Titanium 2p Curve-Fitting Video

Video showing curve-fitting of the titanium 2p (Ti 2p) XPS spectrum using CasaXPS.



Titanium

Initial fitting parameters for the titanium 2p peak were developed using averaged binding energy (BE) data and 2p1/2 – 2p3/2 splitting data from the NIST XPS Database[1] (Table 1). As well, data from readily available standard samples (metal, TiO2) [2,3] were used to clarify the peak-widths, splitting (Δ=6.05 eV for Ti(0), Δ=5.72 eV for Ti(IV)) and shapes (asymmetric for the metallic component) (Table 2) [3]. An example of the use of these parameters is presented for a mixed oxidation state titanium-containing sample in Figure 1. Although C 1s set to 284.8 eV can be used as an internal charge correction it is also possible in this case to use the Ti 2p3/2 metal peak set at 453.7 eV or the clearly defined Ti(IV) (TiO2) 2p3/2 peak set at 458.6 eV. This removes the uncertainty associated with charge correcting to adventitious C especially in situations where the adventitious overlayer is not in good electrical contact with the titanium containing species underneath. The Ti 2p1/2 peak for each species is constrained to be at a fixed energy above the Ti 2p3/2 peak. The intensity ratio of the Ti 2p3/2 and Ti 2p1/2 peaks are also constrained to 2:1. The FWHM’s for the metal and Ti(IV) peaks are derived from the standard sample analyses. The FWHM’s for Ti(II) (at a BE of 455.4 eV) and Ti(III) (at a BE of 457.2 eV), which are likely structurally loosely ordered, are constrained to have equal width to each other and are generally slightly broader than the well ordered Ti(IV) oxide peaks [2,3]. A CasaXPS ready (.vms file) of mixed titanium species can be downloaded here. Further information and expanded discussion can be found in reference [3].

Figure 1. Ti 2p spectrum of a heat-treated Ti-apatite composite using peak fittings derived from Tables 1 and 2.Table 1. Literature values (from [1]) for Ti 2p3/2 spectra.Table 2. Spectral fitting parameters for Ti 2p: binding energy (eV), percentage of total area, FWHM value (eV) for each pass energy, and spectral component separation (eV).


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, B.P. Payne, B.R. Hart, A.P. Grosvenor, N.S. McIntye, L.W.M. Lau, R.St.C. Smart, Quantitative Chemical State XPS Analysis of First Row Transition Metals, Oxides and Hydroxides, IVC-17/ICSS-13 and ICN+T2007, Stockholm July 2-6, 2007, Journal of Physics: Conference Series 100, 012025 (2008).
[3] M.C. Biesinger, L.W.M. Lau, A. Gerson, R.St.C. Smart, Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals, Oxides and Hydroxides: Sc, Ti, V, Cu and Zn, Applied Surface Science, 257 (2010) 887-898.

Titanium Nitride

Entries from the NIST database [1] give the following results for titanium nitride:
Ti 2p3/2 = 455.5 eV +/-0.4 eV
N 1s = 397.1 +/-0.3 eV
The Ti 2p peak for the nitride appears to have an asymmetric peak shape and can, in lower resolution work, be fit similar to the metal.

Recent, excellent, high resolution work by Jaeger and Patscheider [2] shows that the asymmetry is comprised of several shake-ups and plasmons. Bulk and surface plasmons for the Ti 2s peak and N 1s peak are also found in this paper.

Table 1. Titanium nitride binding energies (eV), assignments and FWHM from [2]. Reproduced with permission from Elsevier Limited, Oxford, UK.

Figure 1. Ti 2p peak for titanium nitride from [2]. Reproduced with permission from Elsevier Limited, Oxford, UK.

An excellent account of the species present (Ti and N) in an air exposed film of titanium nitride is presented in reference [3].

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] D. Jaeger, J. Patscheider, J. Electron Spectrosc. Relat. Phenom. 185 (2012) 523-534.
[3] N.C. Saha, H.G. Tompkins, J. Appl. Phys. 72 (1992) 1.

Titanium Carbide

Titanium carbide (TiC) has a very high melting-point (3100 C), is extremely hard and strong, and is electrically conductive. Because of its electrical conductivity its Ti 2p peak-shape will be asymmetric, similar to that for Ti metal (the same peak-shape for the metal is used with good results in the TiC example given below). The Ti 2p3/2 binding energy for the carbide is around 454.9 to 455.1 eV while the C 1s peak for the carbide is around 281.7 to 281.9 eV [1,2,3]. A CasaXPS ready example of titanium carbide can be found here.

References:
[1] J.E. Krzanowski, R.E. Leuchtner, J. Am. Ceram. Soc, 80[5] (1997) 1277-80.
[2] J. Luthin, Ch. Linsmeier, Physica Scripta, T91 (2001) 134-137.
[3] Y.-H. Chang, H.-T. Chiu, J. Mater. Res. 17 (2002) 2779-82.