A group of scientists from Finland has conducted computer simulations that predict the existence of an atomically thin, free-standing 2D liquid phase.
Atomically thin two-dimensional liquid. Image credit: Pekka Koskinen.
2D materials were considered impossible until the discovery of graphene around ten years ago. However, they have been observed only in the solid phase, because the thermal atomic motion required for molten materials easily breaks the thin and fragile membrane.
Therefore, the possible existence of an atomically thin flat liquid was considered impossible.
Now, physicists at the University of Jyväskylä have conducted quantum molecular dynamics simulations that predict a liquid phase in atomically thin gold islands that patch small pores of graphene.
According to the simulations, gold atoms flow and change places in the plane, while the surrounding graphene template retains the planarity of liquid membrane.
“Here the role of graphene is similar to circular rings through which children blow soap bubbles,” said Dr Pekka Koskinen, lead author on the paper published in the journal Nanoscale.
“In general, the existence of a 2D liquid phase requires three conditions. First, the pore template itself has to remain stable at high temperatures, a condition easily met by graphene,” the scientists wrote in the paper.
“Second, edge interactions need to favor planar bonding and be robust enough to endure high temperatures. Our supplementary calculations showed that the gold-carbon interface has bending rigidity comparable to that of the 2D gold membrane, which is sufficient to retain the patch steady under gold diffusion.”
“Third, the membrane itself has to display 2D diffusion before out-of-plane fluctuations grow too large and initiate rupturing.”
Currently the flat liquid exists only in computers and is still waiting for experimental confirmation.
“Unfortunately, simulations suggest that the flat liquid is volatile,” Dr Koskinen said.
“In experiments the liquid membrane might burst too early, like a soap bubble that bursts before one gets a proper look at it.”
“But again, even graphene was previously considered too unstable to exist.”
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Pekka Koskinen & Topi Korhonen. Plenty of motion at the bottom: atomically thin liquid gold membrane. Nanoscale, published online May 04, 2015; doi: 10.1039/C5NR01849H
