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contactpoint3.m

This script is used for automatically locating the contact point. You need to supply z and d coordinates for the force curve, as well as tip parameters and a maximum indentation to use when fitting.

Required arguments:
z: a vector of z values (piezo height) for the force curve. Should be in meters.
d: a vector of deflection values, should also be in meters and have the same number of points as z.
tip: a 3-element struct containing tip parameters:
	tip.k: spring constant in N/m
	tip.type: either 'cone' or 'bead'
	tip.geom: cone angle or tip radius, depending on tip type.
maxind: maximum amount of indentation data to use when fitting, in nm.

The output will be the index value where the contact point occurs.

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afmcntp.m
This script does the actual fitting to give you the E value.
Required arguments:
z: a vector of z values (piezo height) for the force curve. Should be in meters.
d: a vector of deflection values, should also be in meters and have the same number of points as z.
tip: a 3-element struct containing tip parameters:
	tip.k: spring constant in N/m
	tip.type: either 'cone' or 'bead'
	tip.geom: cone angle or tip radius, depending on tip type.
maxind: maximum amount of indentation data to use when fitting, in nm.
plot: either 1 or 0 depending on whether you want it to show a plot.

The output will be the elastic modulus in Pa, the contact point(index value) and the normalized fitting error.


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Example usage:


%import z and d from force curve data
tip.k = 0.06;
tip.type = 'cone';
tip.geom = 35;
maxind = 500;
index = contactpoint3(z,d,tip,maxind);

%index will be the location of the contact point

%now do the fit to get E value
[E ctp err]=afmcntp(z_app,d_app,tip,[index maxind1],1);

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It is possible to construct a simple loop to process many force curves. Example

tip.k = 0.06;
tip.type = 'cone';
tip.geom = 35;
maxind = 500;

%if you start with all of your z and d data in a struct
for i = 1:20
	z = fc(i).z;
	d = fc(i).d;

	index = contactpoint3(z,d,tip,maxind);

	%index will be the location of the contact point

	%now do the fit to get E value
	[E(i) ctp(i) err(i)]=afmcntp(z_app,d_app,tip,[index maxind1],1);
end