Direct Atomic Layer Deposition of Ultrathin Aluminum Oxide on Monolayer MoS<sub>2</sub> Exfoliated on Gold: The Role of the Substrate
Emanuela Schilirò, Raffaella Lo Nigro, Salvatore Ethan Panasci, S. Agnello, M. Cannas, F. M. Gelardi, Fabrizio Roccaforte, Filippo Giannazzo
Abstract
Abstract In this paper, the authors demonstrate the atomic layer deposition (ALD) of highly homogeneous and ultrathin (≈3.6 nm) Al 2 O 3 films with very good insulating properties (breakdown field of ≈10–12 MV cm −1 ) directly onto monolayer (1L) MoS 2 exfoliated on gold. Differently than in the case of 1L MoS 2 supported by a common insulating substrate (Al 2 O 3 /Si), a better nucleation process of the high‐ k film is observed on the 1L MoS 2 /Au system since the ALD early stages. Atomic force microscopy analyses show a ≈50% Al 2 O 3 surface coverage just after 10 ALD cycles, its increase to >90% (after 40 cycles), and a uniform ≈3.6 nm film (after 80 cycles). The Al 2 O 3 density on bilayer MoS 2 is found to be significantly reduced with respect to 1L MoS 2 /Au, suggesting a role of screened interface charges with the metal substrate on the adsorption of ALD precursors. Finally, Raman and photoluminescence spectroscopy show a p‐type doping and tensile strain of 1L MoS 2 induced by the Au substrate, providing an insight on the evolution of vibrational and optical properties after the Al 2 O 3 deposition. The direct ALD growth of Al 2 O 3 on large‐area 1L MoS 2 induced by the Au underlayer can be of wide interest for electronic applications.