In situ observation of melting and crystallization of Si on porous Si3N4 substrate that repels Si melt

•In-situ observation of melting and crystallization of Si on the substrate repelling Si melt was carried out.•At crystallization, ring-like pattern was observed on the surface of spherical Si melt. This pattern may be due to crystal growth at low supercooling.•Preparation of spherical Si crystals is possible using the Si melt-repellent substrate.

High temperature in situ observation of melting and crystallization of spherical Si droplets on a substrate with a porous surface was carried out for the first time using an original in situ observation apparatus. The contact angle between the Si melt and the substrate was measured to be 160°, with the Si melt forming spherical droplets on the substrate. During crystallization, a ring-like pattern was observed on the surface of the spherical Si melt droplets due to crystal growth at low levels of supercooling. The solidified spherical Si crystals consisted of single or twin grains. This demonstrates that high-quality spherical Si crystals can be prepared easily and stably by using a Si melt-repelling substrate.