Chemical State Peak-fits – Examples

Cr2O3, single crystal, freshly exposed bulk

Phosphorus (P), black, as received, native oxide

Magnesium (Mg) metal, as received, native oxide

Magnesium (Mg) metal, as received, native oxide

An alternative peak-fit if FWHM of Oxidized Mg is only 1.2-1.3 eV wide 

Gold Oxide (Au2O3) powder, air-sensitive, easily degrades

GaAs single crystal wafer, freshly exposed bulk

Bismuth (Bi) metal, native oxide,  PE=50 eV

Boron (B) metal, native oxide, with Flood Gun ON

The ESCA Molecule

Ethyl tri-fluoroacetate readily shows four (4) different chemical states thereby showing the power of ESCA (XPS) to reveal chemical states

Silver (Ag) metal, ion etched clean, used to check the energy scale

Copper (Cu) metal, ion etched clean, used to check the energy scale

Copper (Cu) metal, ion etched clean, used to check the energy scale

Gold (Au) metal, ion etched clean, used to check the energy scale

Overlay of pure Magnesium (Mg) metal, ion etched clean, and freshly exposed bulk of MgO single crystal – aligned to same BE

Clearly shows that Metal Oxides have FWHM that is ~2x larger than FWHM of pure metals

Aluminum (Al) metal was analyzed in 1978 at a Synchrotron

Pure aluminum (Al) metal was exposed to Oxygen gas to learn if aluminum builds a chemisorbed state as it forms Al2O3.
From these results, we know that Al2O3 has a Al (2p) BE that is 2.7 eV greater than the 72.9 eV BE of pure Aluminum (Al)  metal.
This means that pure Al2O3 has a true Al (2p) BE at 75.6 eV, not 74.4 eV as listed in various handbooks and BE databases.

Pure Al2O3 has a true Al (2p) BE at 75.6 eV, not 74.4 eV !!!

Peak-fitting of Overlapping Chemical States

When Peak-fitting, we must think about the chemical shifts that exist for the different, but similar, chemical states that exist in a chemical state spectrum.

In general we imagine that most chemical states have chemical state BEs that are ~1 eV apart. This example is a set of two peaks that were shifted by 1 eV, and then added together.  This example also uses peaks that have FWHM ~ 1.1 eV wide.  This is reasonable for many chemical compounds, but some compounds can have FWHM ~1.5 eV.

When there is a 50:50  (1:1) mixture of 2 chemical states that are separated by ~1 eV and have FWHM ~1.1 eV, you see the merged peak set at the top left.
When there is a 66:33  (2:1) mixture of 2 chemical states that are separated by ~1 eV and have FWHM ~1.1 eV, you see the merged peak set at the bottom left.

When there is a 75:25  (3:1) mixture of 2 chemical states that are separated by ~1 eV and have FWHM ~1.1 eV, you see the merged peak set at the TOP RIGHT.
When there is a 80:20  (4:1) mixture of 2 chemical states that are separated by ~1 eV and have FWHM ~1.1 eV, you see the merged peak set at the BOTTOM RIGHT.