| 1. |
|
|
| 2. |
- 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.
|
|
| 3. |
- 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.
|
|
| 4. |
- 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.
|
|
| 5. |
- 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.
|
|
| 6. |
- 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.
|
|
| 7. |
- 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.
|
|
| 8. |
|
|
| 9. |
- 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.
|
|
| 10. |
- 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.
|
|
| 11. |
- 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.
|
|
| 12. |
- 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.
|
|
| 13. |
- 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.
|
|
| 14. |
- 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.
|
|
| 15. |
- Ejebjörk, Niclas, 1984, et al.
(author)
-
Optimization of SiC MESFET for high power and high frequency applications
- 2011
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 1662-9752 .- 0255-5476. ; 679-680, s. 629-632, s. 629-632
-
Conference paper (peer-reviewed)abstract
- SiC MESFETs were scaled both laterally and vertically to optimize high frequency and high power performance. Two types of epi-stacks of SiC MESFETs were fabricated and measured. The first type has a doping of 3×10^17 cm-3 in the channel and the second type has higher doping (5×10^17 cm-3) in the channel. The higher doping allows the channel to be thinner for the same current density and therefore a reduction of the aspect ratio is possible. This could impede short channel effects. For the material with higher channel doping the maximum transconductance is 58 mS/mm. The maximum current gain frequency, fT, and maximum frequency of oscillation, fmax, is 9.8 GHz and 23.9 GHz, and 12.4 GHz and 28.2 GHz for the MESFET with lower doped channel and higher doping, respectively.
|
|
| 16. |
- Elahipanah, Hossein, et al.
(author)
-
Process variation tolerant 4H-SiC power devices utilizing trench structures
- 2013
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783037856246 ; 740-742, s. 809-812
-
Journal article (peer-reviewed)abstract
- Silicon carbide (SiC) is one of the most attractive semiconductors for high voltage applications. The breakdown voltage of SiC-based devices highly depends on the variation of the fabrication process including doping of the epilayers and the etching steps. In this paper, we show a way to diminish this variability by employing novel trench structures. The influence of the process variations in terms of doping concentration and etching has been studied and compared with conventional devices. The breakdown voltage variation (ΔVBr) of 450 V and 2100 V is obtained for the ±20% variation of doping concentration of the devices with and without the trench structures, respectively. For ±20% variation in etching steps, the maximum ΔVBR of 380 V is obtained for the device with trench structures in comparison to 1800 V for the conventional structure without trench structures. These results show that the breakdown voltage variation is significantly reduced by utilizing the proposed structure.
|
|
| 17. |
|
|
| 18. |
- Elmquist, Lennart, et al.
(author)
-
On the Problems of a Migrating Hot Spot
- 2010
-
In: Materials Science Forum. - Roósz : Trans Tech Publication. - 0255-5476 .- 1662-9752. ; 649, s. 443-448
-
Journal article (peer-reviewed)
|
|
| 19. |
- Engberg, Göran, et al.
(author)
-
Modeling microstructure development during hot working of an austenitic stainless steel
- 2013
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 753, s. 423-426
-
Journal article (peer-reviewed)abstract
- A number of physically based models are combined in order to predict microstructure development during hot deformation. The models treat average values for the generation and recovery of vacancies and dislocations, recrystallization and grain growth and the dissolution and precipitation of second phase particles. The models are applied to a number of laboratory experiments made on 304 austenitic stainless steel and the model parameters are adjusted from those used for low alloyed steel mainly in order to obtain the right kinetics for the influence of solute drag on climb of dislocations and on grain growth. The thermodynamic data are obtained using Thermo-Calc© to create solubility products for the possible secondary phases. One case of wire rolling has been analyzed mainly concerning the evolution of recrystallization and grain size. The time, temperature and strain history has been derived using process information. The models are shown to give a fair description of the microstructure development during hot working of the studied austenitic stainless steel. © (2013) Trans Tech Publications, Switzerland.
|
|
| 20. |
- Eriksson, Jens, et al.
(author)
-
Thickness uniformity and electron doping in epitaxial graphene on SiC
- 2013
-
In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 740-742, s. 153-156
-
Journal article (peer-reviewed)abstract
- Large variations have been observed in the thickness uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth. Here we present a study on how the substrate polytype, substrate surface morphology and surface restructuring during sublimation growth affect the uniformity and carrier concentration in epitaxial graphene on SiC. These issues were investigated employing surface morphology mapping by atomic force microscopy coupled with local surface potential mapping using scanning Kelvin probe microscopy.
|
|
| 21. |
- Esteve, Romain, et al.
(author)
-
Comparative study of thermal oxides and post-oxidized depositedoxides on n-type free standing 3C-SiC
- 2010
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 645-648, s. 829-832
-
Journal article (peer-reviewed)abstract
- The electrical properties of oxides fabricated on n-type 3C-SiC (001) using wet oxidationand an advanced oxidation process combining SiO 2 deposition with rapid post oxidation steps havebeen compared. Two alternative SiO 2 deposition techniques have been studied: the plasmaenhanced chemical vapor deposition (PECVD) and the low pressure chemical vapor deposition(LPCVD). The post-oxidized PECVD oxide is been demonstrated to be beneficial in terms ofinterface traps density and reliability.
|
|
| 22. |
|
|
| 23. |
- Fourlakidis, Vasilios, et al.
(author)
-
Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 2 – The influence of carbon composition
- 2014
-
In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 211-216, s. 211-216
-
Journal article (peer-reviewed)abstract
- Investigation of dynamic coarsening in lamellar cast iron is extended over a wide interval ranging from hypoeutectic to eutectic composition. The dendrite morphology is defined on as-cast samples produced under various cooling rates. The as-cast morphology is considered being close to the one at the end of solidification. The obtained relations describing the coarsening process as a function of local solidification time and fraction austenite are compared to results obtained from interrupted solidification experiments. By using the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHyd IP) become possible to characterize the coarseness of a wide range of lamellar cast irons solidified under various cooling rates.
|
|
| 24. |
|
|
| 25. |
- Froitzheim, Jan, 1981, et al.
(author)
-
Nanocoatings for SOFC interconnects - Mitigating chromium volatilization and improving corrosion properties
- 2011
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783037852354 ; 696, s. 412-416
-
Conference paper (peer-reviewed)abstract
- Two important degradation mechanisms in Solid Oxide Fuel Cells (SOFC) are directly related to the metallic interconnects. The formation of volatile chromium oxides from metallic interconnects commonly causes fast degradation in cell performance due to poisoning the cathode. Secondly is the ability of the metallic interconnect to form a thin protective oxide one of the most important lifetime limiting factors for SOFC. Chromium volatilization of various uncoated steels is studied as a function of temperature by a recently developed denuder technique which allows time resolved quantification of volatile chromium species. The inhibition of Cr evaporation by Co thin film coatings (800nm) is investigated; it will be shown that these coatings are more effective than much thicker ceramic coatings that are commonly used for this purpose. In order to increase the lifetime of the metallic components in SOFC nano-coatings of reactive elements (RE) have been investigated as well. The application of such coatings can reduce the corrosion rates substantially and thus increase the lifetime of the fuel cell stack. It will be shown that it is possible to combine the positive effects of RE with the beneficial effects of a Co coating and thus to obtain an interconnect material with low Cr evaporation and increased oxidation resistance.
|
|
| 26. |
- Fu, X. L., et al.
(author)
-
Processing and properties of amorphous magnesium-based eco-materials
- 2011
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 695, s. 186-189
-
Journal article (peer-reviewed)abstract
- Magnesium alloys are the lightest known structural material and have been very attractive for usage in marine and transportation industry (for its weight savings and payload increase), and also for its portability in hand-held devices. It is recyclable and one of the most abundant metal. Lately, it has gained attention for its biocompatibility, and also its biodegradable properties depending on the alloying elements. They can be used as a biomaterial in various applications from heart stents to implant screws and fixtures. In this work, amorphous magnesium alloys have been processed, based on its glass forming ability, by various techniques in order to obtain its amorphous state, and the microstructure are characterized by thermal analysis, X-ray diffraction and electron microscopy. Their mechanical properties are also presented. High temperature tensile tests show similar strength to room temperature strength, while the total failure strain is significantly increased from around 0.5% to 10%.
|
|
| 27. |
- Ghandi, Reza, et al.
(author)
-
Experimental evaluation of different passivation layers on the performance of 3kV 4H-SiC BJTs
- 2010
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 645-648:Part 1-2, s. 661-664
-
Journal article (peer-reviewed)abstract
- In this work, the electrical performance in terms of maximum current gain, ON-resistance and blocking capability has been compared for 4H-SiC BJTs passivated with different surface passivation layers. Variation in BJT performance has been correlated to densities of interface traps and fixed oxide charge, as evaluated through MOS capacitors. Six different methods were used to fabricate SiO2 surface passivation on BJT samples from the same wafer. The highest current gain was obtained for PECVD deposited SiO2 which was annealed in N2O ambient at 1100 degrees C during 3 hours. Variations in breakdown voltage for different surface passivations were also found, and this is attributed to differences in fixed oxide charge that can affect the optimum dose of the high voltage JTE termination.
|
|
| 28. |
- Ghandi, Reza, et al.
(author)
-
High Voltage, Low On-resistance 4H-SiC BJTs with Improved Junction Termination Extension
- 2011
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 706-709
-
Journal article (peer-reviewed)abstract
- In this work, implantation-free 4H-SiC bipolar transistors with two-zone etched-JTE and improved surface passivation are fabricated. This design provides a stable open-base breakdown voltage of 2.8 kV which is about 75% of the parallel plane breakdown voltage. The small area devices shows a maximum dc current gain of 55 at Ic=0.33 A (J(C)=825 A/cm(2)) and V-CESAT = 1.05 V at Ic = 0.107 A that corresponds to a low ON-resistance of 4 m Omega.cm(2). The large area device shows a maximum dc current gain of 52 at Ic = 9.36 A (J(C)=312 A/cm(2)) and V-CESAT = 1.14 V at Ic = 5 A that corresponds to an ON-resistance of 6.8 m Omega.cm(2). Also these devices demonstrate a negative temperature coefficient of the current gain (beta=26 at 200 degrees C) and positive temperature coefficient of the ON-resistance (R-ON = 10.2 m Omega.cm(2)).
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
- Hermannsson, P.G., et al.
(author)
-
Sodium enhanced oxidation: Absence of shallow interface traps after removal of sodium ions from the SiO2/4H-SiC interface
- 2013
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 740-742, s. 749-752
-
Conference paper (peer-reviewed)abstract
- We investigate the strong passivation of shallow interface traps located near the SiC conduction band after enhanced oxidation of Si-face 4H-SiC in the presence of sodium. We find that removing the sodium ions present at the SiO2/SiC interface since oxidation by way of bias stress or annealing does not lead to a significant increase in the density of interface traps. The presence of sodium ions at the SiO2/SiC interface is therefore not responsible for the passivation of such interface traps in oxides formed by sodium enhanced oxidation.
|
|
| 32. |
- Hryha, Eduard, 1980, et al.
(author)
-
Microstructure Development in Powder Metallurgy Steels: Effect of Alloying Elements and Process Variables
- 2014
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 782, s. 467-472
-
Conference paper (peer-reviewed)abstract
- Microstructure of the powder metallurgy (PM) steels and especially mechanism of its formation differs significantly from the microstructure of the conventional steels even if composition will be exactly the same. The difference is not only connected to the presence of the pores, which are inalienable feature of the PM parts. Presence of the prior inter-particle boundaries, which can be contaminated by residual oxides, as well as microstructure heterogeneity are another characteristic features of the microstructure of PM steels. Microstructure heterogeneity is connected to the PM manufacturing process: powder mix, consisting of the base powder and additional alloying elements is compacted and then sintered. Fully prealloyed powder is not always possible to use in standard press & sintering route due to the solid solution strengthening of the ferrite resulting in bad powder compressibility. Hence, in order to provide good powder compressibility only pure iron or low-alloyed (typically
|
|
| 33. |
- Jokubavicius, Valdas, et al.
(author)
-
Geometrical Control of 3C and 6H-SiC Nucleation on Low Off-Axis Substrates
- 2011
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 679-680, s. 103-106
-
Journal article (peer-reviewed)abstract
- Growth of 3C or 6H-SiC epilayers on low off-axis 6H-SiC substrates can be mastered by changing the size of the on axis plane formed by long terraces in the epilayer using geometrical control. The desired polytype can be selected in thick (~200 µm) layers of both 6H-SiC and 3C-SiC polytypes on substrates with off-orientation as low as 1.4 and 2 degrees. The resultant crystal quality of the 3C and the 6H-SiC epilayers, grown under the same process parameters, deteriorates when lowering the off-orientation of the substrate.
|
|
| 34. |
- Jokubavicius, Valdas, et al.
(author)
-
Morphological and Optical Stability in Growth of Fluorescent SiC on Low Off-Axis Substrates
- 2013
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 740-742, s. 19-22
-
Journal article (peer-reviewed)abstract
- Fluorescent silicon carbide was grown using the fast sublimation growth process on low off-axis 6H-SiC substrates. In this case, the morphology of the epilayer and the incorporation of dopants are influenced by the Si/C ratio. Differently converted tantalum foils were introduced into the growth cell in order to change vapor phase stochiometry during the growth. Fluorescent SiC grown using fresh and fully converted tantalum foils contained morphological instabilities leading to lower room temperature photoluminescence intensity while an improved morphology and optical stability was achieved with partly converted tantalum foil. This work reflects the importance of considering the use of Ta foil in sublimation epitaxy regarding the morphological and optical stability in fluorescent silicon carbide.
|
|
| 35. |
- Kahrimanidis, Alexander, et al.
(author)
-
Formation of Multiple Twinned Structural Units in Electrodeposited Nickel after Annealing
- 2014
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783038350736 ; 783-786, s. 2573-2578
-
Conference paper (peer-reviewed)abstract
- Electrodeposition is an advanced synthesis technique which involves the creation of acoating or free-standing material through an electrolytic process. Organic additives such assaccharin have been frequently used in electroplating operations to moderate deposit growth ratesand to control film quality. In the present study, plating of Nickel without additives has resulted in asub-microcrystalline microstructure and a -fibre texture in growth direction. Structural unitsin form of groups of grains possessing a common -zone axis in growth direction and low-Sigmarelationships between them have been found in the microstructure by use of EBSD. Uponannealing, grain growth sets in. However, the structural units and the texture are preserved up to550°C. This means that the structural units stabilize the microstructure; there is no orientationchange when grain growth occurs (e.g. by twinning). The low-Sigma boundaries of the structural unitsare described in detail and texture development upon annealing is discussed in connection withresults from previous studies on Ni and Ni-alloys of different initial texture.
|
|
| 36. |
- Kang, M. -S, et al.
(author)
-
Metal work-function and doping-concentration dependent barrier height of Ni-contacts to 4H-SiC with metal-embedded nano-particles
- 2012
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783037854198 ; 717-720, s. 857-860
-
Journal article (peer-reviewed)abstract
- We investigated the effect of the metal work-function and doping concentration on the barrier height of Ni-contacts with embedded nano-particles (NPs) on 4H-SiC surfaces. Both n-type epitaxial layers with N-D=1x10(16) cm(-3), and layers doped by phosphorus implantation to a doping concentration of similar to 1x10(19) cm(-3) are used. The barrier height is reduced with increasing doping concentration and the silver (Ag) nano-particles (R similar to 18.5 nm) further enhance the local electric field of the electrical contacts to 4H-SiC in comparison to gold (Au) nano-particles (R similar to 20.2 nm). In the case of ion-implanted samples, the barrier height of the fabricated SiC diode structures with embedded Ag-NPs was significantly reduced by similar to 0.09 eV and similar to 0.25 eV compared to the samples with Au-NPs and the sample without NPs, respectively.
|
|
| 37. |
- Karlsson, Sofia, 1982, et al.
(author)
-
KCl-Induced High Temperature Corrosion of Austenitic Stainless Steel 304L – The Influence of SO2
- 2011
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 696, s. 224-229
-
Journal article (peer-reviewed)abstract
- The effect of SO2 on the oxidation of alloy 304L in O2+H2O and O2+H2O+KCl environment has been investigated at 600°C. Exposure time was 1-168 hours. The exposed samples were analyzed by SEM/EDX, XRD and IC. In dry O2, a protective and chromium-rich corundum-type oxide forms. In the presence of H2O(g), chromium is volatilized in the form of CrO2(OH)2(g). The corresponding chromium depletion of the protective oxide triggers a partial loss of protective properties resulting in the formation of oxide islands on the alloy grain centers. The oxide islands consist of an outward growing hematite layer and an inward growing FeCrNi spinel layer. By coating the samples with KCl the chromia depletion of the protective oxide dramatically increases due to the formation of K2CrO4. This leads to breakaway corrosion, a rapidly growing scale forming all over the surface. The resulting thick scale has a similar structure as the oxide islands formed in the absence of KCl. The addition of 300 ppm SO2 to the O2+H2O and O2+H2O+KCl environments results in a drastic reduction of corrosion rate. In O2+H2O environment the effect of SO2 is attributed to the formation of a thin sulphate film on the oxide surface that impedes chromium volatilization and decreases the rate of oxygen reduction on the oxide surface. In O2+H2O+KCl environment the corrosion mitigating effect of SO2 is mainly attributed to the rapid conversion of KCl to K2SO4. In contrast to KCl, K2SO4 does not deplete the protective oxide in chromium by forming K2CrO4. Keywords: Oxidation, Alkali, Breakaway Corrosion, 304L, Chromate, Sulphur
|
|
| 38. |
- Klement, Uta, 1962, et al.
(author)
-
Electrodeposited nanocrystalline Ni-Fe with banded structure
- 2012
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 706-709, s. 1618-1623
-
Conference paper (peer-reviewed)abstract
- The microstructure of a Ni–18 wt.% Fe electrodeposits having a banded structure isdescribed in detail. The aim is to investigate the influence of the banded structure on grain growthbehaviour and texture and to elucidate if there are other mechanisms operative in the stabilization ofnanocrystalline electrodeposits. Spectroscopy techniques have been used to characterize thevariations in alloy/impurity concentration perpendicular to the growth direction. The influence ofthese chemical variations on the microstructural evolution has been monitored by in-situ annealingtreatments in the TEM. Local texture of the annealed material has been determined by use of theelectron backscatter diffraction (EBSD) technique. SEM and TEM investigations have shown thatthe banded structure is not related to phase changes and that grain growth is not affected by thebanded structure, i.e. there is no preferred growth along bands. The first grown grains have , and orientations with the growth direction and upon further grain growth a fibre texture with respect to the growth direction of the electrodeposits is formed. The bandedstructure seems not to affect the general behaviour of nanocrystalline electrodeposits.
|
|
| 39. |
- Klement, Uta, 1962, et al.
(author)
-
Influence of additives on texture development of submicro- and nanocrystalline Nickel
- 2012
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 702-703, s. 928-931
-
Conference paper (peer-reviewed)abstract
- Organic additives such as saccharin have been frequently used in electroplatingoperations to moderate deposit growth rates and to control film quality. In this study, texturedevelopment upon annealing of pulse-electroplated Nickel produced without additives is analyzedby use of electron backscatter diffraction technique.Plating without additives results in a microstructure with slightly elongated grains and a fibre texture in growth direction and this texture is conserved upon annealing up to 600°C.Structural units in form of groups of elongated grains possessing a common zone axis ingrowth direction and twin relationships between themselves are found in the microstructure. Forrevealing the influence of additives, the observations are compared with results obtained for Ni andNi-Fe plated in the presence of additives where during abnormal grain growth the initial fibre texture changes to an energetically more favourable texture by twinning. The lack ofadditives is assumed to be responsible for the observed differences in texture and microstructuredevelopment.
|
|
| 40. |
- Klement, Uta, 1962, et al.
(author)
-
Texture of Electrodeposited Nanocrystalline Ni-Fe with banded structure
- 2012
-
In: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 702-703, s. 912-915
-
Conference paper (peer-reviewed)abstract
- Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Feelectrodeposit revealed the existence of a banded structure perpendicular to the growth direction. Toevaluate if the banded structure is affecting grain growth and texture development, EBSDorientation maps were obtained after annealing for 30 min at 300, 350, and 400°C. Grown grainswere found to be random in shape and no preferential sites for grain growth were observed. Thetexture of the grown grains is changing upon annealing and the final fibre texture parallel togrowth direction of the electrodeposit can be obtained from texture components found at lowerannealing temperatures when performing one or two consecutive twinning operations.
|
|
| 41. |
- Kobayashi, M., et al.
(author)
-
3C-SiC MOSFET with High Channel Mobility and CVD Gate Oxide
- 2011
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 679-680, s. 645-648
-
Journal article (peer-reviewed)abstract
- 3C-SiC MOSFET with 200 cm2/Vs channel mobility was fabricated. High performance device processes were adopted, including room temperature implantation with resist mask, polysilicon-metal gates, aluminium interconnects with titanium and titanium nitride and a specially developed activation anneal at 1600°C in Ar to get a smooth 3C-SiC surface and hence the expected high channel mobility. CVD deposited oxide with post oxidation annealing was investigated to reduce unwanted oxide charges and hence to get a better gate oxide integrity compared to thermally grown oxides. 3C-SiC MOSFETs with 600 V blocking voltage and 10 A drain current were fabricated using the improved processes described above. The MOSFETs assembled with TO-220 PKG indicated specific on-resistances of 5 to 7 mΩcm2.
|
|
| 42. |
- Koptyug, Andrey, 1956-, et al.
(author)
-
Additive Manufacturing for Medical and Biomedical Applications: Advances and Challenges
- 2014
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; , s. 1286-1291
-
Journal article (peer-reviewed)abstract
- Additive Manufacturing (AM) has solidly established itself not only in rapid prototyping but also in industrial manufacturing. Its success is mainly determined by a possibility of manufacturing components with extremely complex shapes with minimal material waste. Rapid development of AM technologies includes processes using unique new materials, which in some cases is very hard or impossible to process any other way. Along with traditional industrial applications AM methods are becoming quite successful in biomedical applications, in particular in implant and special tools manufacturing. Here the capacity of AM technologies in producing components with complex geometric shapes is often brought to extreme.Certain issues today are preventing the AM methods taking its deserved place in medical and biomedical applications. Present work reports on the advances in further developing of AM technology, as well as in related post-processing, necessary to address the challenges presented by biomedical applications. Particular examples used are from Electron Beam Melting (EBM), one of the methods from the AM family.
|
|
| 43. |
- Koptyug, Andrey, 1956-, et al.
(author)
-
Osteoblast Ingrowth into Titanium Scaffolds made by Electron Beam Melting
- 2014
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 783-786, s. 1292-1297
-
Journal article (peer-reviewed)abstract
- Present paper describes early findings from the study of Ti-6Al-4V scaffolds additively manufactured using electron beam melting (EBM®) technology and the influence of surface topography on the initial stages of cell acceptance. The surface topography of the components made by additive manufacturing (AM) processes including EBM® are often hard to control within the desired feature size range without post-processing. Two groups of experiments studying the behavior of human osteoblast-like cells (MG63) on samples with different surface roughness were carried out in vitro: Ti-6Al-4V samples only powder-blasted, and Ti-6Al-4V samples additionally electrochemically polished. The cell migration into powder-blasted Ti-6Al-4V 3D scaffolds with different shapes and dimensions of the lattice structures were studied.
|
|
| 44. |
- Kwasnicki, Pawel, et al.
(author)
-
Optical investigation of 3C-SiC hetero-epitaxial layers grown by sublimation epitaxy under gas atmosphere
- 2014
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 778-780, s. 243-246
-
Journal article (peer-reviewed)abstract
- We investigated three 3C-SiC samples grown on 6H SiC substrate by sublimation epitaxy under gas atmosphere. We focus on the low temperature photoluminescence and Raman measurements to show that compare to a growth process under vacuum atmosphere, the gas atmosphere favor the incorporation of impurities at already existing and/or newly created defect sites.
|
|
| 45. |
- Lanni, Luigia, et al.
(author)
-
Bipolar integrated OR-NOR gate in 4H-SiC
- 2012
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783037854198 ; 717-720, s. 1257-1260
-
Journal article (peer-reviewed)abstract
- An integrated bipolar OR-NOR gate based on emitter coupled logic (ECL) is demonstrated in 4H-SiC. Operated from 27 up to 300 °C on -15 V supply voltage the logic gate exhibits stable noise margins (NMs) of about 1 V in the entire temperature range, and high and low output voltage levels that move towards positive voltages when the temperature increases: from -3 up to -2.7 V and from -5.4 up to -5.1 V respectively. In the same temperature range transistor current gain (β) goes from 46 down to 21.
|
|
| 46. |
- Lanni, Luigia, et al.
(author)
-
High-temperature characterization of 4H-SiC darlington transistors for low voltage applications
- 2013
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783037856246 ; 740-742, s. 966-969
-
Journal article (peer-reviewed)abstract
- 4H-SiC bipolar Darlington transistors (D-BJTs) for low voltage applications have been fabricated, simulated and characterized up to 300 °C, where they exhibit a current gain of 460. The influence on D-BJT current gain of relative current capability of driver and output BJTs has been investigated, and the collector resistance has been identified as the main limitation for the D-BJTs.
|
|
| 47. |
|
|
| 48. |
- Lanni, Luigia, et al.
(author)
-
SiC Etching and Sacrificial Oxidation Effects on the Performance of 4H-SiC BJTs
- 2014
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783038350101 ; 778-780, s. 1005-1008
-
Journal article (peer-reviewed)abstract
- Performance of 4H-SiC BJTs fabricated on a single 100mm wafer with different SiC etching and sacrificial oxidation procedures is compared in terms of peak current gain in relation to base intrinsic sheet resistance. The best performance was achieved when device mesas were defined by inductively coupled plasma etching and a dry sacrificial oxide was grown at 1100 °C.
|
|
| 49. |
- Lee, J. -H, et al.
(author)
-
Local anodic oxidation of phosphorus-implanted 4H-SiC by atomic force microscopy
- 2012
-
In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783037854198 ; 717-720, s. 905-908
-
Journal article (peer-reviewed)abstract
- In this work, local oxidation behavior in phosphorus ion-implanted 4H-SiC has been investigated by using atomic force microscopy (AFM). The AFM-local oxidation (LO) has been performed on the implanted samples, with and without activation anneal, using varying applied bias (15/20/25 V). It has been clearly shown that the post-implantation annealing process at 1650 °C has a great impact on the local oxidation rate by electrically activating the dopants and by modulating the surface roughness. In addition, the composition of resulting oxides changes depending on the doping level of SiC surfaces.
|
|
| 50. |
|
|
