The Nanoscale World

Surface Potential and Probes

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Answered (Not Verified) This post has 0 verified answers | 14 Replies | 9 Followers

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Sheila Gonzalez posted on Tue, May 31 2011 3:55 AM

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

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Bruker Employee

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


Chunzeng
Application Scientist
Bruker

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Bruker Employee

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:

  • RMN-25Pt300B – The most popular RMN probe. Particularly good for C-AFM and KPFM or multi-mode applications.
  • RMN-12Pt400B – The RMN probe with the lowest spring constant. Very useful for SCM and contact AFM applications requiring contact force.
  • RMN-25Pt400B – Similar to the 25Pt300B, but with a lower spring constant.
  • RMN-12Pt300B – Similar to the 12Pt400B, but with a higher spring constant.

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

 

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Fantastic!

Chunzeng

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Answered (Not Verified) Igor replied on Sat, Jun 11 2011 12:20 PM
Suggested by Igor

Hi Sheila,

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

_____________________________________

 

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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

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Hi David, I was curious what you are referring to when you say "no thin-film adhesion problems" ?

Thanks!

Lauren

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Bruker Employee

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

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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

Chunzeng

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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?

Regards

MIthun

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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

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Hi Mithun,

Can you take a screenshot of your settings and send to my email: chunzeng.li@bruker-nano.com

Chunzeng

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