Fragmentation of faceted dendrite in solidification of undercooled B-doped Si melts

Nagashio, Kosuke; Okamoto, Hideki; Kuribayashi, Kazuhiko; Jimbo, Itaru

doi:10.1007/s11661-005-0014-6

Cited by 14 publications

(11 citation statements)

References 21 publications

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“…As solidification proceeds in the confined droplet, both mechanisms for instability will lose magnitude. Indeed, the release of latent heat from partial solidification can lead to the temperature in the liquid increasing close to the melting point of the alloy-a phenomenon known as recalescence (27,28)-by definition reducing thermal undercooling. Second, because of the finite volume, rejection of germanium from the solid gradually decreases the silicon content in the liquid region, which is expected to suppress constitutional supercooling by effectively increasing the critical velocity (29).…”

Section: Resultsmentioning

confidence: 99%

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Gumennik

Levy

Grena

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Crystallization of microdroplets of molten alloys could, in principle, present a number of possible morphological outcomes, depending on the symmetry of the propagating solidification front and its velocity, such as axial or spherically symmetric species segregation. However, because of thermal or constitutional supercooling, resulting droplets often only display dendritic morphologies. Here we report on the crystallization of alloyed droplets of controlled micrometer dimensions comprising silicon and germanium, leading to a number of surprising outcomes. We first produce an array of silicon−germanium particles embedded in silica, through capillary breakup of an alloy-core silica-cladding fiber. Heating and subsequent controlled cooling of individual particles with a two-wavelength laser setup allows us to realize two different morphologies, the first being a silicon−germanium compositionally segregated Janus particle oriented with respect to the illumination axis and the second being a sphere made of dendrites of germanium in silicon. Gigapascal-level compressive stresses are measured within pure silicon solidified in silica as a direct consequence of volume-constrained solidification of a material undergoing anomalous expansion. The ability to generate microspheres with controlled morphology and unusual stresses could pave the way toward advanced integrated in-fiber electronic or optoelectronic devices. multimaterial fibers | microparticles | confined solidification | silicon−germanium spheres | stressed silicon C ontrolling the microstructure or state of stress of microparticles and nanoparticles is often key to attaining the desired properties for a specific application (1-5); however, the ability to do so is strongly limited by the synthesis method. For instance, nonspherically symmetric distributions of inorganic materials are difficult to achieve from bottom-up approaches (4-7). Likewise, controlling the state of stress or strain of semiconductor particles is challenging in unconstrained nucleation-and-growth synthesis methods. However, Janus particles of silicon−germanium (SiGe) could potentially find applications as microswimmers or nanoswimmers owing to asymmetric absorption properties (8), as well as in infrared photodetectors or solar cells for increased infrared absorption (9). Stressed silicon particles, on the other hand, could be used for bandgap tunability in photonic or optoelectronic devices (10-12).In the past few years, thermally drawn multimaterial fibers have emerged as a unique platform for top-down scalable fabrication of microparticles to nanoparticles over a broad range of materials, through controlled in-fiber capillary breakup of the fiber components (13-15). In the case of polymers or chalcogenide glasses, structural control of the particle can be achieved by constructing complex cores at the preform level, which is later broken up in the fiber state to form structured particles (13). However, in the case of traditional semiconductor materials such as silicon and germanium, the same...

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Section: Resultsmentioning

confidence: 99%

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Gumennik

Levy

Grena

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…To estimate the kinetic effect for crystallization, the kinetic coefficient of a-Fe 2 Si 5 was compared with other materials. The kinetic coefficient of a-Fe 2 Si 5 is 0.00052 m s -1 K -1 , which was much smaller than 1.6 m s -1 K -1 for Ni with a cubic structure, [6] 0.4 m s -1 K -1 for Si with a diamond structure, [7] and 0.014 m s -1 K -1 for FeSi with a cubic structure. [8] It is well known that the growth velocity of a pure metal such as Ni is controlled by the dissipation rate of latent heat.…”

Section: Discussionmentioning

confidence: 80%

“…Figure 4 shows the relationship between the growth velocities of a-Fe 2 Si 5 measured from the HSV image and the dimensionless undercoolings. The data of Ni, [6] Si, [7] and FeSi [8] were also plotted for comparison. The solid line is the theoretical calculation based on the dendrite growth model [9] incorporating the kinetic undercooling.…”

Section: Experimental Methodsmentioning

confidence: 99%

Orientation Analysis of Hexagonal Dendrite Formed from an Undercooled Melt of α-Fe2Si5

Nozaki

Nagashio

Kuribayashi

2007

Metall Mater Trans A

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In order to elucidate the solidification process of anisotropic intermetallic compounds in the undercooled melt, the containerless solidification of a-Fe 2 Si 5 was conducted using an electromagnetic levitator with a high-speed video (HSV) recorder. With increased undercooling, the shape of the growing crystal drastically changed from a polyhedron-type crystal to a swordlike dendrite crystal. Notably, the swordlike crystal shows sixfold symmetry, despite the tetragonal structure of a-Fe 2 Si 5 . The growth velocity analysis based on the dendrite growth model suggests that the interfacial attachment kinetics dominantly controls the growth process. Moreover, based on the analysis of crystallographic orientation using an electron backscattering pattern (EBSP) apparatus, we propose that the sixfold symmetry resulted from the three different crystals growing into the 110 h i direction of the (111) plane of the metastable cubic phase of c-FeSi 2 .

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“…At region III, which corresponds to the undercooling larger than approximately 100 K in Ge and 200 K in Si, the growth kinetics is seen to be the linear in character. Figure 8 shows a micrograph of a section of Si solidified at DT = 292 K. 18 In this experiment, a small amount of boron was doped to accentuate the contrast of the interface of the initially formed dendrite. In this figure, cross-like morphologies show the fragments broken up from the initially formed dendrite due to the capillary force that acts on the interface.…”

Section: Discussionmentioning

confidence: 99%

“…The fourfold axial symmetry of the fragments indicates that the initial growth direction indicates formation of h100i dendrites. Nagashio et al 18 reported that in Si when the undercooling exceeds 100 K, fragmentation of dendrites occurs resulting in significant grain refinement with increase of undercooling until DT > 200 K when grain size becomes relatively constant. This effect is due to the cross-like fragments acting as a ''seed'' for new grains.…”

Section: Discussionmentioning

confidence: 99%

Rapid Crystallization of Levitated and Undercooled Semiconducting Material Melts

Ishibashi

Kuribayashi

Nagayama

2012

JOM

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Using a CO 2 laser-equipped electromagnetic levitator, we carried out the containerless crystallization of Si and Ge. From the point of interface morphologies, the relation between growth velocities and undercoolings was classified into three regions. In regions I and II, although the morphologies of growing crystals are different: plate-like needle crystals in region I and facetted dendrite at region II, the growth velocities in these two regions are fundamentally scaled by the thermal diffusivities and the temperature increase caused by the release of the latent heat. This result means that the growth velocity can be expressed by the product of the thermal diffusivity and the growth kinetics. An analysis of the dendrite morphologies revealed that the kinetics of crystal growth in regions I and II represent two-dimensional nucleation at the reentrant corner formed at the edge of the two parallel twins. In region III, thermal diffusion-controlled interface attachment kinetics control as described by a modified Wilson-Frenkel model.

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Fragmentation of faceted dendrite in solidification of undercooled B-doped Si melts

Cited by 14 publications

References 21 publications

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Orientation Analysis of Hexagonal Dendrite Formed from an Undercooled Melt of α-Fe2Si5

Rapid Crystallization of Levitated and Undercooled Semiconducting Material Melts

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