Can the peak force be negative in this mode? If so, what is the physical meaning for negative repulsive force?

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BrukerApplications replied on Tue, Jan 19 2010 4:39 PM

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Suggested by Chunzeng Li

Answered in the application notes: PEAK FORCE TAPPING (Page 2).

Yes, the peak force can be negative. When the tip comes into contact with sample it first feels the long range negative attractive forces. Then the very apex of the tip is in contact with the sample and resulting positive repulsive interaction force. But the overall interaction force (summation of attractive and repulsive forces) may still be negative (attractive). The Peak Force Tapping mode can easily maintain the tip on the sample surface with a negative peak force setpoint. But when the tip is scanning large areas on a rough sample, probe can be parachuting and leave sample surface.