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Hi,
I have some difficulty in engaging the SNL probe in liquid on Innova. I perform the experiment in liquid, the substrate is mica. I tried contact and tapping mode, neither could engage successfully. However, the NPG probe can be engaged easily.
The parameters are: Cantilever-C, resonace frequency ~15kHz, targeting free amplitude 3V, 20×gain，setpoint 2.0, P 0.6, I 0.8, D 0.0, PSPD 1.5V.
Can anyone tell me is there any skills I should care about?
Thanks in advance!!
Zhuoyang
Hi Zhuoyang,
First let me start by saying that it should work.
I am especially puzzled that you can not engage in contact mode. What exactly happens? If you get a "false engage" did you try just hitting "Engage" again?
For Tapping: I assume that PSPD refers to your setpoint. In tapping, especially if you approach from quite far away, a few intial false engages can be common. This is nothing to worry about. Just hit engage again. Once on the surface you may want to slowly lower your setpoint until tracking is stable. I recommend after engage to turn the feedback loop off by hitting the "feedback on/off" toggle button, retract the z-piezo by 500nm (give or take) by entering this number as an offset in the appropriate field, and then run a tune. You may notice that the peak has shifted slightly and so may the amplitude. Just select a proper setting again and go back into feedback. This should work and will result in extremely stable imaging.
Please keep us posted.
Stefan
Hi Stefan,
Thank you for your response. I do not get a false engage. The unsucessful engage means that the scanning window do not appear. It just keep engaging for quite a long time.
Sometimes the tip does not move downwards after hitting the engage button. I doubt that it may be caused by the too low P and I value. Although the cantilever tune exhibit a main peak at 15kHz, I am not sure the 15kHz resonace frequency is suitable ( I got the information from "SNL guidelines for use"). Besides, is the 3V targeting tapping amplitude too low?
I really cannot think of any other possible reasons for this problem.
P.S. I am using SNL in liquid and the sample is cell on mica.
If the system appears like it is still engaging it could mean that it eiter really is if you approached from quite far away or that the centering routing is not finding its setpoint. You may try the following:
Expand the "engage" menu. Here you will see a checkbox called "centering". uncheck that box and try again. The z-piezo will after a sucessful completion of the engage routing now sit wherever the system was when the setpoing was reached. For manual centering, you may just push the small tip and/down icons a few times.
You can always stop the engage routing manually by simply pushing the button again. If the z-piezo bar runs all the way to the top, you know that the system has not reached feedback position. The scan control window can always be opened manually from the menu bar.
Best,
I think I have found out the reason. it indeed is far away from the sample surface. I set the distance of "withdraw tip" button to 0.4um, then engage (not successful), withdraw tip, and re-tune. I think the SNL resonace frequency is very strongly dependant on the distance between sample and tip.Now I can have the probe engaged successfully, although the profile is fluctuating and not easy to keep it stable. At least I can scan a true sample surface now. Thank you for your kind reply.