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Hello,
I have been scanning the PS-LDPE standard with a RFESPA probe for calibration of the tip radius and I am getting a smaller tip radius for deeper deformation depths. Why would this happen? It seems the further from the apex the larger the radius should be... Here are the parameters I set and the response I received.
I set Peak force setpoint to 30nN and get 3 nm deformation in the PS portion of the sample. To make the DMT modulus = 2.0GPa the tip radius must be set to 1.4 nm
I set Peak force setpoint to 80nN and get 8 nm deformation in the PS portion of the sample. To make the DMT modulus = 2.0GPa the tip radius must be set to 0.8 nm
I have been using the auto configure button on the force curve plots to account for the parasitic deflection.
Thanks for any assistance!
Hi Lauren,
The FESP family of cantilevers is too soft to accurately measure the PS area of the sample you are looking at. PS forms a matrix that is quite difficult to indent and requires something like an TESP typ lever. That lever will of course be too stiff for accurately measure the rubber portion of the sample. Having said that that, the qualitative differencs will be still there it is just that you either under or overestimate one of the components depending on the lever you choose.
Best regards,
Stefan
Hi Stefan,
Thank you for your response. I guess this brings up another question then...
The reason I chose the RFESPA probe was because it tracked nicely over my sample and gave me good clear images. When I tried to scan the same sample with an RTESPA probe it would not track well- the trace and re-trace were very mismatched. This being said, I then tried the calibration of the RFESPA probe (per my first post) and using the calibrated radius at 2 nm deformation (I did see this deformation on in the deformation channel when scanning PS despite being too soft a probe) I re-scanned my sample. The modulus was ~1.3GPa for my sample. Since this is in the range of the RTESPA probe and not the RFESPA probe, why then does the RTESPA track so poorly while RFESPA tracks so well?
Thanks again!
Lauren
For QNM your criteria for choosing a cantilever is that it need to have the spring constant necessary to provide the information you want to extract for a given sample. I can not explain why you did not get good tracking with the TESP probe you tried. Being a stiffer probe you caertainly have to reduce your setpoint quite a bit to compensate (when compared to an FESP probe).
If you send me your email I can put you in touch with an Applications/Service person in your area.
Best,
Stefan (stefan.kaemmer at bruker-nano.com)