Tag Archives: fit

Difference spectra

How can I display the difference of simulated and measured spectra?

Sometimes it is advantageous to inspect the difference of simulated and measured spectra in order to find out about appropriate model extensions. Please read the instructions below to activate the drawing of difference spectra.

Open the spectrum for which you want to see the difference with a right-click in the treeview. Select the local menu command File/Options/Difference/Show to turn on the difference display. This menu item is a checked property: Clicking on it changes its status from checked to unchecked or vice-versa.

The additional menu commands File/Options/Difference/Pen and File/Options/Difference/Line mode are used to control the appearance of the difference curve. Use these settings to clearly separate the difference curve from the simulated and measured spectra. You can use, for example, pen 3 (green by default) and line mode 3 (dashed).

Any real result?

Can I get anything real out of a model?

Yes, of course. If your model is good, and your spectra do contain enough information, the parameter values reflect the real values as good as they can.
Please have in mind that in many cases talking about ‘real values’ is using a model in itself. If you ask for the real value of a layer thickness, for example, your question implies that there is something like a layer with a top and a bottom end. You ignore the atomic structure and surface roughness effects, or, if not, you apply (at least in your mind) a certain roughness averaging procedure.

List of fit parameters: New commands in ‘Actions’ submenu

We have added some new commands in the submenu ‘Actions’ which turned out to be practical when fitting many oscillators of organic materials in the infrared.

  • Set active material: Type in the name of a material (must be present in the list of materials) in order to select it for the actions below.
  • Select all parameters: Select all parameters of the active material as fit parameters.
  • Select oscillators: Selects all oscillator parameters of the active material as fit parameters. This is useful while adjusting models for organic materials in the infrared which may may have many oscillators. Manual parameter selection is tedious in such a case. Please note that for Kim oscillators (which are very much recommended) the parameter ‘Gauss-Lorentz switch’ is not selected since we found that in almost all cases absorption bands have a Gaussian line shape which is the default setting of Kim oscillators.
  • Select oscillator strengths: Selects all oscillator strengths of the active material as fit parameters.

Fit sheet resistance values

CODE 3.96

A new OLE command has been implemented: import_measured_sheet_resistance(a_value : float)

Use this command to pass a measured sheet resistance value to CODE. This is useful if you would like to use this value in a fit, in addition to measured optical spectra.

The value is passed to the list of integral quantities. The list must contain an object of type ‘Sheet resistance’ with the name ‘Sheet resistance fit’ – only in this case the value is passed as target value.

In order to use this value you must set the option ‘optimize’ of the sheet resistance object. If you want to fit both spectra and sheet resistance, you must set the global fit option ‘Combine fit deviation of spectra and integral quantities’.