Hi,
I used a cypher AFM with SKPFM (SKPM) technique to measure the surface volta-potential distribution for Mg alloys. But for a bare surface which has just recently been polished, I can not find a fixed potential value. However, it seems that potential difference (Difference between intermetallics and matrix is fixed.
for example if I change the used tip (used just for couple of hours) with a new one, the potential value increases.
Any comment and point is highly appreciated.
Best regards,
Are You sure the value is 'potential' not the 'changes of potential' on the sample surface? As far I know AFM measure distance, rest are multiple mathematical models.
Dear @ Janusz,
This is a technique which is used in some equipments to measure the local Volta potential (V). It is called Scanning Kelvin Probe Force microscopy. The machine workd based on AFM method but with some facilities which measure the potential.
http://www.sciencedirect.com/science/article/pii/S0010938X15003261
I think you are getting confused between the absolute potential of the intermetallic phase and the relative potential difference between the intermetallic phase and the matrix. The absolute potential value of the intermetallic phase should appear on the graph as soon as you remove the offset. When you are performing a dual scan there is no change in potential that occurs, it is only the way in which you want the output. If the offset is applied you will see the relative potential difference. as soon as you remove the offset, the absolute potential should appear. With regards to the tip, as you must be aware that during the scans the tip gets eventually weared, which affects the measurements, which is but obvious and it can be seen on the potential difference values. I guess with repsect to the measurements you should optimize and try to avoid the effect to the tip wear on the potential measurements.
@ S. Pawar: Thank you so much! I think you are right, tips can be weard somehow after touching the surface. Morever, Bare Mg surface can be oxidized very fast and probabely the surface potential would be changed which is very sensitive to the identity of layer.
Btw, do you exavtly use the value obtained from the meaurement? Mg matrix value is around +1.3 to +1.8 V) while some people report in negative values or values close to Zero.
@ Ahmed: What you say is perfectly correct. It is very challenging to get a Mg substrate with minimal oxidation. I think there is a publication which reports on the measurement of surface potential difference of metal surfaces, which differ based on the method of preparation. A precise comparison of the surfaces of the same metal prepared by electropolishing, OPS polishing, diamond polishing, ultra-microtomed and mere grinding. What they report is perfectly understandable, as the surface potential will differ considerably, no matter it is still the same material.
Secondly, about the values you get on the measurement of Mg surface; are you speaking about the absolute potential or relative potential. When some researchers mention about the -ve values they are surely referring to relative potential difference which can be nullified during the processing of the data. However, I think precise data processing is the key to achieve the exact values after measurement.
@ Pawar: I am talking about the absolute value. For example, for alpha-matrix of a Mg alloy, it is coming like 1800 mV while the intermetallic value is for example 1500 mV (-300 mV difference). This matrix value can be correlated to OCP value, because they are both potential but just in different medium with different reference material.But as you mentioned I think well surface preparation and using a fresh tip are very important for getting a correct value.
Thank you very much!
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering