bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pump Wavelength Tuning of Optical Pumping Injection Cavity Lasers for Enhancing Mid-Infrared Operation
Authors: McAlpine Todd C. , Greene Katherine R. , Santilli Michael R. , Olafsen Linda J. , Bewley William W. , Felix Christopher L. , Vurgaftman Igor , Meyer Jerry R. , Yang M. J. , Lee Hao , Martinelli Ramon U. 
Published: April 2011

ABSTRACTRecent efforts to improve the performance of mid-infrared antimonide-based semiconductor lasers have focused on enhancing the absorption of the pump beam to maximize power conversion efficiencies and minimize threshold intensities. One successful approach has been the optical pumping injection cavity (OPIC) laser, in which a type-II W active region is enclosed between distributed Bragg reflector (DBR) mirrors in order to achieve multiple passes of the pump beam and thereby to enhance absorption.Previously, fixed wavelength sources have been used for optical pumping of OPIC laser structures, with limited tuning available by adjusting the incident angle. By tuning the pump wavelength using an optical parametric oscillator, we demonstrate minimum threshold intensities and maximum slope efficiencies at the resonance of the DBR cavity surrounding the active region, further demonstrating the potential of OPIC lasers. A 3.2 μm OPIC laser operated at 350 K in pulsed mode (at the highest operating temperature of the dewar), with a characteristic temperature of 50 K. The power conversion efficiency for a single facet at 300 K was the highest ever observed in the mid-IR, at approximately 4%.Results are presented for two OPIC samples (emitting at ∼3.2 μm and 4.3 μm at high temperature), one of which was designed with a broadened cavity resonance, suitable for pumping with a multi-mode source. Threshold intensities and slope efficiencies measured as a function of pump wavelength demonstrate the strong resonance effect, and that the “broadened OPIC” does in fact manifest a much wider resonance than the non-broadened resonance cavity design.
Elevated Temperature Characteristics of Carbon-Doped GaInP/GaAs Heterojunction Bipolar Transistor Grown by Solid Source Molecular Beam Epitaxy
Authors: Rong Zhang , Fatt Yoon Soon , Kianhua Tan , Zhongzhe Sun , Qingfeng Huang 
Published: April 2011

ABSTRACTThis paper reports the characteristics of GaInP/GaAs heterojunction bipolar transistor (HBT) with carbon-doped GaAs base layer grown by solid source molecular beam epitaxy (SSMBE) using carbon tetrabromide (CBr4) as p-type dopant precursor. Hydrofluoric acid (HF) was used to passivate the GaInP/GaAs HBTs. At base bias voltages below 0.8V in the Gummel plot, the base current of large-area devices after HF treatment was greatly reduced. This indicates that the extrinsic base surface recombination current was greatly reduced. After HF treatment, detailed DC characterization of the device performance from 300K to 380K was carried out and the carrier transport properties were investigated. The base current and collector current ideality factors at 300K were 1.12 and 1.01, respectively. This indicates that the space- charge region recombination current in the base is insignificant. From the temperature- dependent Gummel plot, the activation energies of collector current and base current were obtained. For the collector current, the activation energy is 1.4eV, which is close to the bandgap of the GaAs base. This indicates that the collector current is determined by the drift-diffusion process, in which an energy barrier of the same magnitude as the base bandgap is to be overcome by electrons before they reach the collector. For the base current, the activation energy is also 1.4eV, which is close to the bandgap of GaAs, indicating that band-to-band recombination plays a dominant role in the base current. No trap-related recombination was observed for the base and collector currents, which further indicates the high quality carbon-doped GaAs base material for the HBT structures.
Analysis of Photoluminescence Efficiency of Annealed GaInNAs Quantum Well Grown by Solid Source Molecular Beam Epitaxy
Authors: Khee Ng Tien , Fatt Yoon Soon , Weijun Fan 
Published: April 2011

ABSTRACTThe carrier dynamics of a 7.5 nm GaInNAs quantum well (QW) are studied by photoluminescence (PL) at a low temperature regime of 4 K to 150 K. The PL emission efficiency of the QW is initially evaluated to examine the recombination mechanisms in the QW. A dual-activation-energy model is later found to fit the integrated PL intensity vs. temperature curve better than a single-activation-energy model. The two states that correspond to the above activation energies could have resulted in a much faster PL intensity quenching in the GaInNAs QW as compared to that of a reference GaInAs QW. One of the states is identified as a localized state that traps carriers at a low temperature range of less than ∼100 K. The other state has a larger quenching effect at temperatures higher than 100 K and this state is not studied in this paper. By fitting the original PL spectra with two Gaussian functions, the temperature dependent PL integrated intensity of both Gaussian functions was also studied to further characterize the GaInNAs QW. The analysis gives evidence of the localization behaviour in this QW.
Electrostatic Force Microscopy and Secondary Electron Imaging of Double Stacking Faults in Heavilyn-type 4H-SiC after Oxidation
Authors: Mikhov M. K. , Skromme B. J. , Wang R. , Li C. , Bhat I. 
Published: April 2011

ABSTRACTThermal processing or oxidation of 4H-SiC withn-type doping above about 3×1019cm-3is known to produce double Shockley stacking faults spontaneously. The resulting region of 3C stacking order acts like a quantum well in the 4H matrix and becomes negatively charged due to modulation doping. Some of these quantum well regions penetrate into the lightly-doped epilayers and intersect the wafer surface as straight lines, due to the 8° misorientation of the wafer from thec-axis. These intersections appear as bright lines in secondary electron images, which we tentatively attribute to increased secondary electron yield due to repulsion of secondary electrons from the negative charge in the quantum wells. Electrostatic force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) also produce clear images of the quantum well intersections, independent of surface topography. These images are similar to the SEM images.
1.5 micron InAs quantum dot lasers based on metamorphic InGaAs/GaAsheterostructures.
Authors: Ustinov V. M. , Zhukov A. E. , Kovsh A. R. , Maleev N. A. , Mikhrin S. S. , Vasil'ev A. P. , Nikitina E. V. , Semenova E. S. , Kryzhanovskaya N. V. , Musikhin Yu. G. , Shernyakov Yu. M. , Maximov M. V. , Ledentsov N. N. , Bimberg D. , Alferov Zh.I. 
Published: April 2011

ABSTRACT1.5 micron range emission has been realized using the InAs quantum dots embedded into the metamorphic InGaAs layer containing 20% of InAs grown by MBE on a GaAs substrate. Growth regimes were optimized to reduce significantly the density of dislocations propagating into the active layer from the lattice mismatched interface. 2 mm long InGaAs/InGaAlAs lasers with 10 planes of quantum dots in the active region showed threshold current density about 1.4 kA/cm2 with the external differential efficiency as high as 38%. Lasing wavelength depends on the optical loss being in the 1.44–1.49 micron range at room temperature. On increasing the temperature the wavelength reaches 1.515 micron at 85C while the threshold current characteristic temperature of 55–60K was estimated. High internal quantum efficiency (η>60%) and low internal losses (α=3–4 cm-1 ) were realized. Maximum room temperature output power in pulsed regime as high as 5.5 W for 100 micron wide stripe was demonstrated. Using the same concept 1.3 micron InGaAs/InGaAlAs quantum well lasers were fabricated. The active region contained quantum wells with high (∼40%) indium content which was possible due to the intermediate InGaAs strain relaxation layer. 1 mm stripe lasers showed room temperature threshold current densities about 3.3 kA/cm2 (λ=1.29 micron) and 400 A/cm2 at 85K. Thus, the use of metamorphic InGaAs layers on GaAs substrate is a very promising approach for increasing the emission wavelength of GaAs based lasers.
Characterization of bulk crystals of transition metal doped ZnO for spintronic applications
Authors: Kane M. H. , Varatharajan R. , Feng Z. C. , Kandoor S. , Nause J. , Summers C. , Ferguson I. T. 
Published: April 2011

ABSTRACTIn this work, we report on the material properties of ZnO doped with Mn, Co, and Fe grown by a modified melt growth technique. X-ray diffraction measurements show that transition metals can be incorporated on Zn sites; an increase in the lattice parameter is apparent with increasing doping level. UV-visible transmission and reflectance measurements have also been performed. Absorption bands in the visible regime are distinctive to the individual transition metal dopants. A noticeable shift in the optical band edge has been observed from these Mn/Co/Fe-doped ZnO crystals in comparison with the undoped material. ZnO may also provide a suitable platform for the incorporation of transition metal elements through high temperature near equilibrium growth processes; however, further work is required in order to employ these materials for spintronic applications.
Synthesis and Characterization of Nanocrystalline Oxidizer/Monopropellant Formulations
Authors: Brill Thomas B. , Tappan Bryce C. , Li Jun 
Published: April 2011

ABSTRACTThe objective of this work is to try to create new behaviors of energetic materials by using sol-gel processing and freeze drying to incorporate the energetic material into the fuel matrix at the nano particle size scale. Hydrazinium diperchlorate ([N2H6][ClO4]2) and resorcinol-formaldehyde were chosen in one example, and CL-20 and nitrocellulose were chosen in another. High solids loadings were achieved by the cryogel method. Characterization was carried out by elemental analysis, SEM, TEM, AFM, T-jump/FTIR spectroscopy, DSC, and drop-weight impact testing. The nanoscale formulations do indeed exhibit several different behaviors, such as enhanced burning characteristics and unusual morphologies, and appear to be a promising direction to pursue.
Surface Passivation of Bare Aluminum Nanoparticles using Perfluoroalkyl Carboxylic Acids
Authors: Jouet R. Jason , Warren Andrea D. , Rosenberg David M. , Bellitto Victor J. 
Published: April 2011

AbstractSurface passivation of unpassivated Al nanoparticles has been realized using self assembled monolayers (SAMs). Nanoscale Al particles were prepared in solution by catalytic decomposition of H3Al•NMe3 or H3Al•N(Me)Pyr by Ti(OiPr)4 and coated in situ using a perfluoroalkyl carboxylic acid SAM. Because the Al particles are prepared using wet chemistry techniques and coated in solution, they are free of oxygen passivation. This SAM coating passivates the aluminum and seems to prevent the oxidation of the particles in air and renders the composite material, to some extent, soluble in polar organic solvents such as diethyl ether. Characterization data including SEM, TEM, TGA, and ATR-FTIR of prepared materials is presented.
Preparation of Energetic Metastable Nano-Composite Materials by Arrested Reactive Milling
Authors: Schoenitz M. , Ward T. , Dreizin E. L. 
Published: April 2011

ABSTRACTHighly metastable, nano-scale energetic materials were prepared by Arrested Reactive Milling (ARM). When reactive milling is carried out with materials systems suitable for Self-Propagating High Temperature Synthesis (SHS), reaction between the components occurs spontaneously and violently after a certain period of milling. In this research, metastable nanocom-posites with high energy density, were prepared by arresting the milling process prior to the spontaneous reaction. Products thus obtained are powders with particle sizes in the 10–50 μm range. Individual particles are intimate mixtures of reactive components, comparable to Metast-able Intermolecular Composites (MIC), with near theoretical maximum density. The time of arrest determines the degree of grain refinement and therefore the sensitivity to mechanical, electrical, or thermal initiation. Particle sizes of the product powders can be adjusted by appropriate choice of milling parameters. This paper describes the application of ARM to the material systems Al-Fe2O3 and Al-MoO3. After empirical determination of optimum milling parameters, the reactive composites are structurally characterized by electron microscopy and x-ray diffraction. First results of combustion tests are presented.
Ultrafast spectroscopy of laser-initiated nanoenergetic materials
Authors: Yang Yanqiang , Sun Zhaoyong , Wang Shufeng , Hambir Selezion A. , Yu Hyunung , Dlott Dana D. 
Published: April 2011

ABSTRACTA picosecond laser flash-heating technique is combined with ultrafast spectroscopic probe diagnostics to investigate the fundamental mechanisms of nanoenergetic material performance. The systems studied include Al nanoparticle aggregates in nitrocellulose (NC) oxidizer, size-selected Al nanoparticles in NC and in Teflon oxidizers, and nanoparticle thermites consisting of 30 nm Al and nanometric MoO3. The time-dependence of reactions between Al and the oxidizer on the picosecond to nanosecond time scales are studied using coherent anti-Stokes Raman scattering (CARS) to monitor oxidizer consumption. The time-dependence of energy release is measured using fast optical spectroscopy. The space-dependence of chemical reaction propagation over 100 to 1500 nm distances is studied using the average distance between nanoparticles as a ruler. The distance of reaction propagation from a flash-heated Al nanoparticle increases linearly with energy, which is explained by a hydrodynamic model.
The Shock Initiation and High Strain Rate Mechanical Characterization of Ultrafine Energetic Powders and Compositions
Authors: Field J. E. , Walley S. M. , Proud W. G. , Balzer J. E. , Gifford M. J. , Grantham S. G. , Greenaway M. W. , Siviour C. R. 
Published: April 2011

ABSTRACTThis paper reviews the techniques that have been developed at the Cavendish Laboratory for the study of the mechanical and ignition properties of energetic materials.
Hydrogen Diffusion in Zr-Cu-Ni-Al Metallic Glasses
Authors: Apih Tomaz , Jastrow Lioba , Lyubenova Lyudmila , Dolinšek Janez , Zander Daniela , Köster Uwe 
Published: April 2011

AbstractZr-based metallic glasses are known to absorb high amounts of hydrogen, but exhibiting less severe embrittlement than their crystalline counterparts; therefore, they might be useful for hydrogen storage application. In order to understand kinetics of hydrogen absorption and desorption in more detail, data on hydrogen diffusion are necessary. The aim of this paper is to present hydrogen diffusivities in melt-spun amorphous Zr69.5Cu12Ni11Al7.5 alloys.Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. Hydrogen contents were measured by a microbalance with accuracy of ±1 μg as well as by LECO. Diffusivities of hydrogen atoms were measured at different temperatures by the technique of Nuclear Magnetic Resonance (NMR) diffusion in a static fringe field of a superconducting magnet. The diffusion of hydrogen nuclei in an inhomogeneous magnetic field is accompanied by the change of its NMR resonance frequency, which produces motional destruction of the spin echo signal. The analysis of the echo damping allows a model-independent determination of the hydrogen self-diffusion constant, with the low limit of sensitivity D>10−10 cm2/s.Within the temperature interval between room temperature and 420 K diffusivities in the range between 4×10−8 and 1.2×10−9 cm2/s were observed. The Arrhenius-type temperature dependence indicate a simple classical over-barrier-hopping hydrogen diffusion; the activation energy increases slightly with the hydrogen content. Whereas in a number of metallic glasses hydrogen diffusion is known to increase with the hydrogen content, in Zr69.5Ni12Cu11Al7.5 the opposite effect was observed, at least for hydrogen contents between H/M = 0.2 and 1.2. The results will be compared with other measurements known for Zr-based metallic glasses (e.g., Zr-Ni) and discussed in detail, e.g. in regard to the density of the glass.
Old Technique for New Materials: Characterization of Solid State Hydrogen Storage Materials by Temperature Programmed Reaction
Authors: Rufael Tecle S. , Williams Cabral M. 
Published: April 2011

ABSTRACTThe most common diagnostic tools in studying reversible solid-state hydrogen storage materials involve volumetric or gravimetric approaches. In this study, a mature gas solid analysis technique called Temperature Programmed Reaction (TPR) is presented as an alternative and complementary approach in investigating solid-state hydrogen storage materials. TPR is fast, simple and offers valuable information from a wide range of solid materials. This technique is routinely used to characterize the reduction behavior of metal oxide and sulfide catalysts. In a typical TPR experiment, a sample powder is heated at a constant rate under a non steady-state environment of constant pressure and flow of a hydrogen/inert gas mixture, while monitoring the rate of hydrogen absorption and desorption by a thermal conductivity detector. The principle behind TPR is the high thermal conductivity coefficient of hydrogen when compared to other gases. The detector is sensitive enough that a slight change in hydrogen concentration is reflected by significant changes in the thermal conductivity signal. Hydrogen storage materials exhibit fingerprint type TPR spectra, unique to their composition and structure. Specific rates of hydrogen intake, heats of absorption and desorption as well as extent of activation can be extracted from TPR curves. In addition, multiple absorption and desorption states can be identified from the number of absorption or desorption peaks. Material stability and potential structural or phase changes can also be inferred indirectly. The simplicity and the highly sensitive thermal conductivity measurement provide a number of advantages over the traditional volumetric or gravimetric methods. Metal hydride alloys of AB5-type are used to demonstrate the effectiveness of TPR technique in characterizing hydrogen storage materials.
Using nanoporous carbon membranes in fuel cells
Authors: Ramnarayanan Ramanathan , Rajagopalan Ramakrishnan , Mallouk Thomas E. , Foley Henry C. 
Published: April 2011

ABSTRACTWe have synthesized nanoporous carbon membranes that have monodisperse pores of 4–5 Å. These membranes have excellent size and shape selectivity that makes them an ideal candidate for use as separators in fuel cells. The selectivity of these membranes to gases such as N2, O2 and water gas [carbon monoxide and hydrogen] were measured using a permeation testing unit. These membranes were then tested as separators in fuel cells.
The Influence of Surface Reconstruction and C-impurities on Photocatalytic Water Dissociation by TiO2
Authors: Nie Xiliang , Sohlberg Karl 
Published: April 2011

ABSTRACTTiO2 is well known as a prototype photocatalyst for water dissociation. To understand the mechanism of its photocatalytic water dissociation we performed first-principles calculations. We find that the surface of the catalytically favorable (TiO) termination is very different from the physically favorable (oxygen) termination. The calculated surface energy of the catalytically favorable (TiO) termination is about 10 times larger than that of the physically favorable (oxygen) termination. Analysis of the surface band structure suggests that while O-vacancies are intrinsic active sites for water dissociation into H2 and O2 gas, they are not essential for photocatalytic water dissociation. We also find that carbon impurities decrease the band-gap of TiO2, in agreement with previously reported experimental results. Moreover, we identify the origin of the arcane “double band gap” in carbon doped TiO2. The two onsets seen in the photoabsorption spectrum result from excitations from two of three C p-states within the band gap, not from domains of different composition.
Low-Temperature Aging and Phase Stabiliy of U6Nb
Authors: Hsiung L. M. , Briant C. L. , Chasse K. R. 
Published: April 2011

ABSTRACTAging behavior and phase stability of a water-quenched U-6wt%Nb (U-14at%Nb) alloy artificially aged at 200°C and naturally aged at ambient temperature for 15 years have been investigated using Vickers hardness test, X-ray diffraction analysis, and transmission electron microscopy techniques. Age hardening/softening phenomenon is observed from the artificially aged samples according to microhardness measurement. The age hardening can be rationalized by the occurrence of spinodal decomposition, or fine scale of Nb segregation, which results in the formation of a nano-scale modulated structure within the artificially aged samples. Coarsening of the modulated structure after prolonged aging leads to the age softening. The occurrence of chemical ordering (disorder-order transformation) is found in the naturally aged sample based upon the observations of antiphase domain boundaries (APB's) and superlattice diffraction patterns. A possible superlattice structure is accordingly proposed for the chemically ordered phase observed in the naturally aged alloy sample.
f-Element Influence on the Size of Nanophase Phosphate Inclusions in Silica
Authors: Beitz James V. , Skanthakumar S. , Seifert S. , Thiyagarajan P. 
Published: April 2011

ABSTRACTInsight into the factors that control the formation and size of heavy metal phosphate nanophases in vitreous silica has been gained by combining conventional and anomalous small angle x-ray scattering studies with powder x-ray diffraction and laser-induced fluorescence investigations. Europium, thorium, and uranyl ions were sorbed from aqueous solutions into a chemically functionalized porous silica (termed Diphosil). Aliquots of those samples were heated to a series of temperatures that spanned the pore collapse point. Loading with trivalent europium ions resulted in production of nanophases whose size corresponded to the average number of metal ions per pore. Thorium or uranyl ions resulted in retention of porosity to higher temperature with eventual pore collapse that evidently resulted in formation of nanophases whose size exceeded that determinable under the experimental conditions.
Combinatorial Search for Low-Temperature Combustion Catalysts
Authors: Wolter Tina , Maier Wilhelm F. 
Published: April 2011

ABSTRACTA sol-gel process was used to synthesize potential combustion catalysts based on mixed oxides on several libraries. As mixed oxides a variety of doped Zr-Al-oxides and Ce-oxides were prepared. The catalytic activity of the materials was tested with the combustion of i-octane, n-butane and methane in synthetic air. Several Pt- and Rh-containing sol-gel materials showed effective methane combustion already at 60 °C under rich conditions and at 200 °C under lean conditions. Several noble metal free doped CeO2 catalysts combusted methane already at 300 °C under lean conditions. Combustion of i-octane was catalysed already at 125 °C. The most active catalysts were synthesized conventionally, characterized and catalytic activity was confirmed in a regular gas phase flow reactor.
Multilayer Transparent Conducting Oxide Thin Film Produced by Linear Combinatorial Synthesis
Authors: Li Xiaonan 
Published: April 2011

ABSTRACTMultilayer transparent conducting oxide (TCO) structures consisting of alternating layers of tin oxide (SnO2) and cadmium oxide (CdO) pairs was studied. A low-pressure metalorganic chemical vapor deposition with a linear combinatorial approach was used to fabricate the libraries. Three libraries were studied with the pair thickness range covered from 500 nm to 4 nm. For pairs thicker than 150 nm, the material properties of the multilayer simply show a combination of CdO and SnO2 characteristics. When pair thinner than 70 nm, the interface effect started emerging. As pairs became thinner than 20 nm, the new compound phase was formed.