We present the results of a post-deposition annealing structural study on amorphous tetrahedrally-coordinated carbon (a-tC) films on Si(100) prepared by pulsed-laser deposition. Films as-deposited and post-annealed at 200, 300, 400, 500 and 600 °C, respectively, are studied using combined x-ray reflectivity and low-angle scattering measurements. The scans are fit to the Fresnel equations to obtain values for average film density, film and interface thickness, and film and interface roughness. We observe a correlation between the evolution of film density, roughness and the spacing of quasi-periodic structures in the films as a function of annealing temperature. We relate the evolution of these structural features with previous measurements of the resistivity and the observed stress release in these films.