bluuebunny/crossref_metadata_2025 huggingface dataset:
Positron Annihilation Studies of Microstructure of Ultra Fine Grained Metals Prepared by Severe Plastic Deformation
Authors: Čížek Jakub , Procházka Ivan , Smola Bohumil , Stulíková Ivana , Kužel Radomír , Cieslar Miroslav , Matěj Z. , Cherkaska V. , Brauer Gerhard , Anwand W. , Islamgaliev Rinat K. , Kulyasova Olya B.
Published: March 2009

In the present work, positron annihilation spectroscopy (PAS) is employed for
microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP). Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and
Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the microstructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.
Phase Composition and Microstructure Stability of Al-Ni-Zr Alloys
Authors: Bártová Barbora , Verner Jan , Vojtech Dalibor , Gemperle A. , Čerňanský M.
Published: March 2009

The paper reports on a detailed investigation of microstructure and phase composition of rapidly solidified and annealed AlNi18.5 and AlNi17Zr1.8 ribbons. The ribbons were prepared by the melt spinning (planar flow casting) technique. The microstructure and phase composition have been studied by TEM and XRD. The specimens were annealed and subsequently subjected to microstructure investigations to asses their thermal stability. Rapidly solidified alloys are composed
of a-Al and Al3Ni phase grains. No significant difference in the shape between Al and Al3Ni grains was found. The Al9Ni2 metastable phase was identified in the rapidly solidified AlNi17Zr1.8 alloy and the Al3Zr phase precipitates from the a-Al solid solution in the AlNi17Zr1.8 alloy after the high temperature annealing.
Influence of Material State at a Crack Tip on the Process of Fatigue Striations Formation for Al-Based Alloys
Authors: Shaniavski A.A.
Published: March 2009

Fatigue fracture features such as pseudo- and fatigue striations were investigated for the Al-alloys AL-Si-Mg and Acoustic Emission (AE) was used to analyze plastic deformation processes ahead of a crack tip. Dramatic change of fatigue striations spacing was demonstrated in accordance with AE-signals evolution. Specimens with fatigue crack have not macroscopic significance in plastic deformation process under tension up to the fast fracture when striation spacing is over 2.1x10-7 m. Mechanisms of material deformation and fracture around of a crack tipduring fatigue striations formation process are discussed on the bases of the synergistic approach.
Ideal Strength of Nano-Components
Authors: Kitamura Takayuki , Umeno Yoshitaka , Kushima Akihiro
Published: March 2009

The ideal (theoretical) strength was originally defined as the stress or strain at which perfect crystal lattice became mechanically unstable with respect to arbitrary homogeneous infinitesimal deformation. This has been intensely investigated because the ultimate strength without defects is a fundamental mechanical characteristic of materials. In the analyses, the instability criteria have been
studied on the basis of elastic constants. Recent developments in computational technology make it possible to analyze the ideal strength on the basis of quantum mechanics. On the other hand, it is well known that the mechanical strength of components is dependent not only on (1) material (atom species), but also on (2) loading condition and (3) structure. Because most studies on the strength in terms of atomic mechanics have focused on the factor (1) (materials), analysis has mainly been conducted on simple crystal consisting of perfect lattices (e.g. fcc and bcc) under simple loading conditions (e.g. tension), though some have explored the properties of bulk materials with defects (e.g. vacancy and grain boundary). Small atomic components (nano-structured components) such as nano-films, nano-wires (tubes) and nano-dots (clusters) possess their own beautiful, defect-free structures, namely ideal structure. Thus, they show characteristic high strength. Moreover, utilizing the structure at the nanometer or micron level is a key technology in the development of electronic devices and elements of micro (nano) electro-mechanical systems (MEMS/NEMS). Therefore, it is important to understand the mechanical properties not only for the sake of scientific interest, but also for engineering usefulness such as design of fabrication/assembly processes and reliability in service. In the other words, the effects of structure (factor (3); e.g. film/wire/dot) have to be understood as the
basic properties of atomic components. Thus, the definition of ideal strength should be expanded to include the strength at instability of components with ideal structures under various external loads (factor (2)), which provides fundamental knowledge of nano-structured materials. In this paper, we review works on the strength of ideal nano-structured components in terms of factor (3), mainly under tension.
Textural Fractography of Fatigue Failures under Variable Cycle Loading
Authors: Lauschmann Hynek , Šiška Filip , Nedbal Ivan
Published: March 2009

A new concept of counting time at fatigue processes is proposed, aimed to reach
fractographic compatibility in cases of different loading sequences. Values of cycle effectivity are summarized to give the new reference time. The improvement is shown in application - textural fractography of three specimens loaded by constant cycle, constant cycle with periodic overloading, and a random block, respectively. In contrast to the conventional crack growth rate, the reference crack growth rate is related to common morphologic features of all fracture surfaces.
Effect of Processing Parameters on Microstructure and Properties of Continuously Cast Al-Mg Sheets
Authors: Slámová Margarita , Sláma P. , Homola Petr , Karlík Miroslav
Published: March 2009

Inner panels of modern ecological cars are nowadays manufactured from Al-Mg alloys. Continuously twin-roll cast sheets are a cost effective substitution for direct-chill cast sheets. The effect of composition and down-stream processing on sheet properties should be well understood in order to produce high quality products, which exhibit good formability and high strength. Finegrained microstructure and well-balanced texture are the necessary pre-requisites. Results of the
investigation of twin-roll cast AlMg2Mn0.8 and AlMg3 alloys are reported. Sheets of 1.0 mm gauge were prepared using different processing routes. The route involving homogenisation results in grain coarsening and anisotropy, however, deep-drawing ability is affected only a little.
Effects of Hydrogen Environment on Fatigue Characteristics of 18Cr-8Ni Stainless Steel
Authors: Kawamoto Kyohei , Aoki Y. , Oda Yasuji , Yoshimura Takeshi , Noguchi Hiroshi , Higashida Kenji
Published: March 2009

In order to clarify the effects of hydrogen on the fatigue characteristics of an austenitic stainless steel, bending fatigue tests were conducted in air, in a hydrogen gas and in a nitrogen gas. Main results obtained are as follows. Effects of hydrogen gas environment are not clearly seen on the strain range - fatigue life diagram, because there are opposite effects to crack propagation and to crack initiation;
accelerates crack propagation, but retards crack initiation. Striation spacing or in-situ observation confirms the acceleration. The retardation seems to be attributed to the absence of oxygen or water vapor in the hydrogen gas.
Dip-Test Internal Stress and the Composite Model of Creep Deformation
Authors: Dobeš Ferdinand , Orlová Alena
Published: March 2009

The composite model of plastic deformation is regarded as a realistic approximation of creep behaviour at elevated temperatures in a well-developed substructure consisting of dislocationdense subgrain boundaries (hard regions) and subgrain interiors (soft regions) with relatively low dislocation density. In the present contribution, the model is applied for an estimation of internal stresses that are experimentally measured by the dip-test technique. Two situations are considered
within the model: (i) the density of moving dislocations is the same in both hard and soft regions and (ii) the density of moving dislocations is proportional to the local density in the respective region. The model enables to express the internal stress in terms of microstructural variables found by independent microscopic observations. It is shown that the magnitude of volume fraction of hard and soft region in the composite model has only a small effect on the value of internal stress.
Tangent Moduli of the Hencky Material Model Derived from the Stored Energy Function at Finite Strains
Authors: Kruisová Alena , Plešek Jiří
Published: March 2009

Tangent moduli associated with the linear logarithmic model of hyperelasticity are
derived. These relations are crucial not only to theoretical analyses but also to wave propagation and ultrasonic testing. The tangent moduli as functions of stress determine the speed of propagating acoustic waves and, therefore, indirectly point to a possible occurrence of residual stress fields in elastic solids.
Theoretical Strength of Metals and Intermetallics from First Principles
Authors: Šob Mojmír , Pokluda Jaroslav , Černý Miroslav , Šandera Pavel , Vitek V.
Published: March 2009

The state of the art of ab-initio calculations of the theoretical strength (TS) of materials is summarized and a database of selected theoretical and experimental results presented. Differences between theoretical and experimental TS values are discussed by assessing the stability conditions.
Compatibilizer Effect of Grafted Glycidyl Methacrylate on EPDM/Organoclay Nanocomposites
Authors: Gatos K.G. , Apostolov A.A. , Karger-Kocsis J.
Published: March 2009

The nanocomposite formation in ethylene/propylene/diene rubber (EPDM) mixed with montmorillonite modified with octadecylamine (MMT-ODA) was investigated. The rubber formulation used proved to be critical for the final materials’ properties. The combined action of the curatives and glycidyl methacrylate (GMA), which was grafted on the EPDM, resulted in better intercalation and enhanced mechanical behavior of the rubber nanocomposites.
Influence of Isothermal Transformation Dwell on Tensile and Fatigue Properties of Austempered Ductile Iron
Authors: Vĕchet Stanislav , Kohout Jan , Hanzlíková Klára
Published: March 2009

Two ADI heats transformed at temperatures of 400 and 380 °C during temporal range from 2 minutes to 9 hours were studied in details, with emphasis on structure composition and mechanical properties (tensile and fatigue properties were determined). In the case of the shortest dwells the level of mechanical properties is influenced by martensite, which occurs in the structure as a result of subsequent cooling. UTS and yield stress increase slightly with the dwell of isothermal
transformation while the values of elongation to fracture as well as of fatigue limit are very closely dependent on the amount of the retained austenite in the microstructure.
Damping Measurements of the Magnesium Wrought Alloys AZ31, AZ61 and AZ80 after Indirect and Hydrostatic Extrusion
Authors: Göken J. , Swiostek J. , Letzig Dietmar , Kainer Karl Ulrich
Published: March 2009

Magnesium cast parts as well as indirectly and hydrostatically extruded profiles were used in order to investigate the influence of different microstructures on the damping behaviour of magnesium AZ-alloys. Especially, hydrostatic extrusion leads to a significant grain refinement in the extruded profile compared to indirect extrusion. Strain dependent damping measurements were carried out at room temperature using alloys AZ31, AZ61 and AZ80. Damping was determined as the logarithmic decrement of free bending beam vibrations. The results of these measurements after indirect and hydrostatic extrusion are shown and discussed.
Prediction and Control of Grain Boundary Fracture in Brittle Materials on the Basis of the Strongest-Link Theory
Authors: Watanabe Tadao , Tsurekawa Sadahiro
Published: March 2009

This paper discusses micropstructural aspects of brittleness fracture of polycrystalline materials caused by intergranular fracture. Structure-dependent intergranular brittle fracture in bicrystals and polycrystals are
discussed and predicted theoretically. Experimental evidence for the structure-dependent intergranular fracture is shown and some general features are discussed to demonstrate the relationship between grain boundary structure/character, grain boundary energy and intergranular fracture strength. Theoretical prediction of the fracture toughness based on the strongest-link theory is introduced for polycrystals with different grain boundary microstructures, primarily defined by the grain boundary character distribution, grain boundary connectivity. Finally recent achievements of successful control of intergranular brittleness by grain boundary engineering based on the strongest-link theory are introduced for different materials.
Silicon Carbide for Alpha, Beta, Ion and Soft X-Ray High Performance Detectors
Authors: Bertuccio Giuseppe , Binetti Simona , Caccia S. , Casiraghi R. , Castaldini Antonio , Cavallini Anna , Lanzieri Claudio , Nava Filippo , Le Donne Alessia , Pizzini Sergio , Rigutti L. , Verzellesi G.
Published: March 2009

High performance SiC detectors for ionising radiation have been designed, manufactured and tested. Schottky junctions on low-doped epitaxial 4H-SiC with leakage current densities of few pA/cm2 at room temperature has been realised at this purpose. The epitaxial layer has been characterised at different dose of radiations in order to investigate the SiC radiation hardness. The response of the detectors to alpha and beta particle and to soft X-ray have been measured. High
energy resolution and full charge collection efficiency have been successfully demonstrated.
Manganese Impurity in Boron Nitride and Gallium Nitride
Authors: Assali Lucy V.C. , Machado W.V.M. , Justo João F.
Published: March 2009

We carried out a theoretical investigation on the properties of manganese impurity
centers in cubic boron and gallium nitrides. The calculations were performed using the all electron spin-polarized full-potential linearized augmented plane wave methodology. Our results indicate that manganese in boron nitride, in a neutral charge state, is energetically more favorable in a divacancy site as compared to a substitutional cation site. We present the results on stability, spin states, impurity magnetic moment, hyperfine parameters, and formation and transition energies of manganese at the divacancy site in several charge states.
Structure and Energy of the 90° Partial Dislocations in Wurtzite-GaN
Authors: Savini G. , Heggie M.I. , Ewels C.P. , Martsinovich N. , Jones R. , Blumenau A.T.
Published: March 2009

90 Shockley partial dislocations in GaN are investigated by first-principles calculations. This work is focussed on the electrical properties of dislocation cores, and on investigating the electrical fields around these defects. The band structure analysis shows that both the and core partials possess a midgap state. The -core dislocations give rise to a donor level Ev +0:87 eV that might explain
the absorption peak at 2.4 eV revealed by energy loss spectroscopy measurements. The acceptor level Ev + 1:11 eV localized at the -core dislocations might contribute to the yellow luminescence. These dislocations experience a substantial charge polarization along the [0001] growth axis. In addition, we show that these dislocations tend to charge in a high stress field.
Microscopic Spatial Distribution of Bound Excitons in High-Quality ZnO
Authors: Bertram F. , Forster Daniel , Christen J. , Oleynik N. , Dadgar Armin , Krost A.
Published: March 2009

The surface morphology of the ZnO layers is dominated by a distinct hexagonal
domain structure. While the laterally integrated cathodoluminescence spectrum shows intense and narrow I8 luminescence, a distinct emission line at spectral position of I0/I1 emerges in the local spectra taken at domain boundaries. In contrast, no I0/I1 emission is found inside the domains. Monochromatic images further evidence the selective incorporation of impurities at the grain boundaries of domains. Monochromatic images of the I8 peak wavelength directly visualize the strain relaxation across the domains towards their very center, where a drop in
quantum efficiency indicates enhanced defect concentration.
Evolution Roots of Growth-Induced Polytype Domains in 6H-SiC Single Crystals
Authors: Seo Soo Hyung , Song Joon Suk , Oh Myung Hwan , Wang Yen Zen
Published: March 2009

We present experimental results with regard to the evaluation of growth-induced
polytype domains in 6H-SiC crystals grown by sublimation method and these domains are characterized by using the polarized optical microscopy and micro-Raman spectroscopy. The polytype domains of reverse triangular are generated by local variation of temperature along cdirection and spread-wing shapes normally occurred forming micropipes in many cases. These polytype domains may be generated due to the local variation of supersaturation and/or temperature
at central position during crystal growth. In this work, we try to elucidate the origin and mechanism responsible for growth-induced polytype domains.
Observation of Vacancy Clusters in HTCVD Grown SiC
Authors: Aavikko Reino , Saarinen Kimmo , Magnusson Björn , Janzén Erik
Published: March 2009

Positron lifetime spectroscopy was used to study defects in semi-insulating (SI) silicon carbide (SiC) substrates grown by high-temperature chemical vapor deposition (HTCVD). The measured positron lifetime spectra can be decomposed into two components, of which the longer corresponds to
vacancy clusters. We have carried out atomic superposition calculations to estimate the size of these clusters.
Electron Irradiation Induced Vacancy Defects Detected by Positron Annihilation in 6H-SiC
Authors: Barthe Marie France , Henry L. , Arpiainen S. , Blondiaux G.
Published: March 2009

This paper presents positron lifetime results which give information on the nature of
vacancy defects induced by electron irradiation in bulk nitrogen doped (nD-nA= 2.3x1017 cm-3) Cree 6H-SiC. The electron irradiations have been performed at different energies and with different fluences from 51017 e-cm-2 to 31018 e-cm-2. Positron lifetime have been measured with a 22NaCl source as a function of temperature between 15 and 300 K. The lifetime spectra were analyzed as sums of two exponential lifetime components i weighted by the intensities Ii, convoluted with the resolution function. From the temperature dependence of the lifetime spectra
we can infer that several vacancy defects exist in the electron irradiated n-type 6H-SiC. The nature of detected vacancy defects depends on the electron energy.
Evolution of Defect and Hydrogen-Related Low Temperature Photoluminescence Spectra with Annealing for Hydrogen or Helium Implanted 6H SiC
Authors: Yan Fei , Devaty Robert P. , Choyke Wolfgang J. , Gali Adam , Schmid Frank , Pensl Gerhard , Wagner Günter
Published: March 2009

A set of four lightly p-type 6H SiC boule samples was implanted with H or He and
annealed in isochronal stages from 950°C to 1500°C. Differences in the hydrogen, DI and DII low temperature photoluminescence spectra are observed and compared. Surprisingly, the hydrogen spectrum appears after a 1300°C anneal in the He implanted samples. A number of unidentified damage lines are also reported.
Ab Initio Calculation of Shallow Defects: Results for P-Related Donors in SiC
Authors: Gerstmann Uwe , Rauls E. , Overhof Harald , Frauenheim Thomas
Published: March 2009

The conclusion which is drawn from the EPR line broadening and narrowing of the N
shallow donor in an isotope enriched and non-enriched 4H-SiC and 6H-SiC crystals along with previous ENDOR results shows that the spin-density distribution over the C and Si nuclei differs between the 4H-SiC and 6H-SiC polytypes. The main part of the spin density in 4H-SiC is located on the Si sublattice. In contrast, in 6H-SiC the main part of the spin density is located on the C sublattice. An explanation for the difference in the electronic wave function of the N donor in 4HSiC
and 6H-SiC can be found in the large difference in the band structure of two polytypes and in the position of the minima in the Brillouin zone.
Electron Paramagnetic Resonance of Shallow Phosphorous Centers in 4H- and 6H-SiC
Authors: Son Nguyen Tien , Henry Anne , Isoya Junichi , Janzén Erik
Published: March 2009

Electron paramagnetic resonance (EPR) was used to study 4H- and 6H-SiC doped with P during chemical vapour deposition (CVD) growth. In 6H-SiC, three spectra with C3v symmetry and spin S=1/2, labelled Ph, Pc1 and Pc2, were detected. The g-values and the 31P hyperfine (hf) constants were determined for Ph: g||=2.0046, g^=2.0028, and A||=0.103 mT, A^<0.05 mT; for Pc1: g||=2.0039,
g^=2.0025, and A||=0.615 mT, A^=0.43 mT; for Pc2: g||=2.0038(5), g^=2.0025, and A||=0.40 mT, A^=0.22 mT. The hf interaction with nearest 13C neighbours were also observed for the Pc1 and Pc2 centers, confirming that in CVD grown material the shallow P donor occupies the Si site. The Ph, Pc1 and Pc2 centers are assigned to the ground states of the shallow P at the hexagonal (Ph) and
quasi-cubic sites (Pc1 and Pc2) in 6H-SiC. In 4H-SiC, an EPR spectrum of C3v symmetry with a larger anisotropy in the g-values (g||=2.0065 and g^=2.0006) was observed. The temperature dependence of the spectrum is similar to that of Ph in the 6H polytype. Its 31P hyperfine constants are determined as A||=0.294 mT and A^=0.21 mT.
Theoretical Investigations of Complexes of p-Type Dopants and Carbon Interstitial in SiC: Bistable, Negative-U Defects
Authors: Gali Adam , Hornos T. , Deák Peter , Son Nguyen Tien , Janzén Erik , Choyke Wolfgang J.
Published: March 2009

Interaction of boron and aluminum with interstitial carbon is studied using first principles calculations. It is shown that carbon can form very stable complexes with Al and B, forming a family of negative-U bistable defects with deep levels. The influence of this effect on the activation rate of p-type implants is discussed.
Characterization of SiC Passivation Using MOS Capacitor Ultraviolet-Induced Hysteresis
Authors: Matocha Kevin , Tucker Jesse B. , Kaminsky Ed
Published: March 2009

Different SiC thermal oxide passivation techniques were characterized using UV-induced hysteresis to estimate the fixed charge, Qf, and interface-trapped charge, Qit. Steam-grown oxides have a fixed charge density of Qf=-1x1012 cm-2, and a net interface-trapped charge density of Qit=4x1011cm-2. Addition of a thin low-pressure chemical-vapor deposited (LPCVD) silicon nitride layer decreased these parameters to Qf=-2x1011 cm-2 and Qit=4x1010 cm-2. Dry oxide shows a fixed charge density, Qf=-3x1012 cm-2 and interface-trapped charge density, Qit=4x1011 cm-2 which changes to Qf=+7x1010 cm-2 and Qit=1x1010 cm-2 with the addition of a LPCVD silicon nitride cap. Dry thermal oxide with a silicon nitride cap was used to passivate SiC MESFETs to achieve a power-added efficiency of 60% in pulsed operation at 3 GHz in Class AB bias conditions.
Aluminium Implantation Induced Linear Surface Faults in 4H-SiC
Authors: Wright Nicolas G. , Vassilevski Konstantin , Nikitina Irina P. , Horsfall Alton B. , Johnson C. Mark , Bhatnagar Praneet , Tappin Peter
Published: March 2009

New results are presented of a surface trench defect observed during anneal of
room temperature Al implants. The size of the surface defect is proportional to anneal
temperature and occurs predominantly in the implanted zone. Signs of lattice strain are observed outside the implanted zone as well.
Electrical Behavior of Implanted Aluminum and Boron near Tail Region in 4H-SiC after High-Temperature Annealing
Authors: Negoro Yuki , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: March 2009

The authors have investigated electrical behavior of implanted Al and B atoms near a “tail” region in 4H-SiC (0001) after high-temperature annealing. For aluminum-ion (Al+) implantation, slight in-diffusion of Al implants occurs in the initial stage of annealing at 1700 °C. Nearly all of implanted Al atoms, including the in-diffused Al atoms were activated by annealing at 1700 °C for 1 min. Several electrically deep centers are formed by Al+ implantation. The concentrations of the centers are 3-4 orders-of-magnitude lower than that of implanted Al-atom concentration. For boron-ion (B+) implantation, significant out- and in-diffusion of B implants occur in the initial stage of annealing at 1700 °C. Most of the in-diffused B implants work as B acceptors. A high density of B-related D center exists near the tail region. To suppress the B diffusion, a ten-times higher dose of carbon-ion (C+) co-implantation is effective. However, high concentrations of additional deep centers
are introduced by such high-dose C+ co-implantation.
Homogeneity of Nitrogen and Phosphorus Co-Implants in 4H-SiC: Full Wafer Scale Investigation
Authors: Blanqué Servane , Lyonnet J. , Camassel Jean , Pérez R. , Terziyska P. , Contreras Sylvie , Godignon Philippe , Mestres Narcis , Pascual Jordi
Published: March 2009

We report a full wafer scale investigation of the activation of nitrogen and phosphorus ions co-implanted at room temperature in a 4H-SiC semi-insulating wafer. We used a full 35 mm wafers on which, after implantation and annealing, 77 reticules with Hall bars and TLM motifs were processed. We found an average sheet resistance of 531 W/square with 30 W/square standard deviation.
High Temperature NO Annealing of Deposited SiO2 and SiON Films on N-Type 4H-SiC
Authors: Yano Hiroshi , Hatayama Tomoaki , Uraoka Yukiharu , Fuyuki Takashi
Published: March 2009

High temperature (1250 oC) NO annealing was performed for deposited oxide (SiO2) and oxynitride (SiON) films on n-type 4H-SiC. Interface state density of SiO2 samples was dramatically reduced (one order of magnitude) by NO annealing compared to N2 annealing, resulting in 1x1011 cm-2eV-1 at 0.2 eV below the conduction band edge. In contrast, that of NO annealed SiON samples
showed only 30% decrease and was still in the range of 1x1012 cm-2eV-1. These different effects of NO annealing against SiO2 and SiON are probably due to different reaction mechanism at the interface. Breakdown field of SiO2 samples annealed in NO was as high as 10 MV/cm. Barrier height of this sample was 2.86eV, which is close to the ideal value.
Characteristics of Post-Nitridation Rapid-Thermal Annealed Gate Oxide Grown on 4H-SiC
Authors: Cheong K.Y. , Bahng Wook , Kim Nam Kyun
Published: March 2009

In this paper, the electrical properties of pre- and post-rapid thermal annealed 4H
SiC-based gate oxide grown in 10% nitrous oxide (N2O) and in dry oxygen have been investigated, compared, and reported for the first time. After treating the nitrided gate oxide in rapid thermal annealing (RTA), oxide breakdown characteristic has been improved significantly. This improvement has been attributed to the reduction of SiC–SiO2 interface-trap density and the generation of positive oxide charge, acting as an electron-trapping center. However, deleterious effects have been observed in non-nitrided oxide after subjected to the same RTA treatment. The differences in oxide-breakdown strength of these oxides have been explained and modeled.
Effect of the Metal Composition on the Electrical and Thermal Properties of Au/Pd/Ti/Pd Contacts to p-Type SiC
Authors: Kolaklieva Lilyana , Kakanakov Roumen , Marinova Ts. , Lepoeva G.
Published: March 2009

X-ray photoelectron spectroscopy is used to study the effect of the metal composition on the electrical and thermal properties of Au/Pd/Ti/Pd contacts to SiC. No reactions and interdiffusion between the contact components and SiC are found for the as-deposited contact layer. The steep metal/SiC interface corresponds to the Schottky behaviour observed before the annealing. Annealing at 900 oC causes Pd2Si formation at the SiC interface and ohmic properties appearance. Due to the addition of Ti to the contact composition the carbon resulting from the SiC dissociation during annealing is completely consumed, which leads to improvement of the thermal stability.
Performance of SiC Cascode Switches with Si MOS Gate
Authors: Brezeanu Gheorghe , Boianceanu C. , Brezeanu M. , Mihaila Andrej , Udrea F. , Amaratunga G.
Published: March 2009

The behavior of the MOS switch and of two cascode configurations are evaluated, by using OR-CAD simulations, and the resulting data are comparatively presented. By analytical and numerical investigations, the superior performance of the multiple cascode circuit is demonstrated.
Physical Simulation of Drain-Induced Barrier Lowering Effect in SiC MESFETs
Authors: Zhu C.L. , Rusli E. , Almira J. , Tin Chin Che , Yoon S.F. , Ahn J.
Published: March 2009

The drain-induced barrier lowering (DIBL) effect in 4H-SiC MESFETs has been studied using the physical drift and diffusion model. Our simulation results showed that the high drain voltage typically applied in short-channel 4H-SiC MESFETs could substantially reduce the channel barrier and result in large threshold voltage shift. It is also found that the DIBL effect is more dependent on the ratio of the gate length to channel thickness (Lg/a), rather than the channel thickness itself. In order to minimize the DIBL effect, the ratio of Lg/a should be kept greater than 3
for practical 4H-SiC MESFETs.
Important Role of Parasitic Regions in Electrical Characteristics of SiC MESFETs
Authors: Cha Ho Young , Choi Y.C. , Eastman Lester F. , Spencer Michael G. , Ardaravičius L. , Matulionis A. , Kiprijanovič O.
Published: March 2009

Because SiC does not have velocity overshooting behaviour, the current density of SiC metal-semiconductor field-effect transistors (MESFETs) is restricted by low drift velocity in the parasitic region between source and gate where the applied electric field is low. In addition, the extension of the depletion region toward the drain side at high drain voltages increases the effective channel length and, as a result, lowers the cut-off frequency due to the increased transit time.
Hole-Like Defects in n-Channel 4H-SiC MESFETs Observed by Current Transient Spectroscopy
Authors: Bluet Jean Marie , Gassoumi M. , Dermoul I. , Chekir F. , Maaref H. , Guillot Gérard , Morvan Erwan , Dua Christian , Brylinski Christian
Published: March 2009

Conductance DLTS measurements have been performed on 4H-SiC MESFETs. A broad band due to electron emission by different levels is observed. An additional “hole-like” level with activation energy of 0.9 eV is obtained in linear regime but not in saturation regime. From the results, it is proposed that this “hole-like” signal is due to capture of electron present at a conductive
SiC/SiO2 interfacial layer.
Wannier-Stark Localization Effects in 6H-SiC JFETs
Authors: Sankin Vladimir Ilich , Shkrebiy Pavel P. , Lebedev Alexander A.
Published: March 2009

The dependence of short-circuit photo-current on the voltage applied to the source-gate (or drain-gate) junction Vg was studied. One should consider the fact that the photo-current begins to drop with voltage exceeding certain threshold value. Thus the 6H-SiC JFET behaves uncommonly. Moreover Isd ~Vg dependence shows a drop Isd to zero at a condition that there is a non-pinched-off part of the channel. For a comparison parallel investigations were conducted with two industrial Si JFETs with a structure similar to that of 6H-SiC JFET under study. The results obtained for Si JFETs are trivial for photocurrent and Isd. We believe that the effects observed in 6H-SiC JFET should be attributed to the Wannier-Stark localization regime.
Process and Device Simulation of a SiC Floating Junction Schottky Barrier Diode (Super-SBD)
Authors: Hatakeyama Tetsuo , Nishio Johji , Shinohe Takashi
Published: March 2009

This paper describes process and device simulation results of SiC floating junction
Schottky barrier diodes (Super-SBDs). Two-dimensional process simulation of a SiC device is implemented using the customized ISE’s process simulator “DIOS”. The simulation results reproduce the experimentally observed buried floating junction structure of a SiC Super-SBD. The device simulation method using the anisotropic impact ionization coefficients is formulated. The effect of
anisotropic avalanche breakdown field on termination structures of SiC SBDs is examined. Finally, by the device simulation we have shown that the trade-off between the on-state resistance and the breakdown voltage of the super-SBD that contains two drift layers exceeds that of the conventional SBD.
Influence of Gamma-Ray and Neutron Irradiation on Injection Characteristics of 4H-SiC pn Structures
Authors: Strel'chuk Anatoly M. , Kalinina Evgenia V. , Konstantinov Andrey O. , Hallén Anders
Published: March 2009

The effect of gamma-ray and neutron irradiation on recombination current, injection
electroluminescense and the value of the lifetime of nonequilibrium carriers for 4H-SiC pn structures was investigated. The irradiation was carried out with gamma-ray (dose 5x106 rad) and 1 MeV neutrons in the doses range from 1.2x1014 cm-2 to 6.24x1014 cm-2. Neutron irradiation with a dose 1.2x1014 cm-2 increased the recombination current, decreased the lifetime for deep-level recombination in the space charge region and decreased the intensity of the edge injection
electroluminescense (hnmax » 3.16 eV) by 1.5-2 orders of magnitude; the neutron irradiation with high dose (6.24x1014 cm-2) resulted in increase of the recombination current up to 2 orders of magnitude and decrease of lifetime at least up to 2 orders of magnitude. Gamma-ray irradiation and annealing at temperatures in the range 350-650 K left the recombination current and lifetime
practically unchanged.
Fabrication of Zirconia-Hydroxyapatite Composites for Biological Materials
Authors: Moon Byung Kyu , Choi Dae Ho , Sung Rak Joo , Kim Seung Ho , Niihara Koichi
Published: March 2009

Microstructure and mechanical behaviors of zirconia [ZR; ZrO2+3mol%Y2O3]–nano hydroxyapatite [HA; Ca10(PO4)6(OH)2] nanocomposites were studied.
A pulse electric current sintering (PECS) method was applied to fabricate ZR-HA composites as biomaterials. The reaction between zirconia and hydroxyapatite was successfully avoided. It was a successful preparation of bioactive composites in the quasi-binary system Ca10(PO4)6(OH)2 + ZrO2. One of the most serious problems is that when a mixture of zirconia and nano-hydroxyapatite powders was sintered, extensive chemical reaction between zirconia and hydroxyapatite was
unavoidable. By applying a novel super-fast consolidation technique, pulse electric current sintering (PECS), the deleterious reactions were inhibited kinetically. The specimens contain 0, 10, 20, and 30wt% of hydroxyapatite on zirconia as remainder. Samples were sintered using the PECS method at 1100°C , 1150°C, 1200°C, and 1250°C, with increasing 100°C /min, under a pressure of 50Mpa in
vacuum atmosphere for 5min. Characterization of the samples was carried out using X-ray diffraction analysis at different sintering temperatures. Flexural strength was estimated with 3-point bending test. The relative density was acquired using an Archimedes method in toluene medium.
Phosphate Recovery from Water as Hydroxyapatite with Activated Oystershell
Authors: Lee Chan Won , Kwon H.B , Jeon Hong Pyo , Koopman B.
Published: March 2009

A technology for phosphate recovery was developed using waste oyster shell as a
raw material in a fluidized bed reactor (FBR). Raw oyster shell that causes a major disposal problem in coastal aquaculture regions was converted to activated oyster shell (AOS) by pyrolysis under defined conditions. A prototype of precipitates collection ports was devised relating to AOS particle size and flow velocity. The optimum conditions determined were applied to wastewater for phosphate recovery with the knowledge of mass balance in the FBR system.
Nitride-Related Compounds Preparation from Waste Aluminum Dross by Self-Propagating High-Temperature Process
Authors: Lee Jae Ryeong , Lee Ikkyu , Shin Hee Young , Ahn Jong Gwan , Kim Dong Jin , Chung Hun Saeng
Published: March 2009

Nitride-related compounds containing AlN and AlON were synthesized from aluminum dross using a combustion reaction, irrespective of the content of Al in Al-dross. The formation of AlON is induced by the exothermic reaction between Al and nitrogen. On the occasion of using high-grade dross, unreacted Al was detected in the combustion products. This may be originated from Al in the dross because Al in dross exists in the dispersed oxide layer. Therefore, its reactivity with
nitrogen is relatively lower, compared to Al powder mixed with the dross in the beginning. It is noted that, on the occasion of using low-grade dross, unreacted Al in the product can be controlled by means of adjusting particle size of dross, resulting in improvement of the permeation of nitrogen gas into the compact through the well established open pore channels.
Optical Properties of Bi2O3-ZnO-SiO2 Glass System for Eco Transparent Dielectric in PDP
Authors: Jeon Jae Sam , Cha Myung-Ryoung , Kim Hyung Sun
Published: March 2009

To replace lead oxide glass, Bi2O3-SiO2-ZnO glass, as a Pb-free glass, was examined for optical properties for a transparent dielectric layer of a plasma display panel (PDP). The glass was evaluated for glass transition temperature (Tg) and thermal expansion coefficient (α). The transparent thick films produced with a screen-printing method were evaluated for optical properties.
The transmittance of thick films fired at 560-620°C showed above 80%. The results suggest that the bismuth glass is a suitable candidate for one of the lead-free glasses compositions in a transparent dielectric layer.
The Effect of Sodium Tripolyphosphate on Sodium Silicate-Cement Grout
Authors: Lim Hyung Mi , Yang Hyung Chil , Chun Byung Sik , Lee Seung Ho
Published: March 2009

Sodium silicate has been widely used as starting materials of chemical grout owing to its feasibility and short setting time with reasonable strength. Elution of sodium has been pointed out as the main reason of weak durability of homogel prepared with sodium silicate-cement grout. There are well known series of additives for controlling its setting time, fluidity, and compressive strength. We
studied the structural change on the sodium silicate with additive of sodium tripolyphosphate (STPP) by 29Si nuclear magnetic resonance spectrum and viscosity. The homogel was prepared by mixing cement/water suspension and diluted sodium silicate/STPP mixtures, and aged in the water. The development of compressive strength and its structural change were observed using a universal test machine, X-ray diffraction, and scanning electron microscope. The additive changed the distribution of Si and rheological property of liquid sodium silicate, which caused more uniform distribution of Ca and Si in the homogel to lead to high initial strength and durability.
Preparation of K2O-CaO-P2O5 Eco-Glass Fertilizers and Effect in Crops
Authors: Lee Hoi Kwan , Hwang Sheng Jian , Kang Won Ho
Published: March 2009

For the application of environment conscious glass-fertilizer, K2O-CaO-P2O5 glasses were fabricated by melt-quenching process, and the dissolution properties of these glasses were investigated using pH meter and ICP analyzer. Additionally, the fertilizer effects on rice culture were evaluated. The pH values depended on the glass compositions, and the ICP analysis confirmed that the dissolution amount was inversely proportional to the change of the K2O/P2O5 ratio, which was a
main factor in controlling chemical durability, and which could be controlled by mother glass composition. The results of their application to rice plants indicated that the growth and quantity were similar to those used in chemical fertilizer. Therefore, the phosphate glasses are expected to provide the slow-releasing nutrient fertilizers that are easy to produce, environmentally safe, and widely applicable.
Effect of Oxidizing Agent of Polypyrrole Layer Prepared by Vapor Polymerization
Authors: Cho Jae Hyun , Kim Jung Suk , Yu Jun Boo , Sohn Sung-Ok , Huh Jeung Soo
Published: March 2009

The influence of oxidant on surface morphology and sensing property of polypyrrole (PPy) – poly (vinyl alcohol) (PVA) double layer sensors was investigated. PPy–PVA double layer sensors were prepared by vapor polymerization using FeCl3 as oxidizing agent and PVA as adhesive agent. The surface of PPy–PVA layer was observed on a scanning electron microscope (SEM). The surface morphology of sensor showed homogeneous layer and thickness of 1µm. And the sensing properties were investigated using a flow measuring system. The maximum sensitivity to methanol 1000ppm was proportional to increasing 12wt % FeCl3 concentration at 25°C. The response time was not affected by FeCl3 concentration, but the recovery time increased according to the amount of FeCl3. The best amount of FeCl3 was observed at 12wt%.
Effects of Ca Addition on Microstructure and Mechanical Properties of Mg-RE-Zn Casting Alloy
Authors: Jun Joong Hwan , Park Bong Koo , Kim Jeong Min , Kim Ki Tae , Jung Woon Jae
Published: March 2009

Influences of Ca addition on microstructures and mechanical properties at room and elevated temperatures up to 300oC have been investigated for EZ43 (Mg-4%RE-3%Zn)-(0~1.2)%Ca permanent mould casting alloys, based on experimental results from optical micrography, X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and mechanical tests. With an increase in Ca content, yield strength is increased gradually at all temperatures, whereas elongation shows a decreasing tendency. High level of tensile strength around 150MPa is maintained until 250oC in the EZ43-0.8Ca and EZ43-1.2Ca alloys, meaning that Ca is very effective for improving elevated temperature strength of the Mg-RE-Zn alloy. The microstructural examinations reveal that Ca refines the a grains markedly, increases discontinuity of Mg12RE network intermetallic compound and dissolves into the Mg12RE phase. The refined a grains and Ca-containing Mg12RE with higher thermal stability are considered to be responsible for the improved mechanical properties at room and elevated temperatures for the EZ43-Ca alloys.
Materials Design for High-Strength Mg-Based Alloys by Understanding from Ab Initio Calculation
Authors: Uesugi Tokuteru , Higashi Kenji
Published: March 2009

The applications of ab initio calculations for deformation mechanisms of Mg-based alloys are discussed. First, Peierls stress of pure magnesium is calculated from generalized stacking fault (GSF) energies obtained by ab initio calculations. Second, materials design is applied to develop new Mg-based alloys exhibiting high strength. The atomic size factors of some Mg-based solid solutions are calculated by ab initio calculations as a first step of searching most effective solute element for the solid-solution strengthening.
The Effect of Manganese on the Grain Size of Commercial AZ31 Alloy
Authors: Cao Peng , StJohn David H. , Qian Ma
Published: March 2009

The effect of manganese on grain refinement of a commercial AZ31 alloy has been
investigated using an Al-60%Mn master alloy splatter as an alloying additive at 730 °C in aluminium titanite crucibles. It is shown that grain refinement by manganese is readily achievable in AZ31. Electron microprobe analyses reveal that prior to the addition of extra manganese the majority of the intermetallic particles found in AZ31 are of the Al8Mn5 type. However, after the addition of extra manganese in the range from 0.1% to 0.8%, the predominant group of intermetallic particles changes to the metastable AlMn type. This leads to a hypothesis that the metastable AlMn intermetallic particles are more effective than Al8Mn5 as nucleation sites for magnesium grains. The hypothesis is supported by the observation that a long period of holding at 730 °C leads to an increase in grain size, due probably to the transformation of the metastable AlMn to the stable Al8Mn5. The hypothesis has
also been used to understand the mechanism of grain refinement by superheating.
Effects of Al/Zn Ratio on the Microstructure and Strengthening of Mg-Al-Zn Alloys
Authors: Luo Cheng Ping , Liu Jiang Wen , Liu Hong Wei
Published: March 2009

The morphology and crystallography of precipitates formed in three Mg-Al-Zn alloys
containing various Al/Zn ratios, conventionally designated as AZ91, AZ64 and AZ46, were characterized, and the mechanical properties determined. Three morphologically and crystallographically different types of lath- or rod-shaped γ-(Mg17All2) precipitates were identified in AZ91, and needle-like η-(MgZn2) in addition to γ-(Mg17All2) occurred in the alloys containing higher Zn. With increasing Zn content, i.e. with decreasing Al/Zn ratio, the fraction of γ-(Mg17All2)
decreased, while that of η-(MgZn2) increased. The peak aged hardness and tensile properties of the alloys were slightly decreased, rather than increased, with increasing the Zn content from AZ91 through AZ64 to AZ46. The mechanism by which the γ-(Mg17All2) and η-(MgZn2) precipitates affected the age strengthening of the alloys was discussed in terms of the morphology, crystallography, interfacial structure, and relative quantity of the precipitates, and of their ability to block dislocation basal slip in the Mg-rich matrix.
Overview of Key R&D Activities for the Development of High-Performance Magnesium Materials in Canada
Authors: Jackman Jennifer , Wood Jeffrey , Essadiqi Elhachmi , Lo Jason , Sahoo Mahi , Xu Su , Thomson Jim , Liu Wei Jie
Published: March 2009

Canadian researchers are actively engaged in the development of novel cast, wrought and composite materials that are based on Mg. An overview is provided of Canadian research projects for new applications of Mg alloys that are targeted to the growing needs of the automotive sector. The research work described is funded primarily through two federal programs: the Canadian Lightweight Materials Research Initiative, and the Materials and Manufacturing Theme of the AUTO21 Network of Centres of Excellence. It includes work on mechanical and corrosion
performance of high-pressure die castings, gravity and low pressure castings using permanent and sand molds, sheet Mg development and magnesium matrix composites. The metallurgical research facilities at the CANMET Materials Technology Laboratory are featured.
Preparation of Magnesium-Rare Earth Master Alloy Using Electrowinning Method with Subsidence Cathode
Authors: Zhang D.P. , Fang D.Q. , Wang J. , Tang D.X. , Lu H.Y. , Zhao L.S. , Meng Jian
Published: March 2009

A new series of magnesium-rare earth master alloys have been developed by the
electrowinning method with subsidence cathode in the KCl•NaCl-RECl3 system. The electrolysis conditions were studied. Experimental results showed that the optimum for electrolyte at 850oC and 10~20wt% RECl3 content in the molten salt system. The current efficiency of electrolyte increased with increasing the rare earth content and reach the maximum at the content of 20% RECl3. The current efficiency gradually decreased with increasing cathode current density. The component of
master-alloys was analyzed using ICP-MS and chemical method. A series of magnesium-rare earth master-alloy, Mg-Y, Mg-Nd, Mg-Ce, Mg-La, Mg-Nd-rich and Mg-LPC were successfully prepared and the content of rare earth is adjustable between 5 – 20%.