bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of SiH2 in 1H Nmr of μc-Si:H Deposited with Different Plasma Excitation Frequencies and Silane Concentrations
Authors: Hari P. , Taylor P. C. , Finger F. 
Published: April 2011

AbstractPrevious lH NMR and IR studies of six samples of μc-Si:H prepared under plasma excitation frequencies ranging from 13 MHz to 95 MHz and silane concentrations ranging from 3% to 8% revealed three important results: (1) for a fixed plasma excitation frequency (95 MHz) the hydrogen content increases with silane concentration; (2) for fixed silane concentration the hydrogen content is roughly constant over a wide range of plasma excitation frequencies; and (3) the 1H NMR free induction decay exhibits beat frequencies which correspond to the calculated frequencies due to SiH2 in microcrystalline silicon. In this study we investigate the role of SiH2 in the μc-Si:H structure using 1H NMR measurements. We studied two samples prepared at two different plasma excitation frequencies (13 MHz and 95 MHz). The lU NMR lineshapes of these samples were measured at 300 K and 77 K. The motionally narrowed component of the 1H NMR is not as rapid at room temperature as that observed previously, but the linewidth of this component increases significantly at 77 K. Because of this difference between our results and those reported previously, it is possible that H2 molecules are not responsible for the motional narrowing in our samples. We present plausible arguments for the hindered motion of SiH2 groups in our μc-Si:H samples.
Hall-Effect Studies on Microcrystalline Silicon with Different Structural Composition and Doping
Authors: Backhausen U. , Carius R. , Finger F. , Hapke P. , Zastrow U. , Wagner H. 
Published: April 2011

AbstractHall-effect experiments on <n>-type microcrystalline silicon samples with a wide range of structural composition and doping have been performed. For highly doped samples the conductivity Σ and the mobility μ show a non-singly activated behaviour while the carrier density is almost temperature independent. The comparison of the carrier density with the phosphorous concentration in conjunction with the conductivity gives strong evidence that the Hall-effect data have to be corrected with the crystalline volume fraction Xc. Furthermore, the increase of the mobility with Xc, which is linked in our case to the grain size, can be explained when the length of the transport paths is taken into account. Our results will be discussed in the framework of different transport models. It is concluded that transport in μc-Si:H can not be explained in terms of thermionic emission over barriers with a well defined barrier height; instead a distribution of barrier heights have to be considered. A transport model is suggested where μc-Si:H is viewed as an interconnected network.
The “Micromorph” Cell: a New Way to High-Efficiency-Low-Temperature Crystalline Silicon Thin-Film Cell Manufacturing?
Authors: Keppner H. , Torres P. , Meier J. , Platz R. , Fischer D. , Kroll U. , Dubail S. , Anna Selvan J. A. , Pellaton Vaucher N. , Ziegler Y. , Tscharner R. , Hof Ch. , Beck N. , Goetz M. , Pernet P. , Goerlitzer M. , Wyrsch N. , Veuille J. , Cuperus J. , Shah A. , Pohl J. 
Published: April 2011

AbstractIn the past, microcrystalline silicon (μc-Si:H) has been successfully used as active semiconductor in entirely μc-Si:H p-i-n solar cells and a new type of tandem solar cell, called the “micromorph” cell, was introduced [1]. Micromorph cells consist of an amorphous silicon top cell and a microcrystalline bottom cell. In the paper a micromorph cell with a stable efficiency of 10.7 % (confirmed by ISE Freiburg) is reported.Among sofar existing crystalline silicon-based solar cell manufacturing techniques, the application of microcrystalline silicon is a new promising way towards implementing thin-film silicon solar cells with a low temperature deposition. Microcrystalline silicon can, indeed, be deposited at temperatures as low as 220°C; hence, the way is here open to use cheap substrates as, e.g. plastic or glass. In the present paper, the development of single and tandem cells containing microcrystalline silicon is reviewed. As stated in previous publications, microcrystalline silicon technique has at present a severe drawback that has yet to be overcome: Its deposition rate for solar-grade material is about 2Å/s; in a more recent case 4.3 Å/s [2] could be obtained. In the present paper, using suitable mixtures of silane, hydrogen and argon, deposition rates of 9.4 Å/s are presented. Thereby the dominating plasma mechanism and the basic properties of resulting layers are described in detail. A first entirely microcrystalline cell deposited at 8.7 Å/s has an efficiency of 3.15%.
Crystallization and Evaluation of Non-Stoichiometric Silicon-Carbon Films for Hetero Thin-Film Transistors
Authors: Choi Kwangsoo , Matsumura Masakiyo 
Published: April 2011

AbstractExperimental works have been reviewed on poly-Si/poly-SiCx hetero TFTs aiming at extremely low off-current even under intense light illumination conditions with reasonable field-effect mobility. The results indicated that the hetero TFT having the stacked poly-Si/poly-SiCx layers is promising as a switching device in matrices
Large Crystallite Polysilicon Deposited Using Pulsed-Gas PECVD at Temperatures Less Than 250°C
Authors: Srinivasan E. , Ellis S. J. , Nemanich R. J. , Parsons G. N. 
Published: April 2011

AbstractA pulsed-gas intermittent deposition technique is used to deposit high crystallinity hydrogenated micro- or poly-crystalline silicon using silane and hydrogen. This method has been used to deposit crystallites that are comparable to those obtained using PECVD of fluorinated silanes. RHEED and TEM have been used to understand the nucleation process. The pulsed-gas method is promising for depositing polycrystalline silicon and subsequent use in thin film transistor applications.
Rapid Synthesis of Nanostructural Intermetallics and their Bulk Properties
Authors: Pickard S. M. , Ghosh A. K. 
Published: April 2011

ABSTRACTA rapid physical vapor deposition process (PVD) utilizing a high speed rotating substrate and small substrate-to-source spacing has been used to produce bulk sheet of Ti-Al alloys in the compositional range Ti-12% Al to Ti-75% Al1 at a rate of 1–3 μm/minute. Microstructural architectures produced by the method comprise of either fully homogenous phase mixtures of nano-grains, or nanolaminated material, depending on the substrate rotational rate, with lower rotational rate producing a layered microstructure. Defect populations within the as-deposited material are characterized by TEM and SEM, and hot pressing consolidation of the as-deposited material, which retains a grain size < 1000 nm, has been investigated. While indentation hardness of α2+γ(2 phase) alloys exceeded 7 GPa, brittle failure occurred in the elastic regime at nominally lower tensile stress than that for conventionally produced alloys containing Nb and Cr as solute elements. α2+γ alloys can exhibit tensile elongations of more than 100% at 850°C with retention of fine grain size. Elevated temperature failure occurs by the formation of voids in regions of compositional variability in the composite where single phase α2-Ti3Al structure was present.
Three Dimensional Simulation of the Microstructure Development in Ni-20%Fe Nanocrystalline Deposits
Authors: Li Hualong , Czerwinski F. , Szpunar J. A. 
Published: April 2011

ABSTRACTA Monte-Carlo computer model was applied to simulate a development of the three dimensional microstructure during electrodeposition of nanocrystalline alloys. The driving force for this process was the minimization of free energy of the system. For a particular deposit of Ni-20%Fe, the influence of the overpotential and current density on the grain size was tested. A strong decrease in grain size with increasing overpotential and current density obtained from the simulation is in qualitative agreement with the experimental data.
Magnetic Properties and Thermal Stability of Graphite Encapsulated Cobalt Nanocrystals
Authors: Host J. J. , Dravid V. P. 
Published: April 2011

ABSTRACTSmall particles are of interest for magnetic study due to their range of magnetic properties with particle size and unusual magnetic properties. In this study we produced graphite encapsulated magnetic cobalt particles and measured their structural and magnetic properties both before and after annealing at 550° C for 6 hours. No large change in the structural properties (particle size, shape, and lattice parameter) was observed as a result of the annealing. There were, however, significant changes in the magnetic properties. The coercivity was found to decrease at all temperatures, especially at temperatures below 100° K. The possible reasons for this reduction in coercivity are examined, with the change in the shape of the particles appearing most likely.
Growth of BaTiO3 in Hydrothermally Derived (<100° C) BaTiO3/Polymer Composite Thin Films
Authors: Collins David E. , Slamovich Elliott B. 
Published: April 2011

ABSTRACTComposite BaTiO3/polymer films (<1μm thickness) were processed by the in-situ growth of BaTiO3 particles in a polymer matrix. A solution of a polybutadiene/polystyrene triblock copolymer and titanium diisoproxide bis(ethlyacetoacetate) dissolved in toluene was cast onto a Ag-coated substrate. Subsequent hydrothermal treatment of the films in 1.0 M Ba(OH)2 solutions at 80° C resulted in the nucleation and growth of BaTiO3 within the polymer matrix. The volume fraction/connectivity of BaTiO3 was controlled by varying the relative amounts of titanium precursor and polymer in solution. Growth of BaTiO3 within the polymer was examined by infrared spectroscopy and electron microscopy. The dielectric constant of the composite films increased with BaTiO3 content.
Sol-Gel Routes towards Magnetic Nanocomposites with Tailored Microwave Absorption
Authors: Colomban Ph. , Vendange V. 
Published: April 2011

ABSTRACTCeramic microwave absorbents are of considerable interest for the structural applications with the tailored radar cross-section. The main parameters governing the electromagnetic cross-section are discussed in this paper with the specific interest of the dispersion of Co, Fe (and their alloys) particles in a dielectric aluminosilicate matrix (high Curie temperature, significant absorption in the 0.1–15GHz range) and the advantages of the sol-gel routes for the materials preparation. Three methods have been examined: (i) the first one is the mixing of the (sub)micronic metal powder within a liquid matrix precursor; (ii) the second is the mixing of the alkoxides with an aqueous solution of metal ions; and (iii) the third is the preparation of a porous host matrix impregnated by a concentrated solution of transition metal nitrates. Nanocomposites with diameter 20–200nm were achieved by heating at temperatures between 600 and 1100°C under a H2 atmosphere. The samples were characterized by SEM, TEM, magnetic hysteresis, Mössbauer and Raman spectroscopies and microwave absorption.
Mechanical Anisotropy in Sheets of γ-TiAl Alloys
Authors: Bartels A. , Clemens H. , Hartig C. , Mecking H. 
Published: April 2011

ABSTRACTAt room temperature sheets of γ-TiAl exhibit a higher yield stress in the rolling direction than in the transverse direction. Around 700°C the opposite behavior is observed. The texture mainly consists of a modified cube component. The tetragonal c-axis (001) is aligned in the sheet plane transversely to the rolling direction. Taken into account this special texture and the single crystal yield surface of γ-TiAl we conclude that around 700°C the CRSS of super-dislocations is higher than the CRSS of ordinary dislocations. At RT the relation changes to the opposite.
Influence of Microstructure Refinement on Strength, Ductility and Toughness of TiAl Alloys
Authors: Morris M. A. , Leboeuf M. 
Published: April 2011

ABSTRACTDifferent Ti-Al alloys with grain sizes ranging from 7μm to 320 nm have been prepared by consolidation of atomised and mechanically milled powders of nominal composition Ti-48Al-2Mn-2Nb and containing carbon additions. The materials obtained consist of equiaxed γ grains containing a distribution of α2 phase mostly along grain or powder boundaries. The high flow strength and low fracture toughness obtained from these materials have been correlated to the fine scale of the microstructure and the transfer of slip across adjacent γ grains. The existence of stress concentrations at boundaries between γ grains leads to emission of curved dislocations and twins. The low mobility of emitted dislocations is responsible for the lack of tensile ductility in these alloys which fail by microcrack formation at grain boundaries.
Processing, Properties and Applications of Gamma Titanium Aluminide Sheet and Foil Materials
Authors: Clemens H. , Glatz W. , Eberhardt N. , Martinz H.-P. , Knabl W. 
Published: April 2011

ABSTRACTIntermetallic γ-TiAl based alloys (”γ-alloys”) have a great potential to become important materials for advanced applications in aerospace, automotive and related industries. Research and development on γ-alloys have progressed significantly within the last decade. This research has led to a better understanding of the fundamental correlations between alloy composition and microstructure, processing behaviour and mechanical properties. This paper describes the progress in sheet rolling of γ-TiAl based alloys on industrial scale. Employing an advanced hot-rolling process sheets with lengths >1000 mm have been rolled. Furthermore, first results of foil rolling are presented. The mechanical properties of γ-TiAl sheet material with regard to processing route, alloy composition and microstructure are summarized and discussed. Sheet forming by means of superplastic forming and conventional metal forming techniques has successfully been conducted. Different joining techniques have been studied for γ-alloys including solid-state diffusion bonding. The oxidation resistance of γ-alloys is higher than that of Ti-alloys, however, for long-term applications at temperatures >700°C the need for reliable oxidation protective coatings is anticipated. Recent results of cyclic oxidation tests on coated γ-TiAl sheet are presented. Finally, the results of a stability test conducted on a γ-TiAl panel at 750°C are summarized.
Low Cycle Fatigue of FeAl (42 at. % Al) at Room Temperature
Authors: Hanes D. B. , Gibala R. 
Published: April 2011

ABSTRACTThe monotonie mechanical behavior in tension and compression of FeAl has been well documented. However, very little work has been done on the cyclic deformation behavior of this material. In this work, the behavior of FeAl (42 at. % Al) under low cycle fatigue was studied, including the effects of test environments and surface coatings. It was found that the fatigue life of this alloy is limited by environmental embrittlement. This embrittlement process can be equally well prevented by deformation in an oxygen environment or by coating the alloy with a protective film. The type of film applied appears to have little effect. Similar results were seen in monotonie testing.
Mechanical Properties of Binary Ni3Al Single Crystals
Authors: Bonneville J. , Martin J.-L. , Spätig P. , Viguier B. , Matterstock B. 
Published: April 2011

ABSTRACTThe mechanical properties of binary Ni76.6Al23.4 single crystalline specimens have been studied in compression test over a wide range of temperature (293–1100K). The resolved proof stress (τ0.2%) and the corresponding work-hardening rate (θ0.2%) have been measured as a function of temperature. In addition, a technique of repeated stress relaxations has been used to investigate the related microscopic activation volume (V0.2%) and to characterize the variation in the density of mobile dislocations that occurs during such transient tests. It is observed that not only τ0.2% exhibits an anomalous behavior with temperature but also θ0.2%, while the stress dependence of V0.2% may be considered as normal, i.e. V0.2% is a monotonie decreasing function of stress.
Ductility Response of Ni3Al-Zr-B Base Alloys with Ternary Elements to Strain Rate and High Temperature
Authors: Wang Yinmin , Lin Dongliang , Lin T. L. , Zhang Yun 
Published: April 2011

ABSTRACTThe compressive ductilities of Ni3Al-Zr-B base alloys with sole addition of magnesium (0.02∼0.06wt.%) and combined addition of magnesium(0.02wt.%) and silicon(0.54∼1.08wt.%) respectively responding to strain rate rising from 10-4sec-1 to 10-1 sec-1 have been studied in a high temperature range of 1073∼1273K. The results show that the compressive strains at rupture(CSR) of the alloys have been greatly improved by sole addition of magnesium and the alloys with combined addition of magnesium and silicon reveal even higher CSR values, furthermore, at temperatures of 1073K and 1273K, the strain rate dependence of CSR reveals to be anomalous, i.e, the CSR value increases as the strain rate rises, and then declines until it surpasses the peak value, which is corresponded to the strain rate of 10-3 sec-1 and 10-3 sec-1 respectively.The beneficial effect of magnesium and silicon exists in their competence of reducing strain rate sensitivity exponent values. The mechanisms of the anomalous ductilizing behavior in the Ni3Al as affected by ternary elements are discussed.
Modeling of the Dislocation Dynamics in Ni3Al and the Flow Stress Anomaly
Authors: Devincre B. , Veyssiere P. , Kubin L. , Saada Lem G. 
Published: April 2011

ABSTRACTNi3Al single crystals are known to exhibit a flow stress anomaly between 200 and 800K. The purpose of our work is to examine such an anomaly by means of a simulation of the dislocation dynamics at a mesoscopic scale. The simulation basic rules are: i) the dislocation glide in {111} octahedral planes, ii) the conditions at which screw lines are locked and unlocked by the formation of Kear-Wilsdorf locks, iii) the mobility of jogs in the {100} cube plane. Our results suggest that two different temperature regimes occur in the domain of the anomaly. At low temperatures, the plastic flow is governed by kink bow-out, itself a function of the kink length. At high temperatures, the plastic flow is governed by the unlocking of the weakest Kear-Wilsdorf locks in the microstructure. These outcomes of the simulation are discussed in relation with the existing theoretical models of the flow stress anomaly.
Fabrication of NiAl Intermetallic from Dense Elemental Powder Blends VIA Solid State Reactions
Authors: Farber L. , Gotman I. , Gutmanas E. Y. 
Published: April 2011

ABSTRACTDense NiAl intermetallic was synthesized from very fine elemental powders via solid state reactions. Homogeneous blends of micron size Ni and Al powders were consolidated to full density and heat treated in a 425–800°C temperature range. During heat treatment, formation of various intermediate intermetallics phases: NiAl3, Ni2A13, Ni3Al and NiAl was observed. The sequence and kinetics of these phase formations at different temperatures were studied employing X-ray diffraction analysis (XRD). A model for a description of synthesis reaction kinetics in Ni-Al blends was developed. Based on the obtained results, the synthesis of NiAl was performed in two stages : reactions in 425–550°C range with consumption of Al, followed by a reaction at up to 800°C. It allowed uncontrolled SHS (self propagating high temperature synthesis, resulting in the occurrence of liquid phases and in formation of reaction products in a very fast /explosive manner) to be avoid. The synthesis temperatures are considerably lower than those used currently in processing of NiAl.
Anomalous Temperature Dependence of Yield Stress and Work Hardening Coefficient of B2-Stabilized NiTi Alloys
Authors: Hosoda Hideki , Mishima Yoshinao , Suzuki Tomoo 
Published: April 2011

ABSTRACTYield stress and work hardening coefficient of B2-stabilized NiTi alloys are investigated using compression tests. Compositions of NiTi alloys are based on Ni-49moJ.%Ti, to which Cr, Co and Al are chosen as ternary elements which reduce martensitic transformation temperatures of the B2 phase. Mechanical tests are carried out in liquid nitrogen at 77K, air at room temperature (R.T.) and in an argon atmosphere between 473K and 873K. Only at 77K, some alloys show characteristic stress-strain curves which indicate stress induced martensitic transformation (SIMT), but the others do not. Work hardening coefficient is found to be between 2 and 1 lGPa in all the test temperature range. The values are extremely high compared with Young's modulus of B2 NiTi. Yield stress and work hardening coefficient increase with test temperature between R.T. and about 650K in most alloys. The anomalous temperature dependence of mechanical properties is not related to SIMT but to precipitation hardening and/or anomalous dislocation motion similar to B2-type CoTi. Solution hardening by adding ternary elements is evaluated to be small for Cr and Co additions, and large for Al addition, depending on difference in atomic size of the ternary element with respect to Ni or Ti.
Microstructure of Thermally Crosslinkable Poly(Ethylene Terephthalate) (Pet-co-Xta) Benzocyclobutene Functionalized Copolymers
Authors: Foran Brendan J. , Pingel Elizabeth , Spilman Gary E. , Markoski Larry J. , Jiang Tao , Martin David C. 
Published: April 2011

ABSTRACTThe microstructure and thermal properties of copolymers of polyethylene terephthalate (PET) containing a crosslinkable terephthalic acid, 1,2-dihydrocyc Iobutabenzene 3,6 dicarboxylic acid (XTA) are reported. Wide angle x-ray scattering (WAXS) show that the addition of XTA does not alter the PET crystal structure in copolymers at low XTA contents. However, the degree of crystallinity drops for higher XTA levels. WAXS profiles show that PET-co-XTA 50% is amorphous, and that PEXTA homopolymer has a different crystal structure. Thermal data from DSC and TGA show that crosslinking of the benzocyclobutene groups (∼350°C) occurs at temperatures between melting (∼250°C) and degradation (∼400°C), making it possible to melt process the copolymers into fibers before the onset of crosslinking. Limiting oxygen index (LOI) measurements show that increased oxygen concentrations are required to sustain a stable flame in PET-co-XTA copolymers; whereas unmodified PET had an LOI value of -18%, the copolymers had LOI values near 32%. Further, while unmodified PET melts and drips as it burns, XTA copolymers formed a stable char that inhibiting flame propagation. An increased char was observed in optical micrographs for XTA containing polymers, and crystalline domains were observed near the burn surface in transmission electron micrographs.