"snap-in" in the force curves captured by peakforce tapping

王硕 posted on Mon, Nov 4 2013 6:23 AM

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I perform the peakforce tapping on HOPG in water to extract force curves (MultiMode 8, a SNL-10 cantilever with spring constant 0.35 N/m), the curves looks like the image below.

I find there are "snap-in" and "snap-off" regions in the force curves. In my understanding, if the gadient of the force exceeds the spring constant of the cantilever then there is a "snap-in" and the measured date follows a line which slope is equivalent to the spring constant. However, I find the slope (about 0.05 N/m) is much less than the spring constant in the "snap-in" region, and so does "snap-off" region.

Are there any dynamic properties involves in the force measurement causes this problem? I would greatly appreciate your any help. Thanks.