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´drive phase´ problem in Surface potential detection

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Not Answered This post has 0 verified answers | 3 Replies | 3 Followers

Top 25 Contributor
58 Posts
Points 652
stsolong posted on Tue, Jul 10 2012 10:05 AM

Hi Friends,

How to set the ´drive phase´ of surface potential detection?

I know the drive phase depends on the resonant frequency of the cantilever. I use SCM-PIT tip, with the resonant frequency of 78.4kHz.

I can get the Potential signal since ´drive phase´=85°.  When the ´drive phase´ increases, the data center of ´potential´ shifts apparently, like 1V/5°, but the amplitude of the potential doesn´t change. The range of ´drive phase´ at which the signal of potential appears is roughly from 80° to 110°.

Therefore, I don´t know which drive phase should be the right  one for the surface potential detection. Is there any convention to adjust the drive phase?

Thanks a lot!

  • | Post Points: 12

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Top 25 Contributor
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Bruker Employee
Reply
Chunzeng Li replied on Fri, Jul 27 2012 1:06 PM

As you mentioned, using the right phase for surface potential measurement is critical.

Here is a procedure you can follow to find the proper phase, I can be more specific if I know which version of software you are using (a screenshot of the UI is ideal, you can send to my email):

  1. Turn Surface Potential Feedback off. If this option is not available in your version, you can simply set Input Igain and Input Pgain to 0.
  2. Set Sample Bias to 5V.
  3. Set interleave Lock-in Phase (the lock-in used for surface potential) to 0.
  4. Note the Phase.
  5. Calculate the Lock-in phase: Lockin Phase = 90-Phase.
  6. Set interleave Lock-in Phase as calculated above.
  7. Turn the Potential Feedback on.

Follow the above procedure, and let me know how it works.

Best regards

Chunzeng Li
Application Scientist, Bruker
chunzeng.li@bruker-nano.com

 

Top 25 Contributor
58 Posts
Points 652
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stsolong replied on Mon, Jul 30 2012 3:07 AM

Thanks a  lot Chunzeng.

I am curious about the tuning of Lock- in phase / interleave for a long time. But it is not introduced in the manual book.

The microscope profile of surface potential in our AFM automatically set Lock- in phase/ interleave  to 0 with the green balloon on. By the way, I use software Version 5.23.

I will try your suggestion later and report it here.

Again thanks a lot for your reply!

  • | Post Points: 10
Top 25 Contributor
58 Posts
Points 652
Reply
stsolong replied on Thu, Aug 30 2012 3:43 AM

Hello everyone, here I post my experience of  finding the drive phase of KPFM (NanoScope Version 5.32). Thanks a lot for the help of Chunzeng.

1. Disable the interleave mode and achieve a good topography image first.

2. Set Bias/interleave controls to -2V,  Drive Phase to 0°, Lift scan height to 100 nm and drive amplitude/ interleave controls to  2V.  And activate Interleave mode to Lift.

3. Set both igain and pgain in the Other Controls panel to zero.

4. Settings of 3 Channels: Channel 1 shows height/ Retrace/Main; Channel 2 is Phase/ Retrace/Interleave; Channel 3 is Amplitude/Retrace/ Interleave.

5. Now observe the Phase image. It should be a straight line, e.g.  siting at 84°.

6. Calculate the Drive Phase = 90° - Phase, e.g. Driving phase = 90° -84° = 6°.

7. Now change the Drive Phase to 6° and set igain=0.1 and pgain=1.

8. Change Channel 2 to Potential.

9. Optimize the parameters, like  drive amplitude, lift height, igain, pgain, bias...to get the good images.

  • | Post Points: 10
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