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Ludvig de Knoop, from Chalmers’ Department of Physics, placed a small piece of gold in an electron microscope. Observing it at the highest level of magnification and step-by-step increasing the electric field to extremely high levels he was to study how it influenced the gold atoms. When studying the atoms in the recordings from the microscope, he saw something exciting. The surface layers of gold atoms had actually melted, at room temperature.

- I was really stunned by the discovery. This is an extraordinary phenomenon, and it gives us new, foundational knowledge of gold, says Ludvig de Knoop.

What happened was that the gold atoms became excited. Under the influence of the electric field, they suddenly lost their ordered structure and released almost all their connections to each other. Upon further experimentation, the researchers also discovered that it was possible to switch between a solid and a molten structure.

The discovery of how gold atoms can lose their structure in this way is not just spectacular, but also groundbreaking scientifically. Ludvig de Knoop, together with the theoretician Mikael Juhani Kuisma and coworkers, have opened up new avenues in materials science. The results are now published in the journal Physical Review Materials. Thanks to theoretical calculations, the researchers are able to suggest why gold can melt at room temperature. Possibly, the surface melting can be seen as a so-called low-dimensional phase transition. In that case, the discovery is connected to the research field of topology, where pioneers David Thouless, Duncan Haldane and Michael Kosterlitz received the Nobel Prize in Physics 2016. With Mikael Juhani Kuisma in the lead, the researchers are now looking into that possibility. In any case, the ability to melt surface layers of gold in this manner enables various novel practical applications in the future.

- Because we can control and change the properties of the surface atom layers, it opens doors for different kinds of applications. For example, the technology could be used in different types of sensors, catalysts and transistors. There could also be opportunities for new concepts for contactless components, says Eva Olsson, Professor at the Department of Physics at Chalmers.

For now, those who want to melt gold without an electron microscope, a trip to the goldsmith is still a necessity.

Text:  Joshua Worth (joshua.worth@chalmers.se) and Mia Halleröd Palmgren (mia.hallerodpalmgren@chalmers.se)

For more information: 

• Postdoctoral Researcher Mikael Kuisma (Ä¢¹½Ö±²¥), mikael.j.kuisma@jyu.fi
• Postdoctoral researcher Ludvig de Knoop (Chalmers University of Technology, Sweden), +46 31 772 51 80, ludvig.deknoop@chalmers.se