Lassonde researcher uncovers unique thermal properties in rhenium-based materials

Simone Pisana, an associate professor in the Electrical Engineering & Computer Science department at York University’s Lassonde School of Engineering, recently made a fascinating, yet unexpected, discovery concerning two unique layered crystals: rhenium disulfide and rhenium diselenide.

After examining thermal properties of the two materials using an optically-based method, beam offset frequency domain thermoreflectance (BO-FDTR), Professor Pisana and his graduate student, Sina Tahbaz found that both materials exhibit an extremely valuable property known as thermal conductivity anisotropy.

Materials demonstrating this behaviour conduct heat differently depending on the direction of flow. For example, when heat flows across one direction of the material surface, it can exhibit high thermal conductivity, but when heat flows in another direction it can demonstrate low thermal conductivity.

Thermal conductivity anisotropy is a highly sought-after quality for many material applications, specifically the development of thermoelectric devices, like thermoelectric generators, that can recover waste heat and turn it into usable electric power. These generators are used in various niche applications, including space missions like the Mars Curiosity and Perseverance rovers.

By dissipating heat in one direction and blocking heat in another, materials exhibiting thermal conductivity anisotropy can also be utilized to improve the cooling efficiency of electronic components like sensors and lasers.

“To improve thermoelectric devices, it is beneficial to have a material that is both a good electrical conductor and bad thermal conductor,” says Professor Pisana. “If we can figure out how to direct heat, we can help engineer materials that recover and reuse waste heat.”

Professor Pisana’s groundbreaking discovery regarding rhenium disulfide and rhenium diselenide has the potential to advance the future of thermoelectric devices. However, before these materials can be put to good use, Professor Pisana wants to find the fundamental explanation behind his experimental results.

“This discovery is only the beginning of our work,” says Professor Pisana. “We don’t really have a good explanation for the behaviour of these materials yet.”

Much of the surprise behind the experimental results concerns the size of the anisotropy measured. In the case of rhenium diselenide, the thermal conductivity was found to vary by a factor of four within the crystal’s layers – this level of anisotropy has never been observed before.

“This discovery has really made us wonder: ‘Why are these materials exhibiting this behaviour?’ ‘Are there other materials that act like this?’ and ‘How do we explain this?’”

Now, Professor Pisana and his graduate students are preparing for complex research ahead, working backwards from their experimental findings to establish an accurate scientific theory.

“Heat transport is very difficult to accurately model down to atomic dimensions. So, coming up with a theory behind the behaviour of these materials won’t be easy,” he says. “We are performing some computations with the help of Digital Research Alliance Canada to support our work. Even with advanced supercomputers it can take hours of computing for a small set of calculations. This project is going to require us to invest a lot of time and labour.”

This work is presented in the paper, Extreme in-plane thermal conductivity anisotropy in Rhenium-based dichalcogenides, and published in the scientific journal, Journal of Physics Materials, as part of a special emerging leaders initiative. Being classified among other leading researchers allowed Professor Pisana’s work to gain increased recognition among broad scientific communities.

Learn more about Professor Pisana’s research and his Heat Transport in Electronic Devices Lab.