Phosphorus

Table 1. P 2p3/2 binding energy values [1].  a) and b) are from standard samples analyzed in this laboratory.

P 2p3/2 - P 2p1/2 splitting value is 0.86 +/- 0.05 eV. [2] has it at 0.84 eV.
Note:
(PO4)3- = phosphate
(P2O7)4- = pyrophosphate
(PO3)- = metaphosphate

Further Values for P 2p3/2
P(C6H5)3 = 131.0 eV +/- 0.4 eV, 20 References
PO(C6H5)3 = 132.6 eV +/- 0.4 eV, 9 References (with O 1s at 530.9 to 531.1 eV)
(PF6)- = 136.4 eV +/- 0.8 eV, 17 References

Table 2. P 2s binding energy values [1].

Update: Recent work on stoichiometric Li3PO4 films gave P 2p3/2 binding energies of between 133.20 to 133.35 eV with FWHM of ~1.2 eV. Li 1s was at 55.26 to 55.52 eV with FWHM of 1.4 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] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN, 1992.

Nitrogen

Table 1. Nitrogen 1s binding energy values [1].

a) The binding energy values for nitrogen in organic compounds overlap significantly and can be difficult to decipher especially if there are multiple nitrogen containing groups. An excellent resource is Appendix 4 in the "High Resolution XPS of Organic Polymers - The Scienta ESCA300 Database"[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] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers - The Scienta ESCA300 Database Wiley Interscience, 1992.

Gallium

Ga 3d5/2 binding energies and 3d5/2 L3M45M45 Auger parameters from standard samples and various references sources [1,2,3,4].  a) Argon ion sputter cleaned standard sample analyzed in this laboratory [3].

Ga 3d5/2 - Ga 3d3/2 splitting is 0.45 eV +/-0.01 eV (from reference sources and standard sample).

Ga 3p3/2 binding energies from standard samples and various references sources [1,2,3,4]. a) Argon ion sputter cleaned standard sample analyzed in this laboratory [3].

Ga 3p3/2 - Ga 3p1/2 splitting is 3.53 eV (from standard sample).

Ga 2p3/2 binding energies and 2p3/2 L3M45M45 Auger parameters from standard samples and various references sources [1,2,3,4].  a) Argon ion sputter cleaned standard sample analyzed in this laboratory [3]

Ga 2p3/2 - Ga 2p1/2 splitting is 26.84 eV [5]

Ga 3s: 160 eV
Ga 2s: 1301 eV

XPS survey spectrum of sputter cleaned gallium metal.

Ga LMM spectrum of Ga2O3.

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] S.C. Ghosh, M.C. Biesinger, R.R. LaPierre, P. Kruse, J. Appl. Phys. 101 (2007) 114321.
[3] S.C. Ghosh, M.C. Biesinger, R.R. LaPierre, P. Kruse, J. Appl. Phys. 101 (2007) 114322.
[4] H.A. Budz, M.C. Biesinger, R.R. LaPierre, J. Vac. Sci. Technol. B 27(2) (2009) 637.
[5] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp, Eden Prairie, MN, 1992.

Arsenic

As 3d5/2 binding energies from standard samples and various reference sources [1,2,3,5].  a) Argon ion sputter cleaned sample taken in this laboratory [5],  b) note that GaAS positions can change significantly with dopants, c) vacuum fractured standard sample taken in this laboratory.

As 3d5/2 - As 3d3/2 splitting value is 0.68 eV +/- 0.03 eV (based on 9 literature references). Standard As metal gave a splitting value of 0.70 eV and a standard GaAs gave a value of 0.71 eV. FWHMs for As metal were 0.55 eV and 0.75 eV at 10 eV and 20 eV pass energies. FWHM for GaAs metal was 0.79 eV at 20 eV pass energy. FWHM for arsenopyrite was 0.58 eV at 10 eV pass energy. The oxides had FWHM of 0.97-1.4 eV (20 eV pass energy). In the fitting process we generally set the oxide peaks to have equivalent FWHM.

As 3d fitting of an oxidized GaAs surface.

As 2p3/2 binding energies from standard samples and [3,5].  a) Argon ion sputter cleaned standard samples taken in this laboratory [5].

Some good examples of fitting As spectra using the above data are found in references [4, 5 and 6].

Note that the LMM Auger structure taken with an Al K(alpha) X-ray source for As is quite extensive (see below) and can cause spectral interferences with a wide variety of other elements. 

XPS spectrum of As metal showing the extensive LMM Auger structure (Al X-ray source).

As 3d5/2-3d1/2 splitting: 0.68 eV
As 2p3/2-2p1/2 splitting: 35.8 eV
As 3p3/2: 141 eV
As 3p1/2: 146 eV
As 3s: 205 eV

References:
[1] H.W. Nesbitt and M. Reinke, American Mineralogist, 84 (1999) 629.

[2] A.R. Pratt, H.W. Nesbitt, American Mineralogist, 85 (2000) 619.
[3] 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. 

[4] S.C. Ghosh, M.C. Biesinger, R.R. LaPierre, P. Kruse, J. Appl. Phys. 101 (2007) 114321.

[5] S.C. Ghosh, M.C. Biesinger, R.R. LaPierre, P. Kruse, J. Appl. Phys. 101 (2007) 114322.

[6] H.A. Budz, M.C. Biesinger, R.R. LaPierre, J. Vac. Sci. Technol. B 27(2) (2009) 637.

XPS Imaging Background Corrections

XPS images are corrected for inelastic background and surface topography using Boolean type operations available in CasaXPS (Image Processing tab).  To correct an XPS image (A) taken of an element or from a chemical state of an element a background image (B) from ~ 10-15 eV below the main image binding energy needs to also be taken using the same spectrometer conditions and run time. To correct for inelastic background only (useful if you have very flat samples) subtract image B from image A. To do this in CasaXPS select image A and image B and press the overlay button (or F2), the press the (a-b) button in Image Processing. Image A will now be processed.

To correct for inelastic background and surface topography, the subtracted image (A-B) is then further divided by B.  This can be done as above using the (a-b)/b button in Image Processing. This process has been described in reference [1].

Quantitative XPS imaging is also possible. Some examples of this are described in references [2] and [3].

References:
[1] B.A. Kobe, S. Ramamurthy, M.C. Biesinger, N.S. McIntyre, A.M. Brennenstuhl, Surf. Interface Anal. 37 (2005) 478.
[2] M.C. Biesinger, B.R. Hart, R. Polack, B.A. Kobe, R.St.C. Smart, Miner. Eng. 20 (2007) 152.
[3] B. Kobe, M. Badley, J.D. Henderson, S. Anderson, M.C. Biesinger, D.W. Shoesmith, Surf. Interface Anal. 49 (2017) 1345.

Strontium

Sr 3d5/2 binding energies [1].

Sr 3d5/2 - 3d3/2 doublet separation from [2] is stated as 1.79 eV (for metallic Sr) while an average for the doublet separation from a number of sources/species in [1] is 1.74 eV +/- 0.10 eV (14 citations).
Sr 3p3/2: 270 eV
Sr 3p1/2: 281 eV
Sr 3s: 360 eV
Sr 4p 21 eV
Sr 4s: 39 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] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN, 1992.

Multiplet Splitting

Multiplet splitting arises when an atom contains unpaired electrons (e.g. Cr(III), 3p⁶3d³). When a core electron vacancy is created by photoionization, there can be coupling between the unpaired electron in the core with the unpaired electrons in the outer shell. This can create a number of final states, which will be seen in the photoelectron spectrum as a multi-peak envelope[1]. Figure 1 shows the multiplet structure associated with the Cr 2p_3/2 peak for a vacuum fractured Cr₂O₃ specimen.

Figure 1. Multiplet structure associated with the Cr 2p_3/2 peak for a vacuum fractured Cr₂O₃ specimen.

The early Hartree-Fock calculation of the multiplet structure of core p-valence levels of free ion state first row transition metals by Gupta and Sen[2] graphically shows their multiplet structures (Figure 2). These calculations are an excellent starting point for the examination of multiplet structure observed for transition metal compounds. However, they apply to free ion states only and, in transition metals and their compounds, there may be ligand charge transfer effects that will change the spacing and intensity of the multiplet peaks present in their spectra. These relative changes can be utilized for transition metal compounds to differentiate those more closely approximating free ions from those in which charge transfer from the bonded neighbouring ions may have changed both the effective oxidation state and multiplet splitting of the core transition metal[3,4,5,6]. This change in local electronic structure has been used to explain the differences between the XPS spectra of nickel oxide and its oxy/hydroxides [3,7]. De Groot and Kotani’s text “Core Level Spectroscopy of Solids”[8] provides an excellent advanced analysis of multiplet effects and their use in the modeling of spectra for both XPS and XAS.

Figure 2. Calculated multiplet structure of 2p ionisation created in the free ions as labelled. The zero energy is arbitrary and the intensity normalization is the same for all spectra shown [From 2].

Table 1 summarizes the various first row transition metal species that show multiplet splitting in their XPS spectra. Sc, Ti, V, Cu and Zn species, where multiplet splitting is not present or, if present, is generally not well resolved or shows as peak broadening only[9]. Cr, Fe, Mn, Co and Ni species show significant multilpet spitting[3,4,5,6,7,10,11].

Table 1. First row transition metal species that show multiplet splitting in their XPS spectra. This is for high spin compounds. For low spin Fe(II) and low spin Ni(II) electrons are paired and no multiplet splitting is observed.

References:

[1] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp, Eden Prairie, MN, 1992.
[2] R.P. Gupta, S.K. Sen, Phys. Rev. B 12 (1975) 15.
[3] A.P. Grosvenor, M.C. Biesinger, R.St.C. Smart, N.S. McIntrye, Surf. Sci. 600 (2006) 1771.
[4] N.S. McIntyre, D.G. Zetaruk, Anal. Chem. 49 (1977) 1521.
[5] M.C. Biesinger, C. Brown, J.R. Mycroft, R.D. Davidson, N.S. McIntyre, Surf. Interface Anal. 36 (2004) 1550.
[6] A.P. Grosvenor, B.A. Kobe, M.C. Biesinger, N.S. McIntyre, Surf. Interface Anal. 36 (2004) 1564.
[7] M.C. Biesinger, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Physical Chemistry Chemical Physics, 14 (2012) 2434.
[8] F. de Groot, A. Kotani, Core Level Spectroscopy of Solids, CRC Press, Boca Raton, 2008.
[9] M.C. Biesinger, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Appl. Surf. Sci. 257 (2010) 887.
[10] M.C. Biesinger, B.P. Payne, A.P. Grosvenor, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Appl. Surf. Sci. 257 (2011) 2717.
[11] M.C. Biesinger, B.P. Payne, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Surf. Interface Anal. 41 (2009) 324.

Auger Peaks and the Auger Parameter

Following core ionization by photoelectron emission an outer shell electron can fill the created vacancy and the energy released can result in the emission of an Auger electron. A schematic of the Auger emission process for nickel metal is presented in Figure 1. The energy of an emitted Auger electron will be equal to the emitted photoelectron binding energy (E_b(C₁)) minus the binding energy of electron that fills the vacancy in the core (E_b(C2)), minus the binding energy (in the presence of the core hole) of the level from where the Auger electron is emitted (E_b(C3)):

                 E_k ≈ E_b(C₁) – E_b(C2) – E_b(C3)               (1)

Figure 1.  Schematic of an LMM Auger electron emission from a nickel atom.

Auger spectra have unique peak shapes and positions and are useful for both elemental identification and chemical state analyses. A calculated value from both photoelectron and Auger peak positions is the Auger parameter (α). This parameter is particularly useful for chemical state analysis and can be used without interference of surface charging. Originally defined by Wagner[1,2], the Auger parameter is calculated as follows:

α = E_k(C₁C₂C₃) – E_k(C)                    (2)

where E_k(C₁C₂C₃) is the kinetic energy of the Auger transition involving electrons from C₁, C₂ and C₃ core levels and E_k(C) is the kinetic energy of the photoelectron from core level C. This form of the equation allowed for negative values of α. The Auger parameter was modified by Gaarenstroom and Winograd[3] by addition of the photon energy to α. This modified Auger parameter (α') is independent of the X-ray energy used and is calculated as follows:

α' = E_k(C₁C₂C₃) + E_b(C)                   (3)

where E_b(C) is the binding energy of the core level C. Since any surface charging shifts will be of the same magnitude, but of opposite direction in each of these two components, they will be automatically cancelled out in α'.

The graphical display (scatter plot) of the most intense photoelectron line binding energies (abscissa, oriented in the negative direction) versus the kinetic energy position of the sharpest core-core-core Auger line (ordinate) is known as a Wagner plot, chemical state plot or chemical state diagram. Positions of compounds on these plots indicate both relaxation energy and initial state effects[4,5]. Hence, the modified Auger parameter can be used in addition to the binding energy envelope to give additional insight into the shift in electronic state between transition metal compounds.

There are numerous examples of the use of Wagner plots and Auger parameter in the literature including the study of silicon/silicate materials[6,7] and TiO₂ on different supporting surfaces[8]. The NIST database[9] contains a large collection of Auger parameter values as does the Handbook of X-ray Photoelectron Spectroscopy[10].

Figure 2. Ni 2p_3/2 – Ni LMM Wagner plot for Ni metal, Ni alloys, NiO, Ni(OH)₂ and NiOOH [From 11].

In XPS spectra, measured core level binding energies, E_b, involve both the ground state and the final state relaxation energies. The response of spectator electrons to the creation of a core hole and the Auger deexcitation process causes lowering of the measured binding energy as compared to the initial state (i.e. chemical shift) binding energy and this final state relaxation energy R can vary with chemical environment. Hence, there is a need to distinguish between initial and final state contributions to the measured binding energies. It is therefore important that final state effects are correctly described if binding energy shifts are to yield useful and reliable chemical information as to the electronic structure of transition metals and their compounds. Experimentally, relaxation energy shifts are often estimated by measuring the Auger parameter shift defined by:

Δα' = ΔE_b + ΔE_k                    (4)

It is usually assumed, following the derivation by Morretti[4,5], that the relaxation energy for the doubly core-ionized state created by the Auger process, equals 2R, leading to:

Δα' ≈ 2ΔR                              (5)

In the simplest approximation used by Wagner[12] the shift in core level binding energy ΔE_b and in Auger transition kinetic energy ΔE_k are then:

ΔE_b = − Δε – ΔR                   (6)

ΔE_k = Δε + 3ΔR                     (7)

In this convention, positive values of Δε, initial state contributions, and ΔR, final state contributions, result in a shift to lower binding energy. Initial state effects, Δε, are generally understood to represent the “chemical shift” as a result of ground state electronic structure and are a function of the valence structure of the core atom, which is in turn is a function of bonding to neighboring atomic valence states. These shifts are related to the electronic states (e.g. band structures, bond directionality) and structural parameters (e.g. atomic positions, Madelung constants) of the bonded atoms.

References:
[1] C.D. Wagner, Electron Spectroscopy, in: D.A. Shirley (Ed.), Proceedings of an International Conference held at Asilomar, Pacific Grove, California, USA, 7-10 September, 1971, North-Holland, Amsterdam, 1972, p. 861
[2] C.D. Wagner, Anal. Chem. 44 (1972) 967.
[3] S.W. Gaarenstroom, N. Winograd, J. Chem. Phys. 67 (1977) 3500.
[4] G. Moretti, The Auger Parameter, in: D. Briggs, J.T. Grant (Eds.), Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications, Chichester, UK, 2003, pp. 501-530.
[5] G. Moretti, J. Electron Spectrosc. Relat. Phenom. 95 (1998) 95.
[6] P.S. Arora, R.St.C. Smart, Surf. Interface Anal. 24 (1996) 539.
[7] M. Stevenson, P.S. Arora, R.St.C. Smart, Surf. Interface Anal. 26 (1998) 1027.
[8] J.A. Mejías, V.M. Jiménez, G. Lassaletta, A. Fernández, J.P. Espinós, A.R. Gonzálex-Elipe, J. Phys. Chem. 100 (1996) 16255.
[9] 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.
[10] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp, Eden Prairie, MN, 1992.
[11] M.C. Biesinger, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Physical Chemistry Chemical Physics, 14 (2012) 2434.
[12] C.D. Wagner, J.A. Taylor, J. Electron Spectrosc. Relat. Phenom. 28 (1982) 211.

Charge Compensation

Insulating samples pose a unique challenge for XPS analysis. As photoelectrons are lost during the photoemission process a positive charge will build up on the sample. As this occurs, the kinetic energy of the emitted photoelectrons will decrease resulting in a shift to higher binding energy of the observed peaks in the spectrum. A number of schemes have been developed to compensate for this. Most commonly a low energy electron flood gun is used to replace emitted electrons. A slight overcompensation is normally used [1], setting up an equilibrium state with peaks in the spectrum shifted a few eV to lower binding energy. In post processing the peaks are then shifted back by referencing to a set internal standard such as adventitious carbon or a known species in that particular sample (e.g. a metallic peak, a well characterized oxide peak, a graphitic species, see [2] for further examples).

In some cases only a portion of the sample is insulating with some discrete areas or layers of the sample being conducting or semi-conducting. In these cases a phenomenon known as differential charging can occur. It is possible to imagine a sample with insulating domains or island structures that have varying thicknesses on a conducting surface. The spectral features from these areas will be shifted to lower binding energies by the action of the charge neutralizer whereas the spectral features of the underlying material will not be shifted. This may be complicated if the islands or domain structures behave as semi-conductors and their conductivity varies with thickness. The resulting spectra may be broadened significantly as a result. Layered structures may also charge differentially. The thin oxide layer on a metallic (conducting) material can behave as a conductor, as a semi-conductor, or as an insulator as the film grows in thickness.  The position of the oxide peak in relation to the metallic peak can change depending on oxide thickness and/or changes in charge neutralizer settings. See examples of this for Al oxide on Al metal in references [3] and [4]. A multilayered system may include alternating layers of conducting, semi-conducting and insulating species in a variety of combinations. All of this can result in changes in selected peak positions that must be understood or erroneous assignment of chemical states may result. 

One excellent way to combat differential charging effects is to electrically isolate (or "float") the entire sample from the specimen holder. This "specimen isolation" technique is similar to that used in secondary ion mass spectrometry [5] and effectively makes the entire sample (both insulating, semi-conductive and conductive areas) behave non-conductively. Methods employed with good success here at Surface Science Western include mounting samples on non-conductive double sided tape or mounting on glass slides. Recent work [2] has highlighted the effectiveness of this technique in conjunction with charge correction procedures using adventitious carbon. 

The Kratos AXIS (Supra, Ultra and Nova) systems employ both a low electron flood gun as well as a set of sub-sample magnetic fields that return over-focused and under-focused photoelectrons (that are not being admitted through to the spectrometer) back to the surface of the sample. This system has had excellent success in analyzing a wide range of insulating samples.

Figure 1. Differential charging issues can be caused by both insulating to semi-conductive island structures (top) or by layered systems (bottom).

References:
[1] M.A. Kelly, Analysing Insulators with XPS and AES, in: D. Briggs, J.T. Grant (Eds.) Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications, Chichester, 2003, pp. 191-210.

[2] M.C. Biesinger, Appl. Surf. Sci. 597 (2022) 153681.

[3] A.J. Lizarbe, G.H. Major, V. Fernandez, N. Fairley, M.R. Linford, Surf. Interface Anal. 55 (2023) 651-657.

[4] D.R. Baer, K. Artyushkova, J. Cohen, C.D. Easton, M. Engelhard, T.R. Gengenbach, G. Greczynski, P. Mack, D.J. Morgan, A. Roberts, J. Vac. Sci. Tech. A 38 (2020) 031204.

[5] J.B. Metson, G.M. Bancroft, N.S. McIntyre, W.J. Chauvin, Surf. Interface Anal. 5 (1983) 181-185.

Spin Orbit Splitting

Core levels in XPS use the nomenclature nl_j where n is the principal quantum number, l is the angular momentum quantum number and j = l + s (where s is the spin angular momentum number and can be ±½). All orbital levels except the s levels (l = 0) give rise to a doublet with the two possible states having different binding energies. This is known as spin-orbit splitting (or j-j coupling)[1]. The peaks will also have specific area ratios based on the degeneracy of each spin state, i.e. the number of different spin combinations that can give rise to the total j (see Table 1). For example, for the 2p spectra, where n is 2 and l is 1, j will be 1/2 and 3/2. The area ratio for the two spin orbit peaks (2p_1/2:2p_3/2) will be 1:2 (corresponding to 2 electrons in the 2p_1/2 level and 4 electrons in the 2p_3/2 level). These ratios must be taken into account when analyzing spectra of the p, d and f core levels. An example of this splitting for the Sc 2p peak for Sc₂O₃ is shown in Figure 1. Spin-orbit splitting values (eV) can be found in a variety of databases[2,3]. These values will be needed when fitting spectra where the chemical shifts are larger than the spin-orbit splitting. For example, the As 3d spectrum for an oxidized GaAs surface in Figure 2 shows that all spin-orbit doublets must be fit in order to properly identify the species present. The 3d_5/2 and 3d_3/2 doublet for each chemical specie is constrained to have 3:2 peak area ratios, equal FWHM, and a peak separation of 0.69 eV.

Table 1. Spin-orbit splitting j values and peak area ratios. 

Figure 1. An example of spin-orbit splitting in the Sc 2p spectrum of Sc₂O₃.

Figure 2. The As 3d spectrum of a sample of oxidized GaAs. Each chemical specie is fit with the 3d_5/2 and 3d_3/2 doublet that is constrained to have a 3:2 peak area ratio, equal FWHM for the two peaks of the doublet, and a peak separation of 0.69 eV.

References:
[1] D. Briggs, XPS: Basic Principles, Spectral Features and Qualitative Analysis, in: D. Briggs, J.T. Grant (Eds.), Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications, Chichester, 2003, pp. 31-56.
[2] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp, Eden Prairie, MN, 1992.
[3] 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.