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why the maximum force in the FD curve varies a lot when I do automatic ramping?

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psuxi posted on Thu, Apr 18 2013 5:59 PM

The AFM I'm using is Dimension icon on some bio sample in liquid mode. When I use ramp mode to generate force-distance curves, the maximum force of individual curves are different. For example, I input the "trig threshold" a value of 30 nN, in some samples, the maximum force is arould 30 nN. However, in many experiments, the maximum force varies a lot, from 4 nN to 16 nN and almost not a single curve reach the value 30 nN. When I use 'point and shoot' funcion to target special position. I found that  the higher position in the topography has lower maximum force when the trig threshold is fixed. Why these are happening? How could I control the maximum force?

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Ang Li replied on Tue, Apr 23 2013 9:46 AM

I guess you can try increasing the ramp size. 

Ang Li

 

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Bruker Employee

Can you verify if you are using the relative trigger mode? Using the absolute trigger will likely give you different max applied force values depending on your deflection at the start of each force curve.

Also, which probe are you using? I have not tried to apply such high forces much on Bio-samples but I wonder if it might be possible that your probe is too soft. When you push against the surface, if the probe is not stiff enough then it just keeps deflecting and can't reach the max/trigger force before the laser spot rails on the photodetector.

Best,

Andrea

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