022: XPS for Beginners – Fundamentals 2

For more information on binding energy shifts – see our article titled ‘What influences Binding Energies?‘

For more information on Auger processes – see our article titled ‘The Auger Process and Auger Peaks.‘

To discover an advanced type of Auger process – see our article tiled ‘Coster-Kronig‘

Questions

1: In which order would you expect the following Te 3d orbitals (low to high) to appear? Te metal, TeO₂, CdTe, TeO₃ and TeCl₄

Answer

Our ordering for Te 3d contains an interesting one, CdTe is a common photovoltaic semiconductor.

CdTe < Te metal < TeO₂ < TeCl₄ < TeO₃

Since Te in CdTe is bonded to cadmium (1.7 on the Pauling scale), it is the more electronegative of the two atoms (2.1 on the Pauling scale). This means, Te will pull electron density towards itself and lower the effective binding energy below that of Te metal

2: Arrange the following compounds into order for expected binding energy (low to high)

C 1s: Metal Carbide, Alcohols, Carboxylic Acids, Fluorocarbons (CF3), Alkanes, Ethers, Metal Carbonate
Si 2p: Organic Si, SiO2, Si3N4, Si, Aluminosilicate
mental sulfur (S8), Thiol, Metal sulfide

Answer

When sorting these compounds into ascending expected binding energy order, we must consider oxidation state and potential dipoles/electronegativity influences.

For carbon 1s, we have the order:

Metal Carbides (~283 eV), Alkenes (284.8 eV), Alcohols/Ethers (286 eV), Carboxylic Acids (~288.5 eV), Metal Carbonates (~290 eV), Fluorocarbons (294 eV)

In practice, alcohols and ethers are too close to separate, and exactly where the metal carbonate comes will be highly dependant on the metal – so if you’ve assigned these the other way around don’t worry, you’re thinking in the right way!

For Si 2p, we have the order:

Si, Si₃N₄, Organic Si, Aluminosilicate, SiO₂

Hopefully quite straightforward – aluminosilicates, while oxidic in nature as SiO₂, introduce a perturbation from Al reducing the binding energy of the Si centres.

For sulfur 2p we have:

Metal sulfide, Thiol, Elemental sulfur, Sulfonic acid, Metal sulfate

3: If Ni 2p regions have a binding energy of ~856 eV, and F KLL auger peaks have a kinetic energy of ~630 eV; which excitation source is more suitable for analysis? Al or Mg? Hint: remember B.E. = hv – K.E. – WF (WF can be treated as 0 in this case). For information on the energies of various X-ray sources, look at our article titled ‘X-ray Sources‘

Answer

Al kα hv = 1486.7 eV

Mg kα hv = 1253.6 eV

F KLL binding energy with Al kα source = 856.7 eV

F KLL binding energy with Mg kα source = 623.6 eV

F KLL from an Al source will overlap with the Ni 2p peaks at 856 eV, so the best choice is to use an Mg anode

4: An unknown copper sample recorded a binding energy of 932.5 eV for the 2p region with an Al kα source. The modified auger parameter was calculated to be 1849.4 eV. What was the species of the copper and what was the binding energy of the Cu LMM auger (assume work function = 0 eV)? Reference data for copper may be found on the HarwellXPS Guru Element page for copper. For a reminder of how the modified auger parameter is calculated – see our page titled ‘Auger Parameter‘

Answer

Binding energy for Cu 2p = 932.5 eV

a’ = 1849.4 eV

If we take a look at the reference page for copper, we see that the species = Cu(I)

We can calculate the KE easily from the auger parameter and 2p BE (KE_LMM = a’ – BE_2p): Cu LMM auger kinetic energy = 916.9 eV

Remember: Al kα source = 1486.7 eV

So, using our equation for the photoelectric effect: Cu LMM auger binding energy = 569.8 eV

We will continue on to section 3, where we will learn about why certain peaks produce doublets and others singlets, plus we begin to look at how quantum mechanics influences our XPS spectra.

Continue to Section 3

Further Reading

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022: XPS for Beginners – Fundamentals 2

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