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Hi All,
I have the following problem with the peak force setpoint changing significantly during a 10-um scan size imaging (i.e changing from ~ 500 pN to about 3-4 nN's), while this problem does not show up when imaging the same sample at smaller scan sizes (i.e. less than 5 um).
The sample contains proteins attached to about ~50 nm particles on a mica surface and are imaged in fluid using scanasyst fluid + and scanasyst fluid probes in a multimode 8 system using a vertical engaging E-scanner. When imaging a 10-um scan the peak force setpoint starts around 500-700 pN's during the image, and when the probe images over a large cluster of particles, the setpoint changes to about 2 nN and then continues to steadily increase during the scanning of the image. If I reduce the scan size to about 4 um or less, I have a steady peak force setpoint (~ 1 nN) while scanning the image.
A major concern I have is can I trust the image data with such variations in peak force setpoint?
Thanks in advance for any response.
best,
--Kumar
After you finish a scan with the setpoint set to automatic, take the same picture with the auto setpoint in off position and set the setpoint first to a low value (60O pN) and take one with the hight setpoint ( 3 nN) and compare the height mesurements of the three pictures. I expect ther will be not mutch difference in the height, but there wil be differences in the modules, adhesion, etc due to different force curves and as a result of that different contact times and deformations.
So I expect it depents on what you want to see....
"Meten is weten" as we say in dutch, tranlated it is something like : Measuring is knowing....
Joop
Thanks Joop. I will try that and verify the heights are the same. Best. --Kumar
As you said, the heights of the particles are not changed when imaging a 10-um size image (with a calibrated vertical engage E scanner) when the peak force setpoint is set at ~ 1 nN force and then at ~ 3 nN force. However, the particle height distributions are narrower in the higher peak force setpoint (and on auto mode) compared to the lower fixed setpoint (i.e at 1 nN or less). The quality of the image too seems low resolution, and there seems to be a "helicoptering effect" observed on top of all tall features (i.e. features around the size of 15-20 nm's).
We don't see this problem when scanning in air using scanasyst air tips and the problem is much less (hardly noticeable) when scanning in fluid using smaller scan sizes (i.e < 3-um scan sizes). --Kumar