bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compatibilization Mechanism of Polyimide-Silica Hybrids with Organofunctional Trialkoxysilanes
Authors: Menoyo J. D. C. , Mascia L. , Shaw S.J. 
Published: April 2011

ABSTRACTThe polyimide hybrids that have been most widely studied by the authors contain a silica phase produced from tetraethoxysilane by the sol-gel method. Despite the expected strong interactions, through H-bonds, between the polyamic acid precursor for the polyimide and the large number of hydroxyl groups from the silica phase, it is rather difficult to prevent phase separation and rapid coarsening of the morphology upon removal of the solvent from the original solution mixture. These systems can be compatibilized, however, with the selective use of functionalized trialkoxysilane coupling agents, such as glycidyl and isocyanate types.In the present work we have established that compatibilty is achieved only upon exceeding a critical concentration of coupling agent, which increases linearly with the total silica content up to a certain level. This was found to be connected with the ability of the coupling agent to displace the strongly associated solvent molecules with the amic acid units of the polymer chains in order to develop the required level of interactions across the interface between the organic and inorganic components.
Strain Rate Effects in Porous Materials
Authors: Lankford J. , Dannemann K. A. 
Published: April 2011

ABSTRACTThe behavior of metal foams under rapid loading conditions is assessed. Dynamic loading experiments were conducted in our laboratory using a split Hopkinson pressure bar apparatus and a drop weight tester; strain rates ranged from 45 s−1 to 1200 s−1. The implications of these experiments on open-cell, porous metals, and closed- and open-cell polymer foams are described. It is shown that there are two possible strain-rate dependent contributors to the impact resistance of cellular metals: (i) elastic-plastic resistance of the cellular metal “skeleton,” and (ii) the gas pressure generated by gas flow within distorted open cells. A theoretical basis for these implications is presented.
Mechanical Properties of a Structural Polyurethane Foam and the Effect of Particulate Loading
Authors: Goods S. H. , Neuschwanger C. L. , Whinnery L. L. 
Published: April 2011

ABSTRACTThe room temperature mechanical properties of a closed-cell, polyurethane encapsulant foam have been measured as a function of foam density. Tests were performed on both unfilled and filler reinforced specimens. Over the range of densities examined, the modulus of the unloaded foam could be described by a power-law relationship with respect to density. This power-law relationship could be explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model found in the literature. The collapse stress of the foam was also found to exhibit a power-law relationship with respect to density. Additions of an aluminum powder filler increased the modulus relative to the unfilled foam.
Complex Foamed Aluminum Parts as Permanent Cores in Aluminum Castings
Authors: Simančík F. , Schoerghuber F. 
Published: April 2011

ABSTRACTThe feasibility of complex shaped aluminum foam parts as permanent cores in aluminum castings has been investigated. The foamed samples were prepared by injection of the foam into sand molds. It turned out that sound castings can be produced if the foam core is properly preheated and/or surface treated before casting. The effect of the foam core on the performance of the casting was evaluated by in compression testing and by measuring structural damping. The gain in the related properties turned out to be much higher than the weight increase of the casting due to the presence of the core. The weight increase may be partially offset through a reduction of the wall-thickness of the shell.
Structural Graphitic Carbon Foams
Authors: Kearns Kristen M. , Anderson David P. , Anderson Heather J. 
Published: April 2011

ABSTRACTGraphitic carbon foams are a unique material form with very high structural and thermal properties at a light weight. A process has been developed to produce microcellular, open-celled graphitic foams. The process includes heating a mesophase pitch preform above the pitch melting temperature in a pressurized reactor. At the appropriate time, the pressure is released, the gas nucleates bubbles, and these bubbles grow forming the pitch into the foam structure. The resultant foamed pitch is then stabilized in an oxygen environment. At this point a rigid structure exists with some mechanical integrity. The foam is then carbonized to 800°C followed by a graphitization to 2700°C.The shear action from the growing bubbles aligns the graphitic planes along the foam struts to provide the ideal structure for good mechanical properties. Some of these properties have been characterized for some of the foam materials. It is known that variations of the blowing temperature, blowing pressure and saturation time result in foams of variously sized with mostly open pores; however, the mechanism of bubble nucleation is not known. Therefore foams were blown with various gases to begin to determine the nucleation method. These gases are comprised of a variety of molecular weights as well as a range of various solubility levels. By examining the resultant structures of the foam, differences were noted to develop an explanation of the foaming mechanism.
Formation of Ordered Gas-Solid Structures VIA Solidification in Metal-Hydrogen Systems
Authors: Shapovalov V. I. 
Published: April 2011

ABSTRACTThis work contains theoretical discussions concerning the large amount of previously published experimental data related to gas eutectic transformations in metal-hydrogen systems. Theories of pore nucleation and growth in these gas-solid materials will be presented and related to observed morphologies and structures. This work is intended to be helpful to theorists that work with metal-hydrogen systems, and experimentalists engaged in manufacturing technology development of these ordered gas-solid structures.
GASAR Porous Metals Process Control
Authors: Apprill J. M. , Poirier D. R. , Maguire M. C. , Gutsch T. C. 
Published: April 2011

ABSTRACTGASAR porous metals are produced by melting under a partial pressure of hydrogen and then casting into a mold that ensures directional solidification. Hydrogen is driven out of solution and usually grows as quasi-cylindrical pores normal to the solidification front. Experiments with pure nickel have been carried out under processing conditions of varying H2 partial pressure, total pressure (H2 + Ar), and superheat. An analysis that considers heterogeneous bubble nucleation was developed that identifies processing conditions in which hydrogen bubbles are stable in the liquid before solidification. It is hypothesized that these conditions lead to low porosity because these bubbles float out of the melt and “escape” the advancing solidification front. Experimental data are shown to support this hypothesis.
Growth And Characterization of Thin Wet Oxides Grown by Rapid Thermal Processing
Authors: Sharangpani R. , Das J. , Tay S. P. , Thakur R. P. S. , Yang T. C. , Saraswat K. C. 
Published: April 2011

ABSTRACTThe growth of high quality thin (<10 nm) oxides is one of the most critical steps in the fabrication of the entire spectrum of silicon based devices. Rapid thermal wet oxidation is emerging as a promising technique for this application due to features such as higher throughput, superior oxide quality, faster response and precise thickness control. In this paper, an integrated pyrogenic steam generator -RTP system is described. Theoretical and experimental growth curves along with thickness contour maps and preliminary reliability results are presented.
Selective Oxidation of Si in the Presence of W and Wn
Authors: Lin Boyang , Hwang Ming , Lu Jiong-Ping , Hsu Wei-Yung , Pas Mike , Piccirillo Joe , Miner Gary , OConnor Kathy , Xing Gary , Lopes Dave 
Published: April 2011

ABSTRACTIn various device fabrication processes, such as in metal gate and low resistance word line fabrication, one needs to be able to oxidize Si without oxidizing metals present. We developed such a process using a combination of H2 and O2 in the H2 rich regime. The process developed is safe and is production worthy with excellent uniformity.When carrying out the selective oxidation using H2/O2, a high Si oxidation rate is preferred which requires a high oxygen concentration. At the same time, the increase in metal sheet resistance, if any, must be small. We found that with an oxygen concentration as high as 20%, the increase in W sheet resistance is small. We present data on the oxidation rate of Si under different conditions as well as the selectivity of the process with respect to W and WN.
Improved Thermal Stability of CVD WSi. During Furnace Oxidation by a Rapid Thermal Anneal Pretreatment
Authors: Blosse Alain P. 
Published: April 2011

ABSTRACTIn this paper, we report new results on tungsten silicide ( WSix ) degradation during furnace oxidation. During Poly-oxidation step performed after gate patterning, a deformed oxide is grown on WSix /Poly gate lines giving rise to protrusions (or nodules) at the interface between the two materials. Different parameters were evaluated including oxidation conditions, WSix deposition parameters, WSix capping dielectric and thermal treatments. The first conclusion of these experiments is that protrusions can be eliminated if Si/W ratio in as-deposited material is greater than 2.6 when no furnace thermal treatment is done on the WSix. /Poly stack before furnace oxidation. The more important conclusion is that addition of a Rapid Thermal pretreatment with a temperature range between 700 and 1000 degrees done just after WSix /Poly etch and before furnace oxidation eliminates totally the defects. Both results can be explained with internal stress reduction in the WSix film which lead to suppression of accelerated oxidation kinetics at the interface between polysilicon and WSix films during furnace oxidation after gate patterning.
Advances in Rtp Temperature Measurement and Control
Authors: Peuse Bruce , Miner Gary , Yam Mark , Elia Curtis 
Published: April 2011

ABSTRACTThis paper reviews work to develop and improve the temperature measurement and control technology of a commercial rapid thermal processing (RTP) system. A description of the main features of this system is given, which includes a concentric multi-zone lamp heating source, multi-point temperature measurement system and real time wafer temperature control. Innovations in RTP optical thermometry are described which resulted in improved low temperature performance, a real time spectral emissivity measurement tool which enables emissivity independent temperature measurement and an improved temperature calibration capability. The multi-input multi-output (MIMO) optimal wafer temperature control methodology is discussed. Process results demonstrating an equivalent process temperature performance of 4°C, 3-sigma, all-points-all-wafers will be presented.
Stabilization of Thick Fcc Cobalt Layers by One Monolayer of Manganese in Co/Mn Superlattices
Authors: Pierron-Bohnes V. , Michel A. , Jay J.P. , Panissod P. 
Published: April 2011

AbstractEpitaxial Co/Mn superlattices (0.6 to 4.8 nm thick Co) have been grown on (0002) hcp Ru buffer layer on mica substrates. The face centered cubic (fcc) phase of cobalt is stabilized by the very thin manganese layer. The structural properties of these layers have been studied through x ray diffraction and nuclear magnetic resonance.
Atomic Interactions and the Stability of Surface Clusters
Authors: Koh Seong Jin , Ehrlich Gert 
Published: April 2011

AbstractInteractions dictating the shape and stability of surface islands have been examined for a simple model system, palladium clusters on the W(110) plane. Observations in a field ion microscope of the distribution of two Pd adatoms over the surface yield quantitative values for pair interactions. These are found to be complex, extending over distances longer than 10 A and to vary strongly with the orientation of the pair axis on the (110) surface. Using the measured pair energies it has been possible to infer the magnitude of many-atom effects necessary to account for the equilibrium shape of the clusters. Many-atom interactions turn out to make by far the largest contribution to cluster cohesion; modeling of growth phenomena in terms of nearest-neighbor bonds only is clearly problematic.
Cellular Automaton Modeling of Alloy Solidification Using Local Anisotropy Rules
Authors: Napolitano R. E. , Sanders T. H. 
Published: April 2011

AbstractThe evolution of dendritic morphology is simulated for a binary alloy using a two-dimensional cellular automaton growth algorithm. Solute diffusion is modeled with an alternate-direction implicit finite difference technique. Interface curvature and kinetic anisotropy are implemented through configurational terms which are incorporated into the growth potential used by the automaton. The weighting of the anisotropy term is explored and shown to be essential for overcoming grid-induced anisotropy, permitting more realistic development of dendritic morphologies. Dendritic structures are generated for both uniform and directional cooling conditions.
Bonding Regeneration: The Driving Force of Hetero-Epitaxial Diamond Grain Coalescence on (001) Silicon
Authors: Zhang R.Q. , Jiang X. , Jia C.L. , Lee S.-T. 
Published: April 2011

AbstractThe grain coalescence phenomenon in the growth of heteroepitaxial diamond film on (001) silicon substrate by microwave plasma chemical vapor deposition was examined by using high-resolution electron microscopy. It was shown that this phenomenon evidently occurs between two diamond grains with a small-angle tilt. The coalescence was completed after some more growth steps following the meeting of such two grains, indicating the difficulty for the lattice matching in grain boundary. By performing simulation of a step-by-step growth of two diamond grains on a (001) silicon substrate with molecular orbital PM3 method, it was shown that the bonding regeneration between the two grains is essential for the coalescence and the coalescence is only possible when the orientation difference between the grains is sufficiently small so as to allow efficient overlap of electron cloud in the grain boundary. This study indicates that single crystal diamond growth may be possible by the current CVD growth techniques via further reduction of the surface roughness to gain a heteroepitaxy with very small grain tilting.
Activation Energy for Strength Degradation of Fused Silica Optical Fibers
Authors: Shiue Yunn-Shin , Matthewson M. John 
Published: April 2011

AbstractThe strength degradation behavior of fused silica optical fiber is well known to be sensitive to the temperature and an apparent activation energy can be determined. In addition, it has been observed that the activation energy also depends on the applied stress and the nature of the environment. However, no consistent model for this behavior has emerged. We propose a chemical kinetics model which accounts for the temperature dependence of the dissociation of water which predicts that degradation should be faster in pH 7 buffer than in pure water. Static fatigue of fused silica fibers in both water and pH 7 buffer solution has been carefully studied as a function of temperature to test the model. The apparent activation energies are stress dependent, and, while the dependency is not clear, different environments give different dependencies. These observations support the proposed model.
Bending Stress in an Optical Fiber Interconnect Experiencing Significant Ends Off-Set
Authors: Suhir E. 
Published: April 2011

AbstractA solution to the nonlinear problem of bending of an optical fiber interconnect is considered for the case when the interconnect experiences large deflections due to a significant lateral ends off-set. Thissolution can be helpful in the analysis and design of interconnects subjected to a significant ends off-set. It can be used also to assess the accuracy of the predictions, based on the linear approach.
Critical issues In The Mechanical Reliability of Lightguide Fibers
Authors: Kurkjian C. R. 
Published: April 2011

AbstractIn order to guarantee a minimum initial strength, lightguide fibers are proof-tested. However, the strength of these fibers is known to depend on time (due to fatigue and aging) and this time-dependence must be taken into account in the calculation of fiber lifetimes. While hermetic coatings can be applied to eliminate strength degradation with time, they are rarely used. It is thus necessary to understand the time-dependent behavior well enough to ensure a desired lifetime (without an excessive and costly safety factor), or alternatively, it is necessary to validate a fundamental strength limit. This paper discusses the progress that has been made on issues related to such fiber lifetime predictions. In particular, it is pointed out that the possible variations in flaw character and coating chemistry make simple generalizations difficult and require that fundamental understandings be developed.
Mechanism of Motion of an Optical Fiber Aligned by a Solder Droplet
Authors: Powell Adam , Warren James , Bailey Christopher 
Published: April 2011

AbstractSolder is often used as an adhesive to attach optical fibers to a circuit board. In this proceeding we will discuss efforts to model the motion of an optical fiber during the wetting and solidification of the adhesive solder droplet. The extent of motion is determined by several competing forces, during three “stages” of solder joint formation. First, capillary forces of the liquid phase control the fiber position. Second, during solidification, the presence of the liquid-solid-vapor triple line as well as a reduced liquid solder volume leads to a change in the net capillary force on the optical fiber. Finally, the solidification front itself impinges on the fiber. Publicly-available finite element models are used to calculate the time-dependent position of the solidification front and shape of the free surface.
Dry and Wet Etching for Group III – Nitrides
Authors: Adesida I. , Youtsey C. , Ping A. T. , Khan F. , Romano L. T. , Bulman G. 
Published: April 2011

AbstractThe group-III nitrides have become versatile semiconductors for short wavelength emitters, high temperature microwave transistors, photodetectors, and field emission tips. The processing of these materials is significant due to the unusually high bond energies that they possess. The dry and wet etching methods developed for these materials over the last few years are reviewed. High etch rates and highly anisotropic profiles obtained by inductively-coupled-plasma reactive ion etching are presented. Photoenhanced wet etching provides an alternative path to obtaining high etch rates without ion-induced damage. This method is shown to be suitable for device fabrication as well as for the estimation of dislocation densities in n-GaN. This has the potential of developing into a method for rapid evaluation of materials.
Carrier Dynamics of Abnormal Temperature-Dependent Emission Shift in Mocvd-Grown InGaN Epilayers and InGaN/GaN Quantum Wells
Authors: Cho Yong-Hoon , Little B. D. , Gainer G. H. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P. 
Published: April 2011

AbstractTemperature-dependent photoluminescence (PL) studies have been performed on InGaN epilayers and InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous temperature dependent emission behavior (specifically an S-shaped decrease-increase-decrease) of the peak energy (EpL) of the InGaN-related PL emission with increasing temperature. In the case of the InGaN epilayer, EPL decreases in the temperature range of 10 - 50 K, increases for 50 - 110 K, and decreases again for 110 - 300 K with increasing temperature. For the InGaN/GaN MQWs, EPL decreases from 10 - 70 K, increases from 70 - 150 K, then decreases again for 150 - 300 K. The actual temperature dependence of the PL emission was estimated with respect to the bandgap energy determined by photoreflectance spectra. We observed that the PL peak emission shift has an excellent correlation with a change in carrier lifetime with temperature. We demonstrate that the temperature-induced S-shaped PL shift is caused by the change in carrier recombination dynamics with increasing temperature due to inhomogeneities in the InGaN structures.
Electrical and Photoelectrical Characterization of Deep Defects in Cubic GaN on GaAs
Authors: Lisker M. , Krtschil A. , Witte H. , Christen J. , As D.J. , Schöttker B. , Lischka K. 
Published: April 2011

AbstractNominally undoped cubic GaN epilayers deposited by rf-plasma assisted molecular beam epitaxy on semi-insulating GaAs substrates were investigated by electric and photoelectric spectroscopical methods. As a consequence of the existence of deep levels in the GaAs-substrate itself, special care has to be taken to separate the contributions of the substrate from that of the cubic GaN epilayer in the various spectra. Two different contact configurations (coplanar and sandwich structures) were successfully used to perform this separation. In the cubic GaN epilayer a trap with a thermal activation energy of (85±20)meV was found by thermal admittance spectroscopy and thermal stimulated currents. Optical admittance spectroscopy and photocurrent measurements furthermore revealed defects at EG -(0.04-0.13) eV, EG-(0.21-0.82) eV and two additional deeper defects at 1.91 Ev and 2.1 eV, respectively. These defect related transitions are very similar to those observed in hexagonal GaN.
P- and N-Type Doping of Mbe Grown Cubic GaN/GaAs Epilayers
Authors: As D.J. , Simonsmeier T. , Busch J. , Schöttker B. , Lübbers M. , Mimkes J. , Schikora D. , Lischka K. , Kriegseis W. , Burkhardt W. , Meyer B.K. 
Published: April 2011

AbstractP-type doping with Mg and n-type doping with Si of cubic GaN (c-GaN) epilayers is reported. Cubic GaN films are grown by if-plasma assisted MBE on semi-insulating GaAs (001) substrates at a substrate temperature of 720°C. Elemental Mg and Si are evaporated from thermal effusions cells. Secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (PL) and temperature dependent Hall-effect measurements are used to study the incorporation, optical and electrical properties. A Mg related shallow donor-acceptor transiton at 3.04 eV with an acceptor activation energy of EA= 0.230 eV is observed by low temperature PL. At Mg concentrations above 1018 cm-3 the dominance of a broad blue band indicates that also in c-GaN Mg is incorporated at different lattice sites or forms complexes. Si-doped c-GaN epilayers are n-type with electron concentrations up to 5*1019 cm-3. The incorporation of Si follows exactly the vapor pressure curve of Si, indicating a sticking coefficient of I for Si in c-GaN. With increasing Si-concentration the intensity of the near-band luminescence continuously increases and broadens.