There are several possible reasons for this. Some (list not complete):

-is the zrange displayed here the image display or the measurement setpoint? Because for a 10x10um2 image that's kind of low if it's a measurement input value.

-there can be effects of the scan rate, try varying it in both directions

-same for the amplitude setpoint

-worst case scenario: you have another machine which is not necessarily in the same room which causes electric perturbations. You may require to install some sort of filter in this case.

What is your specimen, and how is it fixed to the table? I have had an issue in the past with a sample moving under the probe, which caused a distortion of the image.

Given the apparent symmetry of the image above and below the distortion, I would suggest that the most likely issue is (as Jürgen Weippert mentioned) interference from another source, effecting the controller module.

Jürgen Weippert Thank you very much for your answer! We are using contact mode, not tapping. The z range is just the data scale, we have set it up to 300 nm as it works the best for the samples we are working with. We changed the scan rate and the figures keep appearing the same going at a slower and faster rate.

The error seems very consistent over time, even between days. If I change the spot sample the image looks different but still with elongations on the same axis. I have worked plenty of times with the same samples and I never had drift or slipping with that tip-sample combination. I also have been using different samples that worked before and keep happening.

Michael Leighton Thank you very much for your fast response as well! We are using different PAHs samples that are vapor-deposited in thin films. The AFM is set up in a vibration-isolation mount and it has been there with no change for the last years, and this issue started happening two weeks ago.

About the electrical perturbation, I am not sure what you mean by it. Could you please elaborate? I am not sure how to test it.

Thank you very very much to both of you!

Electrical perturbations are a tricky thing. Essentially, some sort of device that's attached to an associated power line causes net fluctuations on the power supply of your AFM; that may cause oscillations or contact issues.

Localizing such a perturbation exactly is quite a beast to do.

I have had a suspicion before that I have not been able to find any evidence for; When using contact mode, is it possible that the piezo cannot move the tip further? If so, what does the AFM do? It seems that the slow scan direction is reversed partway through the scan area to move away from the issue and avoid a tip breakage.

I know that it is fully possible for surface forces to affect the scan area coverage, as there can be “scars” in the image when the attractive or repulsive surface force causes a jump in the slow scan direction. This normally appears as a black line in the fast scan direction on the surface image. However, I have never seen it recorded that there is any controller reaction to the issue of tip movement (e.g. to reverse the slow scan direction).

If this is what is happening, it would show that your tip entered a region where the surface adhesion was high, and the tip was not able to make progress down the scan area in the slow scan direction. The tip made some, reduced, progress down the area but the progress was slowed until it could make no further steps (image blurred). The controller then reverses the slow scan direction (image line of symmetry) but had to fight back across the area of high adhesion region (blurred again) before scanning could resume normally (clear symmetrical image).

I would suggest ensuring that the humidity and tip/sample cleanliness are suitable for your scan. If you are interested in topography, try the tapping mode. If you are interested in lateral force, see if there is a higher friction force in the blurred area of the image when compared to the other regions, particularly at the ends of the scan. It might be that the contact load is too high, and you could try reducing the deflection setpoint.

We don't use a Nanoscope, but sometimes at the beginning of a scan, the objects being imaged seem elongated all in the same direction (usually slightly angled), and it usually fixes itself after a minute or we change the scan direction (0° vs 180°) and that "solves" the problem.

Alternatively, maybe the tip is pushing your specimens?

I assume you've tried different tips?

Lastly, do you have a known reference that can be imaged (like gold squares on silicon which can't be displaced) to verify the AFM is in working order?

Start with max Z range. The same problem???

Test with dedicated test sample from bruker. What is the result?

Try to change scan angle, more speed, higher gain and turn on LFM ;).

If not working only with your sample, connect surface of the sample with oposite site of the sample's table (magnetic ring). Let us know what is the result.

Hello everyone,

Thank you very much again for your answers!

I have used different tips and I also used a standard sample (TGZ1) and these were the captures obtained (attached). I changed the scan size between some of the captures, as you can see. Those captures were processed with Gwydion.

I have changed several times all the different values that appear in Nanoscope (scan rate, scan size, scan angle, etc). There are differences in the images, but the problem keeps appearing no matter what.

I changed the line of the power supply and I set the AFM in a separate line. No changes in the image.

Today, I did readings with an oscilloscope in a connector between the AFM and the AFM controller. I compared those signals with previous signals obtained with that AFM. The voltage of the PIN that I think it is x, was modified during the scan when the tip was engaged.

For the value that I think it is y, it reads 0V for almost 3/4 parts of the capture and the values are never negative as expected. In the extremes, the voltage values are around 19V when the tip was in the extremes of the spot.

Any suggestion?

Such stubborn deformations could also result from a kind of obstruction of the scanner motion. Friction forces could be at play, possibly caused by debris or other particles that got stuck in the (narrow) gap between the sample holder and the surrounding area of the stage. If accessible, it could also be worthwhile taking a thorough look at the scanner.

Thank you very much to everyone! Finally got what was going on. The oscilloscope was showing a very small signal in the y axis, but there was some signal so the issue had to be in the amplification signal. We changed the Nanoscope to other Nanoscope we had in lab and the same thing was happening. So the problem was most likely in the AFM itself. Observing the electronics of the base we found a burnt out fuse. We didn't know what was the source of that fuse being burnt out but it ended up being a short-circuit in the piezo. After changing the piezo, the problem is solved. Thank you very much to all of you for so many answers! I wasn't expecting so many great suggestions. Happy to be a part of the community! :)