bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical properties of GaN Photonic Crystal Membrane Nanocavities at Blue Wavelengths
Authors: Choi Yong-Seok , Meier Cedrik , Sharma Rajat , Hennessy Kevin , Haberer Elaine D. , Nakamura Shuji , Hu Evelyn L. 
Published: April 2011

AbstractWe have investigated the design parameters for high-Q photonic-crystal (PC) bandgap modes in the emission wavelengths of InGaN/GaN multiple quantum wells. We demonstrate experimental schemes to realize 2D triangular-lattice PC membrane structures, which is essential to obtain photonic bandgap (PBG) modes, and the optical properties of L7 membrane nanocavities that consist of seven missing holes in the Γ-K direction. L7 cavities show pronounced resonances with Q factors of 300 to 800 in the PBG as well as the enhancement of light extraction of the broad InGaN/GaN multiple-quantum-well emission by the 2D PBG.
Intersecting basal plane and prismatic stacking fault structures and their formation mechanisms in GaN
Authors: Bai Jie , Huang X. , Dudley M. 
Published: April 2011

AbstractComparative TEM studies have been carried out on GaN/AlN epifilms grown on both on-axis and off-cut 6H-SiC substrates to study the defects formed in the GaN/AlN films and the state of strain relaxation at the interface. Prismatic Stacking Faults (PSFs) are observed to form at I1 type substrate steps in both the on-axis and vicinal samples. In the vicinal samples, the PSFs expand into GaN/AlN film forming intersecting stacking fault configurations comprising faults that fold back and forth from the basal plane (I1 Basal-Plane Stacking Faults; BSFs) to the prismatic plane (PSFs). On the other hand, in the on-axis sample the PSFs are observed to mostly annihilate each other to form enclosed domains confined to the near-interface region. In addition, HRTEM studies suggest the existence of Geometric Partial Misfit Dislocations (GPMDs) at the SiC/AlN interface of the vicinal sample, which form at I2 type substrate steps. These GPMDs simultaneously accommodate the lattice mismatch and stacking sequence mismatch present at the SiC/AlN interface. This provides explanation of the improved strain relaxation observed in the vicinal versus the on-axis sample.
Oxygen Segregation to Nanopipes in Gallium Nitride
Authors: Hawkridge Michael E , Cherns David 
Published: April 2011

AbstractThis paper examines the core structure and composition of threading dislocations in GaN grown by hydride vapour phase epitaxy. Transmission electron microscopy showed that screw dislocations have widely varying core structures from open cores (“nanopipes”) to closed cores, with irregular variations between the two observed along the length of many dislocations. New evidence was found demonstrating that the equilibrium structure of screw dislocations is a closed core configuration. Electron energy loss spectroscopy combined with high resolution imaging showed that 1.7±0.3 monolayers of nitrogen were substituted by oxygen at the surfaces of nanopipes. In contrast, closed core dislocations showed little evidence of oxygen segregation. It is argued that these results support a model where nanopipe formation is controlled by the segregation of oxygen to pits predominately associated with, albeit not exclusively, dislocations. The implication of the results in understanding the electronic behavior of dislocations in GaN is also discussed.
Photoluminescence in wurtzite GaN containing carbon
Authors: Reshchikov Michael A. , Patillo Random H. , Travis Kathleen C. 
Published: April 2011

AbstractWe studied photoluminescence (PL) from a set of GaN layers grown on sapphire substrates by metalorganic chemical vapor deposition with the concentration of carbon varied by the growth conditions. One of the remarkable features in these samples is the extremely low intensity of the shallow donor-acceptor pair band. Analysis of the PL data gives the shallow acceptor concentration of less than 1014 cm-3 in most of the C-doped GaN layers. This result shows that C does not form a shallow acceptor, CN, in appreciable concentrations in wurtzite GaN. As for the YL band, there is no clear correlation between its intensity and the degree of C-doping. The question of identification of the deep acceptor responsible for the YL band in undoped and C-doped GaN still remains to be solved.
Characterization of the blue emission of Tm/Er co-implanted GaN
Authors: Roqan Iman , Trager-Cowan Carol , Hourahine Ben , Lorenz Katharina , Nogales Emilio , O’Donnell Kevin P , Martin Robert W , Alves Eduardo , Ruffenach S , Briot Olivier 
Published: April 2011

AbstractComparative studies have been carried out on the cathodoluminescence (CL) and photoluminescence (PL) properties of GaN implanted with Tm and GaN co-implanted with Tm and a low concentration of Er. Room temperature CL spectra were acquired in an electron probe microanalyser to investigate the rare earth emission. The room temperature CL intensity exhibits a strong dependence on the annealing temperature of the implanted samples. The results of CL temperature dependence are reported for blue emission (∼ 477 nm) which is due to intra 4f-shell electron transitions (1G4 → 3H6) associated with Tm3+ ions. The 477 nm blue CL emission is enhanced strongly as the annealing temperature increases up to 1200°C. Blue PL emission has also been observed from the sample annealed at 1200°C. To our knowledge, this is the first observation of blue PL emission from Tm implanted GaN samples. Intra-4f transitions from the 1D2 level (∼ 465 nm emission lines) of Tm3+ ions in GaN have been observed in GaN:Tm films at temperatures between 20–200 K. We will discuss the temperature dependent Tm3+ emission in both GaN:Tm,Er and GaN:Tm samples.
Correlation Between Resistivity and Yellow Luminescence Intensity of MOCVD-Grown GaN Layers
Authors: Hinoki Akihiro , Hiroyama Yuichi , Tsuchiya Tadayoshi , Yamada Tomoyuki , Iwami Masayuki , Imada Katsuhiro , Kikawa Junjiroh , Araki Tsutomu , Suzuki Akira , Nanishi Yasushi 
Published: April 2011

AbstractFor further improvements in AlGaN/GaN heterojunction field-effect transistor performance (HFET), it is necessary to reduce the leakage current of the GaN buffer layer. We found a correlation between the leakage current and the intensity of the yellow luminescence of GaN layers taken by UV lamp excitation. The GaN layers were grown by metal organic chemical vapor deposition on SiC substrates. When the samples were excited by a UV (365 nm) lamp, visible yellow luminescence was observed. The leakage current of the GaN buffer layer was measured after deposition of ohmic metal contact. We confirmed clear correlation between the leakage current and the luminescence intensity based from result that the samples with the larger leakage current showed the stronger luminescence intensity. This correlation gives us useful information to understand the drain-source leakage current of AlGaN/GaN HFET.
Donor-like Deep Level Defects in GaN Characterized by Double-correlation Deep Level Transient Spectroscopy
Authors: Ahoujja Mo , Hogsed M , Yeo Y. K. , Hengehold R. L. 
Published: April 2011

AbstractSi doped GaN grown by molecular beam epitaxy on sapphire substrates were characterized by capacitance transient spectroscopy. Conventional deep level transient spectroscopy (DLTS) measurements displayed six deep level defects, labeled A1, A, B, C1, C, and D, with activation energy ranging from 0.20 to 0.82 eV below the conduction band. Based on the logarithmic dependence of the DLTS spectral peaks on the filling pulse width, it is deduced that the defects A, B, C, and D are concentrated in the vicinity of line dislocations. Double-correlation DLTS (DDLTS) measurements, on the other hand, showed that only defects A (0.82 eV) and D (0.22 eV) exhibited deep donor-like characteristics. Following a 1.0 MeV electron irradiation of the GaN sample, one radiation-induced peak, E, with activation energy less than 0.20 eV was observed in the DLTS spectrum. However, after annealing at 350 °C, this DLTS peak intensity was found to diminish significantly.
Implementing a Hydrogen Energy Infrastructure:Storage Options and System Design
Authors: Ogden Joan , Yang Christopher 
Published: April 2011

AbstractThe development of a hydrogen infrastructure has been identified as a key barrier to implementing hydrogen as for a future transportation fuel. Several recent studies of hydrogen infrastructure have assessed near-term and long-term alternatives for hydrogen supply [1-2]. In this paper, we discuss how advances in material science related to hydrogen storage could change how a future hydrogen infrastructure is designed. Using a simplified engineering/economic model for hydrogen infrastructure design and cost, we explore some potential impacts of advances in storage materials, in terms of system design, cost, energy use, and greenhouse gas emissions. We find that the characteristics of hydrogen storage play a major role in the design, cost, energy use, and CO2 emissions of hydrogen supply infrastructure.
Environmental Life Cycle Inventory of Crystalline Silicon Photovoltaic Module Production
Authors: Wild-Scholten Mariska de , Alsema Erik A. 
Published: April 2011

AbstractTogether with 11 European and US photovoltaic companies an extensive effort has been made to collect Life Cycle Inventory (LCI) data that represents the status of production technology for crystalline silicon modules for the year 2004. These data can be used to evaluate the environmental impacts of photovoltaic solar energy systems.The new data covers all processes from silicon feedstock production via wafer- and cell- to module manufacturing. All commercial wafer technologies are covered, i.e multi- and mono-crystalline wafers as well as ribbon technologies. For monocrystalline silicon wafer production further improvement of the data quality is recommended.
Toxicological Profiles of Nanomaterials
Authors: Rushton Erik K , Oberdörster Günter , Finkelstein Jacob 
Published: April 2011

AbstractWith the passage of the National Nanoscale Initiative in 2001 there has been increasing attention and funding given to nanomaterial research. This has led to a number of new materials developed at the nanoscale (< 100 nm) level, which often possess chemical and physical properties distinct from those of their bulk materials. These unique qualities are proving to be quite useful in a number of new applications. For example, biological applications in imaging, treatment, and drug delivery are particularly promising as well as the increasing engineering potential of nanocircuitry and materials science. As the number of applications increases however, so too does the potential for human exposure to nanomaterials through a number of routes: dermal, ingestion, inhalation, and even injection. Interestingly some of the properties of these nanomaterials that make them useful in these emerging technologies are the same properties that can increase their toxic potential. This is leading to an emerging discipline – nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices. Nanotoxicology research will not only provide information for risk assessment of nanomaterials based on data for hazard identification, dose response relationships and biokinetics, but will also help to further advance the field of nanoresearch by providing information to alter undesirable nanomaterials properties. Although nanotoxicology is in its infancy, there are some preliminary studies with newly developed materials that provide some insight into potential effects, which when coupled with older studies provides some insight on how these nanomaterials impact the biological system. This presentation summarizes results of studies with nanosized particles with a focus on the respiratory system and skin as portals of entry. The ability of particles to translocate from their site of entry, their ability to elicit biological responses, and their presumed mechanisms of action will be highlighted. This will be an attempt to illustrate how pervasive these materials can be, which may or may not be detrimental. With proper toxicological assessment this potential may be harnessed leading to breakthroughs at the nanotechnology – biology interface.
Importance of Turning to Renewable Energy Resources with Hydrogen as a Promising Candidate and on-board Storage a Critical Barrier
Authors: Dillon Anne C. , Nelson Brent P. , Zhao Yufeng , Kim Yong-Hyun , Tracy C. Edwin , Zhang Shengbai B. 
Published: April 2011

AbstractThe majority of the world energy consumption is derived from fossil fuels. Furthermore, the United States (US) consumption of petroleum vastly exceeds its production, with the majority of petroleum being consumed in the transportation sector. The increasing dependency on foreign fuel resources in conjunction with the severe environmental impacts of a petroleum-based society dictates that alternative renewable energy resources be developed. The US Department of Energy's (DOE's) Office of Energy Efficiency and Renewable Energy and the Office of Basic Energy Sciences are currently promoting a vehicular hydrogen-based energy economy. However, none of the current on-board storage technologies are suitable for practical and safe deployment. Significant scientific advancement is therefore still required if a viable on-board storage technology is to be developed. A detailed discussion of the benefits of transitioning to a hydrogen-powered automotive fleet as well as the tremendous technical hurdles faced for the development of an on-board hydrogen storage system are provided here. A novel class of theoretically predicted nanostructured materials that could revolutionize hydrogen storage materials is also presented.
Comparative life cycle assessment of three drink delivery systems
Authors: Martino Dario , Selke Susan , Joshi Satish 
Published: April 2011

AbstractThis paper presents information regarding a comparative life cycle assessment (LCA), including scenario and data uncertainty, based on a hypothetical drink product for which we evaluate three main container material alternatives: (1) a polyethylene terephthalate (PET) bottle; (2) an aluminum can; and (3) a polylactide (PLA) bottle. The scope of results included energy, water use and two characterized impacts are included: global warming potential (GWP) and ozone depletion potential (ODP).The results presented in this study demonstrate that LCI parameter uncertainty seems to have a dominant effect in the outcome of the LCA results considered. Indeed, in most cases there is overlap in the uncertainty intervals (at 95% confidence level), indicating that the three systems under study have similar indicator values, at least with regard to the environmental indicators included here.
Structural Refinement in Al-MoO3 Nanocomposites Prepared by Arrested Reactive Milling
Authors: Umbrajkar Swati , Schoenitz Mirko , Dreizin Edward L 
Published: April 2011

AbstractAl-MoO3 nanocomposites were synthesized based on arrested reactive milling. Altering the milling parameters leads to different scales of refinement in the structure of the reactive nanocomposites. The objective of this work is to determine the range in which the degree of structural refinement can be changed in a controlled manner. The milling intensity was controlled by using different milling media along with varying amounts of process control agent (PCA). XRD, SEM, DSC and wire-ignition tests were performed to analyze the Al-MoO3 nanocomposites. Results indicate that there is a decrease in the crystallite size with increase in the milling intensity. However increase in milling intensity also stimulates the undesired reaction between Al and MoO3. Milling conditions resulting in the highest structural refinement and lowest ignition temperatures were identified.
The Effect of Nanopowder Attributes on Reaction Mechanism and Ignition Sensitivity of Nanothermites
Authors: Puszynski Jan A , Bulian Chris J , Swiatkiewicz Jacek J 
Published: April 2011

AbstractNanothermite composites have several properties that are not typical of conventional thermites. The nanoscale size of individual reactants is responsible for the significant differences in these properties, especially the rate of energy release and mechanism of combustion front propagation. Several thermite mixtures were investigated, including Al-Fe2O3, Al-CuO, Al-MoO3, and Al-Bi2O3. Previous studies have reported on the behavior of these mixtures during unconfined burning and on the characterization of particle attributes such as particle size, surface area, and reactive metal content. This study was focused on several other attributes, including mixing of nanoreactants in water and measurements of reaction kinetics and combustion front propagation characteristics under confined conditions. The nanoscale nature of the thermite components also has an effect on the kinetics of the reaction. Differential scanning calorimetry was used to determine activation energy of these reacting systems. Several experimental setups were used to monitor the nanothermite mixtures during combustion. The mixtures were monitored during combustion in small diameter tubes using high speed video technology and a pressure sensor system. These tests were used to characterize combustion propagation under confined conditions and to determine the effect of pressure and mixture density on propagation rate. Experiments were also performed using both a closed volume pressure cell and recoil force cell to measure the reactive energy of the mixtures.
Role of Constituent Configuration on Shock-Induced Reactions in a Ni+Al Powder Mixture
Authors: Eakins Daniel , Thadhani Naresh 
Published: April 2011

AbstractUltra-fast reactions initiated within or immediately behind the shock front in powder mixtures are of importance in the synthesis of high-pressure phases and next-generation energetic materials. Reactions in nickel and aluminum powder mixtures and the establishment of a reaction threshold have been the source of many studies over the last 20 years. Prior work has suggested that the criterion for reaction is most probably mechanochemical in nature, in which shock loading environment plays a larger role than absolute shock energy input. The mechanisms responsible for intimate mixing of fresh reactants are however still unclear. In this work we are investigating the role of particle size and morphology on the loading, mixing, and their subsequent shock-induced reaction behavior, by performing shock-compressibility experiments on equi-volumetric mixtures of nickel and aluminum powders, with variations in nickel particle size (micron and nano-scale) and shape (spherical and flake). Determination of shock states is accomplished through time-resolved in situ PVDF gauge measurements of input shock stress and shock propagation speed obtained from transit time through the thickness of powder mixture. The reaction product shock-compressibility state is also being calculated based on constant pressure approximations to allow correlation with measured states for inference of the occurrence of shock-induced chemical reactions. The results of this study suggest that powder configuration in the nickel-aluminum system can be modified to encourage or discourage reaction.
Tensile Properties of Hydroxyapatite Whisker Reinforced Polyetheretherketone
Authors: Converse Gabriel , Roeder Ryan 
Published: April 2011

AbstractPolyetheretherketone (PEEK) was reinforced with 0-40 vol% hydroxyapatite (HA) whiskers using a novel powder processing and compression molding technique. A powder mixture was uniaxially pressed into a composite powder compact and compression molded into a flat composite bar using an open-channel die, such that the HA whiskers exhibited a preferred orientation along the length of the bar and tensile specimens. As expected, increased HA whisker reinforcement resulted in increased elastic modulus, but decreased ultimate tensile strength and strain- or work-to-failure. PEEK reinforced with 40 vol% HA whiskers exhibited an elastic modulus of 16-18 GPa. PEEK reinforced with 20 vol% HA whiskers had an ultimate tensile strength of 70-80 MPa. Human cortical bone exhibits an elastic modulus of 17-26 GPa and an ultimate tensile strength of 80-150 MPa in the longitudinal direction (direction of principal stress). Stiffness coefficients measured by ultrasonic wave propagation indicated a level orthotropy also similar to that of human cortical bone tissue.
Local Thermal Analysis: Study of viscoelastic properties and time dependence in Surlyn
Authors: Kulkarni Harsha Prabhakar , Mogilevsky Gregory , Mullins William , Kleinhammes Alfred , Wu Yue 
Published: April 2011

AbstractSelf-healing ability is a fascinating property of some materials. Structural materials with self-healing ability require a subtle combination of flow and stiffness characteristics. A vivid demonstration of self-healing is the automatic sealing of the bullet hole after bullet penetration of the target material. The ionomer Surlyn® satisfies the needs of both structural requirements and self-healing to a certain extent. The viscosity of Surlyn is very high at room temperature, a favorable property for structural applications but unfavorable for self-healing. However, when it was heated to 100°C and then cooled back down to room temperature, its viscosity remains temporarily low at room temperature for a few minutes, a favorable condition for healing. Here we report the measurement of such short-time relaxation effects on flow properties in Surlyn using an atomic force microscope (AFM)-based local thermal mechanical analyzer (LTA).
Local Mineral and Matrix Changes Associated with Bone Adaptation and Microdamage
Authors: Kohn David H. , Sahar Nadder D. , Hong Sun Ig , Golcuk Kurtulus , Morris Michael D. 
Published: April 2011

AbstractSkeletal fractures represent a significant medical and economic burden for society. It is generally thought that a high incidence of musculoskeletal fatigue loading results in damage accumulation at too high of a rate to be efficiently remodeled, leading to skeletal fracture. The state of damage in bone at a given time is therefore the net result of damage and repair processes, and is dependent upon extrinsic factors such as mechanical history, but also upon intrinsic factors, such as composition of bone mineral and matrix. In this invited paper, we review investigations on the coupling of Raman spectroscopy with mechanical loading of bone, providing insight into mechanisms of ultrastructural deformation in bone at smaller scales than previously understood. We also present new data showing that in-vivo mechanical loading results in increased resistance to fatigue damage, coupled with an increase in phosphate to amide I ratio and decrease in carbonate to phosphate ratio. Taken together, the data demonstrates the ability to modulate the mechanical and chemical properties of bone via exogenous mechanical stimulation.