The Viskanta Lecture

The thermal properties of layered materials (like graphene and MoS2) are an active area of investigation, particularly due to their anisotropic and tunable thermal conductivity. We have studied their behavior as part of transistors [1,2], where self-heating is a major challenge for performance and reliability. For instance, the electron saturation velocity in MoS2 transistors is about 2x higher when self-heating is removed [3,4]. For monolayer materials, we have used molecular dynamics (MD) to understand their thermal conductivity in the presence of a substrate, finding that it is always lower than that of a suspended film [5,6]. For multilayer materials, our experiments have found evidence of very long cross-plane phonon mean free paths, ~200 nm at room temperature in MoS2 [7]. Cross-plane heat flow of MoS2 can be tuned in real time by the reversible intercalation of Li, creating the equivalent of a thermal transistor [8]. We have also realized extremely good thermal insulators by layering heterogeneous monolayers (e.g. graphene, MoSe2, WSe2, MoS2), achieving effective cross-plane thermal conductivities approximately 3-times lower than air [9]. A similar concept can be used with layered superlattices as the active material in phase change memory, enabling ultralow power operation [10]. I will also describe how some of our findings apply to electronic systems, where anisotropic materials like h-BN could play a role as heat spreaders [11]. These results broaden our understanding of heat flow in layered materials, and help us explore their applications for thermal management in electronics.

Prof. Eric Pop is the Pease-Ye Professor of Electrical Engineering (EE) and Materials Science & Engineering (by courtesy) at Stanford, where he leads the SystemX Heterogeneous Integration focus area. His research interests include nanoelectronics, data storage, and energy. Before Stanford, he spent several years on the faculty of UIUC, and in industry at Intel and IBM. He received his PhD in EE from Stanford (2005) and three degrees from MIT in EE and Physics. His honors include the Intel Outstanding Researcher Award, the PECASE from the White House, and Young Investigator Awards from the Navy, Air Force, DARPA, and NSF CAREER. He is an APS and IEEE Fellow, an Editor of 2D Materials, and a Clarivate Highly Cited Researcher. In his spare time he enjoys snowboarding and tennis, and in a past life he was a college radio DJ at KZSU 90.1. More information about the Pop Lab is available at http://poplab.stanford.edu and on Twitter @profericpop.

Department of Mechanical Engineering

1. E. Yalon et al., Nano Lett. 17, 3429 (2017)
2. S. Islam et al., IEEE EDL 34, 166 (2013)
3. K. Smithe et al., Nano Lett. 18, 4516 (2018)
4. J. Nathawat et al., Phys. Rev. Mater. 4, 014002 (2020)
5. A. Gabourie et al., 2D Mater. 8, 011001 (2021)
6. A. Gabourie et al., J. Appl. Phys. 131, 195103 (2022)
7. A. Sood et al., Nano Lett. 19, 2434 (2019)
8. A. Sood et al., Nature Comm. 9, 4510 (2018)
9. S. Vaziri et al., Science Adv. 5, eaax1325 (2019)
10. A. Khan et al., Science 373, 1243 (2021)
11. C. Koroglu & E. Pop, IEEE EDL 44, 496 (2023)

Researchers should cite this work as follows:

• Eric Pop (2024), "Thermal Transport in Layered Materials, Devices, and Systems," https://nanohub.org/resources/38829.

  BibTex | EndNote

1. 2D materials and devices
2. 3D heterogeneous integration
3. graphene
4. heterogeneous integration & advanced packaging
5. layered materials
6. materials science
7. molecular dynamics (MD)
8. MOS
9. MoS2
10. SCALE@Purdue
11. SCALE (Scalable Asymmetric Lifecycle Engagement)
12. thermal properties
13. transistors