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In this paper, the atomic layer deposition (ALD) of ultra-thin films (<4 nm)of $Al_{2}O_{3}$ and $HfO_{2}$ on Au-supported monolayer (1L) $MoS_{2}$ isinvestigated, providing an insight on the nucleation mechanisms in the earlystages of the ALD process. A preliminary multiscale characterization of largearea 1L-$MoS_{2}$ exfoliated on sputter-grown Au/Ni films revealed an almostconformal $MoS_{2}$ membrane with the Au topography and the occurrence ofstrain variations at the nanoscale. Ab-initio DFT calculations of$MoS_{2}$/Au(111) interface showed a significant influence of the Au substrateon the $MoS_{2}$ energy band structure, whereas small differences wereaccounted for the adsorption of the $H_{2}O$, TMA and TDMAHf precursors. Thissuggests a crucial role of nanoscale morphological effects, such as localcurvature and strain of the $MoS_{2}$ membrane, in the enhanced physisorptionof the precursors. Therefore, the nucleation and growth of $Al_{2}O_{3}$ and$HfO_{2}$ films onto 1L-$MoS_{2}$/Au was investigated, by monitoring thesurface coverage as a function of the number (N) of ALD cycles, with N from 10to 120. At low N values, a slower growth rate of the initially formed nucleiwas observed for $HfO_{2}$, probably due to the bulky nature of the TDMAHfprecursor as compared to TMA. On the other hand, the formation of continuousfilms was obtained in both cases for N>80 ALD cycles, corresponding to 3.6 nm$Al_{2}O_{3}$ and 3.1 nm $HfO_{2}$. Current mapping by C-AFM showed, for thesame applied bias, a uniform insulating behavior of $Al_{2}O_{3}$ and theoccurrence of few localized breakdown spots in the case of $HfO_{2}$,associated to less compact films regions. Finally, an increase of the1L-$MoS_{2}$ tensile strain was observed by Raman mapping after encapsulationwith both high-k films, accompanied by a reduction in the PL intensity.

Direct atomic layer deposition of ultra-thin $Al_{2}O_{3}$ and $HfO_{2}$ films on gold-supported monolayer $MoS_{2}$