Newly developed two-dimensional (2D) materials such as graphene — which consists of a single layer of carbon atoms — 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 the inability to measure how temperature will affect these new materials, collectively known as transition metal dichalcogenides (TMDs).
Using scanning transmission electron microscopy combined with spectros-copy, a new technique measures the temperature of several 2D materials at the atomic level, paving the way for much smaller and faster microprocessors. The technique also measures how the materials would expand when heated.
Microprocessor chips in computers and other electronics get very hot; researchers must be able to measure not only how hot they can get, but how much the material will expand when heated. 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, rendering the chip useless.
Traditional ways to measure temperature do not work on tiny flakes of 2D materials that would be used in microprocessors because they are too small. Optical temperature measurements, which use a reflected laser light to measure temperature, cannot be used on TMD chips because they don’t have enough surface area to accommodate the laser beam. A method was devised to take temperature measurements of TMDs at the atomic level using scanning transition electron microscopy, which uses a beam of electrons transmitted through a specimen to form an image.
Using this technique, the vibration of atoms and electrons — which is essentially the temperature of a single atom in a 2D material — can be measured. 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 vibration gets higher. At absolute zero — the lowest theoretical temperature — all atomic motion stops.
Microscopic flakes of various TMDs were heated inside the chamber of a scanning transmission electron microscope to different temperatures, and the microscope’s electron beam was then aimed at the material. Using a technique called electron energy-loss spectroscopy, researchers measured the scattering of electrons off the 2D materials caused by the electron beam. The scattering patterns were entered into a computer model that translated them into measurements of the vibrations of the atoms in the material — the temperature of the material at the atomic level.
The technique can also be used to predict how much materials will expand when heated and contract when cooled, which will help engineers 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.