  Chromium atoms in graphene have been proposed to exhibit magnetic moments and
spin-selective conducting states depending on the local bonding geometry within
the graphene structure, which could lead to interesting applications in
spintronics. Despite this interest, there are few direct experimental reports
of Cr dopants in graphene even though it is theorized to be stable. Here, we
demonstrate the introduction of single Cr dopant atoms into the graphene
lattice and onto graphene edges through the controlled use of a focused
electron beam in a scanning transmission electron microscope. We show local
control of doping locations and when coupled with targeted in situ milling
during scanning of the e-beam, these strategies demonstrate an important
component of the fabrication of tailored nanostructured devices in the electron
microscope. The approach is validated with first principles calculations to
understand synthesis pathways during fabrication and reveal the energetics and
local properties of Cr atoms embedded in graphene; e.g., Cr doping can convert
graphene into a magnetic and semiconducting material, which suggests Cr-doped
graphene can be used as a building block for potential electronic devices and a
means to construct them.
