bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Stress Behavior and Deformation Characteristics of Ti-22Al-25Nb Alloys at Elevated Temperature
Authors: Liang Xiao Bo , Li Shi Qiong , Cheng Yun Jun , Zhang Jian Wei
Published: March 2009

The characteristics of deformation of an orthorhombic phase based alloy, Ti-22Al-25Nb (at%), have been studied by hot compression tests in the temperature range of 940-1150°C with the strain rates of 0.01s-1 and 0.1s-1. A flow curves typically controlled by dynamic recovery were observed in the temperature range of 1090-1150 °C for the strain rate of 0.01s-1 , while discontinuous yield phenomena was found for the strain rate of 0.1s-1. The dynamic recovery can be identified by the microstructure characteristics of the deformation specimens. At 1060°C, the
temperature of beta transus, the flow curves and microstructure exhibited the same deformation charateristics as that above the beta transus. At the subtransus temperature, a long period of flow softening followed by the steady-state flow can be observed. During the hot deformation, the hard phases α2 and O elongated, subboundary produced followed by cusp formation in the elongated α2 and O phases, the equiaxed morphology phases occurred by B2 phase penetrating along the subboundaries. The softening mechanism was discussed.
Investigation on the Microstructure and High Temperature Mechanical Properties of Al3Ti-Mo3Al Two-Phase Alloys
Authors: Miura Seiji , Shimamura Hiroyuki , Ohkubo Kenji , Mohri Tetsuo
Published: March 2009

Investigation on the crystallographic orientation relationships among D022-Al3Ti,
A15-Mo3Al and high temperature bcc phase consisting of an Al-Mo-Ti ternary alloy with an equi-axed two-phase structure was conducted by FESEM/EBSD analysis. The grains of intermetallic phases have certain crystallographic orientations each other, while the crystallographic orientation distributions become random after a high temperature deformation. This strongly suggests the grain boundary sliding and grain rotating govern the high temperature deformation, which is consistent with the fact that the strain-rate sensitivity m is 0.3 or higher during a steady-state compressive deformation.
Formation and Control of the Acicular Ferrite in Low Carbon Microalloying Steel
Authors: Shang Cheng Jia , Zhao Y.T. , Wang Xue Min , Hu L.J. , Yang Shan Wu , He Xin Lai
Published: March 2009

The influence of processing parameters on the acicular ferrite formation for the low
carbon microalloying steel was studied. The results showed that the fraction of acicular ferrite could be controlled by the cooling process. The acicular ferrite/ bainitic ferrite dual phase structure can be formed. The multi-phase microstructure is ultra fine. The hardness is sensitively affected by the acicular ferrite fraction.
Effects of the Finish Rolling Temperature on Mechanical Properties and Microstructure Evolution of Line Pipe Steel
Authors: Kim Kee Hyun , Hwang Nong Moon , Lee Byeong Joo , Yoon Jong Kyu
Published: March 2009

Mechanical properties of line pipe steels used in the deep sea or in the severe cold
climate depend on alloying elements and manufacturing processes and many efforts have been made to enhance the properties of the line pipe steels. In this study, for systematic approaches to the process design of line pipe steels, its phase diagram was calculated using a Thermo-CalcTM program. The calculations indicated that A3 is around 840oC. Setting the FRT(Finish Rolling Temperature) above A3 appears to be critical to the increase of strength and toughness of line pipe steels by increasing the amounts of acicular ferrite and at the same time by decreasing the
precipitation of proeutectoid ferrite. In the case of the FRT below A3, relatively large amounts of proeutectoid ferrite are precipitated from the matrix with the carbon contents of the austenite phase around ferrite being enriched.
Hot Deformation Behavior of SiCw/AZ91 Magnesium Matrix Composite in Compression
Authors: Li S.B. , Zheng Ming Yi , Gan Wei Min , Wu Kun
Published: March 2009

The compressive behavior of squeeze cast SiCw/AZ91 composite in the temperature range of 423-723K and in the strain rate range of 0.001-0.25 s-1 was investigated. The compressive true stress-true strain curves were measured and hot deformation microstructures were observed. The strain rate sensitivity exponent (m) of the SiCw/AZ91 composite increased with the increasing of temperature. The activation energy of deformation varied over the range of test conditions
examined indicated that the deformation was controlled by more than one mechanism. The reorientation of SiC whiskers in the composite was observed during compression. During the compression, dynamic recovery and dynamic recrystallization occurred in the SiCw/AZ91 composite.
Laser Cladding Ni-Base Composite Coating on Titanium Alloy with Pre-Placed B4C+NiCoCrAlY
Authors: Meng Qing Wu , Geng Lin , Zheng Zhen Zhu
Published: March 2009

Using a CO2 laser, a process of cladding Ni-base composite coating on Ti6Al4V with
pre-placed B4C and NiCoCrAlY was studied. A good metallurgical bonding coating without cracks and pores was obtained in reasonable ratios of components and low energy laser process. Morphology and microstructure of the coating were analyzed with OM, XRD, SEM and EDS. It is certain that there was a reaction between B4C and Ti during in-situ producing TiB2 and TiC. The Ni-base composite coating is strengthened with TiB2 and TiC reinforcement phases. Vickers Hardness Tester
measured that the average microhardness of the coating is HV1200 and it is 3.5 times of the Ti6Al4V substrate. The high hard coating containing several reinforcement phases greatly enhances wear resistance of titanium alloy.
Influence of Toughening Method on Microstructures and Mechanical Properties of Alumina-Matrix Composites
Authors: Zhou Yang , Zhai Hong Xiang , Huang Zhen Ying , Ai Ming Xing , Zhang Zhi Li , Li Shi Bo , Li Cui Wei
Published: March 2009

Various toughening methods, i.e. partially stabilized zirconia transformation toughening, transformation- SiC whisker reinforcing and transformation-SiC particle reinforcing were used to improve the mechanical properties of alumina ceramic. Influence of various toughening methods on microstructure and mechanical properties of the alumina-matrix composites were studied. On the basis of transformation toughening, by which the strength and toughness of Al2O3 ceramic improved simultaneously, the addition of SiC whisker substantially enhanced the toughness, whereas the addition of SiC particle increased both toughness and strength to a certain degree. Mechanical properties of the testing materials were closely related with their morphologies of fracture surfaces. Toughening mechanisms of the composites were also studied. In the transformation-whisker
reinforced composite or the transformation-particle reinforced composite, the two toughening methods affected with each other and produced a cooperative toughening effect.
Proposal of Pseudo Crack Model for the Un-Cracking Delamination Behavior of Fiber Reinforced Metal Laminates
Authors: Kim Cheol Woong , Song Sam Hong , Oh Dong Joon
Published: March 2009

If Fiber Reinforced Metal Laminates (FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of Al alloy layers and that it depended on the crack growth. When FRMLs with circular holes was un-cracked but was delaminated, it was impossible to analyze them by conventional fracture parameters expressed as the function of cracks. Therefore, a new analytical model called Pseudo Crack Model (PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack consumption rate (Ccrack) and the delamination consumption rate (Cdel) was discussed and it was also known that the effect of the Ccrack was larger than that of the Cdel.
Elevated Sliding Wear Characterization of Al/SiCp Composites
Authors: Kim S.W. , Park J.S. , Kim K.K. , Kim Dong Ki , Woo Kee Do
Published: March 2009

This study was to aimed to investigate on the sliding wear behaviors at both ambient and elevated temperatures in Al/SiCp composites fabricated by the newly developed duplex process. Wear test using wear tester of pin-on-disc type was carried out under the conditions of load 100N , velocity 0.64m/s, distance 4000m. The sliding wear behaviors under the conditions of ambient temperature, 200°C and 200°C-Ar gas and microstructures were studied using OM and SEM. The results obtained from this study are as follows;
Wear amount decreased with the decrease in particle size. The wear resistance at 200°C-Ar on composites was greater than those at 200°C and room temperature in the as-composites.
Mechanical and Damping Properties of Squeeze Cast Hybrid Mg Matrix Composites
Authors: Choi Il Dong , Park Ik Min , Cho Kyung Mok , Park Yong Ho
Published: March 2009

Mg alloy is the lightest material of structural materials and is noticed for lightweight automotive parts because of excellent castability and damping capacity compared with Al alloy. But Mg alloy has poor corrosion resistance and high temperature creep properties. In this study, Mg matrix composites were fabricated by squeeze casting method to improve high temperature creep properties and damping capacity. The creep properties and damping capacity of hybrid Mg composites reinforced with Alborex(Aluminum borate whisker: 9(Al2O3)•2(B2O3)), graphite particle, and carbon fiber were improved in comparison with Mg alloy. Hybrid Mg composites reinforced with carbon fiber and Alborex were better than those reinforced with graphite particle and Alborex in mechanical properties, creep characteristics, and damping capacity, etc.
Effects of Core Material on Extrudability of Cu/Pure Al, Cu/Al3003 Clad Composites by Indirect Extrusion
Authors: Jung Taek Kyun , Kwon Hyouk Chon , Lim Sung Chul , Lee Young Sup , Kim Mok Soon
Published: March 2009

We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/Al3003 was 38, which was larger than 21.39 of Cu/Al(Cu/pure Al). It was because that the difference of flow
stress between copper as the sheath material and Al3003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/Al3003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/Al3003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/Al3003 was higher than that of Cu/Al under the same extrusion conditions.
Oxidation Behavior of BN/(Al-Mg) Metal Matrix Composites
Authors: Woo W.S. , Jung Woo Gwang , Lee Dong Bok
Published: March 2009

Metal matrix composites (MMCs) that consisted of Al-Mg matrix reinforced with initially added BN particles were fabricated using the pressureless infiltration technique, and their oxidation behavior was investigated at 500 and 550oC in air. Initially added BN particles were partly consumed to make AlN, as another reinforcing particles. Another reaction product was MgAlB2 dispersoids. Despite of the presence of these reinforcing particles, the oxidation resistance was not good owing to the formation of MgO-rich scale due to the preferential oxidation of Mg in the MMCs. Detailed microstructures and oxidation mechanism of the prepared MMCs are proposed.
An Experimental Study on the Inhomogeneities of Aluminum Foams Measuring the Thermal Conductivity by Using the Transient Plane Source Method
Authors: Reglero J.A. , Rodríguez-Pérez Miguel A. , Lehmhus D. , Windmann M. , de Saja Jose A. , Fernández A.
Published: March 2009

A collection of AlSi7 closed cell foams were fabricated following the powder metallurgical route [1,2], reaching densities between 540 Kg/m3 and 1350 Kg/m3. Thermal conductivity of the samples was determined using the Transient Plane Source technique (TPS) [3,4], and influence of density was estimated. Several models were tested, and the correlation between experimental data and theoretical results was evaluated. Finally, measurements in different directions were performed, revealing the use of the TPS technique as a non-destructive tool to investigate the existence of in-homogeneities derived from the foaming process.
Undercooling of Eutectic Sn-57wt%Bi Alloy
Authors: de Castro Walman Benício
Published: March 2009

Rapid Solidification Processing (RSP), of metals and alloys, is establish by increasing of the undercooling applying high cooling rates (102 - 106 K/s) or by reduce nucleation sites using low cooling rates (1 K/s). Melt undercooling opens new solidification pathways for new nonequilibrium phases and unusual microstructures. Several techniques have been developed to reduce nucleation sites and produce increased undercooling in metals and alloys including the fluxing technique. The aim of this paper is to study the influence of the undercooling level on microstructures of eutectic Sn-57wt%Bi alloy by using the fluxing technique. A morphological change from eutectic to eutectic plus primary dendrites bSn was observed when the undercooling increase from 10 K to 19 K and a refinement of the primary dendrites bSn was observed when the undercooling increase from 19 K to 29 K. Increasing the undercooling led to a higher growth rate, hence morphological refinement occur.
Gamma and UV Radiation-Induced Color Centers in Optical Fibers
Authors: Girard Sylvain , Régnier E. , Boukenter A. , Ouerdane Y. , Meunier J.-P. , Hamdani D.
Published: March 2009

Radiation-induced losses and paramagnetic centers were investigated in phosphorusdoped and P-free multimode germanosilicate optical fibers after g-rays (~1 MeV) and ultraviolet (5 eV) exposures. After both types of irradiation, the same defects seem to be responsible of the fiber absorption in the spectral range 400 to 1650 nm. In particular, the P1 centers and the Phosphorus Oxygen Hole centers are created in both cases in the phosphorus-doped fibers and explain the high permanent radiation-induced attenuation levels observed in this fiber type. Luminescence and electron spin resonance measurements (77 K, ~9.38 GHz) on irradiated samples confirm that the GeE’, SiE’ and NBOHC defects are also generated in the different irradiated samples. From this study, it seems that the pertinence of a multimode fiber for nuclear space or civil applications could be estimated through low-cost ultraviolet measurements.
Termoluminescent Properties of High Sensitive ZrO2+PTFE for UV Radiation Dosimetry
Authors: Rivera Montalvo T. , Furetta C. , Azorín Nieto J. , Falcony Guajardo C. , García M. , Martínez Eduardo
Published: March 2009

This paper presents the preparation method, luminescent characteristics and the results of studying the thermoluminescence (TL) properties of zirconium oxide (ZrO2) exposed to 260 nm ultraviolet radiation. The glow curve of ZrO2+PTFE pellets exhibited one peak centered at 180°C about 30°C lower than that the commercially available aluminum oxide peak (Al2O3:C). TL response as a
function of spectral irradiance showed good linear in the range from 2.4 to 3000 µJ/cm2 of spectral irradiance. Experimental results of studying the thermoluminescent (TL) properties of ZrO2+PTFE exposed to ultraviolet radiation allow to propose zirconium oxide as an excellent candidate as ultraviolet radiation dosimeter.
Structure of Ti1-XTaxN Thin Films Prepared by DC-Magnetron Sputtering
Authors: Bourbia O. , Guerfi N. , Achour S. , Tabet Nouar , Mosser A.
Published: March 2009

X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) were used to investigate the effect of tantalum addition on the TiN thin films structure. Both the HRTEM and selected area electron diffraction have showed that the films possess a fine grained polycrystalline structure with an average grain size in the order of 10 nm. The chemical composition of the films was determined by the use of the Ti2p, N1s and Ta4f core level peaks. The analysis of Ta4f core level revealed the presence of Ta-N bond indicating that tantalum atoms can occupy the titanium sublattice sites. Moreover, the XPS spectra revealed the presence of Ta2O5 in the films.
Potential and Current Uses of Luminescence in Medical Diagnosis
Authors: Avramaov L. , Borisova E. , Townsend P.D. , Valberg L.A.
Published: March 2009

Biological luminescence stimulated by optical excitation results in signals which are characteristic of the host tissue. The spectrum of the emitted light, the intensity, and the excited state lifetimes are modified as the result of disease or by activation through addition of cell selective phosphors. There is an opportunity to identify diseased tissue both by the spectral signals from activators or, in some cases, by the differences of the natural luminescence responses. For practical reasons, defined by the sensitivity range of standard luminescence detectors, much of the current work has focussed on the short wavelength emissions driven by laser activation. However, the techniques are poised to undergo a dramatic expansion in scope with the advent of higher sensitivity photocathodes with high efficiency responses at long wavelengths. It is now possible to utilise a greater range of emission features with improved discrimination. Further, movement to longer wavelength excitation, and emission, open the way to probe deeper beneath the surface of tissue. The current overview will focus on recent examples from detection of cancer to tooth caries and indicate how the non-destructive luminescence probes can distinguish between tissue changes at an early stage of development.
Dependence of the Refractive Indices in LiNbO3:Cr Crystals Doped with HfO2
Authors: Cantelar E. , Torchia G.A. , Bermúdez Veronica , Jaque D. , Sanz-Gracía J.A. , Lifante G. , Han T.P.J. , Jaque F.
Published: March 2009

The dependence of the refractive indices, absorption edge and optical damage in congruent HfO2-doped LiNbO3 crystal are reported. A small amount of Cr3+ ions (0.1 mol%) was introduced in the doped crystals as optical probe. The experimental data indicates that the extraordinary and ordinary indices depend on the Hf4+ ions concentration showing a singularly for a dopant level of ~ 2.7 mol%. The dependence of the absorption edge also shows a transition region at this Hf4+concentration. The distortion of the transmitted light through samples doped with different concentrations of Hf4+ ions indicates that an inhibition of optical damages is achieved at above 3 mol% of dopant. A charge compensation mechanism is proposed to explain the role of the Hf4+ ions for the observed experimental result.
Preparation of Lead Iodide as Input Material for X-Ray Detectors
Authors: Matuchová M. , Prochazková Olga , Zdanský K. , Zavadil J. , Maixner J.
Published: March 2009

The aim of this work is to study the new method of direct synthesis of lead and iodine as the input material of PbI2. This method has not been studied for this material till now, and seems to be one of the new methods for preparation of the input material. The photoluminescence measurement and measurement of resistivity has been done and compared with the measurements done by precipitation and zone purification.
Determining the Tensile Strength of Glass Metals Using a Theoretical Method
Authors: Zsoldos Ibolya , Janik J.F. , Pellenyi L.
Published: March 2009

A computer algorithm based on a topological model has been created to determine the tensile strength of glass metals in a theoretical way.
Electromagnetic Wave Absorption Behavior of NiZn-Ferrite Prepared via Hydrothermal Method
Authors: Peng Cheng-Hsiung , Wang Hong-Wen , Kan Shih-Wei , Chen San-Yuan
Published: March 2009

Ni0.5Zn0.5Fe2O4 ferrite powders were synthesized by a hydrothermal method. The
nanoparticles of these materials were mixed with a thermal-plastic polyurethane (TPU)polymer in order to form a suitable composite for electromagnetic wave absorber in a frequency range from 2.0 to 15.0 GHz. The effect of particle size on the reflection loss was investigated by comparing nanosized and microsized powders. The reflection loss as a function of frequency ( f ), thickness of the absorber(d), the real and imaginary part of permittivity (ε’ /ε”) and the real and imaginary part of permeability (μ’/μ”) were obtained by calculation using the Bruggeman effective medium theory. The effect of Co2+, Cu2+, and Mg2+
on the reflection loss was also studied.
Frequency-Diffusion Characteristics of Silicic Acid Gels
Authors: Sukharev Yu.I. , Avdin V.V.
Published: March 2009

The discreteness of vibration frequencies of diffusion coefficients of rare - earth elements ions in the forming gel of silicon acid is considered. The existence of at least three vibration frequencies being more probable for the gel system in question is established. The agreement of these results with the experiments studying the behaviour of pacemakers in zirconium oxyhydrate gels is shown. This agreement and the frequency discreteness mentioned prove the early assumption [1]
that structuring of different gels proceeds through the process of formation and interaction of stable sites in a polymer structure of a discrete size (attractor). The system of attractors is of a fractal nature. The regularities established reflect the general nature of the gelation with any types of a gelforming polymer and ions diffusing in the micellar solution.
Field Emission Properties of Nanocrystalline and Amorphous Silicon Carbon Nitride Prepared from Microwave Plasma Chemical Vapor Deposition
Authors: Cheng Wen Juan , Jiang Jin Chun , Zhang Yang , Shen De Zhong , Zhu He Sun
Published: March 2009

Silicon carbon nitride (SiCN) films have been deposited on silicon wafers by microwave plasma chemical vapor deposition (MPCVD). Gas mixture of H2, CH4, N2, and SiH4 was used as precursors, in which the flow rate of N2 was changed. X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy were employed to characterize the composition and bonding structures, while field-emission scanning electron microscopy were used to investigate the microstructure of the films. With increasing the flow rate of N2 from 50 sccm to 300 sccm, the SiCN films changed from amorphous to nanocrystalline. Characteristic current-voltage measurements indicate a low turn-on field of 10.8 V/µm. Field emission current density of 4.5 mA/cm2 has been observed at 20 V/µm.
Site Preference Occupation of Ni and V in Fe3Al-Based Alloys
Authors: Fuks David , Dorfman Simon , Liubich Vlad , Kutsenko Larisa , Mehrer Helmut
Published: March 2009

Nonempirical study of the site preference occupation for Ni and V substituting in Fe3Al has been carried out in the framework of the coherent potential approximation. Obtained values of total energies show in a full agreement with experiments that Ni atoms in the equilibrium configuration occupy the iron sub-lattice for alloying with 5 at % of Ni in the Fe3Al-based alloy.
Calculations of alloys with the V-doped iron aluminide in the D03 phase show differences in bonding and site occupation preferences in comparison with Ni doping. V atoms occupy aluminum sublattice.
Solid Ionic Conductors Based on Salted Chitosan - Fatty Acid Plasticizer Systems
Authors: Yahya M.Z.A. , Puteh R. , Arof A.K.
Published: March 2009

Films of chitosan polymer doped with lithium acetate dihydrate (LiOAc.2H2O) and placticized with oleic acid (OA) and palmitic acid (PA) were prepared by the solution cast technique. The film containing 40.0 wt. % LiOAc and 10.0 wt. % of OA exhibit a room temperature conductivity of ~ 10-5 S cm-1 and the film containing 41.0 wt. % LiOAc and 7.7 wt. % of PA has conductivity ~ 10-6 S cm-1. The plot of ln(sT) versus 103/T for the highest conducting samples obey an Arrhenian relationship in the temperature range between 300 and 363 K implying that the conductivity is thermally assisted. FTIR spectroscopy and XRD techniques have been used for the complexation studies. The LiNiCoO2/chitosan-LiOAc-OA/MCMB electrochemical cell could be charged to a voltage of 4.2 V.
Effect of Ordering on the Elastic Parameters of Multicomponent Ni-Based Systems
Authors: Buršík Jiří
Published: March 2009

Ordering in Ni-based superalloys is the crucial process controlling the development of the characteristic two-phase microstructure and subsequently the mechanical properties. Disordered systems containing up to six alloying elements typical of advanced Ni-based superalloys were modelled in this work. Their ordering at elevated temperatures was simulated using a Monte Carlo approach with phenomenological Lennard-Jones pair potentials. Selected atomic configurations
differing in the degree of order were subject to further studies of elastic parameters. Hydrostatic deformation and uniaxial deformation along high symmetry directions of model crystals were simulated. Molecular dynamics was used to relax local atomic positions in deformed crystals. Changes of elastic parameters due to ordering in face centred cubic lattice are discussed.
Micromechanisms of Cleavage Fracture in HAZ of Low Carbon Steel Welds
Authors: Moya-Gutiérrez C. , Ocaña-Arizcorreta I. , Martín-Meizoso A.
Published: March 2009

The general objective of the present work is to study the brittle fracture of the coarsegrain heat-affected zone (CGHAZ) of a C-Mn steel. The target is to develop a probabilistic model for brittle prediction for the CGHAZ based on microstructural data. The model is based on local approach. In order to validate this model, fracture mechanical test specimens (3-point bend) have been tested at different low temperatures; temperature dependence of fracture toughness was
obtained. Post-morten examination of the fracture surfaces is used to gather information about the nucleation and arresting abilities of the different phases and interfaces respectively. Metallographic analysis has also been carried out for the HAZ.
Parameters Identification for GTN Model and Their Verification on 42CrMo4 Steel
Authors: Kozák Vladislav , Vlček Libor
Published: March 2009

The base of this paper is exact measurement of deformation and fracture material
characteristics in laboratory, evaluation of these parameters and their application in models of finite element analysis modelling the fracture behaviour of components with defects. The base of the work is dealing with ductile fracture of forget steel 42CrMo4. R-curve is modelled by 3D FEM using WARP3D and Abaqus. Crack extension is simulated in sense of element extinction algorithms. Determination of micro-mechanical parameters is based on combination of tensile tests and microscopic observation. Input parameters for the next computation and simulation were received on the base of image analysis, namely fN and fo. The possibility of transferring these parameters to another specimen is discussed.
Epitaxial Growth and Characterisation of Phosphorus Doped SiC Using TBP as Precursor
Authors: Henry Anne , Janzén Erik
Published: March 2009

The phosphorus incorporation into SiC epilayer is studied when varying the CVD process growth parameters and the results are compared with thermodynamical calculations. Photoluminescence spectra are also presented.
Measurements of Charge Collection Efficiency of p+/n Junction SiC Detectors
Authors: Moscatelli Francesco , Scorzoni Andrea , Poggi Antonella , Bruzzi Mara , Lagomarsino Stefano , Mersi Stefano , Sciortino Silvio , Lazar Mihai , Di Placido Annalisa , Nipoti Roberta
Published: March 2009

Silicon carbide is a promising wide-gap material because of its excellent electrical and physical properties, which are very relevant to technological applications. In particular, silicon carbide can represent a good alternative to Si in applications like the inner tracking detectors of particle physics experiments [1]. In this work p+/n SiC diodes realized on a medium doped (1×1015 cm -3), 40 µm thick epitaxial layer are exploited as detectors and measurements of their charge collection properties under beta particle radiation from Sr90 source are presented. Preliminary results till 900 V reverse voltage show a good collection efficiency of 1700 e- and a collection length (ratio between collected charges and generated e-h pairs/µm) equal to the estimated width of the depleted region.
Nickel-Vacancy Complexes in Diamond: An Ab-Initio Investigation
Authors: Assali Lucy V.C. , Larico R. , Machado W.V.M. , Justo João F.
Published: March 2009

The electronic and structural properties of nickel-vacancy complexes in diamond
were investigated by a total energy ab initio methodology. These results are discussed in the context of the electrically active centers, commonly found in synthetic diamond.
LPE of Silicon Carbide Using Diluted Si-Ge Flux
Authors: Filip Octavian , Epelbaum Boris M. , Bickermann Matthias , Winnacker Albrecht
Published: March 2009

Epitaxial growth of 4H-SiC has been carried out at temperatures up to 1650 oC on 4HSiC substrates dipped in strongly diluted Si-based solutions. Liquid Phase Epitaxy (LPE) in conditions of low supersaturation was shown to be an effective technique to overgrow micropipe defects (MPs) in SiC wafers prepared by the Physical Vapour Transport (PVT) technique. The aim of this work was to investigate the SiC growth morphology and the dependence of MP elimination
efficiency on Si-Ge flux composition. Macroscopically flat, single crystalline SiC layers of a thickness up to 10 µm were grown with a growth rate of about 0.5 µm/h. Stepped growth morphology was observed independent of the melt composition. Micropipes with the diameter below 5 µm were closed with an efficiency of about 80%. SEM investigations as well as inspection under reflected/transmitted light did not show any specific distortion of the growth morphology at the micropipe healing place.
Growth of 2 Inches 6H-SiC Single Crystals by Sublimation Method: The Comparison of α- and ß-SiC Powders
Authors: Seo Soo Hyung , Song Joon Suk , Oh Myung Hwan , Wang Yen Zen
Published: March 2009

We examined the formation of poly-crystals and polytypes under the point of view
applying various powder phases. 6H-SiC single crystal was easily grown by using the green (α-SiC) powder, while the poly-crystals were generated when β-SiC powder was utilized. The method of mixed β-SiC and carbon powder and of graphite pipe inserted in β-SiC powder were applied to overcome the generation of poly-crystals, respectively. It was confirmed that the occurrence of poly-crystals in 6H-SiC crystal was successfully suppressed by C-rich environment.
A Study of 6H-Seeded 4H-SiC Bulk Growth by PVT
Authors: Tupitsyn Eugene Y. , Arjunan Arul , Bondokov Robert T. , Kennedy Robert M. , Sudarshan Tangali S.
Published: March 2009

4H-SiC crystals were grown using the seeded sublimation technique (modified
Lely technique) in the temperature range of 1950-2200°C. The nucleation of 4H-SiC on 6HSiC has been optimized and 4H-SiC crystals of 1cm thickness were grown using 6H-SiC seeds. a-face and c-face wafers obtained from the grown boules were characterized by KOH etching, X-ray diffraction, and Raman scattering studies. Complete polytypic homogeneity of 4H SiC was obtained during growth and it was found that the 6H to 4H transition occurs in three ways: 1) without a transition layer, 2) with thick 6H-SiC layer growth, and 3) with traces of 3C SiC inclusions. The crown regions of the grown crystals exhibit an X-ray
rocking curve width of 21 arcsecs.
Formation of Ferromagnetic SiC:Mn Phases
Authors: Syväjärvi Mikael , Nasi L. , Yazdi Gholam Reza , Salviati Giancarlo , Izadifard M. , Buyanova I.A. , Chen W.M. , Yakimova Rositza
Published: March 2009

Ferromagnetic phases in as-grown SiC have been studied. An interpretation about
the formation based on details of the phase appearance in the layers from optical microscopy, AFM, and TEM investigations is related to the growth. Some phases were found to have a nucleation at the edge of the phase and detailed TEM investigations show that the phases have an increased grain density at the edge while the main part of the phase is monocrystalline.
X-Ray Diffraction Analysis of Epigrowth on Porous 4H-SiC Substrates
Authors: Shulpina I.L. , Savkina N.S. , Shuman V.B. , Ratnikov V.V. , Syväjärvi Mikael , Yakimova Rositza
Published: March 2009

The methods of X-ray topography and diffractometry have been applied to characterize the structure of epilayers grown on porous layers. Two geometrical configurations of defects determined to be stacking faults (SF) were revealed: i) with the images of triangular shape with the edge size 560 µm along the <10-10> directions; ii) linear shape along the [11-20] direction. The sources of SFs are located within the epilayer and start from the epilayer / porous layer interface.
We propose that the source of SFs is connected with graphitization of porous layer at the temperature of epitaxy.
Development of a KOH Defect Etching Furnace with Absolute In-Situ Temperature Measurement Capability
Authors: Sakwe Sakwe Aloysius , Herro Z.G. , Wellmann Peter J.
Published: March 2009

Etching temperature and time are important parameters in the etching of SiC single crystals in molten KOH for defect studies. However, comparison of results of different research groups is difficult because of the way temperature measurements are being carried out. Until now the temperature of the melt has been measured indirectly with a temperature sensor placed outside the melt on the outer walls of the crucible of the etching furnace, resulting in varying etching conditions for varying
setup designs. In this paper we developed an etching furnace with the capability of measuring the absolute temperature in-situ directly in the KOH melt. A new thermoelement, resistant to hot molten KOH was developed. Temperature profile measurements of the molten KOH were carried out and a calibration curve of the furnace was obtained. Based on our temperature measurements, we found that
etching at 530 °C for 5 minutes was optimal for defect characterisation, both for defect statistics and for distinguishing between the etch pit morphologies. At 550 °C the etch pits become too large, overlap each other and the etching is no longer defect selective.
Structure of In-Grown Stacking Faults in the 4H-SiC Epitaxial Layers
Authors: Izumi Syunsuke , Tsuchida Hidekazu , Tawara Takeshi , Kamata Isaho , Izumi Kunikaza
Published: March 2009

We investigated the structure of the in-grown stacking faults (SFs) in the 4H-SiC
epilayers. The in-grown SFs exhibited the photoluminescence (PL) peaks representing phonon replicas with bandgap of 2.710 eV. The in-grown SFs were confirmed to be triangular-shaped by PL mapping and KOH etch pit observation. High-resolution TEM image showed that the in-grown SFs have an identical stacking sequence that differ from single or double Shockley SF. In addition, the density of the in-grown SF depended on growth conditions.
Investigation of Stacking Fault Formation in Hydrogen Bombarded 4H-SiC
Authors: Galeckas Augustinas , K.-Nielsen H. , Linnros Jan , Hallén Anders , Svensson Bengt Gunnar , Pirouz P.
Published: March 2009

The effects of hydrogen and proton irradiation on stacking fault formation in 4H-SiC are investigated by an optical pump-probe method of imaging spectroscopy. We report optically stimulated nucleation and expansion of stacking faults (SFs) in 0.6 keV 2H+ implanted n-/n+ and p+/n-/n+ structures. The activation enthalpy for recombination enhanced dislocation glide (REDG) in hydrogenated samples (~0.25 eV) is found to be similar to that in a virgin material. Our results
indicate that SFs mainly nucleate at the internal n-/n+ interface, beyond reach of hydrogen, thus justifying minor SF passivation effect. No REDG could be initiated optically in 2.5 MeV proton irradiated samples due to radiation defects providing alternative recombination channels to bypass the REDG mechanism. The radiation damage was verified by DLTS, revealing several new levels below EC in the range 0.4-0.80 eV, and by PL, showing the onset of D-center related luminescence
band and concurrent increase of the nonradiative recombination rate.
Study of Ion Induced Damage in 4H-SiC
Authors: Lo Giudice A. , Oliveira P. , Fizzotti F. , Manfredotti Claudio , Vittone E. , Bianco Stefano , Bertuccio Giuseppe , Casiraghi R. , Jaksic M.
Published: March 2009

The damage produced by 2 MeV protons on a 4H-SiC Schottky diode has been
investigated by monitoring the charge collection efficiency as the function of the ion fluence. A new algorithm based on the Shockley-Ramo-Gunn theorem has been developed to interpret the experimental results. The fitting procedure provides a parameter which is proportional to the average number of active electrical traps generated by a single ion, which can be profitably used to estimate the radiation hardness of the material.
Effect of Nitrogen Doping on the Formation of Planar Defects in 4H-SiC
Authors: Siche D. , Albrecht M. , Doerschel J. , Irmscher K. , Rost H. J. , Rossberg M. , Schulz D.
Published: March 2009

Planar defects have been found in nitrogen doped 2" 4H-SiC crystals grown on off-axis seeds. The doping level was 1×1019cm-3, which is below the critical one for the thermally activated cubic stacking fault formation in the 4H matrix. Planar defects in the doped region are nucleated on the whole seed surface outside the growth facet. They are coexisting 15R and 6H lamellas of unitcell height as revealed by means of luminescence and high resolution transmission electron microscopy. These inclusions are preferably formed at the rim of the growth facet, where polytype change occurs after switching off the nitrogen flow during growth.
Characterisation of 4H-SiC PiN Diodes by Micro-Raman Scattering and Photoemission
Authors: Thuaire Aurelie , Mermoux Michel , Crisci Alexandre , Camara Nicolas , Bano Edwige , Baillet Francis , Pernot Etienne
Published: March 2009

Structural defects in SiC crystals were investigated and 4H-SiC pin devices were
characterized by micro-Raman scattering and photoemission. With the experimental set-up presented, defects could be successfully detected in SiC crystals but stacking faults could not be detected with micro-Raman scattering, although they could be detected by photoemission. Residual stress could be evaluated in 4H-SiC devices, as well as the temperature increase associated with the devices powering. A good correlation was found between the characterization techniques used:
micro-Raman scattering and photoemission.
Materials Characterization and Modeling of SiC in Europe - From the Viewpoint of a Theorist
Authors: Deák Peter
Published: March 2009

SiC technology is presently still burdened by a number of problems caused by process- or operation-induced defects. Experimental materials characterization in cooperation with atomistic modeling can be helpful in designing strategies against them. In recent years, considerable theoretical effort has been devoted to clarify the dynamics of defect creation and the mechanisms of dopant (de)activation. The investigation of epitaxial growth and of thermal oxidation has also begun. Here
an attempt is made to survey the most important theoretical results of the past four years from Europe.
High-Temperature Stable Multi-Defect Clusters in Neutron Irradiated Silicon Carbide: Electron Paramagnetic Resonance Study
Authors: Baranov P.G. , Ilyin Ivan V. , Muzafarova Marina V. , Mokhov E.N. , Konnikov S.G.
Published: March 2009

The high-temperature stable defect complexes in 6H-SiC crystals created by heavy
neutron irradiation and following high-temperature annealing have been discovered by EPR. After annealing at 1500°C at least five new axially symmetric centers with the electron spin S = 1/2 and S = 1 were shown to arise in 6H-SiC crystals. The striking feature of all discovered centers is a strong hyperfine interaction with a great number (up to twelve) of equivalent host Si (C) atoms. Two
models, a four-vacancy complex VSi-3VC, and a split-interstitial antisite (C2)Si or a pair of two antisites (C2)Si-SiC are discussed. There is a good probability that some of new centers could be related to the famous D1 and DII centers. After annealing at 2000°C the dc1-dc4 centers disappeared and a new triplet center labeled as N-V in the form of a silicon vacancy and a nitrogen atom in neighboring carbon substitutional position has been observed. The parameters of this center are
similar to that for well-known N-V center in diamond.
Ab-Initio Study of Dopant Interstitials in 4H-SiC
Authors: Mattausch Alexander , Bockstedte M. , Pankratov Oleg
Published: March 2009

We investigated the the interstitial configurations of the p-type dopants boron and aluminum and the n-type dopants nitrogen and phosphorus in 4H-SiC by an ab initio method. In particular, the energetics of these defects provides information on the dopant migration mechanisms. The transferability of the earlier results on the boron migration in 3C-SiC to the hexogonal polytype 4H-SiC is verified. Our calculations suggest that for the aluminum migration a kick-out mechanism prevails, whereas nitrogen and phosphorus diffuse via an interstitialcy mechanism.
Numerical Analysis of Growth Condition on SiC-CVD in the Horizontal Hot-Wall Reactor
Authors: Nishizawa Shin Ichi , Pons Michel
Published: March 2009

Growth, etching, and doping features of SiC-CVD in a horizontal hot-wall reactor were numerically analyzed using the improved heterogeneous model. The improved model was able to explain the growth and etching features accurately. In addition, we propose the surface flux, surface carbon and silicon concentration, and its ratio as the universal parameter of the SiC-CVD process. Concerning doping features, the improved model showed that nitrogen and aluminum doping
incorporation could be explained by the site competition model, while taking into account the amount of surface silicon and surface carbon, respectively.
Characterization of Oxide Films on SiC Epitaxial (000-1) Faces by Angle-Resolved Photoemission Spectroscopy Measurements Using Synchrotron Radiation
Authors: Hijikata Yasuto , Yaguchi Hiroyuki , Yoshida Sadafumi , Takata Y. , Kobayashi K. , Shin S. , Nohira H. , Hattori Takeshi
Published: March 2009

Thermal oxide films on SiC epitaxial (000-1) C-faces have been characterized by
angle-resolved photoemission spectroscopy (AR-PES). The structure of wet oxide/SiC C-face interface was compared with that of dry oxide/SiC C-face, as well as that of dry oxide/SiC Si-face, in order to clarify why a MOS device of SiC C-face achieved good electrical properties. The improvement in electrical properties was confirmed by AR-PES measurements, evidencing differences in binding energy between SiC and the Si4+ components in Si2p and valence band region, and in binding energy between SiC and the CHx components in C1s. The reason for the improvement in electrical property of MOS devices by use of SiC C-face are discussed in terms of depth profiles of oxide films calculated from the AR-PES results.
Fabrication of Compact Ion Implanter for Silicon Carbide Devices
Authors: Mitani S. , Yamaguchi Seiji , Furukawa S. , Nakata T. , Horino Yuji , Ono Rudi , Hosokawa Y. , Miyamoto M. , Nishino Shigehiro
Published: March 2009

Most of the ion implanter is large scale, high acceleration voltage and expensive. For research and development, such a huge implanter is not required. Our motivation is to make desktop type ion implanter for SiC device. We report the fabrication of a compact 100 kV ion implanter. In order to miniaturize the equipment,
an ion source, an accelerator tube and a main chamber were vertically arranged. We implanted Argon (Ar) and Nitrogen (N) ions to 6H-SiC substrate and the implanted 6H-SiC substrates were characterized by Fourier Transform Infrared Spectrometer (FTIR), Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS). In this report, concept of desktop ion implanter, evaluation of implanted substrate and its device application are presented. In order to characterize capability, with using the newly made compact ion implanter, it was possible to make implantation on SiC to get amorphous layer suitable for deices.
Ion Beam Analysis and Computer Simulation of Damage Accumulation in Nitrogen Implanted 6H-SiC: Effects of Channeling
Authors: Zolnai Z. , Ster A. , Khánh N.Q. , Kótai E. , Posselt M. , Battistig Gábor , Lohner T. , Gyulai J.
Published: March 2009

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with
respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same
set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.
Experimental Evidence for an Electrically Neutral (N-Si)-Complex Formed during the Annealing Process of Si+-/N+-Co-Implanted 4H-SiC
Authors: Schmid Frank , Frank Thomas , Pensl Gerhard
Published: March 2009

Hall effect investigations taken on Si+-/N+-, C+-/N+- or Ne+-/N+-co-implanted 4H-SiC layers and deep level transient spectroscopy investigations taken on Si+-implanted 4H-SiC layers provide experimental evidence for an electrically neutral defect complex formed during the annealing process at temperatures between 1400°C and 1700°C. This defect complex consumes nitrogen donors and an intrinsic Si containing defect species (interstitial Si or Si-antisite) or Cvacancies. At our present knowledge, we favor an (NX-SiY)-complex.
n+/p Diodes Realized in SiC by Phosphorus Ion Implantation: Electrical Characterization as a Function of Temperature
Authors: Canino Mariaconcetta , Castaldini Antonio , Cavallini Anna , Moscatelli Francesco , Nipoti Roberta , Poggi Antonella
Published: March 2009

n+/p diodes have been realized by 300°C phosphorus ion implantation and subsequent annealing at 1300°C. An electrical characterization of the devices as well as a study of the defects introduced by the implantation process has been made. I-V measurements pointed out that the diodes maintain a good rectifying behavior up to 737K. DLTS analyses detected the presence of three traps, T2, T3 and T4, which are not due to the implantation process, and a high energy trap,
T5, that could be related to the surface states at the Ni/SiC interface.
Study of Carbon in Thermal Oxide Formed on 4H-SiC by XPS
Authors: Zhao P. , Rusli E. , Xia Jun Hai , Tan Chung Ming , Liu Y. , Tin Chin Che , Yoon S.F. , Zhu Weiguang , Ahn J.
Published: March 2009

In this work, we present results on the study of bonding and concentration of
carbon in 4H-SiC MOS structure by x-ray photoelectron spectroscopy (XPS). The XPS spectra were fitted by several Gaussian lineshape functions. It is found that the so-called carbon clusters (C-C bonds) appear at the interface of SiO2/SiC, but are not seen in the oxide bulk. However, there are still some SiOxCy and Si-C bonds inside the oxide and the integrated area ratio of SiOxCy/Si-C bonds increases when further away from the SiO2/SiC interface. These observations can be interpreted in terms of the dynamic oxidation process that transforms Si-C bonds into SiOxCy bonds, which are then further oxidized to form SiO2 bonds.