Atomic-scale mechanism of interfacial bonding and adhesion enhancement via transition-metal doping at the Ag(111)/Cr2AlC(0001) interface

The interfacial bonding between Ag and the Cr 2 AlC MAX phase critically determines the performance of Ag-based electrical contact composites. First-principles density functional theory calculations using the GGA-PBE functional were performed to investigate adhesion, electronic structure, and alloying element doping at the Ag(111)/Cr 2 AlC(0001) interface. Four surface terminations (C, Al, Cr(C), and Cr(Al)) yielded surface energies of 4.30, 3.19, -1.83, and -1.79 J/m 2 , respectively; the Al termination was favored under Al-rich conditions, whereas the Cr(C) termination prevailed under Al-poor conditions. Among the twelve interface models, HCP stacking consistently outperformed the MT and OT configurations, with Cr(Al)-HCP exhibiting the highest work of adhesion (16.86 J/m 2 ) at an equilibrium distance of 2.0 Å, followed by Cr(C)-HCP (15.96 J/m 2 ), C-HCP (15.32 J/m 2 ), and Al-HCP (15.19 J/m 2 ). Electronic analysis revealed that the superior adhesion of Cr(Al)-HCP originated from strong Ag 4d-Cr 3d hybridization mediated by the interfacial Al sublayer. Doping with Cu, Zn, Ni, and Sn at four interfacial sites showed endothermic formation energies from 0.75 eV (Zn at site A) to 1.30 eV (Ni at site A). Ni at site A yielded the highest adhesion (17.4 J/m 2 , +0.54 J/m 2 relative to the undoped interface), followed by Cu at site B and Sn at site A (17.2 J/m 2 ), whereas Zn degraded adhesion at all sites (15.1-16.2 J/m 2 ). Partial density of states analysis indicated that Ni and Cu produced strong Cr- dopant d-d hybridization near the Fermi level, whereas Zn exhibited weak hybridization. These results provide atomic-scale guidelines for optimizing Ag/Cr 2 AlC composite interfaces through selective alloying.