The phase relation between supercooled liquid silicon (l-Si) and amorphous silicon (a-Si) is discussed based on experimental results. Electrostatically levitated l-Si samples were supercooled down to low temperatures, 300 K below the melting temperature (Tcl: 1683 K), and solidified accompanied by the release of latent heat. It was found that solidified Si samples melted again at 1480 K caused by the latent heat. Also, it was found that the Si samples that rapidly quenched near the solidification temperature contained a large amount of a-Si with tetrahedral coordination. These two findings show that the supercooled l-Si samples solidified into a-Si and a-Si melted, confirming the idea of a first-order phase transition between two metastable phases proposed by Turnbull et al. [Metall. Mater. Trans. A 29, 1825 (1998)].
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We performed Car–Parinello molecular dynamics simulations of l-Si at 1338, 1440, 1483, 1583, and 1787 K using the density data of l-Si measured with our electrostatic levitator. It should be noted that the amount of covalent bonds clearly increases between 1583 and 1440 K. The increase of the proportion of the covalent bonds is closely related to the appearance of the a-Si embryos. The details of the simulation will be published in another paper.
