Tuff Pore Water, Yucca Mountain, NV
Authors: Alai Maureen , Carroll Susan
Published: April 2011

We are investigating the evaporation of pore water representative of the designated high-level-nuclear-waste repository at Yucca Mountain, NV to predict the range of brine compositions that may contact waste containers. These brines could form potentially corrosive thin films on the containers and impact their long-term integrity. Here we report the geochemistry of a relatively complex synthetic Topopah Spring Tuff pore water that was progressively evaporated in a series of experiments. The experiments were conducted in a vented vessel in which HEPA filtered air flowed over the 95°C solution. Samples of the evaporating solution and the condensed vapor were taken and analyzed to determine the evolving water chemistry and gas volatility. The final solid was analyzed by X-ray diffraction.

The synthetic Topopah Spring Tuff water evolved towards a complex brine that contained about 45 mol % Cl, 7 mol% NO3, 43 mol% Na, 4 mol % K, and less than 1 mol % each of SO4, Ca, Mg, HCO3 and Si. Trends in the solution data and identification of CaSO4 solids suggest that fluorite, carbonate, sulfate, and Mg-silicate precipitation minimize the corrosion potential of “sulfate type pore water” by removing F, Ca, and Mg during the early stages of evaporation.
New Developments in Field Studies of Low Activity Waste Glass Corrosion and Contaminant Transport
Authors: McGrail B. P. , Bacon D. H. , Meyer P. D. , Ojovan M. I. , Strachan D. M. , Ojovan N. V. , Startceva I. V.
Published: April 2011

Performance assessment calculations for low-activity waste glass to be disposed at the Hanford site depend on simulations of long-term glass corrosion behavior and contaminant transport that are being performed via reactive chemical transport modeling. Confidence in the underlying physical and chemical processes that are being approximated by the computer model could be significantly enhanced through carefully-controlled field testing, which includes studies of buried ancient glasses. Field tests with simulated low-activity waste glasses have been initiated on the Hanford site and at the Ballidon site in the United Kingdom. In addition, a joint PNNL – SIA RADON research project has been initiated to analyze a unique data set collected over 12+ years during a Russian in-situ testing program with actual low-activity waste glass. The glasses buried at Hanford are scaled down cylinders (45 kg mass) and include a representative glass composition for Hanford low-activity waste and a glass designed to be highly reactive. Each glass was doped with chemical analog tracers (Re, Se, and Mo). Design of the lysimeter test facility and sampling locations were done with aid of predictive calculations performed with the STORM code. These same glasses were also buried at Ballidon but in the form of small glass coupons. The coupons will be retrieved over a period of several years for detailed analysis along with core samples of the surrounding limestone, which will be analyzed for contaminant transport profiles. Analysis of porewater from underneath the Russian burial site ha s been compared with modeling calculations. Good agreement between the model and the field data has been obtained so far using estimated parameters for the glass corrosion. Independent laboratory tests are in progress to parameterize the STORM model for quantitative comparisons.
The effect of uncertainties in stability constants on speciation diagrams
Authors: Ödegaard-Jensen Arvid , Ekberg Christian , Meinrath Gunther
Published: April 2011

Speciation calculations are one of the more common ways to describe a chemical system. Speciation diagrams is a convenient way to display such calculations and may also be the basis on which experiments in neighbouring fields of interest, such as sorption are based. In earlier days only very simple problems could be described, e.g. hydroxide species dominance diagrams versus pH. With the aid of computers, however, more complicated systems such as groundwater chemistry may be used. However, as the complexity increase, so does the effect of uncertainties. In this paper we focus on the effect uncertainties in stability constants may have on speciation calculations. The common belief is that the curves will be replaced by narrow bands, while the truth is far from that. In many cases one or several species cover the entire region between 0 and 100%.
Influence of organic matter in the prediction of iodine migration in natural environment
Authors: Reiller Pascal , Moulin Valérie
Published: April 2011

Halogenation of phenolic moieties is one of the most important reactions between humic substances (HS) and iodine or chlorine. These reactions were studied in order to assess the importance of these interactions with reduced (I−) and oxidised (I2) form of iodine. I−was fixed by the addition of Na2S2O3. After separation of HS and I−by ultrafiltration, no significant uptake was evidenced in the time framework of this study. The consumption of I2(aq) by HS was followed by the decay of I−3absorbance (351 nm). It comes out that (i) when I−is fixed by Na2S2O3, no interaction with HS could be quantified; (ii) I2(aq) does react with HS but the kinetics cannot be linearalised. This study confirms the significance of iodine-organic matter interactions as a governing process for iodine migration in surface environment. More studies are on going to develop predictive models of iodination kinetics.
Characterization of the Corrosion Behavior of Alloy 22 after Five Years Immersion in Multi-ionic Solutions
Authors: Wong Lana L. , Fix David V. , Estill John C. , Daniel McCright R. , Rebak Raúl B.
Published: April 2011

Alloy 22 (N06022) is the candidate material for the corrosion resistant, outer barrier of the nuclear waste container. Two of the potential corrosion degradation modes of the container are uniform corrosion and localized corrosion. A testing program is under way at the Lawrence Livermore National Laboratory to determine the susceptibility of Alloy 22 to these two forms of corrosion using immersion tests. Metallic coupons are being exposed to several electrolyte solutions simulating concentrated underground water from pH 3 to 10 at 60°C and 90°C. This paper describes the results obtained after more than a five-year exposure of 122 specimens to the testing electrolyte solutions. Results show little general corrosion and the absence of localized corrosion. The maximum general corrosion rate was 23 nm/yr.
Vapour Phase Hydration of Magnox Waste Glass
Authors: Hyatt Neil C. , Lee William E. , Hand Russell J. , Ojovan Michael I. , Abraitis Paul K. , Scales Charlie R.
Published: April 2011

Vapour phase hydration studies of simulant Magnox waste glass have been undertaken at 200°C, over periods of 5 – 25 days. Electron microscopy studies reveal a thin uniform hydration layer (∼10 μm thick) on 5, 10 and 25 day specimens. The formation of isolated surface alteration products occurs between 5 and 10 days at 200°C. The formation of extensive surface alteration products, in the form of a magnesium sodium aluminosilicate, is observed only in the case of the 25 day specimen. The significance of these observations in the context of the composition of Magnox waste glass, is discussed.
Molybdenum in Nuclear Waste Glasses - Incorporation and Redox state
Authors: Short R. J. , Hand R. J. , Hyatt N. C.
Published: April 2011

The composition and structure of the mixed metal molybdates that can form in simulated high level nuclear waste (HLW) glass melts have been studied. It was found that molybdates of a tetragonal scheelite type were formed upon heat treatment of the simulated glass samples (representative of the slow cools experienced by the real vitrified product), and that these compounds are capable of incorporating the majority of the mono, di, and trivalent cations that would be present in a real HLW glass. In addition, it has been shown that altering the redox conditions prevailing upon melting can promote or suppress crystallisation in simplified model waste glasses that contain molybdenum. Experiments to investigate the effect of redox conditions during melting of simulated HLW glass on molybdate formation are also reported.
A Comparison and Abstraction of the Commercial Spent Fuel Corrosion Experiments in the U.S.
Authors: Siegmann Eric R.
Published: April 2011

This paper compares the results of three different fuel corrosion experiments by taking the existing corrosion data reported for various temperatures and recalculating corrosion rates at a single temperature of 25°C using a temperature dependent model developed elsewhere. Three types of light water reactor fuel corrosion tests (sometimes called dissolution or alteration tests) were performed in support of Yucca Mountain Project. The tests used three water contact modes and various fuel burnups. All measurements were adjusted for temperature differences and then compared. Five different isotopes (cesium, technetium, iodine, strontium, and, in the flow-through tests, uranium) were considered as a measure of corrosion. The data used represent over ten years of experiments with about nine different fuel types. Most experiments were with repository type fluids, containing dissolved constituents such as carbonate, calcium and silicon. The results show that all of the experiments predict similar fuel corrosion rates. Small differences in the isotope release rates are observed and incorporated in the abstracted uncertainty. Water contact mode (flow-through, batch, or drip) does not seem to be very important although the drip tests introduced larger variations. In developing a corrosion abstraction, all of the isotope measurements were considered equally. The distribution of release rates was used directly to develop the uncertainty. The mean corrosion rate was 1.8 × 10-4 fraction/year at 25°C (5%-95% range = 5.7 × 10-5 to 1.7 × 10-3). Using the derived corrosion rate for 25°C, and considering rapid axial splitting of the cladding, the CSNF fuel rod is expected to corrode in less than 2,000 years. The abstraction uses all the available experiments performed with water containing carbonates, silicon, or calcium and irradiated fuel to produce a corrosion rate distribution. Sensitivity studies using this corrosion rate abstraction in the TSPA-SR analysis show very small changes in dose (3%) in response to changes in the UO2 corrosion abstraction.
Development of PZT Suspensions for Ceramic Ink-Jet Printing
Authors: Derby B. , Lee D. H. , Wang T. , Hall D.
Published: April 2011

The direct ink-jet printing of ceramic powders requires the development of highly fluid suspensions of ceramic particles with viscosity < 40 mPas. Here we describe the development of two such ceramic suspensions, which contain up to 30% by volume of PZT particles in either an azeotropic mixture of MEK and ethanol or in an alkane wax at 120 °C. The influence of various processing parameters on fluid rheology are investigated and trial fluids have been passed through an ink-jet printing head.
Fabrication of Micro- and Nanoscale SiC Structures Using Selective Deposition Processes
Authors: Chen L. , Fu X. A. , Zorman C. A. , Mehregany M.
Published: April 2011

A method to fabricate nanometer scale SiC beams and nanoporous SiC shells using conventional microlithographic techniques combined with selective APCVD has been developed as an alternative to nanolithographic patterning and electrochemical etching. The process involves the selective deposition of poly-SiC films on patterned SiO2/polysilicon/SiO2 thin film multilayers on (100) Si substrates using a carbonization-based 3C-SiC growth process. This technique capitalizes on significant differences in the nucleation of SiC on SiO2 and polysilicon surfaces in order to form mechanically durable and chemically stable structures.
Polymer Microvalve Based on Anisotropic Expansion of Polypyrrole
Authors: Berdichevsky Yevgeny , Lo Y.-H.
Published: April 2011

An actuator fabricated from the conductive polymer polypyrrole using microfabrication techniques is presented. This actuator utilizes the anisotropic volume change, which occurs under application of an electric field in polypyrrole grown in the presence of NaDBS. This volume change is in direction normal to the substrate, and is several times larger than lateral volume change utilized in polypyrrole microactuators to date. The actuator is applied in a microfluidic valve where membrane and microchannels are fabricated from a transparent elastomer using soft lithography. The use of elastomer enabled a good valve seal and encapsulation of the electrolyte used for polypyrrole actuation.
Self-Organized Criticality in Nanotribology
Authors: Adler Micha , Ferrante John , Schilowitz Alan , Yablon Dalia , Zypman Fredy
Published: April 2011

We present experimental results on dry friction, which are consistent with the hypothesis that the stick-slip mechanism for energy release is described by self-organized criticality. The data, obtained with an Atomic Force Microscope set to measure lateral forces– examines the variation of the friction force as a function of time – or sliding distance. The materials studied were nominally flat surfaces of mica, quartz, silica and steel. An analysis of the data shows that the probability distribution of slip sizes follows a power law. Our data strongly supports the existence of self-organized criticality for nano-stick-slip in dry sliding friction.
Polyurethane Nanofiber Webs for Sensor and Actuator Applications in Microelectromechanical Systems (MEMS)
Authors: Demir Mustafa M. , Naseer Mansoor , Bechteler Thomas F. , Gurbuz Yasar , Menceloglu Yusuf Z.
Published: April 2011

Sensor application of Polyurethane Nanofiber Webs (PNW) has been explored in this study. PNW were prepared by electrospinning of the polyurethane solution in dimethylformamide. Silver nanoparticles with a size of 60 nm on PNW were produced by precipitation of AgNO3 in alkaline media. A micromachined capacitive pressure sensor has been designed using a special elastic and conducting thin membrane (PNW) as an active electrode sensing the pressure. With an additional inductor and a metal-semiconductor field effect transistor (MESFET), a microwave oscillator has also been designed as part of the system. The capacity variation due to changing pressure results in a frequency shift of this oscillator. This frequency shift is measured and corresponds to the pressure. The simulations performed on this structure show a very good linearity over a wide range of applied pressure which could be detected by change in oscillator frequency. These results indicate that an implementation of PNW as an active material in capacitative sensing applications of MicroElectroMechanical Systems (MEMS) could be feasible.
Structure Analysis of Co/Re Superlattice Grown on an Al2O3 (110) Substrate
Authors: Xu Wentao , Charlton Timothy , De Long Lance E. , Lederman David
Published: April 2011

The structure of a Re(5 nm)/(Co(2 nm)/Re(3 nm))19 sample grown via magnetron sputtering was thoroughly analyzed via x-ray reflectivity (XRR) and transmission electron microscopy (TEM). Cross-sectional TEM results indicate that the sample is epitaxial, with the in-plane c-axis of the superlattice pointing along the c-axis of the substrate. A quantitative analysis of XRR yielded an average thickness of each layer and an interface roughness ∼ 0.4 nm between the Co and Re layers. A careful analysis of the TEM data reveals that the in-plane lattice parameters for Co, Re and Al2O3 are approximately 0.24 nm, 0.43 nm; 0.26 nm, 0.44 nm; and 0.24 nm, 0.44 nm, respectively. The lattice spacings of Al2O3 correspond to a/2 and c/3, where a, and c are lattice parameters, respectively. Interestingly, both high resolution and Z-contrast images show a very uniform period thickness. Z-contrast images, however, show that the initial interface roughness between the Re buffer layer and the first Co layer is amplified as the layers get farther away from the substrate. A high magnification TEM analysis shows that the bottom Co-Re interface roughness is about 0.2 nm, whereas the top Re-Co interface roughness is about 0.7 nm. Previous anistropic magnetoresistance measurements are discussed in light of these new structural data.
Magnetic Properties of Nanocrystalline Fe50Co50 Powders
Authors: Basavaraju Shashishekar , Baker Ian
Published: April 2011

Nanocrystalline stoichiometric FeCo powders were prepared by mechanically alloying elemental Fe and Co powders using a high-energy ball mill. The microstructural evolution was studied as a function of milling time and subsequent annealing using X-ray diffractometry and differential scanning calorimetry. The magnetic behavior of the specimens was characterized using a vibrating sample magnetometer and a magnetic force microscope. A reduction in grain size coupled with an increase in coercivity was observed as function of milling time. The smallest grain size of 4 nm, which exhibited a coercivity of 122 Oe and magnetization of 2 T at room temperature, was obtained after 240 h of milling. The reduction in grain size during milling was not accompanied by enhanced soft magnetic properties.
Genesis and Growth of Nanoparticles during Sol-Gel Synthesis
Authors: Yao Nan , Yeung King Lun , Xiong Guoxing , Sheng Shishan
Published: April 2011

In situ observation of the genesis and growth of silica-alumina structures during the sol-gel process has been carried out. Although the gross structure of the gel network is kinetically stabilized, in situ AFM study reveals that at nanometer scale, the internal structure of the gel is dynamic as shown by the rich and complex morphological transformations.
Mechanism of Surfactant Removal from Ordered Nanocomposite Silica Thin Films by Deep-UV Light Exposure
Authors: Dattelbaum Andrew M. , Amweg Meri L. , Ruiz Julia D. , Ecke Laurel E. , Shreve Andrew P. , Parikh Atul N.
Published: April 2011

In recent years, methods have been developed for the generation of complex ordered nanocomposite materials through organic templating of inorganic structures. One approach involves preparation of composite materials by an evaporation induced self-assembly process involving organization of organic surfactants and formation of inorganic silica from soluble precursors. Recently, we have shown that deep-UV light (185–254nm) is efficient at removing the surfactant microphase for a routine production of well-ordered mesoporous silica thin films. Here we probe the evolution of surfactant removal from nanocomposite thin film silica mesophases as a function of deep-UV exposure using a combined application of FTIR and single wavelength ellipsometry. Taken together, these data indicate that surfactant removal occurs in a step-wise fashion with the formation of oxidized intermediates prior to complete removal of the surfactant from the thin film.
Synthesis and electrochemical properties of mesostructured 12-phosphotungstic acid thin films with hierarchical structures by triblock copolymer templating
Authors: Yun Hui-suk , Kuwabara Makoto , Zhou Haoshen , Honma Itaru
Published: April 2011

Hexagonally mesostructured 12-phosphotungstic acid (PWA) thin films with both large pore size and hierarchical structures have been successfully prepared by using triblock copolymer templates for the first time. The films is composed by three kind of structures; PWA Keggin anion, monoclinic crystal structure consisting of PWA Keggin anion and organic part (hydrophilic component) of block copolymers, and the hexagonal mesostructure of self-arrayed PWA and block copolymers. The calcined PWA films show better electrochemical properties such as a faster faradic processes and larger specific capacity than normal P WA clusters.
Solution Electrospinning of Nylon/Ferrite Nanofibers
Authors: Dhanote Autumn , Ugbolue Samuel C. , Warner Steven B. , Patra Prabir K. , Katangur Phaneshwar , Mhetre Shamal K.
Published: April 2011

With an average diameter of 80–200 nm, nylon fibers embedded with ferrite nanoparticles were electrospun using a point to plate geometry. The nickel-ferrite particles with a diameter range of 20–30 nm were used to prepare the composite electrospun nanofibers. The ferrite nanoparticles were dispersed in the polymer solution using a surfactant dodecyl benzene sulfonic acid (DBSA). Ultrasonication was used to dissolve nylon-6 into the formic acid/particle dispersion. Electrospinning of virgin polymer solution and particle filled polymer system was carried out with polymer concentration of 15% w/v. The particle loading was 3%w/w. SEM of the particle filled fibers show some bead formations and a diameter distribution of about 80–200 nm. The DSC analyses of the neat nylon polymer fibers and ferrite filled nanofibers show an increase in glass transition temperature from 55°C to 72°C. The melting temperature showed a decrease from 226°C to 201°C. The TEM images show the presence and some alignment of particles in the polymer. The electron diffraction pattern of ferrite nanoparticles confirms its crystalline nature.
Carbon/Nafion® Nanocomposite Thin Films as Potential Matrix-free Laser Desorption-Ionization Mass Spectroscopy Substrates
Authors: Kalkan A. Kaan , Fonash Stephen J.
Published: April 2011

Carbon/Nafion® nanocomposite thin films developed through a low-cost procedure were shown to function as high-sensitivity, low-noise, high-throughput laser desorption-ionization mass spectroscopy substrates for small molecule detection without the need of organic matrices. Our nanocomposite approach combines the strong light absorption feature of amorphous carbon with Nafion®'s efficient protonating capability to yield superior laser desorption-ionization.
Hook Formation of Electrically Driven DNA Collisions with Finite-Sized Obstacles
Authors: Randall Greg C. , Doyle Patrick S.
Published: April 2011

We present a comprehensive study of the hooking mechanism of a single DNA molecule in electrophoretic motion colliding with a single microfabricated obstacle. During a collision, DNA impacts an obstacle and deforms. The impact conditions dictate whether this collision results in a “roll-off” event or “hooking” event. Our objective is to better understand the physics of a collision. Specifically, we note that a finite-sized insulating obstacle induces local electric field gradients that can enhance the size-dependent hooking probability. We validate that the hooking mechanism is analogous to a polymer in a transient, non-homogeneous elongational field with a strength characterized by the Deborah number, De. We then show that hook formation increases with De for finite-sized obstacles in the regime De<40.
Simulations of Polymeric Membrane Formation by Immersion Precipitation: Liquid-liquid Demixing
Authors: Zhou Bo , Powell Adam
Published: April 2011

The immersion precipitation process makes most commercial microporous membranes, which enjoy widespread use in filtration and purification. This process begins with liquid-liquid demixing of a nonsolvent/solvent/polymer ternary system into polymer-rich and polymer-lean phases. This demixing step determines much of the final morphology. In this work, a ternary Cahn-Hilliard formulation incorporating a Flory-Huggins homogeneous free energy function is used to simulate phase separation during demixing. Then the formulation is coupled with constant-viscosity interface-driven fluid flow. Simulations begin with uniform initial conditions with small random fluctuations, and then with two-layer polymer-solvent/nonsolvent initial conditions to simulate actual membrane fabrication conditions. The results are presented in 2-D and 3-D, which demonstrate the effects of mp (degree of polymerization), Kij (gradient penalty coefficients) and χij (Flory-Huggins interaction parameters) on phase separation behavior.
Anomalous Kinetics of Depletion Zone Growth with One-Dimensional Geometry: Photobleaching Experiments and Simulations
Authors: Peng Hailin , Park Sung Hyun , Taitelbaum Haim , Kopelman Raoul
Published: April 2011

We studied the kinetics of a diffusion-limited trapping reaction A + T → T in an effective one-dimensional geometry by experiments, supported by simulation calculations. The experiments are based on the photobleaching reaction of fluorescein dyes. The main parameter of interest is the θ-distance, which is related to the expansion of the depletion zone and can be measured directly from experiment. We found that θ-distance scales with t1/2 asymptotically, as predicted by previous theory. In addition, we found that the θ-distance increases faster than t1/2 inside the trap at early times, which has not been explored previously. Furthermore, there is a third, intermediate regime, with a slow increase of slope. Our experimental results are consistent with our simulation results.
Plasma Coating and Enhanced Dispersion of Carbon Nanotubes
Authors: He Peng , Lian Jie , Shi Donglu , Wang Lumin , Ooij Wim van , Mast David , Li W. Z. , Ren Z. F.
Published: April 2011

Ultrathin polymer films have been deposited on both multi-wall and aligned carbon nanotubes using a plasma polymerization treatment. TEM experimental results showed that a thin film of polystyrene layer (several nanometers) was uniformly deposited on the surfaces of the nanotubes including inner wall surfaces of the multi-wall nanotubes. The coated multi-wall nanotubes were mixed in polymer solutions for studying the effects of plasma coating on dispersion. It was found that the dispersion of multi-wall carbon nanotubes in polystyrene composite was significantly improved. The deposition mechanisms and the effects of plasma treatment parameters are discussed.
Strength Variations during Mechanical Alloying Through the Nanostructural Range
Authors: Schuh Christopher A. , Schoen David T. , Lund Alan C.
Published: April 2011

During processes of mechanical alloying the characteristic structural length scales of an alloy, including the phase domain size and the crystallite grain size, decrease gradually to a nanocrystalline or even amorphous final state. This method therefore allows a unique avenue to explore the structure-property relationship over several orders of magnitude in length scale. In this work we have considered an ideal equiatomic Ti-Zr system deformed through multiple cold-rolling passes to refine the structural length scales into the nanometer range. The variation of the hardness of the system with decreasing length scale is discussed in terms of traditional Hall-Petch scaling, chemical mixing and the phase evolution of the system, as well as other possible contributions to the hardness variations during processing.
Structural Stability of Nano-Sized Clusters
Authors: De Hosson J. Th. M. , Palasantzas G. , Vystavel T. , Koch S.
Published: April 2011

This contribution presents challenges to control the microstructure in nano-structured materials via a relatively new approach, i.e. using a so-called nanocluster source. An important aspect is that the cluster size distribution is monodisperse and that the kinetic energy of the clusters during deposition can be varied. Interestingly the clusters are grown in extreme non-equilibrium conditions, which allow obtaining metastable structures of metals and alloys. Because one avoids the effects of nucleation and growth on a specific substrate one may tailor the properties of the films by choosing the appropriate preparation conditions.
Bending of Nanoscale Thin Si Film Induced by Growth of Ge Islands: Hut vs. Dome
Authors: Huang Minghuang , Cuma Martin , Lagally M. G. , Liu Feng
Published: April 2011

We perform atomistic simulations to compute bending of freestanding nanoscale thin Si film induced by strained Ge islands. We show that a larger Ge dome island can induce smaller bending than a smaller hut island and explain the surprising experimental observation for growth of Ge islands on patterned silicon-on-insulator substrate (SOI) with Si template layer thinned down to nanometer scale. This counterintuitive bending behavior is caused by strain sharing between the film and the ultra thin substrate.
Direct Measurement of the Nanoscale Mechanical Properties of NiTi Shape Memory Alloy
Authors: Shaw Gordon A. , Crone Wendy C.
Published: April 2011

The mechanical properties of sputter-deposited NiTi shape memory alloy thin films ranging in thickness from 35 nm to 10 μm were examined using nanoindentation and atomic force microscopy (AFM). Indents made in films as thin as 150 nm showed partial shape recovery upon heating, although film thickness was found to have a marked effect on the results. A modified spherical cavity model is used to describe the findings, which suggest that the substrate tends block the shape memory effect as film thickness decreases below a threshold level which is specific to applied load. This has the net effect of decreasing the indent recovery below the critical film thickness. The fact that the spherical cavity model predicts the critical film thickness at which the shape memory effect is blocked indicates that the increased recovery of nanoscale indentations is due to a suppression of plastic processes rather than an enhancement of shape memory processes.
Effect of Coupling Agent on the Dispersion of PETG Montmorillonite Nanocomposite films.
Authors: Ranade Ajit , D'Souza Nandika , Gnade Bruce , Thellen Christopher , Orroth Caitlin , Froio Danielle , Lucciarini Jeanne , Ratto Jo Ann
Published: April 2011

Polyethylene terephthalate glycol (PETG) is a clear amorphous polymer, which is extensively used in flexible packaging. The dual packaging requirements of recyclability and long-term shelf life are often difficult to achieve. Meeting these needs become more urgent when considering food packaging for large volumes of soldiers positioned in different parts of the world. Our approach is to develop a high barrier PET packaging system via the Montmorillonite layered silicate (MLS) based nano technology. Prior research has indicated the significant impact of the polymer crystalline regions on the properties of the resultant nanocomposite. Therefore we must first investigate the amorphous PETG. We must also investigate the influence of increased matrix polarity on dispersion of the PETG by incorporating maleic anhydride (MA) onto the PETG backbone. The influence of the clay concentration and maleation are independently investigated. The glass transition of the as-processed and annealed samples are analyzed using Differential Scanning Calorimetry (DSC) while the thermal stability is determined using Thermogravimetric Analysis (TGA). Testing showed a slight depression in the glass transition temperature of PETG film when the MLS is introduced into the system. The nanocomposite films also demonstrated a lower thermal stability in relation to the neat PETG films. The barrier properties were determined on an in-house built calibration unit based on atomic mobility under high vacuum. X-ray diffraction and TEM were utilized to determine the dispersion of the MLS in PETG. The results indicate that the dispersion was concentration independent but maleation of the PETG led to a slight decrease in agglomeration. An increased ultimate tensile strength and modulus was observed in PETG nanocomposites. The barrier properties were improved by incorporating the MLS into the system. Maleation of the PETG resulted in significant yellowing of the nanocomposites.
Deformation Behavior of the Raman Radial Breathing Modes of Single-Wall Carbon Nanotubes in Composites
Authors: Lucas Marcel , Young Robert J.
Published: April 2011

Raman spectroscopy is a technique widely used to study the vibrational modes of carbon nanotubes. The low-frequency Radial Breathing Modes (RBMs) are frequently used to characterize carbon nanotube samples. We report a Raman spectroscopic study on the strain-induced intensity variations of the RBMs of Single-Wall Carbon Nanotubes (SWNTs) in epoxy/SWNT composites. The RBM intensities have been found to vary significantly over a range of strain between -0.3% and 0.7%. The trend (increase or decrease) as well as the magnitudes of the intensity variation depends on the nanotube diameter and its chirality. Using tight-binding calculations, we have shown that these intensity variations can be explained entirely by resonance theory. Electronic density of states calculations confirm that the energy separation between the Van Hove singularities shifts with strain. The nanotubes are thus moved closer or further away from resonance, causing the intensity variations. It is demonstrated that through the use of resonance theory, a tentative chirality can be assigned to each type of SWNT from knowledge of its RBM position and the effect of strain upon the RBM intensity, thus determining its entire structure.
Microstructures Of Irradiated And Mechanically Deformed Metals And Alloys: Fundamental Aspects
Authors: Zinkle S.J. , Hashimoto N. , Matsukawa Y. , Stoller R.E. , Osetsky Yu.N.
Published: April 2011

Recent molecular dynamics and transmission electron microscopy results on irradiated metallic materials are reviewed, with an emphasis on defect production in the displacement cascade and the fluence- and temperature-dependent accumulation of defect clusters. Materials analyzed include Fe, V, Cu, austenitic stainless steel, V4%Cr4%Ti, and ferritic/martensitic steel. Intrinsic differences between the defect accumulation behavior of body centered cubic (BCC) and face centered cubic (FCC) metals are highlighted. Results on the temperature-dependent vacancy cluster density of Cu are discussed in terms of thermal stability of stacking fault tetrahedra (SFTs). Finally, recent results on deformation behavior of irradiated, quenched, and deformed metals are discussed, with particular emphasis on flow localization mechanisms (e.g., dislocation channeling), and experimental and molecular dynamics studies of the detailed dislocation-defect cluster interactions.
Diffuse Electron Scattering by Nanometer-sized Defects in Gold and Tantalum
Authors: Kirk M. A. , Davidson R. S. , Jenkins M. L. , Twesten R. D.
Published: April 2011

Diffuse elastic scattering of electrons by single nanometer-sized defects in ion irradiated Au has been measured quantitatively. Results are given for two dislocation loops and compared with published calculations to establish the loop geometry and interstitial or vacancy nature. Defect images using only diffuse scatttering are achieved with high sensitivity and good resolution by a hollow-cone dark-field method.
Ion Beam-Induced Amorphization of the Pyrochlore Structure-Type: A Review
Authors: Ewing R. C. , Lian J. , Wang L. M.
Published: April 2011

This paper reviews the recent developments in the understanding of the radiation-damage processes in A2B2O7 (Fd3m; Z=8) pyrochlore-structure compounds. Pyrochlore structure compounds display a wide range of behaviors in response to ion beam irradiation. Some compositions, such as Gd2Ti2O7, are amorphized at relatively low doses (∼0.2 dpa at room temperature) while other compositions, such as Gd2Zr2O7, do not amorphize (even at doses of 36 dpa at 25 K) and instead disorder to a defect fluorite structure. The response to ion beam irradiation is highly dependent on compositional changes that affect both the structural distortion from the ideal fluorite structure and the associated energetics of the disordering process. Generally, the ionic size of the cations plays a dominant role in determining the radiation response of different pyrochlore compositions. However, the cation ionic radius ratio criteria cannot be applied all-inclusively in predicting the radiation “tolerance” of a pyrochlore. Systematic irradiation studies of the radiation response of rare-earth (A-site) pyrochlores in which B = Ti, Zr, and Sn have shown that the behavior of the pyrochlore also depends on the cation electronic structure, i.e., the type of bonding, which is closely related to the polyhedral distortion and structural deviation from the ideal fluorite structure. These structural changes affect the dynamic defect recovery process directly linked to the material's response to and recovery from irradiation.
Kinetics of alkali ion exchange of irradiated glasses
Authors: Ojovan Michael I. , Lee William E.
Published: April 2011

The kinetics of alkali ion exchange of irradiated glasses were investigated using the structural energy barrier model for ion exchange of glasses. Derived rates of alkali ion exchange depend both on irradiation dose D(Gy) and dose rate q(Gy/s) illustrating that some effects cannot be simulated by external irradiation and require in-situ measurements. Higher D and q lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a 4 – 6 times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures and are diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur at D far below damaging doses.
Radiation-induced structural changes, percolation effects and resistance to amorphization by radiation damage
Authors: Trachenko Kostya , Dove Martin T , Pruneda Miguel , Artacho Emilio , Salje Ekhard , Geisler Thorsten , Todorov Ilian , Smith Bill
Published: April 2011

We combine simulation, theoretical and experimental results to study radiation damage effects in complex oxides under irradiation. In zircon, we study large density variations in the damaged structure, and show how damage percolation results in the enhanced transport extending to macroscopic lengthscale, and suggest that percolation threshold serve as a benchmark for acceptable waste load in a waste form. In perovskite, we identify common defects in the damaged structure, and relate their stability to chemical bonding. Finally, we formulate the criterion for resistance to amorphization by radiation damage: a material is amorphizable if it is able to form a covalent network.
Coupled Kinetic Monte Carlo and Molecular Dynamics Simulations of Implant Damage Accumulation in Silicon
Authors: Otto Gustav , Hobler Gerhard
Published: April 2011

Damage formation during ion implantation is a complex process that cannot accurately be modeled by binary collision simulations alone. Molecular dynamics (MD) simulations are suited to describe the quenching of collision cascades, while thermally activated processes may be treated with the kinetic Monte Carlo (kMC) method.

MD and kMC simulations have widely but separately been used to investigate damage accumulation and annealing in silicon. Simulation of ion implantation at room temperature, however, requires both methods to be coupled. In this paper we describe for the first time a scheme of the coupling between MD and lattice kMC for damage accumulation. Using this scheme we study the dynamic annealing behavior of implantation damage for heavy and light ions.
Thermal Stability of Thin Films of Ion Beam Deposited CNx
Authors: Ingram David C. , Kayani Asghar , Lanter William C. , DeJoseph Charles A.
Published: April 2011

A dual ion beam deposition system was used to deposit thin films of CNx from a carbon target. A 1 keV nitrogen ion beam from a 3 cm Kaufman source was used to sputter carbon from a graphite target, and a second nitrogen ion beam of 50 eV, from an RF ion source, was used to bombard the growing film with nitrogen ions. Using this technique, rather than direct ion beam deposition from methane, it is possible to reduce the amount of hydrogen in these films to less than 5% (atomic), and to boost the nitrogen content to over 30%. These films were then subjected to isochronal heating up to 900°C to determine the stability of the films as compared to those with much higher concentrations of hydrogen.

CNx is a material that is difficult to fabricate without the inclusion of large amounts of hydrogen. A high hydrogen content has the tendency to make the material sensitive to property changes as it is heated over 200°C. Concomitant with a loss of hydrogen is the loss of nitrogen.

In the films that had lower amounts of hydrogen it was found that the loss of nitrogen during heating was delayed until higher temperatures were reached. However, instead of hydrogen being evolved during heating, the amount of hydrogen in the film increases, reaching a maximum concentration of ∼45% at 800°C.
High-speed Processing with Cluster Ion Beams
Authors: Seki Toshio , Matsuo Jiro
Published: April 2011

Cluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Especially, it is expected that extreme high rate sputtering can be obtained using reactive cluster ion beams. High current SF6 cluster ion beams were recently obtained with new modifications in the basic cluster ion beam technique. The cluster size distribution was measured with Time-of-Flight (TOF) method and the mean size of cluster was about 500 molecules. Si substrates were irradiated with SF6 cluster ions at the acceleration energy of 5–45 keV. Sputtering yield with SF6 cluster ions was increased with acceleration energy and was about 2300 atoms/ion at 45 keV. The sputtering yield was about 1000 times higher than that of Ar monomer ions and was also higher than that of Ar cluster ions. It was found that reactive sputtering occurred with SF6 cluster ion irradiation. These results indicate that high-speed fabrication can be realized with reactive cluster ion irradiation at high energy.
Position Controlled GaN Nano-Structures Fabricated by Low Energy Focused Ion Beam System.
Authors: Nagata Takahiro , Ahmet Parhat , Koida Takashi , Chichibu Shigefusa F. , Chikyow Toyohiro
Published: April 2011

We have demonstrated position controlled GaN nano structures with a combination of surface treatments and nucleation sites control assisted by low energy focused ion beam. Ga ions in the range of 100 eV - 10 keV were irradiated onto the surface of the As-terminated Si (100) to create the nucleation sites. The deposited Ga atoms migrated on the surface and were trapped at the nucleation sites to form Ga droplets. Subsequently an excited atomic nitrogen source was supplied to the surface. By SEM observation, the GaN microcrystals of diameter about 800 nm were found to be allocated every 2 μm periodically on the substrates, and cathodoluminescence peaks from GaN nano structures were observed.
Effects of Substrate Orientation on the Spontaneous Ordering of GaAsSb Epilayers Grown by Molecular Beam Epitaxy
Authors: Gorman Brian P. , Norman Andrew G. , Lukic-Zrnic Reiko , Golding Terry D. , Littler Chris L.
Published: April 2011

Spontaneous atomic ordering is investigated in a series of GaAs1−xSbx epilayers (0.51 < x < 0.71) grown by molecular beam epitaxy (MBE) on GaAs substrates with surface orientations of (001), (001) – 8° toward (111)A, (001) – 8° toward (111)B, (115)A, (115)B, (113)A, and (113)B. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by Fourier transform infrared (FTIR) absorption spectroscopy and corroborated by superlattice reflections in transmission electron diffraction and Raman spectroscopy. Contrary to previous investigations of ordering in III-V alloys, a marked energy gap reduction corresponding to CuPt-B type ordering is observed in the GaAs1−xSbx grown on (111)A-type orientations.
Optical Properties of Quantum-Wires Grown Using Lateral Composition Modulation Induced by (InP)1/(GaP)1 Short-Period Superlattices
Authors: Song J. D. , Kim J. M. , Lee Y. T.
Published: April 2011

The optical properties of quantum wires (QWRs) grown using lateral composition modulation (LCM) were studied by photoluminescence (PL) measurement as a function cryostat temperature (Tcr). 3 stacked arrays of QWRs were formed by sequential growth of ∼ 180 Å-thick LCM layers (lateral period: ∼ 90 Å) induced by (InP)1/(GaP)1 short-period superlattices, and 200 Å-thick InGaP spacers at the growth temperature of 490 °C. The formation of QWRs was confirmed by a transmission electron microscopy measurement. By the analysis of the dependence of PL intensity and peak energy of the QWRs on Tcr, the origin of higher energy peak (H) and lower energy peak (L) were investigated. While behavior of the H peak is similar to that of an ordered InGaP, the L peak shows the insensitivity of PL peak energy to Tcr. This is attributed to compensation of the bandgap by competition of strain in the QWR region and indicates the L peak is related to the QWRs. Strong dependence of the L peak on the position of polarizer also supports this. Additionally, the PL peak intensity of the L peak has the maximum value not at the lowest Tcr (10 K) but at 50 K, while the H peak decrease continuously as T increases. We introduced the idea of compensation of the thermal expansion coefficient to explain this phenomenon.
Room Temperature Resonant Tunneling and Coulomb Blockade in Nanocrystalline Si with Double SiO2
Authors: Wu Barriers L. C. , Chen K. J. , Dai M. , Li W. , Yu L. W. , Huang X. F.
Published: April 2011

We studied electron resonant tunneling and Coulomb blockade in nanocrystalline Si (nc-Si) with double SiO2 barriers, which is fabricated in-situ in a plasma enhanced chemical vapor deposition system. In capacitance-voltage measurements, discrete capacitance peaks due to electron resonant tunneling into energy levels of nc-Si dots and Coulomb blockade charging in nc-Si dots have been observed at room temperature. For smaller dots, capacitance peaks are more distinct due to the stronger Coulomb blockade effect. Meanwhile, conductance plateau in the region of capacitance peaks are also observed due to the charging effect in nc-Si dots. Experimental results are in agreement with theoretical evaluation based on the model of Coulomb blockade.
Nanoengineered Quantum Dot Active Medium for Thermally-Stable Laser
Authors: Tokranov Diodes V. , Yakimov M. , Katsnelson A. , Lamberti M. , Agnello G. , Oktyabrsky S.
Published: April 2011

The influence of a nanoengineering procedure on the properties of single- and multi-layer self-assembled InAs quantum dot (QDs) has been studied using photoluminescence, transmission electron microscopy (TEM), and electroluminescence. Optical properties of QDs were optimized by shape engineering via adjustment of a GaAs overlayer thickness prior to a heating (truncation) step. TEM micrographs have confirmed that the employed growth procedure results in truncated pyramidal QDs covered entirely by AlAs with smooth top interfaces. Truncated QDs with two-monolayer-thick AlAs capping have demonstrated a strong blue shift of ground state (GS) energies and up to 10 meV larger separation between GS and first excited state energy levels as compared to non-capped QDs. We believe that AlAs capping, in combination with truncation procedure, results in significant suppression of carrier transport between QDs within the same layer as well as between QD layers. A record high characteristic temperature for GS lasing threshold, T0 = 380 K up to 55 °C, as well as a maximum saturated gain of 16 (5.3 per layer) cm−1, were measured for a 1.22 μm edge-emitting lasers with this truncated triple layer QD gain medium. A maximum saturated gain, 27 (3.9 per layer) cm−1, and T0 = 110 K have been demonstrated in a 1.19 μm lasers with truncated seven layer QD medium.