Researchers at the University of Minnesota have recorded the movement of heat through materials at the nanoscale traveling at the speed of sound, using an ultrafast electron microscope.
The objective of the video recording is to figure out the roles played by individual atomic and nanoscale features to aid in the design of better and more efficient materials – with a wide array of uses such as in personal electronics and alternative energy technologies. This will also ultimately drive down the use of fossil fuels.
To image the movement of heat energy, the researchers used a cutting-edge FEI Tecnai Femto ultrafast electron microscope (UEM) capable of examining the dynamics of materials at the atomic and molecular scale over time spans measured in femtoseconds (one millionth of a billionth of a second).
A brief laser pulse was used to excite electrons and very rapidly heat crystalline semiconducting materials of tungsten diselenide and germanium. Then, very slow-motion videos – waves of energy moving at about 6 nanometers (0.000000006 meters) per picosecond (0.000000000001 second) – of the resulting waves of energy moving through the crystals was captured.
Lead researcher David Flannigan from the University of Minnesota said “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. 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. Literally watching this process happen would go a very long way in building our understanding, and now we can do just that.”
Heat energy is the largest form of waste energy in critical applications including power transmission. In case of transportation, roughly 70 percent of the energy in gasoline is wasted as heat in automobile engines. Mapping the oscillations of energy, called phonons, at the nanoscale is critical step in understanding of the fundamentals of thermal-energy motion.
Image Credits: University of Minnesota