Fitting with singlet peaks

This section exemplifies a fitting process by employing an oxygen 1s spectrum containing two singlet peaks.

  • Step One

    Once your data is plotted, you may create peaks by selecting the “edit peaks with mouse” box located on the right side of the window, and dragging the mouse across the width of the desired peak.

  • Step two

    Repeat this process for as many peaks you might have.

  • Step three

    To erase a bad peak or a miss-click, click the peak while pressing the “control” key. If you want to erase all the peaks drawn on the plot, press the “erase all peaks” near the lower left corner of the window. Once you have inputted your desired number of peaks, your window should look something similar to the following image.

  • Next step

    Back on the “fitting parameters” tab, AAnalyzer already created parameters for as many peaks that were created; you will be able to see these parameters at any time in the “fitting parameters” tab. Each row displays the parameters for an individual peak.

  • Next step

    You may notice that some of the values in the “Fitting Parameters” tab are shown in red and others in black. The red font means that the values in these cells are “free”; these values will be modified by AAnalyzer when performing a fit in order to find an optimum value. The black values are “fixed”; these values will not change during a fit unless the user changes them. You may choose your values to be “fixed” or “free” by selecting the corresponding button near the lower left corner of the “Fitting Parameters” tab. The “limited” option does a similar function to the “free” function; however you must specify the limits in which AAnalyzer must optimize the value. On the other hand, the “correlated” option does a similar function to the “fix” function. This option will “fix” the value of the cell to the value of a different cell. To make reference to a different cell, take the first letter of the name of the column, and match it with its corresponding row number. For example, to make reference to the Gaussian cell of the first peak, input “g0”; -g- for Gaussian, and -0- for row #0. Specify the name of the cell you wish your value to be correlated to, in the space next to “correlated”. Examples of codes for all possible variables are found under the miscellaneous tab in the right side of the window.

  • Next step

    As you can see, the baseline was activated as soon as you inserted the first peak. AAnalyzer has as default the Active Baseline and Background option. Should you prefer to use the traditional (Static) background, select the "use static" checkbox beneath. For more information on active baselines and backgrounds please refer to the "Background Options" instructional tab. Make sure you check your desired background box. For this example, a Shirley background was selected.

  • Next step

    To visualize the modifications made for the baseline and background, click the “Update Peaks” button on the right side of the “data and fits plot” tab. (Remember that the “edit peaks with mouse” box should be checked for this button to be available.) Your peaks should look similar to the following image. Note that the peaks have not been fitted yet.

  • Next step

    To begin the fitting process, click on any of the first two fitting buttons. Fit 1/1 – The first fitting option fits all “free” parameters (parameters in red font) simultaneously. This method provides a fast and efficient fit. Fit 1/1 ? – The second fitting option fits all parameters simultaneously as with the first button. Then, it fixes all free parameters except one and optimizes it individually. This process is repeated for as many “free” parameters you have (each time optimizing a different single parameter). This method provides a more precise optimized value for each parameter. For information about the function of the 3rd and 4th buttons please refer to the “simultaneous fitting” section.

  • Next step

    The fitting process is still incomplete at this point. AAnalyzer automatically fits all peaks using a “fixed” Lorenztian value of 0.085, which corresponds to the natural Lorentzian width of silicon 2p. However, the previous example displays two peaks from oxygen 1s, whose natural Lorentzian width is 0.25. Inputting known “fixed” values to your peak’s parameters will increase the accuracy of the fit. If you know the Lorentzian width of your core level, input the new Lorentzian value in the corresponding peak under the “fitting parameters” tab. Another option would be to set the value as “free”; this will allow AAnalyzer to find an optimum value. A. Herrera-Gomez, F.S. Aguirre-Tostado, M.A. Quevedo-Lopez, P.D. Kirsch, M.J. Kim, R.M. Wallace, J. Appl. Phys. 104 (2008) 103520.

  • Next step

    Make sure to press one of the first two fitting buttons to visualize the changes made in the “fitting parameters” tab. The result is a much more precise fit, as shown in the following image.

  • Next step

    If you need to erase/deactivate any of your peaks, under the “data and fits plot” tab, click a peak while pressing the “ctrl” key to erase a specific peak, or press the “erase all peaks” button to erase all peaks displayed on the “data and fits plot” tab. Both of these functions are only available if the “Edit peaks with mouse” box is checked.

  • Next step

    Ctrl-clicking a peak will only deactivate the peak in the “fitting parameters” tab. The next peak created will replace the deactivated peak. Under the “fitting parameters” tab, uncheck the corresponding “Active” box to deactivate a specific peak. This peak will stop displaying on the “data and fits plot” tab. To permanently erase all peaks, click the “clear all peaks” button near the top left corner of the “fitting parameters” tab. If you are working with more than one file, press the “Make changes extensive to all active data” button in the lower left corner of the window to apply the changes to the rest of the files.

  • Next step

    To save your progress, click the “save” button in the upper right corner of the “data” tab. This will save all information inputted in the “data” tab, as well as parameter information in the “fitting parameters” tab. For more information about other saving options, please refer to the “Saving Options” instructional tab. When you reopen AAnalyzer, you will be able to access any project you worked on by selecting it in the pop up window mentioned at the beginning of this section. The last project you saved will be the default file in the open box.