SURFACE INTERFACE ONTARIO

"CREATING PARTNERSHIPS FOR INNOVATIVE RESEARCH"

X-ray Photoelectron Spectroscopy (XPS)
(also known as Electron Spectroscopy for Chemical Analysis (ESCA))


Back to XPS Main Page

Principles

The basis of the XPS technique is as follows:

  • Incident X-rays cause photoemission of electrons from the sample surface. These are energy analysed, allowing the binding energy of the emitted electron to be obtained.
  • Binding energies are characteristic of each element and can be used for identification. Peak areas allow for quantification.
Survey Spectrum of Dentin from a Cow's Tooth



  • The main strength of XPS is its ability to provide chemical information - chemical shift. The binding energy of a particular electron is affected by the environment the atom is situated in.
  • Thus, information can be obtained on:

    • chemical bonding of the element
    • its particular oxidation state
    • and is quantifiable

C 1s Spectrum of PMMA Obtained Using Monochromatic Al Ka X-rays
Note: 3:1:1 C Ratio

Information:
  • Elements Li and up, on both insulating and conducting samples
  • 0.1 - 1 at.% detection limit, straigtht-forward quantification (±5%)
  • "Chemical-shifts" - bonding information
  • Surface specific (2 - 10 nm)
  • Angle-resolved XPS - non-destructive depth information (to 10 nm)
  • Ion sputtering - deeper depth profiles
  • High spectral resolution200 µm (5 µm in imaging systems)
  • Mapping capabilities - while utilizing small analysis spot
Angle-Resolved XPS (ARXPS)
“Traditional” ARXPS – sample is tilted

Surface Selective Modification of Fluoropolymers by Al Deposition

McKeown et al.
Langmuir
7 (1991) 2146

Parallel ARXPS - Theta Probe

  • Two dimensional detector
  • Measures energy and angle simultaneously
  • 110 channels for snapshot spectroscopy
  • 96 angle channels
  • 60° collection angle (23° - 83°)
  • NO tilting the sample

 

See Workshop presentation Extraction of Depth Information from ARXPS Data for more details.

Diagram courtesy of Thermo Fisher


Useful Links for XPS can be found at:

UK Surface Analysis Forum:

On-line Databases - http://www.uksaf.org/data.html
On-line Surface Science Tutorials: http://www.uksaf.org/tutorials.html

NIST - XPS Database: http://srdata.nist.gov/xps