bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Electron Gain from Forests of Multi-Walled Carbon Nanotubes
Authors: Michan Mario , Nojeh Alireza 
Published: August 2010

AbstractCarbon nanotubes are attractive candidates for electron field-emitters due to their high aspect ratio, mechanical stability, and electrical conductivity. It has previously been shown that an electron beam hitting the tip of a carbon nanotube biased near the threshold of field-emission can stimulate the emission of a large number of electrons from the nanotube tip. Here we report on similar experiments on arrays of free-standing multi-walled carbon nanotubes (nanotube forests) interacting with a scanning electron microscope's primary beam. Electron gains of up to 19,000 were obtained. This can enable applications such as electron detection and multiplication, and vacuum transistors.
Influence of reaction parameters on the photoluminescence properties of free standing functionalized silicon nanocrystals
Authors: Gupta Anoop , Wiggers Hartmut 
Published: August 2010

AbstractWhile silicon nanostructures acquire novel optical properties due to miniaturization, the stability of light emission is severely limited because of exciton trapping due to surface oxidation coming along with the formation of defects. Grafting of organic molecules on a hydrogen-terminated silicon surface via hydrosilylation provides a promising route to stabilize their surface against oxidation. In this communication, we report on the effect of surface passivation on the optical properties of freestanding silicon nanocrystals (Si-NCs). The surface functionalization of hydrogen-terminated Si-NCs with organic molecules was achieved via liquid phase hydrosilylation. We demonstrate that surface functionalization does not preserve the original emission of hydrogen-terminated Si-NCs. It is observed that the emission spectrum of green emitting hydrogen-terminated Si-NCs is red shifted after surface functionalization. We find that the direction of shift does not depend on the type of organic ligands and the reaction conditions, however, the amount of shift can be altered. The factors influencing the shift in the emission spectra of functionalized Si-NCs with respect to hydrogen-terminated samples are discussed.
Improved Spectral Response of Quantum Dot Solar Cells Using InAs Multi-stack High Density Quantum Dot Molecules
Authors: Tangmettajittakul Ong-arj , Changmoang P , Thainoi Supachok , Changmoang Pornchai , Kanjanachuchai Songphol , Rattanathammaphan Somchai , Panyakeow Somsak 
Published: August 2010

AbstractIn this paper, we report the spectral response measurement of Schottky solar cells with conventional quantum dots (QDs) and high-density quantum dot molecules (HD-QDMs) as active layers. 3-stack HD-QDMs Schottky structure is compared to 15-stack QD Schottky structure and control sample without QDs. 15-stack conventional InAs QDs give narrow response peak centered at 907 nm while 3-stack InAs HD-QDMs give broad peak between 915 and 985 nm. Both spectral responses are extended beyond the band edge of GaAs, i.e. 870 nm. 42 % more photovoltaic power could be evident from the extended spectral response curve comparing to that of GaAs bulk sample without dots.
The Use of Thermally Decomposable Ligands for Conductive Films of Semiconductor Nanocrystals
Authors: Wills Andrew , Kang Moon Sung , Khare Ankur , Gladfelter Wayne L. L. , Norris David 
Published: August 2010

AbstractPoor conductivity is a bottleneck hindering the production of nanocrystal-based devices. In most nanocrystal syntheses, ligands with long alkyl chains are used to prepare monodisperse, crystalline particles. When these nanocrystals are incorporated into devices as films, the bulky ligands form an insulating layer that prevents charge transfer between particles. While annealing or post-deposition chemical treatments can be used to strip surface ligands, each of these approaches has disadvantages. Here we demonstrate the use of a novel family of ligands comprised of primary alkyl dithiocarbamates to stabilize PbSe/CdSe core-shell nanocrystals. Primary dithiocarbamates, which can bind to cadmium and lead, are known to decompose to the corresponding sulfides when heated under mild conditions. In our scheme, PbSe/CdSe core-shell nanocrystals are first synthesized with standard ligands. These ligands are then exchanged to short chain dithiocarbamates in solution. When a film is cast and annealed at low temperature, the dithiocarbamates are removed. Electron microscopy reveals that the particles move closer together, and, along with x-ray diffraction, shows that the nanocrystals remain quantum confined. Transport measurements show a 10,000-fold increase in conductivity after annealing.
Excited State Charge Transfer in Dyads of ZnO Nanocrystals and Organic or Transition Metal Dyes
Authors: Saunders Julia E. , Huss Adam S. , Bohnsack Jon , Mann Kent R. , Blank David A. , Gladfelter Wayne L. L. 
Published: August 2010

AbstractTo better understand the specific charge transfer events that occur within a dye-sensitized solar cell (DSSC), we synthesized well-defined ZnO:dye dyads. The ZnO nanocrystals were synthesized following literature procedures from zinc acetate and a hydroxide source in ethanol. The absorption onset of the ZnO nanocrystals was observed using UV-vis measurements, from which estimated nanocrystal diameters were determined. At room temperature, the synthesis yielded nanocrystals ranging in diameter from 2-4 nm. Dispersions of ZnO nanocrystals in ethanol were mixed with solutions containing 5΄΄-phenyl-3΄,4΄-di(nbutyl)-[2,2΄:5΄,2΄΄] terthiophene-5-carboxylic acid. Using FT-IR and fluorescence spectroscopy, it was verified that the dye molecules were adsorbed to the ZnO surface via their carboxylate groups while the number of dye molecules adsorbed to the surface was quantified using a combination of techniques. Adsorption isotherms were employed to probe surface coverage of the dye onto the nanocrystals to yield an adsorption equilibrium constant of 1.5 ± 0.2 x 105 M-1. The ability of ZnO nanocrystals to quench the emission of the dye by an electron transfer mechanism was observed and elucidated using ultra-fast laser spectroscopy where the time-scale for electron injection from the dye to the ZnO was determined to be 5.5 ps.
Capacitance-Voltage Characterization of Solar Cells With CdS in CdTe Matrix
Authors: Jha Rashmi , Liu Xiangxin , Wieland Kristopher , Ordosgoitti Jorhan , Paudel Naba , Sun Kai , Compaan Alvin 
Published: August 2010

AbstractSolar cells fabricated from a sputtering target with 5% cadmium sulfide (CdS) intermixed cadmium telluride (CdTe) material was studied using Capacitance-Voltage (CV) profiling. The average efficiency of a set of these novel solar cells under one sun illumination was observed to be 7.56%. In contrast with standard sputtered CdS/CdTe cells, the junction capacitance of the mixed compound device was observed to show minimal change in the entire reverse bias range. The element mapping of the film using Bright Field Scanning Transmission Electron Microscopy (BF-STEM) was used to determine the distribution of S, Te, Cd, O, and Cl in CdTe film. From these observations, it is believed that the morphology and composition of the film resulted in a built-in potential which was sufficient to completely deplete the film.
Direct Observations of Relaxation of Si/SiGe/Si on Insulator
Authors: Ma Tongda , Tu Hailing 
Published: August 2010

AbstractMicrostructural evolution is directly observed when the cross-sectional film specimen of Si/SiGe/Si on insulator (Si/SiGe/SOI) is heated from room temperature (R.T., 291 K) up to 1113 K in high voltage transmission electron microscope (HVEM). The misfit dislocation at the lower interface of the SiGe layer begins to extend downwards even at 913 K. The lower interface takes the lead in roughening against the upper interface of the SiGe layer. The roughened interface is ascribed to elastic relaxation. As misfit strain is partially transferred to SOI top Si layer and misfit dislocation is prolonged at the lower interface, the roughened interface turns smooth again. Thereafter, the misfit dislocations are introduced into the upper roughened interface of the SiGe layer to release the increased misfit strain. It is suggested that the microscopic relaxation of the SiGe layer is related to dislocation behavior and strain transfer.
Neutron Imaging Methods for the Investigation of Energy Related Materials (Fuel Cells, Battery, Hydrogen Storage and Nuclear Fuel)
Authors: Lehmann Eberhard Helmar , Oberholzer Pierre , Boillat Pierre 
Published: August 2010

AbstractThis article underlines with examples of studies for energy related materials and processes how important and useful the technique of neutron imaging can be for our future energy supply. With the help of the particularly designed configurations for each such study it becomes possible to derive essential information for the material properties and their change in a non-invasive manner.The four mentioned examples (PEM fuel cell, Li-battery, hydrogen storage and nuclear fuel inspection) cover a very wide range of applications and demonstrate the high potential of the various used methods in neutron imaging.
XANES Studies on Eu-doped Fluorozirconate Based Glass Ceramics
Authors: Henke Bastian , Keil Patrick , Pablick Christian , Vogel Dirk , Rohwerder Michael , Wiegand Marie-Christin , Johnson Jacqueline A. , Schweizer Stefan 
Published: August 2010

AbstractThe influence of adding InF3 as a reducing agent on the oxidation state of Eu in fluoro-chloro- (FCZ) and fluorobromozirconate (FBZ) glass ceramics was investigated using x-ray ab-sorption near edge (XANES) and photoluminescence (PL) spectroscopy. For both materials, it was found that InF3 decreases the Eu2+-to-Eu3+ ratio significantly. PL spectroscopy proved that an annealing step leads to the formation of Eu-doped BaCl2 and BaBr2 nanocrystals in the FCZ and FBZ glasses, respectively. In the case of FCZ glass ceramics the hexagonal phase of BaCl2 could be detected in indium-free and InF3-doped ceramics, but only for InF3 containing FCZ glass ceramics a phase transition of the nanoparticles from hexagonal to orthorhombic structure is observed. For the FBZ glass ceramics, the hexagonal phase of BaBr2 can be formed with and without indium doping, but only in the indium-free case a phase transition to orthorhombic BaBr2 could be found.
Mechanism of Ultrafast (Dis)charging of Li Ion Batteries by Heterogeneous Doping of LiFePO4
Authors: Adams Stefan , Prasada Rao R. , Choo Haiping 
Published: August 2010

AbstractMolecular dynamics (MD) simulations with a dedicated force-field and our bond valence (BV) pathway analysis have been employed to reproduce and explain the experimentally observed ultrafast Li+ transport in surface modified LixFePO4-δas a consequence of heterogeneous doping, i.e. the Li+redistribution in the vicinity of the interface between LixFePO4and a pyrophosphate glass surface layer. Over the usual working temperature range of LIBs Li+ion conductivity in the surface modified LixFePO4phase is enhanced by 2-3 orders of magnitude, while the enhancement practically vanishes for T > 700K. Simulations for the bulk phase reproduce the experimental conductivities and the activation energy of 0.57eV (for x ≈ 1). A layer-by-layer analysis of structurally relaxed multilayer systems indicates a continuous variation of Li+mobility with the distance from the interface and the maximum mobility close to the interface, but Li+diffusion rate remains enhanced (compared to bulk values) even at the center of the simulated cathode material crystallites. Our BV migration pathway analysis in the dynamic local structure models shows that the ion mobility is related to the extension of unoccupied accessible pathway regions. The change in the extent of Li redistribution across the interface with the overall Li content constitutes a fast pseudo-capacitive (dis)charging contribution.
Visible-light Photoresponse of Nitrogen-doped TiO2: Excited State Studies Using Time-dependent Density Functional Theory and Equation-of-Motion Coupled Cluster Methods
Authors: Govind Niranjan , Rousseau Roger , Andersen Amity , Kowalski Karol 
Published: August 2010

AbstractTo shed light on the nature of the electronic states at play in N-doped TiO2 nanoparticles, we have performed detailed ground and excited state calculations on pure and N-doped TiO2 rutile using an embedding model. We have validated our model by comparing ground-state embedded results with those obtained from periodic DFT calculations. Our results are consistent with periodic calculations. Using this embedding model we have performed B3LYP based TDDFT calculations of the excited state spectrum. We have also studied the lowest excitations using high-level equation-of-motion coupled cluster (EOMCC) approaches involving all single and inter-band double excitations. We compare and contrast the nature of the excitations in detail for the pure and doped systems using these calculations. Our calculations indicate a lowering of the bandgap and confirm the role of the N3- states on the UV/Vis spectrum of N-doped TiO2 rutile supported by experimental findings.
The influence of palladium impurities on vacancy diffusion in cubic silicon carbide
Authors: Roma Guido 
Published: August 2010

AbstractThe basic properties of palladium impurities in silicon carbide, such as solubility or diffusion mechanisms, are far from being well understood. In a recent paper I presented a systematic study of stability and kinetic properties of Pd in cubic silicon carbide using first principles calculations. In this paper I focus on the effect of the presence of palladium in silicon carbide, even in very low concentrations, on the kinetic properties of carbon vacancies. I apply a odel of Pd diffusion through a vacancy mechanism on the carbon sublattice and extract the correlation factors leading to an enhancement of vacancy migration, due to the coupling of iffusion fluxes between vacancies and palladium impurities.
Chemical Compatibility at High Temperature between the Carbide Fuel UC or (U,Pu)C and SiC Cladding for the Gas cooled Fast Reactor
Authors: Berche Alexandre , Alpettaz Thierry , Chatain Sylvie , Gossé Stephane , Guéneau Christine , Rado Cyril 
Published: August 2010

AbstractThe chemical compatibility at high temperature between the fuel kernel (U,Pu)C and SiC cladding, the reference materials for the GFR reactor, is studied. For that purpose, a thermodynamic database on the U-Pu-C-Si system was developed with the Calphad method to calculate the phase diagrams. Differential thermal analysis experiments were performed to measure phase transition temperatures in Si-U and C-Si-U systems. According to the calculated isopleth section between the hyperstoichiometric uranium carbide UC1.02 and SiC, the materials shall not react below 2056 K, the temperature at which a liquid phase shall form. These calculations are in good agreement with two chemical compatibility tests performed at 1873 K and 2073 K between the materials. Calculations were also performed to study the chemical interaction between the mixed carbide (U,Pu)C1.04 and SiC. The presence of plutonium in the fuel kernel lowers the liquid formation temperature of 167 K.
Structural Evolution of Nuclear Glasses under Forcing Conditions (Irradiation, Alteration)
Authors: Calas Georges , Galoisy Laurence , Cormier Laurent , Delaye Jean Marc , Jollvet Patrick , Peuget Sylvain 
Published: August 2010

AbstractAssessing the long-term behavior of nuclear glass implies the prediction of their long-term performance, and more precisely of their evolution under irradiation and during interaction with water. After briefly recalling the major characteristics of the local and medium-range structure of borosilicate glasses of nuclear interest, we will present some structural features observed under forcing conditions. Specific structural tools (EXAFS/XANES, Neutron/x-ray diffraction, solid state spectroscopic methods…) are correlated with numerical simulations to determine the local structure of glass and provide selective information on glass surface using total electron yield detection. During alteration in near- or under-saturated conditions, some elements such as Fe change coordination, as other elements such as Zr only suffer structural modifications in under-saturated conditions. These structural modifications may explain the chemical dependence of the initial alteration rate and the transition to the residual regime. They also illustrate the molecular-scale origin of the processes at the origin of the glass-to-gel transformation. Molecular scale processes help in predicting the properties of new generations of nuclear glasses required by future production of nuclear energy. Under irradiation, various structural effects are observed, including coordination change, ion migration or disorder effects. These studies show that glasses with a simplified composition do not show the same behavior as more realistic glasses. Molecular dynamics (MD) simulations provide complementary information on elastic effects. Recent direct evidence for B-coordination change under external irradiation together with structural models derived from MD sheds light on the structural mechanisms at the origin of radiation-induced modifications of glass properties, emphasizing the importance of the thermal regime in the cascade core.
Influence of Operational Conditions on Retardation Parameters Measured by Diffusion Experiment in Compacted Bentonite
Authors: Yasuo Ishii , Seida Yoshimi , Tachi Yukio , Yoshikawa Hideki 
Published: August 2010

AbstractInfluence of operation factors in diffusion test of compacted bentonite (such as agitation of test solution in the reservoir, feed rate of the test solution and mass transfer resistance in the filter) on the diffusion data was examined by reservoir depletion (RD) test method using Cs+. The influence of these factors on the diffusion data was also analyzed based on the mathematical sorption-diffusion model which considered the feed of test solution and mass transfer resistance in the filter as well. The reservoir depletion data showed some remarkable influences of these operational conditions, especially in the system with low ionic strength. Change in mass transfer resistance at filter-compacted bentonite due to the operational conditions was found to be potential factor which disturb the diffusion data. The influence was reduced in the system with high ionic strength of solution.
Ion Beam Irradiation of Lanthanum Compounds in the Series La2O3-TiO2
Authors: Whittle Karl , Blackford Mark , Aughterson Robert , Smith Katherine L , Lumpkin Gregory R , Zaluzec Nestor J 
Published: August 2010

AbstractThin crystals of La2O3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions in the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), at the Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1 × 1016 ions cm-2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for TiO2, are discussed with reference to the phase diagrams for La2O3-TiO2 systems and the different local environments within the crystal structures. Results suggest an observable inverse correlation between Tc and melting temperature (Tm) in the two systems.
Nanostructured Silicon-based Composites for High Temperature Thermoelectric Applications
Authors: Bux Sabah , Kaner Richard B , Fleurial Jean-Pierre 
Published: August 2010

AbstractRecently nanostructured bulk silicon and silicon-germanium have achieved large increases in the thermoelectric figure of merit (ZT). The ZT enhancement is attributed to a significant reduction in the lattice thermal conductivity while maintaining relatively high carrier mobility. Silicon-based thermoelectric devices are attractive due to their low-toxicity, thermal stability, low density, relative abundance and low cost of production. Although significant enhancements in ZT have been achieved using the nanostructuring route, additional decoupling of the thermal and electric transport terms is still necessary in order for silicon-based materials to be viable for thermoelectric applications such as waste heat recovery or radioisotope thermoelectric generators. It is theorized that additional increases in ZT could be achieved by forming composites with nanostructured inert inclusions to further scatter the heat-carrying phonons. Here we present the impact of insulating and conductive nanoparticle composites on ZT. The nanostructured composites are formed via ball milling and high pressure sintering of the nanoparticles. The thermoelectric properties and microstructure of the silicon-based composites are discussed.
Hybrid Thermal Behavior from Thermoelectrics to Heat Sinking of a Thin Si Membrane with Stretched Ge Quantum Dots
Authors: Gillet Jean-Numa 
Published: August 2010

AbstractA membranous nanomaterial showing, for the first time, a hybrid thermal behavior between insulating and dissipative regimes is proposed with applications in both thermoelectrics (low thermal conductivity) and passive heat sinking (high thermal conductivity). While other compounds could be chosen, the nanomaterial is made up of a thin Si membrane covered by Ge quantum dots (QDs) with epitaxial facets. The QDs are voluntarily stretched in the direction [010] or y parallel to the membrane to form elongated islands. The broken symmetry induces an exalted phonon wave-guiding in y. Therefore, when hot and cold junctions are connected to the membrane following the stretching direction [010], the anisotropic thermal conductivity shows a significant exaltation with respect to the in-plane orthogonal direction [100] or x, where the Ge islands have the smallest average size. An example nanomaterial is obtained by repetition of molecular supercell slabs containing 4348 atoms each. The thermal conductivity shows a marked exaltation higher than 22 folds, from 1.5 to 33.5 W/m/K when the connection direction between the hot and cold junctions is rotated by 90° from x to y. Therefore, the nanomaterial presents a changing thermal behavior from insulation to passive dissipation when the heat propagation direction is modified from x to y. As a result, it could be used for the design of passive heat sinkers (from the phonons) when the two junctions are connected following [010]. In contrast, a thermal insulating behavior appears when the junctions are linked following [100]. This direction can be as well used for cooling applications. However, in this case, cooling is differently generated using the Peltier effect (from the electrons). Seebeck generation can be also envisioned in the direction [100].
Effect of partial filling of the structural vacant sites on the thermoelectric properties of Zr0.25Hf0.75NiSn half-Heusler alloy
Authors: Makongo Mangan Julien Pierre Amelie , Misra Dinesh , Takas Nathan J. , Stokes Kevin L. , Gabrisch Heike , Poudeu Pierre F. P. 
Published: August 2010

AbstractComposites containing mainly-half-Heusler MNiSn (HH) and full-Heusler MNi2Sn (FH) were prepared by solid state reaction of a mixture of polycrystalline bulk HH alloy with various concentrations of Ni up to 10 wt.%. Electrical conductivities, thermal conductivities and thermopowers of spark plasma sintered specimens of the as synthesized composite materials were measured in the temperature range from 300 K to 750 K. The conduction type of the composite changes from semiconductor to semimetal for Ni concentrations up to 2 wt.% and from semimetal to metal for higher Ni concentrations above 5 wt.%. A strong reduction in lattice thermal conductivity was observed for the composite containing 10 wt. % Ni inclusions.