Diamond-Like Carbon films with thicknesses controlled in the 10 to 100 nm range were sputter-deposited on single crystals of MgO. The substrates were prepared with varying roughness from 5 to 50 nm and varying surface dislocation densities from 100 to 2000 disl./μm2. Mechanical properties of the film and film-substrate interactions were investigated with an atomic force microscope retrofitted with a diamond indenter. The load bearing capacity of the substrate increased with increasing film thickness. As the indenter approached the film-substrate interface, load excursions occurred for the thinner films. No excursion was found for the thick film. Load excursions may be attributed to dislocations nucleating at the interface and/or film delamination.