SiC/Ti3SiC2 interface: Atomic structure, energetics, and bonding

The structural, electronic, and adhesive properties of the 4H-SiC(0001)/Ti3SiC2(0001) interface are systematically investigated by first-principles calculations. A total of 96 candidate interface geometries are considered, encompassing four SiC terminations, each of which involves six Ti3SiC2 terminations and four stacking sequences. We find that the fundamental influence of the SiC substrate on the optimal Si-terminated interface is twofold characterized atomically by pulling the interfacial C atoms of Ti3SiC2 toward the positions that would normally be filled by C in bulk SiC and electronically by forcing the density of states projected on the interfacial C of Ti3SiC2 to approach that of C in bulk SiC rather than bulk Ti3SiC2. Consequently, the interfacial C of Ti3SiC2 is reasonably viewed as a natural extension of the C sublattice of bulk SiC across the interface. In contrast, atomic relaxation in the optimal C-terminated interface results in minor rearrangement, wherein the interfacial C of Ti3SiC2 rests straight above interfacial C of SiC. Regardless of the relaxation and SiC terminations, adhesion is found to be sensitive to choice of Ti3SiC2 termination and interfacial C to be an important factor influencing adhesion strength. Using several analytic techniques, we have characterized the electronic structures thoroughly and determined the interfacial bonding to be of a mixed covalent-ionic nature.