Hi everyone,
For a part of my study on TiO2 nanoparticles, I need to perform atomic ration calculation (O to Ti stoichiometry calculation) using core emissions data from XPS. I have access to SDP software and was wondering if anyone possibly knows how to perform such analysis. Additionally, I have heard that the stoichiometric analysis needs to use the cross section factor for Ti and O to correct the integrated area from XPS data, and how can I get the value of these factors? It can be very tricky.
So, any help to show me how this can be performed and how to get reliable results is greatly appreciated.
Thanks indeed.
For an explanation please refer to Vickermam & Gilmore Surface Analysis book (see link), ch. 3.5, and there is an example in ch. 3.5.3
Another example can be found in the first paragraphs of Sect. III in this paper: DOI: 10.1103/PhysRevB.83.035410
I think, you also need to consider two parameter. First is the relative sensitivity factor for each element. Second is the ration for each series of doublet....p1/2 & p 3/2 = 1:2 ; d3/2 & d5/2= 2:3 and f5/2 & f7/2= 3:4....
1. First, you need a method to get the integral amplitudes from your XPS spectra. One method is to use a predefined software, as CasaXPS. Usually, the photoemission peaks consist of a sum of many sub-components; every single subcomponent may be assigned to a chemical bond. (example: http://www.jpis.org/ArticleImage/1150JPIS/jpis-41-263-g001-l.jpg)
2. You must identify Ti2p components associated to TiO2, with the ones from your O1s spectrum (you should ignore the component due to contamination, if any), and to compute the ratio only between these components. A good database to assign the BE: http://srdata.nist.gov/xps/main_search_menu.aspx
3. The integral amplitude (subcomponent peak area) must be divided by the Atomic Sensitivity Factor (ASF). There are different values of those; you can use those: http://www.uksaf.org/data/sfactors.html
The atomic sensitivity factors for the Ti2p and O1s peaks are part of the instrument that took the data. Whoever took the measurements for you should provide them to you. Otherwise, when you use tabulated values from some other reference, your calculated ratios will be inaccurate.
(a) For some reason the link in my first comment didn't work: http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470017643.html
(b) Just to add to the good points others made, the sensitivity factors can depend on the chemical state. There is a good description of this challenge in the work of Beyreuther and coworkers about n-doping manganites. See particularly Sect. II and IIIa http://journals.aps.org/prb/abstract/10.1103/PhysRevB.73.155425
If you can fit your Ti to a single bonding state the it's just the matter of finding the right reference, so hopefully it will be easier than what's described in that paper.
I suggest a contact with professor A. Herrera from Cinvestav Queretaro Mexico, He is an expert in this topi.c In your group developed a software analyze.
email adress: [email protected]
For quantitative XPS you need the subshell cross section (Yeh, Lindau), the transmission function of your spectrometer and some assumptions on the cleanliness of your sample. As Ti 2p and O1s are pretty close, you can in first order assume the photoelectrons come from the same depth in your sample, Ti 2p is a spin orbit doublet so you have to take both lines to compare with O1s. Looking closer to the spectra you need to identify chemically different phases as e.g. Ti4+ in TiO2 and Ti3+ at defects (shows up as a shoulder in the 2p emission). The same for O in TiO2 and adsorbed water etc. As the kinetic energies are close you can omit the energy dependent transmission function of the spectrometer if you calculate Ti/O as it canceles out.
1. All details of the quantitative analysis are well represented in the International standard ISO 18118 “Surface chemical analysis – Auger electron spectroscopy and X-ray photoelectron spectroscopy – Guide to the use of experimentally determined relative sensitivity factors for the quantitative analysis of homogeneous materials”
2. Usually the O1s spectrum of TiOx, 1,8
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