bluuebunny/crossref_metadata_2025 huggingface dataset:
Cavitation Erosion and Friction Behavior of Stainless Steel as a Function of Grain Size
Authors: Bregliozzi Giuseppe , Ahmed Syed Imad-Uddin , Schino Andrea Di , Kenny Josè M. , Haefke Henry
Published: April 2011

Research conducted on steels is motivated by a technological need to further improve their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a low yield strength. One way of increasing the yield strength is by grain refining. This work presents a study on the cavitation erosion and friction behavior of AISI 304 austenitic stainless steel characterized by two different grain sizes: 2.5 μm and 40 μm. The cavitation erosion behavior in water with different pH values and at room temperature has been studied by using a 20 kHz ultrasonic vibratory apparatus. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH value; decrease of this value produces an increase in surface damage. Using a precision microtribometer, with applied loads in the μN regime, it was found that capillarity plays a dominant role. At the same loads, in high humidity environments, both the fine and coarse grain steels exhibit high friction relative to measurements performed under dry conditions. At high loads (20 mN and above) a reversal in microfrictional behavior occurs in that friction is higher under dry conditions than under moist conditions.
Field Emission from the Carbon Nanotubes Grown over Cylindrical Surface
Authors: Sarangi D. , Karimi A.
Published: April 2011

Carbon nanotubes are excellent field emitters due to their high aspect ratios and small radii of curvature. These properties of the nanotubes offer tremendous possibilities for the realization of field emission devices. For the realization of the field emission devices controlled placement and alignment of the nanotubes over the substrate surface is desirable. Furthermore, field emission of the nanotubes in cylindrical geometry has added advantages over planar geometry. But, it is difficult to grow nanotubes uniformly over non-planar substrates such as long metallic cylinders by conventional CVD techniques. In the present investigation we have adopted a very simple technique called as Cold Plasma Chemical Vapor Deposition (CP-CVD) to grow carbon nanotubes over a catalyst-supported metallic wire by resistive heating in hydrocarbon atmosphere at about 750–C. The localized dissociation of the hydrocarbon gas over metallic wire allows well controlled growth of the nanotubes. The field emission performance of these nanotube coated wires was measured in a cylindrical geometry where the aluminum tube was used as an anode. Emission site density is found to be the most important parameter to control the field emission performance. Comparisons of the field emission properties were made using nanotubes grown in different hydrocarbon gases such as methane and acetylene. The effects of other parameters, such as growth time, was also investigated.
Study of the Pull-In Voltage for MEMS Parallel Plate Capacitor Actuators
Authors: Saucedo-Flores Emmanuel , Ruelas Rubén , Flores Martín , Chiao Jung-chih
Published: April 2011

This paper provides new investigation for the static and dynamic behavior of a MEMS parallel plate capacitor derived by analytical and numerical design modeling programs developed in Matlab. One significant finding is about the role, which has so far overlooked in many analyses, of a dielectric layer normally placed on top of the ground electrode to avoid short circuiting risks. It is demonstrated in this paper that this layer produces an increased force between electrodes that in turns decreases the well-known pull-in voltage, Vpi, as compared to the one calculated when this dielectric layer is not considered on the system's static analysis. Expressions for the static Vpi and its corresponding maximum stable electrode swing xpi are derived to take the above effect into account.

The system dynamic analysis is done with a user-friendly Simulink interface constructed to allow easy introduction of capacitor design dimensions, material parameter values and voltage signal stimuli. The impact of any combination of these parameters on the electro-mechanical system behavior, that is, the voltage-electrode position dependence data can be easily extracted and become of help for design decision making on the early design stages of this type of structures. This modeling tool interface is based on solving the full differential equation that describes the free electrode displacement without relying on linearizing the inverse quadratic electrode separation dependence of the electro-static force term. This approach intrinsically takes into account the voltage dependant k-spring softening effect derived precisely from a linearizing simplification. Finally, by applying a saw-tooth voltage waveform, the dynamic pull-in voltage and the maximum stable electrode travel range are observed to go well beyond the predicted static pull-in voltage and travel range values.
Metastable Phase Formation and Stimulated Transitions in Metallic Nanometer Films
Authors: Meyer Dirk C. , Levin Alexandr A. , Braun Stefan , Gorbunov Andre , Mertig Michael , Pompe Wolfgang , Paufler Peter
Published: April 2011

Due to the non-equilibrium nature of deposition techniques, thin films can exhibit an energetic state far from thermodynamic equilibrium. Energy supply can stimulate a transition into other metastable states. Examples of metastable phase formation presented in this work are thermally stimulated solid state reactions in metallic nanometer Al/Co/Ni multilayers and phase formation and transition in metallic alloy films of the elemental materials system Fe-Cr. An interesting application illustrates the technical potential of metastable nanometer films.
Spin-Dependent STM Tunnelling Study of the Patterned Magnetite (111) Surface
Authors: Berdunov N. , Murphy S. , Mariotto G. , Shvets I. V.
Published: April 2011

Under oxidizing preparation conditions the magnetite (111) surface reconstructs to a highly ordered superlattice. This surface reconstruction represents an oxygen-termination of the magnetite bulk. We employ spin-polarized (SP) STM to study the spin-dependent tunnelling between a magnetite (111) sample and an antiferromagnetic tip through a vacuum barrier. Atomic scale STM images show significant magnetic contrast corresponding to variations in the local surface states induced by oxygen vacancies. The local variations of the tunnelling magnetoresistance around these vacancies correspond to 150%. By employing SP-STM measurements and First principles calculations we could conclude that an oxygen top-layer considerably changes the SP properties of the magnetite surface. We explain the appearance of the superstructure in terms of electron-lattice instability due to the surface strain.
A Thermodynamic Approach in Tuning Phase Stability in Nanocomposite Multilayers
Authors: Thompson G. B. , Banerjee R. , Fraser H. L.
Published: April 2011

Changes in the crystallographic phase stability of individual layers in a multilayered thin film stack are expected to have a significant influence upon the functional properties of the structure. The ability to predict and tune these phase stability states is of relevant importance in order to maximize the functional properties of the multilayer. A classical thermodynamic methodology, based upon competitive volumetric and interfacial free energies, has been used in the prediction and subsequent confirmation of the hcp to bcc phase stability in a Ti/Nb multilayer. An outcome of this model is a new type of phase stability diagram that can be used to predict the hcp Ti and bcc Ti phase stability as a function of length scale and volume fraction. The Ti layers were subsequently alloyed with a bcc-stabilizing element. The alloyed sputtered deposited Ti layers were able to stabilize the bcc Ti phase to a larger layer thickness as compared to the unalloyed Ti/Nb multilayers. The percentage of alloying element added to the Ti layer in controlling the critical transition thickness between the two phase states had good agreement with the predictions proposed by the thermodynamic model.
Low Potential Stable Glucose Detection at Carbon Nanotube Modified Gold Electrodes
Authors: Wang S. G. , Zhang Qing , Wang Ruili , Yang D. J. , Yoon S. F. , Zhang R.
Published: April 2011

The subtle electronic properties and large electroactive surface of carbon nanotubes (CNTs) suggest that they have the ability to promote electron-transfer and favor electrocatalytic behavior in electrochemical reactions when they are employed as an electrode. In this paper, CNT-modified gold electrodes for glucose biosensor have been fabricated using multi-walled carbon nanotubes. The CNT-based electrode exhibits a strong and stable amperometric response toward glucose even at a low potential of +0.35 V versus Ag/AgCl in comparison with the glassy carbon-based electrode.
Effects of DC and AC Magnetic Fields on Grain Growth in Electrodeposited Nanocrystalline Nickel
Authors: Matsuzaki T. , Yamada T. , Jyuami K. , Tsurekawa S. , Watanabe T. , Palumbo G.
Published: April 2011

The effects of DC and AC magnetic fields on grain growth in electrodeposited nanocrystalline nickel were studied. Magnetic annealing was conducted at 573K in the ferromagnetic temperature region and at 693K in the paramagnetic temperature region. Both DC and AC magnetic annealing could enhance the grain growth and produced a homogeneous grain structure at 573K. On the other hand, AC magnetic annealing shortened the incubation time for the late stage abnormal grain growth at 693K in the paramagnetic temperature region, while DC magnetic field could not affect the incubation time.
Macroporous Morphology Induced by Phase Separation in Sol-Gel Systems Derived from Titania Colloid
Authors: Konishi Junko , Fujita Koji , Nakanishi Kazuki , Hirao Kazuyuki
Published: April 2011

Macroporous titania gels have been prepared by the sol-gel method starting from aqueous colloidal dispersion of titania. The use of titania sol instead of highly reactive titanium alkoxide allows us to control the rate of gelation. Macroporous morphology is formed when the transitional structure of phase separation is fixed as permanent structures by the sol-gel transition. The domain size can be controlled reproducibly by changing the starting composition. The crystal structure of the titania gel is transformed from anatase to rutile through the heat treatment at 900°C, while the macroporous morphology remains unchanged.
Contact Compression of Self-assembled Nano- and Micro-scale Pyramid Structures on Au (100) Surface
Authors: Wang J. , Ward D. , Curtin W. A. , Kim K.-S.
Published: April 2011

A process of self-assembly induced by electro-chemical etching was used to produce nano and micrometer scale pyramid-structures on (100) surfaces of gold. The pyramids grew in a self-similar fashion with the facets aligned in (114) plane. Using the unique characteristics of the self-similar pyramid structure, plastic compression of the pyramids by a flat-surface platen was performed to study length scale effects in the plastic deformation. A continuum limit analysis and a finite element simulation as well as molecular dynamics simulations were carried out to predict the deformation and load-displacement behavior of the pyramid compression. The limit analysis predicts that the load of compression is proportional to the square of the contact-compression displacement. The continuum analysis provides estimation on the asymptotic behavior of the elastic-plastic load-deflection response of the pyramid under compression for a large value of displacement. The three dimensional molecular dynamics simulation was utilized to study the dislocation activities during the early stage of the pyramid compression. Experiments were also carried out by pressing the pyramids with an atomically flat mica surface. The deformation of the compressed pyramid was measured using an Atomic Force Microscope (AFM). The continuum analyses predict size independent values of the slope change of the pyramid facets near the contact edge, caused by plastic deformation. However, atomistic simulation predicts an opposite value of the slope change to the prediction of the continuum analyses. The AFM measurements of the slope change show size dependent transition from the prediction of the continuum analyses to that of the atomistic simulations. The transition data provide an apparent characteristic length of the size dependence of plastic deformation in a small volume. Molecular dynamics show that at very small length scale the size effect is strongly influenced by surface adhesion effects.
Nanocomposites of Liquid Crystalline Polyhedral Oligomeric Silsesquioxane Particles and Liquid Crystalline Polymers
Authors: Somlai Alline P. , Iyer Subramanian , Schiraldi David A.
Published: April 2011

A new liquid crystalline nanoparticle has been synthesized by the reaction of a cyanobiphenyl derivative with polyhedral oligomeric silsesquioxane (POSS®*). Two POSS nanoparticles, liquid crystalline POSS (LC POSS 3) and a non-LC isooctyl POSS (OPOSS), were then compounded at 2.5 wt % into thermotropic polyester liquid crystalline polymers (LCPs) poly(hexamethylene 4,4'-bibenzoate), poly(diethylene glycol 4,4'-bibenzoate) as well as a frustrated LCP 45:55 poly(ethylene terephthalate-co-4,4'-bibenzoate). These polymers are currently being studied for potential use in high performance fibers and high barrier packaging materials. A comprehensive study of LCP/LC POSS 3 nanocomposites will focus on any changes in the thermal and mechanical properties of the LCPs with increasing LC POSS 3 concentration. It will be determined how incorporation of LC POSS 3 affects the liquid crystalline phases of an amorphous and crystalline LCP. Of special interest is the incorporation of LC POSS 3 into a frustrated LCP. It is proposed that the LC POSS 3 might help to unfrustrate the LCP.
Controlled Hierarchical Pore Structures in Ethylene-Bridged Polysilsesquioxane Gels
Authors: Kobayashi Yuki , Nakanishi Kazuki , Hirao Kazuyuki
Published: April 2011

Formation of hierarchical macropores and mesopores in ethylene-bridged polysilsesquioxane sol-gel systems via concurrent sol-gel transition and phase separation induced by the incorporation of supramolecular templats has been investigated. A series of poly(ethylene-glycol)-poly(propyleneglycol)- poly(ethyleneglycol) triblock copolymers, EOPOEOs, have been employed as supramolecular templates, while 1,2-bis(trimethoxysilyl)ethane was used as a polysilsesquioxane source. Successful combination of templated mesopores and well-defined macropores due to phase-separation has been found in the system with EOPOEOs having 70 PO units and respective 20 EO units. Although similar macroporous morphology has been obtained for all the EOPOEOs with EO chain longer or shorter than 20 units, the optimum composition for the co-continuous macropores and that for templated mesopores deviated from each other, resulting in the failure of producing hierarchical macropores and mesopores.
Characterization and Applications of Modulated Optical Nanoprobes (MOONs)
Authors: Anker Jeffrey N. , Behrend Caleb J. , McNaughton Brandon H. , Roberts Teresa Gail , Brasuel Murphy , Philbert Martin A. , Kopelman Raoul
Published: April 2011

Modulated optical nanoprobes (MOONs) are microscopic (spherical and aspherical) particles designed to emit different fluxes of light in a manner that depends on particle orientation. When particle orientation is controlled remotely using magnetic fields (MagMOONs) it allows modulation of fluorescence intensity in any selected pattern including square and sinusoidal waves. The broad range of sizes over which MOONs can be prepared allows them to be tailored to applications from intracellular sensors using submicron MOONs to immunoassays using larger MOONs (1–10μm). In the absence of external fields, or material that responds to external fields, the particles tumble erratically due to Brownian thermal forces. These erratic changes in orientation cause the MOONs to blink. The temporal pattern of blinking contains information about the local rheological environment and any forces and torques acting on the MOONs.
Phase Separation of a Binary Liquid System in Controlled-Pore Glass
Authors: Schemmel S. , Akcakayiran D. , Rother G. , Brulet A. , Farago B. , Hellweg Th. , Findenegg G.H.
Published: April 2011

The phase separation behaviour and the dynamics of concentration fluctuations of binary liquid mixtures are strongly influenced by confinement effects. We have investigated this confinement effect for the binary system isobutyric acid iBA + D2O imbibed into a mesoporous silica glass (CPG-10). The dynamics of the mixture are studied in the one-phase region as well as in the phase-separated state by means of neutron spin echo spectroscopy (NSE). Moreover, the averaged structures of the liquid are explored by means of small angle neutron scattering (SANS) leading to a length scale 4 < ξ < 9 nm for the fluctuations. The associated effective diffusion coefficient Deff as obtained for NSE is found to decrease with temperature ny nearly one order of magnitude in the temperature range from 75°C to 25°C.
Single Stranded dna Translocation Through a Fluctuating Nanopore
Authors: Flomenbom O. , Klafter J.
Published: April 2011

We investigate the translocation of a single stranded DNA (ssDNA) through a pore, which fluctuates between two conformations, by using coupled master equations (ME). The probability density function (PDF) of the first passage times (FPT) of the translocation process is calculated, displaying a triple, double or mono-peaked behavior, depending on the system parameters. An analytical expression for the mean first passage time (MFPT) of the translocation process is derived, and provides an extensive characterization of the translocation process.
Electrospinning of Carbon Nanotube Reinforced Nanocomposite Fibrils and Yarns
Authors: Lam Hoa , Titchenal Nick , Naguib Nevin , Ye Haihui , Gogotsi Yury , Ko Frank
Published: April 2011

Single wall (SWNT) and multi-wall carbon nanotubes (MWNT) were electrostatically assembled into nanofibers through an electrospinning process in order to increase the strength and toughness of polyacrylonitrile (PAN)-derived carbon fibers. It was found that the effectiveness of carbon nanotubes (CNT) in reinforcing the PAN precursor is highly dependent on the dispersion and the alignment of the CNT. Alignment was achieved during electrospinning by the flow of polymer, electrostatic charge and diameter confinement. Up to 10 wt. % SWNT co-electrospun with PAN was successfully produced with fiber diameters in the range of 40 nm to 400 nm. With the addition of 1 wt. % SWNT, a two-fold increase in strength and modulus was obtained in the as-spun nanofibers mat. These encouraging results show a promising pathway to produce the next generation of high performance carbon fibers that will help bridge dimensional and properties gap between nanoscopic and macroscopic structures.
Deposition of TiN/NbN Superlattice Hard Coatings by Ionised Magnetron Sputter Deposition
Authors: Long Yi , Stearn Robert J. , Barber Zoe H. , Lloyd Stephen J. , Clegg William J.
Published: April 2011

We have investigated the effect of ion bombardment on the structure and hardness of thin coatings of TiN/NbN multilayered structures and monolithic films of both TiN and NbN. A radio frequency coil was used to generate an additional inductively coupled plasma between the substrate and the target enabling the sample to be bombarded by a high flux of relatively low energy ions under the appropriate conditions. It is shown that the effect of such bombardment in the case of the monolithic films is to reduce the porosity. This gave an increase in the hardness of both the TiN and the NbN films up to a power of 100 W (using a coil with a cross-sectional area of 2 × 103 mm2). Further increasing the power density led to a decrease in hardness. TiN/NbN multilayer coatings were made under the optimum deposition conditions for the monolithic materials and gave hardnesses greater than those observed in either TiN or NbN and approximately 50% greater than that predicted by a mixtures rule.
Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals.
Authors: Baldinozzi Gianguido , Simeone David , Gosset Dominique , Dutheil Michael , Kusinski Jan
Published: April 2011

Accurate neutron powder diffraction experiments at D20, ILL Grenoble, allowed to monitor the reconstructive tetragonal to monoclinic phase transition as a function of the size of zirconia nanoparticles. In the nanocrystals, both phases are identical to the ones generally observed in micrometric zirconia. Rietveld refinements on these samples point out an increase of the tetragonal fraction and a decrease of the lattice parameters when the size of the particle decreases. An uniaxial strain depending on the grain size is also observed. The phase transition definitely occurs above a threshold crystal size. These results are analysed within the Landau theory and they can be understood as a mechanism of size-dependent phase transition where the primary order parameter is altered by the nanoparticle size.
Modeling and Characterization of Elastic Constants of Functionalized Nanotube Materials
Authors: Frankland S. J. V. , Herzog M. N. , Odegard G. M. , Gates T. S. , Fay C. C.
Published: April 2011

Molecular dynamics simulation and equivalent continuum modeling were used to calculate the elastic constants of 1,3-bis(4-aminophenoxy-4′-benzoyl) benzene (1,3-BABB)/single-walled carbon nanotube (SWNT) materials. The calculated Young's moduli are compared with storage moduli measured experimentally with nanoindentation. Excellent agreement is observed between the calculated and measured modulus values for the 1,3-BABB/SWNT materials.
Ultrathin Cu Films on Mo(110) Characterized by Helium Implantation
Authors: Venugopal Vinay , Thijsse Barend J.
Published: April 2011

Point defects and thermal stability of ultrathin Cu films (3–200 Å) deposited on Mo(110) substrate at 300 K have been characterized using thermal helium desorption spectrometry (THDS). Implantation of the samples (10–100 Å Cu/Mo) with 1000 eV He+ aided in detecting He release from monovacancy in Cu films and desorption of the films (above 1200 K) from Mo substrate. A thickness dependent peak is identified in the helium desorption spectra, which is shown to be due to the process of island formation in the Cu films, using pre-implantation annealing treatments for the 40 Å film. Native defects in the films (3–200 Å) were probed using 75 eV He+ implantation.
Study on End-of-Range Defects Induced by Sb Implantation
Authors: Lai Yi-Sheng , Chen J. S. , Ho Y. S. , Sun H. L. , Huang K. B.
Published: April 2011

Extended defects formed by antimony ion implantation in Si(100) was investigated as a function of the implant energy. The implanted layer was examined by cross-sectional electron microscopy (TEM). Post-implantation spike-annealing was also performed from 950°C to 1095°C to examine evolution of defects. From the TEM study, the threshold energy to induce visible defects for Sb implantation was found to be more than 50 keV. A mapping for the location of defects was constructed by TEM and secondary ion mass spectroscopy (SIMS). The end-of-range (EOR) defects, which were possibly formed during the solid phase epitaixy regrowth, were located near the lower bound of the transition region. For 70-keV implantation, extended defects appear at the near-surface and the EOR region. It was observed that the near-surface defects diminished after annealing at more than 1050°C, while the EOR defects became coarsening at 1095°C.
Magnetic Properties in Fe-Ni Invar Alloys Irradiated by High-Energy Ions
Authors: Ono Fumihisa , Komatsu Seiji , Chimi Yasuhiro , Ishikawa Norito , Kambara Tadashi , Iwase Akihiro
Published: April 2011

Anomalously large shift of the Curie temperature has recently been observed in Fe-Ni Invar alloys irradiated with high-energy heavy ions. This large effect can be attributed to the large positive magneto-volume effect essentially originated in the itinerant electron ferromagnetism in Fe-Ni Invar alloys. To investigate the mechanism of the large modification of the ferromagnetism and the structure of the modified portion, measurements of the beam energy dependence of AC-susceptibility-temperature curves have been made. It was found that the amount of the shift of the Curie temperature did not change by increasing the beam energy. On the contrary, the intensity of the susceptibility of the modified portion increased with increasing the ion beam energy. The high-density electronic excitation is considered to be responsible for the large modification of the ferromagnetism in Fe-Ni Invar alloys.
Preparation and Patterning of GaSb Surfaces with Br-IBAE for Antimonide Based Molecular Beam Epitaxy
Authors: Vangala S.R. , Krejca B. , Krishnaswami K. , Dauplaise H. , Qian X. , Zhu B. , Ospina M. , Sung C. , Vaccaro K. , Bliss D. , Goodhue W.D.
Published: April 2011

Bromine Ion Beam Assisted Etching (Br-IBAE) is shown to be useful in removing GaSb wafer chemical mechanical polish (CMP) surface and subsurface damage; creating microstructure patterns in GaSb surfaces through stencil, photoresist, and oxides masks; and stabilizing the as-etched GaSb surface with a thin, easily thermally desorbed oxide layer. Thus, the Br-IBAE technique is well suited as a GaSb surface final-polish technique in overgrowth applications that require “epi-ready” GaSb (100) surfaces for molecular beam epitaxy (MBE) as well as applications such as quantum wires and dots that require high-quality GaSb/AlInGaSb MBE overgrowth over patterned GaSb (100) surfaces.
Self Organized Compound Semiconductor Nanocrystallite Distributions in SiO2 on Silicon Synthesized by Ion Implantation
Authors: Karl H. , Groβhans I. , Stritzker B.
Published: April 2011

The temporal and spatial evolution of sequentially and single ion implanted Cd and Se concentration distributions into thermally grown SiO2 on (001)-Si were investigated. Ex-situ rapid thermal annealing was performed to initiate the reaction-diffusion driven material transport, nanocrystal nucleation and growth. Finally this leads to the formation of buried distinct layers of CdSe nanocrystals. The spatiotemporal evolution of the concentration distributions were quantitatively analyzed by dynamic Secondary Ion Mass Spectrometry (SIMS). It will be shown, that there is a correlated diffusion of Cd and Se when both elements were implanted in overlapping concentration profiles, whereas the single implanted Cd and Se exhibit a completely different diffusion behaviour. In the region of the supersaturated solid solution reaction to thermodynamically stable CdSe clusters takes place. The steep concentration gradient provokes indiffusion of the stoichiometric compound. In the case of a surplus of Cd over Se and long annealing times self-organized, nearly periodic and correlated concentration variations of Cd and Se can be observed. Comparison of the profiles indicate that this pattern formation is controlled by the diffusion and precipitation of the over stoichiometric Cd.
Microanalysis of Self-assembled InAs Quantum Dot Structures Grown for Infrared Detector Applications
Authors: Sarney W.L. , Little J.W. , Svensson S.
Published: April 2011

In an effort to develop materials that are sensitive to mid and far infrared radiation, we examine InAs quantum dot/GaAs matrix multilayer structures grown by molecular beam epitaxy (MBE). Customized electrical and optical properties result from nanoscale-level manipulation of the dots' physical dimensions. The MBE growth temperature can be set to yield dots having the desired lateral dimension; however this leads to dots of insufficient vertical height. It is therefore necessary to grow the dots in a manner that allows independent control of the lateral and vertical dimensions. In this experiment, the vertical dimension is controlled by growing the dots in a multilayer structure with GaAs matrix layers. An initial layer of InAs quantum dots was grown on top of GaAs, followed by a few seconds short growth of GaAs, and then followed by the growth of another layer of InAs dots. The GaAs laterally surrounds, but does not bury, the InAs quantum dots. When the second layer of InAs dots is grown, they tend to self-organize directly on top of the exposed first layer of dots. We then grew a third layer of dots in the same manner. This effectively results in a pseudo-single layer of dots of the desired height which is then completely buried in GaAs. The goal is to develop structures that can be integrated into high operating temperature quantum dot infrared detectors (QDIPs) that have maximum sensitivity, robustness, and portability.
On the Manipulation of Nanoscale Self-Assembly by Elastic Field
Authors: Gao Y.F.
Published: April 2011

Morphological and compositional self-assembly can be manipulated by the long-range elastic field. This paper gives a universal formulation that determines the dependence of energetically favored orientation of those self-assembled structures on the elastic interaction. Elasticity anisotropy can lead to symmetry breaking and herringbone structures. A layered substrate can tune the feature size by modulus mismatch, or tune the orientation if the layers have different orientation preference, or guide the self-assembly by embedded structures. A closed-form result is derived for elastically isotropic layers by using Dundurs parameters. The self-assembled structures can also be affected by a nonuniform residual stress field or external force field. Higher order (nonlinear) perturbation theory, coupling between morphology and composition, and other issues are also addressed in the discussion.
Second- and third-harmonic generation spectroscopy of coupled microcavities formed from all-silicon photonic crystals
Authors: Gusev D. G. , Soboleva I. V. , Martemyanov M. G. , Dolgova T. V. , Fedyanin A. A. , Aktsipetrov O. A.
Published: April 2011

The enhancement of second- and third-harmonic generation (SHG and THG) in all-silicon coupled microcavities (CMC) formed from mesoporous silicon photonic crystals are observed at the resonance of the fundamental radiation with the CMC eigenmodes. Angular splitting of the peaks in intensity spectra of SHG and THG shows monotonous dependence on magnitude of coupling between two identical microcavity spacers controlled by the reflectivity of the intermediate Bragg reflector.
Bias-Voltage Dependence in Atomic-Scale Spin Polarized Scanning Tunneling Microscopy of Mn3N2 (010)
Authors: Smith Arthur R. , Yang Rong , Yang Haiqiang
Published: April 2011

Atomic-scale spin-polarized scanning tunneling microscopy results on the manganese nitride Mn3N2 (010) surface are presented. The images show the row-wise antiferromagnetic structure of the surface. It is shown that the bias voltage between tip and sample affects both the magnetic and non-magnetic components of the height profile. In particular, a reversal of the magnetic contrast is shown to occur at a certain bias voltage.
Neutron Studies of Magnetic Recording Media
Authors: Lee S. L. , Thomson T. , Ogrin F. Y. , Oates C. , Wismayer M. , Dewhurst C. , Cubitt R. , Harkness S.
Published: April 2011

Small-angle neutron studies have been performed on samples of continuous inhomogeneous magnetic recording media. This has allowed the local magnetic structure to be probed at a sub-nanometre resolution, revealing some interesting information about the size and shape of the magnetic grains and their relation to the physical grains.
Heteroepitaxy of InSe/GaSe on Si(111) Substrates
Authors: Jasinski J. , Liliental-Weber Z. , Chaiken A. , Gibson G.A. , Nauka K. , Yang C.C. , Bicknell R.
Published: April 2011

High quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an InxGaySe phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.
Amorphous-to-polycrystal transition in GeSbTe thin films
Authors: Privitera S. , Bongiomo C. , Rimini E. , Zonca R. , Pirovano A. , Bez R.
Published: April 2011

The amorphous-to-polycrystal transition has been studied in Ge2+xSb2Te5 (x = 0.0 and 0.5) films through X ray diffraction analysis and in situ electrical measurements. Phase separation has been observed in samples with excess of Ge, which cannot be completely converted into thence phase at temperatures lower than 170 °C.By using in situ transmission electron microscopy, the growth velocity and the nucleation rate in Ge2Sb2Te5 films have been measured at different annealing temperatures. Activation energies of 2.8 eV and 2.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated.
Application of High Throughput Methods to the Development of Materials For Non-Magnetic Storage
Authors: Ramberg C. Eric , Wang Y. , Fan Q. , McDermott E. , Wang J. , Kenyon K. , Field M. , Hornbostel M. , Guan S. , Nguyen S.
Published: April 2011

High throughput, thin film synthesis methods have been used to make libraries of diverse metallic and metal-chalcogenide compositions. These libraries have been subject to a variety of screening protocols, including X-ray diffraction (XRD) after repeated annealing steps, and the measurement of temperature dependent electrical properties. The application of these methods for the development of materials for non-magnetic storage media is presented.
Study on a Decision Making Methodology with Uncertainties in the Selection Process of Preliminary Investigation Areas
Authors: Tsuchi Hiroyuki , Seo Toshihiro , Metcalfe Richard , Kawano Kenji , Takase Hiroyasu , Bowden Andrew , Suyama Yasuhiro , Toida Masaru , Furuichi Mitsuaki , Matsumura Atsushi , Yoshimura Miyoshi
Published: April 2011

The selection of Preliminary Investigation Areas (PIAs) to be considered in the siting procedure for a Japanese High Level Radioactive Waste (HLW) repository, will require Site-specific Evaluation Factors (SSEF) to be considered. Evaluation of these factors requires a methodology for taking into account various kinds of uncertainties in varied types of literature data. The study described here evaluated the application of Evidential Support Logic (ESL) for this purpose. The approach involves constructing hierarchical process models. Uncertainties are then propagated from the lowest processes, corresponding to data or information, through intermediate processes, to some top level process of interest, such as “assessing the existence of an active fault”. To evaluate the usefulness of ESL a hypothetical site was assessed. The results demonstrate the value of the approach to support decision-making in the selection of PIAs.
Aqueous Dissolution and Surface Alteration Studies of Nd-bearing Zirconolite in 0.001M Citric Acid at 90°C
Authors: McGlinn Peter J. , McLeod Terry , Leturcq Gilles , Aly Zaynab , Blackford Mark G. , Zhang Zhaoming , Li Huijun , Lumpkin Gregory R.
Published: April 2011

Nd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.

Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.

By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.
Radiation Effects in Murataite Ceramics
Authors: Lian J. , Wang L. M. , Ewing R. C. , Yudintsev S. V. , Stefanovsky S. V.
Published: April 2011

Synthetic murataite, an isometric, derivative of the fluorite-structure, has been proposed as a potential host phase for the immobilization of rare earth elements (REE) and actinides. A 1 MeV Kr+ ion irradiation has been performed on synthetic murataite ceramics in the system Ca-Ti-U-Mn-Al-Zr-Ce-O for different structural multiples of the fluorite unit cell. The temperature dependence of the amorphization dose has been determined. A higher critical temperature was obtained for the disordered murataite as compared to that of murataite superstructures, suggesting that murataite becomes more “resistant” to ion beam-induced damage with increasing degrees of structural disorder.
A Comparison of Wasteforms and Processes for the Immobilisation of Iodine-129
Authors: Maddrell E. R. , Abraitis P. K.
Published: April 2011

A range of potential wasteforms for the immobilisation of iodine-129 have been synthesised and compared. The work used both iodosodalite and iodovanadinite, as identified in previous studies, as baseline iodine host phases. Syntheses of related compounds using alternative precursors had varying degrees of success. In addition it was shown that iodine could potentially be isolated in a simple composite wasteform of silver iodide particles in a rutile or anatase matrix. Preliminary leaching studies suggest that iodosodalite dissolves congruently whilst iodovanadinite shows preferential release of iodine at a rate approximately ten times that of matrix alteration.
Cs+ and Sr2+ Ion-Exchange Properties of Microporous Tungstates
Authors: Luca Vittorio , Griffith Christopher S. , Chronis Harriet , Widjaja Jonathan , Li Huijun , Scales Nicholas
Published: April 2011

The hydrothermally prepared hexagonal tungsten bronze (HTB) phase displays promising distribution coefficients (KD) for both Cs+ (2 – 100 ppm) and Sr2+ (0.5 – 60 ppm) in acidic (1M HNO3) radioactive waste simulants. The development of an inorganic ion-exchanger that displays such selectivity has previously eluded researchers in this field. The selectivity for Cs+ and Sr2+ can be modulated by isomorphous substitution of molybdenum into the tungstate framework, and is optimum for material of nominal composition, Na0.2Mo0.03W0.97O3·zH2O (Mo-HTB). Both the parent HTB and Mo-HTB phases display fast ion-exchange kinetics for Cs+ and Sr2+ and cation exchange capacities ca. 50% that of the theoretical capacities of 0.9 and 0.45 mmol.g−1, respectively. The Mo-HTB adsorbent has a modest tolerance to alkali metal ions such as Na+ and K+ in acidic solutions with total Cs+ and Sr2+ uptake dropping by 66% as the concentration of Na+ increases from 9 mmol.L−1 to 1200 mmol L−1.
Phase Relations and Chemical Durability of Ceramics in the Pseudo-Binary System: CaZrTi2O7–GdAlO3
Authors: Mikhailenko N. P. , Ochkin A. V. , Stefanovsky S. V. , Kirjanova O. I.
Published: April 2011

Phase relations in a pseudo-binary system (1-x) CaZrTi2O7- x GdAlO3 suggested for immobilization of a zirconium - rare earth – actinide fraction of high level waste were studied with X-ray diffraction and electron microscopy. Zirconolite and perovskite were found to be major phases in the ceramic samples prepared by cold pressing and sintering at 1400 and 1500 °C. At relatively low perovskite content (x < 0.5) zirconolite is the major host for Gd, which is considered as a trivalent surrogate for Am and Cm. At higher perovskite content, perovskite becomes the major host for Gd. Zirconolite is the major host phase for corrosion products (Al, Fe, Ti, Zr). Leach rates of Gd, 238Pu, and 241Am from the ceramics studied are 10−4–10−5 g/(m2d).
Effect of Synthesis Conditions and Actinide Contents on Phase Composition of Actinide Bearing Ceramics
Authors: Ptashkin A. G. , Stefanovsky S. V. , Yudintsev S. V. , Perevalov S. A.
Published: April 2011

Pu-bearing zirconolite and pyrochlore based ceramics were prepared by melting under oxidizing and reducing conditions at 1550 °C. 239Pu content in the samples ranged between ∼10 and ∼50 wt.%. Phase composition of the ceramics and Pu partitioning were studied using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive system (SEM/EDS). Major phases in the samples were found to be the target zirconolite and pyrochlore as well as a cubic fluorite structure oxide. Normally the Pu content in the Pu host phases was 10–12 wt.%. This corresponds to the Pu content recommended for matrices for immobilization of excess weapons plutonium. At higher Pu content (up to 50 wt.%) additional phases, such as a PuO2-based cubic fluorite-structured solid solution, perovskite, and rutile were found.
Modeling of the Effects of Radiolysis on UO2-dissolution Employing Recent Experimental Data
Authors: Jonsson Mats , Nielsen Fredrik , Ekeroth Ella , Eriksen Trygve E.
Published: April 2011

This study examines the effect of water radiolysis on the dissolution of uranium dioxide. A model is created to describe the system of uranium dioxide fragments in water, and the production and reactions of radiolysis products (using recent kinetic data). The system is evaluated under different conditions using MAKSIMA-CHEMIST. Conditions examined include presence of carbonate in the water and effects of hydrogen. The simulations are compared to experimental results on spent fuel dissolution. Surprisingly, the simulated U(VI)-release agrees within a factor of three with the experimentally found U(VI)-release. The inhibiting effect of hydrogen is clearly demonstrated by the simulations. From the results of the simulations we are also able to conclude that the main inhibiting effect of H2 is the reaction with OH• and not the reduction of U(VI) to U(IV).
Understanding the Influence of Spatially Varying Retardation Effect on the Solute Transport
Authors: Niibori Yuichi , Shimoda Satoko , Tanaka Kouichi , Tochiyama Osamu
Published: April 2011

A two-dimensional approach to understanding the heterogeneity in retardation effect governing the solute transport was carried out. To express the simplified spatial distribution of retardation effect, this study prepared parallel flat boards packed with two kinds of solid materials, where these materials were not mixed, but arranged as two kinds of the layers in a direction parallel to the flow. The ratio of the width of the constituent layer to the total transport distance was assumed to be one of key parameters describing the solute release profile transported through the media. As a tracer, Eu3+ in HNO3 solution was used, and its breakthrough curve was monitored in the experiments. In order to determine the retardation coefficient of the each layer, the retardation coefficients was obtained from the separate column experiment. Moreover, the permeabilities of both layers were confirmed to be almost identical from the one-dimensional, column experiments. A mathematical model was constructed to express the two-dimensional advection and dispersion of the solute through the media with the distribution of retardation effect. The proposed mathematical model and the experimental results showed good agreements, and indicated that the solute release profile strongly depended on the ratio of the width of the constituent layers to the total transport distance and the standard deviation of the retardation.
An Approach to Sorption on Minerals Making Use of Surface Phase Thermodynamics
Authors: Emrén Allan T.
Published: April 2011

In performance assessments for nuclear wastes repositories, Kdvalues are often used to describe sorption of radionuclides on fracture surfaces. The weakness of the Kdconcept is that values determined under certain conditions can only be used when the chemistry is similar to those. Alternatives include surface complexation models. The problem with such models is that the parameters required are not easily determined, and thus are missing for several systems.

Another alternative is to use surface phase thermodynamics. Such a theory has been developed, in which the surface of a solid phase and the species adsorbed upon it are treated as a separate phase of variable composition. The composition is described in terms of pure end members. For each end member, the free enthalpy is described by a series expansion. To calculate coefficients, the theory makes use of the fact that at equilibrium, the chemical potential of a component has the same value in all phases. Thus, speciation of the bulk aqueous phase can be used. Making use of only the linear term in the expansion, one measured Kdvalue is enough to determine the corresponding coefficient.

The theory has been applied to sorption of U(VI) on alumina with the aid of data from the literature. The coefficient was determined from the measured Kdvalues in the interval pH = 4 – 12. The resulting model curve was found to agree reasonably well with observed values, although the Kdvaries by a factor of 200.
Biologically Induced Clay Formation in Subsurface Granitic Environments
Authors: Tuck Victoria A. , West J. M. , Bateman K. , Coombs P. , Milodowski A. E. , Edyvean R.
Published: April 2011

Experiments were conducted to identify the rock-water and microbial interactions influencing accelerated smectite-clay formation. Packed columns and stirred batch reactors contained Äspö granodiorite, artificial groundwater mimicking that from Äspö and combinations of three types of subsurface chemolithotrophic bacteria, two of which were indigenous to the Äspö rocks. Results showed evidence that, within 5 days under anaerobic reducing conditions, all three of the bacterial types produced copious biofilamentous ‘meshes’ across porespaces, apparently using the larger grains as anchor points. The biofilaments quickly became encrusted with fine grained material and surrounded with neoformed clay-like deposits. In contrast, the abiotic controls showed little or no evidence of clay formation suggesting that this process is biologically induced or controlled. A second series of abiotic experiments to determine the effects of increased acidity showed evidence of mineral pitting and dissolution along with an increase in concentration of soluble species thought to be important in smectite formation (i.e. Si, Al, Mg, Fe, Ca, Na). However, there was no evidence of clay formation, and the biotic experiments showed no signs of bulk scale pH change, suggesting that either the bacteria are actively concentrating relevant chemical species at a local level or they are acting as templates or nucleation points for clay formation.