Qiang Chenfei ^{1, 2}, Sun Hao ², Fu Luxiang ¹, Jin Peng ^{1, 2}

(1. School of Materials Science and Engineering, Shenyang University of Chemical Technology, Shenyang 110142, Liaoning, China; 2. Institute of Structured Materials Technology, Liaoning Materials Laboratory, Shenyang 110167, Liaoning, China)

Extended abstract:

[Background and purposes] The rapid advancement of microelectronic devices toward miniaturization and three-dimensional high-density integration has made thermal management a critical issue in semiconductor technology. In particular, wide-bandgap (WBG) semiconductor devices, such as gallium nitride (GaN) and silicon carbide (SiC), operating at high voltages and high frequencies within increasingly compact architectures, inevitably generate high local heat flux densities. This leads to pronounced self-heating effects (SHE), the formation of internal hotspots, degradation carrier transport characteristics and accelerating device failure. Conventional heat dissipation materials, such as copper and aluminum, are becoming increasingly insufficient, because of their limited thermal conductivity under extreme heat-flux conditions and the coefficient of thermal expansion mismatch with semiconductor chips, which may induce detrimental thermal stresses. Consequently, diamond, which possesses one of the highest known bulk thermal conductivity among engineering materials, about 2200 W·m⁻¹·K⁻¹ at room temperature, has emerged as an ideal reinforcement phase for next-generation thermal management composites. Diamond/SiC composites combine the ultrahigh thermal conductivity of diamond with the excellent mechanical properties, thermal stability and low coefficient of thermal expansion of SiC. However, the practical application of such heterostructures remains challenging because of the large lattice mismatch between 3C-SiC and diamond (22%), which can induce high-density dislocations, stacking faults and vacancies at the interface. These defects act as phonon scattering centers, thereby increasing interfacial thermal resistance and limiting heat dissipation efficiency. Among the various SiC planes, the (111) plane is particularly important due to its polar nature and close-packed atomic arrangement. Nevertheless, the atomic-scale bonding mechanisms and their effects on thermodynamic stability remain insufficiently understood. Therefore, this study employs first-principles calculations, combined with experimental characterization, to systematically study the microscopic configuration, bonding mechanisms and thermodynamic stability of diamond (111)/SiC (111) heterointerface, thereby providing a theoretical basis for interfacial optimization of high-performance thermal management composites.

[Methods] The research employed a synergetic approach combining experimental characterization and theoretical simulation. Experimentally, porous diamond/SiC composites were fabricated through a "slurry preparation–hot pressing–reaction sintering" process at 1650 ℃. The interfacial microstructure was characterized by using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), with focused ion beam (FIB) sampling used for site-specific HRTEM specimen preparation. Theoretically, first-principles calculations based on density functional theory (DFT) were performed using VASP software with GGA-PBE functionals. Interfacial models with different terminations (C-terminated and Si-terminated) were constructed to calculate the work of adhesion (Wad), projected density of states (PDOS) and differential charge density to reveal the electronic structure and bonding characteristics at the atomic scale.

[Results] It is experimentally demonstrated that, during reactive sintering, molten silicon infiltrated the pores of the diamond preform and reacted in-situ to form SiC, thereby encapsulating and interconnecting the diamond particles. An atomically sharp and dense interface is present between the diamond (111) and SiC (111) planes, with no detectable amorphous layers, cracks or interfacial voids. According to the selected area electron diffraction (SAED) result, a parallel alignment between the diamond (111) and SiC (111) crystal planes was confirmed, indicating coherent or semi-coherent connection. First-principles calculation results provided a quantitative explanation for the experimentally observed high-quality interfacial bonding. The C-terminated interface was found to be more thermodynamically stable than the Si-terminated interface, with a work of adhesion (Wad) of 5.75 J·m⁻², while that of the Si-terminated configuration was 5.18 J·m⁻². The difference of 0.57 J·m⁻² indicates that the C-C covalent bonding at the interface provides stronger adhesion and higher resistance to interfacial separation than the Si–C bonding. Electronic structure analysis results via PDOS show that both interface types are characterized by sp3 orbital hybridization. In the C-terminated model, the stability originates from the intense overlap of C 2p orbitals in the valence band range of −15 eV to −5 eV, leading to the formation of robust σ covalent bonds. In contrast, the Si-terminated interface exhibits polar covalent bonding accompanied by charge transfer, due to the electronegativity difference between Si and C, resulting in relatively weaker adhesion. Differential charge density maps further support this interpretation, showing significant electron accumulation at the C-C interface, characteristic of strong covalent bonding, whereas the Si–C interface exhibits a more delocalized charge distribution and charge depletion around the Si atoms.

[Conclusions] The preferential bonding behavior of the diamond/SiC (111) interface was elucidated from an atomic-scale perspective. The formation of a high-quality atomically sharp interface in reaction-sintered Diamond/SiC composites was confirmed. First-principles calculation results further revealed that the C-termination interface possessed higher thermodynamic stability than the Si-terminated interface, mainly because of the formation of homonuclear C-C covalent bonds and more favorable orbital matching, which reduce interfacial dangling bonds and enhance interfacial adhesion. These findings provide theoretical guidance for the interfacial engineering of diamond-reinforced composites. In particular, controlling interfacial termination and promoting favorable C-C bonding may be an effective strategy for improving mechanical integrity and thermal transport efficiency in high-performance thermal management materials for advanced power electronic devices.

Key words: first-principles calculation; diamond/SiC porous composites; SiC (111) crystal plane