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Dear friends, I have some problems concerning surface potential detection. The most confusing one is the function of ´Bias´. The following statement is the details. I would be very grateful if you can leave your comments here.
Equipment: Dimension 3100. NanoScope4 controller;
Software: NanoScope V5.23
Sample: Si wafer as substrate, less than 1 mm patterns (inside the patterns, there are inter-metallic compounds) on the surface . The sample is directly put on the sample chuck.
Normally, by varying the interleave ´BIAS´ value, the potential signal shifts accordingly. However, in my case, it only rotates(tilts) the ´Potential´ Scope, instead of shifting it, i.e. the magnitude of ´Potential´ Scope doesn´t change at all, just the slop changes.
I suppose you have tried on the sample chuck (D3100 stage) to see whether the measured potential follows the change in Bias. This is a quick way to verisfy whether the system is set up properly. Once you have done this, you can move on to your sample. For surface potential measurement, a reliable electrical connection to the sample is required; simply sitting the Si wafer on the chuck is usually not enough. It is recommended to scratch the back side of the wafer with a scriber then immediately apply some silver paste (paint) and glue it to a conductive sample puck. It takes 10 minutes for the silver paste to dry. Try this out and let me know whether this solves your problem.
Thanks
Chunzeng LiApplication Scientist, Bruker
Hi Chunzeng, thanks a lot for your advise. I will try them out.
A new question, the silver paint has to be removed every time after measurements. Will it make the sample chuck dirty?
Although the si wafer is directly put on the sample chuck, the contrast seems not so bad. The ´dark´ particles are the inter-metallic compounds,on the top of Si wafer.
surface potential.jpg.aspx
Hi, I guess Chunzeng suggested you glue the wafer on a sample puck that is usually for miultimode sample support, not to directly glue to sample chuck.
Ang Li
Hi Ang Li, you are right. I misunderstood Chunzeng´s suggestion. I will try then and report later.
Hi Chunzeng,
Thank you very much for your suggestion. I have a try and report here.
1) I used a multimeter to verify the voltage on the sample chuck. When the Bias was 1V, the multimeter read as 0.25v. If I entered Bias 2v, the multimeter gave the value 0.5v. I guess some parts of AFM go wrong.
But anyway, the 'actual' voltage seems to be 1/4 of the Bias value. So I moved on to the following tests.
2)Then I have a try directly on the sample chuck. Unfortunately, the Potential scope was tilted as usual while changing in Bias.
3)As you suggested, I scratched the back side of the wafer with a diamond pen, and then immediately applied some silver paste (paint) and glued it to a conductive sample puck(a metal). It seems that it needs less Bias at which a good image can be achieved. For example, I used to apply 8 to 10 Volts Bias, but right now 5-7 volts.
Would you please explain me a little about the situation?
Thanks a lot!
Solong
Sorry, there is no bias voltage problem of AFM. I took the wrong component as reference(i thought it was grounded, but actually not).
The tilt of Potential scope is simply corrected by setting ´Realtime planefit´ to ´Offset´. But it doesn´t solve the root problem, does it?
Realtime Planefit- Offset would not remove the tilt. Can you take a screenshot and send to me.
chunzeng.li@bruker-nano.com
Chunzeng
Oh no, I know what a stupid mistake I have made.
The Potential scope was tilted because I didn´t notice that the ´Realtime planefit´was set to ´Line´ and ´Offline planefit´ to ´Full´.
Actually, the original Potential scope was not tilted. But ´Line´ planefit applies first order planefit on the Potential scope, which makes the Potential scope tilt.
When I set ´Realtime planefit´ to ´offset´, the Potential scope doesn´t tilt and shifts to the center. But it is better to use ´Data center´ instead of setting ´Realtime planefit´ to ´offset´.
Both ´Realtime planefit´ and ´Offline planefit´ should be ´none´.
Please excuse me for bothering every body in this topic.
No problem. It is not entirely your fault, we could have set the default to none.
Best