Principle of XPS
XPS (X-ray Photoelectron Spectroscopy) or ESCA uses a soft X-ray source (AlKα or MgKα) to ionise electrons from the surface of a solid sample. The binding energy of these electrons are measured and are characteristic of the elements and associated chemical bonds (chemical state) in the top few atomic layers of the material.
Samples can be tilted to affect the escape depth of the electrons and thus determine the depths of overlayers on a surface. This non-destructive depth profiling, known as angle resolved XPS, also allows surface bond orientation to be explored particularly relevent for adhesion and joining technology and wetting issues.
For analysis beyond the top 1-5nm an inert gas ion gun (normally Argon) can be used to sputter off the surface layers before analysis. Alternating sputtering and XPS spectral acquisition permits chemical depth profiles to be obtained.
Information from XPS
XPS is a quantitive spectroscopic technique which analyses the average surface chemistry of a sample up to a depth of approximately 3-5nm. This technique quantitatively measures the elemental composition, atomic concentrations and chemical states of elements present at a samples surface. XPS can detect all elements with an atomic number greater than 3, therefore, Hydrogen and Helium are not possible to detect. The area of analysis is typically 10mm2 but small areas down to 150μm x 150μm are possible.
Example Range of Materials
Example Typical Applications
Our site expert on XPS is Dr Stephen Jenkins.