bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, optical and electrical properties of the novel semiconductor alloy ZnOxTe(1-x)
Authors: Porter H. L. , Jin C. , Narayan J. , Cai A. L. , Muth J. F. , Holland O. W.
Published: April 2011

Epitaxial films of undoped ZnOxTe(1-x) have been prepared on double-side polished c-axis oriented sapphire substrates with pulsed laser deposition. The method of epitaxial growth is expected to have the same domain matching epitaxial relationship with sapphire as does pure ZnO, where six lattice planes of ZnOxTe(1-x) match with seven lattice planes of sapphire [1,2]. High quality, single crystal, epitaxial alloys with around 4% Te have been grown that demonstrate excellent optical properties and a pronounced, sharp excitonic peak, in optical transmission. The incorporation of Te makes the compound more covalent, and less ionic than pure ZnO. Transmission electron microscopy (TEM) demonstrates single-crystal growth with a sharp interface. The low-resolution X-ray diffraction (XRD) pattern of ZnOxTe(1-x) films is almost indistinguishable from those of pure ZnO, except a usually diminished intensity of the (0004) peak. The incorporation of Te in ZnO was verified by a shift in excitonic peak position in absorption, and through a shift in cathodoluminescence (CL) peak. X-ray photoelectron spectroscopy (XPS) data verifies incorporation of telluride chemical state of tellurium atoms. Rutherford backscattering/channeling (RBS/C) confirmed crystal quality for the pure ZnO films. Hot-point probe measurements indicate as-grown, undoped films to be somewhat higher in resistivity than pure ZnO with inconclusive carrier type, as compared to the naturally n-type ZnO. This may be a consequence of the more covalent bonding between Zn and Te and suggests a possible strategy for p-type doping.
Intersubband Transitions in InAs/AlSb Quantum Wells
Authors: Li J. , Kolokolov K. , Ning C. Z. , Larraber D. C. , Khodaparast G. A. , Kono J. , Ueda K. , Nakajima Y. , Sasa S. , Inoue M.
Published: April 2011

We have studied intersubband transitions in InAs/AlSb quantum wells experimentally and theoretically. Experimentally, we performed polarization-resolved infrared absorption spectroscopy to measure intersubband absorption peak frequencies and linewidths as functions of temperature (from 4 K to room temperature) and quantum well width (from a few nm to 10 nm). To understand experimental results, we performed a self-consistent 8-band k·p band-structure calculation including spatial charge separation. Based on the calculated band structure, we developed a set of density matrix equations to compute TE and TM optical transitions self-consistently, including both interband and intersubband channels. This density matrix formalism is also ideal for the inclusion of various many-body effects, which are known to be important for intersubband transitions. Detailed comparison between experimental data and theoretical simulations is presented.
Recent Developments in Magnetic Recording Heads
Authors: Tanaka Atsushi , Oshiki Mitsumasa
Published: April 2011

Recently developed and future magnetic head technologies are reviewed. Scaling of dimensions brought about significant increases in recording densities in the last decade. On the recording head aspect, as the read head is narrowed, large improvements in sensitivity are required. Therefore, spin-valve read heads have been improved by introducing synthetic ferromagnetic pinned layers, a spin filter back layer and a specular scattering layer. The current perpendicular to plane (CPP) structure is now being adopted instead of the current in plane (CIP) structure which is the present magnetic head structure. Under heads with a CPP structure, tunneling magnetoresistance (TMR) devices and multilayer GMR are candidates. In CPP mode, we can make better use of “spintronics” or spin-dependent conduction phenomena because device character depends more directly on the spin-dependent electronic states of the materials. Future technologies of read head are also discussed.
Materials selection for SrTiO3-based epitaxial oxide field-effect devices
Authors: Shibuya K. , Ohnishi T. , Kawasaki M. , Koinuma H. , Lippmaa M.
Published: April 2011

We have studied the growth of four wide gap insulator materials, CaHfO3, CaZrO3, NdGaO3, and LaGaO3 on SrTiO3. CaHfO3 was selected as the best material for forming the insulator layer of an all-oxide field-effect device because the films had the best crystallinity on SrTiO3 (100) and the highest breakdown field. (La,Sr)TiO3 was selected as a metallic oxide for fabricating the source and drain electrodes. Metallic layers were obtained by depositing ultrathin amorphous LaTiO3 films at room temperature on SrTiO3 and postannealing at high temperature to promote Sr diffusion from the substrate into the film.
Surface Dynamics of GaAs Thin Film Formation by Pulsed Laser Deposition Investigated Using RHEED
Authors: Pun A. , Durbin S.M. , Kennedy J. , Markwitz A. , Reeves R. , Zheng J.P.
Published: April 2011

Post-growth surface dynamics of epitaxial GaAs (100) thin films grown by pulsed laser deposition (PLD) have been studied using dynamic reflection high-energy electron diffraction (RHEED) in an effort to better understand the growth mechanisms present in pulsed laser deposition. Results have indicated, as expected, that processes occurring at reduced substrate temperatures manifest themselves more slowly than at elevated temperatures. This has been shown through the analysis of static RHEED images and dynamic specular beam intensity as well as profile scans.
Time Resolved Studies of Focused Ion Beam Induced Tungsten Deposition
Authors: Langfischer H. , Harasek S. , Wanzenboeck H. D. , Basnar B. , Bertagnolli E.
Published: April 2011

In this study we investigate the nucleation and growth mechanisms of tungsten films processed by focused ion beam (FIB) induced chemical vapor deposition. For our investigation we use a 50 keV Ga+ ion beam focused on the substrate target and tungsten hexacarbonyl (W(CO)6) as precursor gas. Mediated by the substrate the energy of the impinging ions leads to the decomposition of the tungsten hexacarbonyl molecules adsorbed on the substrate into volatile parts and nonvolatile residues forming a metal deposit. Time resolved FIB secondary electron microscope imaging in combination with atomic force microscopy reveal first the formation of isolated nuclei and further their coalescence finally resulting in the formation of a contiguous metal layer. Despite the local impacts of the ion beam within the irradiated area of the substrate the localization of the nucleation spots is neither correlated to the spot centers nor to the scan path of the ion beam. After formation, the nanoscale tungsten nuclei preserve their positions and typical shapes during further deposition. Only after merging the nuclei to a contiguous tungsten layer, a further regime of growth sets on which is characterized by deposition of tungsten on a tungsten surface. In this regime the deposition process is determined by the total ion dose and the average current density the samples are subjected to. In this regime, deposition yields up to 3.5 atoms per incident gallium ion are achieved. The contiguous layer quality is determined by Auger electron analysis. The measured growth data were interpreted by adopting the analytic Ruedenauer Steiger approach mainly incorporating ion current density, precursor gas transformation rate, and ion induced sputtering. As a result, the critical ion current density, where ion sputtering exceeds deposition, was identified by the model. Because the model shows excellent agreement with the measurement it should be suitable for further survey concerning focused ion beam process development.
Morphological Instability of Solid-on-Liquid Thin Film Structures
Authors: Huang Rui , Suo Z.
Published: April 2011

Subject to a compressive membrane force, a solid film on a liquid layer may form wrinkles. When the solid film is very thin, surface stresses contribute to the membrane force. When the liquid layer is very thin, the two interfaces bounding the liquid interact with each other through forces of various physical origins. We formulate the free energy of the solid-on-liquid structure, and carry out a linear perturbation analysis. A dimensionless parameter is identified to quantify the relative importance of flexural rigidity, membrane force, and interfacial force. Depending on the nature of the interfacial force, several intriguing behaviors are possible; for example, the solid film may remain flat under a compressive membrane force, or form wrinkles under a tensile membrane force.
Buckling of Thin Films on Substrates: From Straight-Sided Wrinkles to Both Worm-Like and Varicose Structures
Authors: George M. , Cleymand F. , Coupeau C. , Colin J. , Grilhé J.W.
Published: April 2011

The evolution from straight-sided wrinkles to both worm-like and varicose structures has been investigated mainly by atomic force microscopy. The elastic energy variation related to the formation of these two buckling structures has been computed and discussed. It is shown that both transitions are energetically favourable above a longitudinal (along the initial wrinkle axis) critical stress of few GPa in compression, that is of the order of the internal compressive stresses present in the thin films.
Correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 films.
Authors: Khamchane K. , Gunnarsson R. , Ivanov Z.G. , Vorobiev A. , Rundqvist′ P. , Gevorgian S.
Published: April 2011

We have investigated the correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 thin films. The films were epitaxially grown by pulsed laser deposition on (001) SrTiO3 substrates in a temperature range of 690–810°C. According to x-ray measurements, the structure of all films is a mixture of highly oriented domains of strained orthorhombic phases (ortho-I and ortho-II) with different lattice parameters. Films deposited at 780°C show a minimum resistivity (270 μΩcm at 300 K) and a maximum magnetoresistance (8% at 5 K). These films consist mainly of ortho-I phase (a=0.393 nm). Films deposited at 690°C (predominantly ortho-II) have the highest resistivity (up to 1700 μΩcm at 300 K) and lowest magnetoresistance (3% at 5K).
Influence of Structure and Chemistry on Piezoelectric Properties of Pzt in a Mems Power Generation Application
Authors: Eakins L.M.R. , Eakins D.E. , Richards C.D. , Norton M.G. , Richards R.F. , Bahr D.F.
Published: April 2011

PZT films between 1 and 3 μm thick were grown using solution deposition techniques to study the effects of crystal structure, orientation, chemistry and PZT/PZT crystallization interfaces on the piezoelectric output of these films. By varying the chemistry of the film from Zr-rich to Ti-rich the film orientation increased towards {h00}. PZT with 60 wt% Ti exhibited tetragonality and produced greater electrical output at a given strain than the rhombohedral films with concentrations less than 50 wt% Ti. Multiple steps of solution deposition left identifiable PZT/PZT interfaces within the film. TEM, FESEM, and Auger spectroscopy were used to characterize these interfaces, which form upon crystallization of the amorphous PZT film. Internal PZT interfaces are associated with both structural defects (voids) as well as chemical variations such as Pb deficiencies.
Phase and Morphology in Mixed CuO-WO3 Films for Chemical Sensing
Authors: El Madi A. , Meulendyk B. , Pilling R. S. , Bernhardt G. , Lad R. J. , Frederick B. G.
Published: April 2011

Semiconducting metal oxide (SMO) chemiresistive sensors are highly sensitive toward a broad range of hydrocarbons. To develop a gas phase sensor with selectivity toward organophosphorus compounds, such as chemical warfare agents and pesticides, we have developed dosimeters based upon a poisoning mechanism. Here, we report the growth and characterization of WO3 thin films, modified with Cu2O. XPS data show that exposure to phosphonate compounds leads to accumulation of phosphate on the surface, together with dramatic changes in the surface segregation of copper. We present XRD and XPS results to characterize the phase changes following growth, annealing, and exposure to phosphonate compounds. The correlation between sensor response and phosphorous accumulation shows that the highest activity occurs at intermediate coverages of Cu2O, in the15–25 Å range, on 500 Å WO3 films.
Effects of Superimposed Pressure on Flow and Fracture of Two Bulk Amorphous Metals
Authors: Wesseling Paul , Lowhahphandu Peravudh , Lewandowski John J.
Published: April 2011

Tension and compression tests have been performed with high alignment fixtures on two different zirconium-based bulk metallic glass specimens at atmospheric pressure as well as with levels of superimposed hydrostatic pressure up to 700 MPa. The results show essentially no difference in applied flow stress or fracture stress between compression and tension specimens over the range of pressures tested. However, a difference in fracture plane angle between compression and tension specimens was observed, suggesting a normal stress effect, as in granular solids, on the flow and fracture behavior of the bulk metallic glass specimens. The data are compared to various flow and fracture theories over a very wide range of normal stresses. Over the range tested, a Mohr-Coulomb flow theory appears to best describe the data.
Crystallization of Glassy Powder from Aluminum-Rare Earth- Transition Metal Alloys
Authors: Vasiliev A.L. , Aindow M. , Blackburn M.J. , Watson T.J.
Published: April 2011

The microstructures exhibited by gas atomized powders of two alloys, Al-6Gd-6Ni-1Fe and Al-5Y-10Ni (at. %), have been analyzed using electron microscopy. It was found that the microstructure depends critically on the particle size obtained during atomization. Small particles (<1μm) tend to be completely amorphous. Larger particles (1–10μm) can also be amorphous, but often contain a mixture of amorphous material and crystalline Al. Three distinct morphologies are observed: nanocrystalline particles, fractal and dendritic growths embedded in an amorphous matrix. The yet larger particles (>30μm) are often fully crystalline, consisting of fine interspersed Al and intermetallic grains.
Single Particle Jumps in a Binary Lennard-Jones Glass
Authors: Vollmayr-Lee K.
Published: April 2011

We study a binary Lennard-Jones mixture below the glass transition with molecular dynamics (MD) simulations. To investigate the dynamics of the system we define single particle jumps via their single particle trajectories. We find two kinds of jumps: metastable jumps, where a particle jumps back and forth between two or more states, and real jumps, where a particle does not return to any of its former states. For both the real and metastable jumps we present as a function of temperature the number of jumps, jump size, time between jumps, and energy.
Electron screening in bulk amorphous Pd-Ni-P and Pd-Ni-Fe-P alloys
Authors: Li Q. , Greig D. , Matthew J. A. D. , Shen T. H. , Seddon E. A. , Beamson G.
Published: April 2011

Ternary and quaternary bulk amorphous Pd-Ni-P and Pd-Ni-Fe-P alloys were prepared by fast quenching in water. X-ray photoemission spectra of Pd-Ni-P have previously been measured by Alamgir et al. (Phil. Mag. B 79, 239 (1999)). These results have been extended by (a) measuring the Auger spectra and the Auger parameters of key elements, (b) cross correlating the data with PdNi binaries, and (c) investigating the effects of adding Fe. It is shown that the Auger parameters change systematically across the composition range and the results are discussed in terms of possible charge transfer, changes in d-band character, and covalent bonding.
Fatigue Behaviour of Some Fe-Based Metallic Glass Wires
Authors: Verduzco J. A. , Hand R. J. , Davies H. A.
Published: April 2011

The fatigue behaviour of melt-spun Fe78-xCrxSi10B12 and Fe77.5-xCrxSi7.5B15 (0≤×≤8) amorphous alloy wires is compared with those of HT steel wires. The wires were tested in a novel bend fatigue testing machine that imparts compressive to tensile stresses. Tensile strength and microhardness were also measured; these and the fatigue performance improved with the substitution of Fe by Cr. The fatigue performance of the glassy alloy wires was generally similar to that of HT steel wires when expressed on the basis of bend strain but inferior when expressed on the basis of bend stress. Fractography studies revealed differences in the fracture surface features for the amorphous wires, depending on the stress range amplitude. It was also observed that corrosion pits nucleated on the surfaces of glassy wires with zero or low Cr content and resulted in crack initiation at these points.
Long-Term Stabilization of Uranium By U(VI) Phosphate Mineralization in Weathered Bedrock and Soils Developed Over a Granite-Hosted Uranium Deposit
Authors: Jerden James L. , Sinha A. K.
Published: April 2011

The unmined Coles Hill U deposit in the Virginia Piedmont represents a unique natural laboratory for studying the long-term containment of U by phosphate minerals. The primary ore assemblage consists of coffinite and apatite and is hosted in foliated granite. Geochemical and mineralogical studies of the weathered bedrock and soils developed over the primary ore body indicate that U transport is inhibited by the precipitation of meta-autunite group minerals. The lower part of the profile, which consists of ground water saturated saprolite, contains 1400 mg/kg U (in the solid). This concentration is 1.5 times greater than the mean ore grade of the deposit, indicating that the saprolites are enriched in U relative to the underlying primary ore. Uranium within the saprolite is dominantly associated with 10 to 500 μm long, tabular crystals of (Ba, Ca, Sr) meta-autunite. Ground waters from this zone contain less than 14 μg/L dissolved U suggesting that the U(VI) phosphate minerals present are capable of controlling dissolved U concentrations at values lower than the US-EPA maximum contaminant level (30 μg/L). Mineralogical characterization of the unsaturated soil horizons indicate that geochemical conditions in these zones are not conducive to U stabilization by meta-autunite mineralization. In the vadose zone U is primarily associated with Al phosphate (crandallite) and with P adsorbed or coprecipitated with iron oxide mineral coatings. Geochemical gradients suggest that significant amounts of U have been leached from the vadose zone by infiltrating fluids and reprecipitated below the water table, where the activity ratio of dissolved phosphate to carbonate increases. Based on regional weathering rates, the processes responsible for stabilization of U within the Coles Hill system are estimated to have been active for hundreds of thousands of years.
Reactions Controlling Äspö Groundwater Chemistry
Authors: Emrén Allan T.
Published: April 2011

Samples of groundwater are often found to be close to saturation with respect to some minerals. A common approach to modelling of groundwater chemistry is to assume that such minerals control some chemical property of the groundwater. As an example, calcite is often supposed to control the pH value (in addition to concentrations of calcium and carbonate). Here, three models have been used to investigate the control of chemical properties of a groundwater from the Äspö site at the Swedish East Coast.

In the first model, a set of minerals has been selected, in which all minerals are close to saturation with respect to the groundwater. Then an attempt has been made to model formation of the groundwater from rain by letting PHREEQE equilibrate the rain with the minerals.

The second model is similar, but the mineral set used is similar to the one observed at Äspö, and includes also minerals that are far from saturation. To handle the complex situation with numerous minerals and spatial variability, the CRACKER program was used to simulate formation of groundwater from rain.

In the third model, the CRACKER program has been used with the observed groundwater. In the simulation, the water has been disturbed locally, and the relaxation of water chemistry has been studied.

Results from all three kinds of models show that no conclusions on regulation of chemical properties in groundwater can be drawn from saturation properties of minerals. Rather, most properties are controlled by complicated interactions, including spatial variability, irreversible reactions and mixing.
Sodium Zirconium Phosphate [NZP] as a Host Matrix for High Level Radioactive Wastes
Authors: Seida Yoshimi , Yuki Mami , Suzuki Kazunori , Sawa Toshio
Published: April 2011

Various elements (Cs, Sr, Ba, Zr, Ru, Pd, Ce, Nd, Gd, Fe, Cr, Ni, Mo and Te) in the simulated high-level radioactive wastes generated from commercial PUREX reprocessing were immobilized by a ceramic solidification using sodium zirconium phosphate, NaZr2(PO4)3 as a host matrix. The convertibility of the elements to the specific M, A and X sites in NZP crystal structure was determined with consideration of stoichiometry, charge balance and ion size of each element. Small disk samples of NZP waste form containing the elements were prepared by the sol-gel synthesis followed by calcination and compression sinteration at high temperature. The physicochemical structures such as produced phase in the waste forms and dispersion of the embedded elements in the NZP waste forms were investigated by means of XRD and SEM/EDX. Chemical behavior of the embedded elements and the limit of substitution of the NZP structure for the elements were investigated by the series of analysis. Moreover, in order to increase the limit of substitution of NZP, the effectiveness of pretreatment with heating the sol-gel products at 473–773K was experimentally investigated. The capability of embedding of NZP for the elements in HLW has been discussed.
Neptunium Substitution into the Structure of Alpha-U3O8
Authors: Finch Robert J. , Jeremy Kropf A.
Published: April 2011

We synthesized powder samples of NpxU3-xO8 with x between 0 and 0.33. Analyses of solids by x-ray absorption spectroscopy indicate that Np occupies U sites and is predominantly tetravalent. Lattice parameters vary smoothly as a function of Np concentration. The a and b parameters (parallel to structural sheets in U3O8) depend strongly on Np concentration below x = 0.3; however, extrapolation of a least-squares fit up to x = 1 (the maximum value of x if Np is tetravalent) suggests little expected change in a or b for values of x greater than approximately 0.5. The c cell parameter (perpendicular to the plane of the sheets) shows relatively small dependence on Np concentration for all values of x. The a and b cell parameters vary in a complementary fashion, such that the a-b plane and unit-cell volumes remain nearly constant for small x (below ∼0.2). The projected volume increase at higher x may be accommodated by expansion along c; the maximum volume expansion for NpxU3-xO8 is projected to be less than 0.2% up to x = 1. Our results demonstrate that NpxU3-xO8 forms a homogeneous solid solution up to (at least) x = 0.33, and that a complete solid solution may exist between α-U3O8 and NpU2O8; however, the structure of NpU2O8 may resemble that of β-U3O8.
Electron Microscopy Study of Reaction Sintered HLW Glass
Authors: Gong Weiliang , Lutze Werner
Published: April 2011

Reaction sintering under pressure can be used to vitrify radioactive waste. We used defense waste simulate with high concentrations of refractory oxide ZrO2 (∼36 wt%). Silicate glasses with 30 to 50 wt% of waste loading were prepared by hot isostatic pressing (800 °C, 28 MPa). Amorphous silica (50 to 70 wt%) was added to calcined waste simulants. The reaction sintered final products were characterized by scanning and analytical electron microscopy. Our results showed that a continuous glass phase formed. Waste components such as Na2O, CaO, MnO2, Fe2O3, and Al2O3 dissolved in the glass phase. ZrO2 dissolved as well but reached its solubility limit. Nanometer size crystals of baddeleyite (ZrO2) suggest that their presence is a result of super-saturation of the glass phase rather than incomplete dissolution. The sodium concentration increases in the early stages of reaction sintering and decreases towards the end and so does solubility of ZrO2 and other oxides. The microstructure of reaction sintered glasses is determined by a) the concentrations of refractory oxides, b) the concentration of reaction sintering agents, c) the particle size of glass formers, and d) sintering conditions, e.g., temperature and time. Evidence is provided by respective analytical data and micrographs.
Phases Formation and Elements Partitioning in the CaO-Gd2O3(UO2)-MnO-TiO2 System: Application to Rare Earth - Actinide Waste Immobilization
Authors: Kirjanova Olga I. , Stefanovsky Sergey V. , Yudintsev Sergey V.
Published: April 2011

Ceramics within the compositional series Ca4-xGdxMn2Ti7O20+x/2 (x = 0, 1, 2, 3, 4) and a sample with Ca2U2Ti7O20 formulation were studied as promising matrices for immobilization of rare earth (RE) and actinide (An) constituents of high level waste (HLW). The samples were prepared by cold pressing of oxide mixtures in pellets at 200 MPa followed by their sintering at 1400 °C or melting at 1500 °C and examined with X-ray diffraction, scanning and transmission electron microscopy. At x=0 and x=1 a perovskite – pyrophanite assemblage occurred. The sample with x=2 consisted of murataite and perovskite. Murataite was a major phase in the sample with x=3 (pyrochlore and perovskite were minor phases) and the only phase in the sample with x=4 prepared under oxidizing conditions (in air). The latter was composed of two murataite varieties with seven- and five-fold fluorite unit cells. The sample with the same formulation but synthesized under reducing conditions contained pyrochlore as an extra phase. Coupled substitution 2 Gd3+ = Ca2+ + U4+ resulted in formation of pyrochlore as the major phase. Mu-rataite and perovskite are considered as the host phases for rare earths and actinides mainly trivalent, including Pu(III), Am(III), and Cm(III), and corrosion products (Mn, Fe, Al) whereas pyrochlore is the host phase for rare earths and tetravalent actinides (U(IV), Np(IV), Pu(IV)). This makes the system of calcium, gadolinium, manganese, and titanium oxides prospective for immobilization of RE – An fraction of HLW containing minor corrosion products (iron group elements).
Zirconolite-based glass-ceramics for actinides immobilization: Effects of glass composition and of actinides simulant nature
Authors: Loiseau Pascal , Caurant Daniel , Bardez Isabelle , Majerus Odile , Baffier Noël , Fillet Catherine
Published: April 2011

Zirconolite (CaZrTi2O7) based glass-ceramics, in which the crystalline phase (aimed at preferentially incorporating minor actinides or Pu) is embedded in a durable calcium aluminosilicate glassy matrix, can be envisaged as good waste form candidates. In this study, the effect of parent glass composition – and particularly of TiO2, ZrO2, CaO and Al2O3 amounts -on the microstructure and the structure of the glass-ceramics obtained after controlled devitrification (nucleation + crystal growth) is reported. It clearly appears that the volume percentage of zirconolite crystals and their nucleation rate in the bulk of the glass strongly depends both on (CaO + ZrO2 + TiO2) and Al2O3 amounts in parent glass. Neodymium is mainly used to simulate trivalent minor actinides whereas several samples were also prepared with other lanthanides (Ce, Eu, Gd, Yb) in order to investigate the effect of simulant field strength in glass on the nature and the composition of the crystals formed. The effect of partial or total molar substitution of ZrO2 by HfO2 in parent glass composition was also studied in order to prepare Ca(Zr1-xHfx)Ti2O7 (0 < × ≤ 1) based glass-ceramics which could be interesting in order to minimize criticality problems.
Neptunium Speciation in Humic Acid-rich Clay Water upon Interaction With Radioactive Waste Glass Samples
Authors: Pirlet V. , Van Iseghem P.
Published: April 2011

Organic complexes of actinides are known to occur upon interaction of high level waste glass and Boom Clay which is a potential host rock formation for disposal of high level waste in Belgium. The solubility and mobility of237Np, one of the most critical radionuclides, can be affected by the high dissolved organic carbon content of the Boom Clay porewater through complexation with the humic substances. The influence of humic substances on the Np behaviour is considered through dissolution tests of Np-doped glasses in Boom Clay water and through fundamental study of the specific interaction between Np(IV) and the humic acids using spectroscopic techniques. High Np(IV) concentrations are found in the glass dissolution tests. These concentrations are higher than what we should expect from the solubility of Np(OH)4, the solubility limiting solid phase predicted under the reducing conditions and pH prevailing in Boom Clay. Studying the specific interaction of Np(IV) with humic acids in Boom Clay porewater, high soluble Np concentrations are also measured and two main tetravalent Np-humate species are observed by UV-Vis spectroscopy. The two species are interpreted in terms of mixed hydroxo-humate complexes, Np(OH)xHA with x = 3 or 4. These species are the most likely species that can form according to the pH working conditions. Using thermodynamic simplified approaches, high complexation constants, i.e. log β131and log β141respectively equal to 46 and 51.6, are calculated for these species under the Boom Clay conditions.

Comparing the spectroscopic results of the dissolution tests with the study of the interaction of Np(IV) with humic substances, we can conclude that the complexation of Np(IV) with the humic acids may occur and increases the solubility of Np(OH)4upon interaction of a Np-doped glass and the Boom Clay porewater.
The Surface Precipitation During UO2 Leaching Process
Authors: Cui Daqing , Devoy Jérôme , Spahiu Kastriot
Published: April 2011

To understand the influence of cations and silica in groundwater on spent fuel corrosion, the leaching behavior of newly reduced UO2.00 in different solutions was investigated. Uranium concentrations in the solutions were measured and the leached UO2 surface and precipitates on it were analyzed by XPS, laser Raman spectroscopy, SEM-EDS and TEM-EDS. It was found that, in air saturated 2 mM HCO3- solutions, the leaching rates of UO2(s) depend on the composition of the leaching solutions. Very similar leaching rates, 0.5 μg • cm-2 • day-1, were obtained in 0.1 M NaCl and 0.1 M KCl solutions, while that in 0.45mM Ca2+ -0.18 mM Mg2+ -0.2 mM SiO2 containing synthetic groundwater was 10 times smaller. Calcite and quartz like precipitates were detected on the corroded UO2(s) surface.
MTU Laser-Based Direct-Write Techniques: Recent Development and Nanoparticles Patterning Results
Authors: Nadgorny Edward M. , Zhou Changgong , Drelich Jaroslaw , Zahn Randy
Published: April 2011

Two laser-based direct-write techniques to guide particles from a mist source to a target substrate by laser beams were recently developed at Michigan Tech. The laser-guided direct-write (LGDW) technique uses a hollow optical fiber, while the laser-guided microsensor patterning (LGMP) technique uses a micrometer-sized aperture. The techniques are suggested to be utilized for patterning microstructures made of nanoparticles that are either crystallized from liquid precursors or directly deposited from nanoparticle-in-liquid suspensions. The computational results based on the paraxial Fraunhofer approximation of a Gaussian beam diffracted by a circular aperture and experimental measurements of corresponding deposition rate under different conditions suggest several factors for setup optimization of LGMP. The results indicate that among the most important factors are the aperture size relative to the laser beam-waist size and the divergence of the beam near the aperture. Examples of gold-thiolate, protein-coated polystyrene, and carbon-polymer composites deposition are presented.
Scanning Probe Characterization of Localized pH Changes on a Sapphire Surface in the Presence of an Applied Field
Authors: Bullard Joseph W. , Kershner Ryan J. , Cima Michael J.
Published: April 2011

Single crystal sapphire substrates were lithographically patterned with a system of parallel platinum electrodes, which were used to manipulate 1.58μm silica particles inplane, in the presence of an aqueous solution. Observation of the motion of these particles revealed the adhesion of some of them to the sapphire surface near the platinum working electrode, even in the range of pH where the zeta potentials of silica and sapphire are of the same sign. This phenomenon suggests the existence of localized differences in pH, attributable to the presence of potential determining ions produced in the faradaic processes occurring at the electrodes during the electrophoretic manipulation of silica particles. Atomic force microscopy (AFM) was used to corroborate this hypothesis, measuring the forces between a silica particle and a sapphire substrate in the presence of an applied field. The resultant force-distance curves demonstrate a change in the interaction forces between particle and substrate as a function of distance from the electrode. Variations in this interaction correspond to localized differences in the zeta potential of the substrate, which, in turn, are related to localized differences in pH. Quantification of these spatial variations in pH as a function of time yields further information about the diffusion of these faradaically produced potential determining ions across the substrate.
Controlling the position and morphology of nanotubes within a polymer thin film
Authors: Lahiff Emer , Minett Andrew I. , Curran Seamus , Ryu Chang Y. , Blau Werner J. , Ajayan Pulickel M.
Published: April 2011

We introduce a new method of producing polymer/nanotube composites where the morphology of nanotubes within the composite can be controlled. The thickness of the composite thin film can also be altered as required. Carbon nanotubes are grown from organo-metallic micro-patterns. The morphology of the tubes is determined by the conditions under which the tubes are grown and also, the type of catalyst used. These periodic nanotube arrays are then incorporated into a polymer matrix by spin-coating a curable polymer film on the as-grown tubes. The density and position of conduction channels through the thin film composite can be easily pre-determined by controlling the morphology of the embedded nanotubes. This technique of producing freestanding nanotube/polymer composite films represents a more efficient method of combining these materials for potential flexible electronic applications in an inexpensive and scalable manner.
Ceramic Microfabrication Techniques for Microdevices with Three-Dimensional Architecture
Authors: Nair Balakrishnan , Wilson Merrill , Akash Akash , Crandall Joe , Lewinsohn Charles , Cutler Raymond , Flinders Marc
Published: April 2011

The term “microfabrication” has been used primarily as an acronym for silicon-based device fabrication. Recent developments in ceramic processing technology have resulted in cost-effective, scalable options of ceramic microfabrication that offer the potential for fabrication of devices with a number of advantages over silicon-based microdevices for specific applications. These advantages include the ability to fabricate devices with three-dimensional architecture, high-temperature operation up to 1200°C, porous layers for gas diffusion, and textured substrate properties for specific applications through wider materials selection. Processing routes for these ceramic microdevices with three-dimensional architecture include established processes such as tape casting, laser machining, lamination and sintering, or new processes such as reaction bonding and lost-mold techniques. The ability to fabricate three-dimensional feature geometries allows the application of these ceramic microfabrication techniques for device fabrication targeted at a number of applications such as point-of-use high purity gas generation, microchannel devices, microreactors, fiber-optic connectors and heat-pipes for microelectronics.
Gas Adsorption Evidence of Single-Wall and Multi-Wall Carbon Nanotube Opening
Authors: Babaa Moulay-Rachid , McRae Edward , Dupont-Pavlovsky Nicole , Delpeux Sandrine , Beguin Francois , Valsaque Fabrice , Ghanbaja Jaafar
Published: April 2011

Carbon nanotubes offer a surface very similar to that of graphite, a reference substrate in physisorption experiments aimed at studying substrate-adsorbate interactions. The curvature, however, introduces new questions. What are the effects of this on condensation pressures or heats of adsorption? Can one experimentally distinguish between different adsorption sites? In this study, we compare adsorption isotherms of several simple gases (Kr, Xe, CCl4) on singlewall (SWNTs) and multi-wall carbon nanotubes (MWNTs), before and after opening. For mechanically opened SWNTs, the accessibility of the adsorption sites and the molecular arrangements of the adsorbed gases are discussed. With the much bigger, well-defined MWNTs, the “cutting method” called upon a nitric acid treatment followed by a CO2 oxidation. TEM investigations and physisorption studies clearly revealed tube opening and that the inner channels became accessible to Kr molecules.
Molecule Derived Nanomaterials: Chemical Concepts for Composition, Morphology and Particle Size Control
Authors: Mathur Sanjay
Published: April 2011

Conventional material synthesis procedures rely on the intrinsic chemical behaviours (e.g., different hydrolysis rates of the reactants in solution phase reactions or different vapour pressure or thermal stability in the gas phase reactions) of the different components, which make the material properties susceptible to inaccuracies due to an increased number of process variables. As a consequence, phase separation and element segregation are present at the nanometer scale, although the global stoichiometry of the product may correspond to the desired composition. In this context, the use of well-defined molecular precursors is a promising approach to grow extended solid-state structures from atomic constituents.
On Molecular Dynamics Simulation of Metal Clusters and Their XRD and ELNES Spectra
Authors: D'Agostino G. , Gusso M.
Published: April 2011

We report on molecular dynamics calculation of few selected metal clusters by means of classical many-body potential. Despite simplicity of the approach, structural and thermodynamic properties have been achieved, such as an estimation of melting temperature lowering with size. As expected, coexistence ranges are observed instead of a single temperature transition. Phonon spectra have been also evaluated. Thermal atomic displacements at low temperature have been, in turn, estimated by means of Bose statistics.

This work is intended as a step toward computer aided interpretation of cluster characterization by X-ray's or electron beams. Therefore, X-rays diffraction patterns and near edge electron energy loss have been simulated for different model structures in order to provide insights on those characterization technique capabilities.
Quaternary–matrix, nanocomposite self-lubricating PVD coatings in the system TiAlCN-MoS2 – structure and tological properties
Authors: Spassov V. , Savan A. , Phani A. R. , Stueber M. , Haefke H.
Published: April 2011

Nowadays the demands placed upon the tooling in processes such as cutting, drilling, milling, stamping, bending, etc. are constantly growing and restrictive. On one hand, productivity, cost efficiency and quality all require high-speed processes to be developed. On the other hand, environmental safety requires very little or no lubricant to be used (dry cutting or minimized spray-lubrication). When combined, these two considerations mean: the tool should wear very little, withstand high temperatures and the friction between the tool and the work piece should be minimized. An apparent approach to simultaneously satisfying such requirements is coating the tools with self-lubricating hard coatings. Quaternary TiAlCN is a rapidly developing hard coating suitable for a number of cutting applications. The well-known wear-resistant coating TiN has been demonstrated to have improved high-temperature oxidation resistance when aluminum is included, i.e. TiAl N. Addition of yet a fourth element, carbon, has the primary effect of lowering the high friction coefficient occurring between the ceramic coating and steel. The high hardness, toughness, heat resistance and low friction coefficient of TiAlCN make it the ideal candidate for applications such as milling, hobbing, tapping, stamping and punching. MoS2 is a well-known solid lubricant widely used as tribological coatings, especially for applications working in vacuum or dry environment. Combining the wear resistance of the quaternary TiAlCN matrix with the lubricating properties of MoS2 has an extremely beneficial effect in further improving the tribological performance of the resulting composite. The coatings were deposited on hardmetal (WC-Co) and Si (100) substrates using reactive magnetron sputtering. The structure of the coatings is studied by plain-view TEM and XTEM, electron diffraction and ED X. The tribological properties were examined by Pin-on-Disk (PoD) tribometer. The adhesion was estimated by scratch test, and the hardness was measured by nanoindentation. All the coatings examined had a very low friction coefficient (typically below 0.09) and volumetric wear rate against 100Cr6 steel (AISI 52100) of 7.10-7 mm3/N/m. The relation of deposition parameters to structure to properties is discussed. To the authors knowledge, this is the first paper describing quaternary TiAlCN matrix with inclusions of MoS2.
Oxidative Dehydrogenation of Ethylbenzene to Styrene Over Graphite Nanofibers
Authors: Xu Xuejun , Terry R. , Baker K.
Published: April 2011

Tubular and platelet graphite nanofibers were used as catalysts for the oxidative dehydrogenation of ethylbenzene to produce styrene at temperatures between 350 and 577 °C in packed bed tubular quartz flow reactors. The performances of GNF catalysts were evaluated in terms of conversion, selectivity and styrene yield. Tubular GNF showed higher activity than platelet GNF, but the latter showed higher selectivity than the former material. Both types of GNF exhibited significantly better performance than a commercial catalyst when operated under the same conditions.
On the development of the <111> fiber texture in nanocrystalline gold during growth and annealing
Authors: Andreasen Klaus P. , Schell Norbert , Jensen Thomas , Petersen Jakob H. , Jensen Martin S. , Chevallier Jacques , Bøttiger J.
Published: April 2011

The evolution during growth and subsequent annealing of the <111> fiber texture in magnetron-sputtered nanocrystalline Au films has been studied experimentally using X-ray diffraction with synchrotron radiation. To quantitatively investigate this fiber texture, grain orientation distributions were recorded in situ during growth and during subsequent annealing using Bragg-Brentano geometry. The (111) diffraction intensity was measured as a function of the sample tilt χ, the tilt axis lying at the intersection of the film surface and the scattering plane. As a quantitative measure of the texture, we used the width of the orientation distributions. The grain-orientation distributions narrowed during annealing. The activation energy for the process behind this texture change was found to be 0.64 ± 0.05 eV, close to the activation energy for grain boundary self-diffusion in nanocrystalline Au. This and the narrowing of the grain orientation distributions led us to suggest that the observed changes in texture originated from grain rotations and not from grain growth. Grain growth did not take place at the lower temperatures, where changes in orientation distributions were observed.
Growth of Single Crystal Tungsten Nanorods by Oblique Angle Sputter Deposition
Authors: Karabacak Tansel , Wang Pei-I , Wang Gwo-Ching , Lu Toh-Ming
Published: April 2011

We report the creation of single crystal tungsten nanorods with unusual simple cubic β-phase. These novel nano-structures were grown by oblique angle sputter deposition with substrate rotation through a shadowing effect. Transmission electron microscopy (TEM) diffraction patterns from individual nanorods clearly show the single crystal structure. It is evident from TEM diffraction measurements, during the oblique angle deposition, both β-phase W(100) and α-phase W(110) islands exist at the initial stages of growth. However, at later stages of the growth the β-phase structure dominates. This is in contrast to the sputter deposition at normal incidence where only the thermodynamically stable bcc α-phase W(110) polycrystalline films were formed when the film grew to a certain thickness. We explain our results by using the shadowing and adatom mobility mechanisms: At the initial stages of growth, the β-phase W(100) islands grow taller due to the lower adatom mobility on these islands. The taller β-phase W(100) islands survive in the competition during oblique angle growth and form isolated nanorods in the later stages, while the shorter α-phase W(110) islands stop growing due to the shadowing effect. In addition, our Monte Carlo simulation results agree well with the experimental measurements.
Photoluminescence of Si/SiO2, RE2O3/Si/SiO2and RE2O3/Si/Al2O3(RE = Er, Nd, Tm) Sputtered Thin Films
Authors: Rozo C. , Fonseca L. F. , Resto O. , Weisz S. Z.
Published: April 2011

Si/SiO2, RE2O3/Si/SiO2and RE2O3/Si/Al2O3films were sputtered. Si/SiO2films were annealed to 1100°C for 30 min in Ar. RE2O3/Si/SiO2films were annealed to 700°C, 1000°C, or 1100°C for 30 min in Ar. RE2O3/Si/Al2O3films were annealed to 700°C for 30 min in Ar. Raman spectra and photoluminescence (PL) obtained for the Si/SiO2films show relation between Si nanocrystal (nc) presence, Si nanoparticle (np) PL and Si target area. Nd2O3co-sputtered films presented PL for the (4F5/2,2H9/2) →4I9/2,4F3/2→4I9/2,4F3/2→4I11/2, and4F3/2→4I13/2transitions. Er2O3co-sputtered films presented PL for the4I11/2→4I15/2, and4I13/2→4I15/2transitions. Tm2O3co-sputtered films presented PL for the3H4→3H6transition. Different spectral shapes were observed for the infrared (IR) PL of the Er3+ions and of the Nd3+ions for the RE2O3/Si/Al2O3films with respect to the RE2O3/Si/SiO2films.
Vanadium Oxide Nanofibers and Vanadium Oxide Polyaniline Nanocomposite: Preparation, Characterization and Electrochemical Behavior
Authors: Lutta Samuel T. , Dong Hong , Zavalij Peter Y. , Whittingham M. Stanley
Published: April 2011

The sol gel reaction of NH4VO3 and polymethylmethacrylate (PMMA) template followed by hydrothermal treatment formed (NH4)xV2O5-Δ.nH2O rods. TGA, SEM, XRD and FTIR characterized this compound. Heating (NH4)xV2O5-Δ.nH2O in oxygen and nitrogen at 250 °C and 300 °C respectively resulted in the formation of vanadium oxides nanofibers of V3O7 and V2O5. Performance of these compounds as cathode in rechargeable lithium battery was investigated in a LiPF6/mixed carbonate electrolyte. The materials show good cycling with capacity greater than 130mAh/g, which translates to the insertion of 0.5 moles of Li+ per vanadium of the active material.
Non-Lipschitzian Control Algorithm for Nanoscale
Authors: Protopopescu Friction V. , Barhen J. , Braiman Y.
Published: April 2011

We present a robust feedback control algorithm and apply it to the nonlinear oscillator array (Frenkel-Kontorova) model of nanoscale friction. The new control approach is based on the concepts of non-Lipschitzian dynamics and global targeting. We show that average quantities of the controlled system can be driven - exactly or approximately - towards desired targets which become additional, linearly stable attractors for the system's dynamics. Extensive numerical simulations show that the basins of attraction of these targets are reached in very short times and the control exhibits very strong robustness. We investigate the efficiency of the control in terms of various parameters (e.g., system size, non-Lipschitzian exponent).