  Ferroelectric oxides interfaced with transition metal dichalcogenides (TMDCs)
offer a promising route toward ferroelectric-based devices due to lack of
dangling bonds on the TMDC surface leading to a high-quality and abrupt
ferroelectric/TMDC interface. In this work, the thermal stability of this
interface is explored by first depositing hafnium zirconium oxide (HZO)
directly on geological MoS2 and as-grown WSe2, followed by sequential annealing
in ultra-high vacuum (UHV) over a range of temperatures (400-800 {\deg}C), and
examining the interface through X-ray photoelectron spectroscopy (XPS). We show
that the nucleation and stability of HZO grown through atomic layer deposition
(ALD) varied depending on functionalization of the TMDC, and the deposition
conditions can cause tungsten oxidation in WSe2. It was observed that HZO
deposited on non-functionalized MoS2 was unstable and volatile upon annealing,
while HZO on functionalized MoS2 was stable in the 400-800 {\deg}C range. The
HZO/WSe2 interface was stable until 700 {\deg}C, after which Se began to evolve
from the WSe2. In addition, there is evidence of oxygen vacancies in the HZO
film being passivated at high temperatures. Lastly, X-ray diffraction (XRD) was
used to confirm crystallization of the HZO within the temperature range
studied.
