Dear Monique,

In force modulation you get several magnitude/channels of information: topography, friction, amplitude and phase. Problem is that from your picture I do not know which one is it.

If it is topography, the color scale bar tells you that dark black areas are deeper than brown areas so they would be a pore certainly. But if it is topography normally the color scale would come in units of nanometers (nm) while in the picture it is labeled as nA, which normally would suggest a current map.

Which AFM are you using?.

Dear Nicolas, thank you for your answer.

I'm using an AFM type: Solver Next SPM from NT-MDT.

The image corresponds to the mag signal of a cement mortar. According to Solver Next manual, mag signal at this mode, is related to the local elasticity of the material so, I consider those dark areas had a smaller elasticity modulus. But as I didn't find this in literature, I'm a little confused if this relation is so direct.

In literature, pore of a cement matrix has a low elasticity modulus, so I could use this map to estimate the superficial porosity of a material.

What did you think about? Is this possible and correct?

Dear Monique Lunardi

Depend of what information you could get such Topography, amplitude and phase, your interpretation from AFM data would be different.

Amplitude and magnitude is one of the significant signals which can be accounting as height topography profile of the surface and will be corresponding to the surface peaks and troughs, if you could compare visually the topography image and magnitude image in your outputs, you would get the same morphological parameters.

But Phase image would categorising the surface texture in a different ways. Phase signals comes out from the difference between the source operational frequencies phase angle and output signals phase lag/angle as it is impacted by the physical viscoelastic properties depending on the materials underneath the probe, so based on hardness, elasticity and other physical properties of surface materials composition you would get a different phase colour pattern.

So to summarise:

- Magnitude/amplitude data is relating to height topography of the surface

- Phase data is relating to physical properties of the materials composition on the surface (like elasticity)

The best example for phase images analysis is in organic OPVs active later blends which is at some points a mixture of two or three different components and with analysing of the surface phase data, the distribution pattern of the surface can be identified.

I hope that's helpful.

Hi Monique, from the info you sent it seems that the amplitude of the oscillation is what they called Mag. What I still don't get it is why the units are in nA, instead of volts which is what you normally get from a good lock-in amplifier.

In principle in Force Modulation smaller amplitude (dark areas in your image) would imply smaller modulus than brown areas.

You can compare that image with the topography image to check if dark areas in Mag image matches with pores in topography.

Problem of Force Modulation is that it is a little bit obsolete as you cannot obtain quantitative data of the modulus (only cualitative). Also, when working with polymers, it can be difficult even to get reliable cualitative results.

Ashkan Nikiyan is mismatching the amplitude /phase description with the dinamic mode (or tapping). There the amplitude is used by the feedback to track the surface and get the topography, while in Force Modulation the static deflection is used for topography.

My suggestion is that you try also to perform static force vs distance curves on the dark and brown areas. There you could estimate the YOung modulus and double check that what you get in the Mag image is correct (higher slope indicates higher stiffness). You can check more here:

https://www.csinstruments.eu/soft-intermittent-contact/

Dear Nicolas and Ashkan, thank you for your answer, it help's me a lot to understand more about the technique and the relationship with de topography and de elasticity. I'm already performing some force x displacement curves in my sample and getting interesting results. Thank you again, with regards, Monique

Hi, Maybe it should be pointed out that the interpretation of the amplitude signal obtained in force modulation mode depends on the relative position of the actuator that generates the vertical displacement modulation.

If it is mounted beneath the sample then the measured cantilever deflection amplitude is large on a stiff area of the sample surface, as only a small fraction of the generated displacement goes into the local sample deformation. On a more compliant area, however, a larger fraction goes into the sample deformation and, thus, a lower cantilever deflection amplitude should be measured than on the stiff area.

Conversely, if the actuator is mounted on the cantilever side, ie integrated with the cantilever holder, then the measured cantilever deflection amplitude is maximum when the tip is well away from the sample surface, and it is much reduced when the tip is in contact with a stiff area of the sample surface.

Hence, the sketch given in Monique's previous post seems to depict the response obtained when the actuator is mounted beneath the sample. Hope the sketch is consistent with your setup. Best wishes, Martin

Dear Martin, thank you for your answer. I'm almost certain that the actuator is located beneath the sample in the AFM that I work on. And, yes, in harder areas the deflection of the cantilever is higher, and the amplitude measure is higher too. In softer areas, the deflection is smaller and gives me small measures on the amplitude axis. Best regards, Monique