I have two samples which consist of nitrogen and carbon element. To reveal the chemical environment of carbon and nitrogen element, I did XPS analysis. The intensity of nitrogen/carbon spectra of the samples were not the same. Should I normalize the spectra of nitrogen/carbon before I proceed to analyze?
Dear Jiawen,
it depends on what you want. If you are interested in the quantification of the different Nitrogen and Carbon species, then you should make use of the measured intensities without any additional normalization. The only correction you have to apply are the different photoionization cross sections and the transmission function of your XPS system. Check the literature for details how to do this. In any case, if you only have C and N in your sample, the related (corrected) signal intensities should add up to 100%. Then you can make a peak assignment and calculate i.e. the amount of C-N, C-C, N-O, C-O, etc bonds.
Good luck, Dirk
You need to model the measured C 1s and N 1s spectra each with a series of peak functions (usually some weighted Gaussian/Lorentzian shape) and a background function. You do not need to normalize the data for this. This modelling procedure should give you an idea of the chemical state and local environment of N and C. You will probably find the N data more diagnostic, because the C data are likely to have a component of adventitious contamination. Sometimes you can quantify this and remove its contribution - we could do it even for some organic compounds. See e.g. Stevens & Schroeder, Surf. Interface Anal. 41 (2009), 453-462.
If you want a quantification of the species in your sample, you must avoid the normalization of the spectra. If you want to determine the chemical environment, you mus analyse the N1s and C1s peaks in terms of the superposition of several Gauss or Voigt-profiles, the position of each peak giving you the kind of binding. To identify the bounds, you must use reference spectra available in the literature. Caution with the carbon that can come from the pollution of your sample by atmospheric CO2, CO, etc.!
I do agree with Dirk. Apart from that, you should first take a survey scan and calculate the % composition for all elements (C N O in your case) present in your different samples and then deconvolute (Gauss or Voigt) your core level spectra with absolute FWHM and position for different components (C-C, C-N, C-O in C(1s) and O-O, O-C, O-N in O(1s)) for different samples. Now, by combining both % composition calculations from survey scan and deconvolted core level, you can extract the information what you desire. Please don't forget to do carbon correction before you analyze, in your case you can put some reference sample to do this correction.
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