  In this work, we studied the pathways for formation of stoichiometric
\tcn~thin films. Polycrystalline and epitaxial \tcn~films were prepared using
reactive direct current magnetron (dcMS) sputtering technique. A systematic
variation in the substrate temperature (\Ts) during the dcMS process reveals
that the lattice parameter (LP) decreases as \Ts~increases. We found that
nearly stoichiometric \tcn~films can be obtained when \Ts~= 300\,K. However,
they emerge from the transient state of Co target ($\phi$3\,inch). By reducing
the target size to $\phi$1\,inch, now the \tcn~phase formation takes place from
the metallic state of Co target. In this case, LP of \tcn~film comes out to be
$\sim$99\p~of the value expected for \tcn. This is the largest value of LP
found so far for \tcn. The pathways achieved for formation of polycrystalline
\tcn~were adopted to grow an epitaxial \tcn~film, which shows four fold
magnetic anisotropy in magneto-optic Kerr effect measurements. Detailed
characterization using secondary ion mass spectroscopy indicates that N
diffuses out when \Ts~is raised even to 400\,K. Measurement of electronic
structure using x-ray photoelectron spectroscopy and x-ray absorption
spectroscopy further confirms it. Magnetization measurements using bulk
magnetization and polarized neutron reflectivity show that the saturation
magnetization of stoichiometric \tcn~film is even larger than pure Co. Since
all our measurements indicated that N could be diffusing out, when \tcn~films
are grown at high \Ts, we did actual N self-diffusion measurements in a CoN
sample and found that N self-diffusion was indeed substantially higher. The
outcome of this work clearly shows that the \tcn~films grown prior to this work
were always N deficient and the pathways for formation of a stoichiometric
\tcn~have been achieved.
