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Thermal Transport in a 2D Amorphous Material

Yuxi Wang1,2,*, Nianjie Liang1,2,*, Xingxing Zhang3,*, Wujuan Yan1,2,*, Haiyu He1,2,*, Alfredo Fiorentino4, Xinwei Tao3, Ang Li5, Fuwei Yang6 et al.

Buxuan Li7, Te-Huan Liu8, Jia Zhu9, Wu Zhou5, Wei Wang2,10, Stefano Baroni4, Lin Zhou3,†, and Bai Song1,2,‡

  • *These authors contributed equally to this work.
  • †Contact author: linzhou@sjtu.edu.cn
  • ‡Contact author: songbai@pku.edu.cn
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Phys. Rev. X 15, 031077 – Published 26 September, 2025

DOI: https://doi.org/10.1103/fjww-9pm3

Abstract

Two-dimensional (2D) crystals proved revolutionary soon after graphene was discovered in 2004. However, 2D amorphous materials down to a single layer of atoms only became accessible in 2020, and they remain largely unexplored. In particular, the thermophysical properties of amorphous materials are of great interest upon transition from 3D to 2D. Here, we probe and simulate thermal transport in monolayer amorphous carbon (MAC). An ultralow cross-plane thermal conductivity (κ) is measured for van der Waals stacked multilayers, which is comparable to that of randomly stacked graphene despite the extra disorder in MAC. This result reveals the predominant role of the weak interlayer interactions in 2D materials. Meanwhile, an unexpectedly high in-plane κ is obtained for freestanding monolayers, which is a few times higher than what is predicted by conventional wisdom for 3D amorphous carbon with a similar sp2 fraction. This observation is primarily attributed to the dimensionality-induced reduction of anharmonicity and the unique low-frequency out-of-plane vibrational modes in MAC. Amorphous materials at the 2D limit open up new avenues for understanding and manipulating heat at the atomic scale.

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Popular Summary

Glasses and other amorphous solids are critically important across countless industries and daily life, but their lack of crystal structure makes their thermal behavior difficult to predict. One major open question is how heat flows in such materials when they are reduced to a single atomic layer. Using a combination of experiments, atomistic simulations, and advanced theoretical modeling, we uncover surprising thermal transport properties in monolayer amorphous carbon (MAC), revealing that the transition from three dimensions to two produces dramatic changes in how heat moves.

For stacked layers of MAC, we find that heat transport across the layers is extremely low due to both structural disorder and weak interlayer van der Waals forces, which resist heat flow. In contrast, when we examine single freestanding MAC sheets, we discover unusually high in-plane thermal conductivity—several times greater than expected from traditional models of amorphous carbon. This enhancement comes from reduced anharmonic vibrations and unique low-frequency modes that emerge only in two dimensions.

These results show that 2D amorphous materials have thermal transport properties very different from their 3D counterparts. By uncovering the link between dimensionality, structure, and heat flow, our work points to new strategies for controlling heat at the atomic scale.

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Phys. Rev. X 15, 031077– Published 26 September, 2025
  • Received 14 March 2025
  • Revised 30 May 2025
  • Accepted 29 July 2025
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