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Scratch Testing of DLC and Silicon Surfaceswith the NanoTest Scratch Module |
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NanoTest dynamic scratch testing consists of monitoring the change in depth of a probe as the normal load is increased and the specimen is moved in a direction perpendicular to the probe axis.
For relatively long scan lengths, it is necessary to level the specimen prior to data acquisition to eliminate the apparent change in depth due to the background tilt of the surface. This is performed automatically using the NanoTest levelling stage. The force resolution and depth resolution are the same as for normal NanoTest indentation measurements. |
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The two results shown below were produced using a relatively sharp trihedral diamond indenter, although small radius spherical diamonds or various fractured ceramic probes can also be used. The applied load is read from the r.h.s. vertical axis and the displacement from the l.h.s. vertical axis. The first, horizontal part of the curve at zero load is used for the elimination of any residual specimen tilt in software, after use of the levelling stage. When the load begins to increase, the stylus begins to penetrate the surface in the usual, 'ideal' way expected for a normal indentation.
At a critical load, the surface fails and scratching commences. As can be seen, the pile-up and fracturing phenomena associated with scratching have a pronounced effect on the probe displacement, allowing the critical load for scratching or adhesion failure to be readily determined. In practice, the critical load is indicated when a cursor is moved to the appropriate point on the scan distance axis.
The result for the 60 nm DLC film clearly indicates the need for nano-scratch evaluation in this case. Although the result is qualitatively similar to that for the silicon surface, failure occurred at a much lower load and at a penetration depth close to the film thickness. |
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