Robert Klie, professor of physics at UIC. Photo: Jenny Fontaine.
Robert Klie, professor of physics at UIC. Photo: Jenny Fontaine.

Researchers at the University of Illinois at Chicago (UIC) have developed a new technique for precisely measuring the temperature and behavior of two-dimensional (2D) materials, which will allow engineers to design smaller and faster microprocessors. They report this technique in a paper in Physical Review Letters.

Newly developed 2D materials such as graphene and transition metal dichalcogenides (TMDs) have the potential to replace traditional microprocessing chips based on silicon, which have reached the limit of how small they can get. But engineers have been stymied by their inability to measure how changes in temperature will affect these 2D materials.

Using scanning transmission electron microscopy combined with spectroscopy, researchers at UIC have now been able to measure the temperature of several 2D materials at the atomic level, paving the way for much smaller and faster microprocessors. They were also able to use their technique to determine how the 2D materials would expand when heated and contract when cooled.

"Microprocessing chips in computers and other electronics get very hot, and we need to be able to measure not only how hot they can get, but how much the material will expand when heated," said Robert Klie, professor of physics at UIC and corresponding author of the paper. "Knowing how a material will expand is important because if a material expands too much, connections with other materials, such as metal wires, can break and the chip is useless."

Traditional ways to measure temperature don't work on the tiny flakes of 2D material that would be used in microprocessors, because they are just too small. Optical temperature measurements, which use reflected laser light to measure temperature, can't be used on TMD flakes, for example, because the flakes don't possess enough surface area to accommodate the laser beam.

"We need to understand how heat builds up and how it is transmitted at the interface between two materials in order to build efficient microprocessors that work," said Klie.

He and his colleagues devised a way to take temperature measurements of TMDs at the atomic level using scanning transition electron microscopy, which passes a beam of electrons through a specimen to form an image.

"Using this technique, we can zero in on and measure the vibration of atoms and electrons, which is essentially the temperature of a single atom in a 2D material," explained Klie. Temperature is a measure of the average kinetic energy of the random motions of the particles, or atoms, that make up a material. As a material gets hotter, the frequency of the atomic vibrations gets higher. At absolute zero, the lowest theoretical temperature, all atomic motion stops.

Klie and his colleagues heated microscopic ‘flakes’ of various TMDs inside the chamber of a scanning transmission electron microscope to different temperatures and then aimed the microscope's electron beam at the material. Using a technique called electron energy-loss spectroscopy, they were able to measure the scattering of electrons from the 2D materials. These scattering patterns were entered into a computer model that translated them into measurements of the vibrations of the atoms in the material – in other words, the temperature of the material at the atomic level.

"With this new technique, we can measure the temperature of a material with a resolution that is nearly 10 times better than conventional methods," said Klie. "With this new approach, we can design better electronic devices that will be less prone to overheating and consume less power."

The technique can also be used to predict how much 2D materials will expand when heated and contract when cooled. This will help engineers to build chips that are less prone to breaking at points where one material touches another, such as when a 2D material chip makes contact with a wire.

"No other method can measure this effect at the spatial resolution we report," said Klie. "This will allow engineers to design devices that can manage temperature changes between two different materials at the nano-scale level."

This story is adapted from material from the University of Illinois at Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.