Reaction mechanism of nickel sulfide atomic layer deposition using bis(N,N'-di-tert-butylacetamidinato)nickel(II) and hydrogen sulfide.

As a unique nanofabrication technology, atomic layer deposition (ALD) has been used in the microelectronics, catalysis, environmental and energy fields. As an energy and catalytic material, nickel sulfide has excellent electrochemical and catalytic activities and has attracted extensive attention. In this work, the reaction mechanism for nickel sulfide ALD from an amidine metal precursor was investigated using density functional theory (DFT) calculations. The results show that the first amidine ligand of bis(N,N'-di-tert-butylacetamidinato)nickel(II) [Ni(tBu-MeAMD)2] can be easily eliminated on the sulfhydrylated surface. The second amidine ligand can also react with the adjacent sulfhydryl group to generate the N,N'-di-tert-butylacetamidine (tBu-MeAMD-H) molecule, which can strongly interact with the Ni atom on the surface and be difficult to be desorbed. In the subsequent H2S reaction, the tBu-MeAMD-H molecule can be exchanged with the H2S precursor. Ultimately, the tBu-MeAMD-H molecule can be desorbed and H2S can be dissociated to form two sulfhydrylated groups on the surface. Meanwhile, the -SH of a H2S molecule can be exchanged with the second tBu-MeAMD ligand. These insights into the reaction mechanism of nickel sulfide ALD can provide theoretical guidance to design the metal amidinate precursors and improve the ALD process for metal sulfides.