Behavior of freezing water could open door to technological advances

Water is the basis of all life on earth. It also could be the key that unlocks radical improvements to everything from solar cells to nanotechnology.

In a paper published in Proceedings of the National Academy of SciencesAlexander Gumennik, an assistant professor of intelligent systems engineering at the School of Informatics and Computing, details how the properties of water freezing into ice inspired him to investigate whether the same thermodynamics of solidification would apply to a silicon-germanium material system. The Si-Ge material is ubiquitous in microelectronics, and by controlling how the substance solidifies after being melted by a laser, researchers can change the properties of the material.

“When translated into semiconductors, the various outcomes can create fascinating results,” Gumennik says.

For instance, quenching—or rapidly cooling—molten Si-Ge droplets inside a sealed glass fiber leads to a dendritic morphology, much like water freezing into a snowflake. The resulting material could be used to create more efficient solar cells. Slowly cooling the droplets, which creates spheres of material, induces compression to tens of thousands of atmospheres, potentially changing the band structure of the material. It also can lead to compositionally segregated Si-Ge Janus particles, which are useful for high-frequency microelectronic and nanorobotic applications.

Previous work by Gumennik, which saw him turn a continuous silicon core in a silica fiber into a periodic chain of distinct spheres by feeding it through a flame, much like water dripping out of a faucet, helped inspire his work with the Si-Ge material.

“I saw that solidifying silicon spheres resulting from such a breakup shatter the fiber if the silica cladding is not thick enough,” Gumennik says. “Literally, the sphere would break the fiber and shoot out like a small bullet. Then I recalled that, similarly to water freezing into ice, diamond cubic semiconductors expand upon solidification. That’s exactly the same effect that breaks a bottle of beer if it is accidentally left in the freezer too long.”

Gumennik’s paper, titled “Confined in-fiber solidification and structural control of silicon and silicon-germanium microparticles," illustrates how fluidic phenomena, which is highly nonlinear and chaotic, can be harnessed to produce solid state devices to be integrated into systems.

Although more research is needed, Gumennik is confident controlling the cooling conditions of an Si-Ge material has the potential to impact a number of applications.

“Properly engineered fluidic chaos can create solid order,” Gumennik says. “I’m not saying I’m defying the laws of thermodynamics or that I found a way to make the entropy, which is known to always grow, to suddenly decrease. I’m just saying that at very specific thermodynamic conditions, fluidic phenomena can be harnessed to self-assemble solid state devices.”

For more on Gumennik’s work, visit the PNAS website.