Deformation behaviour of DLC coatings on (111) silicon substrates

The deformation mechanisms operating in diamond-like carbon (DLC) coatings on (111) silicon substrates have been investigated. A hydrogenated amorphous carbon coating of ∼ 500 nm thickness was deposited by radio-frequency plasma-assisted chemical-vapour deposition onto a (111) oriented silicon substrate. Indentations were performed on the coatings using a spherical indenter with a radius of 5 μm for various loads up to a maximum of 150 mN. The coatings exhibited substantial elastic recovery on unloading. Minor pop-ins appeared for loads above 100 mN and a distinct pop-out was observed following indentation to 150 mN. Focused ion beam microscopy of cross-sections through the indentations revealed localized plastic compression of the coating beneath the indenter and bending at the coating-substrate interface. Although the coating was free from cracking or delamination, the substrate showed evidence of median cracks and lateral cracks for loads above 100 mN. Cross-sectional transmission electron microscopy examination of indentations revealed cracks in the coating, as well as cracks, crystalline defects and a transformation zone in the silicon substrate. These observations have been correlated with the deformation behaviour of the coating-substrate composite.