  In this paper we demonstrated the thermal Atomic Layer Deposition (ALD)
growth at 250 {\deg}C of highly homogeneous and ultra-thin ($\approx$ 3.6 nm)
$Al_2O_3$ films with excellent insulating properties directly onto a monolayer
(1L) $MoS_2$ membrane exfoliated on gold. Differently than in the case of 1L
$MoS_2$ supported by a common insulating substrate ($Al_2O_3/Si$), a better
nucleation process of the high-k film was observed on the 1L $MoS_2/Au$ system
since the ALD early stages. Atomic force microscopy analyses showed a $\approx
50\%$ $Al_2O_3$ surface coverage just after 10 ALD cycles, its increasing up to
$>90\%$ (after 40 cycles), and an uniform $\approx$ 3.6 nm film, after 80
cycles. The coverage percentage was found to be significantly reduced in the
case of 2L $MoS_2/Au$, indicating a crucial role of the interfacial interaction
between the aluminum precursor and $MoS_2/Au$ surface. Finally, Raman
spectroscopy and PL analyses provided an insight about the role played by the
tensile strain and p-type doping of 1L $MoS_2$ induced by the gold substrate on
the enhanced high-k nucleation of $Al_2O_3$ thin films. The presently shown
high quality ALD growth of high-k $Al_2O_3$ dielectrics on large area 1L
$MoS_2$ induced by the Au underlayer can be considered of wide interest for
potential device applications based on this material system.
