bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and characterization of InAs quantum dots on GaAs (100) emitting at 1.31μm.
Authors: Celibert V. , Salem B. , Guillot G. , Bru-Chevallier C. , Grenouillet L. , Duvaut P. , Gilet P. , Million A. 
Published: April 2011

ABSTRACTSelf-organized InAs quantum dots (QDs) were grown in the Stranski-Krastanov regime, by gas-source molecular beam epitaxy (GSMBE), on (100) GaAs substrates. Two important parameters have been optimized in order to grow high quality QDs with a very good reproducibility: InAs growth rate and GaAs cap layer deposition rate. Atomic force microscopy (AFM) analysis shows a unimodal QD distribution and the room temperature photoluminescence (RTPL) spectrum of the optimized sample reveals a 1.3 μm emission with a 19 meV full width at half maximum (FWHM). Photoluminescence (PL) measurements versus excitation power density and photoluminescence excitation (PLE) measurements clearly show multi-component PL emission from transitions associated with fundamental and related excited states of QDs. Furthermore a good growth reproducibility is observed. The results are promising for further work which will lead to laser fabrication.
Optical Properties of Bulk and Epitaxial ZnO for Waveguide Applications
Authors: Ganesan S. , Feng Z. C. , Mehta D. , Kandoor S. , Wornyo E. J. , Nause J. , Ferguson I. 
Published: April 2011

ABSTRACTThis paper investigates the optical properties of bulk and epitaxial ZnO layers. High quality undoped and doped bulk ZnO crystals have been produced by melt growth techniques in addition to ZnO thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on silicon, sapphire and the bulk ZnO substrates. This work focuses on investigating the suitability of bulk and epitaxial ZnO for waveguide applications using various spectroscopic techniques. The photoluminescence showed the dominance of strong and narrow band due to the band edge emissions for undoped ZnO. Ultraviolet-visible transmission data revealed the variation of the bandgap with different doping elements. Raman spectra showed a narrow and strong peak, corresponding to the E2 mode at 438 cm-1, characteristic of the ZnO crystallinity. A broad 2LO peak appeared near 1150 cm-1 due to the coupling between LO phonons and free carriers. A clear variation in refractive index with doping was observed by spectroscopic ellipsometery suggesting that ZnO could be used for waveguide applications.
Spin-Dependent Optical Processes in II-VI Diluted Magnetic Semiconductor Nanostructures
Authors: Oka Yasuo , Kayanuma Kentaro , Sakuma Mio , Uetake Ayahito , Souma Izuru , Chen Zhanghai , Murayama Akihiro 
Published: April 2011

ABSTRACTNanostructures of diluted magnetic semiconductors have potential possibility for the spin electronics application due to their large magneto-optical effects and the quantum confinement effects for band electrons. We have fabricated quantum wells and quantum dots by II-VI diluted magnetic semiconductors of Cd1-xMnxTe, Zn1-xMnxTe and Zn1-x-yCdyMnxSe. These nanostructures showed spin injection, spin switching and ultrafast spin relaxation processes derived in the confined nanostructures. Hybrid structures consisting of diluted magnetic semiconductor and Co showed Mn spin polarizations induced by the Co wire shape.
Mixing Rocksalt and Wurtzite Structure Binary Nitrides to Form Novel Ternary Alloys: ScGaN and MnGaN
Authors: Constantin Costel , Al-Brithen Hamad , Haider Muhammad B. , Ingram David , Smith Arthur R. 
Published: April 2011

ABSTRACTCombination of tetrahedral and octahedral based nitrides are explored. The two cases of MnGaN and ScGaN with low Mn and Sc fractions are examined. It is found that for the MnGaN case, the Mn is incorporated under N rich conditions with little lattice change. However, for the ScGaN case, the Sc is incorporated onto the Ga sites but with a local bond angle distortion.
Nanostructured Energetic Materials with Sol-gel Methods
Authors: Gash Alexander E. , Satcher Joe H. , Simpson Randall L. , Clapsaddle Brady J. 
Published: April 2011

AbstractThe utilization of sol-gel chemical methodology to prepare nanostructured energetic materials as well as the concepts of nanoenergetics is described. The preparation and characterization of two totally different compositions is detailed. In one example, nanostructured aerogel and xerogel composites of sol-gel iron (III) oxide and ultra fine grained aluminum (UFG Al) are prepared, characterized, and compared to a conventional micron-sized Fe2O3/Al thermite. The exquisite degree of mixing and intimate nanostructuring of this material is illustrated using transmission and scanning electron microscopies (TEM and SEM). The nanocomposite material has markedly different energy release (burn rate) and thermal properties compared to the conventional composite, results of which will be discussed. Small-scale safety characterization was performed on the nanostructured thermite. The second nanostructured energetic material consists of a nanostructured hydrocarbon resin fuel network with fine ammonium perchlorate (NH4ClO4) oxidizer present.
The Catalytic Effect on Vertically Aligned Carbon Nanotubes
Authors: Kim Nam Seo , Bae Seung Yong , Park Jeunghee 
Published: April 2011

ABSTRACTWe report the catalytic effect on the synthesis of multiwalled carbon nanotubes (CNTs). The CNTs were grown vertically aligned on the iron (Fe), cobalt (Co), and nickel (Ni) catalytic nanoparticles deposited on alumina substrates by thermal chemical vapor deposition (CVD) of acetylene in the temperature range 900–1000 °C. We also synthesized them on the silicon oxide substrates by pyrolyzing iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), and nickel phthalocyanine (NiPc) at 700–1000 °C. In both syntheses, the CNTs grown using Fe exhibit about 2 times higher growth rate than those using Co and Ni. As the temperature rises from 700 to 1000 °C, the growth rate of CNTs increases by a factor of 45. The Arrhenius plot of growth rates provides the activation energy 30 ± 3 kcal/mol for all three catalysts, which is similar with the diffusion energy of carbon in bulk metal. It suggests that the bulk diffusion of carbon would play a decisive role in the growth of CNTs. The diameter of CNTs is in the range of 20–100 nm, showing an increase with the temperature. As the diameter is below 30 nm, the CNTs usually exhibit a cylindrical structure. The CNTs were intrinsically doped with the nitrogen content 2–6 atomic%. The degree of crystalline perfection of the graphitic sheets increases with the temperature, but depends on the catalyst and the nitrogen content. The graphitic sheets of CNTs grown using Fe are better crystalline than those grown using Co and Ni. As the nitrogen content increases, the degree of crystalline perfection decreases and the structure becomes the bamboolike structure probably due to a release of strains.
Ignition and Combustion Behaviors of Nanocomposite Al/MoO3
Authors: Granier John J. , Pantoya Michelle L. 
Published: April 2011

ABSTRACTFlame propagation in Al/MoO3 thermites is measured as a function of bulk density and initial sample temperature. The composites are composed of nano-scale reactant particles mixed and pressure molded to between 49 and 73% of the theoretical maximum density. A relationship between cylindrical die pressure and final pellet density is derived. Experiments are also performed by initially pre-heating samples to a uniform temperature ranging from 20 to 200 °C. Ignition sensitivity was determined by measuring the ignition delay time and temperature using a 50-W CO2 laser and thermocouples, respectively. Combustion wave speeds were measured using high-speed imaging diagnostics. Results allow comparison of combustion behaviors associated with nano- vs. micron-scale particle composites. The nano-scale particle composites are extremely sensitive to ignition, especially when initially preheated. Combustion wave speeds for the compressed nano-composites were found to double when compared to the micron-scale composites.
Underwater Explosive Behaviour of Compositions Containing Nanometric Aluminium Powder
Authors: Bates Leslie R 
Published: April 2011

ABSTRACTResults from research aimed towards the understanding of the effect that ultrafine aluminium powder has on the explosive performance of underwater explosives are presented. A series of aluminised explosive compositions using a commercially available nanometric aluminium powder (Alex) have been prepared and quantified underwater. The results have been compared with the corresponding compositions using conventional aluminium powders. An enhancement in explosive properties can be seen. The effect is not universal but can be related to the reaction zone length, and time, of the base explosive being sufficiently long for the oxidation of the aluminium, with its substantial energy release, to take place in or close to the reaction zone.
Design of High-Energetic Materials at the Nanoscale
Authors: Rao Bijan K. , Jena Purusottam 
Published: April 2011

ABSTRACTThe amount of energy storage and its release in controllable pathways are two of the fundamental requirements of a high-energy material. The novel chemistry brought about by large surface-to-volume ratio of nanomaterials provides an attractive way to design and synthesize materials that optimize these two requirements. First principles calculations based on density functional theory and generalized gradient approximation have been used to study the potential of AlxLiyOz and Al(MnO4)x clusters as candidates for high-energetic materials. The equilibrium geometries and total energies of these clusters and their fragments are obtained to study the energy stored in these clusters and its release along various pathways. Interesting results include the substantial increase in binding energy by either adding an Al to MnO4 or adding a MnO4 to Al(MnO4)x unit indicating that Al(MnO4)3 may be a potential candidate for energetic materials as well as super-oxidizers. Similar calculations also show that during the combustion of Al addition of small amounts of Li to Al nano-powder helps to reduce the amount of non-combustible Al.
Molecular Dynamics Studies of Nanoparticles of Energetic Materials
Authors: Alavi Saman , Velardez Gustavo F. , Thompson Donald L. 
Published: April 2011

ABSTRACTThe structural properties of several nanoparticles of 2,4,6,8,10,12-hexanitrohexaazaiso-wurtzitane, HNIW or CL-20, are studied by using molecular dynamics simulations. The internal structure of the CL-20 molecule is held rigid and the intermolecular interactions in the nanoparticles are taken from a previously developed force field. [Sorescu et al., J. Phys. Chem. B, 102, 948 (1998)] Molecular dynamics simulations of solid-like and annealed nanoparticles with 48 and 88 CL-20 molecules have been carried out in the solid-state range of temperatures from 50 to 500 K. The center-of-mass to center-of-mass radial distribution functions, dipole-dipole correlation function, the orientations of the surface dipoles, and the density of the nanoparticles were calculated at fixed temperatures for the nanoparticles.
High-Resolution TEM Characterization of Carbon Aerogels as Catalyst Supports
Authors: Kang Dafei , Zhang Ying , Saquing Carl , Erkey Can , Aindow Mark 
Published: April 2011

ABSTRACTCarbon aerogels with tailored pore sizes were prepared by using a combination of sol-gel processing, supercritical CO2 extraction and pyrolysis. Ruthenium particles were incorporated via impregnation of organometallic precursors using supercritical CO2, followed by in situ thermal reduction. TEM studies reveal that the carbon aerogels are characterized by a continuous pore structure and that the ruthenium particles are highly dispersed with a narrow size distribution. It is found that under certain circumstances the carbon aerogels undergo a structural transition under the electron beam, in which the original tortuous aerogel network transforms into onion-like structures.
Nanofibrous Manganese Dioxide for Decomposition of Volatile Organic Compounds
Authors: Chen H. , Xiao T. D. , Liu S. 
Published: April 2011

AbstractVolatile organic compounds (“VOCs”) are widely used in industrial process, transportation fuels, and households. It is inevitable that some VOCs will escape into the atmosphere. Emission of VOCs will cause three major problems, including (1) increased exposure level of the population to know carcinogenic compounds such as benzene and carbon tetrachloride, (2) increased ozone concentration in the atmosphere at ground level, and (3) stratospheric depletion of the ozone layer, which alters global climate and increases exposure to UV radiation. Reducing the concentrations of VOCs will greatly improve air quality. A common method for VOC removal is catalytic decomposition. Most works have only focus on reducing VOC concentrations down to a few parts per million (ppm). Very little research has been conducted on reducing the VOCs down to parts per billion (ppb) levels, or less. This paper reports the decomposition of VOCs using a unique class of nanofibrous bird's-nest superstructure material. This open-inter-woven nanofibrous superstructure provides superb host for catalytic reactions and permits relatively easy flow of the gas stream through the structure. The nanofibrous MnO2 is highly effective in destroy more than 50 VOCs on USEPA's top priority list toxic VOCs to ppb level or less at a 200 − 350°C temperature.
Hydriding Behaviour of Mg-C Nanocomposites
Authors: Bassetti A. , Bonetti E. , Fiorini A. L. , Grbovic J. , Montone A. , Pasquini L. , Antisari M. Vittori 
Published: April 2011

ABSTRACTMagnesium carbon nanocomposites for hydrogen storage have been synthesized by ball milling with different amount of benzene, acting as a lubricant. Their microstructure has been studied by X-ray diffraction and scanning electron microscopy, while the hydrogen desorption temperature has been tested by differential scanning calorimetry. Experimental results show that the microstructure after milling, the hydrogenation capabilities of the material and the reactivity with the air are related to the amount of additives. In particular the carbon to benzene ratio seems to play a major role. In fact, with an optimum value of carbon to benzene weight ratio of 1/6, the amount of carbon being 15 wt% of the milled mixture, a decomposition heat equal to 57% of pure MgH2 was measured, even after air manipulation of the sample.
Hydrogenation of nanocrystalline Mg-based alloys
Authors: Zander Daniela , Lyubenova Lyudmilla , Köster Uwe , Klassen Thomas , Dornheim Martin 
Published: April 2011

ABSTRACTDesirable properties of hydrogen storage in materials include mainly, high hydrogen capacity, high number of hydride / dehydride cycles, low temperature of dissociation and microstructural stability. Hydrogen storage can proceed from the gas phase as well as during cathodic charging.The use of nanocrystalline Mg powder without and with 2 mol% Nb2O5 catalyst as an electrode material for electrochemical hydrogen charging processes in a 6M KOH electrolyte was studied. A strong influence of the compaction parameters and the current density but no influence of the catalyst on the hydrogenation behavior was observed. However, a strong influence of the catalyst on the hydrogen overpotential was observed and is assumed to result into a change of the electrochemical surface reaction. The addition of graphite and PTFE to the Mg/Nb2O5electrodes improves the charging kinetic as well as the hydrogen content up to 1 wt.% hydrogen.
ab-initio modelling of Mg:H interstitial solid solutions
Authors: Messina M. , Cleri F. , Volpe M. 
Published: April 2011

ABSTRACTWe studied the thermodynamics of interstitial Mg:H solid solutions by means of ab-initio electronic structure calculations. Soft pseudopotentials (Troullier-Martins) with non linear core correction and Perdew-Burke-Ernzerhof GGA exchange-correlation functional were employed, in the framework of a DFT plane-wave scheme. We inserted increasing concentrations of interstitial H atoms in the hcp Mg lattice, in both tetrahedral and octahedral positions. We calculated the heat of solution and the volume variation as a function of H concentration. Although the difference in Gibbs free energy is positive at any H concentration above 10−6 at.%, our results show that the enthalpic contribution is negative at any H concentration, therefore locally favouring H clustering. This reflects the existence of a driving force for the subsequent formation of the hydride. The volume deformation was characterized, finding that octahedreal interstitials have a minor effect, while tetrahedral interstitial can induce very large local expansion.
Hydrogen Storage using Carbon Materials at Room Temperature
Authors: Kajiura H. , Tsutsui S. , Kadono K. , Murakami Y. , Kakuta M. , Ata M. 
Published: April 2011

ABSTRACTThe hydrogen adsorption capacity of commercially available carbon materials with different nanostructures was measured at room temperature using an apparatus based on a volumetric method with an error of less than 0.04 wt% per one gram of sample. The obtained results suggest that nanosutures of the sample influence the hydrogen adsorption capacity. To confirm this hypothesis, we prepared nanostructured graphite from graphite powder using a mechanical milling process at a pressure of 2.0 × 10−4 Pa. The untreated graphite adsorbed 0.02wt% of hydrogen at 6 MPa at room temperature, while 0.20 − 0.25 wt% of hydrogen can be repeatedly adsorbed by the nanostructured graphite. Measurements of the hydrogen adsorption rate at constant pressure and pore-size distribution imply that the hydrogen molecules are adsorbed through a diffusion process in pores with a diameter less than 1 nm.
The Electrical Characteristics of a Pd/AlN/Si Thin Film Hydrogen Gas Sensor
Authors: McCullen Erik F. , Prakasam Haripriya E. , Mo Wenjun , Thakur Jagdish , Naik Ratna , Rimai Lajos , Ng K.Y.S. , Auner Gregory W. 
Published: April 2011

ABSTRACTWe have extended our previous investigation of the electrical characteristics of a Pd/AlN/Si thin film sensor for varying thicknesses of AlN, from 300–2000Å. The capacitance vs. voltage, C(V), and conductance vs. voltage, G(V), measurements were utilized to investigate the presence of surface states within the Si gap at the AlN/Si interface. Our previous experiments on 500Å AlN did show the presence of interface traps, with an estimated surface density between 8×1014 and 1.5×1015 m−2eV−1 [1]. In our present work we've examined the effect of AlN thickness on the density of these interface traps. The density is dependent on AlN thickness. The thinner devices, 300Å, showed an interface trap density of 20–30×1015 m−2eV−1. The interface trap density decreased with increasing thickness up to 500Å, where the density remained relatively constant at about 1–5×1015 m−2eV−1 for thicknesses up to 2000Å. We have also shown that the interface trap density is independent of annealing.
Studies on the perovskite-based La4Srn−4TinO3n+2
Authors: Canales-Vázquez Jesús , Tao Shawen , Patrakeev Mikhail , Irvine John T. S. , Zhou Wuzong , Frade Jorge 
Published: April 2011

AbstractPerovskite titanates with nominal stoichiometry ABO3+Δ are frequently reported in SOFC literature as having O3 stoichiometry. Such phases often exhibit quite interesting properties, but are not stoichiometric and the structural characterisation is usually not rigorous. Here we demonstrate how oxygen excess can be incorporated in a titanate perovskite-based lattice as crystallographic oxygen shears giving rise to the homologous series La4Srn−4TinO3n+2. The layered structure is lost for the n=12 member (La4Sr8Ti12O38−Δ), although the oxygen excess is accommodated within the perovskite framework in randomly distributed short-range linear defects. This compound was studied as potential fuel electrode due to its high total conductivity and stability in the most reducing conditions.
The importance of high temperature electron-phonon coupling to the thermodynamic properties of Ce0.9Th0.1 and other f-electron bonded metals
Authors: Manley M. E. , McQueeney R. J. , Fultz B. , Swan-Wood T. , Delaire O. , Goremychkin E. A. , Cooley J. C. , Hults W. L. , Lashley J. C. , Osborn R. , Smith J. L. 
Published: April 2011

ABSTRACTRecent results from inelastic neutron scattering studies on Ce0.9Th0.1 are used to demonstrate the importance of electron-phonon coupling to the physical properties of f-electron bonded metals. In the case of Ce0.9Th0.1, the phonon density of states (DOS) of α-phase shows a significant softening when heated but shows no change across the α-γ transition despite the 11% volume change. This is supported by analysis of the magnetic spectra showing that most of the transition entropy can be accounted for with the crystal field and spin fluctuations. The precursor phonon softening, the lack of any phonon change across the transition, the magnetic spectra, and the volume transition itself can all be explained in terms of the atomic displacement sensitivity of the hybridization of the local f-electrons with conduction electrons. The electron-phonon coupling resulting from these displacement-sensitive electronic states appears to be essential to understanding cerium. Some of the behavior characteristic of these states, a large volume changes and precursor phonon softening, occurs in many other f-electron bonded metals suggesting that the phenomena is not unique to cerium.
Study of Actinides Incorporation in Thorium Phosphate-Diphosphate/Monazite Based Ceramics
Authors: Clavier Nicolas , Dacheux Nicolas , Podor Renaud , Le Coustumer Philippe 
Published: April 2011

ABSTRACTPhosphate materials are usually considered as potential candidates to perform the immobilization of actinides coming from an advanced reprocessing of spent fuel in the field of an underground repository. Among them, Thorium Phosphate-Diphosphate (TPD) and monazites have been already extensively studied. The elaboration of TPD/monazite based materials was thus envisaged in order to immobilize simultaneously tri- and tetravalent actinides and a neutron absorber. Two chemical ways of synthesis were considered and the compounds were easily prepared in the powder and in the pellet form. A good chemical compatibility was found between TPD and monazite since the properties of both phosphates were kept in these composites. Moreover, the relative density of the pellets reached 90 – 95 % of the value calculated from XRD data. The normalized dissolution rates determined in acidic media did not exceed 5.10−4 g.m−2.day−1 which confirmed the very good durability of such materials during leaching tests.
On the Physical Nature of Uranyl Charge Transfer Vibronic Interactions
Authors: Chen X. Y. , Rao L. F. , Liu G. K. 
Published: April 2011

ABSTRACTWe address the electronic properties of uranyl ions in solids and solutions with an emphasis in theoretical understanding of charge transfer vibronic transitions and luminescence dynamics the O-U-O species. A general theory of ion-phonon interaction has been modified for modeling and simulating multi-phonon vibronic spectra. Spectroscopic data for uranyl ions in crystals and solutions have been analyzed to achieve a predictive understanding of the uranyl-ligand vibronic interactions. By adjusting the Huang-Rhys ion-phonon interaction parameters, an excellent agreement between theory and experiment has been accomplished for uranyl ions in the ligand environments we studied. Our modeling and simulation provide insights into the physical nature of uranyl vibronic interaction and its influence on spectroscopic properties, which are commonly utilized in characterizing photochemical properties of uranyl in complexes.