Atomic Layer Deposition of Nickel Using a Heteroleptic Ni Precursor with NH₃ and Selective Deposition on Defects of Graphene

Atomic layer deposition (ALD) of Ni was demonstrated by introducing a novel oxygen-free heteroleptic Ni precursor, (η³-cyclohexenyl)­(η⁵-cyclopentadienyl)­nickel­(II) [Ni­(Chex)­(Cp)]. For this process, non-oxygen-containing reactants (NH₃ and H₂ molecules) were used within a deposition temperature range of 320–340 °C. Typical ALD growth behavior was confirmed at 340 °C with a self-limiting growth rate of 1.1 Å/cycle. Furthermore, a postannealing process was carried out in a H₂ ambient environment to improve the quality of the as-deposited Ni film. As a result, a high-quality Ni film with a substantially low resistivity (44.9 μΩcm) was obtained, owing to the high purity and excellent crystallinity. Finally, this Ni ALD process was also performed on a graphene surface. Selective deposition of Ni on defects of graphene was confirmed by transmission electron microscopy and atomic force microscopy analyses with a low growth rate (∼0.27 Å/cycle). This unique method can be further used to fabricate two-dimensional functional materials for several potential applications.