  We have studied structural and superconducting properties of MgB2 thin films
doped with carbon during the hybrid physical-chemical vapor deposition process.
A carbon-containing metalorganic precursor bis(cyclopentadienyl)magnesium was
added to the carrier gas to achieve carbon doping. As the amount of carbon in
the films increases, the resistivity increases, Tc decreases, and the upper
critical field increases dramatically as compared to the clean films. The
self-field Jc in the carbon-doped films is lower than that in the clean films,
but Jc remains relatively high to much higher magnetic fields, indicating
stronger pinning. Structurally, the doped films are textured with nano-grains
and highly resistive amorphous areas at the grain boundaries. The carbon doping
approach can be used to produce MgB2 materials for high magnetic field
applications.
