University of Nottingham
  

 

Sample Chamber of an XPS Instrument

X-Ray Photoelectron Spectroscopy (XPS)

XPS enables the surface sensitive elemental and chemical state analysis of samples
 

 

XPS at a glance

X-ray photoelectron spectroscopy (XPS) is a very surface sensitive (top ~10nm) analysis technique that measures the elemental composition and chemical state of a material using the feedback from an induced photoelectron effect. It is sometimes known by the alternative name Electron Spectroscopy for Chemical Analysis (ESCA).

Applications

  • Quantitative elemental composition
  • Empirical formula derivation
  • Depth profiling
  • Chemical state identification
  • Electronic state binding energies and densities
  • Elemental mapping (XPS imaging) 

 ISAC's LiPPS XPS system - Advanced X-ray source and sample tolerance

Images Courtesy of Vladimir Korolkov Photography

How does XPS work?

Samples are exposed to incident X-rays. Photons are absorbed by elements in the top few nanometres of the sample surface, leading to ionization and the emission of core (inner shell) electrons. The kinetic energy distribution of the emitted photoelectrons is measured in the spectrometer and the electron binding energies are determined.

For every element, there will be a characteristic binding energy associated with each core atomic orbital and therefore any given element produces a characteristic peak 'fingerprint' in the photoelectron spectrum.
Peak intensities can be related to the concentration of the given element allowing XPS to provide a quantitative analysis of surface composition.

Changes in oxidation state or chemical environment give rise to small variations in binding energy which in turn leads to small changes in peak position. These shifts are known as chemical shifts. The ability to discriminate between different oxidation states and chemical environments is a big advantage of the XPS technique.
XPS is not sensitive to hydrogen or helium, but can detect all other elements.

 

 

Our XPS Facilities

Hosted by the Nanoscale and Microscale Research Centre (nmRC)

ISAC's XPS facilites hosted at the Nottingham Nanotechnology and Nanoscience Centre
ISAC's Liquid Phase Photoelectron Spectroscopy System at the Nottingham Nanotechnology and Nanoscience Centre
 

 

Kratos AXIS ULTRA DLD

  • Monochromated X-ray source Al Kα emission at 1486.6 eV, plus two non-monochromated sources Mg and Al.
  • High throughput multi position programmable stage allows multiple samples in one experiment.
  • Argon ion etching for depth profiling or cleaning.
  • Chamber pressure better than 5 x10-9 Torr.
  • The magnetic immersion lens system allows the area of analysis to be defined by apertures.
  • Electrostatic/magnetic lens system (hybrid lens) and a hemispherical analyser (CHA) to sort photoelectrons according to kinetic energy.
  • Electron detection and counting with a triple channel plate and delay line detector (DLD).
 

 

Kratos Liquid Phase Photoelectron Spectroscopy Machine (LiPPS)

  • Kratos Axis Ultra DLD machine with novel and unique, bespoke additional functionality for liquids and specialist samples:
  • High energy monochromated Ag source
  • Argon gas cluster source for high resolution depth profiling of organic materials (polymers and biological samples) to allow 3D chemical characterisation.
  • Bespoke electrochemistry stage for ‘in-situ’ work in ionic liquids.
 

 

Publications of Interest

  • Spatially Resolved Molecular Compositions of Insoluble Multilayer Deposits Responsible for Increased Pollution from Internal Combustion Engines. Edney, M., Lamb, J., Spanu, M., Smith, E., Steer, E., Wilmot, E., Reid, J., Barker, J., Alexander, M., Snape, C. & Scurr, D., ACS Applied Materials & Interfaces, 12, 51026–51035 (2020). 

  • Additive manufacture of complex 3D Au-containing nanocomposites by simultaneous two-photon polymerisation and photoreduction. Hu, Q., Sun, X.-Z., Parmenter, C. D. J., Fay, M. W., Smith, E. F., Rance, G. A., He, Y., Zhang, F., Liu, Y., Irvine, D., Tuck, C., Hague, R. & Wildman, R., Scientific Reports, 7, 17150 (2017). 

  • Supramolecular networks stabilise and functionalise black phosphorus. Korolkov, V. v, Timokhin, I. G., Haubrichs, R., Smith, E. F., Yang, L., Yang, S., Champness, N. R., Schröder, M. & Beton, P. H., Nature Communications, 8, 1385 (2017). 

  • Resolving X-ray photoelectron spectra of ionic liquids with difference spectroscopy. J., Maxwell-Hogg, S., Smith, E. F., Hawker, R. R., Harper, J. B. & Licence, P., Physical Chemistry Chemical Physics, 21, 114–123 (2019). 

  • An antimicrobial impregnated urinary catheter that reduces mineral encrustation and prevents colonisation by multi-drug resistant organisms for up to 12 weeks. Belfield, K., Chen, X., Smith, E. F., Ashraf, W. & Bayston, R., Acta Biomaterialia, 90, 157–168 (2019). 

  • Reverse Semi-Combustion Driven by Titanium Dioxide-Ionic Liquid Hybrid Photocatalyst. Qadir, M. I., Zanatta, M., Pinto, J., Vicente, I., Gual, A., Smith, E. F., Neto, B. A. D., de Souza, P. E. N., Khan, S., Dupont, J. & Alves Fernandes, J., ChemSusChem, 13, 5580–5585 (2020). 

  • Nanobugs as Drugs: Bacterial Derived Nanomagnets Enhance Tumor Targeting and Oncolytic Activity of HSV-1 Virus. Howard, F. H. N., Al-Janabi, H., Patel, P., Cox, K., Smith, E., Vadakekolathu, J., Pockley, A. G., Conner, J., Nohl, J. F., Allwood, D. A., Collado-Rojas, C., Kennerley, A., Staniland, S. & Muthana, M., Small, 18, 2104763 (2022).

Interface and Surface Analysis Centre (ISAC)

Email: isac@nottingham.ac.uk