X-ray Photoelectron Spin-orbit Splitting

[abstracted6]

I have some XPS spectrums that I am trying to fit (my first time doing so), using XPSpeak.

I understand that for spin-orbit splitting the FWHM, line shape (i.e.% gaussian/lorentzian) must be equal (more or less), peak area ratios set (i.e. 2:3 for 3d3/2 and 3d5/2), and the peak separation (relatively) constant.

My question is, how much can the FWHM vary from different literature sources?

The area I am fitting is the Mo 3d area, if I contrain the FWHM to the values I found at www.xpsfitting.com I get a pretty poor fit. However, if I only constrain the peak FWHM's to be equal (for each doublet), and not explicitly specifiy; I get a good fit.

For example, one doublet is the MoO3 3d. The FWHM (Mo 3d3/2) specified at the website I previously mentioned is about 0.86. If I only specify that the doublet must have FWHM invariance (and not explicitly 0.86) the FWHM becomes 2.82 after optimization.

 

[M Quack]

There are at least two contributions to the FWHM: The intrinsic width of the peak given by the life time (lorentzian) and whatever may influence the peak position (impurities, strain, ..., probably gaussian), and the instrumental resolution (most likely gaussian).

If you measure the same sample on two different instruments with different resolution you will find two different widths.

Try to check your reference literature for specifications of the instrumental resolution.

0.86 sounds more reasonable for intrinsic width than 2.82, so your instrument may have a fairly broad resolution. Are the settings fully optimized?

 

[sum555]

I am working with Mo oxides and trying to fit XPS measurements also. I understand that for doublets, the FWHM value should be the same, and different for each instrument and sample. However, should be the FWHM value the same for the different Mo oxidation states (Mo4+, M05+ and Mo6+) in the same measurement?