bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrodeposition of Bi2Te3 Nanowire Composites
Authors: Prieto Amy L. , Sander Melissa S. , Stacy Angelica M. , Gronsky Ronald , Sands Timothy
Published: June 2019

Widespread applications of thermoelectric materials are limited due to low efficiency. Currently, the most widely used thermoelectric devices consist of alloys based on Bi2Te3. In such devices, the thermoelectric figure-of-merit (ZT) of bulk Bi2Te3 has been increased through doping. It is postulated that further enhancements in ZT may be attained by engineering the microstructure of the material to enhance carrier mobility while suppressing the phonon component of the thermal conductivity. This may be achieved by fabricating Bi2Te3 in the form of one-dimensional (1D) nanowires. We have deposited nanowires of Bi2Te3 with two different diameters (200 nm and 40 nm) by electrodeposition into porous anodic alumina. Characterization of the Bi2Te3/porous Al2O3 composite materials has been accomplished using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) has been used to determine the stoichiometry of the wires.
Theoretical Evaluation of the Thermal Conductivity in Framework (Clathrate) Semiconductors
Authors: Dong Jianjun , Sankey Otto F. , Myles Charles W. , Ramachandran Ganesh K. , McMillan Paul F. , Gryko Jan
Published: June 2019

We have calculated the room temperature thermal conductivity in semiconductor germanium clathrates using statistical linear-response theory and an equilibrium molecular dynamics (MD) approach. A key step in our study is to compute a realistic heat-current J (t) and a corresponding auto-correlation function < J (t) J (0) >. To ensure convergence of our results and to minimize statistical fluctuations in our calculations, we have constructed large super-cell models (2944 atoms) and have performed several independent long time simulations (>1,500 ps in each simulation). Our results show an unexpected “oscillator” character in the heat-current correlation function of the guest-free Ge clathrate frameworks. This is absent in the denser diamond phase and other with simple structural frameworks. We seek to interpret these results using lattice dynamics information. A study of the effects of the so-called “rattling” guest atoms in the open-framework clathrate materials is in progress.
A Low-Frequency Forced Torsion Pendulum for the Measurement of the Mechanical Properties of Granular Media
Authors: D'Anna G.
Published: June 2019

We present a forced torsion pendulum designed to measure the dynamic moduli of granular media. In the method, the oscillating probe of the pendulum is immersed into various materials, such as sand, glass beads, snow. The apparatus operates at low-frequency and provides information about the quasi-static mechanical properties of the medium. In particular, a peak in the losses is ascribed to friction and cohesion between the grains, and a measure of the macroscopic failure limit can be obtained. As an example the effect of moisture-induced ageing in small glass beads, and the effect of sintering of ice grains in snow, are shown.
Investigation of particulate systems using optical pathlength spectroscopy
Authors: Popescu Gabriel , Dogariu Aristide
Published: June 2019

In many industrial applications involving granular media, knowledge about the structural transformations suffered during the industrial process is desirable. Optical techniques are noninvasive, fast, and versatile tools for monitoring such transformations. We have recently introduced optical path-length spectroscopy as a new technique for random media investigation. The principle of the method is to use a partially coherent source in a Michelson interferometer, where the fields from a reference mirror and the sample are combined to obtain an interference signal. When the system under investigation is a multiple-scattering medium, by tuning the optical length of the reference arm, the optical path-length probability density of light backscattered from the sample is obtained. This distribution carries information about the structural details of the medium. In the present paper, we apply the technique of optical path-length spectroscopy to investigate inhomogeneous distributions of particulate dielectrics such as ceramics and powders. The experiments are performed on suspensions of systems with different solid loads, as well as on powders and suspensions of particles with different sizes. We show that the methodology is highly sensitive to changes in volume concentration and particle size and, therefore, it can be successfully used for real-time monitoring. In addition, the technique is fiber optic-based and has all the advantages associated with the inherent versatility.
Particle Fluctuation Velocity in Gas Fluidized Beds - Fundamental Models Compared to Recent Experimental Data
Authors: Cody G. D.
Published: June 2019

The first measurements of the mean squared fluctuation velocity, or granular temperature, of monodispersed glass spheres in gas fluidized beds were recently obtained by two independent techniques: Power Spectral analysis of wall vibrational energy excited by random particle impact or Acoustic Shot Noise (ASN), and Diffusing Wave Spectroscopy (DWS) of reflected laser light multiply scattered by random particle motion. We explore the relevance of this data to the initial stability of the uniform fluidized state and to recent fundamental models for the magnitude, gas flow, and particle diameter dependence of the steady state granular temperature.
Mechanical response of a static granular piling
Authors: Reydellet Guillaume , Vanel Loic , Clément Eric
Published: June 2019

We present the results of different experiments which aim is to investigate the response of a static granular assemblies to various local perturbations. We design a sensitive experimental method to probe the response of a localized stress at the top of a granular piling. The piling is an horizontal 3D granular layer confined in a box and the spatial distribution of loads at the bottom is monitored. This analysis defines some crucial experimental test to inform a currently debated issue on the mechanical status of static granular assemblies.
Monte-Carlo Simulation of Three Dimensional Ion Dynamics in Polymers
Authors: Wagner A. , Kliem H.
Published: June 2019

Dynamic Monte-Carlo simulations of three dimensional ion motions are carried out based on a multi-well potential model. A parallel plate capacitor is modeled with an ionic conducting polymer having two ideal blocking electrodes. Positive ions (maximum 1000) are located on a cubic lattice with a maximum size of 100×100×100 locations. A negative background charge, constant in space and time, is used to provide charge neutrality. The positive ions can perform hops between neighboring sites with a probability corresponding to distributed energy barriers. To calculate the potentials due to an interaction of the ions the method of images is used. The steady state and the dynamic properties are studied after application of a voltage step in dependence on the sample thickness, the ion concentration and the voltage. A simulation of a space charge polarization yields an explanation for the experiments in the time and in the frequency domain.
Modeling Stress and Failure in Shrinking Coatings
Authors: Lei Herong , Francis Lorraine F. , Gerberich William W. , Scriven L. E.
Published: June 2019

Drying or curing of a coating after vitrification or gelation is accompanied by stress development. Evaporation of solvent, polymerization, cross-linking, and cooling all cause shrinkage, but adhesion of the coating to the substrate prevents shrinkage to a stress-free state. The interaction of shrinkage and restraint creates strain and stress. If the local stress grows above the local strength of the coating, it can produce cracking, delamination, or other defects.

A large deformation elastic model based on the Galerkin/finite element method is developed to analyze stress development in coatings subject to uniform shrinkage. The model is used to analyze effects of delamination and surface cracks. The strain energy release rates in both delamination and surface cracking are computed at different crack lengths. In both cases, results show that thicker coatings have larger energy release rates and are more vulnerable to cracking. A key conclusion of this modeling is that a crack can propagate only from an inherent flaw greater than a certain size. If the coating is thin enough so that the maximum energy release rate is less than the crack growth resistance, then no inherent flaws in the coating can grow into a crack, and so the coating remains crack-free. The model also shows how to calculate a critical coating thickness, i.e., the maximum thickness of a coating that can remain crack-free.
Crack Behaviour at Bi-Crystal Interfaces: A Mixed Atomistic and Continuum Approach
Authors: Pillai Arun R. , Miller Ronald E.
Published: June 2019

Interfacial defects like grain boundaries and phase boundaries play an important role in the mechanical behaviour of engineering alloys. In this work the problem of a crack on a bi-crystal interface is studied at the atomic scale, with the goal of elucidating the effects of varrying interatomic interaction on crack behaviour and to assess the suitability of existing fracture criteria to the anisotropic bi-crystal case. Calculations are performed using the Quasicontinuum (QC) method [1]. Using suitable approximations, some of the existing fracture criteria were used to predict ductile or brittle fracture and compared to the QC results.
High Doped p-Type GaN Grown by Alternative Co-Doping Technique
Authors: Iwai Souhachi , Hirayama Hideki , Aoyagi Yoshinobu
Published: June 2019

We investigated the electrical properties of Mg-doped GaN grown by alternative pulse supplies of source and dopant materials in metalorganic vapor phase epitaxy. We obtained the hole concentration of 6×1018cm-3 for p-type GaN grown on a sapphire substrate by repetition of supply and purging of Ga and Mg sources in the constant NH3 flow, while that of p-type GaN grown by the constant feeding of Ga and Mg sources was 2×1018cm-3. By using alternative feedings of Ga source and NH3 with Mg-Si co-doping, we obtained a highly hole concentration of 2×1019cm-3 for p-type GaN which was grown directly on a low temperature AlN buffer layer. We also obtained the hole concentration of 6×1018cm-3 for p-type GaN which was grown on an AlGaN layer on a SiC substrate by alternative co-doping technique. The activation energies for Mg-doped GaN grown by the pulse feedings of source materials were lower than that for GaN grown by continuous supplies of source materials as used in the conventional technique.
Electrical and Optical Properties of Carbon-Doped GaN Grown by MBE on MOCVD GaN Templates Using a CCl4 Dopant Source
Authors: Armitage Rob , Yang Qing , Feick Henning , Park Yeonjoon , Weber Eicke R.
Published: June 2019

Carbon-doped GaN was grown by plasma-assisted molecular-beam epitaxy using carbon tetrachloride vapor as the dopant source. For moderate doping mainly acceptors were formed, yielding semi-insulating GaN. However at higher concentrations p-type conductivity was not observed, and heavily doped films (<5×1020 cm-3) were actually ntype rather than semi-insulating. Photoluminescence measurements showed two broad luminescence bands centered at 2.2 and 2.9 eV. The intensity of both bands increased with carbon content, but the 2.2 eV band dominated in n-type samples. Intense, narrow (∼6 meV) donor-bound exciton peaks were observed in the semi-insulating samples.
Comparative Study of trap levels observed in undoped and Si-doped GaN
Authors: Soh C. B. , Chi D. Z. , Lim H. F. , Chua S. J.
Published: June 2019

In this paper, deep level defects in undoped and Si–doped GaN have been studied using digital deep level transient spectroscopy. Common trap levels at Ec -ET ∼ 0.15-0.20 eV and 0.59-0.62 eV were detected for both undoped and Si-doped samples. For the doped samples, three additional defect levels at Ec-Et ∼ 0.11, 0.28, and 0.45 eV were detected. The concentration of the 0.15-0.20 eV was found to be much higher in undoped GaN that also shows higher dislocation density. Based on this correlation and the logarithmic capture behavior observed for this level, indicative of extended defect nature, we attribute the 0.15-0.20 eV level to dislocation related defects. On the other hand, the 0.28 and 0.45eV trap levels are tentatively attributed to Sirelated defects simply due to the fact that these two levels were observed only in Si-doped GaN. The 0.11eV trap level, which exhibits an exponential capture kinetic, is believed to be related to nitrogen vacancies.
Low-temperature operation of diamond surface-channel field-effect transistors
Authors: Tachiki Minoru , Ishizaka Hiroaki , Banno Tokishige , Sakai Toshikatsu , Song Kwang-Soup , Umezawa Hitoshi , Kawarada Hiroshi
Published: June 2019

Cryogenic operation of the diamond surface-channel field-effect transistors (FETs) is investigated. Metal-insulator-semiconductor FETs (MISFETs) are fabricated using CaF2 as a gate insulator. MISFETs operate successfully even at 4.4 K. At low temperature, field-effect enhances the drain current, even if the surface holes become almost frozen-out. Channel mobility increases as temperature decreases to 4.4 K, which indicates the reduced phonon scattering.
Comparative Analysis of MBE-grown GaN Films on SiC, ZnO and LiGaO2 Substrates
Authors: Yun F. , Reshchikov M. A. , He L. , King T. , Huang D. , Morkoç H. , Nause Jeff , Cantwell Gene , Maruska H. Paul , Litton C. W.
Published: June 2019

We report the growth of GaN films by RF-MBE on SiC, ZnO, and LiGaO2 substrates, without buffer layers. Structural and optical properties of the films were probed by AFM for surface morphology, XRD for crystalline structure, and PL for optical properties. The dependence of GaN layer quality on the substrates and their surface pre-treatment prior to growth was studied within a similar MBE growth parameter matrix for all samples.
Perturbation of Copper Substitutional Defect Concentrations in CdS/CdTe Heterojunction Solar Cell Devices
Authors: Albin D. , Dhere R. , Wu X. , Gessert T. , Romero M.J. , Yan Y. , Asher S.
Published: June 2019

The efficacy of implementing terrestrial-based photovoltaics is dictated by trade-offs in device performance, cost, and reliability. Presently, the highest efficiency polycrystalline CdS/CdTe superstrate solar cells utilize back contacts containing copper as an intentional dopant. Accelerated stress data correlates copper diffusion from this contact with performance degradation. Degradation at the device level exhibits two characteristic modes that are influenced by CdTe surface treatments prior to contacting. Rapid degradation associated with a rapidly decreasing open-circuit voltage can occur in cases where processing favors stoichiometric CdTe surfaces. Slower degradation associated with roll-over is typified by treatments favoring the presence of Te at the back contact. The chemical composition and extent of Te-rich contact interfaces is revealed by transmission electron microscopy. Deep-level transient spectroscopy of NP etched and non-etched devices show Te-rich conditions are necessary for the detection of deep-acceptor CuCd defect levels at (Ev +0.28 to 0.34 eV). Low keV cathodoluminescence measurements show that these defects can be found localized at the back surface of CdS/CdTe devices.
The Elimination of Ion Implantation Damage at the Source/Drain Junction of Poly-Si TFTs
Authors: Jung Sang-Hoon , Lee Min-Cheol , Park Kee-Chan , Han Min-Koo
Published: June 2019

We report a new poly-Si TFT, of which the troublesome implantation damage near the source/drain junction was eliminated, by performing source/drain ion implantation as well as excimer laser annealing (ELA) prior to the gate formation. The recrystallization of a-Si in the channel region and the dopant activation in the source/drain region were simultaneously accomplished by single ELA process step so that the implantation damage, which results in large leakage current of TFT, has been successfully eliminated. TEM image verifies that large poly-Si grains were successfully grown from the ion implanted source/drain region to the channel region. The proposed poly-Si TFT, of which mobility is 171 cm2/Vs, exhibits a large on/off current ratio exceeding 4.1 × 107without LDD or offset structure while those of the conventional TFT, which has been fabricated simultaneously for the comparison purpose, are 86 cm2/Vs and 6.1 × 106.
Synthesis and Application of Electronic Oxides for Solar Energy
Authors: Kestner James M. , Chorney Anna , Robbins Joshua J. , Huang Yen-jung , Vincent Tyrone L. , Wolden Colin A. , Woods Lawrence M.
Published: June 2019

Plasma-enhanced chemical vapor deposition (PECVD) is being developed as a flexible coating technology for a variety of oxides. In this paper we discuss the synthesis of transparent conducting oxides (TCOs), insulating oxides and electrochromic oxides. Tin oxide was synthesized using mixtures of SnCl4 and O2. By proper control of processing conditions the resistivity of this material may be varied from 10-3 < ρ < 105 Ω-cm. Films of varying resistivity were employed as buffer layers in CdS/CdTe solar cells. Preliminary device results have demonstrated that integration of a tin oxide buffer layer was very beneficial for cell performance. In addition, we demonstrate the PECVD synthesis of WO3 from WF6/O2/H2/Ar mixtures. The plasma process space that yielded adherent, transparent tungsten oxide was established. The deposited films were both amorphous and reversibly electrochromic. High temperature annealing above 400°C converted the films into a polycrystalline state.
PZT and Electrode Enhancements of Mems Based Micro Heat Engine for Power Generation
Authors: Olson A.L. , Eakins L.M. , Olson B.W. , Bahr D.F. , Richards C.D. , Richards R.F.
Published: June 2019

The P3 Micro Heat Engine relies on a thin film PZT based transducer to convert mechanical energy into usable electrical power. In an effort to increase process yield for these were used on sputtered Ti/Pt bottom electrodes to compare roughness, grain size, and diffusion for annealing temperatures between 550 and 700 °C. For an optimized bottom electrode, process yield for various sized top electrodes were then studied for PZT thickness between 0.54 and 1.62 for reducing stress concentrations. Two PZT etching geometries on 2.3 μm thick Si/SiO2 membranes, with 1.5-3.5 mm side-lengths, were examined and one was used to increase the strain at failure by at least 40%. Integrating improvements in process yield and strain at failure, single PZT based MEMS devices capable of generating power of up to 1 mW and in excess of 2 volts have been demonstrated operating at frequencies between 300 and 1,100 Hz.
Low Temperature Growth Mechanism of GaN Crystal by Hydride Vapor Phase Epitaxy
Authors: Liu Hai-Ping , Chen In-Gann , Tsay Jenq-Dar , Liu Wen-Yueh , Guo Yih-Der , Hsu Jung Tsung
Published: June 2019

The low temperature growth of GaN crystal using epitaxy lateral overgrowth (ELO) on SiO2 dot pattern below 900°C by hydride vapor phase epitaxy (HVPE) have been studied. It is observed that the growth rate of GaN hexagonal pyramidal crystals along [1101] direction increases as growth temperature decreases. At low temperature of ∼ 850°C, hexagonal GaN columnar crystals with high index facet at the top can be observed. It is proposed that the surface diffusion length of precursors, such as NH3 and GaCl, decreases at lower temperature that reduces the probability of desorption and increase the lifetime. The condensation of Ga liquid droplets on the GaN surface will change the relative stability of {1101} facet. Therefore, the formation of high index planes such as {2122} facet on the top of hexagonal column along with the formation of stacking fault on the (0001) plane can be observed. A detailed study of the effect of growth temperature on the crystal growth mechanism will be presented.
The Refractive Index and Other Properties of Doped ZnO films
Authors: Cai A. L. , Muth J. F. , Porter H. L. , Kvit A. , Narayan J.
Published: June 2019

Ordinary and extraordinary indices of refraction, film thickness and waveguide mode information of zinc oxide, zinc oxide doped with nitrogen and zinc oxide doped with tellurium were measured by using a prism coupling waveguide technique. The films were grown on c-axis sapphire substrates by pulsed laser deposition (PLD). High accuracy waveguide measurements show that the ordinary and extraordinary indices of refraction of ZnO samples change with the introduction of nitrogen or tellurium. The densification of films with annealing could also be tracked with precision refractive index measurement. The crystal structure and the optical properties of the films were also characterized by using x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and cathodoluminescence (CL).
Influence of Ion Energy on the Reactive Ion Etching Induced Optical Damage of Gallium Nitride
Authors: Liem Suk Ing , Reeves Roger J.
Published: June 2019

Reactive Ion Etching (RIE) induces defects in semiconductor materials. These defects can serve as local non-radiative recombination centres for electron-hole pairs, affecting the radiative lifetimes and luminescence efficiencies of the semiconductors. Argon (Ar) and sulphur hexafluoride (SF6) gases were used as etching gases to investigate the influence of ion energy on the RIE induced optical damage of Gallium Nitride (GaN). The significant result of etching by Ar and SF6gases was that these etching induce defects, but as the total PL does not greatly change, it appears that this process is not increasing the density of nonradiative centres.
The Investigation of Preferred Orientation Growth of ZnO Films on the Ceramic Substrates
Authors: Chu Sheng-Yuan , Chen Te-Yi , Water Walter , Huang Tung-Yi
Published: June 2019

Poly-crystal ZnO films with c-axis (002) orientation have been successfully grown on the lead-based ceramic substrates by r.f. magnetron sputtering technique. The deposited films were characterized as a function of deposition time and argon-oxygen gas flow ratio. Crystalline structures of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Highly oriented films with c-axis normal to the substrates can be obtained by depositing under a total pressure of 10mTorr containing 50% argon and 50% oxygen and r.f. power of 70W for 3 hours. The phase velocity, electromechanical coupling coefficient and temperature coefficient of frequency of SAW device with ZnO/IDT/PT-ceramic structure were investigated. It shows that the preferred oriented ZnO film is beneficial for improving the electromechanical coupling coefficient of SAW device.
Abnormal Rectifying Characteristics of a Mg Doped GaN Schottky Diode
Authors: Kim Jae Wook , Cho Byung Kyu , Lee Jhang Woo , Yu Phil W.
Published: June 2019

Electrical properties of Ti/Al Schottky junctions formed on p-GaN layers are investigated using Hall, I-V and C-V measurements in the temperature range of 82∼500K. All data exhibit extremely strong low temperature carrier freeze out effects, assured by huge decreases of the Hall concentration, zero-bias capacitance and also diode current level as the temperature decreases below ∼150K. The dramatic decrease of current level at the low temperature range indicates that tunneling plays a more important role for the low temperature conduction and the junction shows ohmic-like I-V characteristics due to large series resistance. The barrier height estimated with the thermionic model varies with a strong temperature dependency from 1.21eV at 500K to 0.24eV at 82K. High frequency equivalent circuit analysis indicates that the corrected capacitance still shows a strong frequency dependency even after compensating the series resistance effect due to the slow response of Mg acceptor state. The transition frequency of the acceptor state, which is proportional to the emission rate of the deep level, is estimated to be 142KHz at room temperature. Low frequency C-V measurements provide a proper doping profile, revealing the ∼15nm thin layer with a high doping spike of ∼8×1018/cm3 near the sample surface and the constantly doped bulk layer with a doping level of ∼1017/cm3.
Electron Injection-Induced Effects in GaN: Physics and Applications
Authors: Chernyak Leonid , Burdett William
Published: June 2019

Electron injection into p-type GaN and related compounds leads to a pronounced increase in the minority carrier lifetime. This increase is manifested in a multiple-fold elongation of the minority carrier diffusion length as is evident from the Electron Beam Induced Current (EBIC) measurements in-situ in a Scanning Electron Microscope. Minority carrier transport enhancement as a result of electron injection is consistent with the changes observed in the material's luminescent properties. Based on the activation energy for the electron injection-induced effects, we ascribe this phenomenon to charging of Mg-acceptor related levels. In addition, we demonstrate an impact of electron injection on responsivity of GaN p-i-n photodetectors.
Structural Properties of Free-Standing 50 mm Diameter GaN Wafers with (10

1

0) Orientation Grown on LiAlO2
Authors: Jasinski Jacek , Liliental-Weber Zuzanna , Maruska Herbert-Paul , Chai Bruce H. , Hill David W. , Chou Mitch M. C. , Gallagher John J. , Brown Stephen
Published: June 2019

(1010) GaN wafers grown on (100) face of γ-LiAlO2 were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1 type. This is consistent with diffraction contrast experiments.
High Quality Sn-Doped In2O3 Films Grown by Pulsed Laser Deposition for Organic Light-Emitting Diodes
Authors: Kim Heungsoo , Horwitz James S. , Hong Kim Woo , Kafafi Zakya H. , Chrisey Douglas B.
Published: June 2019

High quality Sn-doped In2O3 (ITO) thin films have been grown by pulsed laser deposition (PLD) on glass, flexible polyethylene terephthalate (PET) and single crystal yttria stabilized zirconia (YSZ) substrates for use in organic light emitting diodes (OLEDs). Critical electrode issues for the OLED are related to the optical transparency, electrical resistivity, work function and surface roughness of the ITO film. Our research has focused on improving the properties of the ITO film to increase the efficiency of the OLED. Films were deposited using a KrF excimer laser (248nm, 30 ns FWHM) at fluences of 2 J/cm2 at substrate temperatures ranging from 1 to 100 mTorr. For ITO films (∼ 100 nm thick) deposited at the optimized conditions, a resistivity of 4.1 × 10-4 Ω-cm, 2.2 × 10-4 Ω-cm, 1.8 × 10-4 Ω-cm was observed on PET, glass and YSZ, respectively. The average film transmission in the visible range (400 - 700 nm) was about 90 % and the film surface roughness was about 0.5 nm for the film grown on glass. The Hall mobility and carrier density for ITO films (300 nm thickness) were observed to be in the range of 28 - 34 cm2/V-s and 1.0 - 1.2 × 1021 cm-3, respectively. We have used the ITO films, deposited by PLD on glass, plastic and single crystal YSZ substrates, as an anode contact in OLEDs. The OLED device performance based on PLD ITO anodes is compared with that of the device fabricated on the commercial ITO anode.
Solids Characterization from Hydrothermal Tests with Spent Fuel
Authors: Uziemblo N.H. , Thomas L.E. , Schoenlein L.H. , Mastel B. , Jenson E.D.
Published: June 2019

Reacted solids from 200°C, 25 MPa tests with spent light water reactor fuel and other component materials of a high-level nuclear waste repository in basalt were analyzed by scanning electron microscopy, X-ray powder diffractometry, transmission electron diffraction, Auger electron spectrome- try, and microautoradiography. The work complements solutions analysis from the same tests conducted in Dickson-type rocking autoclaves for the Basalt Waste Isolation Project. Spent fuel reacted very slowly in fuel/water tests, exhibiting noticeable grain boundary etching and uranium silicate formation only after six months. Particle abrasion in the rocking autoclave produced fuel fines that remained apparently unaltered. In spent fuel tests with basalt or basalt and steel, iron smectite clay formed at the expense of mesostasis phases in the basalt. Low concentrations of β-emitters, probably Cs and Tc released from grain boundaries in the fuel, were incorporated in the clay. Steel corroded very slowly under the low-oxygen conditions of the tests, forming minor amounts of magnetite, hematite and wustite. The sluggishness of spent fuel/water and steel/water reactions is attributed to limited availability of oxygen under the test conditions.
Modelling Porewater Chemistry in Hydrated Portland Cement
Authors: Berner Urs R.
Published: June 2019

Extensive employment of concrete is foreseen in radioactive waste repositories. A prerequisite for modelling the interactions between concrete and formation waters is characterisation of the concrete system. Available experimental data from high pressure squeezing of cement pore-water indicate that, besides the high pH due to alkali hydroxide dissolution, cement composition itself influences the solubility determining solid phases. A model which simulates the hydration of Portland cement assuming complete hydration of the main clinker minerals is presented. The model also includes parameters describing the reactions between the cement and blending agents.

Comparsion with measured pore-water data generally gives a consistent picture and, as expected, the model gives correct predictions for pure Portland cements. For blended cements, the required additional parameters can, to some extent, be derived from pore-water analysis.
Attenuation of Pu, Am, Cs and Sr Mobility in Concrete
Authors: Jakubick A.T. , Gillham R.W. , Kahl I. , Robin M.
Published: June 2019

Sorption experiments with 85Sr, 137CS, 239pu and 241Am on four types of concrete (normal density, normal density with fly ash, high density and high density with silica fume) were carried out in a predominantly CaCl2 groundwater, in a predominantly NaCl groundwater and in nitrate solutions. Subsequently, autoradiography was used to identify the sorption pattern on the concrete surfaces. In order to distinguish the effects of chemical sorption from that of variable surface area, the effective surface area was used to derive reactive- surface-related distribution coefficients instead of the geometric- surface-related distribution coefficients.
Standardized Test Methods for Use in Waste Compliance Testing in the Department of Energy'S Waste Acceptance Process
Authors: Mellinger George B.
Published: June 2019

Standardized test methods that are currently in use or under development appear to adequately cover most of the testing that may be required to demonstrate compliance with the WAPS. It may be important to complete standardization of those tests that are under development, and to develop additional standardized tests for those specifications for which no standardized tests exist. A significant amount of work would be involved in this effort. Therefore, before this effort is undertaken, DOE must decide whether there is a need for a set of standardized test methods that would receive an “official approval” for use in waste compliance testing. If a set of approved tests is needed, DOE would need to determine what types of tests to include in the “approved list”, who should develop these tests, and which organizations should review and approve the test methods. Test method review and approval might be accomplished through the use of the Materials Review Board (MRB), an organization that was created by DOE for the purpose of reviewing and approving key test methods and data related to the repository licensing process. Alternatively, other means of standardizing these tests might be considered, such as processing the tests through the American Society for Testing and Materials for publication as ASTM standards.

If a set of approved tests is adopted, producers would not be required to use these tests; however, if a producer wished to propose other tests for compliance testing, it would be reasonable to require that such test procedures undergo a review/approval process similar to that which the officially approved tests had undergone. Once approved, these alternate procedures could be used for compliance testing.
Hydrogen Speciation in Hydrated Layers on Nuclear Waste Glass
Authors: Aines Roger D. , Weed Homer C. , Bates John K.
Published: June 2019

The hydration of an outer layer on nuclear waste glasses is known to occur during leaching, but the actual speciation of hydrogen (as water or hydroxyl groups) in these layers has not been determined. As part of the Nevada Nuclear Waste Storage Investigations Project, we have used infrared spectroscopy to determine hydrogen speciations in three nuclear waste glass compositions (SRL-131 & 165, and PNL 76-68), which were leached at 90°C (all glasses) or hydrated in a vapor-saturated atmosphere at 202°C (SRL-131 only). Hydroxyl groups were found in the surface layers of all the glasses. In addition, molecular water was found in the surface of SRL-131 and PNL 76-68 glasses that had been leached for several months in deionized water, and in the vapor-hydrated sample. The water/hydroxyl ratio increases with increasing reaction time; molecular water makes up most of the hydrogen in the thick reaction layers on vapor-phase hydrated glass while only hydroxyl occurs in the least reacted samples. Using the known molar absorptivities of water and hydroxyl in silica-rich glass the vapor-phase layer contained 4.8 moles/liter of molecular water, and 0.6 moles water in the form hydroxyl. A 15 micrometer layer on SRL-131 glass formed by leaching at 90°C contained a total of 4.9 moles/liter of water, 2/3 of which was as hydroxyl. The unreacted bulk glass contains about 0.018 moles/liter water, all as hydroxyl.

The amount of hydrogen added to the SRL-131 glass was about 70% of the original Na + Li content, not the 300% that would result from alkali-hydronium ion (H30+) interdiffusion. If all the hydrogen is then assumed to be added as the result of alkali-H+ interdiffusion, the molecular water observed may have formed from condensation of the original hydroxyl groups according to:

20H = H20 molecular + 00

where 00 refers to a bridging oxygen, and OH refers to a hydroxyl group attached to a silicate polymer. The hydrated layer on the nuclear waste glasses appears to be of relatively low water content (4 to 7% by weight) and is not substantially hydroxylated. Thus, these layers do not have many of the properties associated with “gel” layers.
Natural Annealing of Alpha-Recoil Damage in Metamict Minerals of the Thorite Group
Authors: Eyal Y. , Lumpkin G. R. , Ewing R. C.
Published: June 2019

Minerals of the thorite (ThSiO4) mineral group have been leached as fine powders in bicarbonate-carbonate solutions for time periods up to 288 days.The radioactivities of the solutions were measured for 238U, 234U, 232Th, 230Th and 228Th by alpha spectrometry, preceded by chemical separation and purification of U and Th. The results confirm the preservation of disordered regions of higher chemical reactivity in an already fully-damaged aperiodic structure. The damage is most evident for the short-lived nuclide 228Th and to a much lesser extent for the long-lived nuclide 234U because the alpha-recoil tracks anneal with time. The calculated mean life of an alpha-recoil track in these metamict thorium silicates is approximately 1,500 to 6,000 years. This study demonstrates that alpha-decay products are selectively leached from damaged, aperiodic materials, but the damage is subject to low-temperature annealing over relatively short periods of time.
Environmental Effects on Crack Characteristics for OSG Materials
Authors: Jacques Jeannette M. , Tsui Ting Y. , McKerrow Andrew J. , Kraft Robert
Published: June 2019

To improve capacitance delay performance of the advanced back-end-of-line (BEOL) structures, low dielectric constant organosilicate glass (OSG) has emerged as the predominant choice for intermetal insulator. The material has a characteristic tensile residual stress and low fracture toughness. A potential failure mechanism for this class of low-k dielectric films is catastrophic fracture due to channel cracking. During fabrication, channel cracks can also form in a time-dependent manner due to exposure to a particular environmental condition, commonly known as stress-corrosion cracking. Within this work, the environmental impacts of pressure, ambient, temperature, solution pH, and solvents upon the channel cracking of OSG thin films are characterized. Storage under high vacuum conditions and exposure to flowing dry nitrogen gas can significantly lower crack propagation rates. Cracking rates experience little fluctuation as a function of solution pH; however, exposure to aqueous solutions can increase the growth rate by three orders of magnitude.
Failure Analysis of Thermally Shocked NiCr Films on Mn-Ni-Co Spinel Oxide Substrates
Authors: Jeon Min-Seok , Song Jun-Kwang , Lee Eui-Jong , Kim Yong-Nam , Shin Hyun-Gyu , Lee Hee-Soo
Published: June 2019

NiCr films were thermally evaporated on the Mn-Ni-Co-O thick-film substrates. The NiCr/Mn-Ni-Co-O bi-layer systems were tested in a thermal shock chamber with three temperature differences of 150, 175 and 200°C. The systems were considered to have failed when the sheet resistance of NiCr films changed by 30% relative to an initial value. As the cyclic repetition of thermal shock increased, the sheet resistance of NiCr coatings increased. The Coffin-Manson equation was applied to the failure mechanism of cracking of NiCr coatings and the SEM observation of cracks and delamination in NiCr coatings due to thermal cycling agreed well with the failure mechanism.
Nonlinear Transient Finite Element Analysis of the Relaxation Mechanisms in Strained Silicon Grown on SiGe Virtual Substrate
Authors: Karoui F. Sahtout , Karoui A. , Rozgonyi G.
Published: June 2019

Strained-silicon (ε -Si) is essential for future nanoscale MOSFET devices. In this paper we report on the dynamics of strain relaxation in Si/SiGe heterostructures, investigated by transient nonlinear finite element analysis. The contribution to total misfit strain is found largely plastic in the graded SiGe layer and the top of the Si substrate, while it is mainly elastic in the strained Si layer and part of the SiGe constant layer. The calculated lattice parameter for the strained Si layer is about 5.47Å for Si0.8Ge0.2 and 5.52 Å for Si0.6Ge0.4. Calculated threading dislocation density was about 5.6x105 cm-2 for x=0.20 and 2.17x106cm-2 for x=0.40. A plastic strain rate of 8.4x10-3s-1 for Si0.8Ge0.2 and 4.1x10-2 s-1 for Si0.6Ge0.4 leading to a density of moving dislocations of ~2.2x109 cm-2 and ~ 1010cm-2, respectively, have been obtained. The elastic strain in the strained-Si layer appeared to increase with increasing the cooling rate, while plastic work was found to be independent of cooling rates.
A Model for Curvature in Film-Substrate System
Authors: Vanamu G. , Khraishi T. A. , Datye A. K.
Published: June 2019

Growth of lattice mismatched films creates bending in the whole structure. There has been great interest in the study of these curvatures in epitaxially-grown materials. An analytical solution for the radius of curvature produced by stresses developed in growing lattice mismatched materials has been obtained. The analyses were based on beam bending theory and strain partitioning theory introduced by our group earlier. The expressions for radius of curvature were obtained for a two-layer heterostructure. The variation of the radius of curvature with the relative thicknesses, relative lattice constants, and relative elastic constants of the layers was determined. The model was verified by applying it to a symmetric tri-laminate structure. The above model can also be extended to determine the curvature for multi-layered heterostructures.
A microtensile set up for characterising the mechanical properties of films
Authors: Cyziute B. , Augulis L. , Bonneville J. , Goudeau P. , Lamongie B. , Tamulevicius S. , Templier C.
Published: June 2019

A computer control deformation set-up has been specifically developed for measuring the elastic and plastic properties of thin films. It combines a piezo-actuated microtensile-testing device, based on an original tripod design, with an optical image acquiring and analysis system for measuring specimen strains. The paper will be partly devoted to describe the experimental deformation set up and its performance through mechanical tests of polyimide and aluminum samples. The Young's moduli, which are deduced from the stress-strain curves, are in good agreement with reported bulk average values. The results confirmed the ability of the equipment for the measurements of very small load and displacement levels, which are a prerequisite for such type of investigations.
Symptomatic and Radiographic Manifestations of Kidney Stone Recurrence and Their Prediction by Risk Factors: A Prospective Cohort Study
Authors: D’Costa Matthew R. , Haley William E. , Mara Kristin C. , Enders Felicity T. , Vrtiska Terri J. , Pais Vernon M. , Jacobsen Steven J. , McCollough Cynthia H. , Lieske John C. , Rule Andrew D.
Published: June 2019

Significance Statement

Kidney stone recurrence can manifest with symptoms from stone passage or with asymptomatic changes in kidney stone burden revealed by radiography. In a multicenter, prospective cohort study, the authors demonstrate that substantially more asymptomatic and self-managed symptomatic kidney stone recurrence occur in stone formers than has been appreciated, as many studies consider only symptomatic recurrence that results in clinical care. Among first-time symptomatic stone formers, 54% had an asymptomatic kidney stone; half of those with such a stone passed it within 5 years (but only half who did so experienced symptoms). The findings also show that when a more comprehensive definition of recurrence that includes all symptomatic and radiological manifestations is used, risk factors better predict kidney stone recurrence, thus supporting a comprehensive assessment of recurrence in clinical trials.

Background

Meaningful interpretation of changes in radiographic kidney stone burden requires understanding how radiographic recurrence relates to symptomatic recurrence and how established risk factors predict these different manifestations of recurrence.

Methods

We recruited first-time symptomatic stone formers from the general community in Minnesota and Florida. Baseline and 5-year follow-up study visits included computed tomography scans, surveys, and medical record review. We noted symptomatic recurrence detected by clinical care (through chart review) or self-report, and radiographic recurrence of any new stone, stone growth, or stone passage (comparing baseline and follow-up scans). To assess the prediction of different manifestations of recurrence, we used the Recurrence of Kidney Stone (ROKS) score, which sums multiple baseline risk factors.

Results

Among 175 stone formers, 19% had symptomatic recurrence detected by clinical care and 25% detected by self-report; radiographic recurrence manifested as a new stone in 35%, stone growth in 24%, and stone passage in 27%. Among those with a baseline asymptomatic stone (54%), at 5 years, 51% had radiographic evidence of stone passage (accompanied by symptoms in only 52%). Imaging evidence of a new stone or stone passage more strongly associated with symptomatic recurrence detected by clinical care than by self-report. The ROKS score weakly predicted one manifestation—symptomatic recurrence resulting in clinical care (c-statistic, 0.63; 95% confidence interval, 0.52 to 0.73)—but strongly predicted any manifestation of symptomatic or radiographic recurrence (5-year rate, 67%; c-statistic, 0.79; 95% confidence interval, 0.72 to 0.86).

Conclusions

Recurrence after the first stone episode is both more common and more predictable when all manifestations of recurrence (symptomatic and radiographic) are considered.
Cyclicality and the Severity of the U.S. Supervisory Stress Test: 2014 to 2018
Authors: Berrospide Jose , Cohen Andrew M. , Hou David , Elul Ronel , Malkhozov Aytek , Rodriguez Marc , Sarama Robert
Published: June 2019

In this study, we provide a measure of the severity of the 2014-2018 US supervisory stress tests, and examine how that severity measure has evolved.
Hot water usage profiling to improve geyser efficiency
Authors: Catherine Quinton , Wheeler Jacques , Wilkinson Richardt
Published: June 2019

This paper presents an intelligent hot water cylinder (HWC) (referred to as geyser) usage profiling system to provide peak demand side management and improve HWC efficiency in a typical household. The study highlights current control topologies used to improve geyser efficiency, as well as the design of the final geyser controller. The system consists of a PIC microcontroller used to determine individually based hot water usage profiles of the user. The controller then regulates the temperature of the geyser according to the demand profile developed. From the results it is apparent that by controlling the geyser temperature and thereby heat loss, savings can be made.
Exergy analysis of a flat plate solar collector
Authors: Chamoli Sunil
Published: June 2019

In this study, exergetic performance analysis of flat plate solar collector has been carried out analytically. A comprehensive mathematical modelling of thermal performance is simulated using MATLAB simulink and optimal geometrical and thermodynamic parameters are predicted pertaining to optimum performance of the system. The optimization procedure was applied to a typical collector and the optimum design points were extracted. The optimum values of collector inlet temperature, mass flow rate, absorber plate area, and fluid outlet temperature for maximum exergy inflow from the system have been obtained.
Experimental study on natural convection greenhouse drying of papad
Authors: Kumar Mahesh
Published: June 2019

In this paper, the convective heat transfer coefficients of papad for greenhouse drying under a natural convection mode are reported. Various experiments were conducted during the month of April 2010 at Guru Jambheshwar University of Science and Technology Hisar, India (29o5’5” N 75o45’55” E). Experimental data obtained for the natural convection greenhouse drying of papad was used to evaluate the constants in the Nusselt number expression by using simple linear regression analysis. These values of the constant were used further to determine the values of the convective heat transfer coefficient. The average value of a convective heat transfer coefficient was determined as 1.23 W/m2 oC. The experimental error in terms of percent uncertainty was also evaluated.