  The spatial resolutions of even the most sensitive isotope analysis
techniques based on light or ion probes are limited to a few hundred
nanometres. Although vibration spectroscopy using electron probes has achieved
higher spatial resolution, the detection of isotopes at the atomic level has
been challenging so far. Here we show the unambiguous isotopic imaging of 12C
carbon atoms embedded in 13C graphene and the monitoring of their
self-diffusion via atomic level vibrational spectroscopy. We first grow a
domain of 12C carbon atoms in a preexisting crack of 13C graphene, which is
then annealed at 600C for several hours. Using scanning transmission electron
microscopy electron energy loss spectroscopy, we obtain an isotope map that
confirms the segregation of 12C atoms that diffused rapidly. The map also
indicates that the graphene layer becomes isotopically homogeneous over 100
nanometre regions after 2 hours. Our results demonstrate the high mobility of
carbon atoms during growth and annealing via selfdiffusion. This imaging
technique can provide a fundamental methodology for nanoisotope engineering and
monitoring, which will aid in the creation of isotope labels and tracing at the
nanoscale.
