C₆₀ⁿ⁺ depth profiling of NPL organic delta layer reference material – SIMS signal as a function of sputtered depth. The inset shows the 3D reconstruction of layer structure.

A recent development in Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS) is the use of cluster ion beams for organic depth profiling. This produces high-resolution 3D molecular images of organic and biomaterials, with depth resolutions ~10 nm and spatial resolution < 1 μm. The challenge is in sputtering away layers of organic materials without inducing severe damage, mixing and surface roughening, which can affect the sputtering and molecular ion yields, and reduce the depth resolution achievable. To investigate these key parameters, NPL developed an organic delta layer reference material, which allows direct comparisons between different laboratories, experimental arrangements, sputtering beam species and energies, and has led to clearer understanding on the most appropriate analysis conditions. Another focus is the quantification of depth profiles to relate molecular signal to the amount of material. This is essential for correct and meaningful interpretation of data, and includes understanding the damage and disappearance cross-sections, matrix effects, and intensity changes at interfaces. In addition to developing the metrology for C₆₀ⁿ⁺, we are in collaboration with Prof Jiro Matsuo at Kyoto University to investigate novel gas cluster ions Ar₁₀₀₀⁺, which has recently shown enormous potential.

NPL organic multilayer materials are available as reference and test materials.

Selected Publications

• Organic depth profiling of a nanostructured delta layer reference material using large Argon cluster ions
  J L S Lee, S Ninomiya, J Matsuo, I S Gilmore, M P Seah and A G Shard
  Anal. Chem. 82(1) (2010) 98-105
• Quantitative molecular depth profiling of organic delta-layers by C₆₀ ion sputtering and SIMS
  A G Shard, F M Green, P J Brewer, M P Seah and I S Gilmore
  J. Phys. Chem. B 12 (9) (2008) 2596–2605
• Analysis of the interface and its position In C₆₀ⁿ⁺ secondary ion mass spectrometry depth profiling
  F M Green, A G Shard, I S Gilmore and M P Seah
  Anal. Chem., 81 (1) (2009) 75-79
• Organic depth profiling of a binary system: the compositional effect on secondary ion yield and a model for charge transfer during secondary ion emission
  A G Shard, A Rafati, R Ogaki, J L S Lee, Simon Hutton, G Mishra, M C Davies and M R Alexander
  J. Phys. Chem. B 113 (2009) 11574–11582

If you require PDF copies of the publications, please contact us below.

Contact: Alex Shard