Video Reveals Heat Movement At Nanoscale

Snapshot of thermal waves moving across a crystalline semiconducting material heated by a laser pulse. Photo by University of Minnesota

MINNEAPOLIS, April 16 (UPI) — For the first time, scientists have captured video of the movement of heat through material at the nanoscale.

Using an ultrafast electron microscope, scientists at the University of Minnesota were able to watch thermal conductivity at the speed of sound.

Whether engineers are building a bridge or designing a computer chip, understanding the movement of heat is vital. Now, scientists can begin to learn how atomic and nanoscale features in different materials affect the movement of heat.

Materials scientists are constantly working to better control the movement of heat, whether it’s to retain energy efficiency or prevent overheating. The latest findings — detailed in the journal Nature Communications — will surely help their cause.

To spark thermal movement, researchers hit crystalline semiconducting materials of tungsten diselenide and germanium with a quick laser pulse. The team of scientists then used a state-of-the-art electron microscope to capture videos slowed to a billionth of the normal speed recording speed.

The record-setting videos captured thermal details at a time scale measured in femtoseconds — one millionth of one billionth of a second.

Scientists were able to watch thermal waves move across the crystalline materials.

“As soon as we saw the waves, we knew it was an extremely exciting observation,” lead researcher David Flannigan, an assistant professor of chemical engineering and materials science at Minnesota, said in a news release. “Actually watching this process happen at the nanoscale is a dream come true.”

Researchers likened the thermal waves to the ripples that emanate from a stone thrown into a pond. The videos revealed photons oscillating outward from the laser pulse.

“In many applications, scientists and engineers want to understand thermal-energy motion, control it, collect it, and precisely guide it to do useful work or very quickly move it away from sensitive components,” Flannigan explained.

“Because the lengths and times are so small and so fast, it has been very difficult to understand in detail how this occurs in materials that have imperfections, as essentially all materials do,” he added.

“Literally watching this process happen would go a very long way in building our understanding, and now we can do just that.”


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