The AFM was used to measure a defect visible by eye on a bio chip. But by optical microscopy it was not possible to decide whether the structure was an elevation or a cavity.
On the right hand side the ideal sinusoidal grid with a period of about 1 µm is visible and on the left hand side the defect. Consequently it could be deduced from the AFM image that the defect was formed during the manufacturing of the master.