The reason of drift is often difficult to find: the sample, the stage, the detector. At least, it looks that you always have some decharging. Did you use silver dag for fixing or carbon? We usually paint from the metal surface to the mounting device a silver "line" in order to be sure that there is no resistance. You should check your ground cable. Remove it, observe the effect and the insert it again. Did you check another sample (Cu, steel, whatever...).? Do you see the same effects? Move the detector away...Does it become less strong? Is the image moving during movement of the detector?

BTW: the current is definitely too high... If the current is 0 you would not have any drift :-)

Are you sure there is no bakelite residue at sample edges? This doesn't look like typical drift. There is beam "jumping" most probably something is highly charged at sample edge what causes some drift but then the charge is released and beam "jumps" this is why you observe the same region scanned several times on the map.

Your probe current is very high; which makes the conduction between your sample and the holder very critical.

Some so-called conductive tapes or carbon may also cause those charging artifacts. Those tapes may be fine for imaging, but not enough for analytical measurements such as EBSD, which involve higher probe currents.

Try to fix your sample so that there is a direct and stable contact between your metal sample and the holder. If possible avoid using carbon tapes. Lower the probe current. Check the surface quality of your sample.

You also seem to have drift problems. Reducing, if not eliminating, the charging problem will reduce the drift problems. If, after eliminating the charging problems, you still have drift, check:

- temperature stability of the SEM room,

- temperature stability of the chiller

- Low-frequency vibrations around the SEM

Try to eliminate the charging problems first. Afterwards concentrate on drift problems.Charging problems may also decrease imaging performance (specifically SEI performance)

2hours mapping

120um aperture size

Accelerate voltage was decreased to 18kv

Still drifting

what is the probably reason ? Gert Nolze Kemal Davut Grzegorz Cios

Is the left side of the map - image an edge of the sample? What is the bright thing there?

Yes this is cross-section and left side the top surface Grzegorz Cios

Is it oxidized?

It is titanium and I think oxidization cannot be avoided. I used to mapping for over 12 hours and there is no such problem which measn oxidization is not the main reason. But after the fixing SEM(our SEM has been fixed ), the drifting problem starts.

If there is no problem with 12 hours scans I would say there is no problem with the stage drifting. Have you tried with any other sample? Reference sample like nickel or steel with no oxidation on the surface?

Is it possible due to the EBSD data saturations ?

If it is how can I prove that the stage is drifting ？@Grzegorz Cios

You simply do not tilt the sample...and use imaging over a longer time and compare the first image with an image after 20 min, for instance. Nevertheless, you should already see the shift during scanning. If it is similar to the tilted condition...it is not the stage. Take care and don't remove the tilt correction since then the drift becomes automatically smaller.

On the other hand, I've never seen a stage jumping so that I would exclude any mechanical impact. Only charging of a) sample, b) stage component, or c) EBSD detector. Since you or sombody else obviously did already EBSD investigation which did not show this effect, you can also exclude the detector. Thus, do you use a special stage? If not...it is your sample.

BTW: Turn your sample about 90° so that the alongated grains should be aligned vertically (which would be in fact the better alignment because of the worse vertical (spacial) resolution).

Regarding your statement: " I doubt the reason is the current is too high. " I can only answer: what do you think is charging there? Neutrons...?

Charging means that the electron transport is hindered. There are two options: either you are using less electrons since you cannot change the discharge of your sample (reduce beam current), or you are looking for a better conductivity in order to remove the arriving electrons faster. However, in both cases it has something to do with your electron current.

I really doubt it is not due to the charging of my sample as I did another Mapping with another titanium sample (laser cladded sample ).

First image took 1 hour while the other one took about 5 hours

As you can see, even it is 5 hours, the image is still drifting .

I doubt that it may be due to data saturation. What you think?

Charging is a really mean effect :-).

You can also describe it as incomplete decharging, and in your case it generates even some jumps caused by sporadic decharging.

Look, you are scanning your sample from bottom to top. Your beam (during charging (in the map a position above your map, or I would expect the EBSD detector) the beam will be shifted faster along Y (vertical axis) as assumed. Then you observe a decharging and the beam jumps back to the correct position (which you already measured before for about 30 min). Thus, you scan the same area again.

If this would be sample drift, the stage or your sample would have to move agains gravity. This is quite inlikely...

The misunderstanding is: you are measuring Bottom-Up and not Top-down. There are a few systems which do it vice versa, but I guess 95% use Bottom-up since it is default.

This you can easily test checking how you mount your sample and how it appears in the image.

If your detector is attached on the left side of your SEM the left-front corner of your sample (not tilted) should appear in the SEM image at the upper left corner. During tilt it moves down and you are scanning bottom-up.

My scanning is Top-down not from bottom to top. I can see it when it is scanning which is from top to bottom. Gert Nolze

It always displays a scanning from top to bottom :-). This is the irritating situation for many EBSD users. But this kind of displaying the scan does not say anything about the real scan in the microscope. "All" systems scan from bottom to top in order to prevent that the next beam path of the next line does not go through the contamination of the former row. Therefore, all manufacturers changed their measurement strategy by rotating the beam scan. bottom left at the sample is top left in the image and top right on the sample is bottom right in the image. Even Scanning electron microscopes scan like this.

It might be of course that you changed this default setting in your software. You should check this first properly. The SEM I know all run like this.

U r right

The EBSD is placed at the left side of the SEM. But from the TV image, as you can see in the image, it is at right side .

When it switch to SE2 signal and tilted, from the Azet image, it shows scanning is from top to bottom. but actually, the beam is from bottom to up!@Ger Nolze

@ xiaojun Shen

This is likely a "charge effect" that depends on the current density, sweep rate, swept area, sample size (thickness and area), and temperature. In the following reference you will find the explanation of the role of these parameters on the instability of the beam. This instability is not a failure of the apparatus and can provide information on the density of defects of the material.

Electron-trapping and energy localization in insulating materials. Technological impact of space charge electron-beam characterization

AIP Advances 8, 095228 (2018); https://doi.org/10.1063/1.5047673

@ Claude Le Gressus

Thank you for your reference.

Instability of the beam could be a reason cuz drifting starts since last maintenance of SEM.

What you mean is electron-trapping and energy localization are the main reason for that drifting ?

To eliminate the effect of the machine take a clean copper sample and check that the instability disappears.

If it is a charge effect, it characterizes your sample and then it must be studied. To change the conditions of the beam, the frequency of the instabilities will change.

Depending on the experimental conditions, there are two types of instabilities.

This type of image obtained by observing nanometric organic layers is at the forefront of my research on electron trapping and de-electroning processes.

I think "instability of the beam" is an improper term. The beam it self is nowadays so stable (from acceleration and beam current) that I would exclude any reasonable instability. If you mean "positioning" you are absolutely right. The scan generator does its best but the how the scan generator should know where the beam finally hits the sample? It is practically a guess (for the case everything works fine).

Please take into account that any dust on the sample but also the EBSD detector is some cause of charging (or imperfect decharging). The problems are mainly the forescattered diodes since they cannot be grounded, other wise thy would not work anymore. Therefore, some other tricks are used to reduce electric potentials as much as possible. This was the reason that I recommend to increase the detector distance a bit in order to find out whether this is the reason. If you increase the distance you loose a bit intensity which slows down the mapping speed. On the other hand the patterns look better since the noisy outer areas are not detected anymore. A distance of 18mm or even 20 should be sufficient. In case it is still not much better and disturbing you should contact the service. It might be some improper connection of the diodes within the detector. I covered my forescattered detectors by an additional Al-foil (their mount with the mount of the detector head.) Since this time this source of drift disappeared practically. I still have drift but this comes mainly from contaminations on the sample.

When I speak of instabilities, I mean in the presence of charges. These charges can be located on the sample if it is insulating, on insulating parts of the chamber (including the collector of the secondary electrons), on dust or a window to see the interior of the chamber. Wherever the charges are they lead to discharges that disturb the spatial stability of the beam (and possibly magnification). It is very convenient to have a metal sample without contamination to check for no parasitic charge in the chamber.

@Xiaojun Shen

Yes electron-trapping and energy localization are the main reason for drift and ... damage.

Claude Le Gressus : We have also drift during investigation of "perfect" iron meteorites or nickel-base superalloys. Carbon steel is a fantastic material to observe contaminations during scanning (using SE signal). In other words, even in case of metals the high tilt of 70° and the applied tilt correction increases the visibility of (vertical) image shift (drift) enormously. It is certainly better than anything else but can also make trouble. Ni is possibly a nice material to investigate and discover the sources of beam drift.

As a reference I use aluminum which after electrochemical polishing does not chemically absorb oxygen or organic contaminants. This type of material has made it possible to study what SEM contamination actually is. Without dielectric layer there is no contamination effect.

@Claude Le Gressus

You are electropolishing the Al sample and the sample itself does not contain organic contaminants? Electropolishing is most frequently done in acid-alcoholic solution and then it is usually rinsed with alcohol but these processes cannot be sources of organic contamination? Al is believed to always have very thin oxygen layer on the surface, how did you check there is not oxygen on the surface after electropolishing?

@Grzegorz Cios

The answers to your questions can be found in the work for the preparation of a reference sample for SEM, ALS, ELS (measurement of secondary electron work function, interpretation of the secondary electron spectrum fine structures and study of the channeling effects in AES) :

1- the reasons for the choice of aluminum: the sheats are textured and on the surface, the plane (111) dominates with a very low disorientation;

2- the oxygen does not adsorb on (111);

3- After electrochemical polishing and annealing at 600 ° C., the absence of contaminants on the surface is verified by Auger spectroscopy, by energy loss spectroiscopy (loss at 4eV, surface plasmon),

4- after air exposure and preservation for several days under argon and after flash of ions Ar +, it is verified that the surface is not contaminated.

In a few days I will prepare a project developing relationships between charge effects, electron beam deviations and the contamination effects ...

Claude Le Gressus :It sounds surprising to me since "Al sheets" are used for many products which are predicted to show a passivation layer. You certainly have a reference for the missing absorption of oxygen on closed-packed {111} layers? "No adsorption": Does it really mean: zero adsorption? In such case, polished Al stubs which everybody has and uses would be ideal for drift tests...? Move to a {111}-oriented grain - no drift, go to another grain: drift.

@Gert Nolze

Excuse me for being a little slow in answering your question. I had to go back to the history of this research. The answer is illustrated by a figure because experience provides more categorical results than current interpretations. Please refer to the attachment.

Sincerely

The Gressus

Hi J. Y. Wang, very helpful instruction. Could you tell which SEM, beam current, electron energy, step width and magnification do you use?

And an image of the map would be perfect. Thanks!