We analyzed the incorporation of C atoms into a ternary alloy Ge1 - x - ySnxCy epitaxial film on Ge substrates on a sub-nanometer scale by using atom probe tomography. Periodic atom distributions from individual (111) atomic planes were observed both in the Ge1 - x - ySnxCy film and at the Ge substrates. Sn/C atoms had non-uniform distributions in the film. They also demonstrated a clear positive correlation in their distributions. Substitutional C atoms were only incorporated into the film when an Sn atom beam was applied onto the substrates under film growth conditions. (C) 2015 Elsevier B.V. All rights reserved.