Thickness-Dependent Cross-Plane Thermal Conductivity Measurements of Exfoliated Hexagonal Boron Nitride

Abstract

Submicrometer-thick layers of hexagonal boron nitride (hBN) exhibit high in-plane thermal conductivity and useful optical properties, and serve as dielectric encapsulation layers with low electrostatic inhomogeneity for graphene devices. Despite the promising applications of hBN as a heat spreader, the thickness dependence of its cross-plane thermal conductivity is not known, and the cross-plane phonon mean free paths (MFPs) have not been measured. We measure the cross-plane thermal conductivity of hBN flakes exfoliated from bulk crystals. We find that submicrometer thick flakes exhibit thermal conductivities up to 8.1 ± 0.5 W m–1 K–1 at 295 K, which exceeds previously reported bulk values by more than 60%. Surprisingly, the average phonon mean free path is found to be several hundred nanometers at room temperature, a factor of 5 larger than previous predictions. When planar twist interfaces are introduced into the crystal by mechanically stacking multiple thin flakes, the cross-plane thermal conductivity of the stack is found to be a factor of 7 below that of individual flakes with similar total thickness, thus providing strong evidence that phonon scattering at twist boundaries limits the maximum phonon MFPs. These results have important implications for hBN integration in nanoelectronics and improve our understanding of thermal transport in two-dimensional materials.

Terahertz phonon engineering and spectroscopy with van der Waals heterostructures

“…The force constants for homolayer coupling in bulk crystals of graphite ( K g ), hBN ( K h ), and WSe 2 ( K w ) are relatively well characterized 28,[35][36][37][38][39] . However, the force constants of heterolayer coupling ( K gh for the graphene/hBN interface and K hw for the hBN/WSe 2 interface) are largely unknown and, more importantly, depend on specific configurations of the interface [40][41][42] such as the twist angle, defects, roughness, and inhomogeneity. Therefore, it is crucial to accurately determine the heterolayer coupling parameters for each sample.…”

Effect of Hydrogen Annealing on Performances of BN-Based RRAM

“…One of the most promising forms of RRAM is based on boron nitride (BN) due to its advantages for aerospace applications, such as a wide-bandgap semiconductor with high thermal conductivity and excellent mechanical and chemical stability [ 7 , 8 ]. In detail, BN has a high thermal conductivity, which makes it an excellent candidate for use in heat dissipation applications, such as thermal management of electronic devices, and for use as a substrate for high-power electronic devices [ 9 , 10 ].…”