The Nanoscale World

Peak force quantitative nanomechanical mapping

rated by 0 users
Answered (Verified) This post has 1 verified answer | 5 Replies | 4 Followers

Top 500 Contributor
2 Posts
Points 24
priya posted on Thu, May 31 2012 6:45 AM

What a negative value of deformation means in a PFQNM result? Is it some calibration error?

 

  • | Post Points: 12

Answered (Verified) Verified Answer

Top 10 Contributor
280 Posts
Points 6,219
Bruker Employee
Verified by priya

That is generally due to poor deflection sensitivity calibration.  If the deflection sensitivity is too large, the change in cantilever bending can be erroneously calculated to be larger than the Z piezo motion.  This causes the deformation calculation to return negative numbers and will cause problems for the modulus channel as well.

--Bede

All Replies

Top 10 Contributor
280 Posts
Points 6,219
Bruker Employee
Verified by priya

That is generally due to poor deflection sensitivity calibration.  If the deflection sensitivity is too large, the change in cantilever bending can be erroneously calculated to be larger than the Z piezo motion.  This causes the deformation calculation to return negative numbers and will cause problems for the modulus channel as well.

--Bede

Top 500 Contributor
2 Posts
Points 24
priya replied on Thu, May 31 2012 12:36 PM

Thank you for your reply. I used a set of probes and deflection sensitivity obtained was from 80 to 120 nm/V.  Is this value too high. can you please tell me the causes for poor deflection sensitivity calibration?

Thank you

Priya

  • | Post Points: 12
Top 10 Contributor
280 Posts
Points 6,219
Bruker Employee

Every time you put in a new probe or change the laser spot alignment or change from air to fluid, you must recalibrate the deflection sensitivity.  For instructions on how to calibrate, please refer to the manual.  The calibration must be done with a sample that is very stiff compared to the cantilever and it must be as clean as possible.  The calibration works on the assumption that there is no deformation of the sample (or tip of cantilever) so that the cantilever is forced up by the same distance that the piezo is extended.

--Bede

replied on Thu, Jun 7 2012 9:03 AM

Priya,

Bede is right. I figured out that many users were used to re-align the laser after the calibration was complete. It's exactly the same as in regular force spectrocopy: after getting the deflection sensitivity and the spring constant, the laser spot should not be moved. The best way to proceed is probably to wait long enough before engaging, like 30 min if needed, until you have no more vertical drift.

I also found out that with many different types of probes, the best deflection sensitivities are ,ost of the time < 25 nm/V.

Best,

 

Alex.

  • | Post Points: 12
Top 10 Contributor
129 Posts
Points 1,429

I guess Alex meant on Catalyst system, for most of the probes, prob <25nm/V, on the other systems it may vary I guess.

Ang 

  • | Post Points: 10
Page 1 of 1 (6 items) | RSS
Copyright (c) 2011 Bruker Instruments