bluuebunny/crossref_metadata_2025 huggingface dataset:
Microscopic Characterization of Polycrystalline APCVD CdTe Thin Film PV Devices
Authors: Ohno Tim R. , Sutter Eli , Kestner James M. , Gilmore A.S. , Kaydanov Victor , Wolden Colin A. , Meyers Peter V. , Woods Lawrence , Romero Manuel J. , Al-Jassim M.M. , Johnston Steve
Published: April 2011

Atmospheric pressure chemical vapor deposition (APCVD) is being studied as an alternative for large-area manufacturing of CdTe thin films. High efficiency research cells have been constructed, but the fundamental materials properties and limitations have not been fully explored. APCVD material is examined with several techniques and compared with close-space sublimation (CSS). Transmission and scanning electron microscopy studies show a similar morphology to CSS CdTe. However high resolution TEM scans show the formation of a disordered layer between the CdTe and CdS, and the removal of defects within some grain structures upon annealing. Cathodoluminescence shows electronic defect states localized to grain boundaries. A large concentration of trap states was also observed with deep-level transient spectroscopy that may correspond to hole traps found in lower amounts in other materials. The presence of traps was also indicated in impedance spectroscopy measurements. The latter studies indicate a high grain boundary resistance contributes to transport.
Electronic Properties of Chemically Etched CdTe Thin Films: Role of Te for Back-Contact Formation
Authors: Kraft D. , Thiβen A. , Campo M. , Beerbom M. , Mayer T. , Klein A. , Jaegermann W.
Published: April 2011

Improvement of electric back contact formation is one of the major issues of the CdTe thin film solar cell research. Chemical etching of CdTe before metallization is accepted to improve contact formation. It is believed that a CdTe/Te contact is formed by this procedure leading to a Fermi level position in the CdTe close to the valence band maximum for low contact resistance. We have studied the electronic properties of chemically etched CdTe surfaces with photoelectron spectroscopy. Etching of the samples was performed in air (“ex-situ“) as well as in an electrochemical setup directly attached to the UHV system (“in-situ“). The formation of a Te layer is clearly shown by (S)XPS. In contrast to previous studies we could not detect the formation of a p-CdTe surface for different experimental conditions. The detected Fermi level position indicates still band bending and hence a blocking Schottky barrier.
Effect of CdCl2 Treatment Conditions on the Deep Level Density, Carrier Lifetime and Conversion Efficiency of CdTe Thin Film Solar Cells
Authors: Sandhu A. , Kobayashi K. , Okamoto T. , Yamada A. , Konagai M.
Published: April 2011

The effect of CdCl2 annealing conditions of glass/TCO/n/CdS/p-CdTe solar cell structures on the deep level density and carrier lifetime of the p-CdTe layer and correlation with the solar cell conversion efficiency was investigated. CdCl2 treatment was carried out at temperatures ranging from 370 to 460°C for 15 min. A clear correlation between trap density, carrier lifetime, conversion efficiency and the CdCl2 annealing conditions was observed. Un-annealed structures had a conversion efficiency of 5.7%, hole trap energy of EV+0.42eV, hole trap density of 8.71×1014cm−3, and decay lifetime of 0.15μs. The optimum CdCl2 annealing temperature was found to be 415°C for structures grown at a substrate temperature of 595°C, where the conversion efficiency, hole trap energy, hole trap density, decay lifetime were 13.4%, EV+0.44eV, 8.10×1012 cm−3 and 0.40μs, respectively.
The Electrical Characteristics of the MOSCAP Structures with W/WNx/poly Si1−XGeX Gates Stack
Authors: Kang S.-K. , Kim J. J. , Ko D.-H. , Ahn T. H. , Yeo I. S. , Lee T. W. , Lee Y. H.
Published: April 2011

We investigated the electrical characteristics of the MOSCAP structures with W/WNx/poly Si1−xGex gates stack using C-V and I-V. The low frequency C-V measurements demonstrated that the flat band voltage of the W/WNx /poly Si0.4Ge0.6 stack was lower than that of W/ WNx /poly Si0.2Ge0.8 stack by 0.3V, and showed less gate-poly-depletion-effect than that of W/ WNx /poly- Si0.2Ge0.8 gates due to the increase of dopant activation rate with the increase of Ge content in the poly Si1−xGex films. As Ge content in poly Si1−xGex increased, the leakage current level increased a little due to the increase of direct tunneling and QBD became higher due to the lower boron penetration.
The influence of Ti and TiN on the thermal stability of CoSi2.
Authors: Detavernier C. , Ru Guo-Ping , Van Meirhaeghe R.L. , Maex K.
Published: April 2011

In this work, AFM and sheet resistance measurements are used to characterize the thermal stability of thin CoSi2 films. We were particularly interested in the influence of different multilayer structures on the topography and surface roughness. Four different multilayer structures (Co/Si, TiN/Co/Si, Ti/Co/Si and Co/Ti/Si) were investigated. Thermal degradation of CoSi2 formed from a standard Co/Si structure is found to have an activation energy of about 4.2 eV, independent of layer thickness (in agreement with previous results by Alberti et al.). A TiN capping layer is shown to improve the thermal stability. However, if the TiN layer is too thick (e.g. 50 nm), a new failure mode is observed: although the TiN prevents grain boundary grooving of the silicide, the thermal stress induced by the TiN causes the CoSi2 layer to crack. For a Ti capping layer, a strong increase of the thermal stability of the CoSi2 layer is observed, even if the Ti capping layer is removed by a selective etching step after the first RTP annealing. The presence of a very thin Ti-O-N containing layer on the CoSi2surface seems to strongly decrease surface diffusion and in this way reduce the tendency for grain boundary grooving.
Thin-Film-Edge-Induced Stresses in Substrates
Authors: Wong S.P. , Peng H.J. , Zhao Shounan
Published: April 2011

We have obtained an analytic solution of linear elasticity for the stress distribution under a thin film edge in isotropic substrates of finite thickness and of infinite extent in the other two directions. The following boundary conditions are considered. At the film/substrate interface and the free surfaces at the top and bottom of the substrate, the normal stress component vanishes. Far from the film edge on the side without the film, all stress components are zero. Far from the film edge under the film, the stress distribution is in accordance with that given by the bimetallic strip theory. Two examples of comparison between theory and experiments were given to demonstrate the validity of this solution. The infrared photoelastic stress fringe pattern obtained by a dark-field plane polariscope in a Si substrate under an oxide film edge was successfully reproduced. The calculated and experimental results of Raman-shift of Si under patterned CoSi2 line structures also showed good agreement with each other.
Field Emission from Novel Room Temperature Grown Carbon Based Multilayered Cathodes
Authors: Satyanarayana B.S. , Nishimura K. , Hiraki A.
Published: April 2011

Low field electron emission from novel room temperature grown multilayered cold cathodes were studied. The cathodes consisted of a layer of nanocrystalline diamond and a layer of nanocluster carbon films. The nanocrystalline diamond was first coated on to the substrate. The nanocluster carbon films and the tetrahedral amorphous carbon films were then deposited on the nanocrystalline diamond coated substrates using the cathodic arc process at room temperature. The heterostructured microcathodes were observed to exhibit electron emission currents of 1µA/cm2 at fields as low as 1 V/µm. The effect of the nanoseeded diamond size and concentration and the properties of different nanocluster carbon films on emission characteristics is presented.
Trends in Microelectronic Systems Integration: From System on a Chip to System in a Package
Authors: Reuss Robert H. , Chalamala Babu R. , Thomas Simon , Chason Marc , Gamota Daniel , Danvir Janice
Published: April 2011

The continued shift towards the integration of diverse functions into single chips and chip assemblies requires a new vision in microelectronic systems integration. Over the last decade or so, there has been a tremendous push towards systems on chip (SoC) approach for increased functionality. While systems on a chip has received much deserved credit for the size and cost reduction of many products, a true system on a chip solution has not been practical for a number of applications. In some cases, this is simply an issue of chip size, in others material compatibility (Si and GaAs), in yet others electrical compatibility (high voltage, RF, analog, with digital) and in some others the overall cost of integration on silicon, even if technically feasible. The need to combine diverse materials and technologies to achieve increased functionality with decreased size and weight, along with the ever present pressure for lower cost, has created the opportunity for new system level integration opportunities. Among the new concepts, system in a package (SiP) and system on a substrate (SoS) have received the most attention. System in a package is a natural extension of system on a chip concept. Currently, there are aggressive programs to develop SiP capabilities to allow rapid, cost effective design and fabrication of subsystem level packages. System on a substrate is an emerging concept based on the integration of technologies in a wide area of electronics. SoS will take the next step to the full system level (e.g. a monolithic radio). However, there is another important concept that seeks the same objective of system-level integration, but with a different set of drivers. In situations where the product is required to be a certain size (e.g. a display or a smart card), further size reductions of the components is no longer productive. This creates the opportunity for alternative technologies such as thin film transistors and plastic substrates. Integration of these technologies offers the potential for significant cost savings because of lower manufacturing costs, and light weight, wearable, flexible products by elimination of today's rigid substrates. Such technologies not only offer new capabilities, but also change the basic premise of the electronics industry. We could move from the microelectronics to the macroelectronics era. In this paper, we will present an overview of this diverse and emerging technology.
Silicide Formation by Pulsed Excimer Laser Annealing
Authors: Lew Connie , Thompson Michael O.
Published: April 2011

Silicide formation may occur at the interface of metal and a-Si films upon annealing with a pulsed excimer laser (XeCl 308 nm; 30 ns). During laser-induced melting, the melt front reaches the Si/metal interface, where liquid phase kinetics allow reaction to occur to form a silicide, despite the <100 ns time-scale. It is thought that silicide reaction would occur if TM, metal ≍ TM, a-Si (1480 ± 50K). The a-Si/metal film stacks that have been investigated include a-Si/Al/Cr, a-Si/Ti, and a-Si/W on thermally oxidized Si. Samples were laser-annealed at varying energy densities in order to determine the onset of melt, and the fluence at which Si/metal interface reaction and film ablation occurs. Rutherford backscattering (RBS), optical inspection, cross-sectional scanning transmission electron microscopy (STEM), as well as parallel and serial electron energy loss spectroscopy (EELS) were used to analyze the films. For the a-Si/Al/Cr and a-Si/W films, no reaction is observed at the Si/metal interface. With a-Si/Ti, intermixing of Si and Ti at the interface is observed, as indicated by RBS and parallel EELS analysis. Laser annealing at higher fluences and further characterization is needed to determine if this mechanism does allow for silicide reaction to take place.
Low-Temperature Poly-Si TFT by Excimer Laser Annealing
Authors: Nishibe Tohru
Published: April 2011

Poly-Si TFT-LCD has begun its way to an advanced display by integrating the driver circuits onto the glass substrate. Improvement of poly-Si TFT is essential in order to achieve value-added display where circuits for various functions are integrated on one substrate. This report the concept of poly-Si TFT display from present state to future scope, and required technologies for each generation. It will also focus on technologies such as crystallization and gate insulator formation at low temperature process.
Recent Progress in High Power Excimer Laser Development for Producing Next Generation Large-Area Electronic Devices
Authors: Demin A. , Vodchits V. , Eltzov A. , Kristoforov O. , Kirukhin Yu. , Vinokhodov A. , Borisov V. , Osmanov R. , Bragin I. , Vogler K. , Rebhan U. , Rahe M. , Stamm U. , Basting D.
Published: April 2011

This paper reviews the results of the development of high power (up to 1 kW), high energy (up to 10J) prototypes of excimer lasers that are of interest to meet expanding requirements of the electronic industry. Some experimental characteristics are presented for various excimer prototypes operating at the important wavelength of 308nm (XeCl). Keywords: Excimer laser, average power, output energy, annealing
Wafer Bonding of Diamond Films to Silicon for Silicon-on-Insulator Technology
Authors: Yushin Gleb N. , Wolter Scott D. , Kvit Alexander V. , Collazo Ramon , Prater John T. , Stoner Brian R. , Sitar Zlatko
Published: April 2011

Polycrystalline diamond films previously grown on silicon were polished to an RMS roughness of 15 nm and bonded to the silicon in a dedicated ultrahigh vacuum bonding chamber. Successful bonding under a uniaxial mechanical stress of 32 MPa was observed at temperatures as low as 950°C. Scanning acoustic microscopy indicated complete bonding at fusion temperatures above 1150°C. Cross-sectional transmission electron microscopy later revealed a 30 nm thick intermediate amorphous layer consisting of silicon, carbon and oxygen.
C-V and G-V Measurements Showing Single Electron Trapping in Nanocrystalline Silicon Dot Embedded in MOS Memory Structure
Authors: Huang Shaoyun , Banerjee Souri , Oda Shunri
Published: April 2011

We prepared a SiO2/nanocrystalline Si (nc-Si)/SiO2 sandwich structure. A clear positive shift in C-V and G-V curves due to electrons trapped in nc-Si dots has been observed at room temperature. The peak in conductance around flat band condition indicates that a trap event had occurred where an electron is stored per nc-Si dot. A logarithmic charge loss function is found and this discharging process is independent of the thermal activation mechanism. The longer memory retention time and logarithmic charge loss in the dots are explained by a “built-in” electric field through the tunnel oxide, which varies with time, resulting in a variable tunneling probability. The electric repulsion induced by the built-in electric field hinders the discharging of electrons remained in the dots.
Fabrication of 3D Feed Horn Shape MEMS Antenna Array using MRPBI (Mirror Reflected Parallel Beam Illuminator) System with an Ultra-Slow-Rotated and Inclined X-Y-Z Stage
Authors: Park Jong-Yeon , Kim Kun-Tae , Moon Sung , Pak James Jungho
Published: April 2011

A 3D Feed horn shape MEMS antenna has some attractive features for array application, which can be used to improve microbolometer performance. Since MEMS technology have been faced many difficulties to fabrication of 3D feed horn shape MEMS antenna array itself. The purpose of this paper is to propose a new fabrication method to realize a 3D feed horn shape MEMS antenna array using a MRPBI(Mirror Reflected Parallel Beam Illuminator) system with an ultra-slow-rotated and inclined x-y-z stage. A high-aspect-ratio 300 [.proportional]m sidewalls had been fabricated using SU-8 negative photo resist. It can be demonstrated to feasibility of realize 3D feed horn shape MEMS antenna array fabrication. In order to study the effect of this novel technique, the 3D feed horn shape MEMS antenna array had been simulated with HFSS(High Frequency Structure Simulator) tools and then compared with traditional 3D theoretical antenna models. As a result, it seems possible to use a 3D feed horn shape MEMS antenna at the tera hertz band to improve microbolometer performance and optical MEMS device fabrication.
Indentation Delamination and Indentation Fracture in ZnO/Si Systems
Authors: Huang Bin , Zhao Ming-Hao , Zhang Tong-Yi
Published: April 2011

Vickers indentation tests were carried out at room temperature with a microhardness tester on ZnO thin films deposited on (100) Si wafers. The films with thicknesses ranging from 0.202 to 1.535 νm were tested under indentation loads varying from 50 mN to 2.0 N. The experiments exhibited a film thickness dependent deformation behavior. When the film thickness is smaller than a critical value, only indentation-induced radical cracking occurred and for a given load, the radical crack size decreased with film thickness. On the other hand, indentation-induced delamination was observed if the film thickness was larger than the critical value. In this case, the radial crack, if induced, had a size smaller than the size of delamination or even smaller than the size of indentation impression. Under a same indentation load, the delamination size increased with the film thickness.
Tensile Test of Bulk- and Surface-Micromachined 0.1-νm Thick Silicon Film using Electrostatic Force Grip System
Authors: Tsuchiya Toshiyuki , Sakata Jiro , Shikida M. , Sato K.
Published: April 2011

Single-crystal silicon films of sub-micrometer thicknesses were tensile tested using a thin film tensile tester with an electrostatic force grip. The tester has been newly designed for this thin film. It uses a servo-controlled balance for small-force measurement with a resolution of less than 100 νN. The specimens were fabricated using bulk- and surface-micromachining starting with a SIMOX wafer, and an epi-SOI wafer. The bulk micromachined specimens were released from a wafer by anisotropic etching from the backside of the wafer. The specimen size was 0 to 500 νm long, 20 or 50 νm wide and 0.14 νm thick. The thinner specimens were fabricated by surface micromachining and dry release process using XeF2 and vapor HF etching to avoid stiction of the specimens. The size was 0 to 600 νm long, 1 to 20 νm wide and 0.05 νm thick. These wafers were (100) oriented and the loading axis of the specimen was <110>. The tensile strength of the bulk micromachined specimens ranged from 1.4 to 4.8 GPa for twelve samples and that of the surface micromachined specimens ranged from 1.0 to 6.8 GPa for seven samples.
Transport properties of Cr-patterned Yba2Cu3O7 thin films
Authors: Chopdekar Rajesh , Dale Darren , Suzuki Yuri
Published: April 2011

Epitaxial thin films of Yba2Cu3O7 (YBCO) have been deposited and patterned on (100) SrTiO3 and (110) NdGaO3 substrates. Wet etchants used in conventional photolithography react too quickly with YBCO thin films, resulting in undercutting of patterned structures. We have implemented a technique to pattern thin lines from films without wet or dry etching. Chromium is evaporated onto the substrates and subsequently patterned. YBCO is then deposited by pulsed laser deposition, which results in an epitaxial YBCO film on patterned areas and randomly oriented YBCO deposited on chromium. An annealing step is required for the chromium to diffuse through the undesired YBCO in order to render those sections insulating. YBCO lines patterned with this technique exhibit resistivity and critical temperatures similar to those of the unpatterned films. As we decrease the width of the YBCO lines, the effect of the edges, where there is chromium-reacted material, on transport becomes more pronounced. The resolution of the patterning technique and the profile of superconducting versus non-superconducting materials at the edges is presented.
Effects of Cation Substitution on the Thermoelectric Properties in Ca-Co-O
Authors: Matsubara Ichiro , Funahashi Ryoji , Shikano Masahiro , Sasaki Kei , Enomoto Hiroyuki
Published: April 2011

We have prepared (Ca1−x−yMxBiy)3Co4Oz (M = Mg, Sr, and Ba) thin films by a combinatorial approach using a solution process. In the systems of (Ca1−x−yMxBiy)3Co4Oz (M = Mg, Sr, and Ba), solid solution range was determined to be × < 0.8 (M = Sr, y = 0), x < 1.0 (M = Mg, y = 0), x = 0.0 (M = Ba, y = 0), and x < 0.4 (M = Bi, x = 0). No solid solution range was obtained for the substitution of Ba for Ca site. The in-plane compressive stress in the CoO2 sublattice is controllable by the cation substitution for Ca in the (Ca2CoO3) sublattice. With increasing in-plane stress, the magnitude of thermoelectric power and resistivity increased.
Thermal and Electrical Properties of Czochralski Grown GeSi Single Crystals
Authors: Yonenaga Ichiro , Akashi Takaya , Goto Takashi
Published: April 2011

Single crystals of Ge1−xSix alloys in the composition range 0 < x < 1 non-doped and doped with boron, gallium, and phosphorus as an impurity were grown by the Czochralski method. The measurements of the thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (α) of the grown crystals were performed in the temperature range 300 – 1000 K. The thermal conductivityκ shows a minimum (κ ∼ 3.5 W/K.m) around the Si content x = 0.5 - 0.7, which can be explained by the phonon scattering due to a distortion of the crystal lattice. The Seebeck coefficientα was 300 - 400 μV/K at 600°C in the impurity-doped GeSi alloys. An ∣α∣ vs ln (σ) plot of highly impurity-doped GeSi alloys obeys a linear relation. The slope of the straight line is 1.2 k/e, indicating the coorporation of the charged impurity into the alloy scattering mechanism.
Thermoelectric Properties of Bi-Sb-Te-X Compounds Prepared by MA-PDS Method
Authors: Park Yong-Ho , Xue-Dong Liu
Published: April 2011

A great potential for further improving the room-temperature figure of merit (Z) has been identified by dispersing a small fraction of Ag in the (Bi0.25Sb0.75)2Te3 alloy. The maximum Z of 3.41×10−3K−1, 17% higher than that of the unadded, is attained at 0.02wt% Ag. Addition of BN, either alone or in combination with Ag, however, does not generate a favorable figure of merit.
Different Mechanisms Leading to Superhard Coatings: Stable Nanocomposites and High Biaxial Compressive Stress
Authors: Veprek S. , Karvankova P. , Prochazka J. , Männling H.
Published: April 2011

A strong enhancement of the hardness above 40 GPa in thin coatings can be achieved either by the formation of a suitable nanostructure (heterostructures and nanocomposites) or by a large biaxial compressive stress of ≥ 5 GPa. Superhard and thermally fairly stable nanocomposites, such as nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a-TiSi2, nc-(Ti1-xAlx)N/a-Si3N4 retain their hardness after annealing to 900-1100°C whereas coatings with a high stress, such as HfB2, CrxN/Ni, ZrN/Ni and others soften to ≤ 20 GPa already after their annealing to 400-500°C due to the relaxation of that stress.
A Novel Silicon-Carbon Precursor for Oligomer Chemical Vapor Deposition of Silicon Carbide for Harsh Environmental Applications
Authors: Futschik Ulrike , Efstathiadis Harry , Castracane James , Kaloyeros Alain E. , Macdonald Leo , Hayes Susan , Fountzoulas Costas
Published: April 2011

Silicon carbide (SiC) films have been successfully deposited on various substrates by oligomer thermal chemical vapor deposition (OTCVD) from a novel, halogen free, oligomer precursor family of polysilyenemethylenes (PSMs) called SP-4000. The high quality films were grown at substrate temperatures in the range of 620°C to 850°C and at process pressures in the range of 1 - 200Torr. SP-4000 is a silicon carbide precursor with formula [-SiH2-CH2-]n, n=2-8, composed of an alternating silicon and carbon backbone with hydrogen side groups. Depositions on Si and graphite substrates yielded SiC films with Si/C ratios in the range 1.1 to 1.2 and thicknesses in the range 0.3 to 50μm.

Structural and chemical characterizations were performed by Auger electron spectroscopy (AES), x-ray diffraction (XRD), nuclear reaction analysis (NRA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

The SiC coatings deposited at substrate temperatures below 1100°C were found to be amorphous. Ex-situ, post deposition annealing in inert gas ambient above 1100°C converted the SiC films to a polycrystalline phase.
Characterization of High Alumina Refractory Ceramics Treated with Combined Two Laser Surface Processing
Authors: Bernstein Johanna R. , Triantafyllidis Dimitris , Li Lin , Stott F. Howard
Published: April 2011

Alumina-based refractory materials are extensively used in high-temperature industrial applications, such as for linings in waste and other incinerators. The existence of porosity and material inhomogeneities can promote chemical degradation due to molten slag penetration, while impacting solid or liquid feedstock can cause erosive-wear damage. Previous research has successfully used single laser energy sources to alter the surface properties of similar ceramics, with emphasis on sealing porosity and enhancing degradation resistance. However, this process has resulted in some solidification cracking at the surface due to large temperature gradients developed during processing. In the present, ongoing work, the surface of the refractory ceramic is modified by combining two laser energy sources to control the thermal gradients and cooling rates, with the objective of eliminating crack formation. The surface morphology and microstructures of the laser-treated areas are analyzed. This paper presents some initial results from the programme.
Fabrication and Nanostructured Surface Layers of Al Alloy by Surface Vibrational Mechanical Attrition
Authors: Wu X. , Hong Y. , Lu J. , Lu K.
Published: April 2011

Nanograins were introduced into the surface layers of an Al-alloy during surface vibrational mechanical attrition. Transmission electron microscopy revealed that microstructures developed with an increase in strain, in the following sequence, i.e., lamellar microbands of elongated subgrains, equiaxed submicro-, and nano-grains respectively. The grain subdivision into the subgrains was found to be the main mechanism responsible for grain refinement. The simultaneous evolution of high boundary misorientations was ascribed to the boundary rotation for accommodating further strains. Results showed that the grains could refine remarkably into the nanometer regime (<100 nm) within the outer surface of the layer. The depth of the nanocrystal layers increased and the grain size decreased with the extension of processing time. The nanocrystal layers evidenced an increase in hardness.
Effect of Pre-Oxidation on The Oxidation Behavior of Ti-2Al-2.5Zr Alloy at 300°C in An Alkaline Steam
Authors: Zu X. T. , Li Y. L. , Zeng G.T. , Huang X. Q. , Wang Z.G. , Lin L. B. , Feng X. D.
Published: April 2011

The long-term oxidation behavior on a Ti-2Al-2.5Zr alloy with and without pre-oxidation oxidized at 300 in an alkaline steam for about 13000h were studied. Some of the samples were subjected to 400°C deionized water steam at a pressure of 10MPa for 72 hours for pre-oxidation. A comparison study has been carried out between the pre-oxidized and without pre-oxidized Ti-2Al-2.5Zr to determine the influence of pre-oxidation upon the properties of oxidation resistance. The result analysis showed that the oxide scales on the Ti-2Al-2.5Zr alloy consisted of Al2TiO5, TiO2, Ti3O5, Ti2O3, Al2O3 and TiO. The oxidation kinetics showed that the weight gains of the pre-oxidized samples were much less than that of the without pre-oxidized samples. The AES results showed that the whole thickness of the pre-oxidized sample thinner than that of the without pre-oxidized one, in contrast the pattern for the stable oxide scale was reversed, i.e. the pre-oxidized sample was much thicker. It is thought that pre-oxidation is an effective method to enhance the oxidation resistance of Ti-2Al-2.5Zr.
Synthesis and Photovoltaic Characterization of Fullerene – Oligo(phenylene ethynylene) Hybrids
Authors: Tsamouras Dimitris , Nierengarten Jean-François , Gu Tao , Krasnikov Victor , Hadziioannou Georges
Published: April 2011

Asymmetrically substituted oligo(phenylene ethynylene) (OPE) derivatives have been prepared by a new iterative method and attached to C60 molecules by a 1,3-dipolar cycloaddition of the azomethine ylides generated in situ from the corresponding aldehydes and sarcosine. The molecules obtained are suitable for the fabrication of photovoltaic devices based on interpenetrating networks of donors and acceptors, with a characteristic length scale of the network topology smaller than the exciton diffusion length. We have constructed a number of photovoltaic cells incorporating the C60-OPEs as the active material between two energetically asymmetric electrode contacts. The device performance has been examined and the functional characteristics have been determined too. These seem to depend systematically on the nature of the attached end-group and on the length of the donating moiety.
Increasing the Carrier Mobility in P3HT by Doping for use in Schottky Barrier TFTs
Authors: Lloyd G. C. R. , Sedghi N. , Raja M. , Lucrezia R. Di , Higgins S. , Eccleston W.
Published: April 2011

Measurements and theory are presented examining the relationship between mobility and doping in regioregular poly(3-hexylthiophene) (P3HT). Mobility is found to increase super-linearly with doping and is comparable to models reported for other conjugated polymers. Schottky measurements have been used to calculate the doping density and bulk mobility of regioregular P3HT. Aluminium Schottky contacts showed signs of native oxide disrupting current flow through the device. This effect was observed to degrade further with the introduction of dopant into the polymer. Titanium devices show a general shift of the Schottky characteristic to higher current levels with increased dopant. Field effect mobility of P3HT films was also calculated using thin-film transistor (TFT) structures. The field effect mobility values were observed to be more than two orders of magnitude higher than the bulk mobility value. The addition of dopant also increased gate leakage currents in TFT devices. The increased conductivity in doped polymer can increase off currents in the device; this is avoided by using Schottky contacts as the source and drain. Preliminary results on Schottky contact TFTs are also presented as well as a description of the operation of such a device.
Ab Initio Study of Vibrational Anharmonic Coupling Effects in Oligo(para-phenylenes)
Authors: Heimel G. , Somitsch D. , Knoll P. , Zojer E.
Published: April 2011

In this study we present a theoretical approach to simulate vibrational anharmonic coupling effects seen in the Raman spectra of oligo(para-phenylenes). Quantum chemical ab inito methods are applied to determine anharmonic force constants and energy corrections on the harmonic vibrational frequencies of the isolated molecules. Semiempirical methods are applied to compute Raman intensities of fundamentals and combination bands. This methodology is then used to characterize a previously unassigned Fermi resonance around 1600 cm-1. The evolution of this quantum mechanical resonance with oligomer length and planarity is compared to experimental data.
Effects of Surface Morphology of ITO Thin Film on the Instability of Organic Light Emitting Diodes
Authors: Kim Ki-Beom , Tak Yoon-Heung , Park Hyoung-Guen , Lee Kwang-Ho , Lee Jong-Ram
Published: April 2011

Surface roughness of ITO (Indium Tin Oxide) was measured by AFM (Atomic Force Microscope) and the existence of spikes was verified. Then OLED (Organic Light Emitting Diode) devices made from those substrates were fabricated and their electrical properties were measured with an I-V measurement system. There is considerable difference in the reverse leakage current of OLEDs depending on the surface roughness of the substrate. We observed a good correlation of reverse leakage current with Rpv (Peak-to-Valley roughness), but the correlations between reverse leakage current and Ra (Average roughness) and Rrms (Root-Mean-Square roughness) are not as good.
Evaluation of The Long-Term Stability of Passive Corrosion On The Drip Shield and Waste Package Under Yucca Mountain Conditions
Authors: Shoesmith D.W.
Published: April 2011

Possible long term corrosion scenarios for the engineered barriers proposed for the Yucca Mountain (Nevada, USA) repository are reviewed.

Introduction:

The materials proposed for the engineered barriers in the Yucca Mountain repository (Nevada, USA), Alloy-22 for the waste packages (WP) and titanium Grade-7 (Ti-7) for the drip shield (DS), appear unlikely to suffer localized corrosion (LC) and have very low passive corrosion (PC) rates (1–3). Since environmental conditions will become more benign as temperatures decline and aqueous environments become more dilute (4), this leads to the prediction of exceedingly long waste package lifetimes. In this review, possible corrosion scenarios are discussed in the context of the anticipated evolution in the repository environment.
Solubility Evaluation for Yucca Mountain TSPA-SR
Authors: Chen Y. , Loch A.R. , Wolery T.J. , Steinborn T.L. , Brady P.V. , Stockman C.T.
Published: April 2011

A systematic evaluation of radionuclide solubility has been conducted for the Yucca Mountain Project. The conventional thermodynamic approach was employed and geochemical model calculations were used to estimate radionuclide solubilities for the base case. The study uses the computer code EQ3/6 as the major geochemical modeling tool. The water composition and environmental conditions are based on the results of in-package chemistry and in-drift chemistry studies. Field observations, laboratory measurements, and thermodynamic and kinetic considerations are utilized to ensure the resulting solubilities are conservative. Fourteen radioelements have been studied (U, Np, Pu, Th, Am, Ac, Tc, I, C, Cs, Sr, Ra, Pa, and Pb) and their solubilities are presented as either functions of environmental conditions or statistical distributions. An alternative source term model for Np, which was based on measurements of spent fuel dissolution experiments rather than conventional thermodynamic considerations, was also developed. Comparison of it with the Np base case solubility model suggests that it is necessary to advance our understanding about the behaviors of Np during the process of spent fuel corrosion.
Structural Alterations in Titanate Pyrochlores Induced by Ion Irradiation: Xray Photoelectron Spectrum Interpretation
Authors: Chen J. , Lian J. , Wang L. M. , Ewing R. C. , Farmer J. Matt , Boatner L. A.
Published: April 2011

Titanate pyrochlores are candidate host materials for the disposition of plutonium from dismantled nuclear weapons. These pyrochlores also have potential applications as solid electrolytes and oxygen gas sensors. The radiation-induced microstructural evolution of titanate pyrochlores has been characterized using x-ray photoelectron spectroscopy (XPS). XPS analysis of the Ti 2p and O 1s binding energy shifts of REE2Ti2O7 (REE: rare earth) surface layers before and after irradiation shows that the primary manifestations of amorphization are distortions or changes in the coordination number of the titanium polyhedra. A model based on glass network structure was developed, and predictions of the relative susceptibilities for amorphization of the titanate pyrochlores are obtained that are consistent with the experimental results.
Heavy Ion Irradiation of Zirconate Pyrochlores
Authors: Lian J. , Wang L. M. , Chen J. , Ewing R. C. , Kutty K. V. G.
Published: April 2011

Zirconate pyrochlores, A2Zr2O7, are important potential nuclear waste forms for Puimmobilization. The binary Gd2(Ti2-xZrx)O7 has been shown to have increasing resistance to ionirradiation damage with the increasing Zr content, and Gd2Zr2O7 is radiation resistant to a 1 MeV Kr+ ion irradiation at 25 K to a dose of 5 dpa. In this study, a 1.5 MeV Xe+ irradiation was completed for zirconate pyrochlores A2Zr2O7 (A=La, Nd, Sm, Gd). The radiation resistance decreases with an increase of the ionic radius of A-site cation. La2Zr2O7 is the first zirconate pyrochlore to be amorphized by ion beam irradiation, and the critical amorphization temperature, Tc, is ∼310 K. The susceptibility of La2Zr2O7 to ion beam damage is related to its structure, which shows the largest deviation from the ideal fluorite structure. These results are also consistent with calculations of the cation antisite formation energy in the pyrochlore structure. The ion irradiation-induced pyrochlore-to-fluorite transformation occurred in all of the irradiated zirconate pyrochlore phases. Based on the results for Gd2Ti2-xZrxO7 and A2Zr2O7, the defect fluorite structures are stable when the ionic radii ratio rA/rB≤1.54; beyond this limit, the defect fluorite structure becomes increasingly unstable relative to the amorphous state.
Porous Crystalline Silica (Gubka) as a Inorganic Support Matrix for Novel Sorbents
Authors: Tranter T. J. , Aloy A. S. , Sapozhnikova N. V. , Knecht D. A. , Todd T. A.
Published: April 2011

Inorganic ion exchange media typically exist as fine powders, making large-scale use impractical, unless the media can be affixed to an appropriate matrix. Likewise, organic chelating agents are typically dissolved in a solvent and absorbed into porous matrices for use in extraction chromatography. The most common matrices utilized in both cases are organic materials, that are not compatible with high radiation fields or acceptable as final waste forms. Recent investigations have shown that ion exchange sorbents can be effectively loaded within a porous crystalline silica (Gubka) matrix. This approach allows for target radionuclides to be adsorbed into a porous micro-crystalline glass matrix which encapsulates the contaminant and becomes the final waste form. Subsequent to adsorption of the radionuclides, the Gubka matrix can be compressed in a hot uniaxial press, resulting in an even greater volume reduction. The porous glass matrix is produced in Russia using fly ash residue from coal combustion power generating plants. It consists of consolidated arrays of hollow glass cenospheres and is termed Gubka which is the Russian word for sponge. This paper describes results of a collaborative research program between the Khlopin Radium Institute, St.Petersburg, Russia, the Institute of Chemistry and Chemical Technologies, Krasnoyarsk, Russia, the Mining and Chemical Combine, Zheleznogorsk, Russia, and the Idaho National Engineering and Environmental Laboratory. Ammonium molybdophosphate (AMP) for the removal of cesium from acidic liquid waste has been successfully incorporated into Gubka matrices. Test results for cesium removal, using AMP-Gubka, are discussed.
Chemical Interactions of UOP IONSIV IE-911 (CST) with SRS Waste Simulants
Authors: Nyman May , Krumhansl James L. , Jove-Colon Carlos , Zhang Pengchu , Nenoff Tina M. , Headley Thomas J. , Su Yali , Li Liyu
Published: April 2011

IE-911 is a bound form of cystalline silicotitanate (CST) that was extensively tested for removing 137Cs from the Savannah River Site (SRS) tank wastes. In some simulant tests, column plugging incidents were observed, which led to thorough investigations to determine the causes and to develop protocols to avoid future plugging incidents. A related problem was the apparent decrease in Cs scavenging capability in some long-term tests. Our studies revealed that the interaction of IE-911 with the highly basic, high ionic strength, SRS average salt simulant could result in precipitation of; 1) poorly crystalline Nb-oxide, or 2) aluminosilicate zeolitic phases. The source for the Nb-oxide precipitate was determined to be a minor impurity phase that is a byproduct of CST manufacturing. The mechanisms of dissolution and re-precipitation of this phase in column pretreatment solution were investigated, and a protocol to rid IE-911 of this impurity was devised. The source material for the aluminosilicate zeolite precipitate was determined to be predominantly from the waste solution rather than the IE-911. Solubility experiments coupled with a thermodynamic analysis provided a protocol to predict when aluminosilicate precipitation will and will not occur. Finally, it was also established that aluminosilicate precipitation on the surfaces of the IE-911 granules could also account for an apparent decrease in equilibrium Kd and decrease in kinetics of Cs sorption.
Assessment of the Evolution with Time of the Instant Release Fraction of Spent Nuclear Fuel in Geological Disposal Conditions
Authors: Poinssot Christophe , Lovera Patrick , Faure Marie-Hélène
Published: April 2011

Under the geological disposal conditions, spent nuclear fuel (SNF) is expected to evolve during the first thousands years while being maintained isolated from the biosphere before water comes in. Under those circumstances, several driving forces would lead to the progressive intrinsic SNF transformations within the rod which would basically modify the physical and chemical state of the fuel and the subsequent release of radionuclides in solution. In this paper, we briefly summarize the mechanisms we estimate to be significant and propose a new framework for the quantitative assessment of the radionuclide (RN) inventory we estimate to be associated to the classically referred to “Instant Release Fraction” (IRF). We hence demonstrate that in this framework, significantly high IRF values have to be expected for the long term due mainly to the presence of athermal diffusion processes.
Alteration of a Zirconolite Glass-Ceramic Matrix under Hydrothermal Conditions
Authors: Martin Christelle , Ribet Isabelle , Advocat Thierry
Published: April 2011

Glass-ceramic matrices based on zirconolite (CaZrTi2O7) are being considered for specific conditioning of plutonium or the minor actinides. The actinides are distributed throughout the zirconolite crystals and the residual glass phase. Since zirconolite alteration is extremely limited, however, actinide release from the glass-ceramic material is mainly attributable to alteration of the residual glass. Zirconolite glass-ceramic specimens and specimens corresponding to the residual glass phase alone were therefore altered under hydrothermal conditions (150°C) and under initial rate conditions (100°C) to compare their kinetic behavior and estimate the effect of the crystals on material alteration. Under hydrothermal conditions, alteration occurred during the first few days: SEM observations showed greater alteration of the glass-ceramic material due to a phenomenon of preferential glass alteration around the zirconolite crystals; after three days the alteration rate had considerably diminished and both specimens exhibited similar behavior. Under initial rate conditions the initial rates differed due to a variation in the reactive surface area of the glass-ceramic.
Low-Temperature Mobility of Rare Earth Elements (REE), U, and Th at the Olkiluoto Site, SW Finland
Authors: Marcos Nuria
Published: April 2011

This work is a first effort to link hydrogeological measurements to structural modeling by using the mobility of rare earth element (REE), U, and Th at the Olkiluoto site. REE, U and Th concentrations were measured in 5 groundwater samples located at depths varying between 132 and 446 m in three drill holes at the Olkiluoto site. The pH of groundwater samples are all about 8 and Eh(Pt) varies from –50 to –200 mV. Also the REE, U and Th concentrations of rock samples collected from core sections in the vicinity of water conducting fractures were measured to examine rock-water interactions in the system. The rock samples were cut into slices parallel to the fracture surface. An aliquot of each slice was leached with 0.5 N acid nitric to examine the readily leachable REE, U and Th fraction of each slice. The groundwater samples were normalized to each of the analyzed rock samples. Although the REE concentrations of the water samples are overall depleted in all the REEs compared to the rocks and leachates, and whole REE spectra could not be obtained for any of the groundwater samples, enrichment in the intermediate REE (IREE) with respect to the light REE (LREE) is observed.

An increasing loss of REE and U from rock matrix towards fracture surface is observed in samples at depths of 141, 159, and 466 m. Loss of U is also observed in a sample at about 246 m depth. Loss of Th is only observed at the depths of 159 and 246 m. The loss of U (readily leachable fraction) in the rock samples was found to be linked to the hydraulic conductivity in the related water-conducting fractures.
Natural Colloids in Groundwater from a Bentonite Mine- Correlation between Colloid Generation and Groundwater Chemistry -
Authors: Kuno Yoshio , Kamei Gento , Ohtani Hiroyuki
Published: April 2011

Colloids, mainly montmorillonite, generated by erosion of compacted bentonite by groundwater flow might enhance the transport of radionuclides from a radioactive waste repository. The influence of aqueous chemistry (i.e. pH, cation concentration and valence) on the dispersion of montmorillonite colloid was studied. Colloids were flocculated under higher cation concentrations ([Na+] > 10−2 M, [Ca2+] > 10−3 M) and/or under acidic condition (pH = 4) by means of batch-type experiments. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to estimate the stability of colloidal dispersion and then the limitation of theoretical calculations was pointed out. Groundwater samples were collected from two galleries at different depths of the Tsukinuno bentonite mine (northern Honshu, Japan) and investigated for the populations of colloids. The groundwater flows vertically through Tertiary sedimentary argillaceous rocks and fine tuff beds which are mined for bentonite. Low colloid concentrations were measured in these groundwater samples. This result suggests that the colloids cannot significantly disperse in the groundwaters under higher cation concentration ([Na+] > 10−2 M) or under acidic conditions. This result is consistent with those of the batch-type experiments.
DNA Templating of Ethylene-Oxide-Coated Nanoclusters
Authors: Jhaveri S. , Foos E. E. , Ancona M. G. , Snow A. W. , Twigg M. E. , Chang E. , Pilobello K. , Goldman E. , Lowy D.
Published: April 2011

Using gel electrophoresis we demonstrate the attachment of short ssDNAs to a new type of water-soluble gold nanocluster that is encapsulated with ethylene oxide ligands. Initial experiments indicate that these DNA/nanocluster conjugates can subsequently be hybridized to a longer DNA template suggesting a pathway for nanofabrication of multi-cluster assemblies.
Fabrication and Application of Protein Crystal Microarrays
Authors: Hosokawa Yoichiroh , Matsumura Satoshi , Yoshikawa Hiroshi Y. , Masuhara Hiroshi , Nakamura Ryosuke , Kanematsu Yasuo , Ikeda Keiko , Shimo-oka Ai , Mori Hajime
Published: April 2011

With the aim of fabricating highly integrated protein microarrays, functional proteins were occluded into a protein crystal, consisting of a proteinaceous occlusion body termed polyhedrin, and the crystals were individually fixed onto a polymer film by using laser trapping and bonding techniques. Individual crystals were trapped by the 1064 nm beam of a Nd3+:YAG laser and placed to the film. The bonding to the film was achieved by irradiating with the single shot of the 800 nm beam of a femtosecond Ti:sapphire laser. Enhanced green fluorescent protein (EGFP) was occluded into the polyhedrin crystal and the crystals were patterned and observed by florescence imaging and single crystal florescence spectroscopy. From these experiments, the biological activity of the bonded crystal was confirmed and their potential as element in protein microarrays was discussed.