Sputtering is the basis of Secondary Ion Mass Spectrometry (SIMS) and is used by other surface analytical methods such as Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) to access deeper layers. Sputtering by atomic ions is well described by Sigmund's linear cascade theory. With cluster primary ions, a non-linear effect, referred to as a 'spike', leads to an enhancement in the sputtering yield and molecular ion yield. This significantly higher sensitivity to large molecules has led to a rapid increase in the use of cluster primary ions for organic analysis. NPL is developing research to improve the understanding of the sputtering mechanism and to allow analysts to compare the effectiveness of different primary ions. Recently, NPL has shown that the molecular ion yield has a power law dependence with the sputtering yield, with the power increasing from unity for small molecules, to 2 (square law) for larger molecules above 1000 u. We have also shown that the mass spectra are composed of the product of two basis spectra, which are raised to powers depending on the primary ion cluster, species and energy. This has important implications for understanding the fundamental sputtering mechanisms, and practical interpretation of the mass spectra.

Selected Publications

[1] Relationships between cluster secondary ion mass intensities generated by different cluster primary ions, M. P. Seah, F. M. Green & I. S. Gilmore, J. Am. Soc. Mass Spectrom., 2010

[2] Cluster primary ion sputtering: secondary ion intensities in static SIMS of organic materials, M P Seah, F M Green and I S Gilmore, J Phys Chem C, 2010

[3] Cluster ion sputtering: molecular ion yield relationships for different cluster primary ions in static SIMS of organic materials, M. P. Seah, Surf. Interface Anal., 2007, 39, 890

[4] Analysis of cluster ion sputtering yields: correlation with the thermal spike model and implications for static secondary ion mass spectrometry, M. P. Seah, Surf. Interface. Anal., 2007, 37, 634

[5] An accurate semi-empirical equation for sputtering yields, I: for argon ions, M P Seah, C A Clifford, F M Green and I S Gilmore, Surf. Interface Anal., 2005, 37, 444.

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

Contact: Martin Seah or Ian Gilmore