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Hi all, I have a Multimode microscope. I have a doubt regarding Surface Potential measurements, I know this method normally does not give absolut values but is possible to have the potential difference between two zones in a sample. My question is how this value could be affected by the probe. I have observed that using the same probe, the potential differences can change, and if the probe gets broken, a change to another probe can change the resultsmore. Could you please commnet on these topics? how is the best method to achieve reproductible results?Thank you.
Sheila
Hi Sheila,
The probe is critical for surface potential measurements, it is required to have a well defined work function and be robust. SCM-PIT probe from Bruker has a Pt-Ir coating which meets these criteria. Also Rocky Mountain Nanotech offers solid Pt probes (25Pt300B) which has the advantage that tip material thus its work function does not change even tip wears or breaks.
Other things to oberve are to use similar settings, most importantly lift-mode settings such as drive frequency, drive phase, drive amplitude, lift-height. Which version of software do you use?
Best regards
ChunzengApplication ScientistBruker
I am happy to inform you that Bruker AFM Probes is now supplying Rocky Mountain solid Platinum probes.
Solid Platinum probes offer excellent conductivity and suffer no thin-flim adhesion problems that occur with metal-coated silicon probes. These probes also have a tip radius (<20 nm) which is difficult to routinely obtain by standard AFM probe processing methods. These probes are ideal for C-AFM, SCM, and KPFM/EFM applications. They are available in a range of spring constants. Each probe tip is individually imaged by FE-SEM to verify that the metallic probe tip radius is below 20 nm.
Choose the probe that is right for your application:
Links to the product page for each of these probes are as follows:
http://www.brukerafmprobes.com/p-3773-rmn-12pt300b.aspx
http://www.brukerafmprobes.com/p-3772-rmn-12pt400b.aspx
http://www.brukerafmprobes.com/p-3775-rmn-25pt300b.aspx
http://www.brukerafmprobes.com/p-3774-rmn-25pt400b.aspx
Fantastic!
Chunzeng
I assume that you are speaking about surface potential which is the work function (if this is the surface potential on nonconductive surfaces, it is the entirely different story.) Did you try Kelvin method? It should give you the absolute value of the surface potential (of course, if your material is sufficiently homogeneous). If you sample is homogeneous within the vicinity of the probe, your relative results should not depend on the probe in Kelvin method (unless your probe is changing during the data collection). Be aware that kelvin method has the limit of sensitivity. If your relative difference is close to that limit, you may have a natural variability of the results even for the same probe. There is a way to increase sensitivity to the surface potential a bit by using the following simple method (we described it in Applied Physics Letters, 2009, v.95, 173105 - I can guarantee that this method has been before by somebody, we didn't investigate it in detail because it was the main topic of our paper). Using classical electrical force microscopy (frequency modulated), you can plot the force gradient (or the resonance frequency shift) the function of the voltage applied between the probe and sample. This can be easily measured for relatively large voltages. It should be a well- defined parabola. So you can then extrapolate the parabola to the point where the resonance frequency shift is minimum. That will be the voltage equal to the difference between the work functions of the probe (typically known or can be found using this method when using a known surface material) and the surface (typically the sought value). So you can find the work function of the surface.
--Igor
_____________________________________ Igor Sokolov, Ph.D. Professor, Department of Physics, Department of Chemistry and Biomolecular Science, Director of Nanoengineering and Biotechnology Laboratories Center (NABLAB), NY Center for Advanced Material Processing (CAMP) , Clarkson University, Potsdam, NY 13699 Phone: 315-268-2375 Fax: 315-268-6610 http://www.clarkson.edu/~isokolov http://www.clarkson.edu/~nablab _____________________________________
_____________________________________
Igor Sokolov, Ph.D.
Professor,
Department of Physics,
Department of Chemistry and Biomolecular Science,
Director of Nanoengineering and Biotechnology Laboratories Center (NABLAB),
NY Center for Advanced Material Processing (CAMP) ,
Clarkson University,
Potsdam, NY 13699
Phone: 315-268-2375
Fax: 315-268-6610
http://www.clarkson.edu/~isokolov
http://www.clarkson.edu/~nablab
Sheila,
I would like to use the Multimode for measuring surface potential of conjugated polymeric systems like thiophenes and their blends. Are you studying organic materials as well?
If so, do you think having the EFM HOLDER AND SCM-PIT tips would be enough to carry out the measurements? Or is it necessary to apply voltage externally to the sample through the piezo or directly? Looking forward to any suggestions on this to carry the work forward.
Mithun
Hi David, I was curious what you are referring to when you say "no thin-film adhesion problems" ?
Thanks!
Lauren
Laura,
On the Pt-Ir coated probes, the coating can wear down or wear off over time while scanning. This is not an issue with the solid metal probes because there is no coating -- the entire probe is solid conductive Platinum.
Dave
Hi Mithun,
Having the EFM HOLDER AND SCM-PIT tips are enough for you to perform surface potential on Multimode; you do not need to apply voltage externally. Surface potential measurement has been done on organic solar cell (BHJ) and its component materials; make sure you electrically connect the underlying conductive substrate (e.g. ITO) to the sample puck, for instance, using silver paste. We have extensive experience doing this, let us know if you have additional questions.
Best
Hi Chunzeng,I am unable to pull up the potential data type in the channel 2. We have a Quadrex extender with the MM and a Nanoscope IIIA controller. WHat should be the setting to get surface potential mapping. Can you send a screenshot of the operational window please? I have selected all the options on the interleave panel as suggested. Since I did not get the POTENTIAL window, I am using the amplitude channel. Does that give the same data? How can I interpret the data, that is the surface potential, vis-a-vis the applied drive amplitude and bias (ac+dc) inputs? Can an absolute measurement of the potential or work function be achieved?RegardsMIthun
Hi Chunzeng, I got the potential window by selecting potential in teh interleave window for feedback type. SO that problem has been solved, but the potential channel does not have anything other than sharp spikes (even at voltage as low as .002 V). Tried changing hte drive amplitude, the lift scan height, the bias, the gains etc. Nothing seemed to have any effect on the potential. The height and phase images are very clear though. Could you please suggest what should be done to get it right? The sample as i told earlier, is organo photovoltaic material on a ITO coated glass, which has been connected to the sample chuck using conducting silver paste. Look forward to your help. Thanks. Mithun
Can you take a screenshot of your settings and send to my email: chunzeng.li@bruker-nano.com
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