Researchers develop new heat test of atomically thin material

Advanced materials, including two-dimensional or “atomic-thin” materials just a few atoms thick, are essential to the future of microelectronics technology. Now a team at Los Alamos National Laboratory has developed a way to directly measure the coefficient of thermal expansion of such materials, the rate at which the material expands as it heats up.

This insight can help address heat-related performance issues of materials involved in microelectronics, such as computer chips. The study was published in ACS Nano.

“It’s well understood that heating a material typically results in expansion of the atoms arranged in the material’s structure,” said Theresa Kucinski, scientist with the Nuclear Materials Science Group at Los Alamos. “But things get weird when the material is only one to a few atoms thick.”

Due to the thinness of two-dimensional materials, until now, the measurement of their thermal expansion could only be achieved indirectly or by using a support structure called a substrate. These limitations have resulted in large discrepancies in thermal expansion measurements.

Using four-dimensional scanning transmission electron microscopy in their experimental setup, paired with a non-circular electron beam and complex computational analysis, the team precisely determined the thermal expansion in the material.

Understanding heat in microelectronic materials

Microelectronics, including computer chips, are small-scale electronics that rely on semiconductor material, such as the tungsten diselenide on which the team experimented.

Given the advances in materials and architectures required by emerging microelectronic devices, and the heat generation that occurs in any such device, key characteristics such as the thermal expansion of two-dimensional component materials must be well understood.

The team grew tungsten diselenide using metal-organic chemical vapor deposition, a technique that uses heat to combine gases and leave a deposit of material just three atoms thick on a 2-inch-diameter glass surface.

The thin-film sample was heated to more than 1,000 degrees Fahrenheit while undergoing the 4D electron microscope experiment — whose tens of thousands of diffraction patterns produced a set of data that, when run through a computational analysis, statistically revealed the nature and extent of changes in the structure of the material.

Synthesis methods such as organic chemical vapor deposition of metals have a large degree of applicability for large-scale microelectronics fabrication. Because the devices generate heat that can lead to degradation, understanding the thermal behavior of two-dimensional materials fabricated by such techniques—and how it compares to the properties of similar materials in bulk—helps predict how they will to bring the material to real application settings under thermal loads.

“Our finding proves that the thermal expansion of two-dimensional tungsten diselenide is indeed more consistent with the thermal expansion we see in bulk materials,” said Michael Pettes, Center for Integrated Nanotechnologies scientist and corresponding author of the paper.

“This is promising as the value is similar to that of conventional materials used in existing integrated microelectronics semiconductors.”