Anisotropic in-plane lattice thermal conductivity in bilayer ReS2

TL;DR

This work addresses anisotropic in-plane heat transport in bilayer ReS2 and how stacking (AA vs AB) mediates this behavior. Using first-principles density functional theory and phonon Boltzmann transport equation calculations, it shows persistent in-plane anisotropy with κyy > κxx and only modest stacking-induced changes, while AB stacking exhibits stronger interlayer coupling and reduced phonon velocities and lifetimes. The study confirms dynamic stability for both stackings and reveals that weak interlayer coupling largely governs the layer-tolerant heat flow, with stacking offering a route to tailor thermal management in devices. Overall, the results highlight stacking-order-driven control of heat conduction in ReS2 and its potential for anisotropic thermal engineering in 2D electronics.

Abstract

The significantly weak interlayer coupling strength and puckered structure provide the novel layer-tolerant and anisotropic features in two-dimensional (2D) ReS2. These unique features offer an opportunity to modulate the optoelectronic, vibrational, and transport properties along different lattice directions in ReS2. Here, using first-principles density functional theory (DFT), we investigated the thermal transport properties of ReS2 in AA and AB stacking orders. The anisotopic ratios for lattice thermal conductivities (\k{appa}) are found to be 1.08 and 1.12 for AA and AB stacking, respectively. This anisotropic nature remains intact even at higher temperatures up to 1000K, demonstrating anisotropic robustness. Lower symmetry in AB stacking leads to higher phonon scattering, which results in lower group velocity, smaller phonon lifetime, and thereby lower \k{appa} along both directions as compared to AA stacking. The strong breathing and shear Raman modes in AB stacking indicate stronger layer coupling, further confirming the dominant contribution of acoustic modes towards thermal transport. The findings underscore that the stacking-order-driven preferential heat flow in ReS2 and opens up a new dimension for optimizing device performance.

Figures (7)

• Figure 1: Structure of ReS$_{2}$ in (a) AA stacking and (b) AB stacking. Yellow and green circles represent Re and S atoms, respectively. The dashed line shows the unit cell of the respective stacking. (c)-(d) Simulated STM images of the corresponding AA and AB stacking arrangements. The bottom layer is denoted by the color red, while the upper layer is blue. The green dashed circles denote the luminous dots in crystal structures and STM images. These dots result from the nearly overlapping atoms of two layers. (e) Phonon dispersion and corresponding atom-projected phonon density of states of AA and AB stacking order. Red and blue dashed lines represent the phonon frequencies present in AA and AB stacking along the high-symmetry directions.
• Figure 2: The evolution of energy with time under the NVT ensemble with 500 and 700 K temperatures and corresponding final snapshots (right panel) (a) AA stacking and (b) AB stacking ReS$_2$ using AIMD simulation.
• Figure 3: Lattice thermal conductivity of ReS$_{2}$ in (a) AA stacking, (b) AB stacking, and (c) monolayer along the in-plane directions. Circle and diamond represent the lattice thermal conductivity values along and x and y-directions, respectively.
• Figure 4: (a) Comparison lattice thermal conductivity between the AB and AA-stacking ($\kappa_{AB}$/$\kappa_{AA}$) orders along two in-plane directions, (b) Anisotropic ratio of lattice thermal conductivity along in-plane directions corresponding to AA and AB-stackings, (c) Energy as a function of interlayer distance of AA and AB-stacking orders, and (d) Grüneisen parameters as a function of phonon frequency of AA and AB stacking order.
• Figure 5: Variation of (a) average phonon group velocity and (b) phonon lifetime as a function of phonon frequencies in the AA and AB stacking.