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Bongsoo Kim - One of the best experts on this subject based on the ideXlab platform.
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Truncated tetrahedron seed crystals initiating stereoaligned growth of FeSi nanowires.
ACS nano, 2012Co-Authors: Si In Kim, Hana Yoon, Kwanyong Seo, Youngdong Yoo, Sungyul Lee, Bongsoo KimAbstract:We have synthesized epitaxially grown freestanding FeSi nanowires (NWs) on an m-Al2O3 substrate by using a catalyst-free chemical vapor transport method. FeSi NW growth is initiated from FeSi nanocrystals, formed on a substrate in a characteristic shape with a specific orientation. Cross-section TEM analysis of seed crystals reveals the crystallographic structure and hidden geometry of the seeds. Close correlation of geometrical shapes and orientations of the observed nanocrystals with those of as-grown NWs indicates that directional growth of NWs is initiated from the epitaxially formed seed crystals. The diameter of NWs can be controlled by adjusting the composition of Si in a Si/C mixture. The epitaxial growth method for FeSi NWs via seed crystals could be employed to heteroepitaxial growth of other compound NWs.
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Truncated Tetrahedron Seed Crystals Initiating Stereoaligned Growth of FeSi
2012Co-Authors: Nanowires Kim, Hana Yoon, Kwanyong Seo, Youngdong Yoo, Sungyul Lee, Bongsoo KimAbstract:We have synthesized epitaxially grown freestanding FeSi nanowires (NWs) on an m-Al2O3 substrate by using a catalyst-free chemical vapor transport method. FeSi NW growth is initiated from FeSi nanocrystals, formed on a substrate in a characteristic shape with a specific orientation. Cross-section TEM analysis of seed crystals reveals the crystallographic structure and hidden geometry of the seeds.Closecorrelation of geometrical shapesand orientations of the observed nanocrystals with those of as-grown NWs indicates that directional growth of NWs is initiated from the epitaxially formed seed crystals. The diameter of NWs can be con
J.m.f. Ferreira - One of the best experts on this subject based on the ideXlab platform.
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Pressureless sintering of in-situ toughened Yb α-SiAlON ceramics by adding seed crystals prepared by combustion synthesis
Journal of Materials Science, 2006Co-Authors: Guanghua Liu, Kexin Chen, Heping Zhou, Xiaoshan Ning, C. Pereira, J.m.f. FerreiraAbstract:Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.
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Low-temperature preparation of in situ toughened Yb α-SiAlON ceramics by spark plasma sintering (SPS) with addition of combustion synthesized seed crystals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Guanghua Liu, Kexin Chen, Heping Zhou, C. Pereira, Junming Guo, J.m.f. FerreiraAbstract:Abstract By applying SPS technique, new Yb α-SiAlON ceramics in situ toughened by rod-like grains were prepared at a relatively low temperature of 1600 °C, with combustion synthesized seed crystals added. The effects of sintering temperature, heating rate, and the addition of seed crystals on the densification process, phase transformation, microstructure development, and mechanical properties of the samples were discussed in detail. The experimental results showed that Yb α-SiAlON ceramics could be almost fully densified quickly by SPS, and the fast heating rate was helpful to reduce the amount of intermediate phases. Higher sintering temperature and appropriate holding time were beneficial to the promotion of phase transformation and grain growth. It was also demonstrated that the added seed crystals played an important role in enhancing the phase transformation and facilitating the growth of rod-like grains. Being toughened by the rod-like grains via the mechanisms such as grain pull-out and debonding, the fracture toughness of as-sintered Yb α-SiAlON ceramics with additive seed crystals was remarkably improved.
S Porowski - One of the best experts on this subject based on the ideXlab platform.
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growth of gan mg crystals by high nitrogen pressure solution method in multi feed seed configuration
Journal of Crystal Growth, 2012Co-Authors: I Grzegory, M Bockowski, B Lucznik, J L Weyher, E Litwinstaszewska, L Konczewicz, B Sadovyi, P Nowakowski, S PorowskiAbstract:Abstract Crystallization of GaN by High Nitrogen Pressure Solution method in multi-feed–seed (MFS) configuration without intentional doping [1] results in: (1) Growth of strongly n-type crystals with free electron concentration increasing with growth temperature in ranges of 2–6×10 19 cm −3 and 1350–1430 °C, (2) stable growth on Ga-polar surface and unstable growth on N-polar surface, crystals slightly brown, (3) improvement of (0001) crystallographic planes curvature (flattening) with respect to bowing of these planes in the seed crystals. The addition of magnesium into the growth solution causes strong compensation of free electrons in the crystals. Therefore, highly resistive GaN crystals can be grown. In this work, the crystallization of Mg doped GaN on flat ∼1 in. seeds (substrates) grown by HVPE in MFS configuration has been studied. It is shown that: (1) Highly resistive GaN:Mg crystals with resistivity higher than 10 7 Ω cm were grown, (2) the growth is stable on N-polar surfaces of the seeds whereas it is unstable on the Ga-polar surfaces, which is opposite to the HNPS growth of the n-type crystals. The GaN:Mg crystals are fully transparent with no visible color, (3) shape of (0001) crystallographic planes improves (flattens) with respect to bowing of these planes in the seed crystals (HVPE substrates).
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multi feed seed mfs high pressure crystallization of 1 2 in gan
Journal of Crystal Growth, 2012Co-Authors: M Bockowski, I Grzegory, B Lucznik, E Litwinstaszewska, B Sadovyi, T Sochacki, G Nowak, P Strak, G Kamler, S PorowskiAbstract:Abstract The growth and physical properties of GaN crystallized in a multi feed-seed (MFS) configuration by High Nitrogen Pressure Solution (HNPS) growth method are presented in detail. The conversion of free standing HVPE-GaN crystals to free standing HNPS-GaN is the basis of the MFS configuration. The influence of the experimental conditions (i.e. growth temperature, temperature gradient, etc.), the c-plane bowing of the initial substrate, the electrical properties of HNPS-GaN, and the rate and mode of growth from solution are analyzed. We show that the HNPS-GaN crystals have better structural quality than their HVPE-GaN seeds. The defect density decreases with increasing growth temperature, reaching 5×10 5 cm −2 for crystals grown at 1420 °C or higher. In contrast, the free carrier concentration in HNPS-GaN increases with increasing growth temperature, reaching 7×10 19 cm −3 for samples crystallized at 1440 °C. Thus the possibility to obtain good quality plasmonic GaN substrates for laser diodes can be realized.
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Growth of GaN:Mg crystals by high nitrogen pressure solution method in multi-feed-seed configuration
Journal of Crystal Growth, 2012Co-Authors: I Grzegory, M Bockowski, B Lucznik, J L Weyher, L Konczewicz, B Sadovyi, P Nowakowski, Elzbieta Litwin-staszewska, S PorowskiAbstract:Crystallization of GaN by High Nitrogen Pressure Solution method in multi-feed-seed (MFS) configuration without intentional doping results in:(1) Growth of strongly n-type crystals with free electron concentration increasing with growth temperature in ranges of 2-6x1019 cm-3 and 1350-1430 °C, (2) stable growth on Ga-polar surface and unstable growth on N-pola rsurface ,crystals slightly brown, (3) improvement of (0001) crystallographic planes curvature (flattening) with respect to bowing oft hese planes in the seed crystals. The addition of magnesium into the growth solution causes strong compensation of freeelectrons in the crystals. Therefore, highly resistive GaN crystals can be grown. In this work, the crystallization of Mg doped GaN on flat 1 in. seeds (substrates) grown by HVPE in MFS configuration has been studied.
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high nitrogen pressure solution growth of bulk gan in feed seed configuration
Physica Status Solidi (a), 2011Co-Authors: M Bockowski, I Grzegory, E Litwinstaszewska, B łucznik, T Sochacki, M Kryśko, Pawel Strąk, Igor Dziecielewski, S PorowskiAbstract:In this paper the growth and physical properties of HNPS-GaN crystallized in "feed-seed" configuration is described. The idea of this configuration is based on the conversion of the free standing HVPE-GaN crystals to the free standing HNPS-GaN. The influence of the c-plane bowing in the initial substrate on quality, rate, and mode of growth from solution is analyzed.
I-wei Chen - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of α-SiAlON seed crystals
Journal of the American Ceramic Society, 2004Co-Authors: Misha Zenotchkine, Roman Shuba, Joo Sun Kim, I-wei ChenAbstract:Single-phase seed crystals of Ca- and Y-α-SiAlONs have been synthesized for tailoring microstructure of α-SiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for α-SiAlON seed preparation and morphology control are provided.
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Synthesis of alpha-SiAlON Seed Crystals
2001Co-Authors: Misha Zenotchkine, Roman Shuba, Joo Sun Kim, I-wei ChenAbstract:Single-phase seed crystals of Caand Y-α-SiAlONs have been synthesized for tailoring microstructure of αSiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for α-SiAlON seed preparation and morphology control are provided. Comments Copyright The American Ceramic Society. Reprinted from Journal of the American Ceramic Society, Volume 84, Issue 7, July 2001, pages 1651-1653. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/41 Synthesis of a-SiAlON Seed Crystals Misha Zenotchkine,* Roman Shuba,* Joo Sun Kim,* and I-Wei Chen* Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272 Single-phase seed crystals of Caand Y-a-SiAlONs have been synthesized for tailoring microstructure of a-SiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for a-SiAlON seed preparation and morphology control are provided.
Guanghua Liu - One of the best experts on this subject based on the ideXlab platform.
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Pressureless sintering of in-situ toughened Yb α-SiAlON ceramics by adding seed crystals prepared by combustion synthesis
Journal of Materials Science, 2006Co-Authors: Guanghua Liu, Kexin Chen, Heping Zhou, Xiaoshan Ning, C. Pereira, J.m.f. FerreiraAbstract:Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.
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Low-temperature preparation of in situ toughened Yb α-SiAlON ceramics by spark plasma sintering (SPS) with addition of combustion synthesized seed crystals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Guanghua Liu, Kexin Chen, Heping Zhou, C. Pereira, Junming Guo, J.m.f. FerreiraAbstract:Abstract By applying SPS technique, new Yb α-SiAlON ceramics in situ toughened by rod-like grains were prepared at a relatively low temperature of 1600 °C, with combustion synthesized seed crystals added. The effects of sintering temperature, heating rate, and the addition of seed crystals on the densification process, phase transformation, microstructure development, and mechanical properties of the samples were discussed in detail. The experimental results showed that Yb α-SiAlON ceramics could be almost fully densified quickly by SPS, and the fast heating rate was helpful to reduce the amount of intermediate phases. Higher sintering temperature and appropriate holding time were beneficial to the promotion of phase transformation and grain growth. It was also demonstrated that the added seed crystals played an important role in enhancing the phase transformation and facilitating the growth of rod-like grains. Being toughened by the rod-like grains via the mechanisms such as grain pull-out and debonding, the fracture toughness of as-sintered Yb α-SiAlON ceramics with additive seed crystals was remarkably improved.