Papers by Keyword: Boron

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Authors: Fujio Abe
Abstract: The effect of fine precipitates, excess dislocations and sub-boundary hardening on creep strain behavior in the transient region has been investigated for tempered martensitic 9%Cr steel at 600 and 650oC. The fine precipitates that form during tempering or during creep decrease the creep rate in the transient region, while excess dislocations produced by cold rolling promote the recovery of dislocations during creep, resulting in higher creep rates. The sub-boundary hardening is enhanced by fine precipitates along lath and block boundaries, which retards the onset of acceleration creep. The movement and annihilation process of dislocations in the transient region is controlled by not only the movement of dislocations in the matrix but also the absorption of dislocations at boundaries. The minimum creep rate is basically determined by the time to minimum creep rate.
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Authors: Guo Sheng Sun, Yong Mei Zhao, Liang Wang, Lei Wang, Wan Shun Zhao, Xing Fang Liu, Gang Ji, Yi Ping Zeng
Abstract: The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52×1020 cm-3 with Hall mobility of about 1 cm2/Vs and resistivity of 1.6~2.2×10-2 Wcm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Wcm for resistivity, 5.3×1018 cm-3 for hole carrier concentration, and 7 cm2/Vs for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.
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Authors: M. Ahmadian, M. Reid, Rian Dippenaar, Tara Chandra, David Wexler, Andrzej Calka
Abstract: The densification behavior of WC composites based on iron aluminide binder was investigated using laser scanning confocal mi¬croscopy (LSCM). Doped Fe60Al40 alloys with boron levels ranging from 0 to 0.1 wt% were used as the aluminide binders. The aluminide binders were prepared using controlled atmosphere ring grinding and then blended with WC powder. The composite powder compacted in an alumina crucible and held in a platinum holder in the confocal microscope. The temperature increased from ambient temperature up to 1500 °C under high purity argon. The presence of boron was found to facilitate compaction of the composites and improve the wetting between WC and FeAl binder during liquid phase sintering. Increasing the amount of boron in the binder resulted in the melting of binder at lower temperature and increasing of the compacting of the intermetallic tungsten carbide composites.
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Authors: T. Paskova, E. Valcheva, Ivan G. Ivanov, Rositza Yakimova, Susan Savage, Nils Nordell, Chris I. Harris
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Authors: S.S. Seyedmomeni, M. Naeimi, Majid Raz, J. Aghazadeh Mohandesi, F. Moztarzadeh
Abstract: Various kinds of bioactive materials are developed as bone substitutes. Bioactive materials may affect attachment, proliferation and differentiation of cells and the subsequent integration in a host tissue. In this research 21%CaO–5%P2O5–64%SiO2–5%ZnO-5%B2O3 and 16%CaO–5%P2O5–64%SiO2–5%ZnO-10%B2O3 bioactive glasses were successfully synthesized by the sol–gel technique. Then the prepared bioactive glasses were soaked into simulated body fluid. Then the prepared samples were characterized using X-ray diffraction (XRD) and Scanning electron microscopy (SEM). It was seen that addition of boron to the structure remarkably enhances the formation of hydroxyapatite on the surface of the bioactive glass and subsequently improves the bioactivity. The obtained results from SEM and XRD were in good agreement with each other. Besides, effect of boron on atomic arrangement of the prepared bioactive glass was studies and compared with previous researches. It was shown that by increasing the boron content, more crystalline domains would be observed.
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Authors: Margareta K. Linnarsson, J. Isberg, Adolf Schöner, Anders Hallén
Abstract: The boron diffusion in three kinds of group IV semiconductors: silicon, silicon carbide and synthetic diamond has been studied by secondary ion mass spectrometry. Ion implantation of 300 keV, 11B-ions to a dose of 21014 cm-2 has been performed. The samples are subsequently annealed at temperatures ranging from 800 to 1650 °C for 5 minutes up to 8 hours. In silicon and silicon carbide, the boron diffusion is attributed to a transient process and the level of out-diffusion is correlated to intrinsic carrier concentration. No transient, out-diffused, boron tail is revealed in diamond at these temperatures.
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Authors: Peter Deák, B. Aradi, Adam Gali, Uwe Gerstmann, Wolfgang J. Choyke
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Authors: Alexander Mattausch, M. Bockstedte, Oleg Pankratov
Abstract: We investigated the the interstitial configurations of the p-type dopants boron and aluminum and the n-type dopants nitrogen and phosphorus in 4H-SiC by an ab initio method. In particular, the energetics of these defects provides information on the dopant migration mechanisms. The transferability of the earlier results on the boron migration in 3C-SiC to the hexogonal polytype 4H-SiC is verified. Our calculations suggest that for the aluminum migration a kick-out mechanism prevails, whereas nitrogen and phosphorus diffuse via an interstitialcy mechanism.
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Authors: Alain Portavoce, Dominique Mangelinck, Roberto Simola, Rachid Daineche, Jean Bernardini
Abstract: Atom redistribution during crystallization of a B and P co-doped amorphous Si layer produced by Si and P chemical vapor co-deposition and B implantation has been investigated. The crystallization of the entire layer is quasi-instantaneous for annealing temperature greater than 650 °C. The crystallization rate is well reproduced by the Avrami-Johnson-Mehl-Kolmogorov model of transformation. The Avrami n is found equal to 4, which is corresponding to 3D bulk crystallization. Crystallization promotes a non-Fickian redistribution of B atoms, allowing for an abrupt interface between B-doped and B-undoped regions. After crystallization, B diffuses in the polycrystalline Si layer for concentrations lower than 1.5  1020 at cm3 via the type B kinetic regime. Crystallization has no significant (or detectable) influence on the P profile. For temperatures higher than 750 °C, P diffuses in the poly-Si layer towards the region of highest B concentration via the type B kinetic regime, leading to P uphill diffusion. This phenomenon can be simulated considering chemical interactions between B and P atoms in both grains and grain boundaries.
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