The use of AFM height images we normally know. But I have doubt regarding the phase image. Is this the original phase information that we are normally getting from XRD and all? What does the color variation in the phase image signifies. Can I correlate this color variation with the polymorphic nature (ie mixture of different phases in case of polymer thin film) of sample? Can I see the crystalline and amorphous component as different colors? Similarly let me know the details of amplitude and amplitude error image? Thanks in advance.
Long time ago Digital Instruments (later Veeco and now Bruker) published few words about phase imaging: http://www.bruker.jp/axs/nano/imgs/pdf/AN011.pdf
In my opinion PhaseImaging give possibility to find region of different properties: eg giving opportunity to clearly visualize grains and boundaries.
Amplitude image I using only for taking best height image - lower amplitude signal = better topography. Amplitude image shows how the tip deflected as it encountered sample surface. Images are similar to topography showing the map of the slope of the sample, but Z scale is no in linear units. Using other words, amplitude image is the image of error signal of amf.
Some time ago I was using PhaseImaging to get information of nanoparticles dispersion in polymer matrix - and it works perfectly.
Dont think PI will give clear information according to crystalline and amorphous 'parts' of sample. On the other hand it may be use to do it. There are a lot of papers where eg LFM was the picture giving information about hydrophobic properties. So,why not to take into consideration the crystals as much more harder than amorphous phases (the results obtained from hundreds of images)? Results may be probably true. But if I were You I would to check it using another methods - just to ensure that crystalline phase content is similar than obtained from PI.
Thank you Janusz Rebis for your detailed reply. Why I asked this is, while working on the PVDF thin films I found that as the film goes from amorphous to semicrystalline (52%), I observed a variation in the phase image also. For amorphous film we could see a phase segregation between grains, whereas this segregation was reduced for semicrystalline film. This reduced phase segregation may be due to increase in % crystallinity.
In order for you to understand the nature of Phase Imaging in SPM, i would recommend you the work by Garcia. (http://www.icmm.csic.es/forcetool/phasecontrast.html)
"he phase lag between the external excitation of the vibrating probe and its response to the tip-surface interactions, referred to as phase shift, is related to the local energy dissipation on the surface. Specifically, the sine of the phase shift f is proportional to the amount of inelastic energy transferred from the tip to the sample surface" This local energy disipation can be related to surface chemistry changes, visco-elastic changes and also (unfortunately) to topography for example.
There is a plethora of uses of phase imaging, which can highlight features on samples totally "hidden" by the standard topography. One can think for example of a Polystyrene blend sample heated up which shows a beautiful phase contrast whilst the topography remains featureless.
As i mentionned in a previous question, there is still debate of what is the true nature of the colour contrast in a phase imaging as very often the samples are not perfectly flat meaning that we have a contirbution of topography creeping in the phase signal. It is not easy to seperate these contributions to one another and therefore quantitative work is still difficult. Nonetheless, phase imaging has produced some outstanding images.
There are other uses of the phase signal (for feedback for eg.) that can also be used in AFM providing a more delicate way of enaging the probe by looking at the phase shift which is detected before a change in amplitude in tapping mode. This is however another topic.
So, if you will have on eg. 25 pcs of AFM phase contrast images 52 volume content of other colour it may be mean that You observed crystalline/amorphous content. Unfortunately it is hard to say how 256 values of colour may visualize value of eg. hardness. In my opinion, what one can measure with AFM is topography and size in X, Y, Z scale. The rest modes are not quantitative but only 'comparative'. It does mean, that PI will give You the image of changes of functions of properties such as hardness, and elasticity and other mentioned in linked pdf.
Mr Laurent Bozec,thanks. What I thinking how PI works I put in my old presentation for students (http://infocentre.pl/animacje/afm/oafm.exe - only Polish lang.) slide no. 10. The topic was many times picked up on any contact with DI/Veeco/Briuker service. All ansewrs ensures me that PI is image of errors in phase oscillation frequency caused another 'echo' from surface during the scan. But of course I agree with all theoretical aspects of this topic.
Phase imaging could be used for studying polarizability of molecules deposited on surfaces either by plane mode, 3D mode or even retrace mode. By applying a negative/positive bias on the tip you get the electrical reaction of molecule that appears as dark parts in the phase image showing that you are in the electrostatic range. The bright parts of the phase mage show that you are in the Van der Waals range and should be excluded from the interpretation. Only the dark parts show that you are in the electrostatic range. when there is no bias applied and you scan in the electrostatic range you observe nothing unless you are in the van der waals. A 3D mode from a certain height reaching the electrostatic and goes down to van der waals can show this easily in phase image.
I've been looking for an answer to this question for a while -
When the results are presented for an AFM phase image, it's always on a scale that goes from a positive to a negative value. How can there be a positive phase shift? i.e. how can a material cause the tip to oscillate ahead of its drive signal? This makes no sense to me.
Can we say in AFM Phase Images that darker areas are softer and brigther areas are harder? Do you have any reference to confirm this?
No way, but if You have diamond particles in polymer matrix and PhaseImaging show dark particles in brighter matrix, probably on the same sample hardness will be similar act on oscillation phase. But if I were You I would like to use QNM or NanoIndentation instead of PhaceImaging.
Thank you very much. I have hard particles in a soft polymer matrix and generally I see the particles brighter and the matrix darker. Do you think then that this doesn't make sense? How can interpretate the colours in this system then?
Phase Imaging shows regions of different hardnes, viscoelasticity, friction, adhesion, and so on. So if You got a lot of problems just show us your pictures (TM and PI) and probably we will be able to say more about it.
good morning,
just by seeing color, it is possible to identify magnetic and non-magnetic domains in sample as done from AFM ?
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