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How work the electronic in photodectector to separate two signals (topo and PFM)

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ozcarlosa posted on Fri, Feb 27 2015 2:29 PM

Regards,

I'm working in PFM technique with Multimode SPM, Nanoscope IIIa, SAM III and Nanoscope Basic extender and I need technical information about How work the feedback loop and electronic in photodectector to separate the PFM signal from the topographical information.

 

Thank you.

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Bruker Employee

Hi Ozcarlosa,

I believe the MultiMode needs at least a Quadrex phase extender (the successor to the Basic phase extender) to be able to do PFM. The Quadrex phase extender essentially has a fully fledged lock-in amp at its core. The basic extender had only a phase detector.

When you do have the right electronic configuration in essence the photodetector output is fed into:

1) the lock-in amp which separates the PFM signal (which is usually driven at 5-15kHz) and

2) the servo loop which uses the signal (on a MultiMode of that age probably low pass filtered at ~2kHz) to track the sample surface.

Email me at ian.armstrong@bruker.com if you have further questions. I can provide you with tech notes or datasheets on the electronics you have, or put you in contact with someone to look at upgrade options for your system to support your future research. MultiModes of any age are upgradeable to the latest technology we have.

Cheers

Ian

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Hi Ian

 

I  have tried to perform PFM measurements on ferrolectrics materials for phase and amplitude, but the results are not good due to high noise in amplitude signal, wrong signal phase from the lock-in (maybe for delay in electronics basic extender+lockin). So I was checking the probe holder and the pin 1 and pin 2 don´t have any connection with A (Gnd) and B parts, the probe holder is right or I need the EFM probe holder?. And the connector in the last image don't have any voltage, Should measure I the voltage from signal generator there?

  


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Bruker Employee

Hi Ozcarlosa,

I see in another thread you asked a question about the NanoScope IV controller. If you have access to a system with a Nanoscope IV controller the PFM setup should be much more straightforward. With regards the cantilever holder: you have a choice in PFM to supply the AC bias to the tip or sample on most instruments. Being able to alternate doing both can be useful as either scheme may have some advantage or disadvantage depending on the probes used, the sample characteristics and the voltage range. If your cantilever holder has no electrical connection to the tip you will have to go with sample biasing. You can make sure this is working by entering the parameters in the software and checking with a multimeter with one electrode on the piezo cap and one on say a screw on the Nanoscope controller box. You can email me offline for an image with the pin readouts for the cantilever holder or base boar connector.

 

Cheers

 

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thank for your help

now I am working pfm in Dimension with nanoscope IV, and I trying with multimode too with the same sample holder and voltage applied to piezo cap and there I can to measure voltage. But is true the electronic in multimode and basic extender isn´t able to work optimally in PFM, my question is why some papers report multimode and external lockin amplifiers in PFM mode?

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Bruker Employee

Hi Ozcarlosa,

It is true - older MultiModes that have the NanoScope III controller and just the "Basic phase extender" are not optimal for PFM. You need at least the "Quadrex phase extender" or later NanoScope IV or V controllers (that have internal lock in amps).

So this is why in fact you see publications that reference older MultiModes used in conjunction with external lock in amplifiers (because our system electronics could not do it at that time). When using an external lock in amp you still need to configure the system correctly with the signal access module and again make sure of electrical connections but it will work when done correctly.

Best regards

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Hi

The Piezoresponse mode works fine with AC voltage applied to the tip and sample grounded, but not in inverse way (AC voltage applied to sample and tip grounded) any idea why?.  Other issue is get deflection sensitivity, I was working this parameter through force-plot in multimode following instruction in user manual, but in Dimension I have two problems: 1. In parameter list the maximum value for "ramp size" is 49nm and 2. Z scan start move a few steps slowly and then stop completely without to finish the curve.

Thank you

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The system show me in error log: "z sensor does not work please check the controller or head hardware", but the engage happen normally. Is this a consequence of problem with deflection vs Z scan plot? 

 

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Top 25 Contributor
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Bruker Employee

Hi Ozcarlosa,

 

I'll have a colleague contact you directly, I think it will be a quicker route than back and forth on this forum to troubleshooting any hardware problems and talking through some of the PFM calibration/ implementation.

 

Best regards

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