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Enumeration	Reference	Cover	Find
1.	Elahipanah, Hossein, et al. (author) 4.5-kV 20-mΩ. cm2 Implantation-Free 4H-SiC BJT with Trench Structures on the Junction Termination Extension 2015 In: Materials Science Forum. - : Trans Tech Publications Ltd. - 0255-5476 .- 1662-9752. - 9783038354789 ; 821, s. 838-841 Journal article (peer-reviewed)abstract A single-mask junction termination extension withtrench structures is formed to realize a 4.5 kV implantation-free 4H-SiCbipolar junction transistor (BJT). The trench structures are formed on the baselayer with dry etching using a single mask. The electric field distributionalong the structure is controlled by the number and dimensions of the trenches.The electric field is distributed by the trench structures and thus the electricfield crowding at the base and mesa edges is diminished. The design isoptimized in terms of the depth, width, spacing, and number of the trenches toachieve a breakdown voltage (VB) of 4.5 kV, which is 85% of thetheoretical value. Higher efficiency is obtainable with finer lithographicresolution leading to smaller pitch, and higher number and narrower trenches.The specific on-resistance (RON) of 20 mΩ.cm2 is measuredfor the small-area BJT with active area of 0.04 mm2. The BV-RONof the fabricated device is very close to the SiC limit and by far exceeds thebest SiC MOSFETs.
2.	Kargarrazi, Saleh, et al. (author) Design and characterization of 500°c schmitt trigger in 4H-SiC 2015 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783038354789 ; 821-823, s. 897-901 Journal article (peer-reviewed)abstract Two versions of Schmitt trigger, an emitter-coupled and an operational amplifier (opamp)-based, are implemented in 4H-SiC bipolar technology and tested up to 500 °C. The former benefits the simplicity, smaller footprint, and fewer number of devices, whereas the latter provides better promise for high temperature applications, thanks to its more stable temperature characteristics. In addition, the measurements in the range 25 °C - 500 °C, shows that the opamp-based version provides negative and positive slew rates of 4.8 V/μs and 8.3 V/μs, ~8 and ~3 times higher than that of the emitter-coupled version, which are 1.7 V/μs and 1 V/μs.
3.	Lim, Jang-Kwon, et al. (author) Temperature-dependent characteristics of 4H-SiC buried grid JBS diodes 2015 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 9783038354789 ; 821/823, s. 600-603 Conference paper (peer-reviewed)abstract 4H-SiC Schottky Barrier Diodes (SBD) have been developed using p-type buried grids (BGs) formed by Al implantation. In order to reduce on-state resistance and improve forward conduction, the doping concentration of the channel region between the buried grids was increased. The fabricated diodes were encapsulated with TO-254 packages and electrically evaluated. Experimental forward and reverse characteristics were measured in the temperature range from 25 °C to 250 °C. On a bare die level, the forward voltage drop was reduced from 5.36 V to 3.90 V at 20 A as the channel doping concentration was increased in order to reduce the channel resistance. After encapsulation in a TO-254 package, the forward voltage drop was decreased by approximately 10% due to a lower contact resistance. The on-state resistance of an identical device measured on the bare die and in the TO-254 package increased with increasing temperature due to the decreased electron mobility in the drift region resulting in higher resistance. The incremental contact resistances of the bare dies were larger than in the packaged devices. One key issue associated with conventional Junction Barrier Schottky (JBS) diodes is a high leakage current at high temperature operation over 200 °C. The developed Buried Grid JBS (BG JBS) diode has significantly reduced leakage current due to a better field shielding at the Schottky contact. The leakage current of the packaged BG JBS diodes is compared to conventional SBD and commercial JBS diodes.
4.	Salemi, Arash, et al. (author) Investigation of the breakdown voltage in high voltage 4H-SiC BJT with respect to oxide and interface charges 2015 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783038354789 ; 821-823, s. 834-837 Journal article (peer-reviewed)abstract Ion implantation in silicon carbide (SiC) induces defects during the process. Implantation free processing can eliminate these problems. The junction termination extension (JTE) can also be formed without ion implantation in SiC bipolar junction transistor (BJT) using a well-controlled etching into the epitaxial base layer. The fixed charges at the SiC/SiO2 interface modify the effective dose of the JTEs, leakage current, and breakdown voltage. In this paper the influence of fixed charges (positive and negative) and also interface trap density at the SiC/SiO2 interface on the breakdown voltage in 4.5 kV 4H-SiC non-ion implanted BJT have been simulated. SiO2 as a surface passivation layer including interface traps and fixed charges has been considered in the analysis. Simulation result shows that the fixed charges influence the breakdown voltage significantly more than the interface traps. It also shows that the positive fixed charges reduce the breakdown voltage more than the negative fixed charges. The combination of interface traps and fixed charges must be considered when optimizing the breakdown voltage.
5.	Toth-Pal, Zsolt, et al. (author) Investigation of pressure dependent thermal contact resistance between silver metallized SiC chip and DBC substrate 2015 In: European Conference on Silicon Carbide and Related Materials, ECSCRM 2014. - : Trans Tech Publications Inc.. - 9783038354789 ; 821-823, s. 452-455 Conference paper (peer-reviewed)abstract Thermal contact resistances between a silver metallized SiC chip and a direct bonded copper (DBC) substrate have been measured in a heat transfer experiment. A novel experimental method to separate thermal contact resistances in multilayer heat transfer path has been demonstrated. The experimental results have been compared both with analytical calculations and with 3D computational fluid dynamics (CFD) simulation results. A simplified CFD model of the experimental setup has been validated. The results show significant pressure dependence of the thermal contact resistance but also a pressure independent part.
6.	Zhang, Andy Zhenzhong, et al. (author) Planarization of epitaxial SiC trench structures by plasma ion etching 2015 In: Materials Science Forum. - 0255-5476 .- 1662-9752. - 9783038354789 ; 821-823, s. 549-552 Journal article (peer-reviewed)abstract In this work, we present a planarization concept for epitaxial SiC trench structures involving reactive ion etching (RIE) and inductive coupled plasma (ICP) dry etching. The general idea is to transfer the flat surface from spun-on BCB/photo-resist layers to deposited silicon dioxide and finally to bulk SiC by applying process conditions with the same etch rate for the different materials. In this way several microns of unwanted material can be removed and planar SiC surfaces are obtained. With this method trench structures filled by epitaxial re-growth can be planarized with smooth surfaces and good homogeneity over the wafer. Cost-efficient device manufacturing can be achieved by using standard semiconductor process equipment. This technology makes it possible to manufacture advanced epitaxial SiC material structures for devices such as trench JBS diodes and double-gate trench JFETs.
7.	Lissel, Linda, et al. (author) Prediction of the microstructural evolution during hot strip rolling of Nb microalloyed steels 2007 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 558-559:2, s. 1127-1132 Conference paper (other academic/artistic)abstract A physically based model is used to describe the microstructural evolution of Nb microalloyed steels during hot rolling. The model is based on a physical description of dislocation density evolution, where the generation and recovery of dislocations determines the flow stress and also the driving force for recrystallization. In the model, abnormally growing subgrains are assumed to be the nuclei of recrystallized grains and recrystallization starts when the subgrains reach a critical size and configuration. The model is used to predict the flow stress during rolling in SSAB Tunnplat's hot strip mill. The predicted flow stress in each stand was compared to the stresses calculated by a friction-hill roll-force model. Good fit is obtained between the predicted values by the microstructure model and the measured mill data, with an agreement generally within the interval +/-15%.
8.	Ahmed, Naeem, et al. (author) The Hydrophilization and Subsequent Hydrophobic Recovery Mechanism of Cold Plasma (CP) Treated Bambara Groundnuts 2022 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 1055, s. 161-169 Journal article (peer-reviewed)abstract Plasma hydrophilization and subsequent hydrophobic recovery in Bambara groundnuts are studied for the first time. Bambara groundnut seeds were treated with cold plasma (CP) for 10 seconds at 10 watts using water as a monomer. The contact angle, as well as physical and chemical changes, were used to determine the kinetics of hydrophobic recovery. The hydrophilic state of Bambara groundnut seeds had decreased after 60 days, but not to original hydrophobicity, and also the recovery rate is slower than those observed on synthetic polymer. However, this slower hydrophobic recovery makes CP treatment as an effective method for long-term seed storage.
9.	Allerstam, Fredrik, 1978, et al. (author) A study of deep energy-level traps at the 4H-SiC/SiO2 interface and their passivation by hydrogen 2009 In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 600-603, s. 755-758 Conference paper (peer-reviewed)abstract This study is focused on characterization of deep energy-level interface traps formed during sodium enhanced oxidation of n-type Si face 4H-SiC. The traps are located 0.9 eV below the SiC conduction band edge as revealed by deep level transient spectroscopy. Furthermore these traps are passivated using post-metallization anneal at 400°C in forming gas ambient. © (2009) Trans Tech Publications, Switzerland.
10.	Allerstam, Fredrik, 1978, et al. (author) Effect of high temperature oxidation of 4H-SiC on the near-interface traps measured by TDRC 2009 In: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9780878493340 ; 615 617, s. 537-540 Conference paper (peer-reviewed)abstract In this work the effect of oxidation temperature of 4H-SiC on the density of nearinterface traps is studied. It is seen that the portion of traps with slower emission times decreases with increasing oxidation temperature. Despite this reduction, high temperature oxidation alone is not useful to achieve low density of interface traps at the SiO2/4H-SiC interface.
11.	Allerstam, Fredrik, 1978, et al. (author) Formation of deep traps at the 4H-SiC/SiO2 interface when utilizing sodium enhanced oxidation 2007 In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 556-557, s. 517-520 Conference paper (peer-reviewed)abstract This paper reports studies of deep acceptor-type interface traps at the 4H-SiC/SiO2 interface. These traps are created during sodium enhanced oxidation of Si-terminated 4H-SiC. The trap concentration is above 3×1012 cm-2 and their activation energy is larger than 0.8 eV.
12.	Andersson, Petter, 1970, et al. (author) Scale growth on austenitic alloys under KCl deposits at 500 deg C 2008 In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 595-598:I, s. 333-342 Journal article (peer-reviewed)abstract The scale growth on two austenitic alloys, Alloy 310 and Sanicro 28, under KCl deposits was examined. This is relevant to the long term corrosion of superheater tubes in biofuel combustion. Coupons were encapsulated in tablets so that 1 mm of KCl with a relative density of 91% covered the metal. Samples were tested at 500 deg C in 5%O2-10%H2O-N2 for 24, 168 and 672 h. After exposure the salt was broken off and the scale was characterised by using SEM-EDX and AES. After 24 h a 50 nm thick oxide surrounded 500 nm thick chromates on the surface. No oxide layer was detected under the chromates and no Cl was found under either layer. The chromate growth requires lateral transportation of Cr along the surface. This reduces the protectiveness of the oxide and accelerates the formation of less protective Fe rich oxides. The formation of chromates also releases HCl inside the KCl tablet. The chromates did not grow significantly between 24 and 168 h, but the oxide grew equally thick beneath and between them and Cl was enriched around the metal oxide interface. After 672 h the oxides were about 5 mum thick and only few chromates were seen. Crystals of KCl formed in areas with thick porous and Fe rich oxides on both alloys.
13.	Anghel, Clara, et al. (author) Gas-tight oxides – Reality or just a Hope 2006 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 522-523, s. 93-101 Journal article (peer-reviewed)abstract A better understanding of the transport properties of gases in oxides is certainly very important in many applications. In the case of metals, a general protection measure against corrosion implies formation of a dense metal oxide scale. The scale should act as a barrier against gas transport and consequently it needs to be gas-tight. This is often assumed but rarely, if ever, confirmed. Hence there is a need for characterization of micro- and/or meso- pores formed especially during the early oxidation stage of metallic materials. This paper presents a novel and relatively straightforward method for characterization of gas release from an oxide previously equilibrated in a controlled atmosphere. The geometry of the sample is approximated to be a plate. The plate can be self-supporting or constitute a scale on a substrate. A mathematical model for calculation of diffusivity and gas content is given for this geometry. A desorption experiment, involving a mass spectrometer placed in ultra high vacuum, can be used to determine diffusivity and amount of gas released with aid of the mathematical model. The method is validated in measurements of diffusivity and solubility of He in quartz and applied in characterization of two Zr-oxides and one Fe oxide. From the outgassed amounts of water and nitrogen the H2O/N-2 molar ratio can be used to estimate an effective pore size in oxides.
14.	Azizov, Talyat, et al. (author) Consideration of the Torsional Stiffness in Hollow-Core Slabs’ Design 2019 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 968, s. 330-341 Journal article (peer-reviewed)abstract The paper discusses the principles of precast concrete hollow-core slabs taking into account their spatial work. It is shown that consideration of spatial work makes it possible to determine the forces in individual floor slabs significantly more precise. The fact that strain redistribution between precast floor slabs depends on slabs’ bending and torsional stiffness is shown. The research has been mostly devoted to the determination of the bending stiffness with regard to the formation of cracks and the change in torsional stiffness, especially considering the presence of normal cracks, which is still unstudied. This paper presents the technique for determining the torsional stiffness of hollow-core slabs with normal cracks. In order to determine the components included in the resolving system of equations, it is proposed to use an approximation method based on the processing of numerical data using spatial finite elements.
15.	Badger, J., et al. (author) Grinding of cermets with cup-wheels 2016 In: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783035710342 ; 874, s. 115-123 Conference paper (peer-reviewed)abstract Cup-wheels are frequently used to grind cermets, a difficult-to-grind material. An investigation was made into the transient geometry of the cup-wheel rim, grit dulling, wheel loading, and wheel self-sharpening with chip thickness. Tests were performed on a saw-tip grinding machine and specific energies, G-ratios and rim geometries were measured. Results showed that, like grinding of tungsten-carbide, loading is prevalent. However, unlike grinding of tungstencarbide, grit dulling is also prevalent and wheel conditioning is of limited use. Much better results, particularly with respect to surface finish, can be obtained if the wheel is trued to a predetermined geometry. In addition, grinding parameters must be chosen to induce wheel self-sharpening. Practical recommendations are given.
16.	Bakowski, Mietek, et al. (author) Silicon carbide APD with improved detection sensitivity stability 2010 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 645-648, s. 1089- Journal article (peer-reviewed)
17.	Bergman, Ola, et al. (author) Influence of sintering parameters on the mechanical performance of PM steels pre-alloyed with chromium 2007 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 534-536, s. 545-548 Journal article (peer-reviewed)abstract Powder grades pre-alloyed with 1.5-3 wt% chromium are suitable for PM steel components in high performance applications. These materials can be successfully sintered at the conventional temperature 1120 degrees C, although well-monitored sintering atmospheres with low oxygen partial pressures (< 10(-17)-10(-18) atm) are required to avoid oxidation. Mechanical properties of the Cr-alloyed PM grades are enhanced by a higher sintering temperature in the range 1120-1250 degrees C, due to positive effects from pore rounding, increased density and more effective oxide reduction. A material consisting of Astaloy CrM, which is pre-alloyed with 3 wt% Cr and 0.5 wt% Mo, and 0.6 wt% graphite obtains an ultimate tensile strength of 1470 MPa combined with an impact strength of 31 J at density 7.1 g/cm(3), after sintering at 1250 degrees C followed by cooling at 2.5 degrees C/s and tempering.
18.	Bertuccio, Giuseppe, et al. (author) Ultra Low Noise Epitaxial 4H-SiC X-Ray Detectors 2009 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 615-617, s. 845-848 Journal article (peer-reviewed)abstract The design and the experimental results of some prototypes of SiC X-ray detectors are presented. The devices have been manufactured on top of 2 inch 4H-SiC wafer with 115 μm thick undoped high purity epitaxial layer, which constitutes the detection’s active volume. Pad and pixel detectors based on Ni-Schottky junctions have been tested. The residual doping of the epi-layer was found tobe extremely low, 3.7 x 1013 cm-3, allowing to achieve the highest detection efficiency and the lower specific capacitance of the detectors. At 22 °C and in operating bias condition, the reverse current densities of the detector’s Schottky junctions have been measured to be between J = 0.3 pA/cm2 and J = 4 pA/cm2; these values are more than two orders of magnitude lower than those of state of the art silicon detectors. With such low leakage currents, the equivalent electronic noise of SiC pixel detectors is as low as 0.5 electrons r.m.s at room temperature, which represents a new state of the art in the scenario of semiconductor radiation detectors.
19.	Bjurenstedt, Anton, et al. (author) Assessment of Quality when Delivering Molten Aluminium Alloys Instead of Ingots 2013 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. - 9783037857663 ; 765, s. 266-270 Journal article (peer-reviewed)abstract Recycled aluminium alloys manufactured at Stena Aluminium, in Älmhult, Sweden, are delivered in special designed transport containers, called thermoses. Thermoses are best described as an insulating layer protected by a steel cover with a heat loss of about 5 degrees/h. Three thermoses are transported by a truck, giving the possibility for a total capacity of about 24 tonnes delivered aluminium just-in-time to the foundry. By delivering a full load of liquid aluminium, about 2 tonnes of carbon dioxide emissions are saved, compared with delivering ingots. The aim of the paper is to assess the quality benefits, in terms of inclusions sedimentation and mechanical properties, assured by delivering aluminiummelts instead of ingots. The results indicate that materials produced by just-in-time melt delivery have slightly improved quality compared to ingots. The trends are explained in terms of quality, density and bifilm indexes, based on microstructural observations as well as tensile test data analysis.
20.	Bora, T., et al. (author) Plasmon resonance enhanced zinc oxide photoelectrodes for improvement in performance of dye sensitized solar cells 2014 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 771, s. 91-101 Journal article (peer-reviewed)abstract Nanocomposites of vertically aligned zinc oxide (ZnO) nanorod arrays incorporated with gold (Au) nanoparticles have been used as photoelectrodes to fabricate dye sensitized solar cells (DSSCs). Due to the surface plasmon resonance of the Au nanoparticles, the nanocomposite photoelectrodes demonstrate enhancement in the visible light absorption resulting in ~8% higher photocurrent compared to ZnO photoelectrode based DSSCs fabricated without any Au nanoparticles. In addition to the higher optical absorption due to the gold nanoparticles, a Schottky barrier forms at the ZnO/Au interface preventing the back electron transfer from the conduction band of the semiconductor nanorods to the redox electrolyte providing improvement in the charge separation at the nanocomposite photoelectrode. Upon incorporation of Au nanoparticles, the overall efficiency of the DSSC increased from 2. 41% to 3. 27%. The role of Au nanoparticles on the performance of the DSSCs for varying concentration of the Au nanoparticles as well as the post-growth annealing treatment of the nanocomposite photoelectrode is reported.
21.	Buono, Benedetto, et al. (author) Current Gain Degradation in 4H-SiC Power BJTs 2011 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 702-705 Journal article (peer-reviewed)abstract SiC airs are very attractive for high power application, but long term stability is still problematic and it could prohibit commercial production of these devices. The aim of this paper is to investigate the current gain degradation in BJTs with no significant degradation of the on-resistance. Electrical measurements and simulations have been used to characterize the behavior of the BJT during the stress test. Current gain degradation occurs, the gain drops from 58 before stress to 43 after 40 hours, and, moreover, the knee current shows fluctuations in its value during the first 20 hours. Current gain degradation has been attributed to increased interface traps or reduced lifetime in the base-emitter region or small stacking faults in the base-emitter region, while fluctuations of the knee current might be due to stacking faults in the collector region.
22.	Buono, Benedetto, et al. (author) Investigation of Current Gain Degradation in 4H-SiC Power BJTs 2012 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 717-720, s. 1131-1134 Journal article (peer-reviewed)abstract The current gain degradation of 4H-SiC BJTs with no significant drift of the on-resistance is investigated. Electrical stress on devices with different emitter widths suggests that the device design can influence the degradation behavior. Analysis of the base current extrapolated from the Gummel plot indicates that the reduction of the carrier lifetime in the base region could be the cause for the degradation of the gain. However, analysis of the base current of the base-emitter diode shows that the degradation of the passivation layer could also influence the reduction of the current gain.
23.	Buono, Benedetto, et al. (author) Simulations of Open Emitter Breakdown Voltage in SiC BJTs with non Implanted JTE 2009 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 615-617, s. 841-844 Journal article (peer-reviewed)abstract Ion implantation for selective doping of SiC is problematic due to damage generation during the process and low activation of dopants. In SiC bipolar junction transistor (BJT) the junction termination extension (JTE) can be formed without ion implantation using instead a controlled etching into the epitaxial base. This etched JTE is advantageous because it eliminates ion implantation induced damage and the need for high temperature annealing. However, the dose, which is controlled by the etched base thickness and doping concentration, plays a crucial role. In order to find the optimum parameters, device simulations of different etched base thicknesses have been performed using the software Sentaurus Device. A surface passivation layer consisting of silicon dioxide, considering interface traps and fixed trapped charge, has been included in the analysis by simulations. Moreover a comparison with measured data for fabricated SiC BJTs has been performed.
24.	Buono, Benedetto, et al. (author) Temperature Modeling and Characterization of the Current Gain in 4H-SiC Power BJTs 2010 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 645-648, s. 1061-1064 Journal article (peer-reviewed)abstract The current gain of 4H-SiC BJTs has been modeled using interface traps between SIC and SiO2 to describe surface recombination, by a positive temperature dependence of the carrier lifetime in the base region and by bandgap narrowing in the emitter region. The interface traps have been modeled by one single level at 1 eV above the valence band, with capture cross section of 1 x 10(-15) cm(2) and concentration of 2 x 10(12) cm(-2). The temperature behavior of SiC BJTs has been simulated and the results have been compared with measurements. An analysis of the carrier concentration has been performed in order to describe the mechanisms for fall-off of the current gain at high collector current. At room temperature high injection in the base and forward biasing of the base-collector junction occur simultaneously causing an abrupt drop of the current gain. At higher temperatures high injection in the base is alleviated by the higher ionization degree of the aluminum dopants, and then forward biasing of the base-collector junction is the only acting mechanism for the current gain fall-off at high collector current. This mechanism and the negative temperature dependence of the carrier mobility can also explain the reduction of the knee current for gain fall-off with increasing temperature. Simulations with different emitter widths have been also performed and analyzed to characterize the emitter size effect. Higher current density caused by reducing the emitter width introduces higher carrier recombination in the emitter region, leading to a reduction of the current gain.
25.	Calmunger, Mattias, et al. (author) Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures 2014 In: Materials Science Forum. - : Trans Tech Publications Ltd. - 0255-5476 .- 1662-9752. ; 783-786, s. 1182-1187, s. 1182-1187 Journal article (peer-reviewed)abstract Nickel-base alloys due to their high performances have been widely used in biomass and coal fired power plants. They can undertake plastic deformation with different strain rates such as those typically seen during creep and fatigue at elevated temperatures. In this study, the mechanical behaviours of Alloy 617 with strain rates from 10-2/s down to 10-6/s at temperatures of 650°C and 700°C have been studied using tensile tests. Furthermore, the microstructures have been investigated using electron backscatter detection and electron channeling contrast imaging. At relatively high strain rate, the alloy shows higher fracture strains at these temperatures. The microstructure investigation shows that it is caused by twinning induced plasticity due to DSA. The fracture strain reaches the highest value at a strain rate of 10-4/s and then it decreases dramatically. At strain rate of 10-6/s, the fracture strain at high temperature is now smaller than that at room temperature, and the strength also decreases with further decreasing strain rate. Dynamic recrystallization can also be observed usually combined with crack initiation and propagation. This is a new type of observation and the mechanisms involved are discussed.
26.	Cao, Haiping, et al. (author) Mechanisms of segregation band defect formation in pressure die-cast magnesium components 2005 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 488-489, s. 381-384 Journal article (peer-reviewed)abstract Initially, when implementing a design automation system the focus is on successfully developing a system that generates design variants based on different customer specifications, i.e. the execution of system embedded knowledge and system output. However, in the long run two important aspects are the modelling and management of the knowledge that govern the designs. The increasing emphasis to deploy a holistic view on the products properties and functions implies an increasing number of life-cycle requirements. These requirements should all be used to enhance the knowledge-base allowing for correct decisions to be made. In a system for automated variant design these life-cycle requirements have to be expressed as algorithms and/or computational statements to be intertwined with the design calculations. The number of requirements can be significantly large and they are scattered over different systems. The aim of the presented work is to provide an approach for modelling of manufacturing requirements, supporting both knowledge execution and information management, in systems for automated variant design.
27.	Cao, Haiping (author) On some characteristics of microstructure and defects in die-cast magnesium components 2005 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 488-489, s. 283-286 Journal article (peer-reviewed)abstract A mapping of fatigue crack growth rates in thick plates of a high strength aluminium alloy has been done. The plate thicknesses investigated was 100, 150 and 200 mm. In this work, material from near edge at near surface and mid-thickness has been investigated. Measurements of crack length has been performed using DC potential drop. Cyclic condensation is used in order to reveal crack growth behaviour for stage I and the earlier part of stage II crack growth. Influence of crack closure, crack branching and slow growing side cracks on fatigue crack growth rate of S-L and L-T oriented specimens are discussed. Variation of difference in growth rate in the upper part of the stage II growth between near surface and mid thickness positioned L-T specimens are found to vary with plate thickness.
28.	Cao, Yu, 1969, et al. (author) Interface Reactions and Electrical Properties of Ta/4H-SiC Contacts 2007 In: Materials Science Forum. - Stafa : Trans Tech Publications Ltd.. - 1662-9752 .- 0255-5476. - 0878494421 ; 556-557, s. 713-716 Journal article (peer-reviewed)abstract This study deals with the interfacial reactions and electrical properties of Ta/4H-SiCcontacts. Tantalum thin films (~100 nm) were deposited onto SiC wafer at room temperature byargon ion beam sputtering. The samples were then heated in high vacuum at 650°C, 800°C or950°C for 30 min. X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction(XRD), Auger electron spectroscopy (AES) and current-voltage (I-V) technique were used forcharacterising the samples. Ohmic contact is formed in the studied samples after annealing at orabove 800°C even though considerable amount of metallic Ta still exists. The reaction zonepossesses a layered structure of Ta2C/Ta2C+Ta5Si3/SiC. High enough temperature is needed toprovide for sufficient interface change to tailor the contact properties.
29.	Cerda, J, et al. (author) New tunnel Schottky SiC devices using mixed conduction ceramics 2002 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 433-4, s. 949-952 Journal article (peer-reviewed)abstract A new tunnel Schottky diode based on SiC and a mixed conductor of BaSnO3 as the gate has been investigated. I-V curves at different operating temperatures and two different gas atmospheres have been measured. The device shows sensitivity to oxygen, with maximum at 400degreesC. A model that describes the behaviour of the device is proposed, which takes into account the different types of conduction of the BaSnO3 due to the temperature.
30.	Ceschini, Lorella, et al. (author) Influence of SDAS on the high temperature tensile behavior of the C355 Al alloy 2014 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 783-786, s. 228-233 Journal article (peer-reviewed)
31.	Choudary Ratnala, Dilipkumar, Doktorand, et al. (author) Development of Functionally Graded Metal–Ceramic Systems by Directed Energy Deposition : A Review 2023 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 1107, s. 105-110 Journal article (peer-reviewed)abstract Ceramics and metals are the two vastly explored classes of materials whose individual characteristics and targeted applications differ significantly. Continuous thrust for space exploration and energy generation demands materials with a wide range of properties. To tackle this demand, ceramic-metal combined structures that club heat, wear, and corrosion resistance of ceramics to the high toughness, good strength, and better machinability of metals are desirable. While various processing routes to combine ceramics and metals have been developed through the years, solutions to address problems associated with the interface, thermal property mismatch, and poor adhesion need to be explored. In this context, Functional Graded Materials (FGMs) have attracted particular attention by virtue of their ability to avoid sharp interfaces and local stress concentrations. Out of all, Additive Manufacturing (AM) routes, particularly the Directed Energy Deposition (DED) technique, is emerging as a productive technique capable of fabricating a wide range of metal-ceramic graded structures. This paper specifically discusses metal-ceramic FGMs ́ capability as a potential high-temperature material with customized multifunctional material properties. It further outlines the primary concerns with the realization of metal-ceramic graded structures and major techniques developed to mitigate problems encountered in processing them. Specific emphasis is laid on the powder-based Laser DED (L-DED) technique of FGM fabrication owing to its control over complex geometries and microstructural engineering.
32.	Chudinova, Ekaterina, et al. (author) In Vitro Assessment of Hydroxyapatite Coating on the Surface of Additive Manufactured Ti6Al4V Scaffolds 2017 In: Materials Science Forum. - Switzerland : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 879, s. 2444-2449 Journal article (peer-reviewed)abstract Custom orthopedic and dental implants may be fabricated by additive manufacturing (AM), for example using electron beam melting technology. This study is focused on the modification of the surface of Ti6Al4V alloy coin-like scaffolds fabricated via AM technology (EBM®) by radio frequency (RF) magnetron sputter deposition of hydroxyapatite (HA) coating. The scaffolds with HA coating were characterized by Scanning Electron microscopy, X-ray diffraction. HA coating showed a nanocrystalline structure with the crystallites of an average size of 32±9 nm. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells was studied using biological short-term tests in vitro. In according to in vitro assessment, thin HA coating stimulated the attachment and proliferation of cells. Human mesenchymal stem cells cultured on the HA-coated scaffold also formed mineralized nodules.
33.	Correia, A., et al. (author) Modelling the mechanical behavior of polymer-based nanocomposites 2013 In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 730-732, s. 543-548 Conference paper (peer-reviewed)abstract Molecular dynamics simulations were employed to analyze the mechanical properties of polymer-based nanocomposites with varying nanofiber network parameters. The study was focused on nanofiber aspect ratio, concentration and initial orientation. The reinforcing phase affects the behavior of the polymeric nanocomposite. Simulations have shown that the fiber concentration has a significant effect on the properties, with higher loadings resulting in higher stress levels and higher stiffness, matching the general behavior from experimental knowledge in this field. The results also indicate that, within the studied range, the observed effect of the aspect ratio and initial orientation is smaller than that of the concentration, and that these two parameters are interrelated.
34.	Dahlquist, Fanny, et al. (author) 2.8 kV, forward drop JBS diode with low leakage 2000 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1179-1182 Journal article (peer-reviewed)abstract High voltage Schottky-, Junction Barrier Schottky (JBS)- and PiN-diodes with an implanted JTE termination have been fabricated on the same 4H-SiC wafer. Blocking voltages of 2.5-2.8 kV were reached for JBS and PiN diodes while the Schottky diodes reach about 2.0 kV. It is shown that the JBS design increases the blocking voltage effectively compared to the Schottky device with less than 10% increase in on-state static losses. Also, a comparison of static losses to a PiN diode gives a decrease of 40% for the JBS. The leakage current is also lowered by two decades compared to the Schottky device at its blocking voltage. Temperature measurements show that the low leakage current is maintained up to at least 225 Â°C.
35.	Dahlquist, Fanny, et al. (author) Junction barrier Schottky diodes in 4H-SiC and 6H-SiC 1998 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 264-268:PART 2, s. 1061-1064 Journal article (peer-reviewed)abstract The Junction Barrier Schottky (JBS) diode in silicon carbide is a promising candidate for a low-leakage power rectifier for high switching frequencies and elevated temperature operation. It has the advantage of a low forward voltage drop while keeping a low leakage current at high blocking voltage. JBS devices have been fabricated in 4H SiC and 6H SiC and then electrically characterised in comparison with pn and Schottky diodes on the same wafer. The JBS devices reached blocking voltages up to 1.0 kV at a leakage current density of 13 ÎŒA/cm2 and the forward conduction was limited by an on-resistance close to the theoretical value.
36.	Danielsson, Erik, et al. (author) A 4H-SiC BJT with an epitaxially regrown extrinsic base layer 2005 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 483, s. 905-908 Journal article (peer-reviewed)abstract 4H-SiC BJTs were fabricated using epitaxial regrowth instead of ion implantation to form a highly doped extrinsic base layer necessary for a good base ohmic contact. A remaining p(+) regrowth spacer at the edge of the base-emitter junction is proposed to explain a low current gain of 6 for the BJTs. A breakdown voltage of 1000 V was obtained for devices with Al implanted JTE.
37.	Danielsson, Erik, et al. (author) Dry etching and metallization schemes in a GaN/SiC heterojunction device process 2000 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1049-1052 Journal article (peer-reviewed)abstract Dry etching and metallization schemes are described for a GaN/SiC heterojunction. GaN was reactive ion etched in a chlorine based chemistry (Cl2/Ar), and an ICP etch was used on 4H-SiC using a fluorine based chemistry (SF6/Ar/O2). The etch rates obtained on GaN was above 400 nm/min. High sample temperature from self heating and large dc-bias was the probable cause for the high etch rate. The ICP etch rate on SiC approached 320 nm/min, and the etch selectivity to GaN was >100. The metallization was based on Ti for both n-GaN and p-SiC. TLM and Kelvin structures were used to extract the specific contact resistivity, ÏC. After a 950 Â°C anneal in N2 ÏC on the GaN samples were below 1Â·10-6 Î©cm2 for sputtered contacts in room temperature, and an order of magnitude higher with evaporation. On p-SiC no ohmic behavior was found with a doping of 4Â·1018 cm-3, but the same contact metallization on highly doped areas (>1020 cm-3) showed ohmic behavior with ÏC below 10-4 Î©cm2.
38.	Danielsson, Erik, et al. (author) Extrinsic base design of SiC bipolar transistors 2004 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 457-460:II, s. 1117-1120 Journal article (peer-reviewed)abstract The SiC npn bipolar junction transistor (BJT) is a very promising device for high voltage and high power switches. The SiC BJT has, due to junction voltage cancellation, potentially a low on-resistance. However, the high resistivity in the base layer can induce a locally forward biased base collector junction and a premature current from the base to collector at on-state. In this work we propose a new technique to fabricate the extrinsic base using regrowth of the extrinsic base layer. This technique can put the highly doped region of the extrinsic base a few tenths of a micron from the intrinsic region. We also propose a new mobility model in our simulations to correctly account for the ionized impurities in minority carrier transport and elevated temperature.
39.	Danielsson, Erik, et al. (author) Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors 2002 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 1337-1340 Journal article (peer-reviewed)abstract Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximmn current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 Â°C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
40.	Danielsson, Erik, et al. (author) Thermal stability of sputtered TiN as metal gate on 4H-SiC 1998 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 264-268:PART 2, s. 805-808 Journal article (peer-reviewed)abstract MOS-structures were made with TiN as metal gate on 4H-SiC. The thermal stability and electrical properties of this gate was determined by CV-measurements. Comparison with Al gates showed that TiN worked well as a gate metal on 4H-SiC. The hysteresis and density of the interface states were comparable for the two gate types. The n-type samples had low leakage and a flatband voltage of a few volts, while the p-type samples had high leakage and a fiatband voltage of around -20 V. The structure showed poor characteristics after a 700Â°C anneal for one hour, which is probably caused by the formation of titanium silicide. The TiN films had a lower content of nitrogen than expected, which could influence the stability.
41.	Danielsson, Örjan, et al. (author) Simulation of Gas-Phase Chemistry for Selected Carbon Precursors in Epitaxial Growth of SiC 2013 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 740-742, s. 213-216 Journal article (peer-reviewed)abstract Numerical simulations are one way to obtain a better and more detailed understanding of the chemical vapor deposition process of silicon carbide. Although several attempts have been made in this area during the past ten years, there is still no general model valid for any range of process parameters and choice of precursors, that can be used to control the growth process, and to optimize growth equipment design. In this paper a first step towards such a model is taken. Here, mainly the hydrocarbon chemistry is studied by a detailed gas-phase reaction model, and comparison is made between C3H8 and CH4 as carbon precursor. The results indicate that experimental differences, which previous models have been unable to predict, may be explained by the new model.
42.	Deng, JN, et al. (author) Textures and local textures in severely cold-rolled and annealed ultra-fine-grained FeCo alloy 2005 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 495-497, s. 731-736 Journal article (peer-reviewed)abstract We find that a severely rolled FeCo alloy has anomalous enhancement of the rotated-cube {100}< 011 > texture component and a decrease of the {111} components after annealing, which is contrast to the recrystalliization behaviors reported in traditional BCC metals and alloys. The local texture measurements show that two kinds of grains with obviously different orientations, i.e. {100} and {111}, are heterogeneously distributed in the deformed specimen and the migration of high-angle grain boundaries is observed after annealing in the disordering temperature region.
43.	Diószegi, Attila, 1962-, et al. (author) Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 1 – Investigation based on interrupted solidification 2014 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 205-210, s. 205-210 Journal article (peer-reviewed)abstract Dynamic coarsening of austenite dendrite in lamellar cast iron has been studied for a hypoeutectic alloy. The common morphological parameter to characterize dynamic coarsening, secondary dendrite arm space has been replaced by the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHydIP) to interpret the dynamic coarsening with respect to the local solidification time. The obtained results demonstrate the coarsening process of both the solid and liquid phase. The interdendritic space is increasing as the contact time between the solid and liquid phase increases. The ratio between the DHydIP/MPD is strongly dependent on the precipitated fraction primary austenite indicating clearly the morphology variation during coarsening. The interrupted solidification method demonstrate that the observed coarsening process is not only a combination of the increasing fraction precipitated solid phase and the rearrangement of the solid - liquid interphase curvature but the volume change due to density variation is also contribute to the coarsening process.
44.	Diószegi, Attila, et al. (author) Fracture Mechanics of Gray Cast Iron 2010 In: Materials Science Forum. - : Trans Tech Publication, Switzerland. - 0255-5476 .- 1662-9752. ; 649, s. 517-522 Journal article (peer-reviewed)abstract The fracture mechanism of gray cast iron was investigated on tension loaded samples produced under different conditions. The parameters studied included the graphite morphology, the carbon content, the inoculation and the cooling condition. The observations made reveal the role of the microstructure on crack propagation. The cracks were found to always propagate parallel with the graphite flakes. The interaction between the metallic matrix precipitated as primary austenite and graphite has been interpreted by a simplified model of the austenite reinforced eutectic cell. The geometrical transcription gave a standard crack component configuration with known mathematical solution. The microstructure observed in the experiments has been analysed by means of a novel interpretation. The fictitious stress intensity at yield and the fictitious maximum stress intensity at failure are strongly related to the relative shape of the eutectic cell and the fraction primary austenite. A different slope is observed for the material cooled at high rate when the precipitation of primary carbide reduces the stress intensity. The observed relations indicate that the tensile strength of the grey cast iron is the result of the collaboration between the toughness of the metallic matrix precipitated as primary austenite and the brittleness of the graphite phase. The shape and distribution of the primary austenite and graphite can be influenced by chemical composition, by inoculation or by the cooling condition, but they will maintain equilibrium with respect to the stress intensity.
45.	Dom, R., et al. (author) Design and development of ferrite composite film electrode for photoelectrochemical energy application 2014 In: Materials Science Forum. - : Trans Tech Publications Ltd. - 0255-5476 .- 1662-9752. - 9783038350675 ; 781, s. 45-61 Journal article (peer-reviewed)abstract Development of efficient photoanodes for water splitting under solar light is desirable to surmount the possible fuel crisis in future. Ferrite systems, with their excellent visible light absorption capability, stability, non-toxicity, cost-effectiveness and abundance, are being preferred to titanates, niobates and sulfides. The present work briefly reviews the modified form of ferrites. Additionally, ZnFe2O4 an n-type semiconductor with the low band gap (~1.9eV) has been considered as special case of visible light PEC application. The work further emphasizes on the utilization of solution processed techniques to develop the ferrite photoanodes. The tuning of photoanode properties by virtue of electrode fabrication parameters say deposition parameters viz., precursor concentration, pH, stoichiometry has been reviewed and discussed. © (2014) Trans Tech Publications, Switzerland.
46.	Domeij, Björn, 1988-, et al. (author) Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA 2018 In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 925, s. 436-443 Journal article (peer-reviewed)abstract Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.
47.	Domeij, Martin, et al. (author) Current gain dependence on emitter width in 4H-SiC BJTs 2006 In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9780878494255 ; 527-529, s. 1425-1428 Journal article (peer-reviewed)abstract This paper reports the fabrication of epitaxial 4H-SiC bipolar junction transistors (BJTs) with a maximum current gain beta = 64 and a breakdown voltage of 1100 V. The high beta value is attributed to high material quality obtained after a continuous epitaxial growth of the base-emitter junction. The current gain of the BJTs increases with increasing emitter width indicating a significant influence of surface recombination. This "emitter-size" effect is in good agreement with device simulations including recombination in interface states at the etched termination of the base-emitter junction.
48.	Domeij, Martin, et al. (author) Current gain of 4H-SiC bipolar transistors including the effect of interface states 2005 In: Materials Science Forum. - ZURICH-UETIKON : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 0878499636 ; 483, s. 889-892 Journal article (peer-reviewed)abstract The current gain (β) of 4H-SiC BJTs as function of collector current (I-C) has been investigated by DC and pulsed measurements and by device simulations. A measured monotonic increase of β with I-C agrees well with simulations using a constant distribution of interface states at the 4H-SiC/SiO2 interface along the etched side-wall of the base-emitter junction. Simulations using only bulk recombination, on the other hand, are in poor agreement with the measurements. The interface states degrade the simulated current gain by combined effects of localized recombination and trapped charge that influence the surface potential. Additionally, bandgap narrowing has a significant impact by reducing the peak current gain by about 50% in simulations.
49.	Domeij, Martin, et al. (author) Reverse Recovery and Avalance Injection in High Voltage SiC PIN Diodes 1998 In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 264-268, s. 1041- Journal article (other academic/artistic)
50.	Dudrova, Eva, et al. (author) Improvement of Mechanical Properties of Fe-Cr-Mo-[Cu-Ni]-C Sintered Sintered Steels by Sinter Hardening 2011 In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 672, s. 31-38 Journal article (peer-reviewed)abstract The effect of high temperature sintering and high cooling rate on shifting themicrostructural composition to the favourably of martensite-bainite structures and thus effectiveimprovement of mechanical properties of sintered steels based on Astaloy CrL powder with anaddition of 1 and 2% Cu or 50% Distaloy AB powder and 0.65% C was investigated. All thesystems were processed by both sinter-hardening and conventional sintering. The vacuum sinteringat high-temperature of 1240 0C and at common temperature of 1180 0C were integrated with high(6 0C/s), medium (3 0C/s) and slow (0.1 0C/s) cooling rates; conventional sintering at 1180 0C withcooling rate of ~0.17 0C/s was carried out in a N2+10%H2 atmosphere. In dependence on chemicalcomposition, the yield and tensile strengths of 890-1150 MPa and 913-1230 MPa respectively andimpact energy of 10-15 J were achieved by sinter-hardening. The yield and tensile strengths areapproximately double than those resulting from conventional sintering.

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