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Hi friends,
I am doing conductive-AFM measurements in contact mode. A repeating pattern of the edge is observed in the height image, as shown below.
What can be the reasons for this phenomenon? A tip with 2 ending? Debris adhesive to the tip apex?
Any of your replies will be appreciated.
Thanks,
Solong
Hi Solong,
I fail to see a pattern in your image but it looks to me that the tip simply picks up material from your sample and drags it around. This appears to be the origin of those streaks in your image. Can you try to lower the setpoint a little bit and see what happens? When you scan the image over again do the streaks disappear?
Regards,
Stefan
I am not so familar with conductive measurements but from the height image you definitely have a double tip. This can often happen in contact mode. It can be hard to tell if this is due to some defect of the probe or a result of the tip picking up some of the material from your sample surface. If the image started out looking good and then suddenly had this doubling effect then it's likely tip contamination.
Best,
Andrea
The set point value seems to be a bit higher. Try to lower the value and re-adjust the gain parameter. This should solve the problem. You should also keep low scanning rate.
Hi Bilal,
You made a good suggestion but it is i) not clear if the setpoint is actually too high and ii) some electrical modes such as conductive AFM might actually require a higher setpoint as you would ordinarily use for simple topographic imaging. Especially semiconductor samples often have a native oxide layer and unless you "push" a bit with your tip you wont get a useful electrical signal.
Dear Stefan,
Yes you may be right. Actually we usually use AFM mainly for the topographical analysis of metallic samples with ceramic coatings. Thats why we dont need higher set point values in it.
Hi Stefan, Andrea, Bilal,
Thank you very much for your active responses and suggestions.
In my case, the sample is semiconductor with metallic coating. I usually keep the ´deflection setpoint´ less than 0.1V higher than ´vertical deflection´, by which the current signal becomes stable and wearing of tip is lowered.
Here I attach one SEM image of an used tip(Si coated with Pt/Ir). The tip apex was totally destroyed. Besides the debris it adsorbed, the Pt/Ir coating looked melted into a ball. This can happen if a large current (due to a large voltage bias) goes through the tip. What is your opinion?
According to my experience, the working duration of this kind of tip(SCM-PIC) on my sample is not long. After each scanning, I should gradually increase the voltage bias. Just after several times, the images look problematic.
Again thank you very much!
what you show is "normal" for contact mode CAFM with the metal coated probes. Melted coating means that your setup has no voltage control based on the feedback from current and/or temperature. That is also rising the question on the reproducibility of the measurements at the unstable probing conditions and the mechanisms of the probe-sample interactions:http://confocal-manawatu.pbworks.com/w/page/46002654/Electrical%20Measurements%20Reproducibility%20AFM
This is the same kind of question the oxidation/etching nanolithography people are facing. Try to switch to more reliable probing techniques:http://confocal-manawatu.pbworks.com/w/page/48266916/CAFM%20Probeswhere the trade off tip radius / maximal working voltage / reproducibility and accuracy of measurements / modification of sample or probe / other factors can still be the issues unless extra means of the controllability of the probe-sample interaction are applied.
From other hand nothing stops you from trying different modes and imaging conditions more adequate to your samples and tasks.
For the urgent solution you might like to contact the Research Marketing Place like Science Exchange:https://www.scienceexchange.com/or MIAWiki:http://confocal-manawatu.pbworks.com/w/page/62302278/MIAWiki%20Consultancy%20Plans%20and%20Pricing
Hope that helped.
Cheers,Dmitry
Thank you very much Dmitry for your answers and suggestions. They are helpful!
The problem you are facing is not uncommon at all for contact mode based electrical measurements. On one hand you would like your interaction forces low enough to preserve the tip and on the other hand you need to ensure a good electrical contact. Furthermore, the metal coatings often used are soft and can wear off rather quickly in certain situations. There are a few things you can do:
You can use more stable tips. Full metal tips and/or diamond tips will not wear off like metal coatings. You can find such tips at : brukerafmprobes.com . The Diamond tip (DDESP-FM) is quite popular due to its stability but be aware that the topographic images from these tip may not always look as 'nice" as with a a super sharp contact mode tip. If the latter is desired, just use an SNL or TESP probe for topography.
PeakForce Tapping. We developed a suite of nanoelectrical modes around PeakForce Tapping and tunneling AFM (TUNA) being one of them. PeakForce avoids the often damaging drag of the tip across the surface and thus enables much better topographic and electrical data acquisition. If you get a chance you should demo PeakForce TUNA!
With kind regards,
Hello Stefan,
Thank you very much for your suggestions!
I have ordered a box of pure Pt tip(Type ´RMN´) already. It has a big problem with tip engagement. I can hardly make this kind of tip successfully engaged. So far I have no idea why the tip engagement fails all the time.
Concerning PF TUNA, I am quite interested in this technique. But first of all, the NS controller 4 has to be updated into 5.