Difficulties in manual modulus determination from X-Y-data

Polis Tyrol posted on Tue, May 28 2013 6:20 AM

rated by 0 users

Dear Community,

I have some difficulties verifying manually my modulus results I measured with PeakForce QNM and I hope you can help me. Below you can find one of my data files ("Example Modulus Determination") showing separation data in the first column and force data in the second one.

(1) First of all: Is it a problem that the force is several hundreds of nN negative? I don't know why this is the case and how I could have avoided that. I think that it shouldn't have any influence on the measured values, right?

(2) But more important is second: I struggled fitting the DMT model to the data. According to what I've read I should obtain a linear force-distance curve by taking the force values (+ 400 nN to make it positive) to the power of 3/2. Well, this is not really the case. Likewise, I tried to fit the Hertzian model to the data in NanoScope Analysis and had to face that the result strongly depended on how I chose the fit limits.

I guess that means that my material doesn't really respond according to the DMT model. However, the modulus at this point is supposed to be at least 2 GPa so the DMT model seems to be fine and the deformation should be good as well (> 2 nm).

I used a fresh tip (RTESPA) for this measurement and calibrated on PS.

Best regards, Dietmar Haba

Here are the used measurement parameters: https://docs.google.com/file/d/0B3HnHi3lPPS_Y2dfb1Y3UXNOaFE/edit?usp=sharing
And here is the measured data: https://docs.google.com/file/d/0B3HnHi3lPPS_MHpTWTVnRDd2ME0/edit?usp=sharing (https://docs.google.com/file/d/0B3HnHi3lPPS_MGZEdWZUVXJES1E/edit?usp=sharing)