  The design and preparation of novel quantum materials with atomic precision
are crucial for exploring new physics and for device applications. Electron
irradiation has demonstrated as an effective method for preparing novel quantum
materials and quantum structures that could be challenging to obtain otherwise.
It features the advantages of precise control over the patterning of such new
materials and their integration with other materials with different
functionalities. Here, we present a new strategy for fabricating freestanding
monolayer SiC within nanopores of a graphene membrane. By regulating the energy
of the incident electron beam and the in-situ heating temperature in a scanning
transmission electron microscope (STEM), we can effectively control the
patterning of nanopores and subsequent growth of monolayer SiC within the
graphene lattice. The resultant SiC monolayers seamlessly connect with the
graphene lattice, forming a planar structure distinct by a wide direct bandgap.
Our in-situ STEM observations further uncover that the growth of monolayer SiC
within the graphene nanopore is driven by a combination of bond rotation and
atom extrusion, providing new insights into the atom-by-atom self-assembly of
freestanding two-dimensional (2D) monolayers.
