bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photodetectors Fabricated from Strain-free GaAs Coupled Quantum Dots
Authors: Wu Jiang , Shao Dali , Manasreh Omar , Li Alvason Zhenhua , Wang Zhiming M , Salamo Gregory J. 
Published: January 2010

AbstractIn this article, an alternative strain-free growth mode is presented where GaAs coupled-quantum dots are grown on lattice matched AlGaAs. The coupled quantum dots were grown at 550 °C in a molecular beam epitaxy system. The GaAs quantum dots were characterized by using a photoluminescence technique and an atomic force microscope. The photodetector was fabricated into normal incident configuration and photoconductivity spectra were measured covering the mid-infrared spectrum of 2.0 – 8.0 micron (intersubband transitions) and the visible-near-infrared spectrum of 0.5 – 0.9 micron (interband or exciton transitions). The photoresponse spectra in mid-infrared spectral range were found to exist at temperatures lower than 80 K, while the photoresponse spectra in the visible-near-infrared range were observed at temperatures as high as 300 K.
Efficient Energy Transfer Between CdS Quantum Dots in Layer-by-layer Self-assembled Films
Authors: Shimura Kunio , Kim DaeGwi , Nakayama Masaaki 
Published: January 2010

AbstractWe have investigated efficient energy transfer (ET) between CdS quantum dots (QDs) measuring photoluminescence dynamics in layer-by-layer (LBL) self-assembled films. The assembly of negatively charged colloidal QDs and positively charged polyelectrolytes results in QD/polymer multilayers. Furthermore, to reveal how the ET rate depends on the distance between CdS QDs, we fabricated bilayer structures consisting of differently sized CdS QDs. It is experimentally verified that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction.
Dynamic Control of Plasmon-Exciton Coupling in Au Nanodisk–J-Aggregate Hybrid Nanostructure Arrays
Authors: Zheng Yue Bing , Juluri Bala Krishna , Jensen Linlin , Jensen Lasse , Huang Tony Jun 
Published: January 2010

AbstractWe report the dynamic control of plasmon-exciton coupling in Au nanodisk arrays adsorbed with J-aggregate molecules by incident angle of light. The angle-resolved spectra of an array of bare Au nanodisks exhibit continuous shifting of localized surface plasmon resonances. This characteristic enables the production of real-time, controllable spectral overlaps between molecular and plasmonic resonances, and the efficient measurement of plasmon-exciton coupling as a function of wavelength with one or fewer nanodisk arrays. Experimental observations of varying plasmon-exciton coupling match with coupled dipole approximation calculations.
Supporting metal catalysts on modified carbon nanocones to optimize dispersion and particle size
Authors: Matelloni Paolo , Grant David M. , Walker Gavin S. 
Published: January 2010

AbstractCarbon nanocones are the fifth allotropic form of carbon, first synthesized in 1997. They have been selected for investigating hydrogen storage capacity, because initial temperature programmed desorption experiments found a significant amount of hydrogen was evolved at ambient temperatures. The aim of this work was to study the effect of impregnation conditions on metal catalyst dispersion and to investigate whether the metal loaded cones had improved hydrogen storage characteristics. Pre-treatment of carbon nanocones with hydrogen peroxide was carried out, followed by metal decoration in aqueous solution by an incipient wetness technique. Two methods of reducing the metal catalyst have been applied: in hydrogen at room temperature (RT) and in an aqueous solution of NaBH4. XRD confirmed the complete metal reduction and TEM showed that the reduction technique affected the catalyst dispersion. Very fine dispersions of ca. 1 nm diameter metal clusters at catalyst loadings of 5 wt.% were achieved and high dispersions were retained for loadings as high as 15 wt.%. Hydrogen uptakes at RT were measured and an increase with metal loading was observed.
The Ammonia-Driven Phase Transition in Bulk and Nanostructured Potassium Graphite KC24
Authors: Lovell Arthur , Kurban Zeynep , Bennington Stephen M. , Srinivas Gadipelli , Skipper Neal T. , Smith Ron I. , Jenkins Derek , Howard Christopher A. , Chapon Laurent 
Published: January 2010

AbstractWe report the synthesis of nanostructured stage-2 potassium graphite, KC24, by intercalation of turbostratic graphite nanofibers produced from an electrospun polymer, and compare its properties with exfoliated graphite-based KC24. The nanostructured KC24sample has low crystalline order and slightly increased interlayer spacing of 8.76 Å, compared with 8.65 Å in the bulk sample, indicating minimal registration of the graphite planes. Time-resolved time-of-flight neutron diffraction on both nanostructured and bulk KC24under ammoniation is suggestive of a more homogeneous and faster pressure-modulated phase transition to the ternary ammoniated potassium-graphite in the nanostructured material. Following ammoniation, negligible hydrogen uptake is observed at 50 K.
First-principles Calculations of Phonon and Thermodynamic Properties of Hydrogen Storage α-LaNi5H
Authors: Saito Shigeki , Katagiri Masahiko , Tserolas Vasileios , Nakamura Jun , Onodera Hidehiro , Ogawa Hiroshi 
Published: January 2010

AbstractThe phonon distribution of hydrogen storage α-LaNi5H with 4h, 6m, 12n, and 12o interstitial hydrogen was calculated by using first-principles potential surfaces with a 2×2×2 supercell model in order to investigate structural and thermodynamic properties. Frequency shifts due to the phonon contribution from the internal energies of 12n < 6m < 12o < 4h appeared in specific modes originating from interstitial hydrogen and in the upper-edge modes with nickel-lattice motion. The thermodynamic stability of 12n interstitial hydrogen in α-LaNi5H due to the wide XZ storage space can be explained by its phonon amplitudes and the charge density around nickel-bonded hydrogen.
Atomistic Simulation on Hydrogen Storage in Metallic Nanoparticles
Authors: Ogawa Hiroshi , Kayanuma Megumi , Katagiri Masahiko 
Published: January 2010

AbstractHydrogen storage in metallic nanoparticles was investigated by classical molecular dynamics and parameter physics. We observed phenomenological variation due to the differences in potential parameters of metal-hydrogen pair and crystal lattices. Three patterns of hydrogen distribution in both b.c.c. and f.c.c. nanoparticles were observed: non-absorbing, homogeneously-absorbing and heterogeneously-absorbing. In the last case, hydrogen atoms distribute just beneath the particle surface to form a hydrogen-rich layer. This layer prevents the diffusive motions of hydrogen atoms into the nanoparticle. We also carried out long simulation runs up to 1 nm to observed the structural variation of nanoparticles due to hydrogenation. Generation of grain boundaries was observed in b.c.c nanoparticles with the condition of strong metal–hydrogen interaction. Most of the grain boundaries were symmetric-tilt type and migrated inside the particle to reduce the interface energies. Formation of grain boundary was not observed in f.c.c. nanoparticles.
Lattice strain effects in graphane and partially-hydrogenated graphene sheets
Authors: Morris James Robert , Averill Frank W. , He HaiYan , Pan Bicai , Cooper Valentino R. , Peng Lujian 
Published: January 2010

AbstractThis paper presents a brief review of recent developments in the studies of fully hydrogenated graphene sheets, also known as “graphane,” and related initial results on partially hydrogenated structures. For the fully hydrogenated case, some important discrepancies exist between published first-principles calculations, and between calculations and experiment, with qualitative differences on whether or not the graphene sheet expands or contracts upon hydrogenation. The lattice change has important effects on partially hydrogenated structures. First-principles calculations of ribbon structures, with interfaces between graphane and graphene regions, show that the interfaces have substantial misfit strains. Calculating the interfacial energy must carefully account for the strain energy in the neighboring regions, and for sufficiently large regions between interfaces, defects at the interface that relieve the strain may be energetically preferable. Tight-binding simulations show that at ambient temperatures, segments of graphene sheets may spontaneously combine with atomic hydrogen to form regions of graphane. Small amounts of chemisorbed hydrogen distort the graphene layer, due to the lattice misfit.
Large H Absorption in Nd2Ni2In; Magnetism in a New Structure Type
Authors: Havela Ladislav , Mašková Silvie , Daniš Stanislav , Stelmakhovych Olha , Miliyanchuk Khrystyna 
Published: January 2010

AbstractSeveral hydrides of Nd2Ni2In with various H concentrations up to 6 H atoms/f.u. have been synthesized. Nd2Ni2In crystallizes in the tetragonal Mo2FeB2 structure type which can be changed upon hydrogenation to an orthorhombic structure, space group Pbma. The unit-cell volume increases by 15.5 % for Nd2Ni2InH4.5 and by 21.6 % for Nd2Ni2InH6. The triangular rare-earth lattice can give rise to magnetic frustration in case of antiferromagnetic interactions in Nd2Ni2In. The frustration is removed upon hydrogenation due to the orthorhombic distortion. The magnetic ordering temperature decreases with H concentration from 8 K in Nd2Ni2In down to 3.5 K in Nd2Ni2InH6.
Hydrogen Sorption in Magnesium Nanoparticles: Size- and Surface-related Phenomena
Authors: Pasquini Luca , Callini Elsa , Piscopiello Emanuela , Montone Amelia , Jensen Torben René , Vittori Antisari Marco , Bonetti Ennio 
Published: January 2010

AbstractThe aim of this work is the investigation of the metal-hydride transformation in magnesium (Mg) nanoparticles both as a function of particle size and in response to surface functionalization by clusters of transition metals (TM): Pd, Ni, Ti.Mg nanoparticles were synthesized by the inert-gas condensation technique, which yields single crystals with six-fold symmetry whose average size can be controlled by tuning the inert gas pressure. After the synthesis the nanoparticles were passivated by slow exposure to oxygen, obtaining a core-shell morphology where a metallic core is coated by a MgO shell of about 5 nm thickness.The material structure was investigated by Transmission Electron Microscopy (TEM), also in High Resolution (HRTEM) mode, and by X-Ray Diffraction (XRD). The sorption kinetics were analysed by a volumetric Sievert apparatus, which also allowed for a determination of the activation energies.Small nanoparticles (≈35 nm) display interesting kinetics with gravimetric capacity of 4.5 wt.% at saturation, limited by the oxide fraction. Hydride formation proceeds by one-dimensional growth controlled by diffusion through the hydride, while the reverse transformation to metal involves interface-controlled three-dimensional growth of nuclei formed at constant rate.On the contrary, large nanoparticles (≈450 nm) exhibit very low reactivity due to reduced probability of hydrogen dissociation/recombination and nucleation at the particle surface. For this reason, large nanoparticles were surface-decorated by TM through in situ evaporation in the inert-gas condensation chamber. This procedure results in clusters of 3-4 nm located over a portion of the MgO shell, as shown by XRD and HRTEM on Pd-decorated sample. This treatment results in dramatically improved hydrogen sorption behavior. In fact, previously inert nanoparticles now exhibit of up to 5.6 wt.%.Real-time diffraction studies using Synchrotron Radiation were carried out during hydrogen desorption on the Pd-decorated nanoparticles. We clearly show that a Mg-Pd intermetallic phase is formed after the first heating treatment and takes active part in the transformation.
Structure and Stability of Multivalent Metal Tetraborohydrides
Authors: Łodziana Zbigniew , Borgschulte Andreas , Germaud Robin , Remhof Arndt , Züttel Andreas 
Published: January 2010

AbstractMetal tetrahydroborates remain interesting materials as potential hydrogen storage media. In the present paper, we analyze thermodynamic stability of borohydrides of Al and Zr by means of extensive density functional calculations. We show that solid phases of these compounds are formed by dispersive Van der Waals forces. These compounds are thermodynamically unstable at room temperature with respect to decomposition to boron and hydrogen. Their stability is explained by formation of diborane as a necessary step in the decomposition path, pointing out to the kinetic factors that are important for the stability analysis of metal borohydrides.
Theoretical Study on N Doping in Carbon Materials for Hydrogen Storage
Authors: Kayanuma Megumi , Ikeshoji Tamio , Ogawa Hiroshi 
Published: January 2010

AbstractInteraction between nitrogen-substituted graphene-like compounds and hydrogen was investigated using ab initio molecular orbital method in the aspect of hydrogen storage. We adopted coronene as a model compound for fragmented graphene-like carbon materials and compared the interaction between hydrogen and pure or N-substituted coronenes by changing nitrogen positions. Among the assumed 19 N-substituted models, polarozabilities and HOMO–LUMO gaps were compared to evaluate physisorption and chemisorption energies. As for chemisorption, two N-substituted models were selected and closely examined to reveal the dependence on both nitrogen-substitution and hydrogen-adsorption positions. Potential energy surfaces as a function of H–H bond length and H2–coronen distance showed that the barrier height for hydrogen chemisorption strongly depends on N-substitution positions. The chemisorbed products of N-substituted coronenes are stabilized or destabilized compared with the pure carbon case depending on the sites of N-substitution and H-adsorption. These results suggest that N-substitution at certain positions possibly improve hydrogen storage properties of graphene-like materials.
Electrochemical Charge for the Formation of Metal Hydrides from LiH+M (M=Mg, Al)
Authors: Hanada Nobuko , kamura Akito , Suzuki Hiroshi , Ichikawa Takayuki , Kojima Yoshitsugu , Takai Kenichi 
Published: January 2010

AbstractFor a formation of metal hydride of MgH2 or AlH3 under room temperature and ambient pressure, the cathode electrodes of metal and lithium hydride are electrochemically charged with Li anode electrodes in the system of Li-ion extraction. For MgH2 formation, the VC (Voltage-Composition) curve of Mg + 2LiH during charge shows a plateau voltage at 0.6 V until the final composition of 1.05 Li extraction. After charge MgH2 phase is observed by the XRD measurement. Therefore MgH2 is produced by the electrochemical charge from Mg and LiH. For AlH3 formation, Al + 3LiH is charged until the final composition of 0.6 Li at a plateau voltage of 0.8 V which corresponds to the reaction between Al and LiH for the formation of AlH3. In the XRD profile after charge AlH3 phase is not detected although the intensities of Al and LiH decrease compared with these before charge, which suggests the reaction leading to the formation of AlH3.
Time and Frequency Resolved Hydrogen Dynamics in deuterated LiBH4
Authors: Gremaud Robin , Andresen Esben R. , Ramirez-Cuesta Anibal J. , Refson Keith , Łodziana Zbigniew , Züttel Andreas , Hamm Peter , Borgschulte Andreas 
Published: January 2010

AbstractWe study deuterated tetrahydroborate LiBH4in the low-temperature (LT) phase, focusing on the BH (BD) stretching vibrations, by infrared (IR) and IR-pump-probe spectroscopy. Calculated infrared spectra by density functional theory allow us to disentangle the contributions coming from all the coexisting BH4-nDn(n = 0…4) molecular units. We report on anharmonicity and vibrational lifetime (1.6 ps) of the BD vibrations, as well as on the BH2D2orientational relaxation by polarization anisotropy IR-pump-probe measurements. We find a constant anisotropy for at least 5 ps confirming the slow reorientational motion and low thermal disorder of the BH4 unit in the LT phase of this potential hydrogen storage material.
First-Principles Study on Hydrogen Atom Hopping in NaAlH4
Authors: Wang Hao , Tezuka Akinori , Ogawa Hiroshi , Ikeshoji Tamio 
Published: January 2010

AbstractHydrogen vacancy effect on the activation energy for self-diffusion is investigated by NEB method. The path was calculated by moving a hydrogen atom from a nearby complex into the vacancy in another complex. Compared with the substitution enthalpy of hydrogen vacancy, the activation energy for self-diffusion is easier to achieve during the dehydrogenation process.
Improvement in Power Density of Rechargeable Air Battery using Hydrogen Storage Alloy
Authors: Morimitsu Masatsugu , Kondo Takahito , Osada Naoki , Takano Koji 
Published: January 2010

AbstractA novel class of secondary battery comprising MH and air electrodes was developed for potential uses in high power density and high energy density applications such as electric or hybrid vehicles and power storage units supporting fuel cell and solar power systems. The air electrode consisted of nickel-based gas diffusion electrode using Ir2Bi2O7-zas oxygen evolution and reduction catalyst. Coin-type of cells using alkaline solutions as electrolyte were designed and fabricated, and the charge-discharge behaviors were evaluated with constant current operation. The discharge voltage and power density were improved by using a thin film membrane, in which the electrolyte was impregnated, between the air and MH electrodes, and the maximum power density was comparable to that of commercially available Ni-MH secondary battery. The MH utilization and the current efficiency of a charge-discharge cycle were found to be more than 90%.
New B,N-hydrides: Characterization and Chemistry
Authors: Anderson Paul , Chater Philip , David Bill , Evans Ian , Kersting Alexandra 
Published: January 2010

AbstractThree different classes of boron and nitrogen containing light metal complex hydrides have been investigated, resulting from the reactions of LiNH2 with LiBH4, NaNH2 with NaBH4 and MHx (where M = Li, Na and Ca) with NH3BH3. A rich variety of new phases has been identified, which exhibit modified decomposition pathways and onset temperatures of hydrogen desorption as low as 40°C. In each case the composition of phases formed has been examined in detail and the products of thermal decomposition—solid and gaseous—have been determined.
IR and XRD Amorphous Synthesis Residue Showing Zeolitic Micropores
Authors: Chiang Anthony S.T. , Fun Sewn-Yi , Wu Jan-Sen , Tsai Tseng-Chang 
Published: January 2010

AbstractIn the preparation of zeolite nanocrystals from the hydrothermal reaction of clear solution, the zeolite products are typically collected by high speed centrifugation. For Beta zeolite, the crystalline yield is often low, thus a good fraction of silicates reminds in the supernatant. These XRD amorphous materials turn out to be uniform nanoparticles that, after calcination, showed similar micropore structure as that of the collected beta zeolite nanocrystals. TPD measurements of hexane isomers further indicated that both the crystalline and the amorphous products were more selective toward the smaller hexane molecule.
Microfibrous Entrapped Catalysts for Low Temperature CO Oxidation
Authors: Punde Shirish S , Tatarchuk Bruce J 
Published: January 2010

AbstractLow temperature CO oxidation is characterized by slow reaction kinetics and CO self-poisoning of the catalyst, which compete with each other. A platinum catalyst with ceria as a promoter supported on a high surface area silica support has been developed. The catalyst has a significant activity for CO oxidation even in the presence of moisture. The catalyst showed a significant increase in activity with decreasing particle size (η<0.95, even at 100μm), indicating a clear transport limitation.In case of larger catalyst particles the diffusional resistances affect the reaction kinetics, leading to greater rates of CO self-poisoning causing deactivation of the catalysts. However, conventional packed bed of smaller particles poses problems such as high pressure drop, packing issues, bed channeling, flow maldistributions, and dead zones in the reactor bed, which result in poor inter-phase heat and mass transfer rates. Most of these problems are related to poor packaging of smaller particles, strongly suggesting the need for immobilization of small particles. A new class of micro-structured materials consisting of sorbents/catalysts entrapped in metal, ceramic, or polymer microfibers (MFES/MFEC) has been developed at Auburn University. These materials immobilize the small particles by sinter-locking them in fiber mesh. The immobilization of particles results in better heterogeneous contacting efficiency. Additional studies have shown that the high voidages and structural uniformity of the MFES lowered the flow maldistributions, eliminated the peaking flows between particles, and helped achieve better radial dispersion. Thus MFEC/MFES improved inter-phase transport rates.The Pt-CeO2/SiO2 catalyst entrapped in metal microfibers demonstrated a significant improvement in CO conversion compared to a conventional packed bed configuration while maintaining a lower pressure drop. Further catalyst entrapment in metal microfibers minimized cold spots in the reactor bed due to better intra-phase heat transfer rate. Higher effective thermal conductivity of MFEC improved the activity of the catalyst, which was particularly visible at high CO concentration wherein the CO inhibition kinetics takes over. For example, MFEC with 1/3 rd of catalyst loading as that of packed bed of same particle size, outperformed packed bed configuration.The catalysts were prepared by incipient wet impregnation. Surface characterization of catalysts was carried out using CO, H2, O2 chemisorption, O2 – H2 titration, N2 physisorption, powder XRD, and was correlated with catalytic activity.This microfibrous entrapped catalyst demonstrated a great potential for low temperature CO oxidation. These MFEC can be used in air purification, emergency escape products, and as a cathode air filter for PEM fuel cells.
Structural, Morphological and Photoelectrochemical Behavior of Hematite Modified by 120 MeV Ag9+ Ions
Authors: Singh Aadesh P. , Kumari Saroj , Shrivastav Rohit , Dass Sahab , Satsangi Vibha R. 
Published: January 2010

AbstractNanostructured hematite thin film for photoelectrochemical (PEC) splitting of water has great potential in the design of low-cost, environmental friendly solar-hydrogen production. Presently, solar-to-hydrogen conversion efficiency of PEC cell using iron oxide is limited by its poor charge transport due to high recombination losses and mismatch of band edges position with the redox level of water. High energy heavy ion irradiation provides the researchers a new dimension to introduce the desired changes in the behaviour of the material, which largely influence their properties. In order to get efficient PEC system, spray-pyrolytically deposited nanostructured hematite thin films were modified by irradiating the samples with 120 MeV Ag9+ ions with fluences ranging from 5×1011 to 1×1013 ions/cm2. Irradiated samples exhibited a partial transition from the hematite to the magnetite phase and reduction in particle size as indicated by XRD and Raman analysis. SEM picture showed a decrease the thickness and porosity of the films after irradiation. These irradiated films, when used in PEC cell showed significantly higher photocurrent density than unirradiated α-Fe2O3.