bluuebunny/crossref_metadata_2025 huggingface dataset:
High Temperature Rapid Thermal Oxidation and Nitridation of 4H-SiC in Diluted N2O and NO Ambient
Authors: Kosugi Ryouji , Fukuda Kenji , Arai Kazuo
Published: March 2009

A high temperature rapid thermal processing (HT-RTP) above 1400oC was investigated for use in the gate oxide formation of 4H-SiC by a cold-wall oxidation furnace. The gate oxide film of ~50nm can be formed for several minutes in the oxidizing atmospheres such as N2O and O2, where the oxidation rates were 8-10nm/min. After the initial oxide formation, the HT-RTPs in various ambient gases were conducted, and the dependences of their MOS interface properties on the gases were evaluated by a capacitance-voltage (CV) measurement. Based on the results, the process sequence of gate oxidation was determined as follows; the initial oxide was formed by the HT-RTO (oxidation) in N2O or in O2 with subsequent post annealing in Ar ambient, and then the HT-RTN (nitridation) in NO was conducted. The total process time becomes 20-50min. The interface trap
density (Dit) of fabricated MOS capacitor shows 3-5x1011cm-2eV-1 at Ec-E~0.2eV. The field-effect channel mobility of fabricated 4H-SiC lateral MOSFETs was ~30cm2/Vs.
New Achievements on CVD Based Methods for SiC Epitaxial Growth
Authors: Crippa Danilo , Valente Gian Luca , Ruggiero Alfonso , Neri L. , Reitano Ricardo , Calcagno Lucia , Foti Gaetano , Mauceri Marco , Leone Stefano , Pistone Giuseppe , Abbondanza Giuseppe , Abbagnale G. , Veneroni Alessandro , Omarini Fabrizio , Zamolo L. , Masi Maurizio , Roccaforte Fabrizio , Giannazzo G. , Di Franco Salvatore , La Via Francesco
Published: March 2009

The results of a new epitaxial process using an industrial 6x2” wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H2>0.05) and an increase of the growth rate until about 20 µm/h has been measured. No difference has been observed in terms of defects, doping uniformity (average maximum variation 8%) and thickness uniformity (average maximum variation 1.2 %) with respect to the standard
process without HCl.
High-Reliability ONO Gate Dielectric for Power MOSFETs
Authors: Tanimoto Satoshi , Tanaka Hideaki , Hayashi Tetsuya , Shimoida Yoshio , Hoshi Masakatsu , Mihara Teruyoshi
Published: March 2009

Thin (~10nm) Si layers have been deposited using Rapid Thermal CVD at temperatures ranging 950°C-1050°C. RTCVD deposited Si layers have been oxidized using N2O at 1300°C during relatively short times (15min) to produce SiO2 layers of 20-30nm. The interfacial characteristics of N2O oxidized RTCVD layers have been studied using the conductance method, showing a reduced traps density and a low band bending fluctuation when compared with conventional N2O grown oxides on 4H-SiC substrates. The surface topology of these layers has also
been analyzed evidencing an adequate topography with low roughness.
Low Density of Interface States in n-Type 4H-SiC MOS Capacitors Achieved by Nitrogen Implantation
Authors: Ciobanu Florin , Pensl Gerhard , Afanas'ev Valeri V. , Schöner Adolf
Published: March 2009

A surface-near Gaussian nitrogen (N) profile is implanted into n-type 4H-SiC epilayers prior to a standard oxidation process. Depending on the depth of the oxidized layer and on the implanted N concentration, the density of interface states DIT determined in corresponding 4H-SiC MOS capacitors decreases to a minimum value of approx. 1010 cm-2eV-1 in the investigated energy range (EC-(0.1 eV to 0.6 eV)), while the flat-band voltage increases to negative values due to
generated fixed positive charges. A thin surface-near layer, which is highly N-doped during the chemical vapour deposition growth, leads to a reduction of DIT only close to the conduction band edge.
Characterization of Aluminium and Titanium Oxides Deposited on 4H-SiC by Atomic Layer Deposition Technique
Authors: Wolborski Maciej , Bakowski Mietek , Pore Viljami , Ritala Mikko , Leskelä Markku , Schöner Adolf , Hallén Anders
Published: March 2009

Aluminium oxide and titanium oxide films were deposited using the Atomic Layer
Deposition method on n-type 4H SiC and p-type Si {001} substrates, with doping 6×1015cm-3 and 2×1016cm-3, respectively, and on 1.2 kV PiN 4H SiC diodes for passivation studies. The Al2O3 and SiC interface was characterised for the existence of an effective negative charge with a density of 1×1012-2×1012 cm-2. The dielectric constant of Al2O3 as determined from capacitance-voltage data was
about 8.3. The maximum electric field supported by the Al2O3 film was up to 7.5 MV/cm and 8.4 MV/cm on SiC and Si, respectively.
Ion-Beam Induced Modifications of Titanium Schottky Barrier on 4H-SiC
Authors: Roccaforte Fabrizio , Giannazzo Filippo , Bongiorno Corrado , Libertino Sebania , La Via Francesco , Raineri Vito
Published: March 2009

The effects of ion irradiation on the Ti/4H-SiC Schottky barrier are discussed. The Ti/SiC interfacial region of test Schottky diodes was irradiated with 8 MeV Si+4 ions at fluences between 1×109 and 1×1012 ions/cm2. By increasing ion fluence, an increase of the Schottky barrier FB was observed, from FB=1.05 eV in the non-irradiated sample to FB =1.21 eV after irradiation at the highest fluence, accompanied by a decrease of the leakage current. Using different experimental
analytical techniques enabled us to correlate the modification of the interfacial region with the contacts electrical behaviour. In particular, the structural and electrical modifications in the nearinterface region (different orientation of the Ti film, defects in the epilayer, dopant deactivation) were responsible for the change of the Ti barrier after irradiation.
Phase Formation at Rapid Thermal Annealing of Nickel Contacts on C-Face n-Type 4H-SiC
Authors: Ferrero Sergio , Albonico A. , Meotto Umberto M. , Rambolà G. , Porro Samuele , Giorgis Fabrizio , Perrone Denis , Scaltrito Luciano , Bontempi E. , Depero L.E. , Richieri G. , Merlin Luigi
Published: March 2009

In this work we report an analysis on Ni/4H-SiC interfaces aimed at optimizing the ohmic contacts. Several thermal cycles have been performed by rapid thermal annealing checking the possible chemical reactions at the metal semiconductor interfaces. Micro x-ray diffraction and micro Raman techniques have been performed in order to study the interface micro structural evolution.
Inter diffusion of each element at the Ni - SiC interface was examined using Auger spectroscopy. Electrical measurements have been performed in order to check the ohmic behavior of the contacts. Finally, a correlation between microstructures evolution and electrical behaviors is reported.
Nucleation and Reaction of Ag on 4H-SiC(0001)
Authors: Soubatch S. , Starke Ulrich
Published: March 2009

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and spectroscopy (STS), and Auger electron spectroscopy (AES) were used for a study of silver interaction with the (3×3) and ° × 30 ) 3 3 ( R surface phases of clean 4H-SiC(0001). The development of the surface structure and morphology after room temperature (RT) deposition and
annealing was investigated. On the (3×3) phase silver forms small clusters leaving the initial reconstruction intact. At high coverages three-dimensional (3D) growth (Vollmer-Weber mode) was found. For the ° × 30 ) 3 3 ( R phase the initial structure seems more disturbed upon Ag deposition and thermally induced diffusion. Yet, no new surface phase develops. In both cases Ag can be
removed from the surface by annealing, but Ag appears to be more stable on the ° × 30 ) 3 3 ( R phase according to AES.
Analysis of Low On-Resistance in 4H-SiC Double-Epitaxial MOSFET
Authors: Harada Shinsuke , Okamoto Mitsuo , Yatsuo Tsutomu , Fukuda Kenji , Arai Kazuo
Published: March 2009

In our previous study, the on-resistance of the SiC-based vertical MOSFET had been reduced in double-epitaxial MOSFET (DEMOSFET). The device exhibited an on-resistance (Rons) of 8.5 mWcm2 with a blocking voltage (Vbr) of 600 V. This study analyzed the characteristics of the DEMOSFET using a numerical simulation. The results showed the trade-off relationship between the specific on-resistance and the blocking characteristics when the concentration of the nitrogen ions increases in the surface of the n-type region between the p-wells. Specially, the specific on-resistance was drastically improved by increasing the concentration of the nitrogen ions. The thick gate oxide on the n-type region between the p-wells had an advantage to suppress the electric field in the gate oxide.
Investigation of Degradation of Inversion Channel Mobility of SiC MOSFET due to the Increase of Channel Doping
Authors: Hatakeyama Tetsuo , Watanabe Takatoshi , Senzaki Junji , Kato Makoto , Fukuda Kenji , Shinohe Takashi , Arai Kazuo
Published: March 2009

This paper reports on the degradation of inversion channel mobility of SiC MOSFET
caused by the increase of channel doping. SiC MOSFETs were fabricated on three wafers, the doping concentrations of the epitaxial layer of which were 16 10 2× cm-3 (sample A), 17 10 2× cm-3 (sample B) and 17 10 4× cm-3 (sample C). The field effect mobility sharply decreases as the doping concentration increases. Hall mobility measurements have been done to investigate the degradation of the mobility
due to doping. The measurement of sample A shows that, as a consequence of the decrease of the free carrier density due to MOS interface traps, the Hall mobility is as much as a factor of ten higher than the field effect mobility. In contrast, in regard to the measurement of sample B and sample C, we encountered unstable Hall voltage and could not obtain reproducible results. This implies that such
high-density traps are generated that a channel disappears in the higher-doping samples.
Gamma and Proton Irradiation Effects on 4H-SiC Depletion-Mode Trench JFETs
Authors: Merrett J. Neil , Williams John R. , Cressler J.D. , Sutton A.P. , Cheng Lin , Bondarenko V. , Sankin Igor , Seale D. , Mazzola Michael S. , Krishnan Bharat , Koshka Yaroslav , Casady Jeff B.
Published: March 2009

4H-SiC vertical depletion-mode trench JFETs were fabricated, packaged, and then
irradiated with either 6.8 Mrad gamma from a 60Co source, a 9x1011 cm-2 dose of 4 MeV protons, or a 5x1013 cm-2 dose of 63 MeV protons. 4H-SiC Schottky diodes were also fabricated, packaged and exposed to the same irradiations. The trench VJFETs have a nominal blocking voltage of 600 V and a forward current rating of 2 A prior to irradiation. On-state and blocking I-V characteristics were measured after irradiation and compared to the pre-irradiation performance. Devices irradiated with 4 MeV proton and gamma radiation showed a slight increase in on resistance and a
decrease in leakage current in blocking mode. Devices irradiated with 63 MeV protons, however, showed a dramatic decrease in forward current. DLTS measurements were performed, and the results of these measurements will be discussed as well.
Growth of Large Diameter SiC Crystals by Advanced Physical Vapor Transport
Authors: Anderson Thomas , Barrett Donovan L. , Chen J. , Emorhokpor Ejiro , Gupta A. , Hopkins R.H. , Souzis Andrew E. , Tanner C.D. , Yoganathan Murugesu , Zwieback Ilya , Choyke Wolfgang J. , Devaty Robert P. , Yan Fei
Published: March 2009

Semi-insulating 6H SiC substrates, 2”, 3” and 100mm in diameter, and n+ 4H SiC
substrates, 2” and 3” in diameter, are grown at II-VI using the Advanced Physical Vapor Transport (APVT) technique [1]. The process utilizes high-purity SiC source and employs special measures aimed at the reduction of background contamination. Semi-insulating properties are achieved by precise vanadium compensation, which yields substrates with stable and uniform electrical resistivity reaching ~ 1011 Ω-cm and higher. Conductive n+ 4H SiC crystals with the spatially uniform resistivity of 0.02 W-cm are grown using nitrogen doping. Crystal quality of the substrates, their electrical properties and low temperature
photoluminescence are discussed.
Influence of Overgrown Micropipes in the Active Area of SiC Schottky Diodes on Long Term Reliability
Authors: Rupp Roland , Treu Michael , Türkes Peter , Beermann H. , Scherg Thomas , Preis Herbert , Cerva Hans
Published: March 2009

Other than open micropipes (MP), overgrown micropipes do not necessarily lead to a^significantly reduced blocking capability of the affected SiC device. However they can lead to a degradation of the device during operation. In this paper the physical structure of overgrown micropipes will be revealed and their contribution to the leakage current will be shown. The possible impact of the high local power dissipation in the surrounding of the overgrown micropipe will be discussed and
long term degradation mechanisms will be described. Failure simulation under laboratory conditions shows a clear correlation between the position of overgrown micropipes and the location of destructive burnt spots.
SiC Super Junction Power Devices: Modeling and Analysis
Authors: Shen Z.J. , Cheng X. , Kang Beom Soo , So K. , Hshieh I.
Published: March 2009

In this paper, we extend the super junction concept to SiC high voltage devices and
further expand the SiC theoretical limit. It is shown that the super-junction concept can reduce the theoretical specific on-resistance by several times to several orders of magnitude for both silicon and SiC. The unique merit of SiC super-junction devices is that the required P and N pillars have a much smaller aspect ratio and may be easier to form than their silicon counterparts. Furthermore,
SiC super-junction devices are much less sensitive to charge imbalance issue than silicon SJ devices.
Electrical Characteristics and Reliability of 4H-SiC PiN Diodes Fabricated on In-House Grown and Commercial Epitaxial Films
Authors: Losee Peter A. , Li Can Hua , Seiler Joseph , Stahlbush Robert E. , Chow T. Paul , Bhat I. , Gutmann Ronald J.
Published: March 2009

4H-SiC pin diodes fabricated on epitaxial films grown in-house on various substrates
along with devices fabricated on commercial epi-material are presented. Defects have been observed using electroluminescence imaging and are correlated with device electrical performance. Most diodes fabricated with in-house epi-layers up to 25µm thick show relatively stable forward biased operation, although stacking fault propagation has been confirmed in all samples using electroluminescence imaging. Significant stacking fault propagation induced in the vicinity of testing probes has been observed and resulting design considerations are discussed.
Demonstration of High-Power X-Band Oscillation in p+/n-/n+ 4H-SiC IMPATT Diodes with Guard-Ring Termination
Authors: Ono Shuichi , Arai Manabu , Kimura C.
Published: March 2009

We fabricated a p+/n-/n+ 4H-SiC IMPATT diode with guard-ring termination. The p+ -
layer and the guard-ring were formed by ion implantation. The diode showed abrupt avalanche breakdown characteristics and we obtained a peak output power of 1.8 W at 11.93 GHz, which is the highest peak output power ever for the SiC IMPATT diodes in X-band.
Study of Forward Voltage Drift in Diffused SiC PiN Diodes Doped by Al or B
Authors: Maximenko S.I. , Soloviev Stanislav I. , Grekov A.E. , Bolotnikov A.V. , Gao Ying , Sudarshan Tangali S.
Published: March 2009

The degradation of diffused SiC PIN diodes during forward-biased operation was studied by first fabricating PIN diodes by diffusion of aluminum or boron into 4H-SiC substrates with n-type 10-15 µm thick epilayers doped by nitrogen up to 5x1015cm-3. The formed diodes were subjected to degradation testing under an applied current density of 200A/cm2 at room temperature. The majority of the Al diffused diodes demonstrated a voltage drift, ΔVf, of more than 2 V, while B-doped diodes
showed no significant change in forward voltage. The EBIC mode of SEM was employed to monitor nucleation and expansion of stacking faults.
Preparation of Porous Hydroxyapatite/TCP Composite Block Using a Hydrothermal Hot Pressing Method
Authors: Kim Y. , Kim Soo Ryong , Song Hee , Yoon Hyeon
Published: March 2009

The hydrothermal hot pressing (HHP) technique is a method by which hard solid bodies of powders can be produced in a short time and at a relatively low temperature under saturated vapor pressure. In this study, the hydrothermal hot pressing (HHP) technique is used for preparing porous hydroxyapatite/TCP block having a high mechanical strength. The SEM result of the sample
shows that all the pores are interconnected from 200µm to 300µm in sizes. The observed X-ray powder diffraction pattern of the sample after sintering at 1200oC is composed of hydroxyapatite and tricalciumphosphste.
Fabrication and Properties of Wall and Floor Tiles Using Waste Glass
Authors: Kim Young Kil , Jung Yeon-Gil , Song Jin Bo , Shin Min Chul , Lee Hee Soo
Published: March 2009

Wall and floor tiles were fabricated by a dry pressing method using waste glass and clay. The properties of the tiles such as absorption, bulk density, porosity, compressive strength, and abrasion loss were investigated with the firing temperature and glass contents. The properties were improved by increasing the firing temperature and glass contents. These properties, except the compressive strength, tended to be saturated from the glass contents of 70 wt % in the case of 1050 °C. The compressive strength showed the maximum values at the glass contents of 70 wt% and then decreased with increasing glass contents. The optimal properties obtained in the tiles were the water absorption of about 0.9 %, the bulk density of about 2.3 g/cm3, the apparent porosity of about 2.1 %,
the compressive strength of about 210 MPa, and the abrasion loss of about 0.022 g, when the composition containing the glass of 70 wt% was fired at 1050°C. These results are better than the properties of commercial clay tiles for easy melting and densification of glassy phase in the tiles.
Investigation on the Alloy Phases in As-Aged ZK60 Magnesium Alloy
Authors: Pan Fu Sheng , Wang Wen Ming , Ma Yan Long , Zuo Ru Lin , Tang Aitao , Zhang Jing
Published: March 2009

Alloy phases in the as-aged (T6) ZK60 magnesium alloy were investigated. More attentions were paid to types and morphologies of main alloy phases in the as-aged ZK60 magnesium alloy. The experimental results indicated that there was an abundant flower-shaped segregation in the solution-treated ZK60 magnesium alloy. A small quantity of undissolved compounds, MgZn2, was also found. They distributed irregularly in the form of similar parallelogram, with a dimension of 200nm~500nm and not sensitive to heat-treatment. Mg2Zn3 was found to be a main secondary compound in the as-aged ZK60 alloy, which precipitated during aging. Another precipitation phase, MgZn, in the as-aged ZK60 magnesium alloy was also
found in the form of long and thin rods with a dimension of 500nm.
Forming Tubes, Extrusions and Sheet Metal from Magnesium AZ31
Authors: Siegert Klaus , Jäger Stephan , Vulcan Mihai , Wizemann C.
Published: March 2009

This paper deals with pneumatic bulging of Magnesium AZ31 sheet metal and AZ31
tubes at elevated temperatures. Flow-stress curves determined by tensile tests and pneumatic bulging at different forming temperatures and strain rates are presented for magnesium AZ31 sheet metal. It is shown that based on basic investigations an automotive sheet-metal component can be formed at elevated temperatures. To determine the material properties of magnesium tubes, tensile tests have been conducted at different forming temperatures and constant strain rate. It is shown
how a forming process followed by a heat treatment process influences the microstructure and the formability of magnesium AZ31 tubes.
Development of Thermoelectric Cooling Devices with Graded Structure
Authors: Kohri Hitoshi , Shiota Ichiro
Published: March 2009

Every thermoelectric material shows high performance at a specific narrow temperature range. The temperature range with high performance can be expanded by joining the materials with different peak temperature. This is the concept of a functionally graded material (FGM) for thermoelectric materials. Bismuth telluride is the best material for cooling devices at around room temperature. Then we investigated the thermoelectric cooling properties for bismuth telluride with two step graded structure. FGM samples were fabricated by three methods. The first FGM was synthesized by in situ method. The second one was fabricated by joining in a hot-press equipment. The last one was composed by joining with solder. Thermoelectric cooling properties were evaluated by observing the maximum temperature drop to electric current when the high temperature side was kept constant. The large temperature difference was obtained when the proper configuration of thermoelectric materials along the temperature gradient were performed. The coincidence of optimum electrical currents of composing materials is also essential to obtain the high cooling performance.
Manufacturing of Structured TiO2-Surfaces for Cell Carrier Application
Authors: Will Julia , Gilbert Ilka , Dittmann Rainer , Haugen Håvard , Schnell-Witteczek Susanne , Wintermantel Erich
Published: March 2009

Titania surfaces were produced via a combined tape and slurry casting process. They were structured in the mm-µm range using structuring the gypsum, embossing the green ceramic, and lasering the sintered ceramic. The resulting structures were analyzed upon surface roughness and optically characterized by SEM. The ra values lay between 19-28 µm. Fibroblasts were seeded onto these structures, incubated for one and three days, and the number of cells was compared using polystyrol petri-dishes and borosilicate glass cover slips as references. It was demonstrated that the structure of the ceramic had an influence on the cell behaviour: larger cell numbers could be observed for the structured ceramics.
Neutron Diffraction Studies of Functionally Graded Alumina/Zirconia Ceramics
Authors: Lukáš Petr , Vrána Miroslav , Šaroun Jan , Ryukhtin Vasyl , Vleugels Jef , Anné Guy , Van der Biest Omer , Gasik Michael M.
Published: March 2009

New functionally graded Al2O3/Y-ZrO2 ceramics are developed as a new material for production of hip prosthesis, especially all-ceramic hip bearings. The used concept of graded ceramics is expected to provide better long-term performance based on improved mechanical properties and lower clinical risks. Mechanical properties are strongly dependent on the distribution of residual stresses resulting mainly from phase specific stresses after cooling from the sintering temperature. However, these stresses could be optimized by an appropriate selection of a concentration profile of constituent phases. The non-destructive neutron diffraction mapping of residual stresses has been used to investigate this problem experimentally. In addition, the smallangle neutron scattering technique was applied to study the porosity in the ceramics as function of the production parameters.
Fabrication of Nanostructure Composites in Functionally Graded Coatings with Supersonic Free-Jet PVD
Authors: Yumoto Atsushi , Yamamoto Takahisa , Hiroki Fujio , Shiota Ichiro , Niwa Naotake
Published: March 2009

Graded Al/AlTi and Al/Al-Si coatings are prepared by depositing nanoparticles with supersonic free-jet PVD (SFJ-PVD). The SFJ-PVD has been developed as a new coating method in which a coating film is formed by depositing nanoparticles with very high velocity onto a substrate. The high velocity of nanoparticles is produced by the supersonic gas flow of inert gas. A smooth, compact and defect-free microstructure is formed both at the interface between substrates and coating films and inside the coating films. The microstructures of Al/AlTi and Al/Al-Si coating films have very fine grain size. Mixing Ti and Al nanoparticles by depositing them onto a substrate produces in-situ syntheses of g-TiAl and a2-Ti3Al intermetallic compounds on the substrate. It is confirmed with nano-indentation hardness tester that graded coatings have graded hardness corresponding to the gradation of composition.
New Multifunctional FGM Coatings Produced Using ESA and TRESS Methods
Authors: Kudryashov A.E. , Zamulaeva E.I. , Vakaev P.V. , Pogozhev Yu.S. , Levashov E.A.
Published: March 2009

The influence of nanodispersed complex additives (ZrO2, Al2O3, W, WC, WC-Co, NbC, Si3N4) to SHS electrode materials on the mass transfer, structure and properties of electrospark coatings has been considered dependent on variation of the energy regimes of processing. The influence of the pulse discharge energy on the structure, composition, and properties of TRESS coatings has been studied. The optimum energy regimes of depositing high-quality multifunctional graded ESA and TRESS coatings have been found. It has been shown that introduction of
nanodispersed complexes into electrode materials promotes improvement of the properties of ESA coatings.
A Simple Galerkin Boundary Element Method for Three-Dimensional Crack Problems in Functionally Graded Materials
Authors: Paulino Glaucio H. , Sutradhar Alok
Published: March 2009

This paper presents a Galerkin boundary element method for solving crack
problems governed by potential theory in nonhomogeneous media. In the simple boundary element method, the nonhomogeneous problem is reduced to a homogeneous problem using variable transformation. Cracks in heat conduction problem in functionally graded materials are investigated. The thermal conductivity varies parabolically in one or more coordinates. A three dimensional boundary element implementation using the Galerkin approach is presented. A numerical example demonstrates the eáciency of the method. The result of the test example
is in agreement with ßnite element simulation results.
On Accurate Numerical Evaluation of Stress Intensity Factors and T-Stress in Functionally Graded Materials
Authors: Kim Jeong Ho , Paulino Glaucio H.
Published: March 2009

This paper revisits the interaction integral method to evaluate both the mixed-mode stress intensity factors and the T-stress in functionally graded materials under mechanical loading. A nonequilibrium formulation is developed in an equivalent domain integral form, which is naturally suitable to the finite element method. Graded material properties are integrated into the element stiffness matrix using the generalized isoparametric formulation. The type of material gradation considered includes continuum functions, such as an exponential function, but the present formulation can be readily extended to micromechanical models. This paper presents a fracture problem with an inclined center crack in a plate and assesses the accuracy of the present method compared with available semi-analytical solutions.
Dynamic Fracture of Functionally Graded Composites Using an Intrinsic Cohesive Zone Model
Authors: Paulino Glaucio H. , Zhang Zheng Yu
Published: March 2009

This paper presents a Cohesive Zone Model (CZM) approach for investigating dy- namic failure processes in homogeneous and Functionally Graded Materials (FGMs). The failure criterion is incorporated in the CZM using both a ßnite cohesive strength and work to fracture in the material description. A novel CZM for FGMs is explored and incorporated into a ßnite element framework. The material gradation is approximated at the element level using a graded element formulation. A numerical example is provided to demonstrate the eácacy of the CZM approach, in which the inàuence of the material gradation on the crack branching pattern is studied.
Numerical Simulation of a Centrifugal Process to Fabricate Permittivity Graded FGM from Alumina/Epoxy Mixture
Authors: Tsuru Shin-ichiro , Hayashi Noriyuki , Onoda Tomohiko , Sakamoto Yasushi , Hara Masanori
Published: March 2009

A new numerical method to simulate the centrifugal process of fabricating functionally
graded materials (FGMs) from solid-particles/viscous-matrix mixtures is proposed, and the simulation method was successfully applied to a practical fabrication process of FGM from an alumina-fillers/epoxy-resin mixture. Gradient profiles of dielectric constant of the resultant FGM were estimated by using the proposed method and compared with the experimental ones, resulting in reasonable agreement between them. Based on the numerical results, gradient pro- files of the number density and size of the dispersed fillers were confirmed, and contribution
of the filler size toward the gradient in the packing fraction was demonstrated. It is concluded that the gradient in the filler distribution can be intentionally regulated by changing not only the centrifugal conditions, but also the size distribution of the fillers.
Design Model and Prediction Model on Preparation of Functionally Graded Material by Co-Sedimentation
Authors: Zhou Zhi Guang , Zhang Lian Meng , Shen Qiang , Gong Dao Ren
Published: March 2009

From the process of sedimentation the mathematical relationship between deposition
volume and powder properties as well as sedimentation parameters was deduced in this paper. The relationship was expressed by using indirect method. Based on the formula, design model and prediction model were set up. The models can be used to design powder properties and predict the volume fraction of FGM. Programs to solve the models were developed in numerical methods. As examples, TiC-Ni system FGM were designed and predicted. The prediction results fit well with the
design. Experiment of Mo-Ti system FGM was used to validate the prediction model.
Thermodynamics and Microstructure of Co-V8C7 Alloy
Authors: Huang Shui Gen , Li Lin , Vleugels Jef , Van der Biest Omer
Published: March 2009

The thermodynamic properties of the Co-V-C and Co-V8C7 systems are of interest for superfine cemented carbide applications. The model parameters for the Gibbs energy of the individual phases have been evaluated using the CALPHAD method by combining the recently optimized phase diagram information of the V-C, Co-C and Co-V system. The isothermal sections of ternary system Co-V-C at 1400 °C and 1600 °C, as well as the vertical section of Co-V8C7 system were extrapolated. The calculated results, especially the liquid forming temperature of Co-V8C7 system was validated with experiments by using differential scanning calorimetry (DSC) analysis. Through controlling the carbon activity, various vertical sections with different carbon activity in Co-V8C7 system are presented.
The Correlation between Hardness and Yield Strength of Hard Materials
Authors: Vandeperre L. , Clegg W.J.
Published: March 2009

The correlation between hardness, H, and yield strength, Y, for hard materials is reexamined using an analytical approach to provide a physical interpretation, which explains the trends observed. Existing analytical predictions using the analogy of the spherical cavity fail to reproduce experimental and finite element results because the accommodation of the intrusion of the indenter due to surface deformation is not taken into account, while experiments made here and elsewhere indicate that the latter can be substantial. A simple modification is proposed, which accounts for this, and allows for a reasonable prediction of the relation between hardness and yield
strength for materials, which have a well determined yield point and do not strain harden. The treatment also allows explaining the effect of indenter geometry on measured hardness for such materials.
Evaluation of SiC-Particle Connectivity in Functionally Graded Al/SiCp Composites by Synchrotron Radiation Holographic Microtomography
Authors: Velhinho Alexandre , Vignoles Gerard , Cloetens P. , Thibault X. , Boller Elodie , Braz Fernandes Francisco Manuel , Rocha L.A. , Botas José D.
Published: March 2009

Reliability of functionally graded metal matrix composites (FGMMCs) for automotive components is still dependent on the detailed knowledge of the mechanisms of the microstructural build-up, for instance on the mechanisms leading to the distribution and relative positions of the reinforcing particles. In order to assess the influence of the SiC particle size on the 3-D inter-particle connectivity in functionally graded Al/SiCp composites produced by centrifugal casting, X-ray
microtomography experiments were performed at the ID19 beamline in ESRF (European Synchrotron Radiation Facility). The FGMMCs consisted of an Al-10Si-2Mg alloy matrix, reinforced by an average SiC particle volume fraction of 0.10; two different average sizes were used: 37 µm and 12 µm. The holographic modification of the X-ray CMT (Computer Micro- Tomography) method allowed to obtain neatly contrasted images, as opposed to classical CMT.Good agreement was found between the particle size evaluated by CMT and by laser interferometry. Particle clustering has been evaluated in number and volume, showing that a lower
mean particle size is related to more clustering. Such an adverse effect relies on the importance of particle/liquid alloy surface tension. Also, the mean particle size has been evaluated as a function of particle number within a cluster: as expected, the larger a cluster, the larger the particles inside it.
Certified Reference Materials for the Characterisation of Multifunctional Materials
Authors: Roebben Gert , Wätjen Uwe , Lamberty Andrée
Published: March 2009

Multifunctional materials are created by intimately integrating different materials. The
assessment of the local properties and composition of the different components of such a multifunctional material necessarily relies on techniques with sufficient spatial resolution. The increased use of these microanalysis or microprobe techniques has created a demand for appropriate quality assurance tools, such as reference materials. In this paper a number of issues related to the certification of reference materials for multifunctional materials are discussed. Examples of reference materials are shown to illustrate the particular challenges the reference material producer is faced with such as micro-homogeneity, minimum sample intake and stability.
Experimental Characterization and Computational Simulation of Glass-Alumina Functionally Graded Surfaces
Authors: Cannillo Valeria , Manfredini Tiziano , Montorsi M. , Siligardi Cristina , Sola A.
Published: March 2009

Functionally graded materials are a new and attractive class of materials incorporating an engineered spatial variation in composition and/or microstructure: this idea has immediately revealed successful since it allows to reach peculiar mechanical properties such as resistance to wear and contact damage. As a matter of fact, the final behaviour of a Functionally Graded Material is mainly influenced by its graded composition and/or microstructure. Therefore a good fabrication technique should provide a high control and reproducibility of the spatial variation in composition and/or microstructure; on the other hand, a reliable model should take into account the gradient in order to accurately predict the final behaviour of a Functionally Graded Material. The present study is focused on glass-alumina FGMs: the compositional variation, which occurs along only one direction, has been realized through percolation of a molten glass into a bulk polycrystalline alumina. The resulting Functionally Graded Coatings have been carefully characterized through Scanning Electron Microscopy, X-ray diffraction, classical mechanical tests and analysis. Moreover, their behaviour has been modeled by means of a microstructure-based FEM method. A great attention has been paid to the validation of the computational model on the basis of the experimental data. Furthermore, the experimental and the computational approaches have been combined in order to define the correlation between fabrication parameters, such as time and temperature, and resulting gradients in composition and microstructure as well as related performances. Since changes in material properties can be easily evaluated, the resulting model may be useful to simulate the material response to a given thermo-mechanical loading and to tailor the gradient as a function of the specific application.
Joining of OFC to TC4 and Structural Control of Joint Interface
Authors: Wang Chuan Bin , Zhang Lian Meng , Shen Qiang
Published: March 2009

In the present work, oxygen-free-copper (OFC) and Ti-6Al-4V (TC4) were joined by diffusion welding at first and then the structural control of the joint interface was mainly analyzed. It was found that firmly welded OFC/TC4 joint was obtained over a temperature range of 1023K~1103K, and the temperature played the key role which mainly affected the thickness of the joint interface. The results also showed that the joining of OFC to TC4 was attributed to the mutual diffusion effect of elements Cu and Ti. The structure of the joint interface was further controlled by
exerting restrictive pressure (10MPa), controlling heating and cooling rates, lower welding temperature and reducing welding time etc. Finally, under certain welding parameters and by employing rational structural control techniques, well welded OFC/TC4 joint without large distortion or damage was obtained.
Effective Permittivity of Composite with Core-Shell Type Inclusions by Self-Consistent Method
Authors: Peng Zhi Jun , Zhai Peng Cheng , Zhang Qing Jie
Published: March 2009

In the paper, firstly self-consistent model (SCM) is used for establishing the predicted formula which can predict the effective permittivity of the composite materials with core-shell type inclusions. Then the factors on the effective permittivity of this kind of composite are investigated on the base of this predicted formula. The researching results indicate the effective permittivity of composite depends on not only the volume fraction of inclusions, but also the permittivity of matrix and inclusions (core and shell). According to our works, the optimal design of composite with core-shell type inclusion must be done if we want to make this composite get better effect of absorbing wave.
Main Problems of Nanostructured Materials Science
Authors: Andrievski R.A.
Published: March 2009

Size effects in nanostructured (nanocrystalline, nanophase or nanocomposite) materials (NMs) and their stability are of great importance for fundamental considerations and modern practice. The size effect peculiarities in NMs are analyzed and the complex influence of grain size and other factors on NM properties is emphasized. New approaches in the development of thermostable NMs are considered with a special attention to the importance of the reproducibility of NM structures and properties.
Morphology and Capacitive Properties of [RuOxHy/Low Surface Area Carbon Black] Composite Materials Prepared by Sol Gel Procedure
Authors: Panić V. , Dekanski A. , Gojković S.Lj. , Milonjić S.K. , Mišković-Stanković V.B. , Nikolić B.
Published: March 2009

The morphology and the capacitive properties of carbon supported hydrous ruthenium oxide (RuOxHy/C), prepared by impregnation of low-surface area carbon black VulcanÒ XC-72 R with solid phase of RuOxHy sol, were investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The oxide sols of different ageing times, prepared by forced hydrolysis of RuCl3, were used for composite preparation. The prepared
composites show considerably higher capacitance values in acid electrolyte if compared to carbon black support. Microscopic investigations show that the extent of impregnation and the composite surface appearance depend on ageing time. The composite capacitance increases with ageing time of oxide sol. A gradual decrease in capacitance of thermally untreated composite with charging/discharging cycles was registered, which appears to be related to the extent of impregnation, too.
Electrochemical impedance spectroscopy measurements indicate an in-depth capacitance distribution through the composite layer. It was found that NafionÒ layer, used to ensure the adhesion of the composite layer to the current collector, influenced the composite impedance behavior, especially on the oxide-rich parts of the composite surface.
Comparative Potentiodynamic Study of Nickel and Hydrogen Underpotential Deposition at Polycrystalline Platinum Electrode in Weak Acid and Neutral Solutions
Authors: Obradović M.D. , Grgur B.N. , Vračar Lj.M.
Published: March 2009

Underpotential deposition of nickel and hydrogen on polycrystalline platinum in weak acid and neutral solutions (3.5 ≤ pH ≤ 7.0), with and without Ni2+-ions, has been examined using cyclic voltammetric technique in the range of temperature from 274 to 313 K. The nickel and hydrogen ad-atom surface coverages were calculated from the voltammetric adsorption and desorption charges. The Temkin isotherm was fitted for both underpotential depositions, and thermodynamic adsorption parameters were calculated for both atoms. The value of the bonding energy between hydrogen and surface in the presence of underpotentially deposited nickel was calculated and found to amount to 287 kJ mol-1, which is 40 kJ mol-1 stronger bond than the same of pure platinum. The presence of nickel on the surface facilitates interfacial transfer of hydrogen into the metal bulk and consequent hydride formation significant in design of hydrogen based fuel cells.
GaAs/AlGaAs Quantum Cascade Lasers Based on Double Resonant Electron – LO Phonon Transitions
Authors: Mirčetić A. , Indjin D. , Milanović V. , Harrison P. , Ikonić Z. , Kelsall R.W. , Giehler M. , Hey R. , Grahn H.T.
Published: March 2009

In this paper a procedure for the global optimization of mid-infrared GaAs/AlGaAs quantum cascade lasers that relies on the method of simulated annealing is presented. We propose a double longitudinal optical phonon resonance design obtained via a ladder of three states, with subsequent pairs separated by optical phonon energy. Addition of an extra level decreases the lower laser level population by enabling an efficient extraction into the injector region. The output characteristics of the optimized structures are calculated using the full self–consistent rate equation model, which includes all of the relevant scattering mechanisms. We also presented the experimentally measured output characteristics of an initial device, which are in agreement with the numerically calculated values, confirming the good design capabilities of the applied procedure.
Crystal Chemistry Approach in Yb Doped Laser Materials
Authors: Viana Bruno , Petit J. , Gaumé R. , Goldner Philippe , Druon F. , Balembois F. , Georges P.
Published: March 2009

The emergence of new laser crystals has allowed progress in ultrashort-pulsed laser technology and high power lasers. Extensive researches on new Yb3+ doped crystals enable development of all-solid-state femtosecond lasers. Thermo-mechanical properties should be taken into account. The review of the state of the art on the Yb doped laser material for high power and ultrafast pulses generation is presented.
Spin Interactions in Cd1-xMnxS Bulk Crystals
Authors: Milivojević D. , Babić-Stojić B.
Published: March 2009

Electron paramagnetic resonance (EPR) linewidth in the Cd1-xMnxS bulk crystals with manganese concentrations x = 0.25, 0.33, 0.35 and 0.42 has been studied in the high-temperature region. An analysis of the infinite-temperature EPR linewidth performed within the exchange narrowing model shows that the contributions of the anisotropic superexchange and magnetic dipolar interaction to the linewidth are nearly the same due to weak anion spin-orbit coupling. The single-ion anisotropy originating from the crystal field of axial symmetry with the parameter
Dsingle= 0.0295 cm-1, as observed in some CdS:Mn crystals, gives a contribution to the linewidth comparable with the influence of the anisotropic superexchange and magnetic dipolar interaction. The calculated infinite-temperature linewidths, including all anisotropic spin interactions examined in this work, are close to the experimental infinite-temperature linewidths estimated from the existing high-temperature data.
Intersublevel Absorption in Stacked n-Type Doped Self-Assembled Quantum Dots
Authors: Veljković Dj. , Tadić M. , Peeters F.M.
Published: March 2009

The intersublevel absorption in n-doped InAs/GaAs self-assembled quantum-dot
molecules composed of three quantum dots is theoretically considered. The transition matrix elements and the transition energies are found to vary considerably with the spacer thickness. For s polarized light, decreasing the thickness of the spacer between the dots brings about crossings between the transition matrix elements, but the overall absorption is not affected by the variation of the spacer thickness. For p-polarized light and thick spacers, there are no available transitions in the single quantum dot, but a few of them emerge as a result of the electron state splitting in the stacks of coupled quantum dots, which leads to a considerable increase of the transition matrix elements, exceeding by an order of magnitude values of the matrix elements for s-polarized light.
Modelling and Experimental Verification of the Oxidation Protection of C/C-Si-SiC Composites with Mullite
Authors: Damjanović Tanja , Argirusis Christos , Borchardt Günter
Published: March 2009

The protectiveness of mullite layers electrophoretically deposited on C/C-Si-SiC
composites, against isothermal oxidation in air in the temperature range from 1200 to 1550 °C, was investigated by means of thermogravimetry (TG). The experimental results are interpreted with the help of a phenomenological model. At lower temperatures or short oxidation times the overall oxidation kinetics is determined by transport processes in the EPD mullite layer, which leads to a linear growth law. At higher temperatures or longer times of oxidation the oxidation rate is controlled by solid-state diffusion processes in the growing silica layer, which leads to a parabolic
growth law. Comparison of experimental parabolic and linear rate constants with calculated ones suggests, in the framework of the model, the conclusion that carbon monoxide (CO) diffusion in the oxide layers is the rate determining step for the overall oxidation of the C/C-Si-SiC substrates.
Curing Characteristics and Dynamic Mechanical Behaviour of Reinforced Acrylonitrile-Butadiene/Chlorosulfonated Polyethylene Rubber Blends
Authors: Marković G. , Marinović-Cincović M. , Valentova H. , Ilavsky M. , Radovanović B. , Budinski-Simendić J.
Published: March 2009

This paper deals with the control of the adhesion strength in metal-elastomer joints by
fillers and the use of rubber blends to produce advanced high performance adhesive systems. The curing behavior of rubber compounds and dynamic mechanical properties of crosslinked rubber composites were considered in this technologically applicable study. The effects of two types of reinforcing filler, used to increase the adhesion strength between steel and rubber matrix based on acrylonitrile-butadiene rubber (NBR) and chlorosulfonated polyethylene rubber (CSM) was investigated. Precipitated silica (with the average size of primary particle 15 nm) and diatomaceous earth (with the average size of primary particle 28 µm) were used for both rubber and its blend (NBR/CSM). The filler loading range was from 0 to 35 phr. The determination of curing characteristics was estimated by Monsanto Rheometer. The crosslink density of the rubber composites was determined by swelling measurement. Dynamic mechanical behavior was measured by mechanical spectroscopy (in a single cantilever bending mode).
Hyperbolic Propagation of a Thermal Signal in an Inhomogeneous Medium
Authors: Galović S. , Miličević Dejan , Suljovrujić E.
Published: March 2009

A numerical procedure for the calculation of space distribution of the thermal field in
thermally inhomogeneous solids with thermal memory induced by a harmonically modulated surface heat source is presented. The procedure is based on the division of the complex hyperbolic heat conduction equation into four real first-order differential equations, followed by employment of the Bulirsch-Stoer method with adoptive stepsize. The applicability of the procedure is then demonstrated in few issues, important for the understanding of thermal signal distribution.