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What is the physical meaning for “Inphase”, “Quadrature” channels in ScanAsyst mode?

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BrukerApplications posted on Tue, Jan 19 2010 6:40 PM

What is the physical meaning for “Inphase”, “Quadrature” channels in ScanAsyst mode?

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I have a similar query...  how can  it be related to the phase  images from the  conventional  imaging  modes?

Can it be utilized to replace the phase  images, especially if one does not have the  peak  force  mode on  ICON  and  only  have the  scanassyst  modes?

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Answered (Not Verified) replied on Thu, Feb 16 2012 1:55 PM
Suggested by Bede Pittenger

Hi Mithun,

Every ICON system has PeakForce Tapping as a standard option. PeakForce Tapping is a scan mode, like contact mode or tapping mode. ScanAsyst is a software algorythm that automates PeakForce Tapping, see e.g. application note #133: http://nanoscaleworld.bruker-axs.com/nanoscaleworld/media/p/1548.aspx

In PeakForce Taping operation we use a sinusoidal signal to move the tip up and down. If fed to a lock-in amplifier one will get X and Y ouputs (or inphase and quadrature). These outputs are similar to "phase" in tapping mode but because of the completly different nature of the underlying scanmode have a different physical meaning.

 

Stefan

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Or, worded another way:

Those are raw outputs from the lock-ins.  They are not used in QNM, and don’t really tie well to a physical property (though dissipation would be the closest).  The point of having them is that they can tell a user that there is a difference in material properties, just not precisely what the difference is.  This is similar to TappingMode Phase Imaging in that users can use it to get an idea of distribution of components in a multicomponent system.  Often, there is a lot of bit noise in those channels.  If the photodiode is well centered, the Deflection Limit can be decreased to help deal with the bit noise.

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Thanks Bede. Is there  any output in the QNM  mode  which is comparable to the phase imaging in  tapping? What is the difference between Inphase and Quadrature outputs, in layman  terms? Why does the quadrarture seem to have more noise? Could you elucidate  which parameters should be modified in the scanassyst mode, if any?  Is the Young's modulus derived from the approach and the adhesion from the  withdraw curve  fronts of a F-d curve in  QNM? 

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Thanks Stefan. Since the cantilever is not being oscillated  anymore, in this mode obviously  there can be no  phase difference. Why and how does the  x and  Y outputs of the lock ins still represent the compositional distribution  within the scan area? Thanks for the link to the document.  I am going through it.

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Bede,  Would you suggest turning the scanasyst auto control to  individual and then  decreasing the set point? As there seems to be appreciable noise as you pointed out, even in the Inphase window. 

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Q: Is there any output in the QNM mode which is comparable to the phase imaging in tapping? What is the difference between Inphase and Quadrature outputs, in layman terms? Why does the quadrarture seem to have more noise?

A: The inphase is the Rcos(theta) and quadrature is the Rsin(theta) outputs from the lockin that is driving the PFT modulation (usually at 2KHz on Multimode or Icon).  This cannot be related to tapping phase since the system is not operating at cantilever resonance.  Actually, none of the PFQNM outputs can be directly related to TappingMode Phase imaging.  If you need to compare to Phase Imaging, HarmoniX is probably the best solution.  If you have the PFQNM option, I would not recommend using Inphase and Quadrature since the Dissipation channel usually shows similar contrast and does not have the bit noise issue.

Q: Could you elucidate which parameters should be modified in the scanassyst mode, if any?

A: The beauty of ScanAsyst is that you don't really have to adjust the parameters.  If you want to enhance the Inphase or Quadrature, however, you might try increasing the setpoint -- this will usually increase the dissipation and may increase your contrast in those channels as well.  Also, don't forget to drop the Deflection limit (assuming your laser spot is well centered).

Q: Is the Young's modulus derived from the approach and the adhesion from the withdraw curve fronts of a F-d curve in QNM?

A: No, both adhesion and modulus are calculated from withdraw data.  Deformation is calculated from approach data.  Dissipation is calculated from both approach and withdraw data.

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Thanks Bede. That was very  helpful. Now we do not have PFQNM but would talk to Jay Anederson to inquire about the pricing etc. because - 1. the noise is quite irritating and defeats the purpose of the efficacy of the scans. 2. I am not certain of the acceptability of the   X /Y lock in  outputs  in the scientific  community as they do not appear to be  tangible quantities. What would be your suggestion till we acquire the PFQNM? The dissipation or adhesion on the other hand would make perfect sense. Have you  published or aware of any peer reviewed publication citing  the inphase /quadrature images? Any help on this line would be appreciated.

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Hi Mithun,

To be clear, the point in providing those channels is to show where in an image material properties change, this can help identify components in a multicomponent system which may not be identifiable in the height signal, but do show up in Inphase and/or Quadrature (for example, in a polymer composite, you might know that 30% of the sample is PS and 70% is PMMA.  You see that 70% of your image is brighter than the rest in the InPhase image implying that component is the PMMA). 

We are not making any claims about what a given value of Inphase or Quadrature mean.  I am not aware of any publication that does this either.

--Bede

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replied on Fri, Feb 17 2012 12:28 PM

Mithun,

I am not sure what you mean by that you are "[...]not certain of the acceptability of the X/Y lock in outputs in the scientific community as they do not appear to be tangible quatitities."[sic]

A lock-in amplifier has revolutionized science since invented so I am not sure what you are hinting at. The ScanAsyst environment that we include with every ICON/MM8/Catalyst system provides you with reliable, easy to obtain, topographic information. The additional lock-in outputs are, as was explained here before, signals that are based of course on the interaction of the tip with the sample but that meaning is not directly related to QNM parameters. This particular fact is similar to "phase imaging" as the phase is a by product, so to speak, of using a lock-in amplifier and in itself does not have a clear meaning in that specific context, i.e. one can not unambiguously deduce a physical property from the signal. Both "Phase" and "Inphase/Quadrature" signals can and have been however used with great success all over the scientific community as qualitative signals.

If you would like to get quantitative nanomechanical information out of your system we do offer the QNM suite where we analyze the raw data obtained during the force curves that form the basis of PeakForce Tapping and present the data in a quantitative manner.

Best regards,

Stefan 

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Hi,

I tried to download the application note but the link does not work. Can someone tell me where I can get it?

Thanks

 

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