NANO-HARDNESS INVESTIGATIONS OF THIN-FILMS BY AN ATOMIC-FORCE MICROSCOPE

Hardness measurements on extremely thin films on a sub-micron scale us ing commercially available depth-sensing instruments require a minimum thickness of 100 nm. In the macroscopic regime hardness is determined by the applied normal load divided by either the curved (surface) are a-(Brinell hardness number, Rockwell hardness number and Vickers hardn ess number) or the projected area of contact between the indenter and the material being tested under load (Knoop hardness number and Berkow ich hardness number (Bushan, 1990). In the microscopic regime it is ve ry critical to determine the hardness of extremely thin films, which a re for example used in modern magnetic media as overcoat for corrosion protection and for the increase of durability. According to the rule of Bueckle the tip of the indentation body should indent only 10 % of the film thickness to avoid the influence of the underlaying substrate (Bueckle, 1965). For protective overcoats with thickness's in the ran ge of 30 nm this rule becomes more and more important to determine the real hardness of the film and not that of the underlaying layers. In this paper we report on a new measurement technique for determining th e nano-hardness of extremely thin films by a modified atomic force mic roscope.