Hardness measurements on thin IBAD CNx films — a comparative study

The hardness of carbon nitride (CNx) films deposited on Si(111) substrates using ion beam assisted deposition (IBAD) with varying deposition parameters was estimated using nanoindentation. For the nanoindentation, the TriboScope®, an atomic force microscope (AFM) add-on, was used, which allowed not only very small applied loads (<25 μN), but also the scanning of the residual indenter impression immediately after the indenter withdrawal. The hardness of the films obtained by the unloading analysis was compared with the hardness estimated using the plastic area measured by the AFM. As the applied load decreases, both hardness measurements show an opposite trend; the load-on hardness decreases whereas the universal load-off hardness increases. Undoubtedly, this is attributable to the different hardness definitions (load-on/off) and further associated with the unusually high elastic recovery of this material. Surprisingly, this elastic recovery occurs not only in the depth and the shape but also in the area of the residual indenter impression. This extreme elastic recovery is a particular feature of indentations in CNx films.