Enhanced Interface Phonon Thermal Conductance via Boron Addition in Copper/Diamond Composites

Copper/diamond composites with various diamond contents are a prototype of thermal management materials and are widely used in many industrial fields due to their excellent thermo-physical properties. It is well known that the carriers of heat in diamond and copper are phonons and electrons, respectively. Scattering and phonon-electron interactions at the interface play a pivotal role on determining the interface thermal conductance. By using this model material the mechanisms of the interface thermal conductance are investigated by experiments and first-principles calculations. The boron addition can promote the thermal conductivity from 261 W/(mK) to 647 W/(mK) or increase the thermal conductivity by 2.5 times for the copper/diamond composite with 60% diamond. The increase of thermal conductivity may be explained by the formation of B4C and Cu-B solid solution at the interface. First-principles calculations show that the interface thermal resistance is mainly attributed to the phonon frequency mismatch and electronic transfer. The B4C phase formed at the interface assists the phonon conductance because the phonon spectrum of the B4C phase spreads across the range of Cu and diamond phonon spectra. The calculated results also show that boron can diffuse toward the interface region with an energy barrier of 0.87 eV and are energetically favorable to form the B4C phase. The present study provides valuable insight into the understanding of atomic mechanisms of thermal conductance at interfaces and a basis for exploring practical applications of the copper/diamond composites.