  The advantage of MoS2, compared with graphene, is the direct growth on
various oxide substrates by chemical vapor deposition (CVD) without utilizing
catalytic metal substrates, which facilitates practical applications for
electronics. The carrier mobility is, however, degraded from the intrinsic
limit mainly due to short-range scattering caused by S vacancies formed during
CVD growth. If the upper limit for the crystallinity of CVD-MoS2 on oxide
substrates is determined by the MoS2/substrate interaction during growth, it
will hinder the advantage. In this study, we investigated the interaction
between monolayer MoS2 and a SiO2/Si substrate and the difference in
crystallinity between the top and bottom S surfaces due to the MoS2/substrate
interaction. Raman and photoluminescence spectroscopy indicated that doping and
strain were induced in MoS2 from the substrate, but they could be removed by
transferring MoS2 to a new substrate using polymers. The newly developed
polymer-transfer technique enabled selective transfer of the bottom or top
surface of CVD-MoS2 onto a new SiO2/Si substrate. The metal-insulator
transition was clearly observed for both the normal and inverse transfers,
suggesting that the crystallinity of CVD-MoS2 is high and that the
crystallinity of the bottom surface interacting with the substrate was similar
to that of the top free surface. These results provide positive prospects for
the further improvement of the crystallinity of MoS2 on oxide substrates by
reconsidering the growth conditions.
