bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional Effects on the Long-Term Durability of Nuclear Waste Glasses: A Statistical Approach
Authors: Ribet Solange , Muller Isabelle S. , Pegg Ian L. , Gin Stéphane , Frugier Pierre
Published: April 2011

As a result of the development of a reference glass formulation for the immobilization of West-Valley nuclear waste, a large number of glass compositions have been tested under a variety of leaching conditions for extended durations. In this work, data from the standard PCT leaching procedure (deionized water, 90°C, S/V = 2000 m-1) are evaluated for a subset of 98 of these glasses, for which the alteration times extend up to fifteen years. Analysis of the leachate data over this extended period has led to a classification of the glass compositions according to their PCT behavior, as characterized by the boron release in solution, the decrease in the rate of alteration, or the occurrence of a resumption of alteration. Three types of behavior are associated with a normalized mass loss of boron after 100 days of around 1, 2, or 5 g m-2 respectively, and a ratio of the rate of alteration at 7 days to the rate at 1000 days of about 30. A fourth type is characterized by a much larger decrease between the rates at 7 and 1000 days with a ratio exceeding 120. Four further categories are associated with late-stage resumption of glass alteration. A statistical analysis of the data has been used to model the leachate data as a function of glass composition. The effects of seven major elements (Si, B, Al, Li, Na, K, Fe) on the long-term glass durability have been studied. As a result of this analysis, the different types of leaching behaviors can be predicted with a good reliability from the composition of the pristine glass.
Comparison of a Non Electrostatic Surface Complexation Model and Surface Phase Theories for Prediction of Future Sorption Properties.
Authors: Emrén Allan T. , Jacobsson Anna-Maria
Published: April 2011

In performance assessments, sorption of radionuclides dissolved in groundwater is mostly handled by the use of fixed Kd values. It has been well known that this approach is unsatisfying. Only during the last few years, however, tools have become available that make it possible to predict the actual Kd value in an aqueous solution that differs from the one in which the sorption properties were measured.

One such approach is surface complexation (SC) that gives a detailed knowledge of the sorption properties. In SC, one tries to find what kinds of sorbed species are available on the surface and the thermodynamics for their formation from species in the bulk aqueous solution. Recently, a different approach, surface phase method (SP), has been developed. In SP, a thin layer including the surface is treated as a separate phase. In the bulk aqueous solution, the surface phase is treated as a virtual component, and from the chemical potential of this component, the sorption properties can be found.

In the paper, we compare advantages and disadvantages of the two kinds of models. We also investigate the differences in predicted sorption properties of a number of radionuclides (Co, Np, Th and U). Furthermore, we discuss under which circumstances, one approach or the other is preferable.
Diffusion of Iodine and Technetium-99 Through Waste Encasement Concrete and Unsaturated Soil Fill Material
Authors: Mattigod Shas V. , Whyatt Greg A. , Serne J. R. , Wood Marcus I.
Published: April 2011

An assessment of long-term performance of low level waste-enclosing cement grouts requires diffusivity data for radionuclide species such as, 129I and 99Tc. The diffusivity of radionuclides in soil and concrete media was collected by conducting soil-soil and concrete-soil half-cell experiments. The soil diffusivity coefficients for iodide were 7.03 × 10−8 cm2/s and 2.42 × 10−7cm2/s for soils at 4% and 7% moisture contents, respectively. Iodide diffusivity in soil is a function of moisture content and is about an order of magnitude slower at lower moisture content. The soil diffusivity coefficients for 99Tc were 5.89±0.80 × 10−8 cm2/s (4% moisture content) and 2.04±0.57 × 10−7 cm2/s (7% moisture content), respectively. The soil diffusivity of iodide and 99Tc were similar in magnitude at both water contents, indicating that these ions have similar diffusion mechanisms in unsaturated coarse-textured Hanford soil. The diffusivity of iodide in concrete ranged from 2.07 × 10−14 cm2/s (4% soil moisture content) to 1.31 × 10−12 cm2/s (7% soil moisture content), indicating that under unsaturated soil moisture conditions, iodide diffusivity is highly sensitive to changing soil moisture conditions. Depending on the soil moisture content, the diffusivity of 99Tc in concrete ranged from 4.54 × 10−13 cm2/s to 8.02 × 10−12 cm2/s. At 4% soil moisture content, iodide diffused about 20 times more slowly than 99Tc, and at 7% soil moisture content, iodide in concrete diffused about 6 times slower than 99Tc.
Using Linear Free Energy Relationship to Predict the Stability Constants of Aqueous Complexes of Metal-Organic Ligands
Authors: Xu Huifang , Wang Yifeng
Published: April 2011

The Sverjensky-Molling linear free energy relationship was originally developed to correlate the Gibbs free energies of formation of an isostrutural family of solid phases to the thermodynamic properties of aqueous cations. In this paper, we demonstrate that the similar relationship also exists between metal complexes and simple metal cations in aqueous solutions. We extend the Sverjensky-Molling relationship to predict the Gibbs free energies of formation or dissociation constants for a family of metal complexes with a given complexing ligand. The discrepancies between the predicted and experimental data are generally less than 1.5 kcal/mol (or one log unit for stability constants). The use of this linear free energy correlation can significantly enhance our ability to predict the speciation, mobility, and toxicity of heavy metals in natural environments. According the obtained results, Gibbs free energies of formation of cations (δG0f, Mn+) can be used as an indicator for the hardness/softness of a metal cation (acid). The higher negative value of a metal cation, the harder acid it will be. It is logical to postulate that the coefficienta*MLcharacterizes the softness of a complexing ligand (base).
Uranium Redox States in Borosilicate Compositions
Authors: Aloy A.S. , Trofimenko A.V. , Iskhakova O.A. , Jardine L.J.
Published: April 2011

The results of the studies of uranium valent states in the borosilicate glasses incorporating the components of uranium-containing sludge of Mining and Chemical Combine (MCC, Zheleznogorsks.) is presented in this work. The glasses were made under oxidative and reducing conditions.

The optical spectrophotometry, nuclear gamma-resonance (NGR) and X-ray diffraction (XRD) showed that glasses produced under oxidative conditions are characterized by the presence of only U(6+), while U(4+) in the reducing conditions is present along with U(6+). The ratio U(6+)/to U(4+) varies in depending on the synthesis conditions.

The glass samples synthesized under oxidative conditions were researched at initial solid state. The others synthesized under reducing conditions was dissolved preliminary without distort of uranium valency.

The effect of U(4+)/U(6+) ratio on the uranium leach rates from the glasses has been studied at 90° using MCC-1 test.
The Dissolution of Uranophane in CaCl2-SiO2(aq) Test Solutions
Authors: Prikryl James D. , Murphy William M.
Published: April 2011

Uranophane [Ca(UO2)2(SiO3OH)2 · 5H2O] is a corrosion product of long-term leaching of spent fuel under oxidizing conditions and is a weathering product of uraninite in uranium ore deposits hosted by siliceous rocks. Incorporation of radionuclides into uranophane by coprecipitation may occur as a result of spent fuel alteration. Dissolution of uranophane leading to release of these radionuclides may therefore influence the longterm dissolved concentration and mobility of radionuclides at the proposed nuclear waste repository at Yucca Mountain, Nevada. In this study, the dissolution of uranophane in Ca- and Si-rich test solutions was investigated. Batch dissolution experiments were designed to approach uranophane equilibrium from undersaturated solutions at nearneutral pH (~6.0). Test solutions had initial U concentrations of 0.0 and 10-7 mol/L in matrices of ~10-2 mol/L CaCl2 and ~10-3 mol/L SiO2(aq). The test solutions were reacted with synthetic uranophane (confirmed by XRD and chemical analyses) and analyzed periodically over 10 weeks. Reaction quotients (Log Qs) derived from aqueous speciations of experimental solutions considered to be near equilibrium with uranophane ranged from 10.54 to 11.06 for the dissolution reaction: Ca(UO2)2(SiO3OH)2 · 5H2O + 6H+ ⇔ Ca2+ + 2UO22+ + 2SiO2(aq) + 9H2O.
Ab-initio Based Diffusive Studies of Plutonium with Relevance to Nuclear Waste Management
Authors: Setty A. K.
Published: April 2011

An approach to study the diffusion of plutonium (Pu) waste into the material of the storage containers is presented. The delta phase of Pu has been examined, in this article, using a spin and orbitally polarized ab-initio (full potential LMTO) approach [1, 2]. These computations are relatively inexpensive, and it is the intention to see if the results obtained would be satisfactory (compared to the accurate SIC-LDA computations [1-2]) for diffusive studies of Pu into the material of storage containers (for example, into FCC iron as a surrogate for steel [2]). The combination of LDA and spin and orbitally polarized LMTO calculations that we use successfully predict a delocalized 5f, (i.e. bonding) monoclinic ground state and a localized FCC excited state with a density about 8% greater than experiment (compared to the 30% error from pure LDA calculations by various groups [3-6]). The density of states is computed and compared to experimental photoemission studies; there is qualitative agreement. The spin, orbital and total magnetic moment for the FCC phase is computed; the results are qualitatively in agreement with those of other studies. An analytical method for studying the time-dependent diffusion of Pu across an interface with another atomic species is presented.
Geopolymers for the Immobilization of Radioactive Waste
Authors: Perera D S , Blackford M G , Vance E R , Hanna J V , Finnie K S , Nicholson C L
Published: April 2011

Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerization to form a solid. They are amorphous to semicrystalline three dimensional aluminosilicate networks. Although they have been used in several applications their widespread use is restricted due to lack of long term durability studies and detailed scientific understanding. Three important tools for the study of geopolymers are transmission electron microscopy (TEM), solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and infra red (IR) spectroscopy.

Cs and Sr are two of the most difficult radionuclides to immobilize and are therefore suitable elements to study in assessing geopolymers as matrices for immobilization of radioactive wastes. In this study Cs or Sr was added to geopolymer samples prepared using fly ash precursors. A commercial metakaolinite geopolymer was studied for comparison.

The geopolymers were mainly amorphous as shown by TEM, whether they were made from fly ash or metakaolinite. In the fly ash geopolymer, Cs preferentially inhabited the amorphous phase over the minor crystalline phases, whereas Sr was shared in both. The MAS NMR showed that Cs is held mostly in the geopolymer structure for both fly ash and metakaolinite geopolymers. The IR spectra showed a slight shift in antisymmetric Si-O-Al stretch band to a lower wavenumber for the fly ash geopolymer, which implies that more Al is incorporated in this geopolymer structure than in the metakaolinite geopolymer.
Enrichment of Uranium inside Wood: a Natural Analog from a Sandstone-hosted Roll-type Uranium Ore Deposit
Authors: X Huifang , Min Maozhong , Zhen Jia , Peng Xinjian , Wang Jinping , Barton Larry , Wang Yifeng
Published: April 2011

Furniture contaminated with uranium will be disposed of, together with U-bearing waste, in ageological repository such as the WIPP site in New Mexico. It is important to understand the effect of the wooden furniture on the migration of uranium in order to predict long-term behavior of uranium in a geological repository environment. In this paper, we present natural uraninite-bearing carbonized wood pieces from a sandstone-hosted roll-type uranium ore deposit in NW China. Results from SEM and TEM observations show that there are nanometer sized, and micron-sized, uraninite crystals that have accumulated on cell walls of the carbonized wood. Some uranitite crystrals display oval and round shapes that may be the result of microbial-induced reduction of uranium from groundwater. The wood carbonized fragments are the most uranium-rich “phase.” In some areas, aggregates of pyrite crystals occur withthe uraninite. It is proposed that organic components from the decay of the wood cells provide nutrientsfor the anaerobic bacteria to grow. The wood pieces with the bacteria inside may serve as scavengers of uranium because of the local reducing chemical environment.
Effects of the Orientation of Clay Particles and Ionic Strength on Diffusion and Activation Enthalpies of I−and Cs+ Ions in Compacted Bentonite
Authors: Sato Haruo
Published: April 2011

Apparent diffusivities (Da) for I− and Cs+ in compacted Na-smectite were studied as a function of smectite's dry density (0.9–1.4 Mg/m3, ionic strength (IS: [NaCl]=0.01, 0.51 M), temperature (22–60 °C) and diffusion directionto the orientated direction of smectite particles. The Da-values for both ions in parallel direction to the orientated direction showed a tendency to be higher than those in the perpendicular direction at lowIS. The Da-values for I− showed different trends depending on diffusion direction and dry density at high IS, but Da-values for Cs+ increased with increasing IS in both diffusion directions. The activation enthalpies (ΔEa) for I−, slightly higher than that of diffusivity in free water (Do) at low IS, similar level to that of Do at high IS, increased with increasing dry density. While, ΔEa-values for Cs+, clearly higher than that of Do for all conditions, increased with increasing dry density. Since it is known that interlayer distance depends on both dry density and IS, diffusive pathway is considered to differ depending on the charge of diffusion species.
Migration Behavior of Ferrous Ions in Compacted Bentonite Under Reducing Conditions Using Electromigration
Authors: Idemitsu Kazuya , Xia Xiaobin , Kikuchi Yoshiro , Inagaki Yaohiro , Arima Tatsumi
Published: April 2011

Carbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. The lifetime of the carbon steel overpack will depend on its corrosion rate. The corrosion rate of carbon steel is reduced by the presence of buffer material such as bentonite. Buffer material will delay the supply of corrosive materials and discharge of corrosion products through it. Carbon steeloverpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. Therefore, it is important to study the migration of iron corrosion products through the buffer material because it may affect the corrosion rate of overpack, migration of redox-sensitive radionuclides, and the properties of the buffer material. Electromigration experiments have been carried out with source of iron ions supplied byanode corrosion of iron coupon in compacted bentonite. The carbon steel coupon was connected as the working electrode to the potentiostat and was held at a constant applied potential between - 200 to 1000 mV vs. Ag/AgCl electrode for 48 hours. Corrosion currents were 0.5 to 2mA initially and depended on the supplied electrical potential, then decreased to approximately 0.1 mA in a few hours. The final corrosion current was independent of supplied electrical potential. It is expected that iron ion could migrate as ferrous ion through interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. The rate-determining process of this experimental configuration could be infiltration rate of ferrousioninto bentonite. Infiltration rate of ferrous ion into bentonite was increasing with dry density of bentonite.
Evaporative Evolution of Carbonate-Rich Brines from Synthetic Topopah Spring Tuff Pore Water, YuccaMountain, NV
Authors: Sutton Mark , Alai Maureen , Carroll Susan
Published: April 2011

The evaporation of a range of synthetic pore water solutions representative of the potential high-level-nuclear-waste repository at Yucca Mountain, NV is being investigated. The motivation of this work is to understand and predict the range of brine compositions that may contact the wastecontainers from evaporation of pore waters, because these brines could form corrosive thin films on the containers and impact their long-term integrity. A relatively complex synthetic Topopah Spring Tuff pore water was progressively concentrated by evaporation in a closed vessel, heated to 95°C in a series of sequential experiments. Periodic samples of the evaporating solution were taken to determine the evolving water chemistry. According to chemical divide theory at 25°C and 95°C our starting solution should evolve towards a high pH carbonate brine. Results at 95°C show that this solution evolves towardsa complex brinethat contains about 99 mol% Na+for the cations, and 71 mol% Cl-, 18 mol% ΣCO2(aq), 9 mol% SO42- for the anions. Initial modeling ofthe evaporating solution indicates precipitation of aragonite, halite, silica, sulfate and fluoride phases. The experiments have been used to benchmark the use of the EQ3/6 geochemical code in predicting the evolution of carbonate-rich brines during evaporation.
Thermal diffusion of Helium and volatil fission products in UO2 and zirconolite nuclear ceramics
Authors: Roudil Danièle , Deschanels Xavier , Trocellier Patrick , Jomard Fran ç ois , Boutry Annick , Jègou Christophe , Peuget Sylvain , Gosset Dominique , Nivet Pierre
Published: April 2011

The behaviour and diffusion mechanisms of helium in nuclear ceramics, such as uranium dioxide spent fuel matrix and zirconolite for the specific conditioning of minor actinides, significantly impact the possible evolution of those matrices in interim storage or disposal conditions. In the framework of spent fuel storage studies, the additional diffusion of gas and fission products in uranium dioxidematrix is also an essential aspect of the R&D. Specific experimental studies have been conducted, devoted to thermal diffusion under 1000 C. Data processing methods, lead to helium diffusion coefficient and associated activation energy of 1.05 eV in the zirconolite and 2 eV in UO2. Comparativelywith the uranium dioxide matrix, the helium diffusion coefficient in zirconolite is 1 to 100 million times higher; this parameter will have to be taken into account to dimension the waste form. Diffusion coefficients measurements between 800 C and 1000 C, investigated by SIMS, showed a very slow diffusion of volatile fission products Xe, I, Te and Cs, with coefficients two or three order of magnitude lower than for helium.
Determination of a stability potential-pO2- diagram of samarium in the eutectic LiCl-KCl
Authors: Córdoba G. , Caravaca C. , Quiñones J.
Published: April 2011

Abstract:Reaction between samarium trichloride and oxide ions was studied in the fused LiCl – KCl eutectic mixture at 723 K, by potentiometry with an yttria-stabilised zirconia membrane electrode. Titration curve demonstrated the existence of a precipitated samarium oxychloride (SmOCl), under this experimental conditions, with a solubility product value of 7.59 ţ 0.3 (molality scale). The combination of this value with the standard potentials allowed setting up the potential–pO2- stability diagram which summarises the properties of Sm species in the eutectic LiCl – KCl melt.
Effect of Gadolinium Doping on the Air Oxidation of Uranium Dioxide
Authors: Scheele Randall D. , Hanson Brady D. , Cumblidge Stephen E. , Jenson Evan D. , Kozelisky Anne E. , Sell Rachel L. , MacFarlan Paul J. , Snow Lanee A.
Published: April 2011

Researchers at the Pacific Northwest National Laboratory (PNNL) investigated the effects of gadolinium oxide concentration on the air oxidization of gadolinium oxide-doped uranium dioxide using thermogravimetry and differential scanning calorimetry to determine if such doping could improve uraniumdioxide's stability as a nuclear fuel during potential accident scenarios in a nuclear reactor or during long-term disposal. We undertook this study to determine whether the resistance of the uranium dioxide to oxidation to the orthorhombic U3O8 with its attendant crystal expansion could be prevented by addition of gadolinium oxide. Our studies found that gadolinium has little effect on the thermal initiation of the first step of the reported two-step air oxidation of UO2; however, increasing gadolinium oxide content does stabilize the initial tetragonal or cubic product allowing significant oxidation before the second expansive step to U3O8 begins.
An Experimental Study on the Influence of Gamma Radiation on Spent Fuel Dissolution in the Presence of a H2 Atmosphere
Authors: Quiñones Javier , Cobo Jose Manuel , Huebra Ángel González de la , Esparza Aurora Martínez
Published: April 2011

Any environmental performance assessment of spent nuclear fuel disposal requires a prediction of the spent fuel matrix alteration rate when contact with groundwater is established. Taking into account the disposal design, the groundwater at the expected depth of the repository are generally reducing. These reducing redox conditions near the spent fuel surface may be changed to oxidising conditions by the radiolysis of water, due to radiation associated with the waste. This study is focussed on determining the influence of the γ radiation on the spent fuel matrix alteration rate under simulated repository conditions. A series of sequential leaching experiments under controlled conditions have been done. The experiments simulate the repository environmental conditions when engineering barriers are degraded and groundwater arrives at the surface of the spent fuel. In these experiments SIMFUEL (SIMulated FUEL) was used as analogue of spent fuel. Two types of leachant (i.e., granitic water and bentonitic-granitic water) were used in the leaching experiments. These experiments were irradiated using γ- radiation at an industrial irradiation facility with a 60Co source. The results obtained in this study show different behaviour as a function of both the leachant used in the leaching experiments and the initial atmosphere used in the experiments. As a preliminary conclusion of this experimental work, under γ radiation and a small partial pressure of H2 (1 bar) in the first steps of the leaching process has a beneficial effect since U in solution is lower than any other conditions and overall alteration rate is minimized. For experimental times longer than one day, a clear increase of the U in solution is revealed in the experimental run products.
Investigation of magnetic properties in Mn incorporated InSb, InP, and GaAs, synthesized through controlled-ambient annealing
Authors: Hollingsworth Joel , Bandaru Prabhakar
Published: April 2011

Magnetic semiconductors are of interest for emerging spintronic applications, such as the integration of electronic information processing with magnetic data storage. We report on a new approach - furnace annealing under controlled ambients – aimed at increasing Mn incorporation and synthesizing new magnetic semiconductors with Tc greater than/around room temperature. These annealing treatments are hypothesized to reduce the effect of Mn interstitials. We have obtained preliminary SQUID magnetometry results which indicate ferromagnetic Curie temperatures of around 130 K in (In,Mn) Sb and 60 K in (In, Mn)P. X-ray diffraction was used to characterize phase homogeneity.
Model for Spin Injection into Conjugated Organic Semiconductors
Authors: Ruden P. Paul , Smith Darryl L.
Published: April 2011

We present a theoretical model to describe electrical spin injection from a ferromagnetic metal contact into a conjugated organic semiconductor. To achieve significant spin current, the organic semiconductor must be driven far out of local thermal equilibrium by an electric current. Effective spin injection therefore requires that equilibration between the conjugated organic semiconductor and the metallic contact be suppressed by an energy barrier to injection that may be due either to a large Schottky barrier or to an insulating tunnel barrier. The results are compared with simulations for a silicon based device structure. Detection of the injected spin current in the organic semiconductor is also addressed.
Growth of mirror-like Zn1−xMnxO diluted magnetic semiconductor thin films by r.f. magnetron sputtering method
Authors: Lee Sejoon , Lee Hye Sung , Kim Deuk Young
Published: April 2011

The Zn1−xMnxO thin films were grown on Al2O3 (0001) substrates by an r.f. magnetron sputtering method. The film grown with employing buffer layer shows mirror-like surface, while the film grown without buffer layer shows the columnar-structured configuration. The mirror-like Zn0.93Mn0.07O thin films have the single crystalline phase with (000ℓ) orientation normal to the substrate surface and show the UV emission originated from the near band-edge-emission for the measurements of x-ray diffraction and photoluminescence, respectively. The mirror-like Zn0.93Mn0.07O film clearly showed a hysteresis loop, which is obvious evidence of ferromagnetism, and the Curie temperature was determined to be 68 K for the characterization of the temperature-dependent magnetization.
Electronic structure of the diluted magnetic semiconductors Pb1−xSnxTe:Yb
Authors: Skipetrov Evgenii , Zvereva Elena , Volkova Olga , Golubev Alexander , Slyn'ko Vasiliy
Published: April 2011

The galvanomagnetic effects in the new diluted magnetic semiconductors Pb1−xSnxTe:Yb were studied to determine the parameters of the electronic structure and to elucidate its influence on the magnetic properties. It was found that the temperature dependencies of the resistivity ρ and the Hall coefficient RH have a “metallic” character, however the RH changes in anomalous manner: its value increases more than by order of magnitude and then passes through maximum with increasing the temperature. Upon an increase of the ytterbium concentration the hole concentration decreases by more than order of magnitude. The results were explained assuming a formation of deep ytterbium-induced defect level in the valence band of the alloys, which moves up to its top with increasing the ytterbium concentration and pins the Fermi level within the valence band. The energy position of the Fermi level was calculated in the frame of two-band dispersion law and used to determine the position of Yb level in the alloys. The diagram of the charge carrier energy spectrum under varying the alloy composition was built.
DNET: The Drexel Nano Engineering Track.
Authors: Li Christopher Y. , Tenneti Kishore , Solari Dan , Zavaliangos Antonios , Kalidindi Surya , Gogotsi Yury , Sohlberg Karl , DiNardo N. John
Published: April 2011

Early exposure of Nanoscale Science, Engineering and Technology (NSET) to undergraduate students is anticipated to play a pivotal role in recruiting highly qualified professionals for industry and in preparing future faculty and researchers for graduate education. Focusing on early undergraduate education in NSET, the newly launched Drexel Nano Engineering Track (DNET) program at Drexel University addresses the urgent need for early NSET education at the University level. The primary objective of the DNET program is to expose freshmen and sophomores in Drexel's College of Engineering to basic concepts in NSET. It is envisioned that the career decisions of a large fraction of students will be directed as they learn the vocabulary of NSET and see potential engineering applications. The current DNET program activities include (1) updating/modifying a series of freshmen/sophomore courses / laboratories to infuse NSET into early undergraduate curriculum. Because of the size of the established tDEC program, this initiative has been able to reach a remarkably large body of students immediately. Over 700 students are enrolled in NSET-revised freshmen courses, and they will progress to NSET-revised sophomore courses the next year. (2) developing a number of modules for NSET education and (3) launching/maintaining a DNET web for information dissemination, performance assessment and outreach activities. The DNET program, together with the existing Nanotechnology Institute and Drexel/Upenn IGERT program that focus on the NSET research and graduate education, offer a stream of NSET education from college to graduate school at Drexel University.
Graduate Teaching Fellows in the Classroom: Connecting University Research and Resources to the K-12 Community
Authors: Hammer Donna , Srikantaiah Deepa
Published: April 2011

University-based education outreach efforts in the areas of science and engineering are continuing to grow and be refined as their success stories rapidly increase. As we have learned, effective outreach to K-12 schools and the broader community requires an understanding of the K-12 educational system, making a long-term commitment to support and enhance the existing curriculum, training researchers, and meeting our own goals of integrating the excitement of new science and technology into the classroom.

The University of Maryland (UMD) Materials Research Science and Engineering Center (MRSEC) Graduate Teaching Fellows Program (GK-12) is making strides to accomplish these objectives. This paper will be a descriptive overview of the of the UMD GK-12 Program. Emphasis will be placed on the importance of developing viable partnerships, integrating research-based concepts into the curriculum (emphasizing materials science related topics), and training research Fellows to develop the necessary skills to take advantage of their research background and to refine their teaching and communication skills within the scope of informal science and engineering education.
Incorporating Diverse Majors and Backgrounds in Materials Science Research Experience for Undergraduates (REU) Sites
Authors: Bahr D.F. , Norton M.G.
Published: April 2011

A summer Research Experience for Undergraduate (REU) site program has been operating at Washington State University for the past five summers. Over this time we have experimented with several modes of organized summer research methods, including students working in individual projects as well as students working in teams. We have balanced the academic standing of the students (freshmen to seniors), as well providing a diverse demographic background. The results of these past five summers will be presented, as well as recommendations for which methods have been the most successful in terms of generating publications and presentations from the students as well as the likelihood of students entering graduate school.
Organically Hybridized In2O3 Thin Film Gas Sensors
Authors: Matsubara Ichiro , Murayama Norimitsu , Shin Woosuck , Izu Noriya
Published: April 2011

Organically hybridized In2O3 thin films have been prepared. The surface of In2O3 thin films was hybridized by organic components with various kinds of functional groups. Upon exposure to CO gas, the electrical resistance of the hybrid sensor with amino group in the organic components increased (R-increasing response), whereas H2 gas caused the decreasing in the sensor resistance. No response was obtained to CH4 gas. For the n-type metal oxide semiconductors, the R-increasing response cannot be explained by the ordinary combustion mechanism. The response of R-increasing or R-decreasing to CO was controlled by functional groups of organic components as in the case of SnO2-based hybrid thin films. The approach of organic-inorganic hybridization is effective to realize the selective detection of reducing gas molecules.
Nano-Design of Oxide Particles and Electrode Structure for High Sensitivity NO2 Sensor Using WO3 Thick Film
Authors: Tamaki Jun
Published: April 2011

Novel sensor design for high sensitivity gas sensors has been proposed for the detection of dilute NO2 using WO3 film. First, concerning nano-design of oxide particles, the disk-shaped WO3 particles (300 nm in diameter, 20 nm in thickness) were deposited on Au comb-type microelectrode (line width: 5 μm, distance between lines: 5 μm) to be WO3 thick film sensor. This sensor showed the excellent sensing properties to dilute NO2 at optimized thickness. Second, the nano-gap electrode with various gap-sizes (110–1500 nm) was fabricated by means of MEMS techniques in order to investigate the effect of microelectrode. When the gap size was decreased less than 800 nm, the sensitivity to dilute NO2 increased with decreasing gap size. This was understood from the facts that the contribution of interface resistance between particle and electrode to total sensor resistance was increased and that the sensitivity at electrode-grain interface was much larger than that at grain boundary. It was found that the designs of not only nano-particles but also nano-electrode were important for the fabrication of high sensitivity gas sensor.
Sensitive, Selective, & Tunable Porous Silicon Gas Sensor
Authors: Lewis Stephen , Gole James , Hesketh Peter J.
Published: April 2011

Hybrid porous silicon, consisting of a microporous framework whose walls are covered with a thin nanoporous layer, proves to be an inexpensive and robust platform for fabrication of rapid, reversible, and sensitive semiconductor sensors. An extremely high surface area provides a mechanism for the detection of ppm and ppb levels of a range of gases including ammonia, NOx, and CO. A general method of coating electroless metal onto the surface provides a basis for nanostructure induced selectivity between these gases. Further, the introduction of FFT analysis to the rapidly reversible and linear response of the porous silicon gas sensor allows the gas response to be acquired and filtered on a drifting baseline.
Sub-micron structured Metal Oxide gas sensors by means of lithographic techniques
Authors: Candeloro Patrizio , Baratto Camilla , Comini Elisabetta , Faglia Guido , Di Fabrizio Enzo M. , Sberveglieri Giorgio
Published: April 2011

In this work we employed lithographic techniques, combined with sputtering depositions, to fabricate semiconductor metal-oxide (MOX) gas sensors with controlled grain dimensions. The basic idea is to replace the continuous sensing film of standard MOX sensors with a pattern of wires in the sub-micron scale, thus controlling the lateral size of the grains. Regarding the fabrication process, we followed two different approaches: a plain lift-off technique and a substrate patterning process. We present a comparison between the results of both the approaches. Furthermore, we tested the electrical responses to several gases and compared them with those of continuous film sensors. The experimental data highlight an improvement for the patterned sensors.
Resistive Oxygen Gas Sensors Using Cerium Oxide Nanosized Powder
Authors: Murayama Norimitsu , Izu Noriya , Shin Woosuck , Matsubara Ichiro
Published: April 2011

Cerium oxide nanosized powder was synthesized by modified precipitation method. The precipitate, which was formed from the addition of NH4OH to Ce(NO3)3 aqueous solution, and was filtered. The obtained gel was mixed with carbon powder with a particle size of about 20 nm by a mechanically rotating mixer. The mixture was dried at 343 K in air. The carbon powder was burned out by heat treatment at 1173 K in air for 4 h, resulting in the formation of CeO2 powder with a size of 50 nm. A thick film was formed on an alumina substrate by screen printing, and was fired at 1373 K. The thick film had porous structure and the grain size was about 120 nm. The resistance of the thick film was almost proportional to P (O2)1/6, where P (O2) is oxygen partial pressure, in the P (O2) range from 10−13 to 105 Pa at 1073 and 1173 K. The response time (t90) was 23 and 7 ms at 1023 K when P(O2) changed from 65 to 25 kPa and 25 to 65 kPa, respectively. The reason for this result was explained on the basis of surface reaction of cerium oxide grain.
HRTEM/EELS Analysis, Structural Characterization and Sensor Performances of Hydrothermal Nano-TiO2
Authors: Ruiz Ana M. , Arbiol J. , Cornet A. , Shimanoe K. , Morante Joan R. , Yamazoe N.
Published: April 2011

Pure nanophased TiO2 with controlled microstructure and resistant to thermal induced grain growth has been prepared by hydrothermal treatments. The synthesized nano-TiO2 presents small size and well defined and faceted surface, as shown by Raman spectroscopy, XRD, EELS and HRTEM. Such performances are slightly changed with the posterior temperature treatments up to 700 °C, maintaining anatase phase structure and grain size about 20nm. The extent of stabilization depended on the pH of the treatment, being pH 2 more convenient for stabilizing the size, and pH 3 for the phase. HRTEM and EELS measurements showed the coexistence of rutile big particles (∼100 nm) with anatase small particles (∼40 nm) at pH 3 and calcination at 900°C. Thick-films of precipitated TiO2 and hydrothermally treated TiO2 were tested for the CO and the ethanol response. The hydrothermal treatment allowed obtaining stable sensitive films which exhibited enlarged sensor response and improved transients, specially in the case of the materials treated at pH 3.
Environmental Sensitivity of Pentacene Thin-Film Transistors
Authors: Breban M. , Mezhenny S. , Hines D. R. , Romero D. B. , Ballarotto V. W. , Williams E. D.
Published: April 2011

By alternating the gate voltage polarity of a pentacene thin film transistor, we show that the drain current is stabilized and thus the bias stress effect is overcome. This allows for controlled testing of the device sensitivity to environmental conditions. We find that the conductivity of the device decreases on the time scale of seconds when the device is exposed to water vapor, which is manifested through a decrease in mobility and a shift in the threshold voltage. Simple recombination modeling suggests that trapping is the responsible mechanism. However, the effects of water vapor can be reversed by exposing the device to dry nitrogen flow. The time scale for recovery is on the order of 10s of minutes.
Sensing Mechanism of NO in Nanocrystalline Ru, Pt, Pd-Doped SnO2: Electron Paramagnetic Resonance, Mössbauer and Electrical Study
Authors: Canevali Carmen , Maria Mari Claudio , Mattoni Mariachiara , Morazzoni Franca , Ruffo Riccardo , Scotti Roberto , Russo Umberto , Nodari Luca
Published: April 2011

The reactivity of nanosized Ru(Pd,Pt)-doped SnO2, obtained by sol-gel synthesis, towards NO/Ar was investigated by Electron Paramagnetic Resonance (EPR), Mössbauer and Electrical Resistance measurements. A sensing mechanism was proposed that involves (i) the formation of bielectronic oxygen vacancies VO, (ii) their single-ionisation to VO•, which injects electrons to SnO2 conduction band, (iii) the transfer of VO• electrons to the transition metal centers reducing them to lower oxidation states. It was suggested that the electronic exchange between oxide and transition metal is responsible for the enhancement of the reactivity in doped SnO2 with respect to the undoped material.
Printed Organic Electronic Devices Made using High Volume Printing Processes
Authors: Xia Yu , Karwa Anupama , Sigg Franz , Clark Daniel M. , Kahn Bruce E.
Published: April 2011

Printing is a promising technique to fabricate commercial organic electronic devices such as OLED, TFT, solar cells and sensors. In this investigation, we report the application of high volume flexographic printing, which makes low cost and batch production possible. Commercial RFID tags have been printed using metallic inks with organic compounds in the Printing Applications Lab (PAL) at Rochester Institute of Technology (RIT). Polyaniline ink was prepared and printed by flexography in the form of test targets and Interdigitated electrodes (IDE). The conductivity can be controlled by different levels of doping. Furthermore, multiple impression printing was used to print overlapping functional layers to obtain all printed organic electronic devices like chemical vapor and humidity sensors. Optical profilometry and SEM were used to analyze the surface and interface structure. Sensitivity was measured and compared with commercial devices.
Encapsulation of Urease in Molybdenum Trioxide Sol-Gel
Authors: Jha Prashant K. , Gouma P. I.
Published: April 2011

Molybdenum trioxide sol-gel matrices were tested for their ability to host biomaterials in their structures without adversely affecting the activity of the encapsulated biomolecules. The sol-gel composites were prepared at room temperature; the urease was added during the hydrolysis step to ensure proper encapsulation in the pore structure of the sol. Phosphate buffer solution was added during this stage to maintain the pH value of the sol in the bio-compatible range. The activity of incorporated urease was tested by exposing composite sol-gel material to standard urea test solutions and measuring the amount of gaseous ammonia (released by the reaction of urea with water in the presence of urease) using an ammonia electrode. The concentration of urea solutions ranged from 1mM to 10mM. An electronic olfactory system (EOS 835) was also employed to detect the presence of gaseous ammonia. Gas sensing tests were done to verify the sensitivity of the matrix to ammonia. Microstructural analysis was carried out by means of scanning and transmission electron microscopy. It was found that urease retained its activity inside molybdenum trioxide sol-gels that are sensitive to ammonia. These hybrid nanoporous composites are useful in the field of biosensors and fuel cells.
Low Voltage and High Speed Silicon Nanocrystal Memories
Authors: Carreras Josep , Garrido B. , Arbiol J. , Morante J. R.
Published: April 2011

We have studied a set of MOS cell structures with 30 nm thick thermal oxide implanted with Si at high doses (10, 15 and 20 atomic % at projected range) in which Si nanocrystals (Si-nc) have been precipitated by annealing at 1100 °C. Energy filtered transmission electron microscopy reveals: i) a central layer of Si-nc with a mean size of 2.8 nm; ii) a control oxide of 12.5 nm completely free of Si-nc and iii) a tunnel oxide of about 2.5 nm. This narrow tunnel oxide enables the direct tunnel for charging and discharging which is a must for high speed and good reliability. However, this results in typical retention times ranging from only few hours to several months, depending on the concentration of Si-nc. For developing low voltage memories we have focused on the highest Si excess sample, which shows fast write times (tens of μs) at very low gate fields (±2 MV/cm or ±6V). The onset of Fowler-Nordheim conduction is of about ±6 MV/cm by J-V measurements (±18V), which means that the structure works in a direct tunnel regime. To increase the retention time we have performed an additional annealing step in diluted O2 for 16 and 32 minutes, resulting in a dramatic increase in the retention times, which is attributed to the re-growth of an additional tunnel oxide which eliminates surface roughness, remaining Si excess and defects at the Si-SiO2 interface. This additional oxidation step produces also a decrease in the mean size of the Si-nc distribution. Thus, we increase the retention time beyond the 10 years standard limit. Finally, the writing times can be traded-off by increasing slightly the program voltage up to ±2.7 MV/cm or ±8V.
Step Coverage and Composition of Pb(Zr, Ti)O3 Capacitors Prepared on Sub-Micron Three-Dimensional Trench Structure by Metalorganic Chemical Vapor Deposition
Authors: Nagai Atsushi , Asano Gouji , Minamidate Jun , Choi Chel Jong , Cho Choong-Rae , Park Youngsoo , Funakubo Hiroshi
Published: April 2011

Pb(Zr, Ti)O3 (PZT) films were deposited into sub-micron trench structure consisting of SiO2/TiAlN/Ti/SiO2/Si to investigate their thickness and composition conformality by pulsed-metalorganic chemical vapor deposition (MOCVD) using liquid delivery source-supply system. Bis(dipivaloylmethanato)lead [Pb(DPM)2], tetrakis(1-methoxy-2-methyl-2-propoxy)zirconium [Zr(MMP)4] and tetrakis(1-methoxy-2-methyl-2-propoxy)titanium [Ti(MMP)4] were used as Pb, Zr and Ti source materials, respectively. In Arrhenius plot, the slopes of the straight lines for the constituents Pb, Zr and Ti in PZT film were almost the same at a lower deposition temperature (Td) region as well as a higher Td one. This means the composition change in the film against the Td can be suppressed by using Pb(DPM)2-Zr(MMP)4-Ti(MMP)4-O2 source system. From the results of Arrhenius plot, the Tds were fixed on 450 and 540°C as lower and higher temperatures, respectively. At both Tds, the sidewall-bottom step coverage (SCs-b) was approximately 70 %, while the sidewall step coverage (SCsw) reached excellent values above 90 %. It is suggested that low SCs-b value was caused by crystallization of the PZT films at the bottom of the trench because underlayer of the film at this area was not SiO2 but crystalline TiAlN. On the other hand, no significant composition fluctuation was observed along the depth direction of the sidewall. These results mean that the film deposited at 540°C had almost the same level in terms of thickness and composition conformality as that deposited at 450°C.
Ferroelectric 1-T memory device—will it be viable for nonvolatile memory applications?
Authors: Han Jin-Ping
Published: April 2011

The quest for a nonvolatile memory FET based on the metal-ferroelectric-(insulator)-semiconductor (MF(I)S) gate stack concept has greatly intensified in recent years. In principle, such a memory device (MF(I)S) could be a building block of an ideal memory technology which offers random access, high speed, low power, high density and non-volatility. In practice, however, none of the reported ferroelectric memory transistors has achieved a memory retention time of more than a few days so far. These results are a far cry from the 10-year retention time requirement for non-volatile memory devices. This paper reveals progress and optimization that grain size, interfacial properties, and crystallinity of the annealed ferroelectric SrBi2Ta2O9 (SBT) films have a strong impact on the size of the memory window, as does the choice of the buffer layer material. The properties of SiN buffer layer sandwiched between SBT and Si are discussed. Switches in the polarization of the ferroelectric SBT play a key role for both the ferroelectric-polarization-dominated and the trapping-dominated memory windows. Preliminary results on MFIS capacitors and transistors are reviewed, limited retention time has been observed. A closer look at the physics of device operation reveals two major causes of the short retention time: (1) depolarization fields; (2) finite gate leakage current and the associated charge trapping. Here, the origins of these problems are analyzed and practical difficulties in attempting to realize nonvolatile ferroelectric 1-T memory devices are illustrated. Two possible solutions have been proposed to circumvent problems associated with the finite retention time in ferroelectric FETtype memories: (1) memory refreshes as done in the FEDRAM cell, (2) single-crystallize the ferroelectric film.