[Spm] RE: Spm Digest, Vol 34, Issue ; RE: Force curves

Sun Jun 3 11:42:12 EDT 2007

Hi Virginijus,

Your question was: 
> The curves (there are two of them: Z and  separation), how is separation
calculated?

In principle, Ben Ohler and others answered your question already.
Nevertheless, I hope my answer could of some use (I found that the long and
too comprehensive answers might be confusing, at least for my students :-)
). So, just direct answer to your direct question. 

Original "force curves", d vs Z transformed into d vs "separation" as
follows:

1. Software finds "the point of contact", a point where the cantilever
deflection just starts to go up. Let it be Zo.

2. The separation, say, h then is found as 
h=Z-Zo+d, where Z is the original vertical relative scanner position (Z=0 at
the maximum cantilever deflection), d is the cantilever deflection (it has
to be shifted to have d=0 when the AFM tip is far from the sample surface).
This formula is just simple geometry..

Possible catches:
a. d has to be correctly found by calibrating vs some rigid surface.
b. Zo can be easily found IF your sample is very rigid AND there are no
long-range forces. If either of those conditions is not valid, Zo should be
found separately (as a fitting parameter, for example).
c. If there is deformation of the surface, say, D, the formula for the
tip-sample separation should be modified by yourself as follows:
h=Z-Zo+d+D.

Please contact me if you have further questions.

Best regards,
Igor

_____________________________________
Igor Sokolov
Associate Professor 
Departments of Physics, Chemistry,
Center for Advanced Materials Processing
Clarkson University
Potsdam, NY 13699-5820, USA

office:      315-268-2375
fax:         315-268-6610  
cell:        315-212-4865
E-mail:      isokolov at clarkson.edu
Web:         http://www.clarkson.edu/~isokolov/
______________________________________

> -----Original Message-----
> From: spm-bounces at spmlist.di.com [mailto:spm-bounces at spmlist.di.com] On
> Behalf Of spm-request at spmlist.di.com
> Sent: Thursday, May 31, 2007 4:22 AM
> To: spm at spmlist.di.com
> Subject: Spm Digest, Vol 34, Issue 14
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> Today's Topics:
> 
>    1. RE: Force curves (Jan Friis Jorgensen)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Wed, 30 May 2007 11:52:49 +0200
> From: "Jan Friis Jorgensen" <jfj at imagemet.com>
> Subject: RE: [Spm] Force curves
> To: "Ben Ohler" <bohler at veeco.com>, "Virginijus Bukauskas"
> 	<virgis at pfi.lt>,	"SPM Forum" <spm at spmlist.di.com>
> Message-ID:
> 	<4854246CDC08714B8E5BBCC919273F3862F9B5 at asgaard.imagemetrology.local
> >
> Content-Type: text/plain;	charset="us-ascii"
> 
> Hi,
> It may interest you to know that the SPIP program can calculate force
> vs. separation automatically, see example at
> http://www.imagemet.com/index.php?main=products&sub=examples&id=50
> 
> Best regards,
> Jan F. Jorgensen
> Image Metrology A/S
> 
> 
> 
> -----Original Message-----
> From: Ben Ohler [mailto:bohler at veeco.com]
> Sent: Tuesday, May 29, 2007 11:07 PM
> To: Virginijus Bukauskas; SPM Forum
> Subject: RE: [Spm] Force curves
> 
> 
> Hi Virginijus,
> 
> The standard way of plotting force curves is deflection versus Z
> position, where Z is either calculated from the Z piezo calibration or
> else based on a sensor built into the Z axis. However, in many cases
> what one really wants to do is plot deflection (i.e. force) as a
> function of tip-sample separation. The separation plot corrects the
> distance (X) axis for the bending of the cantilever by subtracting the
> absolute deflection from the distance axis for each (X,Y) data point.
> The distance data is then offset so that the most extended point is the
> zero separation point and the separation increases from there. On a hard
> sample where there is no indentation this results in a true separation
> plot. However, when indentation occurs it is now the point of maximum
> indentation that gets labeled as the zero separation point, which is
> obviously past the initial point of contact. This may not be ideal but I
> think you appreciate the fact that identifying the true contact point in
> these cas!
>  es is often very difficult.
> 
> One approach to dealing with this issue is to leave the contact point as
> a free fit parameter in whatever model you are using to interpret your
> data. I know, for instance, that this is quite common among groups using
> the Hertz model to extract modulus data from indentation curves. I think
> that this is perhaps the most systematic and unbiased way to go about
> it.
> 
> I will send you a spreadsheet separately that demonstrates the
> separation plot calculations in more detail. Attachments are not
> permitted on the SPM digest, so if anyone else wants the spreadsheet
> just send me an email. The example is just based on fake data, but it
> shows each step in converting from a force vs. distance curve to a force
> vs. separation curve.
> 
> Best Regards,
> 
> -Ben
> 
> 
> Ben Ohler, Ph.D.
> Staff Scientist
> Veeco Instruments
> 112 Robin Hill Rd.
> Goleta, CA 93117
> 805-967-1400 x2426
> 805-967-7717 (fax)
> www.veeco.com
> 
> 
> 
> > -----Original Message-----
> > From: spm-bounces at spmlist.di.com [mailto:spm-bounces at spmlist.di.com]On
> > Behalf Of Virginijus Bukauskas
> > Posted At: Tuesday, May 29, 2007 12:00 AM
> > Posted To: SPM
> > Conversation: [Spm] Force curves
> > Subject: [Spm] Force curves
> >
> >
> > Hello all,
> >
> > I am using "point and shoot" function of NanoScope v6
> > software to capture
> > force distance curves. I am opening *.mca file to analyze the
> > curves. The
> > question is about display type of the curves (there are two
> > of them: Z and
> > separation), how is separation calculated?
> >
> >
> > Regards,
> >
> > Virginijus Bukauskas
> >
> > Semiconductor Physics Institute
> > Sensors Laboratory
> > A. Gostauto 11, Vilnius LT-01108, Lithuania
> > Fax: +370-5-2627123, Tel: +370-5-2627934
> > E-mail: virgis at pfi.lt
> > _______________________________________________
> > Spm mailing list
> > Spm at spmlist.di.com
> > http://spmlist.di.com/mailman/listinfo/spm
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> 
> 
> 
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> End of Spm Digest, Vol 34, Issue 14
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