Assigning Curve Fit Band Dependencies (Doublets)
There are two types of dependencies you can set up between bands – area ratio and peak separation. Setting up dependencies between these bands
allows you to simulate doublets, whereby the parameters of one peak are
dependent on another for fitting. The peak that is dependent on another is the
secondary peak of the doublet; the independent peak is the primary. Multi-level
dependencies are sometimes referred to as multiplets.
Creating a doublet
To create a doublet with a fixed area ratio, first create two bands. Select
the band that is to be the dependent (secondary) band, and click the Area button. From the Area Ratio dialog you
can choose the independent (primary) band, as well as the ratio. (Use What's This help for further information on the individual fields.) Once you dismiss the
dialog, you’ll note that the Ratio column of the dependent band now displays its ratio to
the independent band, as well as the index of the independent band. For
example, if you selected band 2 and fixed its area to band 1 at 0.5, you would see “1-0.5” in the Ratio field of band 2. This means that band 2 maintains an area 0.5
times that of band 1.
To create a doublet with a fixed peak separation, first create two bands.
Select the band that is to be the dependent (secondary) band, and click the Peak button. From the Peak Separation
dialog, you can choose the independent (primary) band, as well as the Separation.
(Use What's This help for further information on the individual fields.) Once you dismiss the
dialog, you’ll note that the Separation column of the dependent band now displays its
separation (in eV) relative to the independent band, as well as the index of the
independent band. For example, if you selected band 2 and fixed its separation
to band 1 at .3, you would see “1-0.3” in the Separation field of band 2. This means that band 2 maintains a
position 0.3eV plus that of band 1.
Note that you can create doublets with both area ratio and peak separation
locking. Simply select an existing dependent band from the list and choose the
desired dependency.
Removing a doublet
To remove a doublet dependency, select a dependent band and click either Area
or Peak. Choose remove to remove that dependency. If a band has both an Area
and Peak dependency, you must remove the dependencies individually.
How doublets affect estimates
The dependencies used to simulate doublets follow some rules as to behavior
when adjusting limits manually and when fitting.
Area Ratio:
a) Adjusting any parameter of the independent band (with the exception of
position) causes the corresponding parameter of the dependent band to adjust in order
to maintain the selected ratio.
b) Adjusting any parameter of the dependent band except for position and
intensity causes the intensity to adjust in order to maintain the selected ratio.
c) Adjusting the intensity of the dependent band causes the FWHM to adjust in
order to maintain the selected ratio.
d) Adjusting the position of the either band does nothing.
In general, note that whatever parameters are adjusted in either the dependent
or independent band, the area ratio is maintained.
Peak Separation
a) Adjusting the position of the independent band causes the position of the
dependent band to adjust in order to maintain the selected peak separation.
b) Adjusting the position of the dependent band causes the peak separation to
change.
Adjusting Individual Curve Fit Band Limits, Invariance, and Locking
Additional Curve Fitting Topics