XPS Reference Pages

This site contains information gained from decades of X-ray photoelectron spectroscopy (XPS) analyses of an enormous variety of samples analyzed at Surface Science Western laboratories located at the University of Western Ontario. Originally this site was designed as a place for students and our clients to access valuable tips and information. It has since been opened to all those interested in the XPS technique. Summaries of literature data, relevant references and unpublished data taken of well characterized standard samples are presented. Also curve-fitting tips, instrument set-up tips (specifically for the Kratos AXIS Supra, Ultra and Nova), and CasaXPS tips pertaining to questions we normally get from our students and clients, and other odd bits of information are presented.




The fine print:
Surface Science Western and the University of Western Ontario does not warranty any of the information shown at this site. Any use of this data in scientific publications or other forms should include referencing to the originally published data referenced herein.

Workshop Exercises: Advanced Chemical State Analysis

1) Carbon 1s - Set up a standard file for the fitting of adventitious carbon. Download the C 1s spectrum here.


2) Use it to charge correct a series of spectra. Download test file.


3) Oxygen 1s - General fitting of the O 1s spectra for metals.  Use file from number 2. Fit the O 1s spectrum, understand and explain all sources of oxygen.


4) Ti 2p - Set up curve-fitting parameters.  Download Ti 2p test file. See titanium literature fitting values.


5) Cr 2p - Set up curve-fitting parameters. Download Cr 2p test file. See chromium literature fitting values.


Notes:
•Cr(VI) Species – mix of oxide and hydrated species
   -One narrow peak FWHM 1.5 eV
  -Range from 579.0 to 580.0 eV
•Cr(III) Species – mix of oxide and hydrated species
  -Cr(OH)3 - One broad peak FWHM of ~2.5 eV, set to 577.5 eV
  -Cr2O3 - Five multiplet peaks of equal FWHM (~0.9 eV) with set areas and separations based on standard sample
•Cr(0) – Metal
  -One asymmetric peak with a FWHM of 0.9 eV
  -Range from 573.9 to 574.5 eV

6) Ni 2p - For the brave, download and give it a try. See Ni 2p literature fitting values and general instructions here.



Workshop Exercises: The Auger Parameter and Wagner Plots

The Auger Parameter

1. Try calculating the Auger parameter for ZnO and Cd metal (click on links to download the spectra). (Compare to zinc and cadmium literature.)
2. Calculate the Auger parameter and use it to determine the chemical state for 3 unknown Cu species (Unknown 1, Unknown 2, Unknown 3).  Click here to access Cu binding energy and Auger parameter values.

Wagner Plots
Handouts will be given or you can download the exercise here.


Use lines of slope 1 and 3 to look at the trends:
1) For the Ga(III) halogen series.
2) Going from Ga(III), Ga(II) to Ga(I).
3) For the metal, alloys and semiconductors (Ga2O3 is also a semiconductor).
Do final state effects dominate (slope of 3) or do initial state effects dominate (slope of 1)?


Graphitic/Graphene/Carbon Nanotube C 1s Curve-Fitting

Materials of a graphitic nature (e.g., graphite, graphene, carbon nanotubes etc.) will have a C 1s main peak, attributed to C=C, which can be used as a charge reference set to 284.5 eV. An average of values for graphite from 21 references from the NIST database [1] is 284.46 eV with a standard deviation of 0.14 eV. Note that the well characterized value of 284.5 eV for graphitic carbon is also a strong indicator that this value is not appropriate as a value to use for AdC charge referencing. While these types of samples are generally conductive and if they can be mounted in a manor (in electrical contact with the sample stage) to take advantage of this one should do so. However, many of these types of samples come as a small volume of powders or flakes which are very difficult to mount. Usually, we mount these on a double-sided adhesive which works well but electrically isolates the sample. Oxidation of these types of samples (e.g., graphene oxide) or their functionalization (e.g., functionalized CNTs) can result in them behaving less conductively or as a mixed conductive/insulating material.  Samples where these materials are mixed with other conducting or insulating compounds can also result in a mixed conductive/insulating sample. For most of these types of samples we now electrically isolate the sample and charge reference to C 1s at 284.5 eV for the graphitic (C=C) peak.[2]

Table 1 from [2] presents general fitting parameters for graphitic, graphene and carbon nanotube type materials. These starting fitting parameters include the main peak asymmetry (defined using an asymmetric Lorentzian (LA) line shape) and π to π* shake-up satellite from a pure graphite standard sample. These fitting parameters are similar to the approach taken by Morgan (Fig. 5, Table 2) [3],  Moeini et al. (Table 1) [4],  and Gengenbach et al.[5]  It is always best to run your own standard (pure graphite, graphene, CNT etc.) to get fitting parameters appropriate for your sample type, instrument and conditions used. Slight differences in the main peak asymmetry and differing shake-up satellite position, shape and intensities are possible for differing classes of graphitic materials. See for example from Morgan[3] where HOPG and nano-onion C 1s spectra show peak-shape differences, likely due to hydrogenation of the sample. However, with this caveat stated, the parameters used based on a graphite standard have worked very well for variety of samples (134) analyzed the five-year data survey from [2]. Figure 1(A) presents the standard graphite spectrum used to obtain the parameters presented in Table 1. The spectra from Figure 1(B, C and D) show the use of these fitting parameters from Table 1 to effectively model a variety of graphitic component containing materials. 


Table 1. General fitting parameters for graphitic/graphene/carbon nanotube type materials. #Line-shape details for CasaXPS. Define asymmetric peak-shape in other software using pure graphite/graphene or CNT sample related your specimens. ##Gaussian/Lorentzian product formula, GL(30) is 30% Lorentzian 70% Gaussian.[2]


Figure 1.  Examples of curve-fitting of graphitic type systems using the parameters from Table 1.  A) pure graphite, B) carbon nanotube-based material modified in caustic solution, C) oxidized graphene and D) acid modified graphene and organic compound mixture.[2]

References:
[1] C.D. Wagner, A.V. Naumkin, A. Kraut-Vass, J.W. Allison, C.J. Powell, J.R.Jr. Rumble, NIST Standard Reference Database 20, Version 3.4 (web version) (http:/srdata.nist.gov/xps/) 2003.
[2] M.C. Biesinger, Appl. Surf. Sci. 597 (2022) 153681.
[3] D.J. Morgan, J. Carbon. Res. 7 (2021) 51.
[4] B. Moeini, M.R. Linford, N. Fairley, A. Barlow, P. Cumpson, D. Morgan, V. Fernandez, J. Baltrusaitis. Surf. Interface Anal. 54 (2022) 67.
[5] T.R. Gengenbach, G.H. Major, M.R. Linford, C.D. Easton, J. Vac. Sci. Technol. A, 39 (2021) 013204.