XPS is much Superior Characterization Technique
Автор: Nano SPEAKs
Загружено: 2024-07-20
Просмотров: 421
Two main advantages of X-rays Photoelectrons Spectroscopy
There are two advantages over other similar characterization techniques, like UPS and EDX
1- Surface sensitivity (∼10 nm) - elemental composition
2- Its ability to distinguish in Chemical Environment
Let's discuss each one in detail:
XPS is a surface sensitive technique:
XPS only detects elements at a very thin region ~10 nm. In fact, x-rays (Al Kα~1486.6 eV and Mg Kα line ~1253.6 eV) can penetrate to a micro meter thick region however, the photoelectrons lost its energy completely owing to inelastic scattering and can not reached the XPS detector. Just below the 10 nm region, the photoelectron may encounter a few inelastic scattering and reach to the XPS detector, but they only contribute to the background of the XPS peaks. The photoelectrons escaped only from the ~10 nm will reach the XPS detector and give rise to XPS photoelectrons and Auger electron Peaks. In XPS, the elemental identification can be achieved by running a survey spectra.
XPS also reveal about the chemical environment:
The chemical environment includes factors like the nearest neighbour elements and oxidation state of the elements, which affects the Binding energy (BE)of the Auger electrons and Photoelectrons Peaks. For example, the BE of a carbon atom in a C=O bond will be different from that in the C-H bond. This small variation in BE is NOT possible with SURVEY Spectra. Therefore, we have to run the High Resolution Spectra.
For instance, it is observed that the BE for C 1s increases significantly when the bonded oxygen atoms increases i.e., the BE for O-C=O is greater than C =O and C-O, it is because oxygen is more electronegative than carbon and will be attracting more electrons away from carbon. This way, the carbon atom should become more positively
charged, resulting in an enhance BE for C 1s.
Similarly, the chemical state of Ti, TiO, and TiO2 with oxidation state Ti (0), Ti(II), and Ti(III), respectively showing different BE their different oxidation states and chemical environment. This variation in the BE can ONLY be possible and can be accomplished by running High Resolution XPS spectra.
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