  The surface steps play dramatic roles in surface dominated processes and the
related properties, in which these roles would be significantly enhanced for
the low-dimensional nano or quantum materials since the ratio of surface atoms
is largely increased. However, the atomic structures of surface steps in the
nano/quantum systems are poorly understood because it is extremely difficult to
controllably introduce these defects experimentally. Here, by utilizing the
focused sub-Angstrom high energy electron beam induced atomic precise etching
in a scanning transmission electron microscope, we fabricate MgO
two-dimensional (100) nanosheet as thin as 2 atomic layers, and controllably
introduced the surface steps in the nanosheet. It is found that the surface
steps could bend the MgO nanosheet and such step-induced bending becomes more
pronounced for the nanosheet with less layer numbers. We reveal that the
bending of the nanosheets is originated from the step induced step force and
the reduced bending stiffness in the nanosheet system.
