[Spm] A question about Image flattening

[Noam]

Hi
I am scanning with tube AFMs (Mutimode IV and PicoSPM II).
A recurring issue is that the images always have a "bow", meaning that flat
surfaces seem to be curved downwards, (i.e. parabolic).
>From what I've read, this is known issue in tube afms and occurs due to
"cross-talking between x-y and z piezos".

I have 2 related issues, and I would appreciate your advice:

1. How to flatten the image? polynomial? what degree? what software? How
much does this flattening affects z-axis resolution?

2. How do I calibrate the AFM...? the grids always appear bowed in the
imaging, and It's quite difficult to determine z-axis heights accurately.

Thanks,
Noam.
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