Lattice thermal transport in two-dimensional alloys and fractal heterostructures

Abstract

Engineering thermal transport in two dimensional materials, alloys and heterostructures is critical for the design of next-generation flexible optoelectronic and energy harvesting devices. Direct experimental characterization of lattice thermal conductivity in these ultra-thin systems is challenging and the impact of dopant atoms and hetero-phase interfaces, introduced unintentionally during synthesis or as part of deliberate material design, on thermal transport properties is not understood. Here, we use non-equilibrium molecular dynamics simulations to calculate lattice thermal conductivity of $${\mathrm {(Mo|W)Se_2}}$$ ( Mo | W ) Se 2 monolayer crystals including $${\mathrm {Mo}}_{1-x}{\mathrm {W}}_x{\mathrm {Se_2}}$$ Mo 1 - x W x Se 2 alloys with substitutional point defects, periodic $${\mathrm {MoSe_2}|\mathrm {WSe_2}}$$ MoSe 2 | WSe 2 heterostructures with characteristic length scales and scale-free fractal $${\mathrm {MoSe_2}}|{\mathrm {WSe_2}}$$ MoSe 2 | WSe 2 heterostructures. Each of these features has a distinct effect on phonon propagation in the crystal, which can be used to design fractal and periodic alloy structures with highly tunable thermal conductivities. This control over lattice thermal conductivity will enable applications ranging from thermal barriers to thermoelectrics.

Possible route to efficient thermoelectric applications in a driven fractal network

“…Consequently, the phonon thermal conductance shows lower values. Such localization in thermal transport has also been studied in asymmetric harmonic chains 35 and observed in 2D fractal heterostructures 47 , 48 , which leads to a very large reduction in the thermal conductivity.…”

A driven fractal network: Possible route to efficient thermoelectric application

“…For the higher generation SPGs, we get more localized phonon modes which we confirm by studying the phonon transport up to the 8th generation SPG (not shown here). Such localization of phonon modes has also been studied in asymmetric harmonic chains 35 and observed in 2D fractal heterostructures 44,45 . The corresponding phonon thermal conductance k ph as a function of temperature is shown in Fig.…”

Probing Phonon Focusing, Thermomechanical Behavior, and Moiré Patterns in van der Waals Architectures Using Surface Acoustic Waves

“…These as-fabricated defects can be introduced during sample preparation (e.g., grain boundaries or isolated vacancies and antisite defects) or transfer (e.g., wrinkles and tears) 8 . Previous studies have shown that defects can be used to tune properties [9][10][11][12] , control strain 8 , and induce moiré patterns in 2D transition metal dichalcogenides 13,14 . However, more work is needed to understand the relationship between intrinsic defects, SAWs, and key material properties.…”