What does SIMS do?

SIMS is a highly sensitive technique for investigating the surface chemistry of samples. It provides:

• Identification of trace elements, organic molecules and polymers on surfaces, with better than 1 ppm sensitivity for some molecules and ppb sensitivity for some elements
• Surface chemical imaging with better than 200 nm resolution
• Extremely surface sensitive information from top 1 nm of sample in static SIMS mode
• 3D elemental / molecular distribution with better than 50 nm depth resolution in depth profiling mode

How does SIMS work?

In SIMS, the surface is bombarded by an energetic primary ion beam in vacuum. This desorbs surface species through a physical process called sputtering. Some of the sputtered fragments are ionised, and they are analysed in a mass spectrometer. The mass spectra show the elements, molecules and molecular fragments on the surface, which reflect the surface chemistry of the sample. SIMS images are obtained by scanning the primary ion beam across the sample and collecting a spectrum at each pixel. This can be combined with the sputter removal of sample layer-by-layer ('depth profilin'), which allows chemical species to be localised and mapped in 3D.

What is SIMS used for?

• Analysis of complex molecules and organics, including wool fibres, biomaterials and drug delivery systems
• Improving the performance of organic LED displays and solar cells, by characterising surface and interfacial chemistry of organic layers and identifying contamination
• Depth profiling of control release coatings of drug on arterial stents used in heart surgery, to measure the drug distribution and migration
• Investigating how conditioners stick to hair using SIMS imaging, and correlating with other physical properties such as friction

See our SIMS measurement services page to find out how SIMS may help with your specific application.

What are the measurement challenges?

The major challenge in SIMS is sputtering and analysing materials without causing extensive damage and fragmentation. NPL is characterising new cluster primary ion beams, such as Bi₃⁺, C₆₀⁺ and Ar₂₀₀₀⁺, which increase the molecular secondary ion signal whilst reducing damage. Another challenge is identifying complex molecules. NPL is developing a fragmentation database to provide a framework for interpreting molecular structure from mass spectra. We are also extending the application of SIMS to difficult samples in industry such as fibres and nanoparticles. New data analysis methods are being developed to cope with the explosion of data, especially for SIMS images.

See our SIMS research page to find out more.