  Moire superlattices are twisted bilayer materials, in which the tunable
interlayer quantum confinement offers access to new physics and novel device
functionalities. Previously, moire superlattices were built exclusively using
materials with weak van der Waals interactions and synthesizing moire
superlattices with strong interlayer chemical bonding was considered to be
impractical. Here using lead sulfide (PbS) as an example, we report a strategy
for synthesizing of moire superlattices coupled by strong chemical bonding. We
use water-soluble ligands as a removable template to obtain free-standing
ultra-thin PbS nanosheets and assemble them into direct-contact bilayers with
various twist angles. Atomic-resolution imaging shows the moire periodic
structural reconstruction at superlattice interface, due to the strong
metavalent coupling. Electron energy loss spectroscopy and theoretical
calculations collectively reveal the twist angle26 dependent electronic
structure, especially the emergent separation of flat bands at small twist
angles. The localized states of flat bands are similar to well-arranged quantum
dots, promising an application in devices. This study opens a new door to the
exploration of deep energy modulations within moire superlattices alternative
to van der Waals twistronics.
