bluuebunny/crossref_metadata_2025 huggingface dataset:
Yield Stress Reversibility and the Operation of Frank-Read Sources in Li2 Alloys in the Anomalous Regime For (111) Slip
Authors: Ezz S. S. , Hirsch P. B.
Published: April 2011

The yield stress τy at small strains (≈ 0.01%) is strain rate independent, and has the same anomalous temperature dependence as that of the 0.2% strain. τy is considered to be the stress at which Frank-Read sources operate in a virgin crystal. For successful operation, τy must exceed the stress τs at which screws propagate dynamically through the crystal, and the source dislocation must pass rapidly through the unstable Frank - Read configuration. This can be achieved by the bowing edge dislocation overcoming local obstacles before reaching that configuration. Loops elongated along the screw direction are expected to be formed in the microstrain region. Under certain conditions such loops are unstable on unloading, thereby generating long edge dislocations which can operate successfully as sources at low but not at high temperatures, explaining the reversibility phenomenon.
A New Interpretation of Stress Relaxations in Ni3(Al,Hf) Single Crystals.
Authors: Bonneville J. , Spätig P. , Martin J.-L.
Published: April 2011

A technique of repeated stress relaxations is used to characterise the strain hardening rate (K) and the mobile dislocation density (ρm) in the flow strength anomaly domain of Ni3(Al,Hf) single crystals. It is shown that there is no independent means for measuring both effects but that reasonable assumptions about the strain hardening rate lead to determine the variation of ρm during relaxation. Preliminary results indicate that during relaxation ρm decreases more rapidly with strain (stress) when the temperature is raised.
Influence of Dislocation Mobility on Room and High Temperature Ductility of <100>-Oriented Nial Single Crystals
Authors: Morris M. A. , Perez J. P. , Darolia R.
Published: April 2011

The dislocation configurations produced by room and high temperature compression of <100> oriented single crystals of binary NiAl and in those containing iron and hafnium additions have been analysed and compared to those obtained by hardness indentation and TEM insitu tensile tests. Kinking occurs during room temperature compression such that <100> dislocations are activated in all cases but the iron-containing alloy also exhibited a large density of <111> screw dislocations. The latter however, appear immobile when they are created by hardness indentations of thin foils, while only pile-ups of <100> segments can propagate. Similarly, although different slip systems are present after high temperature compression, only <100> dislocation segments have been confirmed to be mobile after room temperature hardness indentation of these predeformed thin foils. The improvement in ductility observed at room temperature in the predeformed specimens of the binary and the iron containing alloys has been attributed to the increased production of these mobile <100> dislocations.
Local Electronic Structure and Cohesion of Grain Boundaries in Ni3Al
Authors: Muller D. A. , Subramanian S. , Sass S. L. , Silcox J. , Batson P. E.
Published: April 2011

One of the fundamental questions concerning Ni3Al is why doping with boron improves the room temperature ductility of the polycrystalline material. Boron is thought to prevent environmental embrittlement and increase the cohesive strength of grain boundaries since it changes the fracture mode from intergranular to transgranular. This change in cohesive energy must be reflected in the bonding changes at the grain boundary which can be probed using spatially resolved electron energy loss spectroscopy (EELS). We have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24using EELS, EDX and ADF imaging in a UHV STEM. Ni-enrichment is seen in a 0.5–1 nm wide region at large angle grain boundaries, both in the absence and presence of B. EELS shows that B segregation can vary along the interface. The Ni L2, 3core edge fine structure which is sensitive to the filling of the Ni d-band, shows only the boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. These results demonstrate that boron segregation increases the cohesive energy and hence improves the fracture resistance of the grain boundary, by making the bonding at boundaries similar to that in the bulk. The measured changes in d band filling may also affect the local solubility of hydrogen.
The Effect of Nitrogen on the Oxidation of TiAl
Authors: Dettenwanger Franz , Schumann E. , RÜhle M. , Rakowski J. , Meier G. H.
Published: April 2011

Ti-50(at.%)Al samples were oxidized at 900°C in air for 1 hour and studied by electron microscopy. The application of electron spectroscopic imaging with energy filtered TEM permitted the imaging of the distribution of the relevant elements (Ti, Al, O, N) within the oxide scale. With this method the formation of TiN in the inner part of the scale could be shown. The oxidation in air lead to an alternating scale containing TiN and alumina near the metal/scale interface. The formation of an aluminum-depleted second metallic phase in the metal beneath the oxide scale was observed.
A Non-Linear Behavior Model for SiC/SiC Composites
Authors: Kibler J.J. , Jones M.L. , Yen C.F.
Published: April 2011

An interactive analytical model has been developed for modeling the behavior of Continuous Fiber reinforced Ceramic matrix Composites (CFCC). The model integrates a large number of micromechanics solutions to problems associated with the microstructure of CFCC materials into an easy to use tool for predicting properties, strengths, and stress states for these materials in unidirectional and laminated forms. Particulate reinforcement and voids can be included in the material description. Inherent in the code is a model for handling the accumulation of micro cracks within the matrix as loading is increased, resulting in a nonlinear stress-strain response of the composite. Sufficient material characteristics are retained within the model to enable sensitivity studies to identify principal causes for material behavior.
A Numerical Analysis of Fracture and High Temperature Creep Characteristics of Composites with Discontinuous Ductile Reinforcements
Authors: Biner S. B.
Published: April 2011

The role of the material parameters on the fracture and creep behavior of discontinuous ductile fiber reinforced brittle matrix composite system was numerically investigated. For simulation of fracture behavior, the ductile fibers were modeled using a constitutive relationship that accounts for strength degradation resulting from nucleation and growth of the voids. The matrix is assumed to be elastic and fails according to requirements of a stress criterion. Results indicate that the contribution of ductile reinforcement to the work of fracture value (toughness) of the composite increases with less exhaustion of its work hardening capacity before the onset of matrix failure. At creep regime, for rigidly bonded interfaces, the creep rate of the composite is not significantly influenced by the material properties of the ductile reinforcing phase due to development of large hydrostatic stress and constrained deformation in the reinforcement. Significant increases in room temperature fracture toughness can be achieved without extensively sacrificing the creep strength by ductile discontinuous reinforcements.
The Preparation and Economics of Silicon Carbide Matrix Composites by Chemical Vapor Infiltration
Authors: Roman Yvette G. , Stinton David P.
Published: April 2011

This paper describes a number of processing techniques that are currently in use for the development and production of continuous fiber reinforced ceramic composite materials. The limited number of available processing routes are compared with respect to the resulting material properties.

As it appears, the Chemical Vapor Infiltration technique is one of the most extensively developed methods. During the last decade, at least five different modifications of the isobaric isothermal CVI principle have been developed; each route having its own benefits. CVI techniques have now been developed to the extent that industrial commercialization is being realized. Projected cost aspects of the various CVI manufacturing techniques have been examined and compared.
Resistivity Control by Solid-State Reaction of Perovskite-Type Oxides
Authors: Nagamoto H. , Tanaka H. , Koya T.
Published: April 2011

Resistivity control has been conducted by solid–state reaction of two different perovskite–type oxides. One is La0.5Ba0.5CoO3−δ (LBC) which showed metallic conduction, and its resistivity, ρ was 10−3 Ω.cm at 20 °C. The other is Ba0.998Sb0.002TiO3 (BT) which showed positive temperature coefficient of resistivity (PTCR) effect. The sintered body of the mixiure of the two oxides did not show PTCR effect. The logarithm of the resistivity of the sintered body, log ρmix was expressed using the resistivity of LBC, ρLBC, the molar ratio of BT, x, and temperature dependent constant, α(T) as

log ρmix = (l–x) log PLBC + xα(T)

which holds for 0 ≤ x ≤ 0.8 at the temperature ranging from 20 to 240° C ρmix changed by about 8 orders of magnitude at room temperature. X–ray diffraction analysis suggested that metal ions at the A–site move from one perovskite–type oxide to another and that the sintered body consisted of two perovskite–type oxides different from starting ones.
Correlation Between Changes in Microhardness and Phosphorus Segregation During Post-Irradiation Annealing
Authors: Kameda J. , Gold C. R. , Bloomer T. E.
Published: April 2011

This paper describes the effect of post-irradiation annealing (PIA: 573-873K for 10 h) on the microhardness and intergranular P segregation in P doped and Cu-P doped iron alloys containing residual S. Hardening and softening occurred during PIA at lower and higher temperatures, respectively. PIA-induced hardening was more profoundly observed in the Cu-P doped alloy. Intergranular P enrichment was achieved by lower temperature PIA and P desegregation associated with S segregation dominated at higher PIA temperatures in both the alloys. Changes in the microhardness and intergranular P segregation induced by the PIA were found to be correlated with each other although the Cu-P doped alloy showed more scatter. The dynamic interaction between solute and defects in the grain interior and near grain boundaries during the PIA is discussed in order to explain the experimental observation.
Irradiation Effects on Fe Distributions in Zircaloy-2 and Zr-2.5Nb
Authors: Zou Heilong , Hood G.M. , Roy J.A. , Packwood R.H.
Published: April 2011

Irradiation of large-grained Zircaloy-2 (Zy) and Zr-2.5Nb (ZN) with 1.5 MeV Ar+ ions to fluences of ≈ 1020/m2 (= 10-30 dpa) at 50, 300 and 420 °C, leads to enhanced ∝-phase Fe dissolution. Electron microprobe analyses showed ∝-phase Fe levels of 250-1500 ppma, compared to equivalent, non-irradiated state values of ≈ 70 ppma. In ZN the β-phase Fe levels fell from about 6000 to 3500 ppma: this result accords, qualitatively, with the loss of Fe from the β-phase following in-service neutron irradiation. Concentration vs depth measurements for Zy showed higher Fe levels towards the surface. Limited data for Ni in Zy show similar behaviour.
The Observations of Paramagnetic Centers in Tellurite Glasses
Authors: Prohaska J.D. , Li J. , Kannan S. , Snitzer E. , Wang J.S. , Bartram R.H.
Published: April 2011

This is the first report of ESR observations of three distinct paramagnetic centers in TeO29 glasses. One center is intrinsic to the glass and the other two are induced by KrFexcimer-laser radiation. The intrinsic center with a broad ESR spectrum is tentatively identified as an oxygen-associated hole center. One radiation-induced center fades slowly at room temperature; its proposed structure is that of an electron trapped in a diffuse orbital associated with a modifier ion. The other radiation-induced center is stable at room temperature and corresponds to the Vo· center observed in crystalline paratellurite.
Computer Simulation of Thermal Annealing Effects on Self Implanted Silicon
Authors: Sandre G. DE , Colombo L. , Maric D.
Published: April 2011

We investigate the effects of thermal annealing on the structural, elastic and electronic properties of self implanted silicon by tight binding molecular dynamics. The irradiated samples, after a careful relaxation at room temperature, are annealed at different temperatures and for different times and, finally, their properties are carefully monitored during constant temperature simulations. We further provide a characterization of the chemical bonding in the amorphous network and show the evolution of the point defect distribution against maximum annealing temperature.
Molecular dynamics studies of Radiation Effects in Silicon Carbide
Authors: de la Rubia T. Diaz , Caturla M.-J. , Tobin M.
Published: April 2011

We discuss results of molecular dynamics computer simulation studies of 3 keV and 5 keV displacement cascades in β-SiC, and compare them to results of 5 keV cascades in pure silicon. The SiC simulations are performed with the Tersoff potential. For silicon we use the Stillinger-Weber potential. Simulations were carried out for Si recoils in 3 dimensional cubic computational cells with periodic boundary conditions and up to 175,616 atoms. The cascade lifetime in SiC is found to be extremely short. This, combined with the high melting temperature of SiC, precludes direct lattice amorphization during the cascade. Although large disordered regions result, these retain their basic crystalline structure. These results are in contrast with observations in pure silicon where direct-impact amorphization from the cascade is seen to take place. The SiC results also show anisotropy in the number of Si and C recoils as well as in the number of replacements in each sublattice. Details of the damage configurations obtained will be discussed.
Nucleation with Radiation Dissolution and Resolution
Authors: Russell K.C.
Published: April 2011

Energetic particle irradiation may induce athermal processes in addition to the thermallyactivated single atom addition or subtraction events considered by classical nucleation theory. Displacement cascades could destroy sub-critical precipitates. Similarly, either displacement cascades or energetic knock-on atoms could remove single atoms or groups of atoms from subcritical clusters.

Cluster destruction becomes significant in nucleation when the probability of destruction is comparable to the probability of growth by single atom capture. The model is applied to the nucleation of embrittling precipitates in pressure vessel steels. The scaling of accelerated embrittlement tests on the basis of displacements per atom is found only sometimes to be applicable. Athermal single atom loss, as in ion mixing, may appreciably reduce the nucleation if the rate of loss approaches or exceeds the rate of solute atom capture.
Solution Chemistry Effects on the Nonlinear Optical Properties of Phosphazenes
Authors: Ferris Kim F. , Samuels W. D. , Morita Y. , Exarhos G. J.
Published: April 2011

Using the combination of experimental (DFWM) measurements and electronic structure calculations, ligand electron donating power and explicit solvent interactions were shown to have critical roles in enhancing the χ3 yields for phosphonitrilic materials. Experimental measurements have shown that decreasing solution pH to 1.0 can significantly increase the χ3 yield for P3N3(NHCH3)6 and P3N3(N(CH3)2)6. Corresponding electronic structure calculations indicate replacement of amino by thiomethyl groups will also significantly enhance these yields. Comparison of electrostatic-based solvation effects and explicit water molecules indicates that dielectric stabilization from the solvent plays a minor influence on χ3 in comparison to strategies which affect the strong P-N bond polarity.
Towards a Structure-Rsa Relationship for Non-Linear Optical Materials.
Authors: Bahra G. S. , Griffiths J. , Healy W. , Millar V. , Till S. J. , Till J.
Published: April 2011

Measurements on the reverse saturable absorption (RSA) properties of some polyene dyes are presented. For a series of linear dyes, a correlation is observed between the symmetry of a molecule and its ability to exhibit RSA. To our knowledge, this is the first structure-RSA relationship discovered to date.

Certain of these materials have been studied with semi-empirical quantum chemical techniques and the observed structure-RSA relationship is rationalised in terms of the calculated electronic structures. In this paper, we report primarily on some studies we have carried out on the linear dye systems.
Electro-Optic Power Limiter: Broadband, Self-Actuating Optical Limiter for Visible and Infrared Radiation
Authors: Chang Tallis Y. , McMichael Ian , Hong John H. , Khoshnevisan Monte
Published: April 2011

We present studies of an optical power limiter that uses a combination of the photoconductive and linear electro-optic effects. The electro-optic power limiter (EOPL), first demonstrated using CdTe in the near IR, possesses many desirable qualities including broadband wavelength responsivity, self-actuation, and low threshold power. One unique capability of EOPL, not found in any other nonlinear optical power limiter, is the fact that any light - coherent or incoherent - can be used. Our studies in CdTe, GaAs, and BSO crystals resulted in extending the wavelength range from the visible to MWIR wavelengths.
Deposition of Si Thin Films by Reactive CVD
Authors: Hanna Jun-Ichi
Published: April 2011

A new concept of Reactive CVD is proposed for the low-temperature growth of thin films by CVD and discussed in terms of general features of such film growth. One demonstrated example of the reactive CVD, called Spontaneous Chemical Deposition, features gas phase reactions of silane with fluorine is outlined in terms of the general characteristics of the film growth and properties.

In addition, a second example of reactive CVD, called Reactive Thermal CVD and involving thermal CVD of poly-SiGe from germanium fluoride and disilane, is discussed and low-temperature growth using this method is reviewed.
Growth and Nucleation of Hydrogenated Amorphous Silicon on Silicon (100) Surfaces
Authors: Tanenbaum D. M. , Laracuente A. , Gallagher A. C.
Published: April 2011

A scanning tunneling microscope (STM) has been used to study the topology of the surfaces of a series of thin hydrogenated amorphous silicon (a-Si:H) films deposited by rf discharge from pure silane. The substrates were atomically flat, oxide-free, single-crystal Si (100). Films were grown in our laboratory and transferred to the STM with no air exposure between growth and measurement. A series of thin films between 1 and 50 nm in thickness reveals the initial growth stage of a-Si:H on Si (100). Initial nucleation and islanding can be seen on these films. The surface has a distribution of island sizes. The rms roughness and a surface lateral correlation length were measured as functions of film thickness. The rms roughness grows sublinearly with thickness from 0.3–0.5 nm as the film thickness is raised from 1 to 50 nm. The lateral size of the surface features also grows with film thickness. The growth of the roughness and correlation length can be compared with the dynamic scaling model. In addition, the topographs reveal occasional structures of larger size and low density on the film surface. These structures are nanoparticles of silicon deposited from the plasma during film growth. The frequency of these features scales with film thickness, and represents 10−510−4 of the total film volume.
Below Gap Excitation of Photoluminescence in a-Si:H
Authors: Yin X. , Raikh M. E. , Taylor P. C.
Published: April 2011

PL measurements on device-quality samples of a-Si:H (dark ESR bulk signal, Ns < 3 × 1015spins/cm3) and on a sample with Ng = 1016 spins/cm3 have been performed using excitation energies, E×, from approximately 1.3 to 2.4 eV. Sample temperatures investigated cover the range 4 to 300 K, and PL energies both below and above the excitation energies were measured. PL spectra were recorded from approximately 0.7 to 1.8 eV with a dynamic range exceeding 1012 at constant incident power density. The results permit the separation of the one-photon (band-tail to band-tail) and two-photon (two consecutive excitations through silicon dangling bonds) excitation processes. In contrast to the well-known, strong temperature dependence of the PL efficiencies near the PL peak, the PL at the highest energies (> 1.7 eV) depends only weakly on the temperature at constant Ex.
Dangling-Bond Relaxation and Metastability in P-Type Hydrogenated Amorphous Silicon
Authors: Crandall Richard S. , Carlen Martin W. , Lips Klaus , Xu Yueqin
Published: April 2011

We discuss the subtle effects involved in observing slow dangling bond relaxation by studying capacitance transients in p-type hydrogenated amorphous silicon (a-Si:H). The data suggest that neutral dangling bonds are reversibly converted into metastable positive charged dangling bonds by hole trapping. These metastable positive dangling bonds reconvert to neutral dangling bonds upon annealing at elevated temperature. The annealing kinetics for this process are the same as those observed for annealing of quenched in conductivity changes in p-type a-Si:H.
Investigation of the Surface Morphology of a-Si:H by Atomic Force Microscopy and In-Situ Ellipsometry
Authors: Wanka H. N. , Hierzenberger A. , Schubert M. B.
Published: April 2011

Combining real-time ellipsometry and atomic force microscopy (AFM) the growth of hydrogenated amorphous silicon (a-Si:H), deposited on crystalline silicon wafers with a native oxide layer on top and on fused silica from a dc glow discharge, has been studied from initial nucleation to the final morphology. By in-situ ellipsometry we detected the evolution of morphology changes. The surface structure has been determined by AFM in the nucleation phase and in the subsequent growth stage. During nucleation on crystalline silicon only few (about 40 per 1μm) flat islands of a-Si:H (up to 4 nm high and up to 50 nm in diameter) grow with a strongly enhanced rate compared to bulk deposition. Once the crystalline surface has completely been covered by a-Si:H, the fast deposition of these islands stops and further surface structures, comparable with the initial ones, start to grow gradually until a homogeneous final roughness up to 5nm high is formed. Nucleation of a-Si:H on fused silica yields densely distributed nuclei (up to 1.5 nm high and up to 25 nm in diameter), indicating a shorter surface diffusion length on this substrate compared to the growth on silicon wafers. The ongoing film deposition, however, finally results in a morphology comparable to the one of a-Si:H grown on crystalline silicon. Using hydrogen dilution we found that the final roughness is affected by the dilution ratio; furthermore infrared spectroscopy reveals the surface structure to be correlated with the hydrogen content of the a-Si:H films.
Solubility of Hydrogen in Amorphous Silicon
Authors: Daey Ouwens J. , Schropp R. E. I.
Published: April 2011

We demonstrate that the exisiting ambiguity between the Nuclear Magnetic Resonance (NMR) and the infra-red (IR) interpretation of the density of clustered hydrogen can be removed by monitoring the effective charge of the silicon hydrogen vibrations in a-Si:H versus the hydrogen content. By monitoring the peak position of the low frequency component (2000 cm−1 mode) of the stretching doublet, we conclude that the 2000 cm−1 and the 2100 cm−1 modes can be uniquely attributed to the monohydride and multihydride bonding configurations, respectively.

We show that the parameters describing the IR spectrum depend on the hydrogen content only and do not depend on the deposition technique, deposition conditions or post-deposition annealing treatment.
Fabrication of Boron Compensated Hydrogenated Amorphous Silicon Films with Significantly Improved Stability Using Plasma Enhanced Chemical Vapor Deposition Technique
Authors: Bhan Mohan K.
Published: April 2011

We have systematically investigated the effects of addition of sub-ppm levels of boron on the stability of a-Si:H films and p-i-n devices, deposited by PE-CVD technique. The films thus produced with appropriate amounts of boron, show a significant improvement in stability, when soaked under both AM 1.5 (short-term) as well as 10×sun (long-term) illumination conditions. The opto-electronic properties of the films are quite respectable It is concluded that boron compensates the native impurities by forming donor-acceptor pairs, which reduces the “fast” defects and hence the initial degradation of the films. It is also speculated that boron may also be improving the short-term stability, by reducing the recombination of light generated electrons and holes, by converting D° into D+ states. The long-term stability appears to get affected by hydrogen dilution which seems to reduce the amount of “slow” defects. As a result of B doping of i-layer, the initial conversion efficiency of the devices decreases. It is presumed that our devices may contain an enhanced level of boron impurity, than expected, making them as worse material and to degrade less.
Fabrication of Nanocrystalline Si by SiH4 Plasma Cell
Authors: Otobe Masanori , Kanai Tomonori , Oda Shunri
Published: April 2011

Nanocrystalline silicon (nc-Si) has been fabricated by a very-high-frequency plasma cell attached to an ultra-high-vacuum chamber using SiH4 gas. Nanocrystalline Si is formed in the gas phase of the plasma cell and is extracted out of plasma cell through the orifice to the ultra-high-vacuum chamber. The shape of nc-Si is spherical or octahedral with the diameter of 3–30nm. Giant Si particles about 100nm in diameter are also formed at the lower cell pressure condition. A 1000keV transmission electron microscopy measurement has revealed that the core region of giant Si particle with the diameter about 30nm was crystalline and the shell region is amorphous. We have demonstrated that the spread of particle size can be decreased using pulsed gas supply of H2 into SiH4 plasma.
Investigations of Tail and Defect States in a-Si0.6Ge0.4:H Alloys by PDS and ESR - Implications for the Interaction of Weak and Dangling Bonds
Authors: Drüsedau Tilo P. , Panckow Andreas N. , Schröder Bernd
Published: April 2011

Investigations on the gap state density were performed on a variety of samples of hydrogenated amorphous silicon germanium alloys (Ge fraction around 40 at%) containing different amounts of hydrogen. From subgap absorption measurements the values of the “integrated excess absorption” and the “defect absorption” were determined. Using a calibration constant, which is well established for the determination of the defect density from the integrated excess absorption of a-Si:H and a-Ge:H, it was found that the defect density is underestimated by nearly one order of magnitude. The underlying mechanisms for this discrepancy are discussed. The calibration constants for the present alloys are determined to 8.3×1016 eV−1 cnr2 and 1.7×1016 cm−2 for the excess and defect absorption, respectively. The defect density of the films was found to depend on the Urbach energy according to the law derived from Stutzmann's dangling bond - weak bond conversion model for a-Si:H. However, the model parameters - the density of states at the onset of the exponential tails N*=27×1020 eV−1 cm−3 and the position of the demarcation energy Edb-E*=0.1 eV are considerably smaller than in a-Si:H.
Trends of Research in Active Addressing of LCDS
Authors: Lueder Ernst
Published: April 2011

Active addressing is focused on TFTs and MIMs as pixel-switches. The manufacture of a-Si-TFTs tends to settle down at a three-mask process as long as risky steps can be avoided. Fabrication throughput is being enhanced by increasing the deposition rate for a-Si- and poly-Si-layers processed by PECV.D. For wider process windows and for building row drivers with a-Si-TFTs effective mobility will have to be increased beyond 1 cm2/Vs especially by new TFT-electrodes, a protective sandwich around the a-Si-layer and modified process techniques. Poly-Si-TFTs should be fabricated at temperatures below 450 °C and preferably without laser annealing before they become an economic solution. MIMs still require more materials research to find a dielectric with a larger trap density enhancing speed of operation, lower addressing voltages and electrodes for improved long-term stability. Low-temperature processes are required for LCDs with plastic substrates.
Enhancement of Crystallinity with Fluorinated Amorphous Silicon (a-Si:H;F) Film by XeCl Excimer Laser Annealing
Authors: Choi H. S. , Jang K. H. , Kim K. B. , Han M. K.
Published: April 2011

The Effects of fluorine atoms on laser-induced crystallization have been studied. The defect states of hydrogenated amorphous silicon (a-Si:H) film, which are related to weak hydrogen bonds, were reduced by involving fluorine atoms, before laser annealing. In laser annealing, the crystallinity was also enhanced to 63 %, while that of a-Si:H was 45 % at the energy density of 300 mJ/cm2. It may be considered that the fluorine atoms reduce the hydrogen atoms cause to the degradation of film in laser annealing, and increase the heat capacity which results in promotion of crystallinity in melt-solid phase transition.
DLTS Study on Annealed Low-Temperature GaAs Layers with An n-I(LT)-n Structure Grown by MBE
Authors: Lin Tsai-Cheng , Kaibe Hiromasa T , Okumura Tsugunori
Published: April 2011

Deep levels in the annealed low-temperature molecular beam epitaxial (LT-MBE) GaAs layer were successfully characterized by using the capacitance deep-level transient spectroscopy (C-DLTS) as well as photocapacitance quenching technique in combination with a unique sample structure. In this work, we have fabricated the samples by inserting the LT-GaAs layer into two n-type semi-conductive layers, like a sandwich (n-LT-n structure), grown at normal substrate temperatures. DLTS measurements have revealed that one electron trap dominates the annealed LT-MBE GaAs. The dominant electron trap was very similar to the so-called EL3 level. Moreover, we found the midgap level appeared upon 800-900°C RTA, although no midgap level was detected in the as-grown n-LT-n sample (annealed at 620°C) and confirmed with photoquenching measurements that it is the EL2 level.
Nonstoichiometric Defects in Semiconductor SnTe Thin Films
Authors: Nashchekina O. N. , Rogacheva E. I. , Shpakovskaya L. P. , Pinegin V. I. , Fedorenko A. I.
Published: April 2011

The mono- and polycrystalline films of the SnTe1+x semiconducting phase with controlled content of nonstoichiometric defects (NSD) were grown by thermal evaporation and hot wall epitaxy methods from the charges of different composition. The concentration of NSD was determined using X-Ray diffraction method and the measurements of carrier density. The temperature dependences of electrical conductivity and Hall coefficient were obtained in the temperature range of 77 - 300 K. The best results were obtained for hot wall epitaxy method: the perfect monocrystalline films with NSD content corresponding to x =0-0,025 and high mobility of charge carriers were grown.
Impurity Gettering in MBE Grown Silicon
Authors: Nylandsted Larsen A. , KringhØj P. , Lundsgaard Hansen J. , Shiryaev S. Yu.
Published: April 2011

A MBE growth procedure of epitaxial silicon layers is demonstrated which includes a special designed buried strained compositionally graded Si1−xGex layer. Upon thermal relaxation closed dislocation loops are formed in this Si1−xGex layer without altering the structure of the Si top layer. This dislocated layer is shown to getter contaminants in the Si top layer reducing the concentration of deep levels in this layer to ≈1 × 1012 cm−3.
Hydrogen-Induced Metastability of Polycrystalline Silicon
Authors: Nickel N. H.
Published: April 2011

The presence of H in polycrystalline silicon gives rise to new and hitherto unexpected phenomena. In this paper two of the most recent observations are reviewed: (i) Hydrogen-induced metastable changes of the dark conductivity due to the formation and dissociation of an electrically active H complex and (ii) the generation of acceptor states during prolonged exposure of poly-Si to monatomic H at elevated temperatures. The observed type conversion is clearly due to the diffusion of excess H from the plasma since it does not occur during exposure to other species such as oxygen.
Hydrogen Passivation of Shallow Dopants in Indium Doped Bulk CdTe
Authors: Gurumurthy Suma , Sreedhar A. K. , Bhat H. L. , Sundersheshu B. , Bagai R. K. , Kumar Vikram
Published: April 2011

Hydrogen passivation effects in In doped n-CdTe upon exposure to rf hydrogen plasma have been studied by electrical and photoluminescence measurements. Shallow dopant passivation of approximately an order of magnitude at 150°C and 50% at 170°C is observed. No visual damage is seen. Reverse bias annealing effects are also studied. Results are discussed.
Defect Studies in n-Type GaN Grown by Molecular Beam Epitaxy
Authors: Götz W. , Oberman D. B. , Harris J. S.
Published: April 2011

GaN thin films grown by molecular beam epitaxy (MBE) were characterized by Hall effect measurements in the temperature range from 80 K to 500 K and by photoluminescence spectroscopy (PL) at 2 K and at 300 K. These films were grown by MBE utilizing either electron cyclotron resonance (ECR) plasma activated nitrogen gas or thermally cracked hydrogen azide (HN3) as the source of chemically reactive nitrogen. The electrical properties of the GaN films grown by ECR plasma assisted MBE were found to vary with growth parameters, dominated either by shallow donors with activation energies (ΔE)in the range between 10 meV and 30 meV or deep donor levels (ΔE; > 500 meV). GaN grown by (HN3) gas-source MBE exhibited metallic conduction and electron mobilities <1 cm2/Vs. However, these films displayed sharp photoluminescence lines at 3.360 eV and 3.298 eV and no deep level related luminescence, whereas only broad deep level related emission was observed in the PL spectra of the ECR plasma assisted MBE grown GaN films.
The Role of the Si-SiO2 (CVD) Interface in Degradation Effects for High-Speed Bipolar Transistors
Authors: Lü J.-Q. , Schöttl S. , Stefanov E. , Koch F. , Mahnkopf R. , Klose H.
Published: April 2011

The intent of the present work is to analyze device degradation and reliability in terms of their microscopic origins. The base-emitter junction of the advanced, “double-poly”, self-aligned bipolar transistor contacts the SiO2 sidewall spacer. During normal circuit operation, the base-emitter junction experiences a reverse bias which as a stress in time degrades the current gain of the transistor. Both a decrease of the gain, as well as an increase in the noise are observed. The forward base current increase as a function of stress time follows △IB ∼ tn. We present evidence that the defects are occurring at the Si-Si02 interface from perimeter to area comparisons. The weak temperature dependence of the forward base current in degraded transistors shows that trap-assisted tunneling current through the Si-SiO2 interface states is involved. The random-telegraph-signals observed for the first time in a silicon bipolar transistor are a direct identification of damage at the Si-SiO2 interface. 2D simulation of the potential and field near the interface allows us to show that damage can be expected.
Surface Morphology Investigation of Au and Pt Electroless Contact on ZnCdTe Crystal by Atomic Force Microscopy
Authors: Hu Zhiyu , Hu Zhihua , Chen K. T. , George M. A. , Burger A. , Collins W. E.
Published: April 2011

Gold and platinum metal contacts have been deposited on the cleaved and etched surfaces of ZnCdTe single crystals by “electroless” method from AuCl3, PtCl2 and PtCl4 aqueous solutions with different concentrations and deposition times. Atomic Force Microscopy (AFM) has been employed to reveal the surface morphology of metal contacts and it was found that for AuCl3 and PtCl2 solutions, the surface morphology and grain size are similar, and uniformly distributed. The surface morphology on contact made from PtCl4 shows a larger grain size, higher roughness and non-uniformity. The effect of different heat treatments to the surface morphology will be discussed.
Direct Wafer Bonding of Preamorphized Silicon Wafers.
Authors: Laporte A. , Sarrabayrouse G. , Benamara M. , Claverie A. , Rocher A. , Lescouzères L. , PeyreLavigne A.
Published: April 2011

This paper presents the comparison of the structural and electrical characteristics of Si/Si bonded interfaces depending on whether the surface layers were rendered amorphous by high dose ion implantation prior to annealing or not. While the general structure of the interfaces is the same when the wafers are preamorphized more precipitates are seen in the interface along with a few extended defects propagating into the volume. The most striking difference between both procedures is that the Spreading Resistance profile is more complicated in shape and difficult to master in the case of preamorphized wafers. Careful TEM analysis shows that only in this case the interfacial region is stressed in contrast with the fully relaxed structure obtained by direct bonding of crystalline wafers.

For these reasons, there is little chance that the preamorphization technique will benefit to the bonding procedure of direct Si wafers.
Interaction Between EL5 and EL6 in Bulk GaAs
Authors: Shiraki Hiroyuki , Tokuda Yutaka , Sassa Koichi
Published: April 2011

The interaction between EL5 and EL6 in the n-type bulk GaAs have been observed by using isothermal constant-capacitance voltage transient spectroscopy (CCVTS). Each CCVTS spectrum of EL5 and EL6 was broader than a theoretical one expected for a single level, and was found to be consistently interpreted by two main trap components. With the increase of the filling pulse duration in a wide range, one component of EL6 decreased to about 50 % of its initial value, while one component of EL5 increased and saturated. This variation in peak heights could be reversed by controlling electron occupation fractions of EL5 and EL6 by application of two adjacent filling pulses. Such interaction between both levels was commonly observed in n-type bulk GaAs independent of carrier density.
Modification of Recombination Activity of Dislocations in Si and SiGe by Contamination and Hydrogenation
Authors: Kittler M. , Seifert W. , Higgs V.
Published: April 2011

Temperature-dependent (80 … 300 K) measurements of dislocation recombination activity by the electron-beam-induced-current (EBIC) technique are reported. Controlled Cu contamination (ppb to ppm range), chemomechanical polishing and hydrogenation treatments were applied to alter dislocation properties. Increasing Cu level is found not only to increase the electrical activity of misfit dislocations in SiGe/Si structures at 300 K, but also to change its dependence on temperature. At low contamination, shallow centres control dislocation activity while deep centres are characteristic at higher Cu levels. Heavy Cu contamination results in very strong recombination activity which is attributed to precipitates. Chemomechanical polishing has an effect which is analogous to medium Cu contamination. Hydrogenation was found to passivate recombination activity at 300 K, but did not show pronounced effects on activity at low temperature.
Studies of Exchange Coupling in Fe/Cu/Fe(001) “Loose Spin” Structures
Authors: Kowalewski M. , Heinrich B. , Totland K. , Cochran J.F. , Govorkov S. , Atlan D. , Myrtle K. , Schurer P.
Published: April 2011

The interlayer exchange coupling has been studied in two trilayer structures:

(a) 5.7Fe/5Cu/1FecCu1-c/5Cu/10Fe(001), where c=0.0, 0.1, 0.2, 0.45 0.60

(b) 5.7Fe/5Cu/1CrcCu1-c/5Cu/10Fe(001), where c=0.1, 0.45, 0.8 and 1.0.

The intention of these studies was to identify the role of Fe and Cr atoms in the alloyed FecCu1-c and CrcCu1-c layers on the direct interlayer coupling which is facilitated by the Cu valence electrons. FMR, BLS and MOKE studies were used to determine the interlayer exchange coupling. Mossbauer spectroscopy was used to identify the magnetic state of the Fe atoms in the alloyed layer. The results showed that the presence of foreign atoms inside the Cu spacer significantly decreased the bilinear antiferromagnetic coupling between the Fe layers. In the low concentration limit the Fe and Cr atoms behaved in a similar manner. A significant difference was found in the high concentration limit where the Fe atoms start to be partially magnetically ordered.
Reducing Intergranular Magnetic Coupling by Incorporating Carbon into Co/Pd Multilayers
Authors: Liu Wenhong , Morris Jonathan , Payne Alex , Lairson Bruce
Published: April 2011

The ideal magnetic switching mechanism for many types of data storage, including hard disk recording, is isolated domain coherent rotation (Stoner-Wohlfarth switching). However, in typical Pd/Co multilayers with high coercivity, the dominant switching mechanism is domain wall motion, which causes noise in the read back signal. We show that the proper addition of elements, such as carbon, into Pd/Co multilayers reduces the coupling between adjacent magnetic domains. The reduction of magnetic coupling reduces the length scale over which incoherent switching occurs.
Magnetic Properties of Epitaxial Mbe-Grown thin Fe3O4 Films on MgO (100)
Authors: Van Der Heijden P.A.A. , Hammink J.J. , Bloemen PJ.H. , Wolf R.M. , Van Opstal M.G. , Van Der Zaag P.J. , Jonge W.J.M. De
Published: April 2011

Coherent epitaxial Fe3O4 layers in the range of 0 to 400 Å have been grown by molecular beam epitaxy on single crystal MgO(100) substrates. The magnetic properties were studied by local magneto-optical Kerr effect experiments on a wedge shaped Fe3O4 layer, by ferromagnetic resonance and SQUID. The results show that the magnetic behavior of the Fe3O4 thin films resembles bulk Fe3O4 in the investigated thickness range.
Magnetic Properties of FEXMN1-X/IR(100) Superlattices.
Authors: Fischer H. , Andrieu S. , Bauer Ph. , Piecuch M.
Published: April 2011

We have produced pseudomorphic FexMn1-x/Ir(100) superlattices having different stoichiometry (0.8 ≥ x ≥ 0.3). The alloy crystalline structure is body centered tetragonal with a c/a ratio between 1.18 and 1.26. Iron rich alloys are ferromagnetic when the corresponding bulk alloys are antiferromagnetic. Manganese rich alloys are certainly antiferromagnetic according to bulk magnetization measurements and Mössbauer effect results. The transition from a ferromagnet with a vanishing moment when x = 0.5 to an antiferromagnet is associated with a volume expansion.
Determination of Spin-Dependent Scattering Parameters of NiFe/Cu and Co/Cu Multilayers
Authors: Lenczowski S.K.J. , Gijs M.A.M. , van de Veerdonk R.J.M. , Giesbers J.B. , de Jonge W.J.M.
Published: April 2011

We present magnetoresistance (MR) data of high-vacuum magnetron sputtered NiFe/Cu multilayers (NiFe=Ni80Fe20) grown on Si(100) substrates with a Cu buffer layer and compare these with earlier results on Co/Cu(100) multilayers [1]. Measured MR values are directly proportional to the antiferromagnetically coupled fraction in the multilayers. Extrapolating to full antiparallel alignment, we can make a reliable comparison of the MR with the magnetoresistance model of Levy, Zhang, and Fert [2,3]. For the NiFe/Cu multilayers the deduced spin-asymmetry parameters are for interface and bulk scattering, respectively. Although much smaller than in our Co/Cu multilayers, , it is still the spin dependence of the interface scattering that is the main cause for the large MR values.
Improved Thermal Stability of Gmr Spin Valve Films
Authors: Mcmichael R. D. , Egelhoff W. F. , Ha Minh
Published: April 2011

In order to improve the thermal stability of magnetic multilayer “spin valve” structures, we have measured the magnetic and magnetoresistive properties of a number of samples with the general structure of NiO/Co/Cu/Co/Cu/Co/NiO as a function of annealing time at 250 °C. The magnetoresistance (MR) of the samples annealed in air decreases proportionally to the square root of the annealing time. For samples annealed in a vacuum, the decrease in magnetoresistance is reduced, but not eliminated. Magnetometry of a vacuum annealed NiO/Co/NiO sample shows a magnetization reduction and a coercivity increase which suggest oxidation of the NiO-biased “outer” Co layers of the spin valve structure. For increasing NiObiased Co layer thickness, we show enhanced thermal stability and even increasing MR with annealing time for samples with the thickest outer Co layers.
Improvement of Gmr in NiFeCo/Cu Multilayers by a Layer - by - Layer Magnetic Field Sputtering
Authors: Saito K. , Yanagida Y. , Obi Y. , Itoho H. , Fujimori H.
Published: April 2011

NiFeCo/Cu multilayers fabricated by an improved magnetic field sputtering were investigated in order to achieve the soft GMR (giant magnetoresistance) with a high sensitivity at low magnetic fields. A magnetic field was applied to the film during sputter-deposition, and its field direction was changed alternately from layer to layer. Such an alternate field sputtering is called hereafter layer-by-layer magnetic field sputtering. The best GMR characteristics (large MR at low magnetic fields) were achieved when the angle between the directions of magnetic field applied to neighboring two magnetic layers was 90°. As one of the speculation, it has been considered that the result is attributed to the induced composite magnetic anisotropy which causes the magnetization to occur more dominantly by spin rotation than by domain wall movement.
In Situ Study of The Exposure of Polycarbonate to an Argon Plasma
Authors: Vallon S. , Drevillon B. , Poncin-Epaillard F. , Rostaing J. C.
Published: April 2011

The exposure of polycarbonate to an argon plasma is studied using in situ ellipsometry from the UV to the IR, nuclear magnetic resonance and light scattering measurements. An increase in the refractive index and the existence of two populations of different molecular weights show that structural changes occur in the polymer. They are correlated with modifications at the polymer unit scale, such as formation of new polar groups and decrease in dimethyl groups. Two simultaneous reaction mechanisms must be considered to account for these changes. The adhesion of a silica layer on treated polycarbonate is then discussed.
Interfacial Water and Adhesion Loss of Polymer Coatings on a Siliceous Substrate
Authors: Nguyen T. , Byrd E. , Alsheh D. , McDonough W. , Seiler J.
Published: April 2011

Water is often the main cause of adhesion loss of a polymer coating/substrate system. The buildup of the interfacial water layer and the loss of adhesion of polymer-coated siliceous substrates exposed to liquid water has been investigated. The thickness of the interfacial water layer was measured on epoxy-coated SiO2-Si prisms using FTIR-multiple internal reflection (FTIR-MIR) spectroscopy. Adhesion loss on flat siliceous substrates was determined by a wet peel test on epoxy-coated SiO2-Si wafers and adhesion loss of composites was obtained by measuring the interlaminar shear strengths of epoxy/E-glass fiber composites. Both untreated and 0.1 % silane-treated substrates were used. Little water was observed at the interface of the silanetreated samples but about 10 monolayers of water have accumulated at the interface of the untreated samples after 100 h of exposure to 24°C water. Untreated, flat substrates lost most of their bonding strengths within 75 h of exposure but silane-treated specimens retained 80% of their adhesion after 600 h of exposure to 24°C water. Adhesion loss of untreated composites immersed in 60°C water was greater than that of treated samples; however, the rate of loss of both silanetreated and untreated composites was much lower than that of flat substrates. Adhesion loss was found to follow the same trend as interfacial water buildup.