bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of Piezoelectric Diaphragm Using Lead Zirconate Titanate (PZT) Films
Authors: Hong E. , Krishnaswamy S.V. , Freidhoff C.B. , Trolier-McKinstry S.
Published: April 2011

Piezoelectric diaphragms were fabricated using bulk micromachining. The diaphragms had a unimorph structure, where Pb(Zr0.52Ti0.48)O3 (PZT) and thermally grown silicon oxide (SiO2) films were used as the active and passive layers, respectively. To actuate the diaphragms, two modes were designed: d31 and d33-mode. For d31-mode diaphragms, a Si wafer with Pt/Ti/SiO2 (0.5 νm) was coated with ∼1.2 νm PZT. A Cr/Au top electrode was then evaporated. Each layer including the bottom electrode was patterned into a circular shape. To fabricate d33-mode diaphragms, a Si wafer with thermal SiO2 (0.5 νm) was coated with ∼0.3 νm ZrO2 and ∼1.6 νm of PZT. On top of these layers, a Cr/Au top electrode was deposited and patterned into a ring- shaped interdigitated transducer. Finally, both d31 and d33-mode diaphragms were released using deep reactive ion etching. Diameters of the fabricated diaphragms were in the range of 600 νm and 1000 νm. For d31-mode diaphragms, the dielectric constant and loss of the released piezoelectric layer at 1 kHz were > 800 and < 2%, respectively. The remanent polarization was ∼20 νC/cm2and the coercive field was ∼61 kV/cm. Ferroelectric measurements showed well- developed hysteresis loops for the d33-mode diaphragms. Both d31 and d33-mode diaphragms behave as membranes rather than plates. Their measured resonance frequencies were consistent with calculations from an analytic model for circular membranes and ANSYS finite element analysis.
Palladium Based Micro-Membrane Hydrogen Gas Separator-Reactor in a Miniature Fuel Processor for Micro Fuel Cells
Authors: Karnik Sooraj V. , Hatalis Miltiadis K. , Kothare Mayuresh V.
Published: April 2011

A novel palladium-based micromembrane has been fabricated and tested which has the potential to be used for carbon monoxide shift reaction and hydrogen gas separation in a miniature fuel processor for micro fuel cells. The micromembrane structure is built in silicon substrate, using standard MEMS microfabrication processes. The four layers, viz., copper, aluminum, spin-on-glass (SOG) and palladium form the composite micromembrane. Copper, aluminum and SOG serve as a structural support for the palladium film. Copper also acts as a catalyst in the shift reaction that converts unwanted carbon monoxide gas into hydrogen, which in turn is separated by the palladium micro-membrane. For a particular combination of thicknesses for various layers, the composite micro-membrane withstands a pressure gradient up to 1 atm. The micromembrane separates hydrogen from a 20% hydrogen balance nitrogen gas mixture at room temperature.
The Materials Science of “Permeable Polysilicon” Thin Films
Authors: Dougherty George M , Sands Timothy , Pisano Albert P.
Published: April 2011

Polycrystalline silicon thin films that are permeable to fluids, known as permeable polysilicon, have been reported by several researchers. Such films have great potential for the fabrication of difficult to make MEMS structures, but their use has been hampered by poor process repeatability and a lack of physical understanding of the origin of film permeability and how to control it. We have completed a methodical study of the relationship between process, microstructure, and properties for permeable polysilicon thin films. As a result, we have determined that the film permeability is caused by the presence of nanoscale pores, ranging from 10-50 nm in size, that form spontaneously during LPCVD deposition within a narrow process window. The unusual microstructure within this process window corresponds to the transition between a semicrystalline growth regime, exhibiting tensile residual stress, and a columnar growth regime exhibiting compressive residual stress. A simple kinetic model is proposed to explain the unusual morphology within this transition regime. It is determined that measurements of the film residual stress can be used to tune the deposition parameters to repeatably produce permeable films for applications. The result is a convenient, single-step process that enables the elegant fabrication of many previously challenging structures.
Synthesis, Characterization and Ageing of MgB2
Authors: Serquis A. , Schulze R. , Zhu Y. T. , Coulter J. Y. , Peterson D. E. , Moreno N. O. , Pagliuso P. G. , Indrakanti S. S. , Nesterenko V. F. , Mueller F. M.
Published: April 2011

We studied the influence of sample preparation and defects in the superconducting properties samples using atomic ratios of Mg:B=1:1 and Mg:B=1:2. Samples were characterized by SEM, and XRD, and the magnetization properties were examined in a SQUID magnetometer. The presence of Mg vacancies was determined by Rietveld analysis. Most of the samples exhibited sharp superconducting transitions with Tcs between 37–39 K.

We found a strong correlation between the crystal strain and the Tc. This strain was related to the presence of Mg vacancies. In addition, results showed that some samples degraded with time when exposed to ambient conditions. In these samples the Tc did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. This effect was only present in samples with poor connectivity between grains and smaller grain sizes. The degradation was related to a surface decomposition as observed by X-ray Photoelectron Spectroscopy. No correlation was found between this effect and the presence of Mg vacancies.
Effect of secondary phases in the precursor powders on the transformation to the (Bi,Pb)-2223 phase
Authors: Gundakaram R. , Chang S. C. , Liu R. S. , Woodall L. , Gerards M.
Published: April 2011

The (Bi,Pb)2Sr2Ca2Cu3O2 system [also know as (Bi,Pb)-2223] has shown promise for use in superconducting tapes and wires due to its high transition temperature and high critical current density. The tapes and wires are usually fabricated by the powder-in-tube method, after which they are subjected to thermal and mechanical treatments. Depending on the nature of the heat treatment, phase transformations occur in the powder and it is of paramount importance to understand the response of the powders to different processing conditions. In this study, we have synthesized a precursor powder of the nominal composition Bi1.8Pb0.33Sr1.87Ca2Cu3Oyby spray pyrolysis. The powder was then calcined under controlled conditions between 760 and 800°C in an atmosphere between 0 and 21% O2for 2 to 24 hours with controlled heating and cooling, such that different amounts of Pb are incorporated into the majority phase. The resultant powders were then converted to the (Bi,Pb)-2223 phase with suitable heat treatments. Using powder Xray diffraction and magnetization measurements, the volume fractions of the secondary phases in the precursors were estimated and the effect of the phases on the conversion to the (Bi,Pb)-2223 phase was studied. We show that the ratio of the intensity of the (020) and (115) reflections of the (Bi,Pb)-2212 phase can be used to tune the precursor powders for optimal conversion. While a lower fraction of the secondary phases such as CaO and CuO is desirable in the precursor powders, a higher volume fraction of Ca2PbO4 seems to help in the rapid conversion to the (Bi,Pb)-2223 phase.
High Pressure Synthesis of New Filled Skutterudites
Authors: Takizawa Hirotsugu , Okazaki Ken-ichi , Uheda Kyota , Endo Tadashi , Nolas George S.
Published: April 2011

Filled skutterudites exhibit properties that comply with the concept of a “phonon-glass electron-crystal”, as proposed by Slack. The optimal filled skutterudite would have filler atoms that exhibit large thermal vibration amplitudes in the voids of the crystal structure. It is desirable that these loosely bound atoms give rise to strong phonon scattering without greatly affecting the essential part of the band structure of the skutterudites. This criterion is difficult to meet. Most attempts have employed charge compensation for filling fractions above 50 %. In this report we present the use of a high-pressure technique for the synthesis of new filled skutterudites. By using our high-pressure synthesis technique CoSb3-based skutterudites filled with group-14 elements (Ge, Sn, and Pb) have been synthesized with up to 100 % filling without charge compensation of the host lattice. The structural analysis reveals that the Sn atoms exhibit very large thermal vibration amplitude, indicative of a large “rattling” motion. The Sn-filled specimens exhibit a low thermal conductivity, lower than that of any previously reported filled skutterudite, while the favorable semiconducting nature of the host lattice is not substantially changed by Sn filling. Tin atoms may therefore be better “rattlers” in the CoSb3 host lattice than lanthanide or actinide atoms.
Electronic Structure and Thermoelectric Properties of Ytterbium-Filled Skutterudites
Authors: Anno Hiroaki , Ashida Kazuhiro , Matsubara Kakuei , Nolas George S. , Akai Koji , Matsuura Mitsuru , Nagao Jiro
Published: April 2011

The electronic structure and thermoelectric properties of Yb partially filled CoSb3 skutterudite compounds have been investigated by x-ray photoelectron spectroscopy and band calculation in terms of an itinerant f electron model. In these materials, the significant effect of Yb filling is the large reduction of lattice thermal conductivity, remaining relatively high electron mobility and Seebeck coefficient, resulting in high thermoelectric figure of merit. We discuss the effects of the valence fluctuation between Yb2+ and Yb3+ and the strong hybridization of Yb 4f states with the valence band states on the electronic properties and their relation to thermoelectric properties for Yb partially filled CoSb3 compounds.
Microstructural evolution of La-doped SiB6 high-temperature thermoelectric material during a Spark Plasma Sintering
Authors: Lee D.W. , Won J.H. , Kim K.H. , Matsushita J. , Shim K.B.
Published: April 2011

SiB6 has proved to a potentially useful material because of its excellent thermoelectrical properties above 700°C, low specific gravity, high degree of hardness, and moderate melting point. SiB6, which has poor sinterability with a conventional sintering technique due to the covalent characteristic, has been successfully densified fully using a spark plasma sintering(SPS) method. The SPS-processed specimens consisted of SiB6, SiB4 and SixBy phases. Pure SiB6 powder were densified fully at the sintering temperature of 1600°C. In particular, it was found that the rare earth element was very effective in evolving the microstructure of SiB6 phase, resulting in reducing the sintering temperature and controlling grain growth. These effects were discussed in details in terms of microstructure evolution during the SPS process.
Thermoelectric Properties of PbSe Epitaxial Thin Films and PbSe/EuS Heterostructures
Authors: Dresselhaus Mildred S. , Dresselhaus Gene , Rogacheva Elena I. , Tavrina Tatyana V. , Grigorov Sergey N. , Nasedkin Konstantin A. , Volobuev Valentine V. , Sipatov Alexander Yu.
Published: April 2011

Systematic investigations were performed of the thickness dependences of the thermoelectric properties of PbSe thin films, freshly prepared and exposed to air at room temperature. It is shown that oxidation leads to a sharp change in the thermoelectric properties of the PbSe films including a change in the sign of the dominant carrier type from n-type to p- type at d ≤ 80 nm. Using a two carrier model for thin films (d < 50 nm) and a two-layer model for thick films (d > 50 nm) allows us to give a satisfactory qualitative interpretation of the observed experimental dependences of the thermoelectric properties on the film thickness.
Geometric Effects on the Transient Cooling of Thermoelectric Coolers
Authors: Yang Ronggui , Chen Gang , Snyder G. Jeffrey , Fleuriel Jean-Pierre
Published: April 2011

Transient thermoelectric cooling effect has been known since 1960s. Most of the previous studies focus on the minimum temperature achievable for free standing thermoelectric elements. Practical thermoelectric coolers have a passive mass load, which affect the minimum temperature achievable. This is particularly true for thermoelectric micro coolers because the object to be cooled is comparable to the micro coolers in size. In this paper, we present the performance analysis of the integrated system made of the cooling object and thermoelectric element, and establish the criterion for the utilization of transient cooling effect based on the analysis of the time constants. Effects of thermoelectric element shape on the transient thermoelectric cooling effect are also studied.
Synthesis of Boron-Rich Metal Borides and Their Thermoelectric Properties
Authors: Takeda Masatoshi , Domingo Ferrer , Miura Takahiro , Fukuda Tadahiro
Published: April 2011

Polycrystalline metal borides AlMgB14, CaB6, and MB2 (M: transition metals) were synthesized and their thermoelectric properties were examined. Single phase of orthorhombic AlMgB14, which contains B12 icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 K and 1823 K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500 (μV/K) and 10−1 (1/Ωm) at room temperature, respectively. These values are comparable to those of metal-doped β- rhombohedral boron. Synthesized AlB2-type diborides (MB2; M=Ti, V, Cr, and Mn) exhibited metallic conduction. The MB2's α varied with number of valence electrons, and showed a maximum α in VB2. The variation was similar to that predicted for pseudogap system. The CaB6 also possessed metallic conduction, but the α of the phase was as large as 200 (μV/K) with negative sign.
A Consistent Rationale for the Superior Strength and Ultra-Hardness of Ceramic Nano-Composite Coatings
Authors: Argon A. S. , Veprek S.
Published: April 2011

Nano-structured composite ceramic coatings such as TiN with Si3N4 orT iSi2 prepared by variousforms of plasma assisted CVD, composed of crystalline components of equiaxed TiN of several nm diameter, surrounded by amorphous Si3N4 intercrystalline layers of roughly 0.2 volume fraction have exhibited hardnesses in the range of 70-100 GPa-quite commensurate with polycrystalline diamond layers, and thermal stability up to 1000C. Preliminary considerations indicate that such ultra-hardness, uninfluenced by the usual artifacts of nano-indentations are not governed by processes of crystal plasticity in the crystalline component but by the characteristic flow mechanisms of the often topologically continuous amorphous component exhibiting “liquid-like” behavior in the constrained spaces between the crystalline components.
Preparation of TiFe thin Films by Pulsed Ion Beam Evaporation
Authors: Suematsu Hisayuki , Saikusa Tsuyoshi , Suzuki Tsuneo , Jiang Weihua , Yatsui Kiyoshi
Published: April 2011

Thin films of titanium iron (TiFe) were prepared by a pulsed ion-beam evaporation (IBE) method. A pulsed ion beam of proton accelerated at 1 MV (peak) with a pulse width of 50 ns and a current of 70 kA was focused on TiFe alloy targets. Soda lime glass substrates were placed in front of the targets. Phases in the thin films were identified by X-ray diffraction (XRD). XRD results revealed that the thin films deposited on the glass substrates consist of a TiFe phase. Crystallized Ti-Fe thin films without oxides were successfully obtained. Surface roughness of the thin film was 0.16 m m.
Microstructure and Tribological Behavior of Cr-DLC Nanocomposite Films
Authors: Singh V. , Jiang J.C. , Meletis E.I.
Published: April 2011

Cr-diamondlike carbon (Cr-DLC) nanocomposite films with the Cr content varying up to 27 at. % were synthesized by reactive magnetron sputtering. Their microstructure and tribological properties were studied using transmission electron microscopy (TEM) and pin-on-disc experiments, respectively. Electron diffraction and high- resolution TEM studies show that the films, with ∼ 9 at. % Cr, deposited using low (−200 V) and high (−1000 V) specimen bias during processing are composed of nanocrystalline metallic Cr and face-centered cubic chromium carbide, respectively surrounded by an amorphous matrix. The Cr-DLC film deposited at high bias exhibited enhanced adhesion to Si substrate and wear resistance compared to those deposited at low bias with the same Cr content. Wear rate of the films deposited at high bias is relatively independent of Cr content up to about 10 at. % (of the order of 10−7 mm3/N-m) and then increases with increasing Cr content. The coefficient of friction for the films with a Cr content less than 19 at. % is low and remains between 0.1-0.16.
Characteristics of Cr-Al-N-O Thin Films Prepared by Pulsed Laser Deposition
Authors: Hirai Makoto , Saito Hajime , Suzuki Tsuneo , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: April 2011

Chromium aluminum oxynitride (Cr-Al-N-O) thin films have been successfully prepared by pulsed laser deposition (PLD). Experiments were carried out by changing surface area ratio of the targets (SR = SAlN / (S +SAlN)) from 0 to 100 %. The composition of the thin film prepared at SR = 75 % was determined to be Cr0.11Al0.39N0.25O0.25 by Rutherford backscattering spectroscopy (RBS). The hardness of the Cr-Al-N-O thin film was found to be above HV 4000 when the aluminum content in cations (x) was 25 at. %. The high hardness can be explained by solid solution hardening and/or increasing bulk modulus. The oxidation of the Cr-Al-N-O thin film occurred above 900°C. From the result of grazing angle X-ray diffractometry (GXRD), the oxidation resistance of the Cr-Al-N-O thin film was found to be improved due to the fact that Cr2O3 and -Al2O3 grains are formed at the outermost surface of the thin film.
Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films
Authors: Wang H. , Kvit A. , Zhang X. , Koch C. C.
Published: April 2011

High-temperature materials such as TiN have been successfully applied as wear corrosion protection, decorative coatings, electrical contacts and diffusion barriers in electronic devices. However the poor toughness and ductility have limited some of these applications. To alleviate some of these problems, reduction of grain size can enhance grain boundary sliding and grain boundary diffusion related creep phenomena. We have investigated mechanical and electrical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25oC to 700oC during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Hardness measurements were made using nanoindentation techniques. Resistivity measurements were performed by van der Pauw method. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size in nanoscale. This behavior has been modeled recently involving grain boundary sliding which is particularly relevant in the case of hard materials such as TiN. The dependence of resistivity of TiN as a function of the substrate temperature is discussed and correlated with hardness results.
The Development of Surface Roughness and Implications for Cellular Attachment in Biomedical Applications
Authors: Banks Bruce , Miller Sharon , Groh Kim de , Chan Amy , Sahota Mandeep
Published: April 2011

The application of a microscopic surface texture produced by ion beam sputter texturing to the surfaces of polymer implants has been shown to result in significant increases in cellular attachment compared to smooth surface implants in animal studies. A collaborative program between NASA Glenn Research Center and the Cleveland Clinic Foundation has been established to evaluate the potential for improving osteoblast attachment to surfaces that have been microscopically roughened by atomic oxygen texturing. The range of surface textures that is feasible depends upon both the texturing process and the duration of treatment. To determine whether surface texture saturates or continues to increase with treatment duration, an effort was conducted to examine the development of surface textures produced by various physical and chemical erosion processes. Both experimental tests and computational modeling were performed to explore the growth of surface texture with treatment time. Surface texturing by means of abrasive grit blasting of glass, stainless steel and polymethylmethacrylate surfaces was examined to measure the growth in roughness with grit blasting duration by surface profilometry measurements. Laboratory tests and computational modeling was also conducted to examine the development of texture on Aclar® (chlorotrifluoroethylene) and Kapton® polyimide, respectively. For the atomic oxygen texturing tests of Aclar®, atomic force microscopy was used to measure the development of texture with atomic oxygen fluence. The results of all the testing and computational modeling support the premise that development of surface roughness obeys Poisson statistics. The results indicate that surface roughness does not saturate but increases as the square root of the treatment time.
Formation of Al Nanodot Array by the Combination of Nano-Indentation and Anodic Oxidation
Authors: Shingubara S. , Murakami Y. , Morimoto K. , Sakaue H. , Takahagi T.
Published: April 2011

The control of nanoholes formed by anodic oxidation of aluminum (Al) was investigated using AFM nano-indentation on Al film prior to the anodic oxidation. It is well known that ordered trigonal nanohole arrays are formed under certain voltage conditions of anodic oxidation of Al. We succeeded in forming both tetragonal and trigonal arrays of alumina nanoholes on a SiO2/Si- substrate by using nano-indentation on the surface of sputtered pure Al film. The ordered array of nanoholes was obtained at indentation intervals that were close to the nearest neighbor distance of nanoholes in the self-organization condition. Furthermore, we fabricated tetragonal and hexagonal Al nanodot arrays by the selective removal of porous alumina film.
Micro- and Nanofabricating Lipid Patterns Using a Polymer-Based Wet Lift-Off
Authors: Orth Reid. N. , Hafez Ismail , Wu Min , Ilic Bojan , Baird Barbara , Clark Theodore G. , Craighead Harold G.
Published: April 2011

Accurate placement of biomaterials at nanoscale resolution opens new capabilities for biological sensing, cell manipulation, and control of cellular transduction cascades. We demonstrate that lipid molecules can be patterned on silicon using a polymer lift-off technique. Patterned lipid bilayers serve as biomaterial patterning platforms useful for studies of cellular function. Submicron feature sizes were achieved using this templating technique which is suitable for delicate biomaterials1. Projection lithography and reactive ion etching were used to pattern a Parylene-coated surface. The patterned surface was subsequently exposed to 100 nm unilamellar lipid vesicles that bound to the native oxide surfaces of silicon and spread to form supported lipid bilayers. The nanoscale pattern is realized as the polymer is peeled away in deionized water. The versatility of this method is demonstrated by the successful preparation of functionalized lipid bilayer surfaces. Specific intermolecular interactions were demonstrated between supported membranes: DPPE-PE (2000) biotin/avidin, dinitrophenol (DNP)-conjugated lipids/anti-DNP IgE, and cationic lipid and M13 dsDNA:YOYO-1.
Patterning 2D Metallic Surfaces by Soft Lithography
Authors: Toprak M. , Kim D. K. , Mikhailova M. , Muhammed M.
Published: April 2011

In this study, we report on the development of a μCP technique, where the ink used on the surface of the stamp is made of aminopropyl trimethoxy silane (APTMS). The stamps for the μCP are prepared by polymerizing polydimethylsiloxane (PDMS) on photolithographically defined masters. Si wafers were used as the substrate on which a self assembled layer of APTMS was formed at the contact regions of the stamp. The regions of contact were subsequently used for the deposition of gold coated magnetite nanoparticles, resulting in 2D patterned metallic surfaces. The colloidal particles were analyzed by TEM and XRD, and the printed substrates were characterized by AFM.
Synthesis of Polyaniline Using Electrostatically Layered Hematin Assemblies
Authors: Ku Bon-Cheol , Lee Soo-Hyoung , Liu Wei , Kumar Jayant , Bruno Ferdinando F. , Samuelson Lynne A.
Published: April 2011

The enzyme horseradish peroxidase has been recently used for the polymerization of water-soluble conductive polyaniline. Hematin, an ironporphyrin molecule that catalyzes the oxidative polymerization of aniline and phenol, is a robust and inexpensive biomimetic alternative to horseradish peroxidase. Composite thin film assemblies were fabricated by electrostatic layer-by-layer (ELBL) alternate deposition of a polyelectrolyte, poly(dimethyl diallylammonium chloride), and hematin. These multilayer assemblies were then used for the polymerization of aniline in the presence of a polystyrene sulfonate as a template. It was found that the polymerization rate depends on both pH and the concentration of hematin deposited and the polyaniline synthesis was possible both onto the ELBL surfaces and in solution. It was also discovered that it is possible to reuse the ELBL assembled hematin substrates for multiple aniline polymerizations.
Improved Thin Film Transistor (TFT) performance using fractionated Poly-3-hexylthiophene (P3HT)
Authors: Raja Munira , Lloyd Giles , Sedghi Naser , Lucrezia Rafaella di , Higgins Simon J. , Eccleston W.
Published: April 2011

By using the Trznadel method, it has been possible to increase molecular weight, the regio-regularity, and probably to decrease the residual catalyst of poly-3-hexylthiophene thin films. The drift mobility of holes, normal to the surface of cast films, in air, has been found using Schottky diodes, and field-effect mobility has been measured with Thin-Film Transistors. Three types of film have been studied using the two methods of assessing mobility. The as-synthesised films are compared with those that have been fractionated. The third set of films involves doping with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The doped films show a field effect mobility of 0.2 cm2V-1s-1: all others being lower. Field effect mobility is approximately two orders of magnitude greater than that in the bulk normal to the plane of the film. Doping levels in the films are found to be similar, probably because of the process conditions.
Simulation of chirally-induced excitonic optical effects in biscyanine dye with shiff base (optical and molecular structure simulations)
Authors: Andraud C. , Plucinski K.J. , Kityk I.V.
Published: April 2011

For the first time simulations of chirally-induced excitons have been carried out, using molecular dynamic simulations and self-consistent quantum chemical calculations within the RHF [Restricted Hartree-Fock ] and DFT [Density Functional Theory] approaches. We found that the DFT approach gave substantially better agreement than the RHF. Comparison of theoretical and experimental results for biscyanine dye with a Shiff base showed a sufficiently good level of agreement.
Chemical modification of indium-tin-oxide electrodes by surface molecular design
Authors: Ganzorig Chimed , Fujihira Masamichi
Published: April 2011

Indium-tin-oxide (ITO) is the most widely used material as a transparent electrode due to its excellent transparency and high conductivity. The devices based on bare ITO, however, exhibited inefficient hole injection due to insufficient high work function and required high drive voltages. Thus, various surface treatments of ITO have been attempted to change the work function of ITO in order to reduce the hole injection barrier height. Electroluminescent (EL) characteristics of devices were improved dramatically using ITO chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive -COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in p-position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (-SO2Cl, -COCl, and -PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in p-position.
Photoelectric Response from Nanofibous Membranes
Authors: Senecal Kris J. , Ziegler David P. , He Jinan , Mosurkal Ravi , Schreuder-Gibson Heidi , Samuelson Lynne A.
Published: April 2011

Electrospinning has been used to prepare nanofibrous composite membranes of semi-conducting particles (TiO2) and photovoltaic dyes. Electrospinning is a relatively simple technique where electrical forces are used on polymeric solutions to produce nanoscale fibers. The resulting nanofibrous membranes have surface areas that are roughly one to two orders of magnitude higher than conventional thin films. It is believed that this higher surface will allow for more efficient light harvesting in photovoltaic devices. Our research has focused on the fabrication of organic/inorganic hybrid solar cells featuring dye sensitized nanocrystalline semiconductor particles using electrospinning. Phthalocyanine and N3 (cisdi(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium(II)) photoactive dyes were electrospun with semi-conductive TiO2 nanoparticles into a matrix polymer, polyacrylonitrile (PAN). Electron microscopy and elemental analysis of the electrospun membranes shows that each component is present and uniformly dispersed in the nanofibrous membranes. In general, the dye membranes electrospun with the TiO2 nanoparticles exhibited a greater photoelectric response than the membranes with dye only. The N3 dye membranes however showed the greatest photoresponse in comparison to the phthalocyanine dyes, with or without the TiO2 nanoparticles. Photoelectric responses on the order of 30 μA and 280 mV were achieved with dye-sensitized membranes and are believed to be the first demonstration of a photoelectric response from an electrospun nanofibrous membrane.
Integrated Analysis for Long-Term Degradation of Waste Package at the Potential Yucca Mountain Repository for High-Level Nuclear Waste Disposal
Authors: Lee Joon H. , Mon Kevin G. , Longsine Dennis E. , Bullard Bryan E. , Moniba Ahmed M.
Published: April 2011

The technical basis for Site Recommendation (SR) of the potential repository for high-level nuclear waste at Yucca Mountain, Nevada has been completed. Long-term containment of the waste and subsequent slow release of radionuclides from the engineered barrier system (EBS) into the geosphere will rely on a robust waste package (WP) design, among other EBS components as well as the natural barrier system. The WP and drip shield (DS) degradation analyses for the total system performance assessment (TSPA) baseline model for the SR have shown that, based on the current corrosion models and assumptions, both the DSs and WPs do not fail within the regulatory compliance time period (10,000 years). From the perspective of initial WP failure time, the analysis results are encouraging because the upper bounds of the baseline case are likely to represent the worst case combination of key corrosion model parameters that significantly affect long-term performance of WPs in the potential repository. The estimated long life-time of the WPs in the current analysis is attributed mostly to the following two factors that delay the onset of stress corrosion cracking (SCC): (1) the stress mitigation to substantial depths from the outer surface in the dual closure-lid weld regions; and (2) the very low general-corrosion rate applied to the closure-lid weld regions to corrode the compressive stress zones. Uncertainties are associated with the current WP SCC analysis. These are stress mitigation on the closure-lid welds, characterization of manufacturing flaws applied to SCC, and general corrosion rate applied to the closurelid weld regions. These uncertainties are expected to be reduced as additional data and analyses are developed.
Thermodynamic Functions of Zirconolite and their Uses in Computer Simulation
Authors: Bergman George A. , Navrotsky Alexandra , Ojovan Michael I. , Klimov Vsevolod L. , Karlina Olga K. , Pavlova Galina Yu.
Published: April 2011

The enthalpy of melting and the heat capacity of liquid zirconolite (CaZrTi2O7) are estimated as equal to 200 ± 20 kJ·dmol−1 and 350 ± 50 J·mol−1·K−1, respectively. Thermodynamic functions of solid and liquid zirconolite are calculated based on these estimated data and the results of Navrotsky et al. On the basis of these thermodynamic functions, computational thermodynamic simulation is performed on the thermochemical synthesis of zirconolite-bearing materials. Demonstration indicates that synthesis of zirconolite-like matrix materials is possible using the self-sustaining exothermic reaction.
Preliminary Studies of the Disposition of Cesium in a Glass-Bonded Sodalite Waste form
Authors: Lambregts Marsha J. , Frank Steven M.
Published: April 2011

Argonne National Laboratory has developed an electrometallurgical treatment for DOE spent metallic nuclear fuel. Fission products are immobilized in a durable glass bonded sodalite ceramic waste form (CWF) suitable for long term storage in a geological repository. Cesium is estimated to be in the waste form at approximately 0.1 wt.%. The exact disposition of cesium was uncertain and it was believed to be uniformly distributed throughout the waste form. A correlation of X-ray diffractometry (XRD), electron microscopy (EM), and nuclear magnetic resonance spectroscopy (NMR) performed on surrogate ceramic waste forms with high cesium loadings found a high cesium content in the glass phase and in several non-sodalite aluminosilicate phases. Cesium was not detected in the sodalite phase.
Accommodation of Uranium into the Garnet Structure
Authors: Yudintsev Sergey V. , Lapina Marya I. , Ptashkin Alexander G. , Ioudintseva Tatiana S. , Utsunomiya Satoshi , Wang Lumin M. , Ewing Rodney C.
Published: April 2011

One promising host for actinide wastes is garnet-type phases of general formula AVIII3BVI 2[XO4]3. To determine the isomorphic capacity of garnet for uranium, the CaO – Fe2O3 – Al2O3 – SiO2 – ZrO2 – Gd2O3 – UO2 system was studied. Experiments were performed in air medium at 1400 – 1500 °C and 1 atm. The garnets have high capacity for Gd and Zr, while incorporation of U was found to be greatly dependent on the phase composition. Uranium content decreased from 18 wt.% in Ca-Zr-Fe garnet to 0.6 wt.% in Si-doped phases. Heavy ion irradiation (1.0 MeV Kr++) experiments were carried out for a garnet with maximal U content, (Ca2.7U0.3)VIII(Zr1.7Fe0.3)VI(Al1.1Fe1.9)IVO12. Amorphization dose of the phase was equal to 1.63×1014 ions/cm2 that is close to the other actinide hosts, such as pyrochlore Gd2Ti2O7.
Alpha-Decay Radiation Damage Study of a Glass-Bonded Sodalite Ceramicwaste form
Authors: Frank S.M. , Barber T. L. , DiSanto T. , Goff K. M. , Johnson S. G. , Jue J-F , Noy M. , O'Holleran T. P. , Sinkler W.
Published: April 2011

Effects of alpha decay on the ceramic waste form used to immobilize fission products and actinides accumulated from electrometallurgical treatment of Department of Energy metallic spent nuclear fuel is being studied. This involved the preparation of a surrogate ceramic waste form containing two-weight percent plutonium-238 and monitoring changes to the waste form resulting from alpha-decay damage. The phase assembly of the ceramic waste form consists of glass-bonded sodalite with small quantities of nepheline, halite and plutonium dioxide. The waste form has been monitored for three years and has acquired an internal alpha-decay dose of 1 × 1018 disintegrations per gram of material. Methods used to monitor the material include: density determination, chemical durability measured by immersion testing, microscopy and powder xray diffraction. The investigation has, to date, found little alteration to the waste form due to alpha-decay damage. X-ray diffraction analysis has detected a unit cell volume increase of 0.7 percent of the plutonium dioxide phase. Furthermore, bubbles and/or voids have been observed by transmission electron microscopy in the sodalite and glass phase. The origin of these defects is unclear and under investigation.
Ion Irradiation Effects in Synthetic Garnets Incorporating Actinides
Authors: Utsunomiya Satoshi , Wang Lu-Min , Yudintsev Sergey , Ewing Rodney C.
Published: April 2011

Radiation durability of garnet [A3B2(XO4)3; Ia3d; Z=8] has been examined by 1.0 MeV Kr2+ irradiation with in situ transmission electron microscopy over the temperature range of 50 to 1070 K. The targets were five synthetic garnets incorporating various contents of actinides and andradite, Ca3Fe2Si3O12. The synthetic garnets were silicates (N series) and ferrate-aluminate series (G series).

The critical amorphization temperatures (Tc), above which amorphization does not occur, were determined to be 1050 K for N77, 1130 K for N56, 1100 K for G3, 890 K for G4 and 1030 K for andradite. Tc of the synthetic garnets increased as the average atomic mass of the garnet increased. The maximum transferred energy by ballistic interaction was positively correlated to the atomic mass. The larger cascade size that formed due to the larger Emax might lead to the higher Tc.
Experimental Determination of the Deliquescence Relative Humidity and Conductivity of Multicomponent Salt Mixtures
Authors: Yang Lietai , Pabalan Roberto T. , Browning Lauren
Published: April 2011

The conductivity of hygroscopic salt deposits containing Na+, K+, NO3– and Cl– ions was measured in air as a function of relative humidity at constant temperatures. The deliquescence relative humidity (DRH) of multicomponent salts containing Na+, K+, NO3– and Cl– was also determined experimentally. The results of the conductivity experiments show that the conductivity of initially dry salt deposits start to increase after reaching a relative humidity value that is 15 to 20% lower than the DRH of the salt. When the DRH is reached, the conductivity increases dramatically as the salt dissolves and transforms into a saturated aqueous phase. The increase in conductivity at humidities below the DRH is attributed to the adsorption of water on the surface of the salt particles. Because of the increase in conductivity, the initiation of aqueous corrosion of metals in contact with hygroscopic salts may occur at a relative humidity much lower than the DRH of the salt. Thus, the onset of aqueous corrosion of metallic nuclear waste package and the drip shield may be earlier, the duration may be longer, and the temperature at which it occurs may be higher than assumed based on the DRH of the salt. The results of the DRH experiments show that the DRH of a salt mixture is usually significantly lower than that of any of its component pure salt.
Effect of Redox Conditions on the Sorption of Plutonium onto Geological Materials
Authors: Berry J.A. , Brownsword M. , Ilett D.J. , Linklater C.M. , Mason C. , Tweed C.J. , Yui M.
Published: April 2011

This paper presents the latest results from a programme of generic sorption studies undertaken to increase confidence in data underpinning the performance assessment for a potential high-level radioactive waste repository in Japan. The sorption of plutonium onto basalt and sandstone was studied as a function of redox conditions that ranged from strongly reducing to oxidising. Geochemical modelling was used to aid experimental design and the interpretation of results.
Incorporation of Cerium and Neodymium in a Uranyl Hydroxide Solid
Authors: Kim C.W. , Wronkiewicz D.J. , Finch R.J. , Buck E.C.
Published: April 2011

The migration behavior of radionuclides in a nuclear-waste repository will be influenced, in part, by their equilibrium solubilities in the presence of radionuclide-bearing solids and/or adsorption affinities as trace components onto the surfaces of solid host phases. Uranium phases that precipitate on the surface of altered spent nuclear fuel may thus influence the mobility of radionuclides released in the near-field environment, since by proximity, these will be the first phases that the radionuclides encounter following their release from the spent fuel matrix.

We have evaluated the potential for incorporating radionuclides into crystalline compounds by precipitating uranyl phases from aqueous solutions containing dissolved rare earth elements (REE; 2.1 ppm Ce4+, 4.6 ppm Ce4+, or 286 ppm Nd3+). Rare earth elements serve both as monitors for evaluating the potential behavior of REE radionuclides and as surrogate elements for the actinides (e.g., Ce4+ and Nd3+ for Pu4+ and Am3+, respectively). Although the crystalline compound that formed in the present set of experiments has not been positively identified, x-ray diffraction profiles suggest the presence of a uranyl hydroxide (UO2(OH)2) as the principal reaction product. An analysis of the crystalline products indicate a progressive decrease in concentration of cerium; from 26, to 20, and finally 11 ppm for crystals produced in 7-, 35-, and 190-day tests, respectively (Kd = 14, 11, 3, respectively). Results with neodymium display a similar trend, with concentrations in the solid decreasing from 1240 to 922 ppm between 7 and 35 days of reaction (Kd = 14 and 11, respectively). The decreasing concentration of REEs in the uranyl crystals can be correlated with both a coarsening in crystal size and a decrease in the concentration of dissolved uranium over time. Thus, REE incorporation in the crystalline solids decreases in conjunction with a decrease in the ratio of surface area/volume of the crystals, a decrease in the rate of crystal growth as uranium concentrations are lowered, or both. These data also suggest that adsorption of REE (and by analogy, actinides) onto crystal surfaces and subsequent trapping by crystal overgrowth processes may play key roles in the limiting the mobility of radionuclides in a nuclear waste repository.
Demonstration of the Feasibility of Recovering Americium and Curium Isotopes from a Lanthanide Borosilicate Glass
Authors: Rudisill Tracy S. , Peeler David K. , Edwards Thomas B.
Published: April 2011

A solution containing kilogram quantities of highly radioactive isotopes of americium and curium (Am/Cm) is currently stored in a process tank at the Department of Energy's Savannah River Site. This tank and its vital support systems are old, subject to deterioration, and prone to possible leakage. To address the stabilization of this material, vitrification of the isotopes has been considered. Potentially, the glass could be shipped to the isotope production and distribution programs at the Oak Ridge National Laboratory for californium-252 production and use by the transplutonium research community. However, before the Am/Cm could be used in these programs, it must be recovered from the glass.

To demonstrate the feasibility of recovering the Am/Cm isotopes from a glass, a series of small-scale experiments was performed as part of a compositional variability study. Glasses fabricated during the study utilized lanthanide elements as surrogates for Am/Cm due to the high specific activity of these materials. In the dissolution tests, glass formulations representative of potential uncertainties in the composition of the Am/Cm solution were fabricated, ground to a -35 to +60 mesh particle size, and dissolved in 8M nitric acid at 110°C. Under these conditions, at least 98% of the lanthanide oxides in the glass dissolved in less than 2 h meeting a recoverability criterion established for the vitrification process and imposing no limitations on the acceptable glass composition region.

Dissolution of the lanthanide borosilicate glasses was described by a spherical particle model based on the observation that the rate of change of the mass to surface area ratio remains constant. Calculation of dissolution rates using the model showed that the rate was proportional to the lanthanide oxide concentration in the glass. When silicon oxide (SiO2) was replaced with a lanthanide element at higher (simulated Am/Cm) loadings, the glass became more easily dissolved in nitric acid due to the solubility of the lanthanide oxides compared to SiO2.
Aging of a Bitumen Waste form in Wet Repository Conditions
Authors: Ojovan M.I. , Ojovan N.V. , Golubeva Z.I. , Startceva I.V. , Barinov A.S.
Published: April 2011

SIA ‘Radon’ has been performing field tests of bitumen waste forms holding low and intermediate level wastes (LILW) for about three decades. The waste forms were made at an industrial bituminization plant from the actual LILW wastes. This paper presents results from analyzing the samples of the bitumen waste material taken from the bulky bitumen block with waste salts loading 31 wt.% after storing the block in a shallow-ground repository for 12 years. Rich in natrium nitrate NPP-operational waste was incorporated in bitumen.

Salts were separated from bitumen in some waste form samples. Non-homogeneous distribution of both salts and radionuclides was detected in vertical direction of the bitumen block. Specific radioactivity of the extracted bitumen was of the same order as the specific radioactivity of salts, in some cases even greater.

Bitumen samples free of salts were further separated into three main bitumen fractions, asphaltenes, saturated and aromatic hydrocarbons, using methods of solvent extraction. Essentially all radioactivity of the bitumen was associated with the asphaltene fraction. Aging of the bitumen waste form led to increase in asphaltene fraction content (with minimum 4%) and hardening of the waste material. The study has revealed a significant transfer of the waste salts radioactivity to the asphaltene fraction of the bitumen matrix. Changes in the properties of the bitumen waste form will be taken into consideration in modeling the long-term behavior of the bitumen waste materials under repository conditions.