bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epitaxial Iridium Growth on Strontium Titanate
Authors: Dai Z. , Li A.P. , Bednarski C. , McCann L. I. , Golding B. 
Published: April 2011

AbstractEpitaxial (100) iridium films have been grown on (100) SrTiO3 (STO) substrates by electron beam evaporation. The epitaxial relationship between the iridium film and STO substrate was determined to be Ir(001)[100]//STO(001)[100]. A systematic study of the role of STO substrate surface preparation, Ir thickness, and substrate temperature on Ir film crystallinity and morpholo- gy has been performed. The best Ir films typically have small Ir(200) XRD linewidths < 0.3 °, surface roughness of 0.2 nm, and low ion channeling yields, χmin≤ 4%, when deposited at 800 °C. Films generally become smoother with better crystallinity when the film thickness approaches 300 nm. A growth mode with initial island formation and subsequent layer-by-layer appears to take place at higher substrate temperatures, whereas at lower temperatures the film grows in a 3D mode.
Enzymes and Cells Confined in Silica Nanopores
Authors: Livage Jacques , Roux Cécile , Coradin Thibaud , Fennouh Souad , Guyon Stéphanie , Bergogné Laurie , Coiffier Anne , Bouvet Odile 
Published: April 2011

AbstractThe sol-gel process opens new possibilities in the field of biotechnologies. Sol-gel glasses are formed at room temperature via the polymerization of molecular precursors. Enzymes can be added to the solution of precursors and trapped within the growing silica network. Small substrate molecules can diffuse through the pores allowing reactions to be performed in-situ, within the silica gels. Enzyme are encased by the hydrated silica in a cage tailored to their size, they retain their biocatalytic activity and may even be stabilized within the sol-gel matrix.Whole cell bacteria have also been immobilized within sol-gel glasses. They behave as a "bag of enzymes" and their membrane protects enzymes against denaturation and leaching. The cellular organization of bacteria cells is preserved upon encapsulation. Experiments performed with Escherichia coli induced to β-galactosidase show that they still exhibit noticeable enzymatic activity. Some degradation of the cell walls may even occur increasing the “measured” activity. However silica gels made from aqueous precursors seem to prevent bacteria from natural degradation upon ageing.Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cell protozoa have been encapsulated without any alteration of their cellular organization. For medical applications, trapped parasitic protozoa have been used as antigens for blood tests with human sera. Antigen-antibody interactions were followed by the so-called Enzyme Linked ImmunoSorbent Assays (ELISA).
Spectrophotometric Observations of Gel-Free Reaction Front Kinetics in Confined Geometry
Authors: Park Sung Hyun , Parus Stephen , Kopelman Raou , Taitelbaum Haim 
Published: April 2011

AbstractWe present a new experimental system to study the kinetics of the reaction front in A + B→C reaction-diffusion systems with initially-separated reactants. The set-up is composed of a CCD camera monitoring the kinetics of the front formed in the reaction-diffusion system Cu2++ tetra→1:1 complex (in aqueous, gel-free solution) inside a 150 micron gap between two flat microscope slides. This is basically a two-dimensional system. The results are consistent with the theoretical predictions for the anomalous time dependence of the front's width, height,and location.
Anomalous Surface Conformation for Polymeric Gas-Hydrate-Crystal Inhibitors
Authors: King H.E. , Hutter Jeffrey L. , Lin Min Y. , Sun Thomas 
Published: April 2011

AbstractWe have used both conventional small-angle neutron scattering and contrast variation techniques to characterize the polymer conformations of two non-ionic water soluble polymers: poly(ethylene oxide) and poly(N-vinyl-2-pyrollidone). The second of these is able to kinetically suppress hydrate crystallization, and an objective of these studies is to obtain a understanding of this inhibition mechanism. The dilute-solution polymer conformation in a hydrate-forming tetrahydrofuran/water fluid shows only a small difference between the polymers. The single- chain characteristics are unperturbed, but the hydrate inhibitor polymer seems to show an enhanced tendency to form aggregates in solution. This is evidenced by excess low-q scattering following a q-2.5 power law. Much more evident is the strong perturbation in the conformation of the inhibitor polymer upon crystallization of the hydrate. We utilize contrast variation methods to resolve the scattering of the polymer on the hydrate surface. Unlike expectations from polymer scaling laws, the resulting layer is considerably thicker (550) than the single- chain radius of gyration, 80. Also surprising, only 2 percent of the available crystal surface is covered. Within the covered areas, the polymer concentration is significantly enhanced over that in the surrounding solution, about 2.5c* (where c* is the overlap concentration). This suggests a coverage of clumps of polymer widely separated from one another. Consideration of the concentration and implied spacing of such clumps on the hydrate surface suggests that they can effectively inhibit crystal growth.
Relaxation Method Simulation of Confined Polymer Dispersed Liquid Crystals in an External Field
Authors: Castro J. J. , Valladares R. M. , Calles A. 
Published: April 2011

AbstractPolymer dispersed liquid crystals (PDLC) are materials formed by nematic liquid crystals droplets with radii of a few hundred Å embedded in a polymer matrix. We discuss the use of relaxation methods for the study of the response of the director of a PDLC under the switching of an external electric field. We simulate the confining system by considering different boundary conditions at the droplet surface.
“Open structure” semiconductors: Clathrate and channel compounds for low thermal conductivity thermoelectric materials
Authors: Nolas George S. 
Published: April 2011

ABSTRACTIn a good semiconductor the electrons (or holes) propagate through the lattice structure of well ordered atoms without being scattered by the coherent vibrations of the crystal. Thus semiconductors are good conductors of electrons (or holes) and as such have given rise to modern microprocessors that are revolutionizing the way we live. In the same semiconductors the vibrations of the lattice atoms mainly carry the heat. Due to the covalent nature of the bonding in these materials the thermal conductivity is very large. These are therefore poor materials for thermoelectric applications. If the atomic vibrations, or phonons, can be localized so that the heat transfer is essentially an atom-to- atom propagation, then the thermal conduction can be drastically reduced. A semiconductor can, in principle, have the thermal conductivity of a glass. Amorphous semiconductors are of course very poor conductors of electricity therefore one does not want the electrons to propagate through a glass-like material. Instead one wants the electrons to travel as though they only “see” the well-ordered, periodic structure of a crystal while the phonons are scattered by localized disorder within the covalently bonded lattice. “Open structure” semiconductors do, in fact, exist and recent research has given rise to new thermoelectric materials.
Micromagnetic and Magnetoresistance Studies of Ferromagnetic La0.83Sr0.13MnO2.98 Crystals
Authors: Popov Guerman , Kalinin Sergei V. , Alvarez Rodolfo A. , Greenblatt Martha , Bonnell Dawn A. 
Published: April 2011

ABSTRACTMagnetic force microscopy (MFM) and atomic force microscopy (AFM) were used to investigate the surface topography and micromagnetic structure of La0.83Sr0.13MnO2.98 single crystals with colossal magnetoresistance (CMR). The crystals were grown by fused salt electrolysis and characterized by chemical analysis, X-ray diffraction, magnetic and transport measurements. The crystals are rhombohedral (R 3 c). Magnetic and transport measurements indicate that the ferromagnetic ordering at 310 K is associated with an insulator-metal transition at the same temperature. A maximum negative magnetoresistance (-62 %) is observed at 290 K in an applied magnetic field of 5 T. The magnetoresistance increases in magnitude sharply (1.8 %), comparing to the rest of the change, with increasing magnetic field up to 20 G, and then it increases slowly with increasing field.MFM and AFM were used to study the (110) surface as well as a number of unspecified surfaces. Surface topography of an as-grown crystal exhibits well-developed surface corrugations due to extensive twinning. The corrugation angle at twin boundaries can be related to the unit cell parameters, surface and twinning planes. Magnetic force microscopy images show that magnetic domain boundaries are pinned to the crystallographic twins; a small number of unpinned boundaries are observed. The statistical analysis of domain boundary angle distribution is consistent with cubic magnetocrystalline anisotropy with easy axis along [100] directions for this material. Unusual magnetization behavior in the vicinity of topological defects on the surface is also reported. MFM contrast was found to disappear above the ferromagnetic Curie temperature; after cooling a new magnetic structure comprised of Bloch walls of opposite chiralities developed.
Frameworks of Transition Metals and Linkers with Two or More Functional Groups
Authors: Sevov Slavi C. 
Published: April 2011

ABSTRACTHybrid inorganic/organic materials with open-framework or layered structures are known for many transition metals linked by functionalized organic molecules such as organic diphosphonates, polycarboxylates, polynitriles, etc., species with more than one equivalent functional groups. We have studied the effect of pH on such a system of cobaltmethylenediphosphonate and report three new compounds, Na3Co[(O3PCH2PO3)(OH)],Na2Co(O3PCH2PO3)•H2O, and Co2[(O3PCH2PO3)(H2O)], that form at very basic, moderately basic, and acidic conditions, respectively. More interestingstructural chemistry should be expected from linkers with two or more different functionalities. Both the carboxylic and phosphonic groups in carboxyethylphosphonic acid are used to coordinate to cobalt or calcium atoms in the new compounds Co3(O3PCH2CH2COO)2•6H2O and Ca(O3PCH2CH2COOH)•H2O. Taking one more step further in complexity we have also studied linkers with three different functional groups, phosphonated amino acids. The structures of two new compounds, Zn(O3PCH2CH(NH3)COO) and Zn(O3PCH2CH2CH(NH3)COO), are threedimensional frameworks made of zinccoordinated by both the carboxylic and phosphonic ends of the organic molecules. The amino groups are protonated and terminal in the voids of the frameworks.
Manganese Vanadium Oxide Compounds as Cathodes for Lithium Batteries
Authors: Ngala J. Katana , Zavalij Peter Y. , Whittingham M. Stanley 
Published: April 2011

ABSTRACTA pure form of the compound [(CH3)4N]0.2Mn0.06V2O5+δ•0.2H2O has been synthesized by the hydrothermal technique. A manganese richer compound, [(CH3)4N]0.18Mn0.1V2O5+δ•0.35H2O, has also been synthesized. By comparison to [(CH3)4N]0.17Fe0.1V2O5+δ•0.17H2O, the structure of these compounds consists of double sheets of vanadium oxide with tetramethyl ammonium ions in the interlayer spaces. Both compounds display reversible lithium intercalation with sharp end points. The lithiation capacity is lowered by the increase in manganese content.
Structural Changes in Amorphous Silicon Annealed at Low Temperatures
Authors: Pivac Branko , Dubček Pavo , Milat Ognjen , Zulim Ivan 
Published: April 2011

ABSTRACTThe hydrogen dilution in the course of production of amorphous silicon (a-Si) influences its structural properties, which affect significantly light-induced degradation. We used FTIR, X-ray reflectivity and GISAXS analysis to monitor the structural changes occurring during the low temperature annealing of undoped a-Si:H films. FTIR results show that upon annealing at very low temperatures, hydrogen is moved from its positions (voids) where it was accumulated unbonded to silicon and is subsequently trapped at dangling bonds, enhancing disorder. X-ray reflectivity and GISAXS measurements confirmed the enhancement of the void size.
Excimer Laser Recrystallization of Selectively Floating a-Si Active Layer for Large-Grained Poly-Si Film
Authors: Kim Cheon-Hong , Yoo Juhn-Suk , Song In-Hyuk , Han Min-Koo 
Published: April 2011

ABSTRACTWe report a new excimer laser annealing method by employing selectively floating a-Si active layer structure in order to increase the grain size of poly-Si film. The floating a-Si region blocks the heat conduction into the underlying substrate due to high thermal-insulating property of an air so that the lateral temperature gradient is successfully induced by the proposed simple air-gap structure. Our experimental results show that large grains were grown in the lateral direction from the edge to the center of the floating active region. The large grains exceeding 4 m were successfully obtained with only one laser irradiation.
Growth, Structural Characterization, and Optical Band Gap Anomaly in Cu-III3-VI5 and Cu-III5-VI8 Ternary Compounds
Authors: Wasim S. M. , Rincón C. , Marín G. , Márquez R. , Pérez G. Sánchez , Guevara R. , Delgado J. M. , Nieves L. 
Published: April 2011

ABSTRACTA comparative study of the chemical composition, crystal structure, carrier concentration, mobility, and the energy gap at room temperature of the selenides and tellurides of normal Cu- III-VI2 and ordered defect Cu-III3-VI5and Cu-III5-VI8 compounds, grown by Bridgman techniques, is made. It is established that these compounds have a chalcopyrite-related structure with the exception of CuIn5Se8 and CuGa5Te8 that have hexagonal and cubic structure, respectively. Smaller volume of the unit cell and lower concentration of the charge carrier of the 1:3:5 and 1:5:8 phases, as compared to the 1:1:2, are attributed to the presence of the ordered vacancies. A new mechanism of the scattering of the charge carriers with the donor-acceptor defect pair (DADP) is suggested to explain the low value of mobility in these compounds. The anomaly observed in the band gap is explained in terms of the relative shift of the conduction band minimum and valence band maximum due to the donor-acceptor defect pairs and cation vacancies, respectively.
Cu(In,Ga)S2 Phase Formation from Metallic Cu-In-Ga Precursor Stacks in Rapid Thermal Processes
Authors: Neisser Axel , Álvarez-García Jacobo , Calvo-Barrio Lorenzo , Klenk Reiner , Matthes Thomas W. , Luck Ilka , Lux-Steiner Martha Ch. , Pérez-Rodríguez Alejandro , Morante J.R. 
Published: April 2011

ABSTRACTThis contribution compares the growth of Cu(Ga,In)S2 based thin film solar cell absorbers in rapid thermal systems using sulfur vapor Sx or H2S/Ar as reactive atmosphere, focusing on Ga-related influences on film growth and phase formation. Cu-In alloying in the precursor is kinetically hindered by the presence of Cu-Ga phases. In sulfur vapor Ga-containing samples sulfurize via an intermediate CuIn2S8 phase, thereby delaying the full sulfurization and recrystallization of the layer. In contrast, in H2S/Ar fast Ga-In interdiffusion and no intermediate chalcogenide phases are observed. The inhomogeneous Ga depth distribution usually reported for sequentially prepared Cu(In,Ga)S2 films can be assigned to the segregation of CuGaS2 prior to CuInS2.
Effect Of Grain Size, Morphology and Deposition Temperature on Cu(InGa)Se2 Solar Cells
Authors: Shafarman William N. , Zhu Jie 
Published: April 2011

ABSTRACTCu(InGa)Se2 films have been deposited by multisource elemental evaporation at substrate temperatures from 550 to 400°C to determine the effect of temperature on grain size and morphology and on solar cell performance. Films were deposited with different flux profiles to compare cases where a copper selenide phase is formed during different stages of growth or not at all. The grain size and surface area of the films are determined by analysis of atomic force microscope images. With the Cu-rich growth, the mean lateral grain area decreases from 1.8 to 0.3 μm2 as substrate temperature decreases. Device efficiency decreases with the lower temperature but cannot be simply attributed to changes in grain size, surface area, or the availability of sodium which diffused from the glass substrate. Instead the decrease in open circuit voltage and fill factor are attributed to a greater density of intra-grain trap states in the Cu(InGa)Se2.
The Influence of Stressing at Different Biases on the Electrical and Optical Properties of CdS/CdTe Solar Cells
Authors: Townsend S. W. , Ohno T. R. , Kaydanov V. , Gilmore A. S. , Beach J. D. , Collins R. T. 
Published: April 2011

ABSTRACTCadmium Sulfide/Cadmium Telluride (CdS/CdTe) devices are subject to stress under various biases. Striking differences are observed with the Current-Voltage, and Capacitance- Voltage measurements for cells degraded at 100°C in dark under forward (FB), open circuit (OC), and reverse (RB) biases. RB stress provides the greatest degradation, and the apparent doping density profile shows anomalous behavior at the zero bias depletion width. Thin films of CdS, both doped and undoped, with Cu are characterized with photoluminescence (PL). The PL spectra from the CdS films are correlated with the CdS spectra from stressed devices, revealing that Cu signatures in the CdS layer of stressed devices are a function of stress biasing. Device modeling using AMPS-1D produces IV curves similar to that in RB degraded devices, by only varying the trap level concentration in the CdS layer.
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

ABSTRACTAtmospheric 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

ABSTRACTImprovement 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTIn 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.