  Ordered atomic-scale superlattices on surface hold great interest both for
basic science and for potential applications in advanced technology. However,
controlled fabrication of superlattices down to atomic scale has proven
exceptionally challenging. Here we demonstrate the segregation-growth and
self-organization of ordered S atomic superlattices confined at the interface
between graphene and S-rich Cu substrates. Scanning tunneling microscope (STM)
studies show that, by finely controlling the growth temperature, we obtain
well-ordered S (sub)nanometer-cluster superlattice and monoatomic superlattices
with various periods at the interface. These atomic superlattices are stable in
atmospheric environment and robust even after high-temperature annealing (~ 350
oC). Our experiments demonstrate that the S monoatomic superlattice can drive
graphene into the electronic Kekul\'e distortion phase when the period of the
ordered S adatoms is commensurate with graphene lattice. Our results not only
open a road to realize atomic-scale superlattices at interfaces, but also
provide a new route to realize exotic electronic states in graphene.
