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Dear community,I am using a Dimension Icon AFM with NanoScope 8.15 software in the PeakForce QNM mode. The system works well during the calibration process (measurement of the deflection sensitivity on a sapphire sample, finding the spring constant with thermal tune, followed by checking the tip radius on a Ti roughness sample) and it is possible to obtain correct modulus data from the PS-LDPE calibration sample with TESPA probes. However when the rough surface of ceramics is scanned, characteristic patterns start to occur in the Modulus, Adhesion and Dissipation channels.
Rough ceramic sample scanned in PF-QNM mode with TAP525A probe, 3D height with LogDMTModulus skin:Ceramic_TAP525A_PF-QNM_3D_LogDMTModulus-skin_5um.jpg.aspx
Ti roughness sample scanned in PF-QNM mode with TAP525A probe, 3D height with Adhesion skin:Ti-RS_TAP525A_PF-QNM_3D_Adhesion-skin_5um.jpg.aspx
The baseline part of the Force vs. Time curve becomes increasingly wavy with the observed sample's surface roughness. This behavior can be seen in the four force curves attached below: (a) was obtained while scanning a sapphire calibration sample; (b) scanning a PS-LDPE calibration sample; (c) scanning a Ti roughness sample with height differences ; (d) scanning a ceramic sample with maximum height differences of about 2 µm within the scan size of 5 µm.
Force_vs_Time-Z_curves.JPG.aspx
Regarding the problems stated above I would like to ask, how the oscillating values could be explained and how it would be possible to acquire trustworthy QNM data from rough surfaces? I used low scan rates resulting in tip velocities of 1 - 2 µm/s and had ScanAsyst Auto Control switched on, despite the Auto Control for the Peak Force Setpoint.Another problem I am facing is, that during the 'Engage' step in the work-procedure, ScanAsyst seems to increase the Peak Force Setpoint to values of up to 1.5 µN - during scanning the setpoint was set to 200nN. I am afraid, that unnecessarily high forces are wearing off the tip very fast. After performing 6 scans on rough ceramic surfaces the TAP525A tip got totally blunt (see scan of Ti roughness sample). Is it possible to limit the peak force setpoint during the automatic 'Engage' procedure?
Thank you for your replies in advance!
Gabor