Undercooling of molten silicon

Abstract

Droplets of uncoated molten Si (0.4–0.8 mm diameter) have been undercooled 250 °C. Ge droplets of similar size have been undercooled 280 °C in a B2O3 flux. The observed nucleation onset temperatures of both Si and Ge droplets are at or below the predicted amorphous phase melting temperatures Ta1. The solidified structures were polycrystalline. The nucleation frequency I, calculated from the Si data (2×104/cm3 s at 240±20 °C undercooling), should be an upper limit of the homogeneous nucleation frequency of the crystal phase, since we did not establish that nucleation was homogeneous in our experiments. However, this limiting I for Si indicates that homogeneous nucleation of crystal would not become appreciable in laser pulsing experiments until the liquid Si is undercooled to well below Ta1.

Molecular simulations of solid-liquid interfacial tension of silicon

“…[4][5][6] Shao and Spaepen 3 processed pure Si drops about 1 mm in diameter surrounded by a SiO 2 -BaO -CaO flux and achieved a maximum undercooling of 350 K. This undercooling is much deeper than that ͑270 K͒ of the first undercooling experiment with quartz tubes. 7 Again, based on the classical theory of nucleation, the estimated ␥ sl ϳ 0.38 J / m 2 , slightly higher than 0.34 J / m 2 from the laser-melting measurement. Using electromagnetic levitation method, 4 Li and Herlach achieved the deepest bulk undercooling of 420 K in liquid Si ͑with the drop size of about 7 mm in diameter͒.…”

Undercooling and solidification of Al-50 at. pct Si Alloy by electromagnetic levitation

“…[21][22][23][24][25] They have shown a transition in growth mode and refinement of the grain structure beyond critical undercoolings. For Al-Si alloys, rapid-solidification experiments of the kind previously outlined have been used to infer correlations between the morphology of the primary silicon and the melt undercooling.…”

“…One reason for this is that we want to emphasize the solidification behavior of the primary silicon phase, which is known from the experiments on pure silicon to go through a growth-mechanism transition with undercooling. [21][22][23][24][25] The higher concentration of silicon in the Al-Si alloy ensures that the primary phase is silicon and that its growth is less influenced by the eutectic. [14,15,16] The second reason is from the consideration that a higher silicon concentration corresponds to a higher liquidus temperature (ϳ1340 K at 50 at.…”

Morphologies of silicon crystals solidified on a chill plate

“…More recently, research has focused on melt undercooling, crystal morphology, growth mechanisms, and metastable phase formation in undercooled melts, both for germanium [17][18][19][20][21][22][23][24] (which is isomorphous with silicon) and for silicon itself. [25][26][27][28][29] Deeply undercooled bulk melts of pure silicon have been obtained only in a few investigations using containerless processing techniques, which can reduce or eliminate contamination of the sample and heterogeneous nucleation on container walls. Containerless processing has been achieved by electromagnetic levitation, [26,27] electrostatic levitation, [28] and flux processing.…”