X-ray photoelectron spectroscopy (XPS)

About this technique

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X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA), provides elemental (down to approximately 0.1 atom %) and chemical information (oxidation state) of the outermost approximately 10 nm of any solid. It is non-destructive and can be used with both amorphous and crystalline materials.

Soft X-rays (1486.6 eV) are used to bombard the sample under an ultra-high vacuum resulting in the ejection of the core-level electrons (the photoelectrons) from the surface atoms. The measured binding energy provides the elemental and chemical information.

Sub-surface layers can be analysed after removal of the outer layers by in-situ ion beam milling. Bulk analysis can be performed after appropriate sample preparation such as crushing (to provide a fresh new surface), fracturing and scraping.

Typically, data is taken from an area of approximately 800 x 300 µm. The smallest area that can be analysed is approximately 15 nm. Elemental imaging, typically over 200 x 200 µm enables the area of analysis to be identified. Data acquisition time is from 5–60 minutes depending on the extent of chemical information required.

There is no specific sample preparation but it is critical that sample is NOT handled as surface contamination is always an issue considering that the detected electrons are originating from only the top 10 nm.