Microtribological tests.
© Fraunhofer IST

Friction and wear tests can also be conducted on micrometer surfaces with a special add-on for the AFM (company Hysitron). A conical diamond tip is moved laterally over the surface with a defined load and the friction and wear are determined. Scratch tests with an increasing load (see graphic), oscillating tests with a constant load and surface wear tests are possible as well. This process also supports scratch and wear tests on very thin films (thickness 5–500 nm), which is not possible with conventional scratch or tribology tests.

Micro-scratch test with increasing load on AF45 glass, maximum load 3.6 mN

Micro-scratch test with increasing load on AF45 glass.
© Fraunhofer IST

The example initially shows the topography of the intact surface before the scratch, the penetration depth of the tip during the test, and the remaining residual depth in the surface after the scratch. Conclusions can be drawn from the latter two regarding the proportion of elastic resilience and plastic deformation of the material. The friction coefficient under load can supply additional information about the failure of the film (such as wearing through, crack formation).