Forums
Bruker Media
Community Media
Bruker AFM Probes
SPM Digest
Application Notes
NanoTheater
Website
中文
Brochures & Datasheets
Publications
Probes Catalog
Events
Manuals & Documentation
Presentations
Guide to AFM Modes
News
Journal Club
Webinars & Video
Nanovations
Other
Hi,
We're using a Bioscope Catalyst with the latest release of the nanoscope software.
We're trying to get modulus data from hydrogel samples with regions of varying stiffness and height. Currently we are able to scan the samples in contact mode using MCLT-D probes submerged in water. When we switch to peakforce QNM in the newest software release this tip seems too soft to engage the surface, so we've had to use MLCT-E. While we're able to engage the surface and get height images, and we are able to get reasonable deflection sensitivities from ramp mode and spring constants from the thermal tune function, we have not been successful with adjusting the tip radius to change the modulus (using the relative calibration method). It seems that no matter what we change the radius to, the sneddon modulus values do not change at all, and are either close to 0 or in the MPa range . We're getting deformation values that drift between 100nm-500nm, but are mostly around 300nm. The sample we're trying to use as the reference sample is our own control hydrogel with a bulk modulus measured by DMA of 250kPa.
Should the sneddon modulus automatically and immediately change when the tip radius is changed? (because that's not happening)
Do we need to worry about the tip half angle? we have not changed it from the default.
What should the deformation of a soft sample be for the relative calibration?
If we are eventually able to correctly calibrate the tip radius, supposedly we should adjust the peak force setpoint on the experimental sample so that the deformation is the same, but if we have regions of different stiffness, the deformations may be different within one image. How should be adjust the peakforce setpoint to get accurate modulus maps for an entire image with varying deformation and modulus?
thanks for any help.
Darice
Hi Darice,
The Sneddon model should be the better option for the modulus range of your samples. Unlike the DMT model, Sneddon does not use the tip radius so changing that shouldn't affect the modulus value in the Sneddon channel (you don't even need to calculate it). It does, however, use the tip half angle. You will need to set that in order to get proper values. The Sneddon model does require you indent the sample more than the DMT (cone vs sphere). It should be at least 10nm - but sounds like you are getting much more than that. Just try to keep the same deformation for your reference as your sample.
With such soft sample I have found I have needed to try several probes to find one that is soft enough to use. MLCT E is good but you could also try some softer ones.
Best,
Andrea
This post is 1 year old but my answer could help somebody else.
I had the same problem while engaging with a very soft probe (DNP-D) in fluid in the PFQNM mode. the default engage step is 15 um, You will be able to engage with a lower engage step (microscope menu > engage settings), you could also use a lower gain.
kind regards
Celine