Why DMT modulus and Deformation seems to be drifting during the measurement? How can I prevent the drifting? Why does Set Point variation cause Modulus and Deformation value change? How to choose the correct Set Point for the accurate modulus measurement f

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BrukerApplications replied on Tue, Jan 19 2010 6:34 PM

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DMT modulus and Deformation drift can be caused by a few reasons. On is the when the probe tip is worn or contaminated, the tip radius changes and resulting in DMT modulus drift. Another possible reason is that the Peak Force Setpoint is changed during the scanning. When the ScanAsyst Setpoint Control is turned on, the Peak Force Setpoint is automatically adjusted to keep the probe tracking the sample and avoiding parachuting. But when the Peak Force Setpoint is increased, the Deformation on the sample will be increased. The increased deformation results in larger the effective tip height from apex during indentation. The probe tip usually have larger effective tip radius with larger height apex. The Modulus can also drift due to setpoint changes.

Too large Peak Force Setpoint will introduce large force in the sample cause probe and sample damage. Too small Peak Force Setpoint may not be able to deform the sample and cause inaccuracy in the Modulus measurement. The general criteria is to keep the Peak Force Setpoint low but enough to generate 2nm Deformation in the sample. In addition to that, for the relative method, user should try to keep the Deformation the same for the reference sample and the measurement sample by adjusting Peak Force Setpoint.

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psuxi replied on Thu, Aug 9 2012 1:51 PM

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How does the software know that the tip radius changes when the tip is worn or contaminated during the scanning?

In addition, How does the software know the tip radius for different tips?

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replied on Mon, Aug 13 2012 1:03 PM

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Hi Psuxi,

The SW does not know that the radius changes during measurements. That is at this point in time a judgement call by the user. The tip radius can always be verified by scanning an appropriate sample like e.g. the tip-check sample, and having Nanoscope Analysis calculate it.

Stefan