Dear Kim,

The surface looked like so flat is always not the flat due to the nanoscopic roughness present on the surface. However, the vertical scale bar present in image 1 (10 nm) and image 2 (50 nm) is not the same to traverse all the asperities of your samples. So, Initially, it appears low roughness. If you are scanning through the tapping mode the tip initialization takes times however after multiple scans tip can be able to traverse all the asperities in the samples and a more detailed image can be found. So, the perfect scan can get after multiple time scanning on the same frame and two identical frames in two consecutive scans can ensure the quality of your surface. The problem you are facing typically appears for the relatively smooth (nanoscopic rough) samples.

Thanks,

Poulomi

According to my experience of handling AFM, the atmospheric temperature affected your sample.

Since you mentioned that you're 3rd try become normal as like first try. I don't think it's true. take a close look there might be a small change. (If you could upload the 3rd trial picture will be better to analyze).

Dear Kim,

The surface looked like so flat is always not the flat due to the nanoscopic roughness present on the surface. However, the vertical scale bar present in image 1 (10 nm) and image 2 (50 nm) is not the same to traverse all the asperities of your samples. So, Initially, it appears low roughness. If you are scanning through the tapping mode the tip initialization takes times however after multiple scans tip can be able to traverse all the asperities in the samples and a more detailed image can be found. So, the perfect scan can get after multiple time scanning on the same frame and two identical frames in two consecutive scans can ensure the quality of your surface. The problem you are facing typically appears for the relatively smooth (nanoscopic rough) samples.

Thanks,

Poulomi

Since then have you done the same thing again? Beyond a one our of three, is this something you have reproduced? Have you done any further mapping of larger areas? If it is real then there are intermittent locations of less smooth areas. Or as Lokesh is talking about are you having a measurement issue? Were these done one after another or at different times where the AFM location might be experience different conditions with AC being off or on, humidity being different?

If this was run in non-contact mode and it picked up a small fragment at the tip I would then expect the force constant to change; enough to still give you an image but a false topography that is a false height. the fragment comes off and you are back to the original image.

So maybe try some different scan areas looking for defects, be careful of the air conditions, and be careful of the surface cleanliness that would not influence an error in the mode while it measures. Good luck. .

Hello. There are many sources of artifacts in AFM imaging. Check out this paper Article AFM image artifacts

Jieun Kim

The property of any substance depends on its structure. You have not reported the structure of the substance. Therefore, my answer will not be complete.

The principle of AFM operation is based on electron tunneling. If you received an image, then we can assume that the AFM is working correctly, especially since it shows a change in time. There are many substances with tunneling processes. Even water on a substrate with AFM shows proton tunneling.

https://www.nature.com/articles/nphys3225.pdf

We study proton tunneling in aqueous surfactant solutions by different methods.

https://www.researchgate.net/publication/325169774_Quantum_entanglement_in_micellar_solutions_of_ionic_surfactants

Therefore, pay attention to the interaction of the tunnelled electrons.

As per my experience with the AFM Machine ( PARK SYSTEMS AFM), when you locate your camera to choose a location for scan, it may look smooth because camera is not a nano-scale viewer. Therefore, though the film looks smooth, it may not result in a smoother AFM scan.

About the images 1 and 2 the answer is as told by Miss Poulomi Chakrabarthy, the size of the image that you have chosen in the issue. Scanning for any number of times on the location with same size will not alter the result unless you have aligned the laser beam on your PSPD properly.

Regards

Mohammad Hayath Rajvee.

Dear Jieun Kim ,

Besides looking at the papers about AFM artifacts recommended by Hakan Alaboz

i) You are scanning a small area, only 500 nm lateral size, and you are going too slow: you should increase the scan rate to 1 or 2 Hz to avoid thermal drift.

ii) You should play with the oscillation amplitude: if it is too small water necks between tip and sample may develop, whereas if it is too large you lose resolution (since the amplitude changes related to the tip-sample interaction, which constitute the feedback signal, are hindered). Obviously, the material the thin film is made of, it is important: it is not the same to deal with a soft polymer than with a metallic surface.

iii) I strongly suggest to look at the phase channel as well.

Finally, Yuri Mirgorod misunderstood: this is AFM instead of STM, so no tunneling is involved here.

Good luck!

Jieun Kim, Jose-Miguel Garcia-Martin

Take a look at the samples. They are clearly organic. Possibly biological molecules. They were obtained by evaporation (water?) on silicon. Despite evaporation from the sample, water remains in it. It affects the interaction of the needle and sample + water with a different tunnel barrier depending on the drying. This tunneling will affect the AFM and STM images.

Dear Jieun Kim ,

Based on my experience, I can say that since your thin film is obtained by evaporation you might be experiencing solvent induced noise (as also mentioned in comments above). Maybe you can check again by properly drying off the sample, obviously if your experiment allows you to do so. And also your scan area is pretty small, so with each scan frame there might be small drift in the area, due to which you are obtaining variation in the image with each frame. Maybe take a large area scan before you gradually zoom to smaller areas to be sure of the topography and also scans of different areas will help.

Dear Jieun Kim ,

Welcome to the world of AFM :). it happens more often that you may imagine.

Looking to your images, from my experience, first image could be silicon substrate (you can google silicon AFM image and will find many with similar morphology for the same scan size) or silicon with very small amount of film ; 5 mV scale on the amplitude channel means that the substrate is very flat. While the second image could be some area corresponding to the thin film.

So one possibility would be that there are parts where the film is not deposited.

Try to image bare silicon sample just to have a reference.

Other possibility would be, as the other people stated, that your film is being deformed at the same time that you are imaging (case of a soft thin film).

Suggestions from my side:

- Try to scan bigger areas just to have a look to the uniformity (20 to 50 microns).

- To check the properties of your thin film:

a) Keep scanning for a while an small area (less than 2-5 microns) and after that change the size to 20-50 microns. You normally would see something in the center (normally an square) where you were scanning the previous image. Depending on the material of the thin film and the force that you are applying while imaging you will notice differnces with the surroundings or not.

b) Try also in contact mode (if your material is very soft maybe is not a good idea).

- To check the properties of the tip-sample interaction: try a Deflection vs Zpiezo curve (in contacto mode) or Amplitude vs Zpiezo (tapping mode). There you could have an idea about the stiffness and adhesion. When you have some contaminant attached to the tip these two can change very much and eventually if the contaminant is detached you recover initial values.

- If you are using a tapping cantilever (i.e. 40 N/m) try to change to a softer one ( 1 N/m for example) and see if you get similar morphology or not.

- Change to a new tip and check if you get similar results. (80 % of the times is something related to the tip).

Hope it helps.

BR

Paco

Hello.

What I do also, since my PhD, is establish at least more or less what the tip radius is before any experiment. Even if the cantilever is the same and then use the same imaging regime to measure the sample. When imaging, there are several regimes one can use. In this paper we split into small amplitude attractive, bi-stable region and repulsive. Unless you specify the tip radius and the regime of imaging, it is very difficult that the images will look similar enough, particularly when you image small stuff in the 1-10 nm region.

Article A method to provide rapid in situ determination of tip radiu...

Im speaking mostly of amplitude modulation AFM here but it applies to most modes.