Heat transport in pristine and polycrystalline single-layer hexagonal boron nitride

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Hexagonal boron nitride (h-BN) is a promising material for thermal management applications due to its unique properties.
• Understanding heat transport in h-BN, especially in polycrystalline forms, is crucial for optimizing its performance.
• Grain boundaries are known to significantly influence thermal properties in crystalline materials.

Purpose of the Study:

• To investigate the heat transport properties of bicrystalline and polycrystalline single-layer hexagonal boron nitride (h-BN).
• To quantify the Kapitza thermal resistance across h-BN grain boundaries and its dependence on boundary characteristics.
• To determine the thermal conductivity of polycrystalline h-BN and its relationship with grain size and phonon behavior.

Main Methods:

• Utilized a phase field crystal model to generate large-scale bicrystalline and polycrystalline h-BN samples.
• Employed molecular dynamics (MD) simulations with the Tersoff many-body potential for thermal property analysis.
• Calculated Kapitza thermal resistance using the inhomogeneous nonequilibrium MD method.
• Determined thermal conductivity via an efficient homogeneous nonequilibrium MD method.

Main Results:

• Kapitza thermal resistance at h-BN grain boundaries strongly depends on tilt angle, line tension, and defect density.
• Calculated thermal conductivity of pristine and polycrystalline h-BN showed different grain size scaling for in-plane and out-of-plane phonons.
• Extracted Kapitza conductance values were comparable to those of large-tilt-angle grain boundaries in bicrystals.

Conclusions:

• Grain boundary characteristics are critical factors governing heat transport in h-BN.
• The distinct phonon behavior in polycrystalline h-BN influences its thermal conductivity scaling with grain size.
• The findings provide valuable insights for designing h-BN-based materials with tailored thermal management capabilities.