Another method of friction and wear testing is nano-scratch. The concept is simple: a diamond tip is brought into contact with a flat specimen, a constant or ramped load is applied while the sample moves, and the friction is measured. The residual wear can then be measured with an AFM. Typical loads are in the mN range, scratch lengths in 100’s of µm range, and depths can be as shallow as a few nm. Nano-scratch can also be used to measure hardness at very shallow depths which is particularly useful in areas where very thin (~50 nm) films or coatings are used such as hard disk drives. A representative image of a ramped load experiment is shown below.
(Zhang and Huan, 2004)