Temperature-Dependent Phonon Dynamics in Two-Dimensional Materials

Two-dimensional (2D) materials such as graphene, transition-metal dichalcogenides and hexagonal boron nitride exhibit unique vibrational properties that govern their thermal and electronic behaviour. Phonons—quanta of lattice vibrations—mediate heat transport and influence electron–phonon interactions in ultrathin crystals. As temperature varies, phonon frequencies shift and lifetimes change due to anharmonic interactions, thermal expansion and substrate coupling. Nonlinear temperature dependence of optical phonon modes, observed by Raman spectroscopy, reveals the balance between three- and four-phonon processes and in-plane versus out-of-plane lattice dynamics. Substrate support can modify phonon scattering and introduce biaxial strain, while suspended films highlight intrinsic anharmonicity. Quantitative models incorporating thermal expansion coefficients and anharmonic decay pathways enable extraction of fundamental parameters such as Grüneisen parameters, thermal expansion coefficients and phonon scattering rates. Understanding these effects is critical for thermal management in nanoelectronics, the design of high-performance photonic devices and the optimisation of thermoelectric materials.

Research from Nature Portfolio

Recent studies have provided quantitative insights into the temperature evolution of optical phonons in atomically thin semiconductors. Investigations of monolayer WS₂ grown by chemical vapour deposition revealed pronounced nonlinear temperature shifts of the in-plane and out-of-plane Raman modes over 84–543 K. By fitting a physical model combining thermal expansion and three- and four-phonon anharmonic processes, the thermal expansion coefficients of the E′ and A₁′ phonon modes were extracted, along with distinct contributions of anharmonicity in low- and high-temperature regimes. Complementary work on few-layer MoS₂ compared suspended and substrate-supported films across 77–557 K. The study demonstrated that substrate-induced strain and thermal expansion coefficient mismatch lead to divergent temperature dependence of Raman shifts, including negative thermal expansion below ≈175 K. These measurements allowed determination of intrinsic expansion coefficients for varying layer numbers and highlighted the role of bending vibrations in ultrathin layers.

Temperature-Dependent Phonon Dynamics in Two-Dimensional Materials publication trend

The graph below shows the total number of articles in temperature-dependent phonon dynamics in two-dimensional materials across all publications each year (not limited to Nature Index journals).

Technical terms

Phonon: A quantised lattice vibration that carries thermal energy in crystalline solids.

Anharmonicity: Deviation from a perfectly harmonic potential in lattice vibrations, leading to phonon–phonon scattering.

Raman spectroscopy: An optical technique that measures inelastic scattering of light to probe vibrational modes.

Thermal expansion coefficient: A parameter describing the relative change in lattice dimensions with temperature.

References

1. Quantitative Analysis of Temperature Dependence of Raman shift of monolayer WS2. Scientific Reports (2016).
2. Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy. Scientific Reports (2021).
3. Temperature-dependent phonon dynamics of supported and suspended monolayer tungsten diselenide. AIP Advances (2019).
4. Temperature Dependence of Raman-Active In-Plane E2g Phonons in Layered Graphene and h-BN Flakes. Discover Nano (2018).
5. Phonon and Thermal Properties of Thin Films Made from WS2 Mono- and Few-Layer Flakes. The Journal of Physical Chemistry C (2021).