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Some Peak Force QNM questions regarding calibration

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Jerome S. Jourdan posted on Thu, Feb 14 2013 9:13 AM

Apologies if these questions have been asked ad-nauseum, but I've been unable to find them in my searches.

I'm performing Peak Force QNM in air on polymer samples (ABS) and have a couple of questions regarding calibration (Nanoscope V and MultiMode 8):

1. During Thermal Tune I get a status message indicating "Internal Thermal Tune Gains have not been calibrated. Contact Service".  I'm able to acquire a thermal tune and get a spring constant, but does this error message indicate wrong values for 'k'? A latest calibration of a ScanAsyst-Air probe gave me 0.18 N/m value.

2. When performing tip qualification on the Titanium roughness sample which value should I choose for Estimated Tip radius? ETR 1 (smaller) or ETR 2 (larger ) value?  I seem to to get closer values for Reduced Modulus when I scan the PS/LDPE sample (PS ~ 3 GPa).

3.  Lastly, If I'm performing a Peak Force scan on a polymer surface and see nice images for Height, Peak Force Error, Amplitude and Dissipation, but get lousy contrast (lots of streaking) in the Modulus and Log Modulus images, is this a function of wrong probe?

Thanks,

Jerry 

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Hi Jerome,

  1. Please see the other post as Joop notes.  It seems that you are not the only one that has lost their calibration lately.
  2. The two different ETRs are calculated at different distances from the tip apex (there are parameters in the analysis view, so you can control the distances).  You should figure out roughly how much penetration you have (how far is the tip going into the surface) and calcalate the ETR at a distance similar to the penetration value.  Note that the DMT model is not strongly dependent on R (it goes like the square root), so this will probably not have a huge effect on your modulus value.
  3. Usually this is caused by an incorrect deflection sensitivity (remember this needs to be calibrated in ramp mode on a sample that is much harder than the sample under study), an incorrect DMTModulus limit (usually too low), or using a cantilever that is too soft for the material being measured.

I hope that helps!

--Bede

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Top 10 Contributor
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Suggested by Bede Pittenger

  1. See answer from Bede http://nanoscaleworld.bruker-axs.com/nanoscaleworld/forums/t/1336.aspx, you probably lost some calibration settings while upgrading to 8.15
     
  2. I have not looked at the calibration procedure (I am at home) but it is written there, but if I remember  right it was ETR2 depending on some values you find during the calibration.
     
  3. Do you set the range of the modulus in the settings, sometimes that helps! Perhaps just to be sure use the Sens. Deflection value of the tip found on the Titanium, do not use the Sens. Deflection of the polymer. If you update the Sens Deflection while on polymer you will also see the streaking in the modulus pictures because he does only measures the same polymer value all the time. 

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Top 10 Contributor
280 Posts
Points 6,219
Bruker Employee

Hi Jerome,

  1. Please see the other post as Joop notes.  It seems that you are not the only one that has lost their calibration lately.
  2. The two different ETRs are calculated at different distances from the tip apex (there are parameters in the analysis view, so you can control the distances).  You should figure out roughly how much penetration you have (how far is the tip going into the surface) and calcalate the ETR at a distance similar to the penetration value.  Note that the DMT model is not strongly dependent on R (it goes like the square root), so this will probably not have a huge effect on your modulus value.
  3. Usually this is caused by an incorrect deflection sensitivity (remember this needs to be calibrated in ramp mode on a sample that is much harder than the sample under study), an incorrect DMTModulus limit (usually too low), or using a cantilever that is too soft for the material being measured.

I hope that helps!

--Bede

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