The effect of the presence of diamondlike carbon coatings deposited on (100) Si substrateson the deformation mechanisms operating in the silicon substrate during contact loadinghave been investigated by both cross-sectional transmission electron microscopy andmodeling of the stresses generated beneath the indenter tip. The observed subsurfacemicrostructures were correlated to the Tresca shear stress and the hydrostatic stressgenerated in the silicon substrate beneath the indenter tip. The presence of the coatingaltered the stresses generated in the substrate, and changed the deformation mechanismfrom one of principally phase transformation in uncoated Si to predominantly dislocationmotion in the silicon substrate for the diamondlike C¿Si system. The magnitude anddistribution of the shear and hydrostatic stresses in the substrate were found to depend onboth the indentation load and the thickness of the coating. Furthermore, the observedwidth of deformation, parallel to the interface, which was found to increase with coatingthickness, was correlated to the wider distribution of the Tresca shear stress in thesubstrate brought about by the presence of the coating.