Z centre goes out of range

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Andrea Slade replied on Wed, May 22 2013 12:53 PM

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Hi Mehdi,

If your AFM signals that it is engaged but then the Z scanner immediately goes to being fully extended, this typically indicates that your AFM has false engaged. The scanner fully extends in an attempt to find the surface.

You may need to check your cantilever tuning parameters (resonance peak, drive ampltitude. Are you operating in air or fluid? Which type of probe are you using? Are you doing a manual tune or auto tune?

Best,

Andrea

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Mehdi replied on Wed, May 22 2013 2:21 PM

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Hi Andrea,

Thank you for taking the time to answer.

This was my assumption too, there is a problem when engaging the surface, in contact mode when I change the setpoint I directly change the distance between the Tip and the surface and then I can get a correct signal, but in Tapping mode I can't act directly on the distance between the tip and surface.

Concerning your questions, I am using an auto tune and I get good resonance peak, I am operating in air and I used many type of probe: n-type silicon sharp and ultrasharp, normal DNP.

You think I should use a manual tune?

Best,

Mehdi

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Andrea Slade replied on Thu, May 23 2013 12:47 PM

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Hi Mehdi,

The auto-tune should be okay for operating in air (we use the manual tune for fluid imaging). I would verify that the target frequency range in your auto-tune parameters matches the range given for the probe you are using. If not, then sometimes the peak the auto-tune chooses may not be the actual resonance peak.   

With regards to the probes you are using: the silicon TESP type probes are what are commonly used for TappingMode in air (I assume that is what you mean by 'n-type' silicon probes). DNP's do not work well in air. They are too soft to get a good, reliable drive amplitude response. They are typically used for contact mode in air or TappingMode in fluid.

I am not familiar working on the d3100 with Nanoscope version 4 software but there could be a couple of reasons why it is false engaging.

- You might want to try increasing the target amplitude in your auto-tune. I think it should be targeted to 1V for the system you are using and the peak offset should be 5-10%. Depending on the type of sample you are imaging, you may need a little larger amplitude to get you to the surface. I will usually tune my probe, engage on my surface, and then lower my amplitude as low as I can while maintaining surface tracking.

- If the system false engages and the scanner fully extends, and if your system allows you, just click on engage again. This will start the engage procedure from the point you are currently. Meaning, do not withdraw and then engage again.

- If you are false engaging quite near the surface, you can also try using the stepper motor to move the tip closer to the surface (this would be effectively what you are doing in contact mode). 

- I do not know what the correct engage settings/parameters should be for your system but if someone perhaps changed any of these values (sewing, min engage setpoint%, etc) this could cause consistent false engaging.

Another thought is that this could possibly be sample related. Some samples, when imaged in air, develop an electrostatic charge on their surface. This can sometimes make engaging the probe on their surface difficult. If you can monitor the vertical deflection signal from yuor photodetector while you are engaging, you will see it start to steadily creep towards +12V as the probe nears the surface.

Best,

Andrea

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Mehdi replied on Thu, May 30 2013 9:29 AM

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Hi Andrea,

Thank you for your advises, I will let you know once I get a result.

Best,

Mehdi