Direct Atomic Layer Deposition of Ultrathin Aluminum Oxide on Monolayer MoS₂ Exfoliated on Gold: The Role of the Substrate

Abstract

In this paper, the authors demonstrate the atomic layer deposition (ALD) of highly homogeneous and ultrathin (≈3.6 nm) Al2O3 films with very good insulating properties (breakdown field of ≈10–12 MV cm−1) directly onto monolayer (1L) MoS2 exfoliated on gold. Differently than in the case of 1L MoS2 supported by a common insulating substrate (Al2O3/Si), a better nucleation process of the high‐k film is observed on the 1L MoS2/Au system since the ALD early stages. Atomic force microscopy analyses show a ≈50% Al2O3 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 Al2O3 density on bilayer MoS2 is found to be significantly reduced with respect to 1L MoS2/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 MoS2 induced by the Au substrate, providing an insight on the evolution of vibrational and optical properties after the Al2O3 deposition. The direct ALD growth of Al2O3 on large‐area 1L MoS2 induced by the Au underlayer can be of wide interest for electronic applications.

Substrate-Driven Atomic Layer Deposition of High-κ Dielectrics on 2D Materials

“…More recently, the direct thermal ALD of an ultra-thin and pinhole-free Al 2 O 3 layer has been demonstrated on monolayer (1 L) MoS 2 residing on a gold substrate [22]. During the last few years, several research groups have investigated mechanical exfoliation on gold as an effective way to separate large-area (cm 2 ) 1 L MoS 2 membranes from bulk molybdenite crystals by exploiting the strong S-Au interactions [71][72][73].…”

“…Furthermore, the exfoliated membranes could be transferred from gold to insulating substrates, demonstrating electrical and optical properties comparable to the best-quality MoS 2 crystals [71,74]. Recently, Schilirò et al [22] compared the thermal ALD of Al 2 O 3 on 1 L MoS 2 residing on gold and on 1 L MoS 2 , transferred on an insulating Al 2 O 3 substrate. Using identical ALD conditions, inhomogeneous ALD coverage by Al 2 O 3 islands was obtained in the case of the 1 L MoS 2 /Al 2 O 3 /Si (see Figure 10a).…”

“…More recently, the direct thermal ALD of an ultra-thin and pinhole-free Al2O3 has been demonstrated on monolayer (1 L) MoS2 residing on a gold substrate [22]. Du the last few years, several research groups have investigated mechanical exfoliatio gold as an effective way to separate large-area (cm 2 ) 1 L MoS2 membranes from The thickness and the insulating properties of the uniform Al 2 O 3 layer on MoS 2 /Au were also evaluated by C-AFM measurements according the schematic in Figure 11a.…”

“…The localized behavior of the breakdown was also c firmed by the current map in Figure 11e, illustrating the changes in the leakage curr spatial distribution by increasing the bias from 3 V to 4 V and then decreasing it back V. The appearance of localized breakdown spots is clearly visible in the current map gion at 4 V of applied bias. Images adapted with permission from [22], copyright Wiley, 2021.…”

“…As an example, Dlubak et al [21] demonstrated the direct ALD growth of uniform Al 2 O 3 layers on 1 L graphene as grown by CVD on metal substrates (Cu and Ni-Au). More recently, Schilirò et al [22] showed the deposition of highly homogeneous and ultra-thin Al 2 O 3 films by direct thermal ALD on 1 L MoS 2 supported by a gold (Au) substrate. In both cases, the high-quality ALD growth was explained by the enhanced adsorption of the ALD precursor molecules on 1 L graphene or MoS 2 surfaces during the nucleation stage.…”