Valence electron engineering of transition metals in MAB phases: a DFT calculation for Al-layer etching

This study employs density functional theory (DFT) to investigate the etching mechanisms of M₂AlB₂ (M = Sc, Ti, V, Cr, Zr, Mo, Hf, W) phases by analyzing their electronic structure, vacancy dynamics, and bonding interactions. Key findings reveal that Al-layer etching is governed by the thermodynamic and kinetic stability of Al vacancies, with lower formation energies and migration barriers correlating to preferential Al removal. Electronic structure analyses including density of states (DOS) and charge density difference (CDD) demonstrate weaker electron redistribution at M−Al interfaces compared to stronger M−B bonds. Local partial density of states (LPDOS) and hybridization trends further rationalize bonding strength variations: M−Al interactions weaken when hybridized states approach the Fermi level, while increased valence electrons in transition metals stabilize these bonds by shifting hybrid states to lower energies. These insights establish a multiscale framework linking electronic structure, vacancy dynamics, and etching selectivity.