XPS

X-ray Photoelectron Spectroscopy (XPS)

Technique:

Kratos AXIS Supra (front) and Kratos AXIS Nova (rear) X-ray photoelectron spectrometers

Kratos AXIS Supra (front) and Kratos AXIS Nova (rear) X-ray photoelectron spectrometers at Surface Science Western.

X-ray photoelectron spectroscopy (XPS or ESCA), is an analytical technique that depends upon the measurement of the energies of photoelectrons that are emitted from atoms when they are irradiated by soft X-ray photons (1 – 2 keV). When used to study solids, XPS analysis has a number of powerful attributes, including a high (and variable) range of sensitivities to structures on the outermost surface of the solid (outer few nanometres), an ability to identify such structures chemically, a reasonable capacity for elemental quantification, as well as the ability to determine structure thickness. As a method for characterizing surface composition, there is no single other technique that can compare with XPS, in terms of the wealth of useful information, reliability of the data, and ease of interpretation.

xps cr 2p spectrum

Cr 2p high resolution XPS spectrum.

Advancements in XPS spectrometer technology have resulted in major improvements in spectral resolution and counting efficiency over the past 20 years. This has dramatically improved the level of confidence in spectral positions, and the ability to carry out analyses in numbers that have much better statistical significance. The exploitation of the imaging developments is likely the most exciting prospect, because, historically, little research has been done using highly-resolved XPS images. The recognition of co-localization of different species (elemental or chemical) will be one of the most powerful elements shaping XPS analysis in the future.

The principal XPS at SSW is a Kratos AXIS Supra spectrometer. The AXIS Supra delay-line detector offers unrivalled spectroscopic and imaging performance with high energy resolution, large area – high sensitivity analysis, small spot analysis and XPS imaging. This instrument is also equipped with the latest gas cluster ion source (GCIS) for the ultimate in depth profile and surface cleaning flexibility.

The second XPS at SSW is a Kratos AXIS Nova spectrometer. The AXIS Nova employs a monochomatic Al Kα X-ray source with a delay line detector (DLD) system. This detector allows for fast image acquisition, enhanced small spot analysis sensitivity, and true quantitative XPS imaging. The system employs an automated multiple sample platen system that allows for increased sample throughput.

Instrument:
Kratos AXIS Supra Spectrometer

System Capabilities:

  • In-situ fracturing at low temperature
  • Sample heating (800° C) and cooling (-100° C)
  • Variable angle sample orientation (angle resolved analysis)
  • High precision automated stage for remote or non-attended operation
  • Depth profiling in with both monoatomic Ar+ and gas cluster beams (up to Ar3000+)
  • Interfaced to a glove box for chemical preparation under inert atmosphere
  • Analysis of sample sizes up to 30 mm x 75 mm and up to 10 mm thick
  • Elemental and chemical imaging, small spot analysis
  • Multiple X-ray sources including monochromatic Al Kα, monochromatic Ag Lα, He(I) and He(II)
  • Ion scattering spectroscopy (ISS) equipped

Instrument:
Kratos AXIS Nova Spectrometer

System Capabilities:

  • Variable angle sample orientation (angle resolved analysis)
  • High precision automated stage for remote or non-attended operation
  • Depth profiling (low energy beam)
  • Sample platens can hold numerous samples of varying sizes (up to 10 mm thick). Eight inch wafer analysis possible (some restrictions apply)
  • Elemental and chemical imaging, small spot analysis
  • Monochromatic Al Kα X-ray source
  • MCP delay-line detector allowing for scanned and snapshot data collection as well as elemental and chemical imaging, small spot analysis
  • Equipped with a specially designed inert transfer vessel allowing for mounting of air sensitive samples in a glove box, and transferring to the instrument without air exposure
  • Transfer vessel can also be used to transfer samples in vacuum to our ToF-SIMS instrument
X-ray Photoelectron Spectroscopy (XPS) Reference Pages

The XPS team at SSW also maintains the X-ray Photoelectron Spectroscopy (XPS) Reference Pages website. This site is a collection of curve-fitting procedures, reference materials, and useful tips on XPS analyses and spectral interpretation.

Selected Applications in Industry:

  • Reactions of water vapour with polycrystalline iron: near surface compositions revealed using QUASES™ evaluation of XPS spectra
  • XPS analysis of an adhesive failure
  • Estimation of oxide thickness
  • High resolution spectrum from magnesium oxide on glass substrate
  • Angle resolved study of pyrite surfaces
  • Imaging XPS study of a Monel 400 corrosion pit
  • Studies of chromium compounds
  • Analysis of surface stains on mirrored surfaces