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Hi!
I was wondering if the nanoscope analysis software was filtering the force curves it was generating during imaging before fitting them. Does it keep only the ideal curves for the fittings? Some odd, incomplete, curves may sometimes be generated using point and shoot or hsdc. Are these curves eliminated during the data processing?
Also, would it be possible to have specifications concerning the fittings that are made using the DMT model on the retracting curve. Does the software start the fit where the tip is withdrawn from the surface of the sample (after adhesion forces)?
Is the 10-85% calculated from the top or bottom of the curve, using ramp? deflection? number of data points?
These specifications will help me understand the fittings
Thank you
☺☻
Hi Lauren,
Usually the behavior that you speak of results from the DMTModulus Limit being set too high. You are probably seeing bit noise. Please check the DMTModulus Limit and decrease it to ~ 10-100x the maximum value in the data channel. The limits are configured for the ScanAsyst-Air probe, so using a different probe usually requires some adjustment.
Our calibration sample kit is here: http://www.brukerafmprobes.com/a-3736-pfqnm-smpkit-12m.aspx and it contains a LDPE and a PS sample that can be used to calibrate RTESPA probes. We have not been able to find a supplier for a good standard in the range between those two, but we are working on it.
You can get a csv (ASCII) file of all of the modulus values in a map by using the ASCII export function from the browser. Just right click on the image (in the browser) and choose Export>ASCII... A dialog will appear that allows selection of a bunch of options (like channel number). Note: like the image data itself, the system will already have rejected negative slope curves. If you want to see those, you will need to use teh HSDC.
--Bede
Hi Helene,
If the retracting curve is lower than zero force, the curve is still fit (assuming that you have some points to fit -- the fit region is defined relative to the peak force and the adhesion point).
All of the force separation curves that do not indicate increasing deformation with decreasing force are included (I called this 'negative slope' earlier. That was an error. Actually the rejected curves have positive slope given the coordinate system of our force-separation plots. This would be the equivalent of having a negative slope in a load-displacement curve from a nanoindenter). If your deflection sensitivity is too large, this type of force-separation curve can result. If you see this problem, you should recalibrate on a hard sample. Also, check and be sure you have the correct probe type for your modulus range.
In some cases, the system may fit a region that is too large or too small. This is more likely if the background subtraction is not working correctly and you don't have a flat area of zero force to act as a baseline. Curves like this will contribute to the value of data in the image.
I'm not able to see your images, but I'll try to answer your questions anyway...
1. Nanoscope is not filtering the curves before fitting, but it does reject any curves that have force distance curves where the slope doesn't make sense (i.e. increasing deformation with decreasing force). In that case, the data will show the same value as the previous 'good' curve, so this will appear in the image as repeated pixels with exactly the same value. To see all of the curves that the system attempted to fit, you can use Nanoscope Analysis' offline HSDC features to look at the individual curves (and analyze them if you like -- the new version has some useful analysis tools).
2. The online manual (from Nanoscope, hit the F1 key or click on the blue icon with the '?') describes how the parameters control the fitting. Look in the experiment guide>imaging modes>Nanomechanical mapping>PeakForce QNM control parameters section.
Hi Bede,
I have a question related to point 1. in your response. For some samples, wen I use PF-QNM and look at the histogram of modulus values there are only maybe 5 - 8 different values, likewise it shows this way in the graphical map. Could this be because many force curves are being filtered out per your explanation? What would cause this? Is it likely the probe is inappropriate for the sample?
Also, does Bruker (or any other manufacturer you know of...) sell modulus standards of PP or HPDE as is suggested for calibrating RTESPA tips in the manual? One more question- I would like to get a csv file of each modulus value in the map (not just the histogram of values), is it possible to do this in the Nanoscope software or is that only possible for a particular line that you capture during scanning?
Thanks!
Lauren
I have more questions concerning the DMTModulus Image and the curve filtering...
I'll try explaining the images I tried to add in my first post...
If the first point of the retracting curve (when tip starts retracting) is lower than the force at 0 (no more tip-sample interaction, is the curve ignored?
I know you don't consider curves with negative slopes but what about does that do not present any sign of pull off or jump to contact and doesn't show a horizontal (force=0) line before the actual curve (linear incresing slope)? Is that considered by the software?
One last thing... If my deflection sensitivity is set just a little too high, its technically impossible to fit a force curve since the separation actually decreases when the tip is actually retracting form the sample and only starts increasing as a normal force curve would at a certain point in the force-separation curve... The slope can be awkardly fitted using the Nanoscope Analysis Software in this case... Is that how the Images DMT is also calculated? Is the only way of fixing this to lower deflection sensitivity until a good DMT image can be seen?
Thank you so much for the specifications, they help understanding our measurements
Helene
Singh posted the question below and I was also interested about the answer. Thank you
"hello
While going through one of the Application Support Bulletin By Bruker regarding nanoindentation calculations I found the following:
"It is difficult to get Young's modulus with the NanoScope AFM nanoindenting technique. The modulus depends on the slope of the unloading curve of the indent and the indent force curves generated with this technique are not true sample deformation, but instead the sum of cantilever deflection and sample deformation, which is typically difficult to decouple"
Is it impossible to calculate Young's Modulus using Nanoscope AFM or Is there any way to calculate this property of certain material using Nanoscope AFM.
Thanks
SAndeep"
Wilson
Thanks for the specifications :)
Hi Wilson,
I answered this in the other thread. Please look here:
http://nanoscaleworld.bruker-axs.com/nanoscaleworld/forums/p/1063/2831.aspx#2831
How can the "limit" be changed? where can it be accessed through in the software? I have been having trouble in getting any signal in dissipation and inphase window and was suggested to lower the limit
You can change the Deflection Limit to help improve the inphase bit noise, but you must make sure that the absolute deflection does not go outside the range (eg. if the range is 4V, deflection should never go to >2V or <-2V). If you have PeakForce QNM, there will also be a Dissipation Limit in the PF Mapping Limits list. To see these parameters, please be sure that you are looking at the expanded list (click on the red icon in the toolbar that looks like four puzzle pieces).
--BEde