Three-Fold Enhancement of In-Plane Thermal Conductivity of Borophene through Metallic Atom Intercalation

We studied the thermal conductivity of Al-intercalated bilayer δ₄ borophene sheet by solving phonon Boltzmann transport equation based on density functional theory. Although the overall atomic density of Al-intercalated borophene is larger than that of δ₄ borophene, it possesses significant enhancement in in-plane thermal conductivity. With metallic atom intercalation, the armchair-direction thermal conductivity increases from 53.8 to 160.2 W m^-1 K^-1 and that along the zigzag direction increases from 115.7 to 157.2 W m^-1 K^-1. This pronounced enhancement is attributed to the bunching of the acoustic branches in the Al-intercalated borophene, which decreases the phase space for the high frequency three acoustic phonon scattering processes. In addition to the pronounced increased thermal conductivity, the Al-intercalation also tunes the in-plane anisotropy. This study illustrates the importance of metallic atom intercalation in the in-plane thermal conductivity of 2D van der Waals materials and also has practical implications for fields ranging from thermal management to thermoelectrics design.