Extended Data Fig. 6: Demonstration of the controlled surface solidification process of a liquid EBiGa film.

a, Liquid EBiGa before solidification. b, Solidification triggered by touching the liquid metal surface with a Ga-crystal-coated tip. c, Solidification process during which the SSF propagates across the sample. d, Fully solidified sample. Scale bars: 2 mm. The EBiGa liquid metal sample was spread on a silicon substrate and kept at 25 °C. Due to such small supercooling ∆T (about 5 °C), the sample would not solidify automatically. A Ga-crystal-coated tip was then brought in touch with the liquid metal surface to overcome the nucleation barrier so that the solidification process could take place (Supplementary Video 5). The snapshots from the recorded video of the solidification process show that the solidification front propagates out from the ‘artificial’ nucleation site (the tip location), gradually covering the entire sample surface. The formation of the solidification front is supposed to be a result of localised nucleation at the alloy surface in the early stage of solidification. Of the two processes (nucleation and crystal growth) in solidification, the first process, nucleation is a statistic event. As discussed in our main text, the liquid metal surface favours nucleation. Once localised nucleation occurs on the surface, the growth of nuclei, which is faster in comparison to the nucleation process, creates a solidification front propagating outward from the nucleation sites on the surface.