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HarmoniX v. PeakForce QNM

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BrukerApplications posted on Mon, Jan 11 2010 7:14 PM

What can HarmoniX do but PeakForce QNM can not?

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Suggested by Bede Pittenger

HarmoniX is a secondary mode based on TappingMode. The feedback control remains tapping amplitude. HarmoniX uses special torsional probes and reconstructs tapping force curves from lateral deflection signals. PeakForce QNM mode is a primary imaging mode that directly generates force curves while feedback precisely controls the peak force. Currently in HarmoniX mode, the probe touches the sample at a rate of tens of kHz compared to a few kHz for PeakForce QNM so the time resolution of force curve on HarmoniX mode is one order of magnitude higher than PeakForce QNM.

Since HarmoniX is fundamentally tapping mode there is a traditional Phase data channel.  PeakForce QNM has Inphase and Quadrature channels.  While similar in some ways to Phase, Inphase/Quadrature data are a result of an off-resonance feedback mode and shouldn't be considered to be identical to Phase.  Like Phase data, Inphase and Quadrature can show contrast and sample variability but it isn't always safe to make assumptions about what those differences on the sample surface are.  Both HarmoniX and PeakForce QNM have separate data channels to separate out contributors to phase contrast.

Another difference between the modes is the range of modulus that be covered by a single probe.  The HarmoniX probe is designed to work over a wide range of sample modulus by tranlating periodic vertical forces onto the horizontal axis where the response is not overwhelmed by the tapping feedback frequency response.  PeakForce QNM uses standard probes but the trade-off is a reduced modulus range with each probe.

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Patrick Markus replied on Wed, May 26 2010 7:43 AM

An extra comment to Mike's last statement about reduced modulus range with a single probe; It is indeed so that the probes spring constant needs to be selected depending on the sample at study for proper quantitfication of sample modulus. However, since regular probes can be used for PFQNM (in stead of asymetrical probes for HMX) a very broad range of spring constants can be selected (from down to 0.05 N/m al the way up to 300 N/m) resulting in a wider effective range of modulus measurements compared to HarmoniX.

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