Lock-in-phase in Surface Potential Detection

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Ian Armstrong replied on Wed, Feb 20 2013 7:17 PM

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My preferred method of finding the correct lock-in2-phase is:

Obtain a good topography image then enable Lift Mode at 50nm for example

Hit generic sweep

Set lift height at 50nm

Click interleave radio button

When it asks if you want to unlink parameters click “no”

Sweep lock-in2-phase versus amplitude2 and potential

You should get two “square wave” traces. Each will show a 180 degree phase window that would be a suitable lock-in2-phase. In the amplitude channel that suitable range should be where the trace is zero, as if the potential feedback is working correctly the system will drive the physical cantilever response to zero by homing in on the correct DC offset. Similarly in the potential channel the suitable range should be where the potential value integrates to a finite value (as opposed to shooting off the chart scale). If the graph traces do not look as I described check your electrical connections and potential feedback gains, maybe try on a HOPG sample silver painted to the chuck, or better yet our surface potential artefact which has Gold/Aluminium/ Silicon sections you can measure in one scan before any unknown sample.

Best regards

Ian

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RAZAFITIANA replied on Sat, Feb 23 2013 12:59 PM

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Hi Ian,

Thank you for you answer.  I will try next week.

I have another question regarding to electrical connexions. Do you think that using a silicium wafer (one polished side and another silver painted) is a proper substrate.
The measurement of surface potential is performed on a sample of clay particles embedded in the starch film deposited on Si wafer (polished side).
In this way, I check the variation of surface potential versus the concentration of particles.

I will keep you informed of my tests.

Best regards,

Maharavo

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Ian Armstrong replied on Mon, Feb 25 2013 2:54 PM

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Hi Maharavo,

The sample substrate sounds ok to me. To my understanding the surface potential technique will be most sensitive to the uppermost conductive layer of your sample, and also any trapped charge. So if there is charge associated with the embedded clay particles this could well show up in the surface potential channel. The depth from the surface of the particles will also be an important factor in the images obtained.

Best regards

Ian

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Wilson replied on Wed, Apr 24 2013 3:20 PM

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Ian

1.       Is Surface Potential AFM quantitative for electrical measurements?

2.       How can I calibrate Surface Potential AFM to get quantitative electrical measurements (potential)?

3.       How can we get the work function of the tip and how can we load that in the system?

4.       We acquired our Icon in July of 2012. My guess is that we may not have Peak Force KPFM on our system. Please clarify this.

5.       If I have two separate samples, can I be able to map out the potential of the two samples differently or can I only get relative measurements within one sample?

6.       Can I be able to do both KPFM-FM as well as KPFM-AM with our Dimension Icon AFM?

7.       I have SRAM standard sample (from Bruker) with me. Can this sample be used also as a standard for KPFM-AM and KPFM-FM? What is the potential of this sample? Does the potential depend on the type of the tip used?

8.       In the webinar (KPFM by Bruker) presentation slide (attached page 11), how did they get 30mV and 105mV?Did they get that by drawing a cursor profile? Also in the same webinar (page 13), how did they get a potential of 150mV?

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replied on Thu, Apr 25 2013 12:00 PM

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Hi Wilson,

I answered your post here: http://nanoscaleworld.bruker-axs.com/nanoscaleworld/forums/t/430.aspx

Stefan