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. 2019 Jun 25;4(6):11126-11134.
doi: 10.1021/acsomega.9b01003. eCollection 2019 Jun 30.

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

Minsu Kim  1 , Shunichi Nabeya  2   3 , Dip K Nandi  2 , Kazuharu Suzuki  3 , Hyun-Mi Kim  1 , Seong-Yong Cho  4 , Ki-Bum Kim  1   1 , Soo-Hyun Kim  2
Affiliations

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

Minsu Kim et al. ACS Omega. .

Abstract

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.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Molecular structure of the Ni precursor Ni(Chex)(Cp).
Figure 2
Figure 2
Reactant tests. (a) XRD analysis of ALD Ni films obtained using O2, H2, and NH3 reactants at a deposition temperature of 320 °C and (b) resistivity of deposited films. XPS analysis of the NH3-340 °C Ni film. Spectra of (c) C 1s, (d) N 1s, (e) O 1s, and (f) Ni 2p.
Figure 3
Figure 3
Growth behavior. Growth rate as a function of the pulse time of (a) the precursor and (b) the reactant. (c) Film thickness as a function of the number of ALD cycles.
Figure 4
Figure 4
Postannealing process. (a) Resistivity of the Ni film as a function of annealing temperature. (b) XPS analysis of the film after annealing at 380 °C. (c) XRD result of the films before and after annealing. (d) Calculated grain size as a function of annealing temperature based on the fcc Ni (111) peaks in (c). (e) Tilted cross-sectional SEM images of the films before and after annealing. The number of ALD cycles is 300, and τNi is the thickness of the film.
Figure 5
Figure 5
Selective deposition on defects of graphene. (a) SEM images of graphene before and after Ni ALD. (b) TEM image of graphene after 500 cycles of Ni ALD. (c) Electron diffraction patterns of graphene for the regions shown in (b); z is the zone axis. (d) Electron diffraction pattern of fcc Ni and fcc NiO on graphene. (e) High-resolution TEM images and FFT of islands (selected regions D and E) on the graphene.
Figure 6
Figure 6
AFM analysis of the selective deposition of Ni on graphene. (a) AFM images of graphene before and after Ni ALD. (b) Surface RMS roughness of graphene and (c) average height of the lines as a function of the number of ALD cycles.
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