Gold melts at room temperature

Researchers are observing completely new phenomena in the precious metal

In a strong electric field, the tip of this gold cone melts - at room temperature. Er Alexander Ericson
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Surprising discovery: researchers have for the first time succeeded in melting gold at room temperature through an intense electric field. The previously ordered atomic lattice at the tip of the tiny gold sample lost its order and thus made a phase transition. This melt on the atomic scale is reversible and could allow completely new applications, as the scientists emphasize.

Gold is not only regarded as the noblest of all metals, it is also something special chemically and physically. Because it refuses almost all chemical reactions, even after millennia still shows its unique splendor and has its origins in huge cosmic catastrophes. Moreover, how the terrestrial gold deposits originated is only partially clarified.

Melted top

Now researchers around Ludvig de Knoop from the Chalmers University of Technology in Sweden have discovered another peculiarity of gold - almost by accident. Actually, the scientists only wanted to observe what happens when a small, pointed-cone gold sample is exposed in electron microscopes of different electric fields. For this they gradually increased the field strength to extremely high values.

The surprising result: the gold layers at the top of the sample began to melt. The atoms lost their ordered structure and dissolved their connections with each other. "I was completely surprised by this discovery, " says de Knoop. "This is an extraordinary phenomenon and it gives us a whole new insight into the behavior of gold." It was the first time that such melting was observed at room temperature for gold.

Dissolved compounds

But what is behind it? Using molecular-dynamics computer models, the researchers tried to understand the strange happenings. These suggested that it must be a so-called low-dimensional phase transition. The excited by the electric field gold atoms change their state of aggregation - the top atomic layer of the probe tip loses its connection to their neighbors. display

"The simulations reveal that the mechanism behind this structural change can be attributed to the energy cost of surface defects disappearing in strong electric fields, " explain de Knoop and his colleagues. In simpler terms, it is more favorable for the gold atoms to give up their ordered lattice formation and become disorderly melts under these conditions.

All new applications

Not only is this astonishing and reversible reaction of gold to electric fields unusual, it could enable entirely new practical applications. "It could be used in a variety of sensors, catalysts and transistors, " says co-author Eva Olsson of the TU Chalmers. But also in nanotechnology and nanophotonics, this localized and controlled phase transition of gold could be useful.

First, however, the scientists want to first find out more exactly what is going on at the atomic level in gold and whether their simulations correctly reproduce the event. (Physical Review Materials, 2018; doi: 10.1103 / PhysRevMaterials .2.085006)

(Chalmers University of Technology, 21.11.2018 - NPO)