First-principles studies of MoF₆ absorption on hydroxylated and non-hydroxylated metal oxide surfaces and implications for atomic layer deposition of MoS₂

Significant interest in two-dimensional transition metal dichalcogenides has led to numerous experimental studies of their synthesis using scalable vapor phase methods, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). ALD typically allows lower deposition temperatures, and nucleation of chemical precursors requires reactions with surface functional groups. A common first-principles method used to study ALD modeling is the calculation of activation energy for a proposed reaction pathway. In this work we calculated the partial charge densities, local density of states (LDoS), Bader charge analysis, adsorption energies, and charge density difference using density functional theory (DFT) to investigate the nucleation of MoF₆ on three oxide surfaces, including Al₂O₃, HfO₂, and MgO. Our findings indicate that hydroxyl groups (OH) help lower the reaction barrier during the first half-cycle of MoF₆ and promote the chemisorption of a precursor on the oxide substrates. This discovery is supported by the formation of highly ionic MF_x (M = metal, x = 1, 2, 3) bonds at the oxide surfaces. By comparing surfaces with and without hydroxyl groups, we highlight the importance of surface chemistry.