Forums
Bruker Media
Community Media
Bruker AFM Probes
SPM Digest
Application Notes
NanoTheater
Website
中文
Brochures & Datasheets
Publications
Probes Catalog
Events
Manuals & Documentation
Presentations
Guide to AFM Modes
News
Journal Club
Webinars & Video
Nanovations
Other
Dear community,
I use PeakForce QNM and I am particularly interested in the modulus data. Due to the high modulus of my material, I use the "relative method" for calibration of the tip and calibrate it on the "PSfilm" polystyrene test sample. However, I always struggle adjusting the tip radius and spring constant values: The measured modulus of the PSfilm is way higher than what it is supposed to be - about 7 GPa instead of 2.7 GPa. I usually need to go below the given "minimum" spring constant given by the supplier in order to obtain the 2.7 GPa.
Is that usual? Is it possible that the test sample has aged? It isn't that old, maybe two years, so it shouldn't change that strongly. What could I do to prove the test sample hasn't changed already?
Sincerely, Dietmar Haba
Hi, I guess you have some misunderstanding in following the relative method. You should have calibrated deflection senstivity and spring contant and then adjusted the tip radius to get the specified modulus value on the standard sample. Don't worry about getting an odd number of tip radius, say 100nm or 1nm, using relative method, tip radius is not physically meaningful anymore, it's just a scaling factor one can adjust to compensate the errors from deflection sensitivity and spring contant calibrations.
Ang Li
Dear Ang Li,
Thanks for the answer. Yes, I do calibrate the deflection sensitivity prior to calibration. Indeed, I do not calibrate the spring constant separately. I always choose the "lowest given" spring constant, say 20 N/m when it is given that it should lie between 20 and 80 N/m and try to adjust the tip radius afterwards. Yhould I measure the spring constant separately? Does it make sense to work with a tip radius of 100 nm if your scan size is only 500 nm? I know that it is only a scaling factor, but when I get those huge numbers, either the tip radius or the spring constant must be way off the given value, right? Or there is a problem with the reference sample...
Best regards, Dietmar Haba