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Hi all
We are trying to measure the DMT modulus using PeakForce QNM for some nano-fibers but for some reason we are seeing negative values.
While we are taking the images, the data shown on the screen shows positive values ranging from 50-100 MPa for the fibers (see the first screenshot below), but when we capture the complete image and try to measure the values again, it shows negative values.
Why does the fiber section show negative values in the above image? It seems like Nanoscope is scaling the values somewhere. How can we retain the original values as it shows while imaging.
Thank you
When you collected your data, the Offline Planefit parameter (called "OL Planefit" in the software) was set to "Offset." This will offset the average Z value of the image to the center of the data scale in the saved image. So, it centered the modulus values of the image at 0 MPa when the image was saved. This is why your modulus data is offset so that you are getting negative values. When you are collect the DMTModulus data channel (and the other PeakForce QNM channels such as Adhesion, Deformation, Dissipation, and LogDMTModulus), setting the Offline Planefit (OL Planefit) parameter to "None" will prevent this problem and save the raw data values.
Hope this helps.
John
Thirst thing coming to mind: You are flattening the picture. check if the flatening is off when you record ( not on full after recording), also don't flatten after saving.
But perhaps i am wrong.....
Thank you for the reply. Yes, OL Planefit was set to Offset and when we turned it off, we are now able to see the raw data and all values are positive.
But sometimes we get streaks in the DMT Modulus image even when the height image is spotlessly clean. Which parameter should be adjusted to remove these streaks?
Height image:
How can we get a clean image as shown on page 3 (fig. c) of this brochure? https://www.bruker.com/fileadmin/user_upload/8-PDF-Docs/SurfaceAnalysis/AFM/Brochures/PeakForce_Quantitative_Nanomechanical_Property_Mapping_b.pdf
Three things you should check:
We are using the TAP150A probe. I had calibrated the deflection sensitivity on the glass side before starting the imaging.
In another slide, we got this image:
But even here we don't see a sharp contrast between the DMT Modulus readings of the fibers and the background.