bluuebunny/crossref_metadata_2025 huggingface dataset:
Superplastic Bulging Capability of Ti-6Al-4V Butt-Welded Plate by High Energy Beam Welding
Authors: Wang G. , Zhang Kai Feng , Han Wen Bo , Wu D.Z. , Wang C.W.
Published: March 2009

The superplastic bulging capabilities of Ti-6Al-4V butt-welded plates with 0.8mm in
thickness with high energy beam welding methods namely plasma arc welding (PAW), electron beam
welding (EBW) and laser beam welding (LBW) are studied in virtue of superplastic bulging tests.
Superplastic bulging tests are performed at the superplastic forming temperature 925°C under 1MPa
gas pressure. The superplastic bulging capability is represented by the maximum relative bulging
height h after fracture. Experimental results suggest that all of butt-welded plates with high energy
beam welding methods possess good superplastic bulging capability. Among them, the maximum
relative bulge height of LBW is the highest, that of EBW is slightly lower and that of PAW is the
lowest. The higher the input energy density is, the bigger the bulge height will be. Furthermore their
microstructure evolutions of various weld metals during superplastic bulging were systematically
analyzed via metallographical tests. The relation between the microstructure of weld metal and its
superplasticity is found. Metallographical analysis shows that the microstructure of Ti-6Al-4V weld
metal with high energy beam welding methods is composed of fine acicular martensite. The higher
the input energy density is, the finer the martensite structure will be. Upon heating, this martensite
changes to a basketweave-like structure and upon bulging, the martensite structure have the trend of
transforming to fine equiaxed grain. This can explained the reason why the Ti-6Al-4V butt-welded
plates with high energy beam welding methods have excellent superplastic bulging capability.
Superplastic Titanium Tanks for Propulsion System of Satellites
Authors: Sato Eiichi , Sawai S. , Uesugi K. , Takami T. , Furukawa K. , Kamada M. , Kondo M.
Published: March 2009

Institute of Space and Astronautical Science (ISAS/JAXA) in collaboration with
Mitsubishi Heavy Industries (MHI) has developed fuel and gas tanks for reaction control system and
orbital control system of satellites; A tank is fabricated through welding of two thin, hemi-spherical or
conical parts, which are fabricated by superplastic blow forming. Mass-productivity is not an
important factor but the forming precision and flexibiliry in the process are important for this
application. ISAS and MHI, therefore, developed a new blow-forming technique, which has high
flexibility in terms of tank size because it requires a furnace but not a hot-press machine. Some typical
propulsion tanks fabricated through this process are presented.
Superplastic Properties of γ+α2 Titanium Aluminide Alloy Ti-43Al-(Nb,Mo,B) in Cast + Post-Solidification Heat Treated Condition
Authors: Imayev V.M. , Imayev Renat M. , Khismatullin Timur G. , Salishchev Gennady A.
Published: March 2009

A novel approach to fabrication of globularized fine-grained structure in γ+α2 titanium
aluminide alloys has been proposed. The approach included the use of a specially designed alloy
Ti-43Al-X(Nb,Mo,B) and heat treatment. It was found that the ingot structure of the alloy might be
partially globularized on a scale of bulk material using only globularization anneal excluding any hot
working procedure. The microstructure and tensile mechanical properties of the alloy in the cast +
heat treated condition were investigated. The tensile mechanical tests were performed in air in the
temperature range of T=900-1130°C at an initial strain rate of ε′=1.7×10-4 s-1. High elongation
(δ=160-230%) and low flow stresses (σ=36-100 MPa) typical of superplastic behavior were measured
at T=1050-1130°C. It was demonstrated that the sheet material produced by spark cutting of the cast +
heat treated alloy might be successfully hot formed.
The Applications of SPF/DB Combined with Welding Technologies
Authors: Li Zhi Qiang , Li X.H.
Published: March 2009

Superplastic forming and diffusion bonding (SPF/DB) processes have been growing
mature and titanium SPF/DB components have found wide application in aerospace industry. With
the development of industrial SPF/DB technology, the size of SPF/DB components become bigger
and bigger, and the shapes of components become more complex. However, the component sizes are
limited by equipments, dies and the size of sheet. SPF/DB combined with welding technologies could
be one of the possible solutions to form larger and more integrated structures due to many advantages
compared with conventional process. This paper studied the combination processing of SPF and other
welding methods besides diffusion bonding, such as electron beam welding and laser beam welding,
and explained the experiments performed in different processes, including SPF after welding plate
and welding plate after SPF. The results show that the material exhibits both reasonable formability
and excellent mechanical properties. Application samples such as covers were manufactured by the
combination processing. Furthermore, prospects of the combining technology were discussed at the
end of paper.
Superplastic Deformation Behavior of Electrodeposited Nickel Matrix Nanocomposite
Authors: Chan K.C. , Wang C.L. , Wang Guo Feng , Zhang Kai Feng
Published: March 2009

In this paper, the superplastic deformation behaviour of a pulse electrodeposited Ni-SiC
nanocomposite was further studied at temperatures ranging from 330 to 530oC. It was found that
optimum temperature of the composite was 450oC, and the shape of its flow stress vs strain rate
curves is similar to that of conventional superplastic materials. The microstructures of the composite
before and after deformation were examined using SEM and TEM. Dislocations and deformation
twinning were observed in the deformed samples, and there was significant grain growth during
deformation. The deformation mechanisms were also discussed in the paper based on the
experimental findings.
Gas Pressure Forming of Amorphous Fe78Si9B13 Alloy
Authors: Li Xi Feng , Zhang Kai Feng , Han Wen Bo , Wang Guo Feng
Published: March 2009

The deformation behavior of gas pressure forming of amorphous Fe78Si9B13 alloy was
investigated under equibiaxial tension. The gas pressure forming was carried out in the temperature
range of 430°C~530°C below the crystallization temperature Tx and die apertures of 5mm~10mm.
The dome height and amorphous ribbon thickness of deformed specimens at the pole was measured. It
was found that amorphous Fe78Si9B13 alloy had exhibited good plasticity in the experimental
temperature range. The near-semisphere specimens of the radius 5mm and the height 4.5mm were
obtained from the gas-pressure forming at 450°C and 530°C for 30min, which is similar to the
superplastic forming.
Cavity of Al-Cu-Mg Alloy during Superplastic Deformation
Authors: Wang Min , Guo Hong Zhen , Liu Y.J.
Published: March 2009

According to the characteristic of appearing cavitation in the metals during superplastic
deformation, the influence of strain rate on cavity evolvement, the influence of cavity on superplastic
deformation capability, and the formation, development process of cavity were investigated for
Al-Cu-Mg alloy (i.e. coarse–grained LY12). The results show that: ①The pore nucleation occurs not
only at triangle grain boundaries, but also along nearby the second phase particles, and even within
grains. The cavities at the triangle grain boundaries are present in V-shape, others near the second
phase particles and within grains are present in O-shape. These cavities may result from disharmony
slippage of grain boundaries. ②The tendency of cavity development decreases with increasing of
strain-rate. In lower strain-rate condition, though Al-Cu-Mg alloy has better superplasticity, many big
cavities in the specimen may reduce the room temperature properties of the alloy. In higher strain-rate
condition, Al-Cu-Mg alloy has certain superplasticity and room temperature properties as well as few
cavities forming. By analyzing, viscous layer on grain boundaries is very thin and grain sizes can be
refined during their extruding and rotating each other in higher strain-rate superplastic deformation
condition. ③Growth and coalescence of cavity are the main reason of the superplastic fracture of
Al-Cu-Mg alloy. And small and a certain amount of cavities with dispersion and independence state
are very useful to crystal boundary slippage.
Mathematical Model for Super Plastic Flow in Advanced Structural Materials
Authors: Muñoz-Andrade Juan Daniel
Published: March 2009

Everything in the universe is a result of their own evolution, in consequence all advanced
structural materials are physical objects spatially extended in a permanently cosmic connection with
the advanced structural universe. In this context, the nature expansion rate of the universe (ξ u) was
obtained in a similar way of super plastic flow in terms of the rate reaction theory, with the strong
temperature dependence of strain rate as follow:
exp 70( / sec)/ 2.26854593 . 18 1
0
− − = =  


 


−  


 


= = km Mpc s
kT
c Q
H
P
P
P
u λ
ξ
Where, QP = the Planck activation energy of the system at the Planck scale (QP = 1.221x1028eV), λP =
Planck length (λP = 1.62x10-35m), c = the speed of light (c = 299 792 458 m/s), (c/λP) = the overall
frequency factor, k = the Boltzmann constant (k = 8.617x10-5eV/K), TP = the Planck temperature (TP
= 1.010285625x1030K) and H0 = the Hubble constant. On the basis of this mathematical expression
and their combination with the Orowan equation, it was obtained the mathematical model to predict
the activation energy (Q) that is necessary to the glide cellular dislocations during deformation of the
super plastic advanced structural materials. Consequently, in this work the application of this
mathematical model for super plastic flow in advanced structural materials and the concept of cellular
dislocation are reviewed in order to integrate in a general form the unified interpretation of Hubble
flow, plastic flow and super plastic flow [1-3].
Vibration Analysis of a Ni-Ti Shape Memory Alloy Rod
Authors: Ghazinejad M. , Shokuhfar Ali
Published: March 2009

In this paper the effect of stress induced phase transformation on the vibration response
of SMA structures has been studied. To this end, a Ni-Ti clamped-free rod in the superelastic range
which is subjected to axial harmonic loading has been considered. Subsequently, the dynamic
behavior of the superelastic rod has been analyzed using Auricchio’s superelastic model, which can
reproduce the superelastic behavior of the sample during stress induced phase transformation, and
Finite Element Method. Obtained Results show that due to the phase transformation the dynamic
behavior of superelastic rod is highly nonlinear. Also, it can be deduced that superelastic
components with large hysteresis loop has the potential for use in vibration attenuation of
structures.
Evaluation of Thermal and Mechanical Filler Gas Influence on Honeycomb Structures Behavior
Authors: Vesenjak Matej , Öchsner Andreas , Ren Zoran
Published: March 2009

In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.
Characterization of Niobium Carbonitride Coating on AISI D2 Steel
Authors: Şen Uğur , Şen Şaduman
Published: March 2009

Thermo-diffusion coatings containing Nitrogen, Carbon and Niobium (N+C+Nb) on
AISI D2 steel have been carried out by an initial tufftriding process followed by saturation with
Niobium. The properties of the diffusion layer, namely microstructure, phase composition and
micro-hardness of the Niobium carbonitride layer, have been studied. The influence of treatment
time of Niobizing on the thickness of the metallized layer and its phase composition has been
studied. Nitriding treatment was performed at 575°C for 2 h. Then, the Niobizing treatment was
performed by pack method in the powder mixture consisting of ferro-Niobium, ammonium chloride
and alumina at 1000°C for 1–4 h. The phases formed on the Niobium carbonitride coated steel were
NbN and NbC, confirmed by X-ray diffraction (XRD) analysis. The longer the treatment times, the
thicker the Niobium carbonitride layer became. The thickness of Niobium carbonitride layer was
changing between 6.53 3m and 17.45 3m, depending on treatment time and temperature. The
microhardness of Niobium carbonitride layer formed on the AISI D2 steel was changing between
2132±203 and 2814±245 HV0.01 from surface to interior.
Monte Carlo Calculation of X-Rays Deposited Energy in CdZnTe Detector
Authors: Stanković Srboljub J. , Petrović M. , Kovačević M. , Vasić A. , Osmokrović P. , Lončar B.
Published: March 2009

CdZnTe detectors have been employed in diagnostic X-ray spectroscopy. This paper
presents the Monte Carlo calculation of X-ray deposited energy in a CdZnTe detector for different
energies of photon beam. In incident photon direction, the distribution of absorbed dose as
deposited energy in detector is determined. Based on the dependence of the detector response on the
thickness and different Zn fractions, some conclusions about changes of the material characteristics
could be drawn. Results of numerical simulation suggest that the CdZnTe detector could be suitable
for X-ray low energy.
Emulsion Stability Evaluation Using Fractal Dimensions Approach
Authors: Pašalić Snezana , Jovanić P.B. , Bugarski B.
Published: March 2009

There are many developed strategies for evaluating emulsion stability, aimed at determining the
life circle of emulsions. Most of them are based on rheological properties of emulsions. There are, however,
very few based on direct emulsion observations. In this paper we present a developed method for the
emulsion stability evaluation by direct observation of optical emulsion properties. We propose the fractal
dimension approach as a stability quantification measure. The method is based on the measure of emulsion
transmittance properties, which are directly dependent on the emulsion stability at the moment of
measurement. The oil in water emulsion was used as a test emulsion. The system is classified as stable
emulsion and our intention was to find the moment when it starts to break. Emulsion transmittance properties
were measure applying a system for acquisition of visual information, which is based on a CCD camera and
a fast PC configuration equipped with the capturing software. The acquired sets of visual information were
analyzed by the OZARIA software package. The fractal dimensions were determined by the box counting
method. For these experiments, 100 boxes of different sizes were used. Experimental emulsions were
measured after 7, 14, 21 and 28 days from the moment of creation. A slight increase in fractal dimensions
was observed, which indicates that the emulsions are still in the stable region, or from the fractal point of
view emulsion are still regular and no significant irregularities were observed. From the first experiments the
applied methodology proved to be sensitive enough to be used for emulsions stability evaluation.
Structural Investigation of Ba2+ and Sr2+ Diphyllosilicates Doped with Yb3+ Ions
Authors: Nedić B. , Dondur V. , Kremenović A. , Dimitrijević R.
Published: March 2009

Ceramic materials, barium and strontium diphyllosilicates doped with ytterbium ions, were obtained by thermal treatment from Ba–LTA and Sr–LTA zeolites. The samples were characterized with Differential Scanning Calorimetry, Infra–Red Spectroscopy and Scanning Electron Microscopy. The crystal structures of diphyllosilacetes have been refined.
Synthesis of Pure and Doped LaMnO3 Powders from Citrate Precursors
Authors: Djuriš Katarina , Branković G. , Branković Z. , Bernik Slavko , Počuča M. , Poleti D. , Antić B.
Published: March 2009

In this work pure and doped LMO were prepared using modified Pechini method from
lanthanum and manganese citrates. Lanthanum citrate was prepared starting from La2O3, while
manganese citrate was prepared from Mn(NO3)2. Valence state of the manganese was controlled by
adjusting pH value of the solution and confirmed by EPR and UV/VIS analysis. Thermal treatment
conditions for preparation of LMO powders were determined from TG/DTA of dried precursors.
XRD results confirmed that pure perovskite phase was successfully prepared in single LMO and Cadoped
LMO. SEM and measurements of specific surface area of the powders showed the existence
of large agglomerates consisting of submicronic primary particles.
Influence of Urea as Homogeneous Precipitation Agent on Sonochemical Hydroxyapatite Synthesis
Authors: Jevtić Marija , Uskokovic Dragan P.
Published: March 2009

The main purpose of the present work was to investigate the influence of urea concentration on hydroxyapatite (HAp) synthesis. Calcium nitrate and ammoniumdihydrogenphosphate were used as Ca and P sources. A homogeneous precipitation agent – urea - was applied in the field of ultrasonic irradiation. Different Ca : P : urea molar ratios were applied and the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The results reveal the influence of the urea concentration on the phase composition of the system, crystallite size and the particle morphology. Different Ca : P : urea molar ratios led to various system formation: from biphasic OCP and HAp to monophasic HAp. The estimated HAp crystallite size was 24.4 nm. An explanation of the mechanism of the HAp synthesis is given, regarding the formation of the intermediate and final product during ultrasonic irradiation.
Phonon Thermodynamics in Crystalline Nanofilms
Authors: Šetrajčić J.P. , Zorić V.M. , Vučenović S.M. , Mirjanić D.Lj. , Sajfert V.D. , Jaćimovski S.K. , Ilić D.I.
Published: March 2009

The dispersion law and density of states of phonons in ultrathin films was analyzed in
this paper. It turned out that phonons in a thin film require activation energy for exciting. This leads
to extremely low specific heat and specific conductivity at low temperatures. Consequences of
quoted facts were discussed in detail and their influence on kinetic and thermodynamic properties of
thin films is estimated.
Experimental and Theoretical Investigation of Hydrogen Storage in Magnesium Based Composites
Authors: Grbović Novaković Jasna , Brdarić T. , Novaković N. , Matović Lj. , Montone Amelia , Mentus S.
Published: March 2009

Magnesium based composites MgH2 + X (X=Ti, Co) were synthesized by ball milling in
an argon atmosphere using stainless steel vial and balls. The crystallographic behavior of the
resulting powders was examined by XRD. Thermal stability and hydrogen desorption properties
were investigated by thermal analysis methods. In order to obtain a deeper insight into bonding
mechanisms of the transition metal in MgH2 relaxed structure, ab initio electronic structure
calculation of MgH2 + X (X=Ti, Co) was performed using Full Potential Linearized Augmented
Plane Wave method, implemented in WIEN2K code. DOS analysis, confirmed by DTA
measurements, resulted in the conclusion that, in the composite, in comparison to MgH2, the
bonding Mg-H was weakened, on account of the shortening of interatomic distances hydrogentransition
metal.
Up-Conversion in Yb,Er-Doped Y2O3 Nanoparticles for Cell Imaging
Authors: Bessière Aurelie , Pellé Fabienne , Mathieu Claire , Viana Bruno , Vermaut Philippe
Published: March 2009

Y2O3:19%Yb,1%Er nanoparticles were synthesized with the aim of imaging the
luminescent cell. Coprecipitation and combustion synthesis were used to obtain particulate sizes
ranging from 25 up to 140 nm. The powders showed predominant red upconversion and the
emission efficiency is controlled by the particle size. A colloidal route was also followed and 2-5
nm-large agglomerated nanoparticles were obtained. In that case, the luminescence of Er3+ was only
observed by direct excitation and no upconversion light has been detected on these very small
particles.
Alginate Microbeads as Cell Support for Cartilage Tissue Engineering: Bioreactor Studies
Authors: Obradović B. , Osmokrović A. , Bugarski B. , Bugarski D. , Vunjak-Novaković G.
Published: March 2009

Alginate was shown to be a suitable support for entrapment and cultivation of
chondrocytes and bone marrow stromal cells, which under appropriate in vitro conditions
synthesized cartilaginous components. The main limitation in these cultures may be low rates of
mass transport through the alginate matrix governed by diffusion. In this study, we have designed
and utilized a bioreactor system based on a packed bed of alginate beads with immobilized
chondrogenic cells. Continuous medium perfusion provided convective mass transport through the
packed bed, while small diameters of beads (2.5 mm and down to 500 μm) ensured short diffusion
distances to the immobilized cells. During up to 5 weeks of cultivation, the cells synthesized
extracellular matrix components merging beads together and indicating potentials of this system for
precise regulation of the cellular microenvironment in cartilage tissue engineering.
Fraction Scaling and Dynamical Properties of Elastomer Materials
Authors: Plavšić M.B. , Pajić-Lijaković Iva
Published: March 2009

Scaling of the real and the imaginary part of dynamic moduli with frequency, for fully
cured elastomer materials as gum and active carbon black filled butyl rubbers, is considered
experimentally and theoretically. For gum rubber in different ranges of frequency complete
agreement with G''-scaling predicted by the Rouse theory is obtained. Obtained slopes for all G' and
G'' of filled rubber are much lower.
Rubber Elasticity Study of Polyurethane Networks Prepared by Cyclotrimerisation Crosslinking Reaction of Isocyanate Groups
Authors: Budinski-Simendić J. , Ilavsky M. , Šomvarsky Jan , Špírková M. , Korugić-Karasz Lj. , Radičević R. , Dikić T. , Dušek K.
Published: March 2009

The aim of this contribution was to study the rubber elasticity of dry and swollen
networks obtained by cyclotrimerization crosslinking reaction of isocyanate groups located at a
linear telechelic network precursor. Telechelic diisocyanates were prepared in the undiluted state
from 2,4-tolylene diisocyanate, α,ω,dihydroxypoly(oxypropylenes) and different contents of the
monool component 2-(2-metoxyetoxy) ethanol. The network synthesis proceeded in a bulk.
Detailed network topology was calculated by the theory of branching processes. The equilibrium
swelling degree of prepared samples was related to the parameters, which are experimentally
accessible for a network arising from an end-linking process using the Flory-Rehner theory. The
experimental data for network modulus were compared with those arising from the "affine" model,
"phantom’ model" and the model of constrained junctions.
Numerical and Analytical Modelling of Elastic-Plastic Fracture Mechanics Parameters
Authors: Milović Lj. , Sedmak Aleksandar , Sedmak Stojan , Putić S. , Zrilić Misa
Published: March 2009

Structural integrity and service reliability depend on the fracture resistance of a material.
Cracks in the material are the locations of stress concentration, and elastic-plastic deformation can
occur causing the development of mixed-mode type of fracture ahead the crack tip. Crack behavior
in the elastic-plastic region is analyzed applying numerical and analytical simulation based on
fracture mechanics parameters, characterizing the response of the material at the crack tip.
Numerical and analytical results are compared with the corresponding experimental results obtained
in previously performed fracture mechanics tests with standard single-edge notch bending –
SEN(B) specimens. The comparison shows an acceptable level of agreement, enabling application
of the proposed numerical model of crack growth in the mixed-mode fracture analysis for structural
integrity assessment.
Properties of TiN Coatings Deposited on Nitrogen Ion Implanted Steel C1045
Authors: Peruško D. , Bibić N. , Petrović S. , Popović M. , Novaković M. , Radović I. , Milosavljević M.
Published: March 2009

The effects of nitrogen pre-implantation of AISI C1045 steel substrates on the properties
of deposited TiN coatings were investigated. Nitrogen ion implantations were performed at 40 keV,
to the fluences from 5x1016 – 5x1017 ions/cm2. On so prepared substrates we deposited 1.3 μm thick
TiN layers by reactive sputtering. Structural characterizations of the samples were performed by
grazing incidence X-ray diffraction analysis (GXRD), standard X-ray diffraction analysis (XRD),
and scanning electron microscopy (SEM). Microhardness was measured by Vicker’s method. The
obtained results indicate the formation of iron-nitrides in the near surface region of the substrates,
more pronounced for higher implanted fluences. The structure of the deposited TiN coatings shows
a strong dependence on the pre-implantation of the substrates, which is attributed to the changed
local structure at the surface. Ion implantation and deposition of hard TiN coatings induce an
increase of the microhardness of this low performance steel of more than eight times.
Negative Refraction and Left-Handedness in 2D Archimedean Lattice Photonic Crystals
Authors: Gajić Rados , Meisels R. , Kuchar F. , Jovanović Dj. , Hingerl K.
Published: March 2009

Study of the refraction and rightness effects in 2D Archimedean lattice photonic crystals
is presented. A special emphasis is placed on possibilities of negative refraction and left-handedness
in these structures. Besides the familiar Archimedean lattices like square, triangular, honeycomb
and Kagome ones, we consider also, the less known 32,4,3,4 (ladybug) and 3,4,6,4 (honeycombring)
structures. This involves the calculations of band structures, band-gap maps, equifrequency
contours, FDTD simulations of electromagnetic propagation through the structures, as well as an
experimental verification of negative refraction at microwaves.
New Diode Designs Compatible with Vertical 4H-SiC JFET Fabrication Process
Authors: Brosselard Pierre , Tournier Dominique , Vellvehi Miquel , Montserrat Josep , Godignon Philippe , Millan José
Published: March 2009

In this paper, we propose new designs of Schottky, JBS and PiN diodes, which process
technology is compatible with that of vertical power SiC JFETs. Three novel diode designs are
proposed and we report their electrical characteristics. The P+ buried layer implant of the JFET is
used for the PiN anode formation and for the P+ islands of the JBS. The Schottky diode differs from
a standard Schottky diode since buried rings below the Schottky contact region have been included
and the anode metal layer also contacts the buried P+ region at the diode periphery. With this last
approach, the resulting Schottky diodes show low leakage currents and surge current capability,
with a lower on-state voltage than the JBS.
High Quality Uniform SiC Epitaxy for Power Device Applications
Authors: Zhang Jie , Romano Esteban , Mazzola Janice , Sunkari Swapna G. , Hoff Carl , Sankin Igor , Mazzola Michael S.
Published: March 2009

In this paper we present highly uniform SiC epitaxy in a horizontal hot-wall CVD reactor
with wafer rotation. Epilayers with excellent thickness uniformity of better than 1% and doping
uniformity better than 5% are obtained on 3-in, 4° off-axis substrates. The same growth conditions
for uniform epitaxy also generate smooth surface morphology for the 4° epiwafers. Well controlled
doping for both n- and p-type epilayers is obtained. Abrupt interface transition between n- and pdoped
layers in a wide doping range is demonstrated. Tight process control for both thickness and
doping is evidenced by the data collected from the epi operations. The average deviation from target
is 2.5% for thickness and 6% for doping. PiN diodes fabricated on a standard 3-in, 4° epiwafer have
shown impressive performance. More than half of the 1 mm2 devices block 1 kV (2.3 MV/cm) with
a low leakage current of 1 μA.
Current Transport in Ti/Al/Ni/Au Ohmic Contacts to GaN and AlGaN
Authors: Iucolano Ferdinando , Roccaforte Fabrizio , Giannazzo Filippo , Alberti A. , Raineri Vito
Published: March 2009

In this work, the structural and electrical properties of Ti/Al/Ni/Au contacts on n-type
Gallium Nitride were studied. An ohmic behaviour was observed after annealing above 700°C. The
structural analysis showed the formation of an interfacial TiN layer and different phases in the
reacted layer (AlNi, AlAu4, Al2Au) upon annealing. The temperature dependence of the specific
contact resistance demonstrated that the current transport occurs through thermoionic field emission
in the contacts annealed at 600°C, and field emission after annealing at higher temperatures. By
fitting the data with theoretical models, a reduction of the Schottky barrier from 1.21eV after
annealing at 600°C to 0.81eV at 800°C was demonstrated, together with a strong increase of the
carrier concentration at the interface. The reduction of the contact resistance upon annealing was
discussed by correlating the structural and electrical characteristics of the contacts.
Influence of Micropipe and Domain Boundary in SiC Substrate on the DC Characteristics of AlGaN/GaN HFET
Authors: Sazawa Hiroyuki , Kato Tomohisa , Kojima Kazutoshi , Furuta K. , Hirata K. , Kosaki M. , Kinoshita M. , Mitani Takeshi , Nakashima Shinichi , Okumura Hajime
Published: March 2009

AlGaN/GaN HFETs were fabricated around micropipes and on a domain boundary
in a semi-insulating silicon carbide (SI-SiC) substrate and the DC characteristics of the
fabricated devices were measured. Devices around micropipe showed no pinch-off or large
gate leakage. The devices on the domain boundaries showed no degradation in the
performances, even though an X-ray topographic analysis indicated that crystal imperfections,
due to the defects, propagated to the GaN layer across the hetero interface. Based on these
results, we concluded that micropipe degrades the DC characteristics and that the domain
boundary does not affect the DC characteristics. From Raman analysis on the devices
around the micropipes, these degradations could be attributed to the free carriers introduced
into the GaN crystal by the micropipes.
High SiC Growth Rate Obtained by Vapour-Liquid-Solid Mechanism
Authors: Boutarek N. , Chaussende Didier , Madar Roland
Published: March 2009

The growth of 3C-SiC polycrystal and 6H-SiC homoepitaxial layers from Metal-Si
alloys is carried out as function of temperature and propane partial pressure. Based on the vapourliquid-
solid mechanism, we present a new configuration for the growth of SiC which could allow
first to simplify the liquid handling at high temperature and second to precisely control the crystal
growth front. 3C-SiC crystals exhibiting well-faceted morphology are obtained at 1100-1200°C
with outstanding deposition rates, varying from 1 to 1.5 mm/h in Ti-Si melt. At 1200-1300°C, thick
homoepitaxial 6H-SiC layers were successfully obtained in Co-Si melts, with growth rates up to 200
,m/h. Details on the experiments will be given and the potentialities of such process for the growth
of bulk crystals will be discussed..
Improved Mesa Designs for the Growth of Thin 4H-SiC Homoepitaxial Cantilevers
Authors: Trunek Andrew J. , Neudeck Philip G. , Spry David J.
Published: March 2009

The lateral expansion of thin homoepitaxial cantilevers from mesas has been used to
produce areas of on-axis 4H-SiC completely free of dislocations. Cantilever expansion is influenced
by the geometric shape and crystallographic orientation of the pregrowth mesa. In order to form
larger areas of defect free silicon carbide (SiC), progressive coalescence must occur when adjoining
cantilevers merge. The progressive coalescence is largely dictated by the shape and orientation of
the pregrowth mesa. We report on refinements to the pregrowth mesa geometry and orientation that
allows rapid initiation of cantilever growth and promotes progressive coalescence of merging
cantilevers. These modifications to the pregrowth mesa geometry permit larger areas of defect free
4H-SiC to be realized.
In Situ Measurement of Nitrogen during Growth of 4H-SiC by CVD
Authors: VanMil Brenda L. , Lew Kok Keong , Myers-Ward Rachael L. , Holm Ronald T. , Gaskill D. Kurt , Eddy Charles R.
Published: March 2009

Real-time analysis of downstream nitrogen process-gas flows during 4H-SiC growth is
reported. A Hiden Analytical HPR-20 quadrupole mass-spectrometer (QMS) was used to measure
the process gas composition in the gas-stream of a hot-wall chemical vapor deposition (CVD)
reactor. Using the 28 amu peak, it was found that the nitrogen partial pressure measured by the
mass spectrometer directly correlates to the expected partial pressure of nitrogen in the process cell
based on input flows. Two staircase doping samples were grown to track doping variations. The
nitrogen mass flow was varied and corresponded to doping levels ranging from 1x1015 cm-3 to
8x1018 cm-3. Electron and nitrogen concentrations in the epilayers were measured by capacitancevoltage
(CV) profiling and secondary ion mass spectrometry (SIMS), respectively. These efforts
show real-time QMS monitoring is effective during growth for determining relative changes in
nitrogen concentration in the gas flow, and thus, the level of nitrogen incorporation into the growing
layer.
Growth and Characterization of 13C Enriched 4H-SiC for Fundamental Materials Studies
Authors: Jang Yeon Suk , Sakwe Sakwe Aloysius , Wellmann Peter J. , Juillaguet Sandrine , Peyre Hervé , Camassel Jean , Steeds John W.
Published: March 2009

We have carried out the growth and basic characterization of isotopically enriched 4HSi
13C crystals. In recent years the growth of 13C enriched 6H-SiC has been performed in order to
carry out fundamental materials studies (e.g. determination of phonon energies, fundamental
bandgap shift, carbon interstitial defect study, analysis of the physical vapor transport (PVT) growth
process). For electronic device applications, however, the 4H-SiC polytype is the favored material,
because it offers greater electron mobility. In this paper we present the growth of 4H-Si13C single
crystals with up to 60% of 13C concentration. From a physical point of view we present first results
on phonons as well as the fundamental bandgap energy shift due to 13C incorporation into the SiC
lattice.
Progress in Cold-Wall Epitaxy for 4H-SiC High-Power Devices
Authors: Rowland L.B. , Dunne Greg , Fronheiser Jody , Soloviev Stanislav I.
Published: March 2009

Cold-wall vapor phase epitaxy was utilized to grow uniform 4H-SiC layers with abrupt
doping interfaces on 4o off-axis substrates. Concentrations of Al were reduced roughly 200x after
0.1 μm of epitaxy after trimethylaluminum flow was stopped. Thickness uniformity of cold-wall
epitaxy across 3” wafers was as good as 3.2%. Minority carrier diffusion lengths of 27 μm-thick
4H-SiC epitaxy grown in a cold-wall design were as high as 58 μm.
Scaling of Chlorosilane SiC CVD to Multi-Wafer Epitaxy System
Authors: Wan Jian Wei , Loboda Mark J. , MacMillan Mike F. , Chung Gil Yong , Carlson E.P. , Torres V.M.
Published: March 2009

A SiC epitaxy process based on chlorosilane/propane chemistry has been successfully transferred
from a single-wafer R&D system to a multi-wafer CVD reactor. The optimized process results in
very smooth epi surface (RMS~0.24nm) and minimum surface pits (less than 0.5/cm2). Both n-type
and p-type doping in a wide range are demonstrated using nitrogen and aluminum, respectively. The
high performance benchmarks for thickness uniformity (intra-wafer variation <1% and inter-wafer
variation <1%) and doping uniformity (intra-wafer variation <6% and inter-wafer variation <3%)
are achieved on 5 x 3-inch wafers. The carrier lifetime in these epilayers measured by μ-PCD is
over 5 μs, the longest value reported so far for SiC epitaxial wafers.
Selective Epitaxial Growth of 4H-SiC with SiO2 Mask by Low-Temperature Halo-Carbon Homoepitaxial Method
Authors: Krishnan Bharat , Das Hrishikesh , Lin Huang De , Koshka Yaroslav
Published: March 2009

Previously reported CVD epitaxial growth of 4H-SiC at temperatures down to and below
13000C using CH3Cl precursor offered a promise of new device applications that could benefit from
lower-temperature growth process. In this work, selective epitaxial growth (SEG) of 4H-SiC mesas
using conventional SiO2 low temperature mask is reported. Virtually no nucleation on the mask
could be observed after SEG at 13000C. The mask could be easily removed after the growth, with
no degradation of the surface of SiC substrate under the mask. For the growth conditions that
normally resulted in growth rate of 2 /m/hr and defect-free epilayer morphology during regular
full-wafer (non-SEG) epitaxy, the epilayer morphology during SEG was significantly degraded by
the appearance of oriented triangular defects, while the growth rate increased more than three times
in comparison to the blanket epitaxial growth due to the loading effect. The growth at optimized
growth conditions and lower growth rate resulted in significant reduction of the surface defects,
making this approach promising for obtaining device-quality mesas. The crystal quality of the
mesas, defects at the mesa walls, formation of facets during SEG, and other effects are reported.
Carbonization of Porous Silicon for 3C-SiC Growth
Authors: Vasin A.V. , Ishikawa Yukari , Shibata Noriyoshi , Salonen Jarno , Lehto Vesa Pekka
Published: March 2009

In the present work, the carbonization of porous silicon for the subsequent 3C-SiC
growth has been systematically studied. The effect of temperature and acetylene flow-rate on the
chemical state of the surface and structure relaxation was studied. It was found that the porous
nano-crystalline morphology is unstable and tends to recrystallize in temperature range typical of
3C-SiC growth on Si (10000C-13000C). The carbonization impedes recrystallization at 10000C, but
at 13000C the full recrystallization takes place. Pyrolytic amorphous graphite-like carbon was found
on porous silicon carbonized at temperature and with acetylene flow-rate above critical values.
Carbonization Study of Different Silicon Orientations
Authors: Severino Andrea , Bongiorno Corrado , Leone Stefano , Mauceri Marco , Pistone Giuseppe , Condorelli Giuseppe , Abbondanza Giuseppe , Portuese F. , Foti Gaetano , La Via Francesco
Published: March 2009

3C-SiC/Si heteroepitaxy is hampered by large mismatches in lattice parameters (19.7%)
and thermal expansion coefficient (8%) leading to 3C-SiC films containing high defects density. To
reduce the presence of defects, a multi-step growth process in a CVD reactor is used. The aim of the
work is to study the effect of carbonization on differently oriented Si surfaces, experiencing a
200°C-wide temperature range in a CVD reactor, to improve the crystalline quality. TEM analysis
are carried out to evaluate thickness, crystal orientations and defects of carbonized layers with
respect to the time-dependence of the process and to the different orientations of the Si substrate. It
will be shown that process-related defects are strictly correlated to the substrate orientation either
for size, density, occupied area, shape or thickness. Uniform, flat and crystalline thin SiC films are
obtained with a low defect density.
Hetero-Epitaxial Growth of 3C-SiC on Si (111) by Plasma Assisted CVD
Authors: Shimizu Hideki , Kato Akira
Published: March 2009

The effects of C3H8 on the microstructures of the films on Si (111) have been
investigated by changing the concentration of C3H8 from 0.5% to 5%. 3C-SiC film on Si (111)
grown at the C3H8 concentration of 1% with relatively high flow rate of SiH4 (30 sccm) is single
crystal and free from the contamination of W2C. By comparing the deposition rates of the films on
Si (111) and Si (100) at different concentrations of C3H8, SiC growth on Si (111) is much more
dependent on C3H8 concentration than that on Si (100). From these results it is suggested that SiC
growth on Si (111) is strongly influenced by hydrogen radicals generated from C3H8 decomposition
by the plasma and forms single crystal easier than on Si(100). It is expected that 3C-SiC epitaxial
growth on Si (111) has higher deposition rate and lower substrate temperature than on Si (100). The
crystallinity has been investigated by a reflection electron diffraction (RED) and a X-ray diffraction
(XRD). The thickness and the surface roughness of the films were investigated by an ellipsometric
measurement.
How to Grow 3C-SiC Single Domain on α-SiC(0001) by Vapor-Liquid-Solid Mechanism
Authors: Soueidan Maher , Kim-Hak Olivier , Ferro Gabriel , Chaudouët Patrick , Chaussende Didier , Nsouli Bilal , Monteil Yves
Published: March 2009

We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS)
mechanism on various α-SiC substrates, namely on- and off-axis for both 4H and 6H-SiC(0001), Si
and C faces. The Si-Ge melts, which Si content was varied from 25 to 50 at%, were fed by 3 sccm
of propane. The growth temperature was varied from 1200 to 1600°C. It was found that singledomain
3C-SiC layers can be obtained on 6H-SiC off and on-axis and 4H-SiC on-axis, while the
other types of substrate gave twinned 3C-SiC material. As a general rule, one has to increase
temperature when decreasing the Si content of the melt in order to avoid DPB formation. It was also
found that twinned 3C-SiC layers form at low temperature while homoepitaxy is achieved at high
temperature.
Increased Growth Rates of 3C-SiC on Si (100) Substrates via HCl Growth Additive
Authors: Reyes M. , Shishkin Y. , Harvey S. , Saddow Stephen E.
Published: March 2009

Growth rates from 10 to 38 μm/h of single crystal 3C-SiC on planar Si (001) substrates
have been obtained in a low-pressure horizontal hot-wall CVD reactor. The propane-silanehydrogen
gas chemistry system with HCl added as a growth additive, which allows an increased
amount of silane to be introduced into the reactor during growth, was used. The 3C-SiC film growth
rate versus silane mole fraction was found to be a linear function in the range from 0.43x10-3 to
1.50x10-3. Nomarski optical microscopy, scanning electron microscopy, Fourier transform infrared
spectroscopy, atomic force microscopy and X-ray diffraction were used to characterize the
deposited layers. The X-ray rocking curve taken on the (002) diffraction plane of a 12 μm thick 3CSiC
(001) layer displayed a FWHM of 360 arcsec, which indicates the films are mono-crystalline.
Mechanism of Orientation Selection for the Growth Of (111) Twin Boundary Free 3C-SiC Single Crystals on Hexagonal Basis
Authors: Latu-Romain Laurence , Chaussende Didier , Rapenne L. , Pons Michel , Madar Roland
Published: March 2009

The development of 3C-SiC crystals from <0001> oriented hexagonal seed has always
suffered from the systematic twinning which appears during the nucleation step of the layer. Using
the continuous feed – Physical Vapour Transport (CF-PVT) growth process, we succeeded in
growing single domain 3C-SiC crystals. To explain that, we propose in this work, a model based on
the interaction between the lateral expansion anisotropy of 3C-SiC nuclei and the step flow growth
front. Depending on the step edges direction, we can obtain one 3C orientation developing
simultaneously with the vanishing of the other one. This model is confirmed by cross sectional
HRTEM observation of the α-β interface.
Growth Induced Stacking Fault Formation in 4H-SiC
Authors: Siche D. , Albrecht M. , Rost H. J. , Sendzik Andreas
Published: March 2009

C-plane substrates with off-orientation to <1120 > may stabilize the grown polytype, but
the stacking fault density (SFD) increases from zero in the on-axis sample to 4500 cm-1 (7.7° off).
The SF form preferentially at the seed-crystal-interface by a kinetically induced rearrangement of
surface ad-atoms on m-facets. Most SF start in bundles with an average distance of 100 .m, which
are subdivided in smaller bundles with 8 .m distance. They start preferentially from the upper
corner of the vertical non-polar plane of bunched steps, which may be composed of small pyramids
with m-facet surfaces. The dislocation density could decrease with increasing SFD by a pinning
mechanism.
Dislocation in 4H n+ SiC Substrates and their Relationship with Epilayer Defects
Authors: Wu Ping , Emorhokpor Ejiro , Yoganathan Murugesu , Kerr Thomas , Zhang Jie , Romano Esteban , Zwieback Ilya
Published: March 2009

Several morphological defects in 4H SiC epitaxial wafers, including Comets and
Triangles, may significantly impact on the yield and reliability of SiC devices. The formation of
these epilayer defects is closely related to the substrate quality. This paper focuses on the study of
the substrate quality and its relationship with defects in the epilayers. The crystalline quality of 4H
n+ substrates has been characterized by x-ray diffraction, and the distribution of dislocations has
been determined using etching in molten KOH. The relationship between Comet and Triangle
epilayer defects and the dislocations has been established. A 10-fold reduction in the overall
dislocation density in the 4H SiC substrates was achieved through technological improvements. The
improvement was validated by the reduction in the number of the epilayer defects.
Hydrogen Effect on SiC Single Crystal Prepared by the Physical Vapor Transport Method
Authors: Kim Jung Gon , An Joon Ho , Seo Jung Doo , Kim Jung Kyu , Kyun Myung Ok , Lee Won Jae , Kim Il Soo , Shin Byoung Chul , Ku Kap Ryeol
Published: March 2009

We investigated the effects of hydrogen addition to the growth process of SiC single crystal
using sublimation physical vapor transport (PVT) techniques. Hydrogen was periodically added to an
inert gas for the growth ambient during the SiC bulk growth. Grown 2”-SiC single crystals were
proven to be the polytype of 6H-SiC and carrier concentration levels of about 1017/cm3 was
determined from Hall measurements. As compared to the characteristics of SiC crystal grown without
using hydrogen addition, the SiC crystal grown with periodically modulated hydrogen addition
definitely exhibited lower carrier concentration and lower micropipe density as well as reduced
growth rate.
Nondestructive Analysis of Stacking Faults in 4H-SiC Bulk Wafers by Room-Temperature Photoluminescence Mapping under Deep UV Excitation
Authors: Hoshino Norihiro , Tajima Michio , Hayashi Toshihiko , Nishiguchi Taro , Kinoshita Hiroyuki , Shiomi Hiromu
Published: March 2009

The advantage of room-temperature photoluminescence (PL) mapping was demonstrated
for nondestructive detection of stacking faults (SFs) in off-oriented 4H-SiC epitaxial and bulk wafers.
In mapping of the SF-related emission at 2.9 eV on the wafers, the SFs in the surface region appeared
as a bar-shaped pattern with the long side perpendicular to the off-cut direction. The use of 266 nm
light excitation is essential to detect the SF pattern in the bulk wafers because of its shallow
penetration depth. The dark lines crossing the bar-shaped patterns in the epitaxial wafers are
ascribable to the basal plane dislocation located close to the SF-planes.