bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Wire-EDM Finishing Processes through Adaptive Fuzzy Logic Control Algorithm
Authors: Hsue Albert Wen Jeng
Published: March 2009

This paper presented tries to improve finishing accuracy through monitoring the lateral
gap-width by an adaptive fuzzy logic controller. Since the complexities and stochastic properties
inherited in EDM processes, it seems promising to introduce soft computing algorithm in such a
process control application. The adaptive fuzzy logic system (AFLS) composed of a fuzzy logic
system and a nearest neighborhood-clustering algorithm, which adjusts not only the parameters of
fuzzy system but also its own structure. A detailed material removal mechanism was established
through the concept of discharge-angle for analysis on the machining processes. Formation of
lateral gap width was analyzed through material removal swept by the discharge angle. Combined
with discharge power and other operation conditions, a feasible gap-width estimation model was
established. And an adaptive control based on the AFLS was proposed to improve the conventional
servo-voltage strategy in both the machining accuracy and the stability aspects. Experiment results
showed that the proposed estimation model is effective, and the proposed control strategy help
significantly in improving the geometric accuracy of Wire-EDM’s finishing process.
Real-Time Interpolator and Contour Tracking in Link-Space for a 3 DOF Parallel Mechanism
Authors: Cheng Yuan Ming , Kuo Chien Hsun , Chin Jih Hua
Published: March 2009

Parallel mechanisms could be hardly used in contour tracking because of their
mechanism features. This study proposed a link-space real time contour tracking for a 3 DOF (Z、α
and β) hydraulic parallel mechanism. The essence of this approach is to convert control points of
command trajectory to link space by inverse kinematics. A real-time interpolator was created and
the multi-axis cross-coupled pre-compensation control (MCCPM) was constructed for link-space
contour tracking. It was shown that a contour-accurate trajectory tracking could be performed which
was impossible in the original Z-α-β space. Other advantages of this link-space approach were time
efficiency and the uniform tracking velocity.
Investigating the Dynamics of Organelle-Actin Assembly with Dielectrophoresis
Authors: Chen Shu Hsing , Li Cheng Ho
Published: March 2009

Dielectrophoresis is a technique of using high-frequency electric fields to manipulate
dielectric particles. This work applies this technique to study the changes of intracellular properties
in response to environmental changes. In a number of plant cells, chloroplasts change their positions
for optimizing photosynthetic light absorption. Only between 2 and 20% of the light energy
absorbed by algae and higher plants is actually used in CO2 fixation. Comparing with other
micro-manipulative methods, dielectrophoresis is a relative simple method for investigating the
microscopic mechanisms involved in chloroplast repositioning.
Leaves of Egeria densa were subjected to different lighting conditions before conducting
dielectrophoresis. Under dim light, chloroplasts situate on the periclinal wall. Under high-intensity
light, chloroplasts move from the periclinal wall to the anticlinal walls. Under electric fields,
chloroplasts treated with different lighting condition exhibit different motions. It is expected that
actin configuration as well as chloroplast-actin binding strength contributes to the repositioning of
chloroplasts.
Parametric Design and Design Associability in 3D CAD
Authors: Wang Song Hao , Melendez Steven , Tsai Chyi Shyan , Wu Chi Wei
Published: March 2009

The purpose of this research is to make design automation possible by parametric
design and design associability in 3D CAD.
Applications of the technology in liquid food packaging machinery and its advantages are
presented in the paper. For regular shapes such as circles or lines, parameters are used to link the
dimensions of relative parts while for irregular shapes such as curves, associability is used to do
the job in an assembly. Commercial 3D CAD software and Microsoft Excel software were used
for the application.
It is proved that same merit applies to designs of other machineries, on reducing design time and
design mistake, enhancing consistency and easy documentation， therefore liberating designers
from redundant day-to-day routine computer-paperwork to make more innovative contributions
to their job. The impact of the design-automation technology on machine design is great.
Bending Die Design for a Pre-Formed Sheet Metal with a Golden Finger Feature
Authors: Sheu Jinn Jong , Fang Sheng Hao
Published: March 2009

In this paper, authors proposed an effective quality index of bending operation and a new
punch profile design method to prevent defects. The proposed quality index is presented in terms of
distance of fracture location with respect to the topmost plane of blank, the maximum von Mises
stress, and the maximum shear stress. The Taguchi method with L18 orthogonal array was adopted to
evaluate the effects of design parameters and find out the optimum design of punch profile. A new
punch feature called “golden finger” was proposed to control the material flow and move the fracture
defects out of the trimming line. The results of this study had demonstrated the optimum die design
can be achieved with the proposed golden finger feature to obtain a sound product.
Fabrication and Analysis of Nano-Aluminum-Induced Low-Temperature Polycrystalline Silicon Film
Authors: Chu Hsiao Yeh , Weng Ming Hang , Yang Ru Yuan , Huang Chien Wei , Liu Chien Cheng
Published: March 2009

In this paper, we successfully fabricate polycrystalline silicon films with very large and
uniform-size grains by the method of nanometer thick aluminum induced crystallization (nano-AIC)
on the a-Si:H film deposited by plasma enhanced chemical vapor deposition (PECVD). The effect
of annealing ramp-up time is discussed. Four different annealing ramp-up time, 1,5,10,20 hours, are
tested. The results show the maximum average grain size obtained in this paper is about 60 μm
under the condition of 20-hour annealing ramp-up time. The nano-AIC specimens show a much
better leakage current characteristics than the AIC specimens since the Al layer in AIC process is
much thicker and was not removed completely from the polycrystalline silicon film during Al wet
selective etching process.
Improvements in Electrical Properties of SiC Surface Using Mechano-Chemical Polishing
Authors: Hotta Kazutoshi , Hirose Kenji , Tanaka Yayoi , Kawata Kenji , Eryu Osamu
Published: March 2009

To use SiC substrate as a semiconductor device and epitaxial growth, the surface of SiC
substrate should be made smooth at an atomic level in the state of monocrystalline. But, the past
slurry caused defects such as the pit and the scratch on the surface. This tendency was very strong in
(000-1) C-face. We achieved ideal surface for SiC devices using newly developed slurry. In this
surface, the roughness (Ra) of (0001) Si face and (000-1) C face evaluated by the AFM were 0.1nm
or less, and confirmed that the surface were monocrystalline by CAICISS measurement. From these
results, it is thought that the crystal face obtained by the slurry newly developed. In addition, the
Schottky barrier diode was formed directly on the polished surface, that was obtained the breakdown
voltage of 1.2kV or more. We thought that this results is possible to make the Schottky barrier diode
without epitaxial growth.
Interlaboratory Comparison of Positron Annihilation Lifetime Measurements
Authors: Ito Kenji , Oka T. , Kobayashi Yoshinori , Shirai Y. , Wada K. , Matsumoto M. , Fujinami M. , Hirade Tetsuya , Honda Yoshihide , Hosomi H. , Nagai Yasuyoshi , Inoue Koji , Saito Haruo , Sakaki Keiji , Sato K. , Shimazu Akira , Uedono Akira
Published: March 2009

An interlaboratory comparison for positron annihilation lifetime (PAL) measurements for pure nickel and fused silica was performed. Based on the reported positron (for nickel) and positronium (for fused silica) lifetimes, the uncertainties in the PAL measurements were estimated.
Free Volume and Oxygen Permeability in Polymers Related to Polymer Electrolyte Fuel Cells
Authors: Mohamed Hamdy F.M. , Ohira A. , Kobayashi Yoshinori
Published: March 2009

The mechanism of gas permeation in sulfonated polymers such as Nafion and sulfonated polyethersulfone (SPES) for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Free volume was quantified using the positron annihilation lifetime (PAL) technique and O2 permeability was measured as a function of temperature or ion exchange capacity (IEC). Good linear correlations between the logarithm of the permeabilities and reciprocal free volume indicate that gas permeation in the sulfonated polymers depends strongly on the free volume. Comparison of Nafion with SPES and other relatively flexible chain polymers showed that the stiff chains of the perfluoroethylene backbone in Nafion make the O2 permeability much smaller than the corresponding flexible chain polymer with a similar free volume size. The O2 permeability in the K+-form of Nafion is systematically smaller than the H+-form, showing that the chain stiffness is enhanced by the ion exchange.
Today’s Mainstream Microelectronics - A Result of Technological, Market and Human Enterprise
Authors: Grimmeiss Hermann G. , Kasper Erich
Published: March 2009

Microelectronics is a central area within information technology, which is still one of the most important global technologies. It will be shown that the development of integrated circuits is based on a long and fascinating history, which is unique in modern time. Yet, the fantastic growth in semiconductor electronics is due to a unique combination of basic conceptional advances, the perfection of new materials and the development of new device principles. A brief survey of the development of microelectronics is given by not only focusing on the history of microelectronics but also taking into account materials and market aspects. Since microelectronics is an extremely complex area, a few criteria and reference points for integrated circuits are given. Thereafter, some examples are presented indicating the rapidly changing state-of-the-art. It will be shown that the development of material science within the area of microelectronics is not always driven by scientific curiosity but often by arbitrary and not always obvious preferences. After a short discussion of the performance advantages and disadvantages of germanium, silicon and III-V compound semiconductors, the SiGe heterojunction bipolar transistor is taken as an example for demonstrating a few important differences in the performance of all-silicon devices with regard to silicon-based heterojunction devices in general. In conclusion, the impact of human enterprise and research policy on the development of microelectronics is briefly discussed.
The Influence of Defects and Impurities on Electrical Properties of High-k Dielectrics
Authors: Dąbrowski Jaroslaw , Miyazaki Seiichi , Inumiya S. , Kozłowski G. , Lippert G. , Łupina G. , Nara Y. , Müssig Hans Joachim , Ohta A. , Pei Y.
Published: March 2009

Electrical properties of thin high-k dielectric films are influenced (or even governed) by the presence of macroscopic, microscopic and atomic-size defects. For most applications, a structurally perfect dielectric material with moderate parameters would have sufficiently low leakage and sufficiently long lifetime. But defects open new paths for carrier transport, increasing the currents by orders of magnitude, causing instabilities due to charge trapping, and promoting the formation of defects responsible for electrical breakdown events and for the failure of the film. We discuss how currents flow across the gate stack and how damage is created in the material. We also illustrate the contemporary basic knowledge on hazardous defects (including certain impurities) in high-k dielectrics using the example of a family of materials based on Pr oxides. As an example of the influence of stoichiometry on the electrical pa-rameters of the dielectric, we analyze the effect of nitrogen incorporation into ultrathin Hf silicate films.
Investigation of Deep Interface Traps in Very-Thin Oxide/Si Structures Prepared at Low Temperatures Using Chemical Solutions
Authors: Rusnák Jaroslav , Ružinský Michal , Imamura Kentaro , Matsumoto Taketoshi , Štefečka Miloslav , Takahashi Masao , Kobayashi Hikaru , Pinčík Emil
Published: March 2009

An advanced equipment for the charge version of deep level transient spectroscopy (Q-DLTS) and C-V measurements with newly developed software on LabView platform is presented. The ability to record several Q-DLTS behaviors with different rate windows simultaneously is the most important property of the equipment. Q-DLTS with excitation of the MOS structures by low-voltage step and time domain C-V measurements were used to determine interface properties. The contribution presents mainly results obtained on very-thin oxide/n-type crystalline Si structures prepared by oxidation at very low temperatures in nitric acid solutions with various concentrations.
Preparation and Characterization of Microporous Membranes Prepared by Wet Phase Inversion. Application to Ni (II) Transport
Authors: Bey Said , Bounomenna M.G. , Benamor M. , Drioli Enrico
Published: March 2009

Wet phase inversion is used to prepare and control morphology of membrane based on PEEKWC in DMA at 14wt %. A comparison study has been done with Polysulfone and PVDF as basic materials for membrane preparation. The effect of the coagulant bath is studied by using water and ethanol as nonsolvent. Excepting for PVDF, the micrographs shows that no strong effect in the structure of the membranes. The macro-voids still exist but less numerous and large in the case of membrane immersed in ethanol coagulant bath. Microporous membrane in some cases was obtained. These membranes were used in supported liquid membranes experiments for Ni(II) metal ions transports using 2-diethyl hexyl phosphoric acid (D2EHPA ) as carrier.
Effect of Chromium and Vanadium on Nanolayered Ternary Carbides: AB Initio Study
Authors: Merad A.E. , Kanoun M.B.
Published: March 2009

The Cr2AlC and V2AlC nanolayered ternary carbides are studied by performing APW-lo ab initio total energy calculations within the recent Wu-Cohen generalized gradient approximation GGA. Using full relaxation procedure of the volume and the atomic positions we obtained the structural parameters and electronic structure of the optimization hexagonal. Results were compared with the experimental ones. Interesting features are deduced. In fact, we have shown why these materials are conductors.
Functionalization of ISE Sensor for Metal Ion Detection
Authors: Morakchi K. , Zazoua A. , Hamel A. , Zougar Saida , Kherrat R. , Jaffrezic-Renault Nicole
Published: March 2009

In this work, we report the study of functionalized platinum (Pt) electrodes based on a polymeric membrane (PVC) including an ionophore (ethyln diamin tetracetic EDTA) sensitive for mercury ions Hg2+. The optimised working conditions of the sensors have been studied with regard to the sensitivity performances; in particular, the polarisation was adjusted to - 0.2V/SCE. Ion sensitivity of sensors have been tested for Hg(II) via Cd(II) in aqueous solution. A layer of EDTA deposited on platinum electrode has been characterised by impedance spectroscopy and cyclic voltammetry methods.
Thin Layered Structures Analysis Using NUR Reflectometer
Authors: Izerrouken M.
Published: March 2009

Reflectometry technique in Centre de Recherché Nucléaire de Draria (CRND) is operational since 2002. The instrument is used for investigation of monochromators and supermirrors. In this communication, several monochromators: 10 and 40 nickel-titanium bilayers deposited on a float-glass substrate with different period are analysed. The investigation of magnetic multilayers (25 silicon-iron bilayers monochromator) is also performed. From the results, Bragg peaks were identified indicating the periodicity of the multilayers.
In Vitro Cytotoxicity Study of the Nano-Hydroxyapatite/Bacterial Cellulose Nanocomposites
Authors: Chen Yan Mei , Xi Ting Fei , Zheng Yu Dong , Wan Yi Zao
Published: March 2009

The nanocomposite of nano-hydroxyapatite/bacterial cellulose (nHA/BC) obtained by depositing in simulated body fluid (SBF), incorporating their excellent mechanical and biological properties, is expected to have potential applications in bone tissue engineering. However, the biological response evaluation of biomaterials is required to provide useful information to improve their design and application. In this article, the in vitro cytotoxicity of composites nHA/BC as well as its degradation residues was studied. Scanning electron microscopy (SEM) was used to observe the morphology of original materials and their degradation residues. The degree of degradation was evalued by measuring the concentration of reducing sugar (glucose) by ultraviolet spectrophotometer. Bone-forming osteoblasts (OB) and infinite culture cell line L929 fibroblasts were used to measure the cytotocixity of materials with MTT assay. Both kinds of cells in infusion proliferate greatly in a normal form and their relative growth rate (RGR) exceeds by 75%, which shows the cytotoxicity of materials is graded as 0~1, according to the national standard. Nevertheless, bone-forming OB cells, as a kind of target cells, are more susceptive on the cytotoxicity than infinite culture fibroblast cells L929. The results suggest the nanocomposite of nHA/BC without cytotoxicity is greatly promising as a kind of scaffold materials for bone tissue engineering and tissue functional cells are more suited to evaluate the cytotoxicity of biomedical materials.
Synthesis and Characterization of Rare Earth (Sm,Y) Light Conversion Film
Authors: Ni Ya Ru , Wu Lian Chao , Lu Chun Hua , Xu Zhong Zi
Published: March 2009

In this article, Sm(Sal)xPhen, SmyY1-y(Sal)3Phen were synthesized and its films were prepared. They were characterized by infrared spectra (IR), ultra-violet visible spectrometer (UV), X-ray diffraction (XRD) and fluorescence spectroscopy. Sm/Y complexes and its mixture doped with the polyvinyl alcohol (PVA) showed photoluminescence at the wavelength of 646 nm. There was an excellent compatibility among Sm/Y complexes, the polyvinyl alcohol (PVA) and dimethyl sulphoxide (DMSO), which were used to prepare the resin film. The results indicated that Sm/Y rare earth light conversion films were better light conversion films with good compatibility in resins, and with emission wavelength suitable for plants’ photosynthesis.
A Study of Hot Extrusion of 6063 Aluminum Alloy-Clad AZ31B Magnesium Alloy Bar
Authors: Huang Guang Sheng , Xu Wei , Huang Guang Jie , Pan Fu Sheng
Published: March 2009

The magnesium alloys have poor corrosion resistance because of their low equilibrium potential and loose oxide film, while the aluminum and its alloys have good corrosion resistance due to their compact oxide film. In this study, a kind of aluminum and magnesium bimetallic bars, 6063 aluminum alloy-clad AZ31B magnesium alloy bars, were acquired through hot extrusion. The experimental results showed that the extrusion temperature of 653K or lower, as well as an extrusion speed of 2m/min or lower be used during the extrusion. The interfacial structure and mechanical properties of the bimetallic bars were studied. The interface between aluminum alloy and magnesium alloy was metallurgic bonding with the shear bonding strength of 53Mpa for as extruded sample. As annealing temperature or holding time increased, the jointed layer between aluminum alloy and magnesium alloy was broadened, which decreased of shear bonding strength, indicating that the heat treatment is deleterious. The bimetallic bars have lower identity, good corrosion resistance and preferable mechanical properties, which are promising constructional materials.
Study on Corrosion and Degradation Behavior of Mg-Ca Alloy in Simulated Body Fluid
Authors: Gao Jia Cheng , Wu S. , Wang Yong , Qiao Li Ying
Published: March 2009

The corrosion and degradation behavior of Mg-Ca binary alloy in simulated body fluid (SBF) were studied by immersion of pure Mg and Mg-Ca alloys with different Ca contents in SBF. The corrosion process was carried out by real-time measurement of sample weight, pH value of SBF and the microstructures of the immersed samples at different immersion time observed by electron microscopy. The result shows that Mg-Ca alloy with 0.7% Ca has better corrosion resistance than the one with 2.0% Ca. The product generated on the surface of Mg-0.7Ca during the immersion was identified by X-ray diffraction and energy spectrum analysis.
Transformation Plasticity - The Mechanism and Some Applications
Authors: Inoue Tatsuo
Published: March 2009

A phenomenological mechanism of transformation plasticity is discussed, in the first part of the paper, why the transformation plastic deformation takes place under a stress level even lower than the characteristic yield stress of the material: This is principally based on the difference in thermal expansion coefficient of mother and new phases. Some calculated data of induced stress and strain depending on applied stress are represented. Bearing in mind that it is also a kind of plastic strain, a unified plastic flow theory is derived by introducing the effect of progressing new phase into the yield function of stress, temperature and plasticity related parameters. Thus obtained strain rate reveals to include the transformation plastic part in addition to thermo-mechanical plastic components. Application of the theory is carried out to simulate some complicated cases of varying stress and temperature, and the results are compared with experimental data.
Comparison of Surface Nanostructured Electrodeposited Cu Produced from Different Power Types: Microstructure and Tensile Properties
Authors: Chan H.L. , Lu Jian
Published: March 2009

Different Power types and parameters in the electrodeposition process result in different microstructures and hence mechanical properties. In this paper, direct current and double pulse power with different combinations of on and off time have been used for electrodeposition. The tensile properties of the electrodeposited (Ed) Cu with different parameters in process have been studied and also the microstructures of the Cu obtained have been examined by SEM. This paper aims at explaining the effects of one of the important parameters in electrodeposition: different power types on the tensile properties. The tensile properties of Ed Cu after Surface Mechanical Attrition Treatment (SMAT) are also shown in this paper.
Nano-Size Surface Materials Stabilized by Weak Interaction
Authors: Tanaka Kenichi , Jiang Xiao Hong
Published: March 2009

Scanning tunneling microscopy (STM) proved the existence of quasi-compounds on solid surfaces. A typical example is (-Ag-O-) or (-Cu-O-) chains grown on Ag(110) or Cu(110) surface by exposing to O2. The (-Ag-O-) chains on a Ag(110) reacts with Cu atoms to form a new quasi-compound of (-Cu-O-) chains on the Ag(110) surface. The (-Cu-O-) on the Ag(110) readily decomposes at ca. 570ºK to form Cu6 dots, and a reversible reaction of (Cu2)3 + O2. ↔ (-Cu-O-) takes place by exposing to O2. Deposited Zn, Sn and Ag atoms on a Si(111)-7x7 surface stabilize by forming Zn3, Sn2 and Sn, and Ag in a half unit cell. Layer-by-layer growth of Zn3 clusters occurs in a half unit cell, which results in the growth of a semi-conductive honeycomb layer of Zn3 clusters on the Si(111)-7x7 surface. By prohibiting hopping migration of Ag atoms on the Si(111)-7x7 surface by the adsorption of C2H5OH, nano-size Ag dots grow layer-by-layer in a limited mold spacing. The band gap of Ag-dots becomes narrower and narrower and becomes metallic at higher than 6 layers.
Radiation Hard Silicon for Medical, Space and High Energy Physics Applications
Authors: Härkönen Jaakko , Tuovinen Esa , Luukka Panja , Tuominen Eija , Li Zheng , Eremin Vladimir , Verbitskaya Elena
Published: March 2009

The objective of this paper is to give an overview on how silicon particle detector would survive operational in extremely harsh radiation environment after luminosity upgrade of the CERN LHC (Large Hadron Collider). The Super-LHC would result in an integrated fluence 1×1016 p/cm2 and that is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies. The Czochralski silicon (Cz-Si) has intrinsically high oxygen concentration. Therefore Cz-Si is considered as a promising material for the tracking systems in future very high luminosity colliders. The fabrication process issues of Cz-Si are discussed and the formation of thermal donors is especially emphasized. N+/p-/p+ and p+/n-/n+ detectors have been processed on magnetic Czochralski (MCz-Si) wafers. We show measurement data of AC-coupled strip detectors and single pad detectors as well as experimental results of intentional TD doping. Data of spatial homogeneity of electrical properties, full depletion voltage and leakage current, is shown and n and p-type devices are compared. Our results show that it is possible to manufacture high quality n+/p-/p+ and p+/n-/n+ particle detectors from high resistivity Czochralski silicon.
Fabrication of Magnetite Nanoparticals and Drug Delivery Observation of Hydrophobe Ferrofluid by SPring-8 Synchrotron Radiation
Authors: Ju Dong Ying , Bian Pei , Nakano Masahiro , Matsuura Hiroyuki , Makino K. , Noda N. , Koide Kazuharu , Nemoto Tetsuya
Published: March 2009

Magnetic nanoparticles are widely used in magnetic fluid, magnetic grinding materials, magnetic controllers, magnetic sensors, biomedicine fields and so on. Recently, more and more attentions were focused upon DDS (Drug Delivery System). In this study, Magnetite nanoparticles about 8nm size were synthesized by liquid phase precipitation method. Then the nanoparticles coated with surfactant were dispersed throughout kerosene and inject the solutions into biomaterials. Using strong photon beams in SPring-8 facility, we observed the distribution state and the effect of magnetic field on the behaviour of nanoparticles in biomaterials.
High Strength Nanocrystallized Multilayered Structure Obtained by SMAT and Co-Rolling
Authors: Waltz Laurent , Retraint Delphine , Roos Arjen , Olier Patrick , Lu Jian
Published: March 2009

. In the present study, a method is presented combining surface nanocrystalline treatment (SMAT) and the co-rolling process. The aim of this duplex treatment is the development of a 316L stainless steel semi-massive multilayered bulk structure with improved yield and ultimate tensile strengths, while conserving an acceptable elongation to failure by optimizing the volume fraction and distribution of the nano-grains in the laminate. To characterize this composite structure, tensile tests as well as sharp nanoindentation tests were carried out to follow the local hardness evolution through the cross-section of the laminate. Furthermore, transmission electron microscope (TEM) observations were carried out to determine the correlation between the microstructure, the local hardness and the mechanical response of the structure.
A Versatile Micromechanical Model for Estimating the Effective Properties of Isotropic Composite Materials
Authors: He Qi Chang , Le Quang H.
Published: March 2009

This work is concerned with a versatile and efficient model for estimating the effective moduli of isotropic composites consisting of isotropic phases whose microstructure may be of matrix-inclusion type, disordered or intermediate. This extended version of generalized self-consistent model (GSCM) is built by inserting a composite sphere embedded in an infinite unknown effective medium has the core made of the unknown effective medium and coated by the constituent phases. The volume fraction of the constituent phases in this composite sphere is the characteristic parameter of the relevant microstructure. By imposing the an energy equivalency condition, the equations thus obtained to estimate the effective bulk and shear moduli involve the microstructural parameter which turns out to be capable of describing in some sense how far a microstructure is from the host matrix/inclusion morphology
Experimental Evaluation of the Size Effect on the Ductile and Brittle Fracture Toughness of a Steel Pressure Vessel
Authors: Wang Zhao Xi , Shi Hui Ji , Lu Jian
Published: March 2009

Experiments of fracture toughness with non-standard SENB specimens of five different thicknesses were performed to investigate the size effect on the ductile and brittle fracture for different temperatures. From the experimental results it is found that size effects both brittle and ductile fracture with the same trend but for different mechanical reasons. The ductile fracture toughness increases firstly with increased plastic deformation zone size and plastic fracture strain under general yielding conditions, and then drops down due to the plastic deformation zone size not changing much which is less than the residual ligament width and the increase of the proportion of the high stress triaxiality zone to the whole specimen. The fracture toughness of the lower shelf increases with increasing thickness of the plastic deformation zone size under small scale yielding conditions, and then drops down due to the increase of the high out-of-plane constraint.
Synthesis and Properties of an Ultrafine Grained Ti-45Al-2Cr-2Nb-1B-0.5Ta Alloy Prepared by Double Mechanical Milling and Spark Plasma Sintering
Authors: Chen Yu Yong , Kong Fan Tao , Yu Hong Bao , Zhang De Liang
Published: March 2009

Ti-45Al-2Cr-2Nb-1B-0.5Ta (at.%) bulk alloys with dense and ultrafine grains were fabricated by Double Mechanical Milling (mechanical milling + heat treatment + mechanical milling) and spark plasma sintering method. The phase composition and microstructure of the milled powder and bulk alloy sintered by SPS at different temperature (900oC, 1000oC and 1100oC), and the relationship between microstructure and properties of bulk alloys were investigated. The results demonstrate that high-quality composite powders (low contaminant, size uniform distribution and elements homogeneous dispersion) can be obtained by double mechanical milling. The composite powders prepared by primary mechanical milling were uniform and partially solid solution. Ti3Al、Ti、Al3Ti and TiAl phases were found after heat treatment while Al phase disappeared. The fined grain size and particle size were achieved by subsequent mechanical milling. The whole mechanical milling leads to alloying and the refined grain and particle, which also cause lattice distortion and powders system energy increased. SPS results showed that the densified and ultrafine grained Ti-45Al-2Cr-2Nb-1B-0.5Ta alloy is mainly consisted of TiAl, Ti3Al phase and a small quantity of TiB2 phase. With the increasing of sintering temperature, grain size of TiAl based alloy increase. The mechanical properties depend on microstructure and grain size. The relationship between compression properties, bending properties and microstructure was discussed.
Residual Stress Gradient Study of Laser Shocked Aluminum Alloy by GIXRD Analysis and FEM Simulation
Authors: Song Hong Bin , Peyre Patrice , Ji Vincent , Pelletier Hervé
Published: March 2009

Laser shock processing (LSP) is a new and competitive technology in comparison with classical mechanical surface treatments for alloys strengthening. The compressive residual stress could be induced by LSP, which further significantly affects materials surface properties. Aluminum based alloy 6056 is used for aeronautic components and their surface strengthening is very important to increase components’ durability. The main factors of LSP, which affect the surface properties of alloys, such as surface roughness and residual stress gradient, are studied and analyzed in present study. The sin2* method with pseudo-grazing incidence X-ray diffraction (GIXRD) is used to determine the residual stress gradient after LSP treatment. In addition, the FEM simulation of residual stress distribution induced by LSP is also carried out and the results are compared with experimental data.
Device Characteristics Dependence on Diamond SDBs Area
Authors: Umezawa Hitoshi , Ikeda Kazuhiro , Kumaresan Ramanujam , Tatsumi Natsuo , Shikata Shinichi
Published: March 2009

Device size scaling of pseudo-vertical diamond Schottky barrier diodes (SBDs) has been characterized for high-power device applications based on the control of doping concentration and thickness of the p- CVD diamond layer. Decreasing parasitic resistance on the p+ layer utilizing lithography and etching makes possible to get a constant specific on-resistance of less than 20 mOhm-cm2 with increasing device size up to 200 µm. However, the leakage current under low reverse bias conditions is increased markedly. Due to the increase in the leakage current, the reverse operation limit is decreased from 2.4 to 1.3 MV/cm when the device size is increased from 30 to 150 µm. If defects induce an increase in leakage current under the reverse conditions, the density of the defects can be estimated to be 104–105/cm2. This value is 5–10 times larger than the density of dislocations in single crystal diamond substrate.
Uniformity Improvement of Planetary Epitaxial Growth Processes through Analysis of Intentionally Stalled SiC Wafers
Authors: Oliver James D. , Ponczak Brian H. , Parikh Rinku P. , Adomaitis Raymond A.
Published: March 2009

A method to improve the uniformity of epitaxial wafers grown in planetary rotation reactors through analysis of intentionally stalled wafer measurements is described. A set of basis functions that are completely uniform when rotated in the reactor environment are described and used to construct a nearest uniformity producing profile (NUPP). The methodology for use of stalled wafer profiles and comparison to the NUUP allows easy identification of the changes in process parameters necessary for more uniform epitaxial growth. Although described here as applied to SiC epitaxial growth, this method is applicable to all planetary rotation reactors which are utilized for SiC and III-V semiconductor epitaxial growth.
The Effect of 4H-SiC Substrate Surface Scratches on Chemical Vapor Deposition Grown Homo-Epitaxial Layer Quality
Authors: Zhang Ning , Chen Yi , Sanchez Edward , Black David R. , Dudley Michael
Published: March 2009

The influence of substrate surface scratches on the quality of CVD grown 4H-SiC homo-epitaxial layers has been studied using a combination of post-growth Monochromatic Synchrotron X-ray Topography (MSXT) and KOH etching. MSXT observations suggest that the scratches on the substrate surface act as dislocation nucleation centers during the growth. When the scratch is along the off-cut direction, only TED-TED pairs are generated. As the inclination of the scratch to the off-cut direction increases, an increasing number of TED-BPD pairs are generated. A model is presented for a possible mechanism for the nucleation of dislocations at scratches.
Control of the Surface Morphology on Low Off Angled 4H-SiC Homoepitaxal Growth
Authors: Kojima Kazutoshi , Okumura Hajime , Arai Kazuo
Published: March 2009

We have carried out detailed investigations on the influence of the growth conditions and the wafer off angle on the surface morphology of low off angle homoepitaxial growth. We found triangular features to be also serious problems on a 4 degree off 4H-SiC Si-face epitaxial layer surface. The control of the C/Si ratio by controlling the SiH4 flow rate is effective in suppressing the triangular features on 4 degree off Si-face homoepitaxial layer. As regards epitaxial growth on a vicinal off-axis substrate, the small off angle difference of a tenth part of a degree has an influence on the surface morphology of the epitaxial layer. This tendency depends on the face polarity and a C-face can be obtained that has a specular surface with a lower vicinal off angle than a Si-face. By controlling this off angle, a specular surface morphology without a bunched step structure could be obtained on a vicinal off angle 4H-SiC Si-face.
Extended Study of the Step-Bunching Mechanism during the Homoepitaxial Growth of SiC
Authors: Camarda Massimo , La Magna Antonino , Severino Andrea , La Via Francesco
Published: March 2009

We discuss the possible source of surface instabilities (with specific reference to the step bunching phenomena) during the growth of cubic and hexagonal Silicon Carbide polytypes. For this analysis we use: results from super-lattice Kinetic Monte Carlo simulations, atomic force microscope surface analysis and literature data. We show that only hexagonal polytypes with misorientation cut toward the <11-20> direction suffer “intrinsically” the step bunching phenomena (i.e. it are present, independently on the growth conditions) whereas cubic polytypes and hexagonal ones with misorientation cut toward the <10-10> direction do not.
Inverted Pyramid Defects in 4H-SiC Epilayers
Authors: Shrivastava Amitesh , Muzykov Peter G. , Sudarshan Tangali S.
Published: March 2009

In this work we identified the nucleation sites of inverted pyramid defects in 4H-SiC epilayers using AFM and KOH etching and proposed a mechanism for its formation. Partial dislocations, bounding the stacking faults, mostly aligned along the <11-20> directions, were found at the base of the inverted pyramid defects. It is shown that the basal plane dislocations, serve as nucleation centers for stacking faults, and eventually the formation of inverted pyramid defects. A geometrical model is formulated to explain the formation mechanism of inverted pyramid defects.
Liquid Phase Epitaxy of 4H-SiC Layers on On-Axis PVT Grown Substrates
Authors: Kusunoki Kazuhiko , Kamei Kazuhito , Yashiro Nobuyoshi , Hattori Ryo
Published: March 2009

We performed liquid phase epitaxial growth of SiC layers on on-axis 4H-SiC substrates using Si solvent. It was found that the polytype controllability of the epilayer significantly depends on the growth process conditions. By optimizing them, polytype mixing in the epilayers can be completely suppressed. It is shown that the density of basal plane dislocations in the epilayers is much less than in the substrates due to on-axis growth. SIMS analysis showed that the concentrations of trace impurity elements (B,Al,Ti,V,Cr,Fe,Ni,P) in the epilayers are under lower detection limit. The only impurity is nitrogen resulting in an n-type layer. Carrier concentrations Nd-Na ranging from high 1016 to low 1017cm-3 are achievable.
LPE Growth of Low Doped n-Type 4H-SiC Layer on On-Axis Substrate for Power Device Application
Authors: Hattori Ryo , Kamei Kazuhito , Kusunoki Kazuhiko , Yashiro Nobuyoshi , Shimosaki S.
Published: March 2009

LPE (liquid phase epitaxy) growth of low nitrogen unintentionally doped SiC epitaxial layer on on-axis 4H-SiC substrate using nitrogen getter Si based solution was investigated to realize basal plane dislocation (BPD) free epitaxial layer. A significant reduction in BPD was demonstrated.
High Quality Single Crystal 3C-SiC(111) Films Grown on Si(111)
Authors: Locke Christopher , Anzalone Ruggero , Severino Andrea , Bongiorno Corrado , Litrico Grazia , La Via Francesco , Saddow Stephen E.
Published: March 2009

We have developed a high-quality growth process for 3C-SiC on on-axis (111)Si substrates with the ultimate goal to demonstrate high quality and yield electronic and MEMS devices. A single-side polished 50 mm (111)Si wafer was loaded into a hot-wall SiC CVD reactor for growth. The 3C-SiC process was performed in two stages: carbonization in propane and hydrogen at 1135°C and 400 Torr followed by growth at 1380°C and 100 Torr. X-ray diffraction rocking curve analysis of the 3C-SiC(222) peak indicates a FWHM value of 219 arcsec. This is a very interesting result given that the film thickness was only 2 µm, thus indicating that the grown film is of very high quality compared with published literature values. X-ray polar figure mapping was performed and it was observed that the micro twin content was below the detection limit. Therefore TEM characterization was performed in plan view to allow assessment of the stacking fault density as well as confirmation of the very low micro twin concentration in this film. TEM analysis indicates a low concentration of stacking faults in the range of 104 cm-1.
P-Type Doping of Epitaxial 3C-SiC Layers on Silicon (001)
Authors: Wagner Günter , Schmidbauer M. , Irmscher K. , Tanner P. , Fornari R.
Published: March 2009

Single-crystalline 3C-SiC epitaxial layers were grown on on-axis Si (001) substrates by low-pressure hot-wall chemical vapour deposition. Aluminium from a trimethylaluminium (TMA) source was used for p-type doping. The atomic Al and carrier concentrations in the layers were determined as a function of the partial pressure of the TMA source gas. Secondary ion mass spectroscopy (SIMS), Hall-effect measurements at room temperature and four-point electrical resistivity method were applied to measure the atomic and electrically active Al concentrations. The crystalline perfection of the layers was characterized by high-resolution x-ray diffraction (HRXRD). At TMA-partial pressures ranging from 510-7 mbar up to 1.510-4 mbar corresponding aluminium concentrations from 21015 cm-3 up to 1.31019 cm-3 were measured in the epitaxial layers. On increasing the Al concentration from 1x1017 cm-3 to 1x1019 cm-3 the layer electrical resistivity decreases from 17 cm to 0.8 cm, while no influence on the crystalline quality of the layers was observed. The average full width at half maximum (FWHM) of the rocking curve for a 5µm thick 3C-SiC layer is about 500 arcsec. With increasing layer thickness (up to 16 µm) the FWHM of the rocking curve decreases to about 300 arcsec.
Structural Properties of 3C-SiC Grown by Sublimation Epitaxy
Authors: Beshkova Milena , Syväjärvi Mikael , Vasiliauskas Remigijus , Birch Jens , Yakimova Rositza
Published: March 2009

The present paper deals with morphological and structural investigation of 3C-SiC layers grown by sublimation epitaxy on on axis 6H-SiC(0001) at source temperature 2000 °C, under vacuum conditions (<10-5 mbar) and different temperature gradients in the range of 5-8 °C/mm. The layer grown at a temperature gradient 6 °C/mm has the largest average domain size of 0.4 mm2 assessed by optical microscope in transmission mode. The rocking curve full width at half maximum (FWHM) of (111) reflection is 43 arcsec which suggests good crystalline quality. The AFM image of the same layer shows steps with height 0.25 nm and 0.75 nm which are characteristic of a stacking fault free 3C-SiC surface and c-axis repeat height, respectively.
Two-Dimensional Nucleation of Cubic and 6H Silicon Carbide
Authors: Vasiliauskas Remigijus , Syväjärvi Mikael , Beshkova Milena , Yakimova Rositza
Published: March 2009

The initial stage of heteroepitaxial growth of 3C-SiC and homoepitaxial growth of 6H-SiC on nominal 6H-SiC on-axis substrates has been studied. Before 3C-SiC starts to nucleate, 6H-SiC grows in a step-flow growth mode due to a slight off-orientation of the substrate surface already at about 1500oC. In the 1650-1700oC temperature interval 3C-SiC nucleates as 2D islands. A distance away from the 3C-SiC island 6H-SiC grows in step-flow mechanism. In the vicinity of the 3C-SiC islands the 6H-SiC growth steps start to change direction and even split into two steps with the equal height of 0.5 nm, which is approaching the unit cell size of cubic SiC. When the supersaturation is lower in comparison with the conditions for 3C-SiC growth, there is only formation of 6H-SiC, i.e. homoepitaxial growth. The growth mode of 6H-SiC is dependent on temperature. At the lowest temperature there is spiral growth while at higher temperature 2D nucleation is preferred.
TEM Investigations of Graphene on 4H-SiC(0001)
Authors: Borysiuk Jolanta , Strupiński Wlodek , Bożek Rafał , Wysmolek Andrzej , Baranowski Jacek M.
Published: March 2009

Transmission Electron Microscopy (TEM) investigations of graphene layers on Si terminated 4H-SiC(0001) are presented. The graphene layers have been grown in a standard method using decomposition of silicon carbide. Two kind of graphene layers have been investigated: 1) grown on substrates with on-axis orientation, 2) grown on substrates with 4° and 8° off-axis orientation in respect of c-axis of SiC. In the case of 0° orientation the high resolution TEM micrographs revealed that a thin layer graphene is present: 1-3 monolayers were obtained. It was found that the first carbon layer was about 2Å from the SiC surface. This result indicates that a strong covalent bonds between carbon layer and silicon atoms on the SiC surface exist. The subsequent graphene layers have been found spaced by 3.4 Å - similar as in the graphite. That indicates a weak van der Waals bonding between subsequent carbon layers. In the case of 4° and 8° off-axis orientation a thicker layer of about 5-6 monolayers of graphene were obtained. Relative spacings of graphene layers were the same as in the case of on-axis orientation.
Spatial Profiling of Planar Defects in 4H-SiC Epilayers Using Micro-Photoluminescence Mapping
Authors: Feng Gan , Suda Jun , Kimoto Tsunenobu
Published: March 2009

The micro-photoluminescence (micro-PL) spectroscopy and its intensity mapping have been utilized to investigate the planar defects, stacking faults (SFs), in 4H-SiC epilayers. Strong PL emissions from the SFs are observed even at room temperature. It is found that each kind of SF shows the distinct PL emission behaviours. Three kinds of SFs: intrinsic Frank SFs, double Shockley SFs, and in-grown SFs, have been identified in the samples based on the micro-PL spectra. At the same time, the micro-PL intensity mapping at the emission band of each SF has been performed to spatially profile the SFs. The shapes, distributions, and densities of SFs in the epilayers are then presented. The PL emission behaviours of each SF at low temperature are also studied.
An Effective Method of Characterization of SiC Substrates
Authors: Mynbaeva Marina G. , Lebedev Alexander A.
Published: March 2009

An effective low-cost technique for rapid characterization of SiC ingots at the early stage of substrate manufacturing process is proposed. The method allows for revealing simultaneously open-micropipes, polytype inclusions, low grain boundary regions, and non-uniform resistivity. The idea of the method is to subject full-size single SiC wafer cut from an ingot to anodization treatment. The porous structure formed as a result of the treatment decorates existing defect regions via the effect of non-homogeneity in the porous structure caused by the defect-related internal stress, as well as by non-uniformity in the doping level across the wafer. The method is inexpensive, not time consuming and not fully destructive. It can also be combined with the standard selective KOH-etching technique.
Features of Hot Hole Transport in 6Н-SiC
Authors: Sankin Vladimir Ilich , Shkrebiy Pavel P. , Lepneva Alla A. , Ostroumov Andrey G. , Yakimova Rositza
Published: March 2009

In materials with a small degree of ionicity ranging 10-15%, such as in SiC, carrier scattering on polar optical potential is possible. Unlike scattering on deformation potential, the drift mobility in this case increases continuously. As this phenomenon may be realized in SiC hot hole transport, I-F characteristics in 6H-SiC with Na-Nd ~ 5x1017 cm-3 have been studied at electrical field 1-150 kV/cm for temperature from 300 to 600K. Furthermore, we studied the breakdown of Al impurity.
A TEM Study of Inversion Domain Boundaries Annihilation Mechanism in 3C-SiC during Growth
Authors: Mantzari Alkyoni , Lioutas Christos B. , Polychroniadis Efstathios K.
Published: March 2009

The aim of the present work is to study the evolution and the annihilation of inversion domain boundaries in 3C-SiC during growth. For this investigation conventional and high resolution transmission electron microscopy were employed. It is shown that the physical mechanism which results in the annihilation of inversion domain boundaries in 3C-SiC starting from the 3C-SiC/Si interface is the change of the crystallographic planes in which inversion domain boundaries propagate into the {111} ones. In all cases modeling and simulation analysis by EMS software [1] are in agreement with the experimental results.