To calculate work function of AFM tip I did KPFM of HOPG (as a reference) and in response I got a potential map with -6 to +6 mV scale.
How to calculate work function of tip from this map?
Hi Robin
Please refer to this link.
http://www.kelvinprobe.com/MRS%20Seminar%20-%20Notes.pdf
You may find your answer in this document
Hi Robin!
If the measurement has done properly, this map should show the contact potential difference (CPD) between the tip of the probe and the HOPG surface.
CPD is the the work function difference between the tip and the sample (CPD=φtip – φsample” or “φsample- φtip” depends on where the bias voltage is routed to. If the bias is routed to the tip, then the software, measured potential (CPD) is “φtip – φsample”).
In order to calculate the work function of HOPG, you need to have the work function of the tip/probe and the CPD map (which you have already).
Hope this helps
Good luck!
Hi Khoshi,
Actually I am trying to calculate work-function of tip. But here problem is that potential map is in a range of 10mV but it should be in range of 500-600 mV.
Robin
Is this a raw data or you used a software analysis to edit this mapping, for instance by flattening or other types of editing?
Flattening usually changes the scale and the measurement values. How does the potential mapping look like before doing any editing? same scale?!
On HOPG I am getting avg potential of +480 mV without flattening.
What is workfunction of my AFM tip ?
4.6 - 0.48
or
4.6 + 0.48
Hi. I've come across this quite late, would say. However, Robin: if you are biasing positive the tip, above you have to add: 4.6+0.48
I attached my KPFM data. I am new to this measurement and totally confused in this data analysis. I also want to calculate the work function. Is -400 mV CPD value? Furthermore, I applied positive bias to the tip while measuring the surface potential. The work function of the tip is 5.2 eV. Please help and suggest.
Hi Gaurav. Yes, it looks like -.40 V is your sample potential Vs. If tip is positive vs sample, it should be eVs=WFt-WFs, where index s or t means tip and sample, respectively, (WF is work function). This happens to be if the tip is positive vs the sample (set to ground) same as, BTW, in my Asylum Research AFM, while I know that eg in the Park one it is sample positive, so the above WF will be inverted in sign. In your case, it appears that WFs=V-WFt=-0.4-5.2=-5.6: negative? Are you sure the tip is positive? What AFM are you using?
Marco Salerno Thank you for the answer sir. I am using Bruker multimode 8 AFM. I am confused about the sign in the equation, which one is correct in my case.
again, it should be like that eVs=WFt-WFs if tip biased positive and sample se to gnd; eVs=WFs-WFt if sample biased positive and tip se to gnd. However, there may be a sign inversion in the Vs as well, this depends on the sw of your instrument. Go find in the literature a paper on SKPM by people who used a similar instrument as yours (at least, by the same company). And check. Use materials with known WF to check, eg HOPG or Au. Good luck, and let us know!
You may find my minireview (open) useful, perhaps:
https://www.mdpi.com/1996-1944/11/6/951
I want to know the work function of my sample. I have calculated the CPD value of my sample in 4 different regions in the Assylum KPFM, among all, I have attached one here. R1=113.78mV, R2= 32.932mV, R3=64.41mV & R4=48.095mV. Tip used is Ti/Ir of Dia=56nm and kept the Delta height at 50nm. The WFt=4.9eV. The tip is calibrated with the standard HOPG.
Thank you.
well, you should:
-have measured the WF of your tip, first, by:
WFtip=WFsample+Po,
on a sample with known (better, assumed known!) WF,
eg 5.1 for Au, or 4.6 for HOPG
-have measured your unknown sample
in optimum conditions, ie surface-contamination
(including Oxygen doping from ambient air) free,
viz in vacuum or glove-box
Then, you use the same equation above,
where this time WFtip is known,
and WFsample is the unknown.
However, I see that you have quite a widespread value of Po
on your sample, from 114 mV to 33 mV,
so what is that? mean+-std dev, something like 73+-30mV?
Ok, I see only now that the tip was calibrated on HOPG,
that's fine. But, that as well should probably occur in vacuum/glovebox.
EVen if it is true that we use to peel-off the HOPG fresh, I'm not sure
it is stablke enough, on the scale of minutes.
Probably it adsorbs moisture on the surface in few tens seconds.
People out there, what do you think about this point?
So apparently your WFsample=WFtip-Po=4.90-0.07=4.83 eV, if I didn't make mistakes.
Take care.
looks like you planefitted the image, and so shifted the mean to zero, is it? You measured with an Asylum Research, may I ask you the model? How much was your Delta Height elevation? 50 nm? 100?
@ Gaurav Khandelwal:
was your AFM a Park? Looks like, after the fuzzy in-line fluctuations.
In that case you don't have to set the Delat Height, kit's a single-pass, I suppose. Can you kindly comment?
I see. I don't know that system. Does it acquire in a single pass or in lift-mode?
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