
Optical image of a recrystallized sapphire surface.
Using a CO2 heating laser, substrates for thin-film growth can be heated to very high temperatures. The laser can easily melt sapphire (Al2O3), which happens at a temperature of 2040 °C. After sustaining a small ‘melt pool’ on the sample surface for about 15 minutes, the laser was switched off abruptly. This rapidly freezes the molten surface, yielding a variety of objects in many shapes and sizes. In this particular image, spherical drops surround a mesa-type structure, reminiscent of a single-cell biological organism on the verge of dividing, given the two cores. The shapes and sizes of such structures are dictated by the balance of surface energies in a solid-state crystal.

Sapphire Hanoi towers:
Optical image of a recrystallized sapphire surface.
Using a CO2 heating laser, substrates for thin-film growth can be heated to very high temperatures. The laser can easily melt sapphire (Al2O3), which happens at a temperature of 2040 °C. After sustaining a small ‘melt pool’ on the sample surface for about 15 minutes, the laser was switched off abruptly. This rapidly freezes the molten surface, yielding a variety of objects in many shapes and sizes. In this particular image, stacks of disks have emerged, reminiscent of the disk-stacking puzzle of the ‘Hanoi towers’ (inset). The shapes and sizes of such structures are dictated by the balance of surface energies in a solid-state crystal.

Sapphire rice fields:
Optical image of a recrystallized sapphire surface.
Using a CO2 heating laser, substrates for thin-film growth can be heated to very high temperatures. The laser can easily melt sapphire (Al2O3), which happens at a temperature of 2040 °C. After sustaining a small ‘melt pool’ on the sample surface for about 15 minutes, the laser was switched off abruptly. This rapidly freezes the molten surface, yielding a variety of objects in many shapes and sizes. In this particular image, spherical drops are spread out on a landscape of flat terraces with curvy edges. One can imagine these as microscopic versions of the rice-growing fields, commonly observed in the hills of Southeast Asia. The shapes and sizes of such structures are dictated by the balance of surface energies in a solid-state crystal.
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Bottom: Optical microscopy images of a chip containing 16 FETs.


HAADF STEM image of a SrRuO3 quantum dot with the size of 30 nm grown on (100) SrTiO3.

AFM micrograph of epitaxially-grown SrRuO3 nanodot arrays on SrTiO3. Atomic terraces of the substrate are visible. The width of the terrace is ≈ 250 nm.
