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 wideÂ
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)Â 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 50:50Â (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 66:33Â (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 75:25Â (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 80:20Â (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.